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- Front Matter: Volume 7734
- Current and Planned Facilities: Ground I
- Current and Planned Facilities: Ground II
- Current and Planned Facilities: Ground III
- Current and Planned Instruments: Ground
- Current and Planned Facilities and Instruments: Space I
- Current and Planned Facilities and Instruments: Space II
- Observing Techniques I
- Facilities--Future: Ground I
- Facilities--Future: Ground II
- Observing Techniques II
- Observing Techniques III
- Space Interferometer Technologies I
- Space Interferometer Technologies II
- Current and Planned Facilities
- Critical Subsystems I
- Critical Subsystems II
- Critical Subsystems III
- Technologies I
- Technologies II
- Software I
- Software II
- Space Interferometer Technologies III
- Observing Technologies
- Posters: Current and Planned Facilities and Instruments
- Posters: Facility Issues
- Posters: Observing Techniques
- Posters: Technologies
- Posters: Critical Subsystems
- Posters: Software
- Posters: Space Interferometer Technology
Front Matter: Volume 7734
Front Matter: Volume 7734
Show abstract
This PDF file contains the front matter associated with SPIE
Proceedings Volume 7734, including the Title Page, Copyright
information, Table of Contents, and the Conference Committee listing.
Current and Planned Facilities: Ground I
Recent progress at the Keck Interferometer
Show abstract
The Keck Interferometer (KI) combines the two 10m diameter Keck telescopes providing milliarcsecond angular
resolution. KI has unique observing capabilities such as sensitive K-band V2, L-band V2 and N-band nulling operations. The instrument status of the Keck Interferometer since the last SPIE meeting in 2008 is summarized. We discuss the
performance of new visibility observing capabilities including L-band and self-phase referencing modes. A simultaneous
dual-beam-combiner mode in the K and L-band has been demonstrated, nearly doubling operational efficiency for bright
targets. Operational improvements including simplified reliable operations with reduced personnel resources are
highlighted. We conclude with a brief review of the current and future developmental activities of KI. Details of ASTRA
developments, nulling performance and science results are presented elsewhere at this conference.
An update on the CHARA Array
Show abstract
The CHARA Array is a six-telescope optical/IR interferometer operated by the Center for High Angular Resolution
Astronomy of Georgia State University and is located at Mount Wilson Observatory just to the north of Los Angeles
California. The CHARA Array has the largest operational baselines in the world and has been in regular use for scientific
observations since 2004. In this paper we give an update of instrumentation improvements, primarily focused on the
beam combiner activity. The CHARA Array supports seven beam combiners: CHARA CLASSIC, a two-way high
sensitivity K/H/J band system; CLIMB, a three-way K/H/J open air combiner, FLUOR, a two-way K band high
precision system; MIRC, a four/six-way H/K band imaging system; CHAMP, a six way K band fringe tracker; VEGA, a
four way visible light high spectral resolution system; and PAVO, a three-way visible light high sensitivity system. The
paper will conclude with a review of science results obtained over the last few years, including our most recent imaging results.
The very large telescope Interferometer: 2010 edition
Show abstract
The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four
1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two
VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the operation, the instruments
developments are pursued, and new modes are studied and commissioned to offer a wider range of scientific possibilities
to the community. New configurations of the ATs array are discussed with the science users of the VLTI and
implemented to optimize the scientific return. The monitoring and improvement of the different systems of the VLTI is a
continuous work. The PRIMA instrument, bringing astrometry capability to the VLTI and phase referencing to the
instruments has been successfully installed and the commissioning is ongoing. The possibility for visiting instruments
has been opened to the VLTI facility.
Current and Planned Facilities: Ground II
Instrumental developments for the Sydney University Stellar Interferometer
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The Sydney University Stellar Interferometer (SUSI) has been enhanced by installation of the PAVO beam combiner,
which uses an electron-multiplying CCD detector giving a fast, low-noise 2D readout. This allows PAVO to provide
wide-band wavelength dispersed beam combination, which improves sensitivity and scientific productivity. PAVO also
provides pupil segmentation which improves the instrumental fringe visibility. A remote operations facility has been
established, which allows SUSI to be operated from Sydney or elsewhere. A new control system for the longitudinal
dispersion corrector and siderostats is under development. Installation has commenced of a high precision differential
astrometry system (MUSCA) which aims to detect planets in binary star systems.
Magdalena Ridge Observatory Interferometer: advancing to first light and new science
Show abstract
The Magdalena Ridge Observatory Interferometer is a 10 x 1.4 meter aperture long baseline optical and near-infrared
interferometer being built at 3,200 meters altitude on Magdalena Ridge, west of Socorro, NM. The interferometer layout
is an equilateral "Y" configuration to complement our key science mission, which is centered on imaging faint and
complex astrophysical targets. This paper serves as an overview and update on the status of the observatory and our
progress towards first light and first fringes in 2012.
Imaging beyond the fringe: an update on the LINC-NIRVANA Fizeau interferometer for the LBT
Show abstract
We present an update on the construction and integration of LINC-NIRVANA, a Fizeau-mode imaging interferometer
for the Large Binocular Telescope (LBT). The LBT is a unique platform for interferometry, since its two, co-mounted
8.4 meter primary mirrors present an orientation-independent entrance pupil. This allows Fizeau-mode beam
combination, providing 23-meter spatial resolution and 12-meter effective collecting area for panoramic imagery
LINC-NIRVANA will sit at one of the shared, bent focal stations, receiving light from both mirrors of the LBT. The
instrument uses visible wavelength radiation for wavefront control, and the near-infrared bands for science and fringe
tracking. LINC-NIRVANA employs a number of innovative technologies, including multi-conjugated adaptive optics,
state-of-the-art materials, low vibration mechanical coolers, active and passive control, and sophisticated software for
data analysis.
The instrument is in its final construction and integration phase. This paper reports on overall progress, including
insights gained on large instrument assembly, software integration, science planning, and vibration control. A number of
additional contributions to this conference focus on individual subsystems and integration-related issues.
Current and Planned Facilities: Ground III
First results from VLTI near-infrared interferometry on high-mass young stellar objects
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Due to the recent dramatic technological advances, infrared interferometry can now be applied to new classes
of objects, resulting in exciting new science prospects, for instance, in the area of high-mass star formation.
Although extensively studied at various wavelengths, the process through which massive stars form is still only
poorly understood. For instance, it has been proposed that massive stars might form like low-mass stars by mass
accretion through a circumstellar disk/envelope, or otherwise by coalescence in a dense stellar cluster. Therefore,
clear observational evidence, such as the detection of disks around high-mass young stellar objects (YSOs), is
urgently needed in order to unambiguously identify the formation mode of the most massive stars.
After discussing the technological challenges which result from the special properties of these objects, we
present first near-infrared interferometric observations, which we obtained on the massive YSO IRAS 13481-6124
using VLTI/AMBER infrared long-baseline interferometry and NTT speckle interferometry. From our extensive
data set, we reconstruct a model-independent aperture synthesis image which shows an elongated structure with
a size of ~ 13 x 19 AU, consistent with a disk seen under an inclination of - 45°. The measured wavelengthdependent
visibilities and closure phases allow us to derive the radial disk temperature gradient and to detect a
dust-free region inside of 9.5 AU from the star, revealing qualitative and quantitative similarities with the disks
observed in low-mass star formation. In complementary mid-infrared Spitzer and sub-millimeter APEX imaging
observations we detect two bow shocks and a molecular outflow, which are oriented perpendicular to the disk
plane and indicate the presence of a bipolar outflow emanating from the inner regions of the system.
Mid-infrared interferometry with high spectral resolution
Edward H. Wishnow,
William Mallard,
Vikram Ravi,
et al.
Show abstract
The Infrared Spatial Interferometer (ISI) is a three telescope interferometer system that operates near 11 microns
wavelength using heterodyne detection with CO2 lasers as local oscillators. Stellar measurements have been made using
consistent instrumentation for 20 years, allowing comparisons of stellar sizes of red giant and Mira stars over time
intervals which are long in comparison to stellar luminosity periods. Recent visibility and closure phase measurements
of the star Betelgeuse have been fitted to simple image models and these results have been added to the 17 year record of
stellar observations. A new area of investigation of stellar properties at very high spectral resolution will begin in the
2010-2011 observing season. The design of a new digital spectrometer-correlator system is discussed. This system will obtain visibility measurements on-and-off individual spectral lines and the continuum, simultaneously.
Stellar intensity interferometry: astrophysical targets for sub-milliarcsecond imaging
Show abstract
Intensity interferometry permits very long optical baselines and the observation of sub-milliarcsecond structures. Using
planned kilometric arrays of air Cherenkov telescopes at short wavelengths, intensity interferometry may increase the
spatial resolution achieved in optical astronomy by an order of magnitude, inviting detailed studies of the shapes of
rapidly rotating hot stars with structures in their circumstellar disks and winds, or mapping out patterns of nonradial
pulsations across stellar surfaces. Signal-to-noise in intensity interferometry favors high-temperature sources and
emission-line structures, and is independent of the optical passband, be it a single spectral line or the broad spectral
continuum. Prime candidate sources have been identified among classes of bright and hot stars. Observations are
simulated for telescope configurations envisioned for large Cherenkov facilities, synthesizing numerous optical baselines
in software, confirming that resolutions of tens of microarcseconds are feasible for numerous astrophysical targets.
Adaptive optics for the CHARA array II
Show abstract
The efficiency of the CHARA Array has proven satisfactory for a wide variety of scientific programs enabled by the
first-generation beam combination and detector systems. With multi-beam combination and more ambitious scientific
goals, improvements in throughput and efficiency will be highly leveraged. Engineering data from several years of
nightly operations are used to infer atmospheric characteristics and raw instrumental visibility in both classic optical and
single-mode fiber beam combiners. This information is the basis for estimates of potential gains that could be afforded
by the implementation of adaptive optics. In addition to the very important partial compensation for higher order
atmosphere-induced wavefront errors, the benefits include reduction of static and quasi-static aberrations, reduction of
residual tilt error, compensation for differential atmospheric refraction, and reduction of diffractive beam propagation
losses, each leading to improved flux throughput and instrumental visibility, and to associated gains in operability and
scientific productivity.
Current and Planned Instruments: Ground
Recent science highlights from the Keck Interferometer
Show abstract
The addition of new observational capabilities and continued sensitivity improvements have allowed observations
with the Keck Interferometer to encompass new areas of astrophysics and expanded significantly the available sample size in areas which had been the focus of previous work. The technical details of the instrument techniques (including nulling, L-band and increased spectral resolution) are covered in other contributions to this conference. Here, we will highlight the astrophsyics enabled by these instruments including: a summary of the NASA Exo-zodical Dust Survey Key Project, observations across a range of dust temperatures with K and L-band measurements and faint target studies of active galactic nuclei and young stellar disks.
Performances and first science results with the VEGA/CHARA visible instrument
Show abstract
This paper presents the current status of the VEGA (Visible spEctroGraph and polArimeter) instrument installed
at the coherent focus of the CHARA Array, Mount Wilson CA. Installed in september 2007, the first science
programs have started during summer 2008 and first science results are now published. Dedicated to high angular (0.3mas) and high spectral (R=30000) astrophysical studies, VEGA main objectives are the study of circumstellar environments of hot active stars or interactive binary systems and a large palette of new programs dedicated to fundamental stellar parameters. We will present successively the main characteristics of the instrument and its current performances in the CHARA environment, a short summary of two science programs and finally we will develop some studies showing the potential and difficulties of the 3 telescopes mode of VEGA/CHARA.
Status of PRIMA for the VLTI or the quest for user-friendly fringe tracking
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The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope
Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Most of the tests have been
concentrated on the characterization of the Fringe Sensor Unit (FSU) and on the automation of the fringe
tracking in preparation of dual-field observations. The status of the facility, an analysis of the FSU performance
and the first attempts towards dual-field observations will be presented in this paper. In the FSU, the phase
information is spatially encoded into four independent combined beams (ABCD) and the group delay comes from
their spectral dispersion over 5 spectral channels covering the K-band. During fringe tracking the state machine
of the optical path difference controller is driven by the Signal to Noise Ratio (SNR) derived from the 4 ABCD
measurements. We will describe the strategy used to define SNR thresholds depending on the star magnitude
for automatically detecting and locking the fringes. Further, the SNR as well as the phase delay measurements
are affected by differential effects occurring between the four beams. We will shortly discuss the contributions
of these effects on the measured phase and SNR noises. We will also assess the sensitivity of the group delay
linearity to various instrumental parameters and discuss the corresponding calibration procedures. Finally we
will describe how these calibrations and detection thresholds are being automated to make PRIMA as much as
possible a user-friendly and efficient facility.
MI-6: Michigan interferometry with six telescopes
Show abstract
Based on the success of four-telescope imaging with the Michigan Infrared Combiner (MIRC) on the CHARA
Array, our Michigan-based group will now upgrade our system to combine all six CHARA telescope simultaneously.
In order to make this observationally efficient, we have had to improve a number of subsystems and
commission new ones, including the new CHAMP fringe tracker, the introduction of photometric channels, the
upgrading of the realtime operating systems, and the obvious hardware and software upgrades of the control
system and the data pipeline. Here we will discuss the advantages of six-telescope operation, outline our upgrade
plans and discuss our current progress.
Current and Planned Facilities and Instruments: Space I
SIM Lite Astrometric Observatory progress report
Show abstract
The SIM Lite Astrometric Observatory (aka SIM Lite), a micro-arcsecond astrometry space mission, has been developed
in response to NASA's indefinite deferral of the SIM PlanetQuest mission. The SIM Lite mission, while significantly
more affordable than the SIM PlanetQuest mission concept, still addresses the full breadth of SIM science envisioned by two previous National Research Council (NRC) Astrophysics Decadal Surveys at the most stringent "Goal" level of
astrometric measurement performance envisioned in those surveys. Over the past two years, the project has completed
the conceptual design of the SIM Lite mission using only the completed SIM technology; published a 250 page book
describing the science and mission design (available at the SIM website: http://sim.jpl.nasa.gov); been subject to an
independent cost and technical readiness assessment by the Aerospace Corporation; and submitted a number of
information responses to the NRC Astro2010 Decadal Survey. The project also conducted an exoplanet-finding
capability double blind study that clearly demonstrated the ability of the mission to survey 60 to 100 nearby sun-like
dwarf stars for terrestrial, habitable zone planets in complex planetary systems. Additionally, the project has continued
Engineering Risk Reduction activities by building brassboard (form, fit & function to flight) version of key instrument elements and subjecting them to flight qualification environmental and performance testing. This paper summarizes the progress over the last two years and the current state of the SIM Lite project.
Potential of balloon payloads for in flight validation of direct and nulling interferometry concepts
Show abstract
While the question of low cost / low science precursors is raised to validate the concepts of direct and nulling
interferometry space missions, balloon payloads offer a real opportunity thanks to their relatively low cost and reduced
development plan. Taking into account the flight capabilities of various balloon types, we propose in this paper, several
concepts of payloads associated to their flight plan. We also discuss the pros and cons of each concepts in terms of
technological and science demonstration power.
The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII)
Show abstract
Astronomical studies at infrared wavelengths have dramatically improved our understanding of the universe. The
relatively low angular resolution of these missions, however, is insufficient to resolve the physical scale on which mid-to
far-infrared emission arises. We will build the Balloon Experimental Twin Telescope for Infrared Interferometry
(BETTII), an eight-meter Michelson interferometer to fly on a high-altitude balloon. BETTII's spectral-spatial capability,
provided by an instrument using double-Fourier techniques, will address key questions about the nature of disks in
young star clusters and active galactic nuclei and the envelopes of evolved stars. BETTII will also lay the technological
groundwork for future space interferometers.
Current and Planned Facilities and Instruments: Space II
Direct imaging of Earth-like planets: why we care about exozodis
Show abstract
The presence of large amounts of exozodiacal dust around nearby main sequence stars is considered as a potential
threat for the direct detection of Earth-like exoplanets (exoEarths) with future space-based coronagraphic and
interferometric missions. In this paper, we estimate the amount of exozodiacal light that can be tolerated around
various stellar types without jeopardizing the detection of exoEarths with a space-based visible coronagraph or a
free-flying mid-infrared interferometer. We also address the possible effects of resonant structures in exozodiacal
disks. We then review the sensitivity of current ground-based interferometric instruments to exozodiacal disks,
based on classical visibility measurements and on the nulling technique. We show that the current instrumental
performances are not sufficient to help prepare future exoEarth imaging missions, and discuss how new groundor
space-based instruments could improve the current sensitivity to exozodiacal disks down to a suitable level.
