Insight into the faint galactic white-dwarf population: calibration tools for future deep synoptic surveys

In addition to studying galaxies and the early Universe, future deep synoptic surveys will be essential to our understanding of the structure and history of the Milky Way (MW) by providing unprecedented data on the faint galactic stellar populations. However, observing stars at unrivalled depths presents challenges in identification and calibration. Using the unprecedented 27.1-mag median depth of the Canada-France-Hawai‘i Telescope Large Area U-band Deep Survey (CLAUDS), we precisely studied the galactic stellar populations among over 15 billion of astronomical objects, over 20 square degrees. In the absence of parallax measurements in the CLAUDS data, we devised photometric methods relying solely on colours to select stars in a survey designed to observe galaxies. We demonstrated the usefulness of precise measurements in determining properties of foreground stars, particularly white dwarfs (WDs). Furthermore, through the analysis of WDs in the CLAUDS data, we developed a powerful technique for reducing systematics in synoptic surveys, such as the Legacy Survey of Space and Time (LSST). This technique could significantly enhance data quality in future deep synoptic surveys.