  The spectroscopic class of subdwarf A-type (sdA) stars has come into focus in
recent years because of their possible link to extremely low-mass white dwarfs,
a rare class of objects resulting from binary evolution. Although most sdA
stars are consistent with metal-poor halo main-sequence stars, the formation
and evolution of a fraction of these stars are still matters of debate. The
identification of photometric variability can help to put further constraints
on the evolutionary status of sdA stars, in particular through the analysis of
pulsations. Moreover, the binary ratio, which can be deduced from eclipsing
binaries and ellipsoidal variables, is important as input for stellar models.
In order to search for variability due to either binarity or pulsations in
objects of the spectroscopic sdA class, we have extracted all available high
precision light curves from the Kepler K2 mission. We have performed a thorough
time series analysis on all available light curves, employing three different
methods. Frequencies with a signal-to-noise ratio higher than four have been
used for further analysis. From the 25 targets, 13 turned out to be variables
of different kinds (i.e. classical pulsating stars, ellipsoidal and cataclysmic
variables, eclipsing binaries, and rotationally induced variables). For the
remaining 12 objects, a variability threshold was determined.