The Fourier-Kelvin Stellar Interferometer (FKSI) - infrared detection and characterization of exozodiacal dust to super-earths: a progress report
Show abstract
The Fourier-Kelvin Stellar Interferometer (FKSI) is a structurally connected infrared space interferometer with 0.5 m
diameter telescopes on a 12.5 m baseline, and is passively cooled to ~ 60K. The FKSI operates in the thermal infrared
from 3-8 μm in a nulling (starlight suppressing) mode for the detection and characterization of exoplanets, debris disks,
and extrasolar zodiacal dust levels. The FKSI will have the highest angular resolution of any infrared space instrument
ever made with its nominal resolution of 40 mas at a 5 μm center wavelength. This resolution exceeds that of Spitzer by
a factor of 38 and JWST by a factor of 5. The FKSI mission is conceived as a "probe class" or "mid-sized" strategic
mission that utilizes technology advances from flagship projects like JWST, SIM, Spitzer, and the technology programs
of TPF-I/Darwin. During the past year we began investigating an enhanced version of FKSI with 1-2 m diameter
telescopes, passively cooled to 40K, on a 20-m baseline, with a sunshade giving a ± 45 degree Field-of-Regard. This
enhanced design is capable of detecting and characterizing the atmospheres of many 2 Earth-radius super-Earths and a
few Earth-twins. We will report progress on the design of the enhanced mission concept and current status of the
technologies needed for this mission.
Progress in the development of MANIC: a monolithic nulling interferometer for characterizing extrasolar environments
Show abstract
We present progress in the development of the monolithic achromatic nulling interference coronagraph (MANIC),
an optic designed for enabling direct detection and characterization of exoplanetary systems around nearby stars.
MANIC is a fully symmetric implementation of a rotational shearing interferometer consisting of fused quartz
prisms and a symmetric beamsplitter optically contacted in an arrangement that geometrically flips the fields
in the TR and RT arms about orthogonal axes such that upon recombination, a centro-symmetric, theoretically
achromatic null is produced. In addition to a small inner working angle (⪅ 1λ/D), built-in alignment and
stability are inherent benefits of the compact monolithic design, which make MANIC a competitive alternative
to conventional discrete element nullers proposed for imaging exoplanetary environments. Following MANIC's
initial fabrication, the path error between its TR and RT arms was measured. This measurement was used to
fabricate compensator plates of varying thicknesses that were bonded to the optic to reduce dispersion imbalance,
thereby improving broadband nulling performance. In performing this correction, initial OPD was reduced from
949 ± 44 nm to 63 ± 10 nm, which in the absence of any other asymmetries, corresponds to an increase in a
107 R-band (λc = 648 nm) nulling bandpass from monochromatic to 25%, or at the 106 level, from 5% to 50%.
Current benchtop laser and polychromatic nulling strategies are described. The potential science return from
using MANIC on a sub-orbital platform is discussed.
SIM-Lite narrow-angle modeling and processing
Show abstract
This paper examines how narrow-angle (NA) processing of data from the SIM Lite optical interferometry mission can be
undertaken when realistic spacecraft and mission operational constraints are taken into account. Using end-to-end
mission simulations we show that the goal of 1 μas single measurement accuracy (SMA) is obtainable, and hence the
detection of earth-like planets is achievable with the SIM Lite mission.
Observing Techniques I
First Keck Interferometer measurements in self-phase referencing mode: spatially resolving circum-stellar line emission of 48 Lib
Show abstract
Recently, the Keck interferometer was upgraded to do self-phase-referencing (SPR) assisted K-band spectroscopy at R ~ 2000. This means, combining a spectral resolution of 150 km/s with an angular resolution of 2.7 mas, while maintaining
high sensitiviy. This SPR mode operates two fringe trackers in parallel, and explores several infrastructural requirements
for off-axis phase-referencing, as currently being implemented as the KI-ASTRA project. The technology of self-phasereferencing
opens the way to reach very high spectral resolution in near-infrared interferometry. We present the scientific
capabilities of the KI-SPR mode in detail, at the example of observations of the Be-star 48 Lib. Several spectral lines of the
cirumstellar disk are resolved. We describe the first detection of Pfund-lines in an interferometric spectrum of a Be star, in
addition to Br γ. The differential phase signal can be used to (i) distinguish circum-stellar line emission from the star, (ii) to directly measure line asymmetries tracing an asymetric gas density distribution, (iii) to reach a differential, astrometric
precision beyond single-telescope limits sufficient for studying the radial disk structure. Our data support the existence of
a radius-dependent disk density perturbation, typically used to explain slow variations of Be-disk hydrogen line profiles.
Perspectives for the AMBER Beam Combiner
Show abstract
The Astronomical Multi-BEam Recombiner (AMBER), has been operational at the Very Large Telescope Interferometer
(VLTI) for many years. We present here some of the constant improvements we have been providing
while still operating the instrument, with a heavy load of visitor and service observing programs, most of the
nights of the year. In particular, we present here improvements regarding the spectral calibration and correction
of the atmospheric loss in squared visibility due to path difference jitter, allowing the instrument to achieve
greater precision.
Keck Interferometer nuller instrument performance
Show abstract
The Keck Interferometer combines the two 10 m Keck telescopes as a long baseline interferometer. It is funded by
NASA as a joint development among the Jet Propulsion Laboratory, the W. M. Keck Observatory, and the NASA
Exoplanet Science Institute. In February 2008, the 10 um nulling mode began a 32 night observing program with three
key science teams to perform a survey of nearby stars for exozodiacal dust. This program has recently concluded, and
has been followed by nuller observing on a variety of science topics through the standard proposal process. We provide a
review and update of the nuller implementation, and describe the data reduction process, including the calibration
approach. We then review the technical performance of the instrument based on the full key science data set, including
sensitivity and systematic errors. We also provide some summary data on atmospheric effects applicable to the cophasing approach.
Phase closure nulling: results from the 2009 campaign
Show abstract
We present here a new observational technique, Phase Closure Nulling (PCN), which has the potential to obtain
very high contrast detection and spectroscopy of faint companions to bright stars. PCN consists in measuring
closure phases of fully resolved objects with a baseline triplet where one of the baselines crosses a null of the
object visibility function. For scenes dominated by the presence of a stellar disk, the correlated flux of the star
around nulls is essentially canceled out, and in these regions the signature of fainter, unresolved, scene object(s)
dominates the imaginary part of the visibility in particular the closure phase. We present here the basics of the
PCN method, the initial proof-of-concept observation, the envisioned science cases and report about the first
observing campaign made on VLTI/AMBER and CHARA/MIRC using this technique.
Assembly and integration activities moving toward commissioning of the Magdalena Ridge Observatory Interferometer
Show abstract
The Magdalena Ridge Observatory Interferometer (MROI) has completed its design phase and is currently in the
construction phase. The first telescope will be deployed at the MROI site in 2011. Five different vendors are involved
in the design and fabrication of a unit telescope, and a much larger number for the full observatory.
This paper addresses the steps that the MRO Interferometry project will undertake to integrate subsystems developed by
different parties, through commissioning into an operational optical interferometer.
Finally we present the commissioning plan to bring the interferometer to an operational mode. We have developed
"performance verification milestones" that successively increase the "science readiness" of the interferometer and
transitions to an operational phase.
PACMAN: PRIMA astrometric instrument software
Show abstract
The dual feed astrometric instrument software of PRIMA (PACMAN) that is currently being integrated at the VLTI will
use two spatially modulated fringe sensor units and a laser metrology system to carry out differential astrometry. Its
software and hardware compromises a distributed system involving many real time computers and workstations
operating in a synchronized manner. Its architecture has been designed to allow the construction of efficient and flexible
calibration and observation procedures. In parallel, a novel scheme of integrating M-code (MATLAB/OCTAVE) with
standard VLT (Very Large Telescope) control software applications had to be devised in order to support numerically
intensive operations and to have the capacity of adapting to fast varying strategies and algorithms. This paper presents
the instrument software, including the current operational sequences for the laboratory calibration and sky calibration.
Finally, a detailed description of the algorithms with their implementation, both under M and C code, are shown together
with a comparative analysis of their performance and maintainability.
Facilities--Future: Ground I
Signatures of strong gravity with GRAVITY
Show abstract
The dynamics of stars and gas undoubtedly shows the existence of a 4 million solar mass black hole at the
center of the Milky Way: Sagittarius A* (SgrA*). Violent flare emission allows us to probe the immediate
environment of the central mass. Near-infrared polarimetry now shows signatures of strong gravity that are
statistically significant against randomly polarized red noise. Using these signatures we can derive spin and
inclination information of SgrA*. A combined synchrotron self Compton (SSC) and adiabatic expansion model
with source components peaking in the sub-mm domain can fully account for the observed flare flux densities
and the time delays towards the (sub-)mm flares that have been reported in some cases. We discuss the expected
centroid paths of the NIR images and summarize how the geometrical structure of the emitting region (i.e.
spot shape, presence of a torus or spiral-arm pattern etc.) affects this centroid tracks. While most of the
mentioned geometries are able to fit the observed fluxes, future NIR interferometry with GRAVITY at the
VLT will break some of the degeneracies between different emission models. In this contribution we summarize
several GRAVITY science cases for SgrA*. Our simulations propose that focusing GRAVITY observations on
the polarimetry mode could reveal a clear centroid track of the spot(s). A non-detection of centroid shifts cannot
rule out the multi-component model or spiral arms scenarios. However, a clear wander between alternating
centroid positions during the flares will prove the idea of bright long-lived spots occasionally orbiting the central
black hole.
GRAVITY: a four telescope beam combiner instrument for the VLTI
Show abstract
GRAVITY is an adaptive optics assisted Beam Combiner for the second generation VLTI instrumentation. The
instrument will provide high-precision narrow-angle astrometry and phase-referenced interferometric imaging in the
astronomical K-band for faint objects. We describe the wide range of science that will be tackled with this instrument,
highlighting the unique capabilities of the VLTI in combination with GRAVITY. The most prominent goal is to observe
highly relativistic motions of matter close to the event horizon of Sgr A*, the massive black hole at center of the Milky
Way. We present the preliminary design that fulfils the requirements that follow from the key science drivers: It includes
an integrated optics, 4-telescope, dual feed beam combiner operated in a cryogenic vessel; near-infrared wavefrontsensing
adaptive optics; fringe-tracking on secondary sources within the field of view of the VLTI and a novel metrology
concept. Simulations show that 10 μas astrometry within few minutes is feasible for a source with a magnitude of
mK = 15 like Sgr A*, given the availability of suitable phase reference sources (mK = 10). Using the same setup, imaging of mK = 18 stellar sources in the interferometric field of view is possible, assuming a full night of observations and the corresponding UV coverage of the VLTI.
Science with the Keck Interferometer ASTRA program
Show abstract
The ASTrometric and phase-Referenced Astronomy (ASTRA) project will provide phase referencing and astrometric
observations at the Keck Interferometer, leading to enhanced sensitivity and the ability to monitor
orbits at an accuracy level of 30-100 microarcseconds. Here we discuss recent scientific results from ASTRA,
and describe new scientific programs that will begin in 2010-2011. We begin with results from the "self phase
referencing" (SPR) mode of ASTRA, which uses continuum light to correct atmospheric phase variations and
produce a phase-stabilized channel for spectroscopy. We have observed a number of protoplanetary disks using
SPR and a grism providing a spectral dispersion of ~ 2000. In our data we spatially resolve emission from dust
as well as gas. Hydrogen line emission is spectrally resolved, allowing differential phase measurements across the
emission line that constrain the relative centroids of different velocity components at the 10 microarcsecond level.
In the upcoming year, we will begin dual-field phase referencing (DFPR) measurements of the Galactic Center
and a number of exoplanet systems. These observations will, in part, serve as precursors to astrometric monitoring
of stellar orbits in the Galactic Center and stellar wobbles of exoplanet host stars. We describe the design
of several scientific investigations capitalizing on the upcoming phase-referencing and astrometric capabilities of ASTRA.
Facilities--Future: Ground II
ASTRA: astrometry and phase-referencing astronomy on the Keck interferometer
Show abstract
ASTRA (ASTrometric and phase-Referencing Astronomy) is an upgrade to the existing Keck Interferometer
which aims at providing new self-phase referencing (high spectral resolution observation of YSOs), dual-field
phase referencing (sensitive AGN observations), and astrometric (known exoplanetary systems characterization
and galactic center general relativity in strong field regime) capabilities. With the first high spectral resolution
mode now offered to the community, this contribution focuses on the progress of the dual field and astrometric modes.
Magdalena Ridge Interferometer: assembly, integration and testing of the unit telescopes
Show abstract
AMOS is in charge of the development of the unit telescopes for the MRO interferometer. This paper depicts the
progress of the project and presents the results of the factory acceptance tests that were performed at AMOS facilities.
Those tests are the earliest verifications of the telescope performance. AMOS has now extensive experience in testing
small and large instruments, including optical testing, alignment, mechanical static, dynamic measurements, system
identification, etc. It is this combination of various techniques of measurement that produce accurate and reliable results.
Magdalena Ridge Observatory Interferometer automated alignment system
Show abstract
Here is presented the current outline and progress of MROI's automated alignment system design. Depending on the
location of each of MROI's unit telescopes (UT), light can travel distances ranging from 460 to 660 meters via
several reflections that redirect the beam's path through the beam relay system (BRS), delay line system (DLS),
beam compressing telescope (BCR), switchyards and finally to the beam combiners (BC). All of these sub-systems
comprise three major optical axes of the MROI which must be coaligned on a nightly basis by the AAS. The AAS
consists of four subsystems: the primary fiducial-for beam injection, the UT tilt and shear measurement
components (TASM), the BC TASM components, and the secondary fiducial-for quick alignment checks. All of
these subsystems contribute to the unique design of the AAS which will allow for simultaneous measurements from
the visible to the near-IR wavelengths, full automation, the capability to perform optical path difference (OPD)
alignment and spectral calibration, making it cost effective and saving on realty in the beam combining area (BCA).
The AAS is nearing completion and assembly of the various subsystems is expected to commence soon. The latest
results on all of the following are reviewed here.
The GRAVITY acquisition and guiding system
Show abstract
GRAVITY is a VLTI second generation instrument designed to deliver astrometry at the level of 10 μas. The
beam transport to the beam combiner is stabilized by means of a dedicated guiding system whose specifications
are mainly driven by the GRAVITY astrometric error budget. In the present design, the beam is monitored using
an infrared acquisition camera that implements a mosaic of field, pupil and Shack-Hartmann images for each of the telescopes. Star and background H-band light from the sky can be used to correct the tip-tilt and pupil lateral position, within the GRAVITY specifications, each 10 s. To correct the beam at higher frequencies laser guiding beams are launched in the beam path, on field and pupil planes, and are monitored using position sensor detectors. The detection, in the acquisition camera, of metrology laser light back reflected from the telescopes, is also being investigated as an alternative for the pupil motion control.
Observing Techniques II
The Fomalhaut debris disk seen from every angle with interferometry
Show abstract
In this paper, we present the results of three different studies of the Fomalhaut debris disk with infrared interferometry.
First, VLTI/AMBER measurements are used to determine the position angle of the slightly oblate
rapidly rotating photosphere by means of differential phase measurements across the Br-gamma photospheric
line. This measurement allows us to confirm that the debris disk is located in the equatorial plane of its host
star. Second, we use VLTI/VINCI to search for resolved near-infrared emission around the stellar photosphere,
which would correspond to the presence of large amounts of hot dust grains located between the sublimation
radius and the habitable zone. Our observations reveal a small excess of 0.88%±0.12% in K band relative to the
photospheric flux. Finally, we use the Keck Interferometer Nuller in order to derive additional constraints on the
nature of the resolved infrared emission. Our observations suggest a marginal detection of a circumstellar excess
at 10 μm, which we use together with the VINCI detection to model the circumstellar emission. Preliminary results from this modeling effort are discussed.
Image reconstruction in optical interferometry: applications to the inner regions of protoplanetary disks
Show abstract
Planets are believed to form in circumstellar disks around newly born stars at distances ranging from 0.1 to 10 AUs.
