A TESS Cycle 2 Survey of Candidate Variable Hot Subdwarf Stars Identified from Anomalous Gaia DR2 Flux Errors

Hot subdwarf stars are known to exhibit photometric oscillations due to stellar pulsations (sdO/BV stars), eclipses (sdO/B+dM/BD; HW Vir binaries), the reflection effect (sdO/B+dM/BD), ellipsoidal modulation (sdB+WD), and even Rossby waves. Detailed studies of their light curves can constrain stellar parameters through asteroseismological analyses or binary light curve modeling and generally improve our capacity to draw a statistically meaningful picture of this enigmatic stage of stellar evolution. Additionally, they can reveal orbiting exoplanets through timing analyses, SN Ia progenitors, and even gravitational wave verification sources for LISA. While several members are known for all classes of binary and pulsating hot subdwarfs, they would each benefit from additional members. From an analysis of Gaia DR2 flux errors, we have identified nearly 800 hot subdwarf stars with inflated flux errors for their magnitudes, strongly indicative of variability. We obtained 2-min cadence TESS Cycle 2 observations of 250 of these hot subdwarfs to both find new variables and collect high signal-to-noise light curves of known systems. We find that more than 90% of the targets with anomalously-high Gaia DR2 flux errors show significant photometric variations in their TESS light curves. Although the majority of new systems found are cataclysmic variables, we also report the discovery of one new HW Vir binary, several new reflection effect systems, and one potential Roche lobe filling system.