  We present an analysis of the ultraviolet light curves of five Hot DQ white
dwarfs recently observed with the Cosmic Origins Spectrograph (COS) on board
the Hubble Space Telescope (HST). These light curves were constructed by
extracting the time-tag information from the FUV and NUV spectroscopic data.
Single-color light curves were thus produced in 60 s time bins. The Fourier
analysis of these data successfully recovers the main pulsation modes of the
three stars previously known to be variable from ground-based observations. We
also report the discovery of pulsations in another object, SDSS J1153+0056,
making it only the fifth member of the new class of variable Hot DQ stars, and
the first pulsating white dwarf to be discovered from space-based observations.
The relatively high amplitudes of the modes observed in the FUV -- 2 to 4 times
that observed in the optical -- as well as the high fraction of stars variable
in our sample suggest that most, if not all, Hot DQ white dwarfs might be
pulsating at some level when observed at high enough sensitivity. Our results
also underline the vast potential of the time-tag capability of the HST/COS
combination.