This location corresponds to milli-arcsecond scales at the distance of the closest star forming regions and to temperatures
ranging from a few hundred to a few thousand Kelvin. To conduct observations of close environments of such disks
at the milli-arcsecond scale, infrared interferometry is a suitable tool that can be employed to observe T Tauri, FU Ori
and Herbig Ae/Be stars. However, the data obtained so far consist of a small number of measurements which can only
constrain theoretical models. With the advent of recent multi-aperture interferometers, the interferometric data can be used
to reconstruct images independently of any parametric model, as is routinely done in the radio frequency range. On the
other hand, in the optical range, not enough measurements are available to univocally reconstruct an image and some a
priori must be introduced. In this contribution, we present systematic tests performed on the MiRA algorithm (an image
reconstruction algorithm developed for optical interferometry) in order to evaluate the feasibility of the technique. The
methodology allows deriving some practical rules for the user and has been applied to an YSO (HD 163296). I present the
results of the image reconstruction, providing the first images of a complex YSO.
PSF and field of view characteristics of imaging and nulling interferometers
François Hénault
Show abstract
In this communication are presented some complements to a recent paper entitled "Simple Fourier optics formalism for
high angular resolution systems and nulling interferometry" [1], dealing with imaging and nulling capacities of a few
types of multi-aperture optical systems. Herein the characteristics of such systems in terms of Point Spread Function
(PSF) and Field of View (FoV) are derived from simple analytical expressions that are further evaluated numerically for
various configurations. We consider successively the general cases of Fizeau and Michelson interferometers, and those
of a monolithic pupil, nulling telescope, of a nulling, Sheared-Pupil Telescope (SPT), and of a sparse aperture, Axially
Combined Interferometer (ACI). The analytical formalism also allows establishing the exact Object-Image relationships
applicable to nulling PSTs or ACIs that are planned for future space missions searching for habitable extra-solar planets.
MIRC closure phase studies for high precision measurements
Show abstract
To date, about 17 hot Jupiters have been directly detected by photometric and/or spectroscopic observations.
Only 2 of them, however, are non-transiting hot Jupiters and the rest are all transiting ones. Since non-transiting
hot Jupiter systems are analogs of high contrast binaries, optical/infrared long baseline interferometers can resolve
them and detect the planets if highly stable and precise closure phase measurements are obtained. Thus, this is
a good opportunity for optical/infrared interferometers to contribute to the field of exoplanet characterization.
To reach this goal, detailed calibration studies are essential. In this paper, we report the first results of our
closure phase calibration studies. Specifically, we find strong closure phase drifts that are highly correlated with
target positions, i.e., altitude and azimuth angle. The correlation is stronger with altitude. Our experiments
indicate that the major cause of the drifts is probably longitudinal dispersion. We are able to find a strategy with
multiple approaches to reduce this effect, and are able to model the closure phase drift with a quadratic function
of both altitude and azimuth. We then use this model to calibrate the drifts, and test this new calibration scheme
with the high contrast binary ε Per. Although we can find a better orbital solution with this new method, we
have also found difficulties to interpret the orbit of ε Per, which may stem from possible mis-calibrations or the
influence of the third component in the system. More investigations are definitely necessary to address this issue
and to further confirm our calibration strategy.
Speckle imaging with the SOAR and the very large telescopes
Show abstract
Astronomical speckle imaging is a well established technique for obtaining diffraction limited images of binary
and multiple stars, low contrast solar features and nearby extended objects such as comets and solar system
planets, with large ground-based telescopes. We have developed a speckle masking code to reconstruct images
of such objects from the corresponding specklegrams. This code uses speckle interferometry for estimating the
Fourier amplitudes and bispectrum for estimating the Fourier phases. In this paper, we discuss a few technical
issues such as: What is the photometric and astrometric accuracy that can be achieved with this code? What is
the closest separation between the components of a binary star that can be clearly resolved with sufficient signal
to noise ratio with this code? What is the maximum dynamic range? What kind of calibration schemes can be used in the absence of a bright calibrator close to the object of interest? We address these questions based on computer simulations. We present a few sample reconstructions from the real data obtained from the SOAR telescope. We also present the details of a technical feasibility study carried out with NACO-cube mode at the VLT.
Observing Techniques III
Stellar intensity interferometry: imaging capabilities of air Cherenkov telescope arrays
Show abstract
Sub milli-arcsecond imaging in the visible band will provide a new perspective in stellar astrophysics. Even
though stellar intensity interferometry was abandoned more than 40 years ago, it is capable of imaging and
thus accomplishing more than the measurement of stellar diameters as was previously thought. Various phase
retrieval techniques can be used to reconstruct actual images provided a sufficient coverage of the interferometric
plane is available. Planned large arrays of Air Cherenkov telescopes will provide thousands of simultaneously
available baselines ranging from a few tens of meters to over a kilometer, thus making imaging possible with
unprecedented angular resolution. Here we investigate the imaging capabilities of arrays such as CTA or AGIS
used as Stellar Intensity Interferometry receivers. The study makes use of simulated data as could realistically
be obtained from these arrays. A Cauchy-Riemann based phase recovery allows the reconstruction of images
which can be compared to the pristine image for which the data were simulated. This is first done for uniform
disk stars with different radii and corresponding to various exposure times, and we find that the uncertainty
in reconstructing radii is a few percent after a few hours of exposure time. Finally, more complex images are
considered, showing that imaging at the sub-milli-arc-second scale is possible.
Stellar intensity interferometry: experimental steps toward long-baseline observations
Show abstract
Experiments are in progress to prepare for intensity interferometry with arrays of air Cherenkov
telescopes. At the Bonneville Seabase site, near Salt Lake City, a testbed observatory has been set
up with two 3-m air Cherenkov telescopes on a 23-m baseline. Cameras are being constructed, with
control electronics for either off- or online analysis of the data. At the Lund Observatory (Sweden),
in Technion (Israel) and at the University of Utah (USA), laboratory intensity interferometers simulating stellar observations have been set up and experiments are in progress, using various analog and digital correlators, reaching 1.4 ns time resolution, to analyze signals from pairs of laboratory telescopes.
The potential of rotating-baseline nulling interferometers operating within large single-telescope apertures
Show abstract
The use of a rotating-baseline nulling interferometer for exoplanet detection was proposed several decades ago, but the
technique has not yet been fully demonstrated in practice. Here we consider the faint companion and exozodiacal disk
detection capabilities of rotating-baseline nulling interferometers, such as are envisioned for space-based infrared
nullers, but operating instead within the aperture of large single telescopes. In particular, a nulling interferometer on a
large aperture corrected by a next-generation extreme adaptive optics system can provide deep interferometric contrasts,
and also reach smaller angles (sub λ/D) than classical coronagraphs. Such rotating nullers also provide validation for an
eventual space-based rotating-baseline nulling interferometer. As practical examples, we describe ongoing experiments
with rotating nullers at Palomar and Keck, and consider briefly the case of the Thirty Meter Telescope.
Direct imaging with a hypertelescope of red supergiant stellar surfaces
Show abstract
High angular resolution images obtained with a hypertelescope can strongly constrain the radiative-hydrodynamics simulations of red supergiant (RSG) stars, in terms of intensity contrast, granulation size and temporal variations of the convective motions that are visible on their surface. The characterization of the convective pattern in RSGs is crucial to solve the mass-loss mechanism which contributes heavily to the chemical enrichment of the Galaxy. We show here how the astrophysical objectives and the array configuration are highly dependent to design a hypertelescope. For a given field of view and a given resolution, there is a trade-off between the array geometry and the number of required telescopes to optimize either the (u,v) coverage (to recover the intensity distribution) or the dynamic range (to recover the intensity contrast). To obtain direct snapshot images of Betelgeuse with a hypertelescope, a regular and uniform layout of telescopes is the best array configuration to recover the intensity contrast and the distribution of both large and small granulation cells, but it requires a huge number of telescopes (several hundreds or thousands). An annular configuration allows a reasonable number of telescopes (lower than one hundred) to recover the spatial structures but it provides a low-contrast image. Concerning the design of a pupil densifier to combine all the beams, the photometric fluctuations are not critical (Delta photometry < 50%) contrary to the residual piston requirements (OPD < λ/8) which requires the development of an efficient cophasing system to fully exploit the imaging capability of a hypertelecope.
Space Interferometer Technologies I
Systems engineering and application of system performance modeling in SIM Lite mission
Show abstract
The SIM Lite Astrometric Observatory will be the first space-based Michelson interferometer operating in the visible
wavelength, with the ability to perform ultra-high precision astrometric measurements on distant celestial objects. SIM
Lite data will address in a fundamental way questions such as characterization of Earth-mass planets around nearby
stars. To accomplish these goals it is necessary to rely on a model-based systems engineering approach - much more so
than most other space missions. This paper will describe in further detail the components of this end-to-end performance
model, called "SIM-sim", and show how it has helped the systems engineering process.
On-orbit dynamics and controls system architecture for SIM Lite
Show abstract
The dynamic stability of white light fringes formed on the guide and science interferometers in SIM-Lite
along with the pointing stability of each arm of each interferometer affect the visibility of fringes and the length of
the fringe camera integration time for the observatory. Hence, tight fringe and pointing stability requirements are
needed to reduce science interferometer camera integration times, which in turn help increase the all important
instrument's observing efficiency. The SIM-Lite Instrument Dynamics and Controls (D&C) System Architecture
deals with such dynamic issues through a "tailored" system dynamics design complemented by a comprehensive
active control system. The SIM-Lite on-orbit System architecture is described in this paper. Key roles played by
the resulting D&C System are also established, while the system design is clearly linked to the four nominal phases
of on-orbit operations for the observatory (Tile to Tile slew & settling, guide star acquisition, science observation, &
science interferometer retargeting). Top driving requirements dictating system interferometric-baseline stability and
repeatability, instrument pointing stability, and fringe stability are discussed here together with the resulting high
level Error Budget. Key system sensitivities and currently known D&C related design challenges are also discussed.
SIM Lite mission spectral calibration sensitivities and refinements
Show abstract
SIM-Lite missions will perform astrometry at microarcsecond accuracy using star light interferometry. For typical
baselines that are shorter than 10 meters, this requires to measure optical path difference (OPD) accurate to tens of
picometers calling for highly accurate calibration. A major challenge is to calibrate the star spectral dependency
in fringe measurements - the spectral calibration. Previously, we have developed a spectral calibration and
estimation scheme achieving picometer level accuracy. In this paper, we present the improvements regarding the
application of this scheme from sensitivity studies. Data from the SIM Spectral Calibration Development Unit
(SCDU) test facility shows that the fringe OPD is very sensitive to pointings of both beams from the two arms of
the interferometer. This sensitivity coupled with a systematic pointing error provides a mechanism to explain the
bias changes in 2007. Improving system alignment can effectively reduce this sensitivity and thus errors due to
pointing errors. Modeling this sensitivity can lead to further improvement in data processing. We then investigate
the sensitivity to a model parameter, the bandwidth used in the fringe model, which presents an interesting trade
between systematic and random errors. Finally we show the mitigation of calibration errors due to system drifts
by interpolating instrument calibrations. These improvements enable us to use SCDU data to demonstrate that SIM-Lite missions can meet the 1pm noise floor requirement for detecting earth-like exoplanets.
SIM Lite: ground alignment of the instrument
Show abstract
We present the start of the ground alignment plan for the SIM Lite Instrument. We outline the integration
and alignment of the individual benches on which all the optics are mounted, and then the alignment of the
benches to form the Science and Guide interferometers. The Instrument has a guide interferometer with only
a 40 arc-seconds field of regard, and 200 arc-seconds of alignment adjustability. This requires each sides of the
interferometer to be aligned to a fraction of that, while at the same time be orthogonal to the baseline defined
by the External Metrology Truss. The baselines of the Science and Guide interferometers must also be aligned
to be parallel.
The start of these alignment plans is captured in a SysML Instrument System model, in the form of activity
diagrams. These activity diagrams are then related to the hardware design and requirements. We finish with
future plans for the alignment and integration activities and requirements.
SIM Lite Guide-2 telescope system identification, control design and pointing performance evaluation
Show abstract
The Guide-2 telescope (G2T) is an important subsystem of the new SIM Lite Astrometric Observatory. In this paper we present system identification experiments, design and implementation of the G2T stellar pointing loop that achieves milliarcsecond resolution of spacecraft attitude. Special emphasis was placed on characterization and modeling of PZT hysteresis since this nonlinearity plays an important part in the control loop performance. Power spectral densities of the star image centroids were use to evaluate the pointing loop performance with and with out the presence of simulated ACS disturbances injected via a fast steering mirror (FSM).
Space Interferometer Technologies II
The SIM Lite Astrometric Observatory: engineering risk reduction activity
Show abstract
The SIM Lite Astrometric Observatory is a mission concept for a space-borne instrument to perform micro-arcsecond
narrow-angle astrometry to search 60 to 100 nearby stars for Earth-like planets, and to perform global astrometry for a
broad astrophysics program. The main enabling technology development for the mission was completed during phases A
& B. While the project is waiting for the results of the ASTRO2010 Decadal Survey to proceed into flight
implementation, the instrument team is currently converting the developed technology onto flight-ready engineering
models. These key engineering tasks will significantly reduce the implementation risks during the flight phases C & D of
the mission.
The main optical interferometer components, including the astrometric beam combiner (ABC), the fine steering
mechanism (FSM), the path-length control and modulation optical mechanisms (POM & MOM), focal plane camera
electronics (ATC & FTC), camera cooling cryo-heat pipe, and the siderostat mechanism are currently under
development. Main assemblies are built to meet flight requirements and have been or will be subjected to flight
qualification level environmental testing (random vibration and thermal cycling) and performance testing. The Spectral
Calibration Development Unit (SCDU), a white light interferometer testbed has recently demonstrated how to perform
the spectral calibration of the instrument. The Guide 2 Telescope testbed (G2T) has demonstrated the 50 micro-arcsecond
angle monitoring capability required by SIM Lite to perform astrometry. This paper summarizes recent progress
in engineering risk reduction activities.
SIM interferometer testbed (SCDU) status and recent results
Show abstract
SIM Lite is a space-borne stellar interferometer capable of searching for Earth-size planets in the habitable zones of
nearby stars. This search will require measurement of astrometric angles with sub micro-arcsecond accuracy and optical
pathlength differences to 1 picometer by the end of the five-year mission. One of the most significant technical risks in
achieving this level of accuracy is from systematic errors that arise from spectral differences between candidate stars and
nearby reference stars. The Spectral Calibration Development Unit (SCDU), in operation since 2007, has been used to
explore this effect and demonstrate performance meeting SIM goals. In this paper we present the status of this testbed
and recent results.
Flight qualification and performance testing of SIM precision optical mechanisms
Show abstract
The SIM-Lite project has designed and built PZT driven precision optical mechanisms for pointing and optical pathlength
phasing. This paper will discuss the designs, the flight qualification, and performance in a space representative
environment of these dynamic optical devices. We will also discuss performance of the strain gauges bonded to the PZTs
of the SIM Fine Steering Mirror.
Photonic technologies for a pupil remapping interferometer
Show abstract
Interest in pupil-remapping interferometry, in which a single telescope pupil is fragmented and recombined using
fiber optic technologies, has been growing among a number of groups. As a logical extrapolation from several
highly successful aperture masking programs underway worldwide, pupil remapping offers the advantage of spatial
filtering (with single-mode fibers) and in principle can avoid the penalty of low throughput inherent to an aperture
mask. However in practice, pupil remapping presents a number of difficult technological challenges including
injection into the fibers, pathlength matching of the device, and stability and reproducibility of the results.
Here we present new approaches based on recently-available photonic technologies in which coherent threedimensional
waveguide structures can be sculpted into bulk substrate. These advances allow us to miniaturize
the photonic processing into a single, robust, thermally stable element; ideal for demanding observatory or
spacecraft environments. Ultimately, a wide range of optical functionality could be routinely fabricated into
such structures, including beam combiners and dispersive or wavelength selective elements, bringing us closer to
the vision of an interferometer on a chip.
Picometer stable scan mechanism for gravitational wave detection in space
Show abstract
Detection and observation of gravitational waves requires extremely accurate displacement measurement in the
frequency range 0.03 mHz to 1 Hz. The Laser Interferometer Space Antenna (LISA) mission will attain this by creating a
giant interferometer in space, based on free floating proof masses in three spacecrafts. Due to orbit evolution and time
delay in the interferometer arms, the direction of transmitted light changes. To solve this problem, a picometer stable
Point-Ahead Angle Mechanism (PAAM) was designed, realized and successfully tested. The PAAM concept is based on
a rotatable mirror. The critical requirements are the contribution to the optical path length (less than 1.4 pm / rt Hz) and
the angular jitter (less than 8 nrad / rt Hz). Extreme dimensional stability is achieved by manufacturing a monolithical
Haberland hinge mechanism out of Ti6Al4V, through high precision wire erosion. Extreme thermal stability is realized by placing the thermal center on the surface of the mirror. Because of piezo actuator noise and leakage, the PAAM has to be
controlled in closed-loop. To meet the requirements in the low frequencies, an active target capacitance-to-digital
converter is used. Interferometric measurements with a triangular resonant cavity in vacuum proved that the PAAM meets the requirements.
