Opening new dimensions in the study of ultra-short variability and asteroseismology of compact pulsators with BlackGEM

Stellar variability studies have recently undergone immense boosts thanks to recent photometric surveys done with ground-based telescopes and with the CoRoT and Kepler space telescopes. This wealth of data led to huge progress in the understanding and improving of the theory of stellar structure and evolution, mainly thanks to asteroseismic applications. Unfortunately, some crucial phases in the life of stars could not or only hardly be studied from these surveys, either because the integration times were too long (above 10 minutes) or the majority of class members was too faint, or the flexibility in target selections was too small.

With this project, we open the new window of ultra-short variability studies of faint stars with the BlackGEM instrument. The main reason to build BlackGEM is to provide an optical array for gravitational waves astrophysics. We will not treat this science case, but we have bought ourselves into the consortium to use BlackGEM for a unique ensemble study of the variability of subdwarf and white dwarf pulsators. Our study requires multicolour photometry with integration times of a minute for large faint samples, during at least one week. This is precisely the type of data that BlackGEM shall deliver. It will allow us to perform ensemble asteroseismology of subdwarfs and of white dwarfs, along with modelling of the borders of their instability strips.