Program: GN-2022B-Q-123

The Euclid space telescope will survey 15000 square degrees of extragalactic sky. Using weak gravitational lensing and galaxy clustering as cosmological probes, Euclid will address fundamental questions about the accelerated expansion of the Universe, dark matter, and the validity of General Relativity on cosmological scales. A few years later, the Nancy Grace Roman space telescope will conduct - among others - a cosmological survey over 2000 square degrees to greater depth. The joint legacy value of both missions is tremendous. Their spectro-photometric flux calibration will be based on six White Dwarf standard stars, and a very red extragalctic source. The aim of this proposal is to obtain time series photometry for all six White Dwarfs to rule out variability on short- and long time scales. We also need to measure the SED of the red spectrophotometric source, obtain its redshift, and identify any AGN signatures.