Current and Planned Facilities
MATISSE cold optics opto-mechanical design
Show abstract
MATISSE is a mid-infrared spectro-interferometer combining beams of up to four telescopes of the ESO VLTI providing phase closure and image reconstruction using interferometric spectra in the LM and N band. This paper presents the opto-mechanical design of the two cold benches containing several types of cryogenic mechanisms (shutter,
Tip/Tilt) used for cryogenic alignment. Key aspects are detailed such as the highly integrated opto-mechanical approach
of the design in order to guarantee component stability and accuracy specifications in the order of nanometers and arcseconds.
Stellar intensity interferometry: optimizing air Cherenkov telescope array layouts
Show abstract
Kilometric-scale optical imagers seem feasible to realize by intensity interferometry, using telescopes primarily
erected for measuring Cherenkov light induced by gamma rays. Planned arrays envision 50-100 telescopes, distributed
over some 1-4 km2. Although array layouts and telescope sizes will primarily be chosen for gamma-ray
observations, also their interferometric performance may be optimized. Observations of stellar objects were numerically
simulated for different array geometries, yielding signal-to-noise ratios for different Fourier components
of the source images in the interferometric (u, v)-plane. Simulations were made for layouts actually proposed for
future Cherenkov telescope arrays, and for subsets with only a fraction of the telescopes. All large arrays provide
dense sampling of the (u, v)-plane due to the sheer number of telescopes, irrespective of their geographic orientation
or stellar coordinates. However, for improved coverage of the (u, v)-plane and a wider variety of baselines (enabling better image reconstruction), an exact east-west grid should be avoided for the numerous smaller telescopes, and repetitive geometric patterns avoided for the few large ones. Sparse arrays become severely limited by a lack of short baselines, and to cover astrophysically relevant dimensions between 0.1-3 milliarcseconds in visible wavelengths, baselines between pairs of telescopes should cover the whole interval 30-2000 m.
LINC-NIRVANA piston control elements
Show abstract
We review the status of hardware developments related to the Linc-Nirvana optical path difference (OPD) control. The
status of our telescope vibration measurements is given. We present the design concept of a feed-forward loop to damp
the impact of telescope mirror vibrations on the OPD seen by Linc-Nirvana. At the focus of the article is a description of
the actuator of the OPD control loop. The weight and vibration optimized construction of this actuator (aka piston
mirror) and its mount has a complex dynamical behavior, which prevents classical PI feedback control from delivering
fast and precise motion of the mirror surface. Therefore, an H-; optimized control strategy will be applied, custom
designed for the piston mirror. The effort of realizing a custom controller on a DSP to drive the piezo is balanced by the
outlook of achieving more than 5x faster servo bandwidths. The laboratory set-up to identify the system, and verify the
closed loop control performance is presented. Our goal is to achieve 30 Hz closed-loop control bandwidth at a precision of 30 nm.
The LINC-NIRVANA fringe and flexure tracker: control design overview
Show abstract
The Fringe and Flexure Tracker System (FFTS) of the LINC-NIRVANA instrument is designed to monitor and
correct the atmospheric piston variations and the instrumental vibrations and flexure at the LBT during the
NIR interferometric image acquisition. In this contribution, we give an overview of the current FFTS control
design, the various subsystems, and their interaction details. The control algorithms are implemented on a realtime
computer system with interfaces to the fringe and flexure detector read-out electronics, the OPD vibration
monitoring system (OVMS) based on accelerometric sensors at the telescope structure, the piezo-electric actuator
for piston compensation, and the AO systems for offloading purposes. The FFTS computer combines data from
different sensors with varying sampling rate, noise and delay. This done on the basis of the vibration data and the
expected power spectrum of atmospheric conditions. Flexure effects are then separated from OPD signals and
the optimal correcting variables are computed and distributed to the actuators. The goal is a 120 nm precision
of the correction at a bandwidth of about 50 Hz. An end-to-end simulation including models of atmospheric
effects, actuator dynamics, sensor effects, and on-site vibration measurements is used to optimize controllers and
filters and to pre-estimate the performance under different observation conditions.
Critical Subsystems I
Testing and alignment of the LBTI
Show abstract
The Large Binocular Telescope Interferometer (LBTI) has been developed and tested and is almost ready to be installed
to LBT mount. In preparation for installation, testing of the beam combination and phasing of the system have been
developed. The testing is currently in progress.
The development of a telescope simulator for LBTI has allowed verification of phasing and alignment with a broad band
source at 10 microns2. Vibration tests with the LBTI mounted to the LBT were carried out in July 2008, with both
seismic accelerometers and an internal optical interferometric measurement. The results have allowed identification of
potential vibration sources on the telescope. Plans for a Star Simulator that illuminates each LBT aperture at the prime
focus with two artificial point sources derived from a single point source via fiber optics are presented. The Star
Simulator will allow testing of LBTI with the telescope and the adaptive secondaries in particular. Testing with the Star
Simulator will allow system level testing of LBTI on the telescope, without need to use on-sky time. Testing of the Star
Simulator components are presented to verify readiness for use with the LBTI.
Fringe detection and piston variability in LINC-NIRVANA
Show abstract
We present the latest status of the fringe detecting algorithms for the LINC-NIRVANA FFTS (Fringe and Flexure
Tracker System). The piston and PSF effects of the system from the top of the atmosphere through the telescopes and
multi-conjugate AO systems to the detector are discussed and the resulting requirements for the FFTS outlined.
Critical Subsystems II
GRAVITY: design and performance of the fringe tracker
Show abstract
GRAVITY is a second generation instrument for the VLTI. It will combine four telescopes in the K band and perform fringe tracking on stars as faint as 10 magnitude with a lambda/8 accuracy, thus counterbalancing atmospheric piston and UTs longitudinal vibrations, despite flux drop-outs due to residual tip-tilt jitter. To achieve such a performance, new developments have to be tested. We have developed a complete simulator so as to improve algorithms and establish an efficient fringe tracking strategy. In addition, a prototype of the fringe tracker for GRAVITY is being built up in order to demonstrate the results of this simulator. We present here the current status of these developments, achieved by simulating realistic tracking at VLTI.
First results using PRIMA FSU as a fringe tracker for MIDI
Show abstract
We report first results obtained from observations using a PRIMA FSU (Fringe Sensor Unit) as a fringe tracker for MIDI on
the VLTI when operating with the 1.8-m ATs. Interferometric observations require the correction of the disturbance in the
optical path induced by atmospheric turbulence ("piston"). The PRIMA FSU is able to compensate for such disturbances
in real-time which makes it a suitable facility to stabilize the fringe signal for other VLTI instruments, like AMBER,
MIDI or later MATISSE. Currently, the atmospheric coherence time in the N band (8 to 13 μm) observed by MIDI,
as well as the thermal background in this band, require a minimum target flux of 20 Jy and a correlated flux of 10 Jy (in
PRISM/HIGH SENSE mode and using the ATs under standard conditions) to allow self-fringe-tracking and data reduction.
However, we show that if the fringes are stabilized by the FSU, coherent integration allows a reliable data reduction even
for the observation of faint targets (Fcorr <10 Jy) with MIDI at standard detector exposure times. We were able to measure the correlated flux of a 0.5 Jy source, which pushes the current limits of MIDI down to regions where numerous new targets
become accessible on ATs. For faint object observations we will discuss the usage of VISIR photometry for calibration
purposes. The observational tests done so far and the obtained results represent a first step towards Phase Referenced
Imaging with the VLTI in the mid-infrared.
The fringe detection laser metrology for the GRAVITY interferometer at the VLTI
Show abstract
Interferometric measurements of optical path length differences of stars over large baselines can deliver extremely
accurate astrometric data. The interferometer GRAVITY will simultaneously measure two objects in the field
of view of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) and
determine their angular separation to a precision of 10 μas in only 5 minutes. To perform the astrometric
measurement with such a high accuracy, the differential path length through the VLTI and the instrument has
to be measured (and tracked since Earth's rotation will permanently change it) by a laser metrology to an even
higher level of accuracy (corresponding to 1 nm in 3 minutes). Usually, heterodyne differential path techniques
are used for nanometer precision measurements, but with these methods it is difficult to track the full beam size
and to follow the light path up to the primary mirror of the telescope. Here, we present the preliminary design of a differential path metrology system, developed within the GRAVITY project. It measures the instrumental differential path over the full pupil size and up to the entrance pupil location. The differential phase is measured by detecting the laser fringe pattern both on the telescopes' secondary mirrors as well as after reflection at the primary mirror. Based on our proposed design we evaluate the phase measurement accuracy based on a full budget of possible statistical and systematic errors. We show that this metrology design fulfills the high precision requirement of GRAVITY.
First results from fringe tracking with the PRIMA fringe sensor unit
Show abstract
The fringe sensor unit (FSU) is the central element of the phase referenced imaging and micro-arcsecond astrometry
(PRIMA) dual-feed facility for the Very Large Telescope interferometer (VLTI). It has been installed
at the Paranal observatory in August 2008 and is undergoing commissioning and preparation for science operation.
Commissioning observations began shortly after installation and first results include the demonstration
of spatially encoded fringe sensing and the increase in VLTI limiting magnitude for fringe tracking. However,
difficulties have been encountered because the FSU does not incorporate real-time photometric correction and its
fringe encoding depends on polarisation. These factors affect the control signals, especially their linearity, and
can disturb the tracking control loop. To account for this, additional calibration and characterisation efforts are
required. We outline the instrument concept and give an overview of the commissioning results obtained so far. We describe the effects of photometric variations and beam-train polarisation on the instrument operation and propose possible solutions. Finally, we update on the current status in view of the start of astrometric science operation with PRIMA.
Critical Subsystems III
The polarization-based collimated beam combiner and the proposed NOVA fringe tracker (NFT) for the VLTI
Show abstract
The Polarization-Based Collimated Beam Combiner efficiently produces pairwise interference between beams from multiple
telescopes. An important feature is achieving "Photometric Symmetry" whereby interference measurements have
no first-order sensitivity to wavefront perturbations (or photometric variations following spatial filtering) which otherwise
entail visibility measurements with increased error, bias, and nonlinearity in phase determination. Among other proposed
applications, this topology has been chosen as the basis for the design of the NOVA Fringe Tracker (NFT), a proposed 4
or 6 telescope second-generation fringe tracker for the VLTI. The NFT takes advantage of the photometric symmetry thus
achieved making it capable of tracking on stars resolved beyond the first visibility null, as well as interfering a telescope
beam with one which is 20 times brighter, a design goal set by ESO. By not requiring OPD modulation for interferometric
detection, the detector exposure time can be increased without performance reduction due to time skew nor is sensitivity
reduced by removing optical power for photometric monitoring, and use of two-phase interferometric detection saves one
half of the photons being diverted for detection of the other two (mainly) unused quadrature phases. The topology is also
proposed for visibility measuring interferometers with configurations proposed for the achievement of balanced quadrature
or 3-phase interferometric detection. A laboratory demonstration confirms >>100:1 rejection of photometric crosstalk in a
fringe tracking configuration where atmospheric OPD fluctuations were simulated using a hair dryer. Tracking with a 30:1
intensity ratio between the incoming beams was performed while rejecting large introduced photometric fluctuations.
The planar optics phase sensor: a study for the VLTI 2nd generation fringe tracker
Show abstract
In a few years, the second generation instruments of the Very Large Telescope Interferometer (VLTI) will routinely
provide observations with 4 to 6 telescopes simultaneously. To reach their ultimate performance, they will need
a fringe sensor capable to measure in real time the randomly varying optical paths differences. A collaboration
between LAOG (PI institute), IAGL, OCA and GIPSA-Lab has proposed the Planar Optics Phase Sensor concept
to ESO for the 2nd Generation Fringe Tracker. This concept is based on the integrated optics technologies,
enabling the conception of extremely compact interferometric instruments naturally providing single-mode spatial
filtering. It allows operations with 4 and 6 telescopes by measuring the fringes position thanks to a spectrally
dispersed ABCD method. We present here the main analysis which led to the current concept as well as the
expected on-sky performance and the proposed design.
Multi-axial integrated optics solution for POPS, a 2nd-generation VLTI fringe tracker
Show abstract
POPS (Planar Optical Phase Sensor) is a second-generation fringe tracker for the Very Large Telescope Interferometer
(VLTI), intended to simultaneously measure the cophasing and coherencing errors of up to six Unit
Telescopes (UT) or Auxiliary Telescopes (AT) in real time. The most promising concepts are probably based on
the utilization of Integrated Optics (IO) components, and were the scope of a Phase A study led by Observatoire
de Grenoble (LAOG). Herein is described a tentative design built around a multi-axial IO chip whose fringes
are dispersed downstream on a detector array, and a Chromatic Phase Diversity algorithm presented in another
paper of this conference . We depict the foreseen opto-mechanical, detection and software implementations,
and provide numerical results from a realistic simulation model in terms of group and phase delay measurement
accuracy and limiting magnitudes in the K band. The ultimate performance of the method is discussed and
compared with the original 2nd generation VLTI fringe tracker requirements.
Coherent integration: to real time or not to real time? That is the question.
Show abstract
Performing long coherent integrations is now widely accepted as one of the best methods for improving the
signal-to-noise ratio of fringe measurements. There are two basic ways of carrying out coherent integration.
One method, real-time coherent integration, stabilizes the fringes on a detector in real time using a separate
detector and feedback loop. In order for this to work, the fringes must be stabilized (nominally to less than
one radian) and the response-time of the fringe-tracking loop must be less than a coherence time. The other
method, post-processing coherent integration, records the fringe and instrument data with minimum integration
and assembles the coherently integrated visibilities after the fact. While recording fringe data for post-processing
coherent integration it is only necessary to stabilize to less than the coherence length of the individual channels.
In terms of fringe stabilization, in the absence of read-noise, post-processing performs significantly better than
real-time coherent integration, one the order of a factor two smaller fringe tracking error. This results in improved
SNR, reduced integration time, and the ability to coherently integrate on fainter targets. In cases of sufficiently
large detector read noise the situation can change to the point where real-time coherent integration produces
better SNR. Real-time coherent integration is thus the less efficient of the two, and should only be employed
when detector read noise prevents post-processing coherent integration.
Technologies I
The 2008-2009 outburst of the young binary system Z CMa unraveled by interferometry with high spectral resolution
Show abstract
Z CMa is a young binary system consisting of an Herbig primary and a FU Ori companion. Both components
seem to be surrounded by active accretion disks and a jet was associated to the Herbig B0. In Nov. 2008,
K. Grankin discovered that Z CMa was exhibiting an outburst with an amplitude larger than any photometric
variations recorded in the last 25 years. To study the innermost regions in which the outburst occurs and
understand its origin, we have observed both binary components with AMBER/VLTI across the Br
emission
line in Dec. 2009 in medium and high spectral resolution modes. Our observations show that the Herbig Be,
responsible for the increase of luminosity, also produces a strong Br
emission, and they allow us to disentangle
from various origins by locating the emission at each velocities through the line. Considering a model of a
Keplerian disk alone fails at reproducing the asymmetric spectro-astrometric measurements, suggesting a major
contribution from an outflow.
Implementation of the chromatic phase diversity method on the SIRIUS test bench
Show abstract
As for large interferometers, the crucial point to solve is the cophasing issue. Indeed, the cophasing device must
be both efficient and independent of the number of telescopes allowing a large capture range and accurate piston
measurements while being easy to implement. We developed such a cophasing method named the Chromatic
Phase Diversity (CPD) method. Actually, using three spectral channels, the CPD method can determine the
piston errors without ambiguity and on a range much larger than ± half a wave. This method makes it possible
to work whether in coherencing mode or in cophasing mode. We designed and implemented this method on
the SIRIUS test bench1 at the Observatoire de la Cote d'Azur, France. We present the instrument design, the
results obtained with the CPD method. The performances such as the achieved capture range, the accuracy of
the piston values extraction and the attainable magnitude are described and analyzed.
