  Combined studies of variable stars and stellar clusters open great horizons,
and they allow us to improve our understanding of stellar cluster formation and
stellar evolution. In that prospect, the Gaia mission will provide astrometric,
photometric, and spectroscopic data for about one billion stars of the Milky
Way. This will represent a major census of stellar clusters, and it will
drastically increase the number of known variable stars. In particular, the
peculiar Gaia scanning law offers the opportunity to investigate the rather
unexplored domain of short timescale variability (from tens of seconds to a
dozen of hours), bringing invaluable clues to the fields of stellar physics and
stellar aggregates. We assess the Gaia capabilities in terms of short timescale
variability detection, using extensive light-curve simulations for various
variable object types. We show that Gaia can detect periodic variability
phenomena with amplitude variations larger than a few millimagnitudes.
Additionally, we plan to perform subsequent follow-up of variables stars
detected in clusters by Gaia to better characterize them. Hence, we develop a
pipeline for the analysis of high cadence photometry from ground-based
telescopes such as the 1.2m Euler telescope (La Silla, Chile) and the 1.2m
Mercator telescope (La Palma, Canary Islands).