Wavefront calibration and correction of an optical train path: a compliant static deformable mirror approach
Show abstract
For ground-based optical interferometry, the simple specification of high surface quality flat relay mirrors is not the end
of the story for obtaining high quality fringes. The Navy Prototype Optical Interferometer array transports the stellar
radiation from six primary collectors through a 10-reflection vacuum relay system, resulting in six separate combinable
wavefronts. The surface error of each of the 60 relay mirrors is specified to be no greater than 32 nm peak-to-valley for
fabrication purposes. However, once mounted in the 10-element optical train the errors from each mirror do not
necessarily cancel one another, but can add and increase the resultant wavefront distortion for that path. This leads to
fringe contrast reduction, reduced ability to fringe track, and a reduction in the limiting magnitude of observable objects.
Fortunately, the total wavefront distortion for each train can be measured, calibrated, and nullified by using a phaseshifting
interferometer combined with a compliant static deformable mirror and control system. In this paper we
describe a system that mitigates the resultant wavefront distortion.
The Fiber Coupler subsystem of the future VLTI instrument GRAVITY
Show abstract
We present the Fiber Coupler subsystem of the future VLTI instrument GRAVITY. GRAVITY is specifically designed
to deliver micro-arcsecond astrometry and deep interferometric imaging. The Fiber Coupler is designed to feed the light
from a science and a reference object into single-mode fibers. The Fiber Coupler consists of four independent units. The
units de-rotate the FoV. A motorized half-wave plate allows rotating the liner polarization axis. Each unit provides
actuators for fast piston actuation, tip-tilt correction and pupil stabilization for one of the beams from four VLT
telescopes. The actuators are operated in closed-loop. Together with a dedicated Laser Guiding System, this allows to
stabilize the beams and maximize the coherently coupled light. The fast piston actuator provides the crucial fringe
tracking capability at a bandwidth of >220Hz. A special roof prism design allows to either split the FoV or to serve as a
50/50 beam splitter without changing the optical path. This offers the possibility of on-axis as well as off-axis fringe
tracking. The optical train consists solely of mirrors, which ensures an achromatic behavior and maximum throughput.
The sophisticated optical design compensates for aberrations which are introduced by off-axis parabolic mirrors. This
allows to achieve Strehl ratios of >95% across the FoV.
Reliable optical pump architecture for highly coherent lasers used in space metrology applications
Show abstract
Laser-based metrology has been identified as an enabling technology in the deployment of large, spaceborne
observatories, where nanometer-level knowledge of fiducial displacement drives overall system performance. In
particular, Nd:YAG NPRO (non-planar ring oscillator) based lasers have received considerable attention in this
application because of their inherent high coherence at wavelengths of interest (1064 and 1319nm). However, the use of
NPRO based lasers in decade long space missions is limited by typical 800nm-band pump laser diode wearout and
random failure rates. Therefore, reliably achieving multi-hundred milliwatt NPRO power over prolonged mission
lifetimes requires innovative pump architectures. In this paper we present a pump architecture capable of supporting
continuous NPRO operation over 5.5yrs at 300mW with reliability exceeding 99.7%. The proposed architecture relies
on a low-loss, high port count, all-fiber optical coupler to combine the outputs of multiple single-mode pump laser
diodes. This coupler is capable of meeting the exacting environmental requirements placed by a space mission, such as
SIM Lite.
'OHANA-Iki: a test-bed for the 'OHANA beam combiner and delay line at CFHT
Show abstract
The possibility of interferometrically coupling large telescopes using single-mode (SM) fibers is a very
attractive one, especially at topographically complex and culturally sensitive astronomical observing sites
such as the Mauna-Kea summit in Hawaii. The 'OHANA project (Optical Hawaiian Array for Nanoradian
Astronomy) aims to link up seven of the large telescopes on Mauna-Kea. The concept of using SM fiber
links for interferometry has been demonstrated using the two W. M. Keck telescopes. A beam-combiner and
optical delay line has been installed at the Canada France Hawaii Telescope (CFHT) to link up Gemini North
and CFHT. In order to test the CFHT beam-combiner without making use of CFHT and Gemini observing
time, the idea of using two small, 20 cm aperture telescopes to inject starlight into the 'Ohana interferometer
fibers was devised. This project, dubbed 'OHANA-Iki, is also exploring the concept of a "soft" optical
interferometer, specifically one in which the telescopes are easily movable and would not require the heavy,
fixed infrastructure found in conventional freespace interferometers such as the VLTI.
Technologies II
Recent progress in wide-field imaging interferometry
Show abstract
The Wide-Field Imaging Interferometry Testbed (WIIT) at NASA's Goddard Space Flight Center and a computational
model of the testbed were developed to demonstrate and learn the practical limitations of techniques for wide-field
spatial-spectral ("double Fourier") interferometry. WIIT is an automated and remotely operated system, and it is now
producing substantial amounts of high-quality data from its state-of-the-art operating environment, Goddard's Advanced
Interferometry and Metrology Lab. In this paper, we discuss the characterization and operation of the testbed and present
recently acquired data. We also give a short description of the computational model and its applications. Finally, we
outline future research directions. A companion paper within this conference discusses the development of new widefield
double Fourier data analysis algorithms.
The NULLTIMATE test bench: achromatic phase shifters for nulling interferometry
Show abstract
The NULLTIMATE project developed and realized three concepts of achromatic phase shifters for nulling interferometry.
One of the concepts is based on dispersive plates made of three materials which where fully
characterized regarding their refractive index and thermo-optic behavior between 100K and 330 K. The other
two concepts are based on mirror optics, one of which uses the phase shift of π when crossing a focus, the
other the reversal of electric fields at reflection. An optical bench has been set up to test and characterize these
phase shifters at wavelengths 2 − 2.4 μm with the option of changing to the 10 μm domain. We summarize the
development of the achromatic phase shifters and report on the current status of the test bench.
Software I
Estimating the phase in interferomety: performance comparison between multi-mode and single-mode schemes
Show abstract
In this paper we compare the performance of multi and single-mode
interferometry for the estimation of the phase of the complex
visibility in presence of detector, photon and atmospheric noises. We show that, despite the loss of flux
occurring when injecting the light in the single-mode component, the spatial
filtering properties of such single-mode devices often enable
higher performance than multimode concepts. In
the high flux regime speckle noise dominated,
single-mode interferometry is always more efficient, and its performance is
significantly better when the correction provided
by adaptive optics becomes poor, by a factor of 2 and more when the Strehl
ratio is lower than 10%. In detector noise regime, multimode interferometry reaches better performance, yet the gain never exceeds 20%, which corresponds to the percentage of photon loss due to the injection in the guides.
We finally show that
single-mode interferometry is also more robust to the turbulence
in both cases of fringe tracking and phase referencing, at the exception of narrow field of views. We conclude that fringe trackers built using single-mode optics should be considered as a solution both practical and competitive.
Analysis of LBT LINC-NIRVANA simulated images of galaxies
Show abstract
LINC-NIRVANA (LN) is a Fizeau interferometer that will provide coherent images in the near-IR combining the
beams from the two Large Binocular Telescope (LBT) arms, by adopting a Multi-Conjugate Adaptive Optics
system (MCAO) that allows for atmospheric turbulence compensation. We applied the software AIRY-LN for
the simulation and the reconstruction of LN images in order to investigate the dependence of the image quality
from the magnitude of the star used for the PSF extraction. A good knowledge of this dependence is a crucial
point for the LN observations, especially for the extragalactic target where the presence of a bright psf-star
within the LN field of view of 10×10 arcsec is not granted. Our results, although still preliminary, show that
while from the morphological point of view the use of psf-star up to a magnitude of 18 is still acceptable, from
the photometric point of view the use of psf-star fainter than Ks ~ 16 mag could cause considerable problems.
A novel imaging algorithm for broadband aperture synthesis data
Show abstract
I developed a new imaging algorithm allowing the combination of multi-channel interferometric data in a single
image. The method is applicable to sources emitting optically thick radiation where the dependence of the source
structure on wavelength can therefore be described by a single parameter, i.e. the (local) effective temperature.
The result of the imaging process is an intensity map as well as a map of the effective temperature across the
source. The advantage of this method over the independent imaging of data in each channel is the benefit of a
much better DB ("dirty beam", also PSF) when combining the aperture coverage of each channel over a wide
range of wavelengths. I present results from applications to composite spectrum binaries and stellar surfaces of
rotating stars based on simulated data.
My imaging algorithm is based on the well known CLEAN method, adding the effective temperature as an
additional parameter for each image pixel. This information can be used to scale the PSF in each channel with
the blackbody law and subtract it from the combined residual map. Once a cleaned map has been obtained
(using regular phase self-calibration techniques) and thus a set of phase-corrected visibilities, individual channel
maps are obtained by running the CLEAN restricted to non-zero pixels. The cleaned channel maps together
with the total flux spectrum can then be used to estimate the blackbody temperature for each non-zero image
pixel, and used for the next iteration of the modified CLEAN algorithm.
Software II
A novel image reconstruction software for optical/infrared interferometry
Show abstract
Imaging large intensity gradients for rapid rotators, complicated spot patterns on rotating RS CVn binaries,
and diffuse disk emission around Young Stellar Objects requires advanced imaging methods beyond the current
image reconstruction paradigms in optical/infrared interferometry. We report on the ongoing development of
SQUEEZE, a flexible software for optical and infrared interferometry capable of simultaneous model-fitting and
image reconstruction, and possessing useful new capabilities such as imaging on a spheroid. We treat the problem
of the local minimas due to the "missing phase" and explore the use of non-pixel-based reconstructions within
the Bayesian evidence and compressed sensing frameworks.
Spectral regularization and sparse representation bases for interferometric imaging
Show abstract
This paper presents some methods being developped for relaxing the underdetermination of the image reconstruction
from interferometric data. We consider, in a first part, the advantages of using spectro-differential data
for having a more accurate and complete set of complexe visibilities. We formulate some regularization criteria
along the spectral dimension, in order to express some prior knowledge on the correlation between the brightness
distributions in different wavelength. These spectral prior terms are inspired by, and combinable with, some
spatial regularization functions already in use in existing Image Reconstruction sofwares.
We also show that the interferometric image reconstruction problem can benefit from being reformulated as
a sparse approximation problem in redundant dictionaries. The dictionary is composed from union of representation
bases, whose atoms correspond to geometric features of the image. Different bases (e.g. impulsions,
wavelets, discrete cosine transform) correspond to different features. The sparse approximation approach consists
in selecting the geometrical features that best explain the interferometric data, by imposing that only a few
such features should be necessary to reconstruct the image. Simulations showing images reconstructed using this
method are presented.
Space Interferometer Technologies III
New concept for direct detection and spectra of exoplanets
Show abstract
We present a novel spectral imaging method for characterization of exoplanets. This method uses 4 collecting telescopes,
in a pattern similar to TPF-I or Darwin, combined with phase chopping. Focusing on contiguous observing wavelengths
in space, the (u, v) plane can be simultaneously filled by the use of the contiguous observing wavelengths instead of
continuously rotating the baselines. For a target comprising a star and a planet, observations on two baselines are
sufficient to extract an image of the planetary system and a spectrum of the planet. Our simulations show that this new
method allows us to detect an analog Earth around a Sun-like star at 10pc and to acquire its spectrum over the
wavelength range from 8 to 18μm.
Development of a CELestial Infrared Nuller Experiment (CELINE) for broadband nulling and new single-mode fiber testing
Show abstract
The small angular distance (<100 mas) and the huge flux ratio (107) between an Earth-like exoplanet in the socalled
habitable zone and its host star makes it very difficult to direct image such systems. Nulling interferometry
consists of a very powerful technique that combines destructively the light from two or more collectors to dim
the starlight and to reveal faint companions in its vicinity. We have developed a new nulling experiment based
on the fiber nuller principle. This fully symmetric reflective nulling bench aims at testing broadband nulling
in both H and K bands as well as characterizing photonic fibers for modal filtering. We present in this paper the
design, the development as well as preliminary results of the experiment.
PERSEE: experimental results on the cophased nulling bench
Show abstract
Nulling interferometry is still a promising method to characterize spectra of exoplanets. One of the main issues
is to cophase at a nanometric level each arm despite satellite disturbances. The bench PERSEE aims to prove
the feasibility of that technique for spaceborne missions. After a short description of PERSEE, we will first
present the results obtained in a simplified configuration: we have cophased down to 0.22 nm rms in optical
path difference (OPD) and 60 mas rms in tip/tilt, and have obtained a monochromatic null of 3 · 10-5 stabilized
at 3•10-6. The goal of 1 nm with additional typical satellite disturbances requires the use of an optimal
control law; that is why we elaborated a dedicated Kalman filter. Simulations and experiments show a good
rejection of disturbances. Performance of the bench should be enhanced by using a Kalman control law, and we
should be able to reach the desired nanometric stability. Following, we will present the first results of the final
polychromatic configuration, which includes an achromatic phase shifter, perturbators and optical delay lines.
As a conclusion, we give the first more general lessons we have already learned from this experiment, both at
system and component levels for a future space mission.
Observing Technologies
The 2010 interferometric imaging beauty contest
Show abstract
We present the results of the fourth Optical/IR Interferometry Imaging Beauty Contest. The contest consists
of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test
data consists of spectral data sets on an object "observed" in the infrared with spectral resolution. There were 4
different algorithms competing this time: BSMEM the Bispectrum Maximum Entropy Method by Young, Baron
& Buscher; RPR the Recursive Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo
algorithm by Baron, Monnier & Kloppenborg; and, WISARD theWeak-phase Interferometric Sample Alternating
Reconstruction Device by Vannier & Mugnier. The contest model image, the data delivered to the contestants
and the rules are described as well as the results of the image reconstruction obtained by each method. These
results are discussed as well as the strengths and limitations of each algorithm.
Optical Long Baseline Interferometry News (OLBIN)
Show abstract
The Optical Long Baseline Interferometry News (OLBIN) is a website and forum for scientists, engineers, and
students who share a common interest in long-baseline stellar interferometry. Through OLBIN you will find
links to projects devoted to stellar interferometry, as well as news items, recent papers and preprints, notices of
upcoming meetings, and resources for further research. This paper describes the history of the website, how it
has evolved to serve the community, and the current plans for its future development. The website can be found
at http://olbin.jpl.nasa.gov/.
Developing achromatic coronagraphic optics for LMIRCam and the LBT
Show abstract
The Apodizing Phase Plate (APP) is a simple optic that provides coronagraphic suppression of diffraction without
the need for any focal plane occulters. We present the design of a broadband APP (the BAPP) for LMIRCam
that is optimised for the direct imaging of cool extrasolar giant planets around nearby stars at thermal infrared
wavelengths. These optics have a high throughput and require no precision alignment. We cover earlier results
using a chromatic APP, the basic principle and manufacture of the optic.
Coherent integration results from the NPOI
Show abstract
In this paper we will discuss the current status of coherent integration with the Navy Prototype Optical Interferometer
(NPOI). Coherent integration relies on being able to phase reference interferometric measurements, which in turn relies on making measurements at multiple wavelengths. We first discuss the generalized group-delay approach, then the meaning of the resulting complex visibilities and then demonstrate how coherent integration
can be used to perform very precision measurement of stellar diameters. The phase of the complex visibility is
particularly attractive as a data product because it is not biased in the same way as visibility amplitudes. We
discuss the relative SNR of triple-product phases and single-baseline phases. We then demonstrate how singlebaseline
phases can be used to make accurate measurements of magnitude differences and separations of binary stars.
Toward the stability required for direct observations of exoplanets with nulling interferometry
Show abstract
In the literature you could find requirements for nulling IR interferometry in terms of nulling ratio nl and
stability of this nulling ratio σnl for the observation of a exo-Earth gravitating at 1au of a solar type star
located at 10pc from the Earth: nl = 10-5 between 7 and 20um and σnl = 3•10-9 over 10 days.1 These
requirements are very demanding. We report on studies made to obtain the technological requirements in
terms of nulling ratio and stability of this nulling ratio in function of the targeted planets and stars. Finally
we will present methods of dithering developed for the NULLTIMATE testbench to achieve to the maximum
stability.
Development of a statistical reduction method for the Palomar Fiber Nuller
Show abstract
A unique statistical data analysis method has been developed for reducing nulling interferometry data. The idea
is to make use of the statistical distributions of the fluctuating null depths and beam intensities to retrieve the
astrophysical null depth in the presence of fluctuations. The approach yields an accuracy much better than is
possible with standard data reduction methods, because the accuracy of the null depth is not limited by the
sizes of the phase and intensity errors but by the uncertainties on their statistical distributions. The result is
an improvement in the instrumental null depth measurement limit of roughly an order of magnitude. We show
in this paper that broadband null depths of 10-4 can be measured in the lab with our infrared Fiber Nuller
without achromatic phase shifters. On sky results are also dramatically improved, with measured contrasts up to
a couple of 10-4 with our instrument mounted on the Hale telescope at the Palomar Observatory. This statistical
analysis is not specific to our instrument and may be applicable to other interferometers.
Integrated optic beam combiners for stellar interferometry and nulling at near- and mid-infrared wavelengths
Show abstract
Integrated optic, stellar interferometric two-beam and three-beam combiners have been designed and fabricated
for operation in the L band (3 μm - 4 μm). The devices have been realized in titanium-indiffused, x-cut lithium
niobate substrates, and on-chip electro-optic fringe scanning has been demonstrated. White light fringes were
produced in the laboratory using the two-beam combiner integrated with an on-chip Y-splitter. Furthermore, a
new design for next-generation, broadband, achromatic, astronomical, beam combiners operating in the N band
(8 μm - 12 μm) is proposed and analyzed. The design is based on adiabatic mode-evolution couplers fabricated
using Ge/Si heterostructure rib waveguides.
Posters: Current and Planned Facilities and Instruments
Review of OCA activities on nulling testbench PERSEE
François Hénault,
Paul Girard,
Aurélie Marcotto,
et al.
Show abstract
We present a review of our activities on PERSEE (Pégase Experiment for Research and Stabilization of Extreme Extinction) at Observatoire de la Côte d'Azur (OCA). PERSEE is a laboratory testbench aiming at achieving a stabilized
nulling ratio better than 10-4 in the astronomical bands K and M, in presence of flight-representative spacecraft
perturbations. The bench has been jointly developed by a Consortium of six French institutes and companies, among
which OCA was responsible for the star simulator and of the opto-mechanical studies, procurement and manufacturing
of the optical train. In this communication are presented the alignment and image quality requirements and the optomechanical
design of the illumination module and main optical train, including a periscope Achromatic Phase Shifter
(APS), tip-tilt mirrors used to introduce and then compensate for dynamic disturbances, delay lines, beam compressors
and fiber injection optics. Preliminary test results of the star simulator are also provided.
High precision interferometer: MIRC with photometric channels
Show abstract
We have designed and constructed a prototype of Photometric Channels for Michigan Infrared Combiner (MIRC).
Photometric Channels provide direct real-time measurements of fluxes from individual telescopes, improving the
precision of visibility and close phase calibration. While this prototype has increased the MIRC data quality
since the commissioning in August 2009, it leaves several issues unresolved, such as the changing polarization
of starlight due to the CHARA beam train. We are planning to make an improvement of the prototype in
conjunction with the six-beam combiner upgrade in the summer 2011.
Measuring the effective wavelength of CHARA classic
Show abstract
This paper presents the first empirical measurement of the K1-band effective wavelength and bandwidth of the
CHARA Classic beam combiner on the CHARA Array. Prior to this work, the accepted effective wavelength
value used for CHARA Classic data (2.1501μm) came from a model of the system; it was not derived from
measurements done on the system directly. We employ two data collection methods for our observations: using
the Optical Path Length Equalizer (OPLE) cart to scan through the interference fringes and using the dither
mirror to scan through the fringes. The two observational methods yield similar effective wavelength measurements
(2.141±0.003μm with the OPLE cart and 2.136±0.002μm with the dither mirror). Both of these results are lower than the previously adopted effective wavelength value, but by less than 0.7%. The bandwidth values
measured by the two methods differ from each other by almost 5% (0.334 ± 0.002μm with the OPLE cart and
0.351±0.003μm with the dither mirror). Our results establish the first estimate of the uncertainty in the effective
wavelength and bandwidth.
The LINC-NIRVANA fringe and flexure tracker: first measurements of the testbed interferometer
Show abstract
LINC-NIRVANA is the near-infrared Fizeau interferometric imaging camera for the Large Binocular Telescope (LBT).
For an efficient interferometric operation of LINC-NIRVANA the Fringe and Flexure Tracking System (FFTS) is
mandatory: It is a real-time servo system that allows to compensate atmospheric and instrumental optical pathlength
differences (OPD). The thereby produced time-stable interference pattern at the position of the science detector enables
long integration times at interferometric angular resolutions.
As the development of the FFTS includes tests of control software and robustness of the fringe tracking concept in a
realistic physical system a testbed interferometer is set up as laboratory experiment.
This setup allows us to generate point-spread functions (PSF) similar to the interferometric PSF of the LBT via a
monochromatic (He-Ne laser) or a polychromatic light source (halogen lamp) and to introduce well defined, fast varying
phase offsets to simulate different atmospheric conditions and sources of instrumental OPD variations via dedicated
actuators.
Furthermore it comprises a piston mirror as actuator to counteract the measured OPD and a CCD camera in the focal
plane as sensor for fringe acquisition which both are substantial devices for a fringe tracking servo loop. The goal of the
setup is to test the performance and stability of different control loop algorithms and to design and optimize the control
approaches.
We present the design and the realization of the testbed interferometer and comment on the fringe-contrast behavior.
OVMS: the optical path difference and vibration monitoring system for the LBT and its interferometers
Show abstract
Characterisation, mitigation and correction of telescope vibrations have proven to be crucial for the performance
of astronomical infrared interferometers. The project teams of the interferometers for the LBT, LINC-NIRVANA
and LBTI, and LBT Observatory (LBTO) have embarked on a joint effort to implement an accelerometer-based
vibration measurement system distributed over the optical elements of the LBT. OVMS, the Optical Path
Difference and Vibration Monitoring System will serve to (i) ensure conditions suitable for adaptive optics
(AO) and interferometric (IF) observations and (ii) utilize vibration information, converted into tip-tilt and
optical path difference data, in the control strategies of the LBT adaptive secondary mirrors and the beam
combining interferometers. The system hardware is mainly developed by Steward Observatory's LBTI team and
its installation at the LBT is underway. The OVMS software development and associated computer infrastructure
is the responsibility of the LINC-NIRVANA team at MPIA Heidelberg. Initially, the OVMS will fill a data archive
provided by LBTO that will be used to study vibration data and correlate them with telescope movements and
environmental parameters thereby identifiying sources of vibrations and to eliminate or mitigate them. Data
display tools will help LBTO staff to keep vibrations within predefined thresholds for quiet conditions for AO
and IF observations. Later-on real-time data from the OVMS will be fed into the control loops of the AO systems
and IF instruments in order to permit the correction of vibration signals with frequencies up to 450 Hz.
GRAVITY spectrometer: metrology laser blocking strategy at OD=12
Show abstract
A two stage blocking system is implemented in the GRAVITY science and the fringe tracking spectrometer optical
design. The blocking system consists of a dichroic mirror and a long wave band-pass filter with the top level
requirements of high transmission of the science light in the K-Band (1.95 - 2.5 μm) region and high blocking power
optical density (OD) ≥ 8 for the metrology laser wavelength at 1.908 μm. The laser metrology blocking filters have been
identified as one critical optical component in the GRAVITY science and fringe tracker spectrometer design.
During the Phase-B study of GRAVITY we procured 3 blocking filter test samples for demonstration and qualification
tests. We present the measurements results of an effective blocking of the metrology laser wavelength with a long wave
band-pass filter at OD=12.
The GRAVITY integrated optics beam combination
Show abstract
Gravity is a 2nd generation interferometric instrument for VLTI. It will combine 4 telescopes in dual feed in the K band
to study general relativity effects around the Galactic Center black hole. The concept of Gravity is based on two
equivalent beam combiner instruments: the scientific one fed by the science target (Sgr A*) and the fringe tracker fed by
a bright reference star (See Gillessen et al.1). Both beam combination instruments are based on silica on silicon
integrated optics (IO) component glued to fluoride glass fiber array. The beam combiners are implemented in a
cryogenic vessel cooled at 200°K and back-illuminated by a high power laser used for metrology (Bartko et al.2). This
paper is dedicated to the description of the development of the integrated beam combiner assembly.
The GRAVITY spectrometers: optical design and principle of operation
Show abstract
Operating on 6 interferometric baselines, i.e. using all 4 unit telescopes (UTs) of the Very Large Telescope
Interferometer (VLTI) simultaneously, the 2nd generation VLTI instrument GRAVITY will deliver narrow-angle
astrometry with 10μas accuracy at the infrared K-band. At this angular resolution, GRAVITY will be able to
detect the positional shift of the photo-center of a flare at the Galactic Center within its orbital timescale of
about 20 minutes, using the observed motion of the flares as dynamical probes of the gravitational field around
the supermassive black hole Sgr A*.
Within the international GRAVITY consortium, the 1. Physikalische Institut of the University of Cologne is
responsible for the development and construction of the two spectrometers of the camera system: one for the
science object, and one for the fringe tracking object. In this paper we present the phase-B optical design of the
two spectrometers as it got derived from the scientific and technical requirements and as it passed the preliminary
design review (PDR) at the European Southern Observatory (ESO) successfully in late 2009.
The hydrogen emission of young stellar objects: key science for next-generation instruments and facilities
Show abstract
The hydrogen emission line is a defining characteristic of young stellar objects probing the planet forming regions
of the disks. The limiting sensitivity of current interferometers has precluded it's detailed study. We'll review
our current understanding of hydrogen emission, recent results and project the science that can be achieved with
sensitive interferometers such as the PRIMA off-axis mode and GRAVITY.
PIONIER: a visitor instrument for VLTI
Show abstract
PIONIER is a 4-telescope visitor instrument for the VLTI, planned to
see its first fringes in 2010. It combines four ATs or four UTs
using a pairwise ABCD integrated optics combiner that can also be
used in scanning mode. It provides low spectral resolution in H and K band. PIONIER is designed for
imaging with a specific emphasis on fast fringe recording to allow
closure-phases and visibilities to be precisely measured. In
this work we provide the detailed description of the instrument and
present its updated status.
Posters: Facility Issues
Evaluation of performance of the MACAO systems at the VLTI
Show abstract
Multiple Application Curvature Adaptive Optics (MACAO) systems are used at the coud´e focus of the unit
telescopes (UTs) at the La-Silla Paranal Observatory, Paranal, to correct for the wave-front aberrations induced
by the atmosphere. These systems are in operation since 2005 and are designed to provide beams with 10 mas
residual rms tip-tilt error to the VLTI laboratory. We have initiated several technical studies such as measuring
the Strehl ratio of the images recorded at the guiding camera of the VLTI, establishing the optimum setup of
the MACAO to get collimated and focused beam down to the VLTI laboratory and to the instruments, and
ascertaining the data generated by the real time computer, all aimed at characterizing and improving the overall
performance of these systems. In this paper we report the current status of these studies.
Posters: Observing Techniques
Status of the VLTI-UT performances wrt vibrations
Show abstract
The ESO Very Large Telescope Interferometer (VLTI) offers the unique access to the combination of the four 8-meter
Unit Telescopes (UT) of Cerro Paranal. The quality of the scientific observations in interferometric mode is strongly
related to the stability of the optical path difference (OPD) between the telescopes. Vibrations at the level of the
telescopes and affecting the mirrors were shown to be an important source of perturbation for the OPD.
ESO has thus started an important effort on the UTs and VLTI to tackle this effect. Active controls based on
accelerometers and phase measurements have been developed to provide real-time correction of the variation of OPD
introduced by vibrations. Systematic studies and measurement of the sources of vibration (instruments, wind, telescope
altitude, ...) have been performed. Solutions to reduce the vibrations via design modification and/or new operation
configurations are studied and implemented. To ensure good operational conditions, the levels of vibrations are regularly
monitored to control any environmental change. This document will describe the modifications implemented and
foreseen and give a status of the VLTI-UT vibrations evolution.
Comparison between closure phase and phase referenced interferometric image reconstructions
Show abstract
We compare the quality of interferometric image reconstructions for two different sets of data: square of the
visibility plus closure phase (e.g. AMBER like case) and square of the visibility plus visibility phase (e.g.
PRIMA+AMBER or GRAVITY like cases). We used the Multi-aperture image Reconstruction Algorithm for
reconstructions of test cases under different signal-to-noise ratios and noisy data (squared visibilities and phases).
Our study takes into account noise models based on the statistics of visibility, phase and closure phase. We
incorporate the works developed by Tatulli and Chelly (2005) on the noise of the power-spectrum and closure
phase in the read-out and photon noise regimes,1 and by Colavita (1999) on the signal-to-noise ratio of the
visibility phase.2 The final images were then compared to the original one by means of positions and fluxes,
computing the astrometry and the photometry. For the astrometry, the precision was typically of tens of
microarcseconds, while for the photometry, it was typically of a few percent. Although both cases are suitable
for image restorations of real interferometric observations, the results indicate a better performance of phase
referencing (V2 + visibility phase) in a low signal-to-noise ratio scenario.
The effects of atmospheric calibration errors on source model parameters
Show abstract
Optical long-baseline interferometric data is commonly calibrated with respect to an external calibrator, which is either an unresolved source or a star with a known angular diameter. A typical observational strategy involves acquiring data in a sequence of calibrator-target pairs, where the observation of each source is obtained separately. Therefore, the atmospheric variations that have time scales shorter than the cadence between the target-calibrator pairs are not always fully removed from the data even after calibration. This results in calibrated observations of a target star that contain unknown quantities of residual atmospheric variations. We describe how Monte Carlo simulations can be used to assess quantitatively the impact of atmospheric variations on fitted model parameters, such as angular diameters of uniform-disk models representing semi- and fully-resolved single stars.
Dual three-way infrared beam combiner at the CHARA Array
Show abstract
Two identical three-way beam combiners have been installed at the CHARA Array. The new setup is an extension of the
two-beam pupil plain combiner, which has been in use thus far. Using the new beam combiners we can now obtain
phase closure data in H, K or J band on two sets of three telescopes. A new optical design has been implemented to
image the six outputs of the combiners onto six separate pixels in the infrared detector array. The new optical
arrangement provides reduced background and spatial filtering. The magnitude limit of this beam combiner has reached
7.8 in K magnitude mainly as a result of better image quality by the new infrared camera optics.
Detection of a geostationary satellite with the Navy Prototype Optical Interferometer
Show abstract
We have detected a satellite via optical interferometry for the first time, using a 16 m baseline of the Navy
Prototype Optical Interferometer (NPOI) to observe the geostationary communications satellite DirecTV-9S
during the "glint" seasons of February-March 2008 and 2009 when the sun-satellite-NPOI geometry was favorable
for causing specular reflections from geostationary satellites. We used the US Naval Observatory Flagstaff
Station 1 m telescope to generate accurate positions for steering the NPOI. Stars are the easiest targets for
optical/infrared interferometers because of their high surface brightness. Low surface brightness targets are
more difficult: if they are small enough not to be resolved out by typical baselines, they are likely to be too faint
to produce detectable fringes in an atmospheric coherence time. The 16 m NPOI baseline, the shortest available
at the time of our observations, resolves out structures larger than ~ 1.5 m at the geostationary distance, while
a typical size for the solar panel arrays is 2 m x 30 m. Our detection indicates that a small fraction of the
satellite glinted, not surprising given that the solar panels are not accurately flat. Our fringe data are consistent
with a two-component image consisting of a 1 to 1.3 m higher surface brightness component and a significantly
larger lower surface brightness component. The brightness of the glints (2.m 4 and ~ 1.m 5 for the two detections in March 2009) and the size scale suggest that the compact component has an albedo of 0.06 to 0.13, while the
larger-scale component is much darker, if circular geometry is assumed.
Imaging simulations of selected science with the Magdalena Ridge Observatory Interferometer
Show abstract
We present simulated observations of surface features on Red Supergiant (RSG) stars and clumpy dust structures
surrounding Active Galactic Nuclei (AGN) with the Magdalena Ridge Observatory Interferometer (MROI). These
represent two of the classes of astrophysical targets enumerated in the MROI Key Science Mission that are typical of the
types of complex astrophysical phenomena that the MROI has been designed to image. The simulations are based on
source structures derived from recent theoretical models and include both random and systematic noise on the measured
Fourier data (visibility amplitudes and closure phases) consistent with our expectations for typical such targets observed
with the MROI. Image reconstructions, obtained using the BSMEM imaging package, are presented for 4-, 6- and 8-
telescope implementations of the array. Although a rudimentary imaging capability is demonstrated with only 4
telescopes, the detailed features of targets are only reliably determined when at least 6 telescopes are present. By the tine
8 telescope are used, the reconstructed images are sufficiently faithful to allow the discrimination between competing
models, confirming the design goal of the MROI, i.e. to offer model-independent near-infrared imaging on sub-milliarcsecond
scales.
A publication database for optical long baseline interferometry
Show abstract
Optical long baseline interferometry is a technique that has generated almost 850 refereed papers to date.
The targets span a large variety of objects from planetary systems to extragalactic studies and all branches of
stellar physics. We have created a database hosted by the JMMC and connected to the Optical Long Baseline
Interferometry Newsletter (OLBIN) web site using MySQL and a collection of XML or PHP scripts in order to
store and classify these publications. Each entry is defined by its ADS bibcode, includes basic ADS informations
and metadata. The metadata are specified by tags sorted in categories: interferometric facilities, instrumentation,
wavelength of operation, spectral resolution, type of measurement, target type, and paper category, for example.
The whole OLBIN publication list has been processed and we present how the database is organized and can
be accessed. We use this tool to generate statistical plots of interest for the community in optical long baseline
interferometry.
Observations of binaries with the NPOI
Show abstract
We present the results of Navy Prototype Optical Interferometer observations of the binary stars θ2 Tauri and
HR7955. These data are reduced using standard methods, as well as coherent integration, and were fitted using
three different methods to measure the separation and position angle of the components, and their magnitude
differences. We used the traditional technique of fitting the V2's, triple amplitudes and triple phases, we also
fitted the baseline phases obtained through coherent integration, and measured the separation of the components
directly on images reconstructed using complex visibilities and phase self calibration. We find that fitting baseline
phases produces the highest precision. The results obtained from imaging are similar to these, although with
higher uncertainties, while the traditional method has the lowest precision. We attribute this result to the fact
that the traditional method combines multiple measurements, e.g. triple phases, thus increasing the errors and
reducing the amount of information that can be fitted. We also obtain a preliminary fit to the orbit of HR7955.
SIM-Lite detection of habitable planets in P-type binary-planetary systems
Show abstract
Close binary stars like spectroscopic binaries create a completely different environment than single stars for the
evolution of a protoplanetary disk. Dynamical interactions between one star and protoplanets in such systems provide
more challenges for theorists to model giant planet migration and formation of multiple planets. For habitable planets the
majority of host stars are in binary star systems. So far only a small amount of Jupiter-size planets have been discovered
in binary stars, whose minimum separations are 20 AU and the median value is about 1000 AU (because of difficulties in
radial velocity measurements). The SIM Lite mission, a space-based astrometric observatory, has a unique capability to
detect habitable planets in binary star systems. This work analyzed responses of the optical system to the field stop for
companion stars and demonstrated that SIM Lite can observe exoplanets in visual binaries with small angular
separations. In particular we investigated the issues for the search for terrestrial planets in P-type binary-planetary
systems, where the planets move around both stars in a relatively distant orbit.
Homothetic apodization of circular aperture HACA: simulation results
Show abstract
In this paper we describe a new technique of circular aperture apodization. It is produced by interferometry.
The light, which is diffracted by a circular aperture, is split into two beams of different amplitudes where one of
them has undergone an homothety to change its radial dimensions, by using an afocal optical system. The two
beams are then combined coherently to form an apodized point spread function (PSF). This procedure allows
us to reduce the diffraction wings of the PSF with different reduction factors depending on the combination
parameters.
Tunable spatial heterodyne spectroscopy (TSHS): a new technique for broadband visible interferometry
Show abstract
In the study of faint, extended sources at high resolving power, interferometry offers significant etendue advantages
relative to conventional dispersive grating spectrometers. A Spatial Heterodyne Spectrometer (SHS) is a compact format
two-beam interferometer that produces wavenumber dependent 2-D Fizeau fringe pattern from which an input spectrum
can be obtained via a Fourier transform. The sampled bandpass of SHS is limited by the highest spatial frequency that
can be sampled by the detector, which is typically less than 10 nm. This limitation has made these instruments useful
primarily for studies of single emission line features or molecular bands. To date there have been few broadband
implementations. We describe here continuing progress toward development of a broadband tunable SHS (TSHS) that is
based on an all-reflective format where a single grating operates simultaneously as a beam-splitter, dispersive element,
and beam combiner. The narrow spectral coverage of the TSHS is moved to different tuning wavenumbers by adjusting
the angle of the pilot mirrors that guide the interfering beams through the optical path, thus slewing the acceptance band
over a much broader spectral range. Our present effort involves a breadboard laboratory prototype of a secondgeneration
TSHS in which we address several technical limitations of an earlier version. In particular the new design
reduces wavefront distortions on the pilot mirrors, solves problems with magnification and focus of the fringe
localization plane onto the detector, and addresses the variability in sensitivity and resolving power limitations of using a
single grating over a large bandpass.
From fringes to the USNO Navy Prototype Optical Interferometer Astrometric Catalog
Show abstract
We report progress on the United States Naval Observatory, Navy Prototype Optical Interferometer, Astrometric Catalog
(UNAC). This catalog uses observations from eight astrometric observation runs (Jan. 2005 - Nov. 2009) at the Navy
Prototype Optical Interferometer (NPOI). The goal of the first release of the UNAC is to provide an astrometric catalog
of at least 100 bright (V < 6) stars with precise positions accurate to < 16 milliarcseconds. In this paper we report on
some of the data processing methods used to obtain absolute astrometric positions from optical interferometer data. We
also discuss plans for assessing the accuracy of our interferometrically derived absolute astrometric positions.
Limb-darkened angular diameters of stars with combined infrared and optical interferometry
Show abstract
We present the angular diameters, physical radii, and effective temperatures of five stars observed using both
the Palomar Testbed Interferometer (PTI) and the Navy Prototype Optical Interferometer (NPOI). These preliminary
results are part of a larger project focused on measuring the angular diameters of the 62 stars that have
been observed with both instruments. We plan to achieve diameter accuracies of 0.5% or better through the
combination of infrared- and visible-wavelength data from PTI and the NPOI, respectively. The difference in
limb-darkening effects between the two wavelength regimes, together with other external parameters, will allow
us to test the atmospheric models on which the limb-darkening corrections are based. High quality angular diameters
for these stars will also lead to more accurate physical diameter measurements and effective temperature determinations.
Posters: Technologies
A very wide-field wavefront sensor for a very narrow-field interferometer
Show abstract
The LINC-NIRVANA wavefront sensors are in their AIT phase. The first Ground-layerWavefront Sensor (GWS)
is shaping in the Adaptive Optics laboratory of the Astronomical Observatory of Padova, while both the Mid-
High Wavefront Sensors (MHWSs) have been aligned and tested as stand-alone units in the Observatory of
Bologna (MHWS#1 aligned to LINC-NIRVANA post focal relay optics).
LINC-NIRVANA is a Fizeau infrared interferometer equipped with advanced, MultiConjugated Adaptive
Optics (MCAO) for the Large Binocular Telescope. The aim of the instrument is to allow true interferometric
imagery over a 10" square Field of View (FoV), getting the sensitivity of a 12m telescope and the spatial resolution
of a 22.8m one. Thanks to the MCAO concept, LINC-NIRVANA will use up to 20 Natural Guide Stars (NGS)
which are divided, according to Layer-Oriented Multiple Field of View technique, between the GWSs and the
MHWSs. To find such a large number of references, the AO systems will use a wide FoV of 6' in diameter and
the light coming from the references used by each WFS will optically sum on its CCD camera.
The MHWSs will detect the deformations due to the high layers and will select up to 8 NGSs in the inner 2'
FoV.
The GWSs, instead, will reconstruct the deformations introduced by the lower atmosphere, which was found
out to be the main source of seeing. Their peculiarity is the highest number of references (up to 12) ever used
in a single instrument, selected in an annular 2'-6' FoV.
Monolithic Michelson Interferometer as ultra stable wavelength reference
Show abstract
Ultra-stable Monolithic Michelson interferometer can be an ideal reference for highprecision
applications such as RV measurement in planet searching and orbit study.
The advantages include wide wavelength range, simple sinusoidal spectral format,
and high optical efficiency. In this paper, we report that a monolithic Michelson
interferometers has been in-house developed with minimized thermal sensitivity with
compensation tuning. With a scanning white light interferometer, the thermal sensitivity is measured ~ 6x10-7/°C at 550 nm and it decreases to zero near 1000 nm.
We expect the wideband wavelength reference source to be stabilized better than 0.3 m/s for RV experiments
Development of a high-dynamic range imaging instrument for a single telescope by a pupil remapping system
Show abstract
We present the laboratory demonstration of a very high-dynamic range imaging instrument FIRST (Fibered Imager foR
Single Telescope). FIRST combines the techniques for aperture masking and a single-mode fiber interferometer to
correct wavefront errors, which leads to a very high-dynamic range up to 106 around very near the central object (~ λ/D)
at visible to near-infrared wavelengths. Our laboratory experiments successfully demonstrated that the original image
can be reconstructed through a pupil remapping system. A first on-sky test will be performed at the Lick Observatory 3-
m Shane telescope for operational tests in the summer of 2010.
Three-dimensional photonic combiner for optical astro interferometry
Stefano Minardi,
Thomas Pertsch,
Ralph Neuhaeuser
Show abstract
We put forward an innovative scheme allowing multiple beam combination and closure-phase retrieval by means of a three dimensional array of coupled optical waveguides. Light propagation in an array of evanescently coupled waveguides is similar to conventional diffraction, however it is bound to a system with finite degrees of freedom. We have demonstrated that the latter feature allows relating uniquely the intensity pattern at the end of a 3x3 waveguide array to the amplitude and relative phases of three monochromatic fields coupled to suitable input waveguides. The method is scalable to arbitrary large arrays of telescopes and baselines.
Development of Monolithic Michelson Interferometer for RV measurement in IR
Show abstract
We present a fixed delay interferometer to be installed in IR-ET (Infra-Red Exoplanets Tracker). We introduce
the design, fabrication and testing processes. In particular, we present a new methodology of computing the
fundamental limit of radial velocity (RV) measurement given by photon noise for DFDI (Dispersed Fixed Delay
Interferometer) method as opposed to conventional echelle method. The new method is later used to determine
the optical path difference (OPD) of the IR-ET interferometer. In addition, we introduce a novel method
of monitoring the stability of the interferometer for IR-ET in broad-band using fourier-transform white-light
scanning interferometry technique. The new method can be potentially expanded and applied to thermo-optic
effect measurement if temperature control system is introduced into the experiment. The thermal response of
the optical system is 3500 m/s/°C. We find that the RV calibration precision of 'Bracketing' method is 1.74
m/s without temperature control.
Single-mode mid-infrared waveguides for spectro-interferometry applications
Show abstract
In the astrophysical context of the search for Earth-like extrasolar planets, an important research effort has been done for
the realization of single-mode integrated optics devices for mid-infrared space-based interferometry. Preparatory projects
like FKSI [3], where rejection of high order modes is required to a level better than 40dB, will need photonic devices
that achieve modal filtering and beam combination in the mid-IR band. In this context, we present results on midinfrared
planar integrated optic beam combiners characterized at LAOG using chalcogenide and silver halide materials.
We show results on FTS measurements, allowing to determine the single mode spectral domain, as well as interference
fringes obtained from Y-junctions realized on these materials.
Feeding the wavefront sensors of LINC-NIRVANA: the dedicated Patrol Camera
Show abstract
LINC-NIRVANA is the IR Fizeau interferometric imager that will be installed within a couple of years on the Large
Binocular Telescope (LBT) in Arizona. Here we present a particular sub-system, the so-called Patrol Camera (PC),
which has been now completed, along with the results of the laboratory tests. It images (in the range 600-900 nm) the
same 2 arcmin FoV seen by the Medium-High Wavefront Sensor (MHWS), adequately sampled to provide the MHWS
star enlargers with the positions of the FoV stars with an accuracy of 0.1 arcsec. To this aim a diffraction-limited
performance is not required, while a distortion free focal plane is needed to provide a suitable astrometric output. Two
identical systems have been realized, one for each single arm, which corresponds to each single telescope. We give here
the details concerning the optical and mechanical layout, as well as the CCD and the control system. The interfaces (mainly software procedures) with LINC-NIRVANA (L-N) are also presented.
A new embedded control system for SUSI
Show abstract
The Sydney University Stellar Interferometer uses embedded processors to control each siderostat station as
well as other major components of the instrument. The maintenance of the original controllers has become a
significant issue and we set out to design a new system that would be inexpensive, suitable for the relatively harsh
operating environment and simple to maintain. We have demonstrated that the new system works satisfactorily
and we are currently replacing the existing controllers with new ones.
Custom beamsplitter and AR coatings for interferometry
Show abstract
We report on final fabrication tests for the dielectric coatings for the Magdalena Ridge Observatory Interferometer
(MROI) fringe tracking beam combiner. The broadband anti-reflection (1.1 μm to 2.4 μm) and beamsplitter (1.49
μm to 2.31 μm) coatings required have been designed with both optical and mechanical constraints in mind. Not
only do these coatings have very low optical losses, but they induce minimal bending of their substrates, thereby
giving very low fringe contrast reductions. Performance tests on the deposited coatings at our manufacturers (Optical Surface Technologies, Albuquerque, NM) demonstrate reflection losses of less than 0.5% over the full bandpass of the AR coating, and deviations from the desired 50:50 intensity ratio of the beamsplitter coating of no more than 2%. When combined with the measured wavefront perturbations these results imply that the total fringe visibility losses induced by imperfect coating quality will be no more than 2% for all outputs of the MROI fringe tracking beam combiner.
Fringe modulation for an MROI beam combiner
Show abstract
We report on the testing of the modulators within the MROI fringe tracking beam combiner. Modulation in
the beam combiner will be performed via modulators introducing an optical path difference in increments of λ/4
into the beams. Knowledge of the path difference introduced needs to be accurate to within 1!. To achieve this accuracy, the modulators are characterized and the desired step waveform optimized through a Fourier analysis technique. Control is implemented in an FPGA embedded system and performance will be monitored by means of a slow loop Fourier algorithm. Details of the progress on characterization, optimization and future implementation are presented here.
Fresnel diffraction in an interferometer: application to MATISSE
Show abstract
While doing optical study in an instrument similar to the interferometers dedicated to the Very Large Telescope (VLT),
we have to take care of the pupil and focus conjugations. Modules with artificial sources are designed to simulate the
stellar beams, in terms of collimation and pupil location. They constitute alignment and calibration tools. In this paper,
we present such a module in which the pupil mask is not located in a collimated beam thus introducing Fresnel
diffraction. We study the instrumental contrast taking into account the spatial coherence of the source, and the pupil
diffraction. The considered example is MATISSE, but this study can apply to any other instrument concerned with Fresnel diffraction.
Hybrid sol-gel technology for fast prototyping in astronomical interferometry
Show abstract
Hybrid sol-gel technology was used for fabrication of prototypes of coaxial two, three and four telescopes beam
combiners for astronomical applications. These devices were designed for the astronomical J-band and have been
characterized using an optical source with emission centered at 1265 nm and with a spectral FWHM of 50 nm.
Interferometric characterization of the two, three and four beam combiners, showed average contrasts respectively
higher than 98%, 96% and 95%. Interferometric spectral analysis of the beam combiners revealed that the chromatic
differential dispersion is the main contributor to the observed contrast decay in the latter cases. The laser direct writing
technique was used for fabrication of a coaxial two beam combiner on sol-gel material; it showed a contrast of 95%. The
measured high contrast fringes confirm that the procedures used lead to performant IO beam combiners. These results
demonstrate the capabilities of the hybrid sol-gel technology for fast prototyping of complex chip designs for astronomical applications.
MAMMUT: mirror vibration metrology for VLTI
Izabela Spaleniak,
Frank Giessler,
Reinhard Geiss,
et al.
Show abstract
MAMMUT (Mirror vibrAtion Metrolology systeM for the Unit Telescope) is an ESO funded feasibility project
for the development of a fiber interferometer prototype designed for optical path laser-metrology along the optical train
of the Unit Telescopes (UT) of the Very Large Telescope Interferometer (VLTI). Fast mechanical vibrations originating
in the VLTI cause fast variations of the optical path difference between two arms of the stellar interferometer, thus
reducing the contrast of measured interference fringes. MAMMUT aims at monitoring in real time the optical path
variations inside the Coudé train of the UT, for active control purposes.
MAMMUT features a 250-meter-long optical fiber which can be used to deliver and inject a laser beam at 1353 nm into
the UT. The injected beam can be dropped from the telescope in the Coudé room and interfered with a phase reference,
provided by the second 250-meter-long arm of the fiber interferometer. The optical path variations are measured
by means of an active homodyne scheme. Coherence between the beam at the injection point and the phase reference
is provided by active fiber stabilization, made possible by the implementation of an internal metrology channel
in MAMMUT.
Here we present the initial laboratory performance results of the MAMMUT prototype, which will be able to sense
optical path variations of +/- 5 μm with sub-10 nm precision within a bandwidth of at least 100 Hz.
Posters: Critical Subsystems
The atmospheric piston simulator as an integral part of the calibration unit of LINC-NIRVANA
Show abstract
The atmospheric piston simulator is an integral part of the calibration unit of LINC-NIRVANA, the Fizeau
interferometric imager for the Large Binocular Telescope. The calibration unit will be necessary to align and set
up the different opto - mechanical subsystems of the instrument. It will assist in (1) the alignment of the optics
via reference fibers; (2) establishing zero optical path difference using a balanced fiber splitter; (3) flat fielding of
the detectors with an integrating sphere; (4) correction of the non-common path aberrations using a fiber-based
phase diversity source; and (5) calibration of the adaptive optics with a rotating reference fiber plate. Substantial
testing and verification of the fringe tracker under as realistic as possible conditions in the lab is desirable, since
the performance of the fringe tracker will ultimately determine the high angular resolution imaging capability
of LINC-NIRVANA as a whole. We are therefore also constructing an atmospheric piston simulator working in
the J and H photometric bands. As with many of the other calibration unit sub-systems, our design concept
is mainly fiber based. Opto - electronic phase modulators will be used to introduce the piston sequences. The
control system of the piston modulators will allow for easy implementation of different vibration power spectra.
This will enable us to test and demonstrate the capabilities of the fringe tracker under realistic conditions.
The LINC-NIRVANA fringe and flexure tracker: laboratory tests
Show abstract
LINC-NIRVANA is the NIR homothetic imaging camera for the Large Binocular Telescope (LBT). In close
cooperation with the Adaptive Optics systems of LINC-NIRVANA the Fringe and Flexure Tracking System
(FFTS) is a fundamental component to ensure a complete and time-stable wavefront correction at the position
of the science detector in order to allow for long integration times at interferometric angular resolutions. In this
contribution, we present the design and the realization of the ongoing FFTS laboratory tests, taking into account
the system requirements. We have to sample the large Field of View and to follow the reference source during
science observations to an accuracy of less than 2 microns. In particular, important tests such as cooling tests
of cryogenic components and tip - tilt test (the repeatability and the precision under the different inclinations)
are presented. The system parameters such as internal flexure and precision are discussed.
Beam combination with a large number of apertures
Show abstract
Mozurkewich presented a beam combiner design suitable for use with a large number of apertures. Such a system
has applications both in space and as a camera for single-aperture, ground-based telescopes. We implemented a
version of this design which accommodates ~ 90 apertures and resolves the fringes into more than 100 spectral
channels. The resulting system, which has been tested in the laboratory, provides over 50,000 simultaneous,
independent fringe measurements. Implementation details and test results are presented.
Mechanical design of the Magdalena Ridge Observatory Interferometer
Show abstract
We report on the mechanical design currently performed at the Magdalena Ridge Observatory
Interferometer (MROI) and how the construction, assembly, integration and verification are planned
towards commissioning. Novel features were added to the mechanical design, and high level of automation
and reliability are being devised, which allows the number of reflections to be kept down to a minimum
possible. This includes unit telescope and associated enclosure and transporter, fast tip-tilt system, beam
relay system, delay line system, beam compressor, automated alignment system, beam turning mirror,
switchyard, fringe tracker and vacuum system.
Modified telescope alignment procedure for improving the beam quality of the CHARA Telescopes
Show abstract
We present the procedure used to optically align the CHARA telescopes. We show that the beam quality,
delivered by the CHARA telescopes E1, E2 and W2, is significantly better now than in 2008. RMS wavefront
error is about 200 nm. The astigmatism observed in W1 is more likely due to a combination of a mechanical
problem in the mounting and misalignment. We present wavefront quality results from four telescopes. Further
beam quality improvements can be expected when the second part of the alignment procedure (tuning) will be
carried out later this year.
The MROI fringe tracker: first fringe experiment
Show abstract
The MROI fringe tracking beam combiner will be the first fringe instrument for the interferometer. It was designed to
utilize the array geometry and maximize sensitivity to drive the interferometer for faint source imaging. Two primary
concerns have driven the design philosophy: 1) maintaining high throughput and visibilities in broadband polarized light,
and 2) mechanical stability. The first concern was addressed through tight fabrication tolerances of the combiner substrates, and custom coatings. In order to optimize mechanical stability, a unique modular design approach was taken that minimizes the number of internal adjustments. This paper reports initial laboratory fringe and stability measurements.
A new control architecture for multi-beam fringe tracker
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Fringe-tracking is a critical issue for modern astronomical ground interferometry. The incoming generation of
fringe trackers is intended to simultaneously co-phase a large number of telescopes, bringing new questions related
to control and redundancy. In this paper, a new control architecture is proposed for the 4/6-telescope Second
Generation Fringe Tracker. Such a system is currently under study for the Very Large Telescope Interferometer
(VLTI). The main features of the proposed solution lie in the explicit handling of many aspects that is rarely
taken into account altogether. These are: delay in the transmission of set-points, coupling between the different
delay lines and redundancy in the measurement. The proposed solution is based on Linear Quadratic Regulator
design together with an extended dynamic observer that recovers the first moments of the disturbance dynamics
(atmospheric pistons). The resulting multi-variable solution enables in particular to tune the different baselines
control-related weighting coefficients according to the quality of the related measurements. While state-space
framework underlines the proposed control design methodology, the resulting controller can still be expressed
in a transfer function form to fit classical implementation scheme generally adopted in the targeted application
community. The efficiency of the proposed solution is illustrated through dedicated simulations involving realistic
data.
The LINC-NIRVANA fringe and flexure tracker: an update of the opto-mechanical system
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LINC-NIRVANA (LN) is a German/Italian interferometric beam combiner camera for the Large Binocular
Telescope. Due to homothetic imaging, LN will make use of an exceptionally large field-of-view. As part of LN,
the Fringe-and-Flexure-Tracker system (FFTS) will provide real-time, closed-loop measurement and correction
of pistonic and flexure signals induced by the atmosphere and inside the telescope-instrument system. Such
compensation is essential for achieving coherent light combination over substantial time intervals (~ 10min.).
The FFTS is composed of a dedicated near-infrared detector, which can be positioned by three linear stages
within the curved focal plane of LN. The system is divided into a cryogenic (detector) and ambient (linear
stages) temperature environment, which are isolated from each other by a moving baffle. We give an overview
of the current design and implementation stage of the FFTS opto-mechanical and electronic components. We
present recent important updates of the system, including the development of separated channels for the tracking
of piston and flexure. Furthermore, the inclusion of dispersive elements will allow for the correction of atmospheric
differential refraction, as well as the induction of artificial dispersion to better exploit the observational-conditions
parameter space (air mass, brightness).
Design of the MROI delay line optical path compensator
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The delay lines for the Magdalena Ridge Observatory Interferometer in New Mexico are required to provide up to 380m
optical path delay with an OPD jitter of better than 15nm, in vacuum, using a single adjustable stroke. In order to meet
these demanding requirements in a cost-effective manner a unique combination of techniques has been used in the design
and construction of the delay line trolley which operates continuously within 190m of evacuated pipe. These features
include contactless delivery of power and control signals, active control of the cat's eye optics and the use of composite
materials to achieve good thermal stability. A full-size prototype trolley has been built and fully tested and the first
production trolley is under construction. We describe the system's key design features and review the construction and
alignment of the delay line trolley. Results obtained with the trolley operating in an evacuated 20m-long test rig under
the full range of conditions required for successful astronomical observations are presented. An OPD jitter of typically
10nm is achieved over the total tracking velocity range from 0 to 15mm/s.
Posters: Software
Bias-free imaging at low light levels
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Measurements from long-baseline interferometry are commonly analysed in terms of the power spectrum and the bispectrum
(or triple-product) of the fringe patterns, as these estimators are invariant in the presence of phase instabilities. At low
light levels, photon and detector noise give rise to systematic "bias" in the power spectrum and bispectrum. This paper extends previous work on computing the expected biases and variances for these quantities by introducing a general method
which can be applied to any fringe-encoding scheme where the measurement equation is linear and to measurements affected
by a combination of photon noise and detector noise. We apply our method to a number of interesting practical
cases, including systems with unevenly-sampled fringe patterns and in the presence of read noise.
The data-reduction software for micro-arcsecond astrometry with PRIMA at the VLTI
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PRIMA (Phase-Referenced Imaging and Microarcsecond Astrometry) is an ESO/VLTI instrument designed for
phase-referenced imaging and narrow-angle astrometry, dedicated to exoplanet detection. The astrometric datareduction
software (ADRS) is a key component of the system, calculating very precise (~ 10 μas) differential
angular separations projected on the sky. For an interferometer with a baseline of 100 m, this separation
corresponds to measuring the (differential) optical path difference with a precision of 5 - 15 nanometers. This
precision can only be achieved with careful calibration of the instrument, including effects that are irrelevant for
almost any other scientific application. PRIMA is currently being commissioned on Paranal, and we expect to obtain the first astrometric data in September 2010. These data will provide a new insight into the operation and calibration of the instrument.
The third version of the AMBER data reduction software
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We present the third release of the AMBER data reduction software by the JMMC. This software is based on
core algorithms optimized after several years of operation. An optional graphic interface in a high level language
allows the user to control the process step by step or in a completely automatic manner. Ongoing improvement
is the implementation of a robust calibration scheme, making use of the full calibration sets available during
the night. The output products are standard OI-FITS files, which can be used directly in high level software
like model fitting or image reconstruction tools. The software performances are illustrated on a full data set of
calibrators observed with AMBER during 5 years taken in various instrumental setup.
GPU-accelerated image reconstruction for optical and infrared interferometry
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The advent of GPU hardware and associated software libraries for scientific computing renders possible acceleration
of parallelisable problems by a typical factor of 10-100. We present the first GPU-accelerated and open
source image reconstruction software for optical/infrared interferometry, making use of the OpenCL library. Finally
we evaluate how this improvement in speed may translate in terms of improvement in image reconstruction quality for currently computationnally intensive algorithms.
Building the 'JMMC Stellar Diameters Catalog' using SearchCal
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The JMMC1 Calibrator Workgroup has long developed methods to ascertain the angular diameter of stars, and provides
this expertise in the SearchCal2 software. SearchCal dynamically finds calibrators near science objects by querying CDS3
hosted catalogs according to observational parameters. Initially limited to bright objects (K magnitude ≤ 5.5), it has been
upgraded with a new method providing calibrators without any magnitude limit but those of queried catalogs. We
introduce here a new static catalog of stellar diameters, containing more than 38000 entries, obtained from SearchCal
results aggregation on the whole celestial sphere, complete for all stars with HIPPARCOS4 parallaxes. We detail the
methods and tools used to produce and study this catalog, and compare the static catalog approach with the dynamical
querying provided by SearchCal engine. We also introduce a new Virtual Observatory service, enabling the reporting of,
and querying about, stars flagged as "bad calibrators" by astronomers, adding this ever-growing database to our
SearchCal service.
SCDU testbed automated in-situ alignment, data acquisition, and analysis
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In the course of fulfilling its mandate, the Spectral Calibration Development Unit (SCDU) testbed for SIM-Lite produces
copious amounts of raw data. To effectively spend time attempting to understand the science driving the data, the team
devised computerized automations to limit the time spent bringing the testbed to a healthy state and commanding it,
and instead focus on analyzing the processed results. We developed a multi-layered scripting language that emphasized
the scientific experiments we conducted, which drastically shortened our experiment scripts, improved their readability,
and all-but-eliminated testbed operator errors. In addition to scientific experiment functions, we also developed a set of
automated alignments that bring the testbed up to a well-aligned state with little more than the push of a button. These
scripts were written in the scripting language, and in Matlab via an interface library, allowing all members of the team to
augment the existing scripting language with complex analysis scripts. To keep track of these results, we created an easilyparseable
state log in which we logged both the state of the testbed and relevant metadata. Finally, we designed a distributed
processing system that allowed us to farm lengthy analyses to a collection of client computers which reported their results
in a central log. Since these logs were parseable, we wrote query scripts that gave us an effortless way to compare results
collected under different conditions. This paper serves as a case-study, detailing the motivating requirements for the
decisions we made and explaining the implementation process.
Posters: Space Interferometer Technology
The fulfillment of two-level control in experimental optical delay line of Michelson Stellar Interferometer
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This article is focused on the two-level control system of ODL, which are divided into bottom layer control of linear
motor and upper layer control of Piezoelectric Transducer(PZT).This ODL are designed to compensate geometrical
optical path difference, which results from the earth rotation, and other disturbances, with high-accuracy and real time.
Based on the PLC of PMAC controller, the linear motor tracks the trajectory of the simulated optical path difference to
compensate roughly. PZT then compensates the rest error measured by ZLM almost real time. A detailed fulfillment of
this method is shown in the article, and the first result data is produced. The result implies that this method is efficient.
This article offers the reference for the ODL development with the practical high accuracy of compensation.
Results of the Guide-2 telescope testbed for the SIM Light Astrometric Observatory
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The SIM Lite Astrometric Observatory is to perform narrow angle astrometry to search for Earth-like planets, and global
astrometry for a broad astrophysics program, for example, mapping the distribution of dark matter in the Galaxy. The
new SIM Lite consists of two Michelson interferometers and one star tracking telescope. The main six-meter baseline
science interferometer observes a target star and a set of reference stars. The four-meter baseline interferometer (guide-1)
monitors the attitude of the instrument in the direction of a target star. The Guide-2 telescope (G2T) tracks a bright star
to monitor the attitude of the instrument in the other two orthogonal directions. A testbed has been built to demonstrate
star-tracking capability of the G2T concept using a new interferometric angle metrology system. In the presence of
simulated 0.2 arcsecond level of expected spacecraft attitude control system perturbations, the measured star-tracking
capability of the G2T testbed system is less than 43 micro-arcsecond during single narrow angle observation.
Mitigation of angle tracking errors due to color dependent centroid shifts in SIM Lite
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The SIM-Lite astrometric interferometer will search for Earth-size planets in the habitable zones of nearby stars. In this
search the interferometer will monitor the astrometric position of candidate stars relative to nearby reference stars over
the course of a 5 year mission. The elemental measurement is the angle between a target star and a reference star. This is
a two-step process, in which the interferometer will each time need to use its controllable optics to align the starlight in
the two arms with each other and with the metrology beams. The sensor for this alignment is an angle tracking CCD
camera. Various constraints in the design of the camera subject it to systematic alignment errors when observing a star of
one spectrum compared with a start of a different spectrum. This effect is called a Color Dependent Centroid Shift
(CDCS) and has been studied extensively with SIM-Lite's SCDU testbed. Here we describe results from the simulation
and testing of this error in the SCDU testbed, as well as effective ways that it can be reduced to acceptable levels.
SCDU (Spectral Calibration Development Unit) testbed narrow angle astrometric performance
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The most stringent astrometric performance requirements on NASA's SIM(Space Interferometer
Mission)-Lite mission will come from the so-called Narrow-Angle (NA) observing scenario,
aimed at finding Earth-like exoplanets, where the interferometer chops between the target star
and several nearby reference stars multiple times over the course of a single visit. Previously,
about 20 pm NA error with various shifts was reported1. Since then, investigation has been under
way to understand the mechanisms that give rise to these shifts. In this paper we report our
findings, the adopted mitigation strategies, and the resulting testbed performance.
Progress on SIM-Lite brassboard interferometer integration and test
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Main brassboard Michelson interferometer components have been recently developed for the future flight phase
implementations of SIM Lite mission. These brassboard components include two fine steering mirrors, pathlength
modulation and cyclic averaging optics and astrometric beam combiner assembly. Field-independent performance tests
will be performed in a vacuum chamber using two siderostats in retro-reflecting positions and a white light stimulus. The
brightness and color dependence of the angle and fringe tracking performance will be measured. The performance of
filtering algorithms will be tested in a simulated spacecraft attitude control system perturbation. To demonstrate
capability of a dim star observation, the angle and fringe tracking CCD sensors are cooled to -110 C using a cold diode
heat pipe system. The new feed-forward control (angle and path-length) algorithms for the dim star observation will be
tested as well. In this paper, we will report the recent progress toward the integration and performance tests of the
brassboard interferometer.