A High Cadence Study of Stellar Variability: Searching for Habitable Planetary Companions Orbiting White Dwarfs with the DECam Minute Cadence Survey

Abstract

One outstanding question in astronomy is what happens to planetary systems as their host star evolves. Though indirect evidence such as metal polluted white dwarf atmospheres and debris disks around white dwarfs, and recent observations of a disintegrating transiting planetesimal around the white dwarf WD 1145+017, suggest that something must survive, we have yet to observe a solid body planetary companion orbiting a white dwarf. In this dissertation, we search the 90219 pount sources identified in the DECam minute cadence survey for evidence of planetary eclipses around white dwarfs, as well as other sources of stellar variability. We find no evidence of eclipse-like events consistent with a planet orbiting a white dwarf, though we do find evidence of two unexpected $\sim$minute duration dips around the likely M-dwarf J0856-0416. Galaxy models predict 802 white dwarfs in the survey, and we constrain the occurrence rate for habitable earth-sized planets around white dwarfs to $\leq$ 37% at the 95% confidence level, consistent with previous studies when adjusted for differences in sample size. Additionally, we detect 132 variable systems, 97 of which are new detections. We find 77 binary systems, including two eclipsing white dwarf + M dwarf systems and one system containing a likely extremely low mass white dwarf, 29 $\delta$ Scuti pulsators, 13 RR Lyrae, seven ZZ Ceti pulsators, two of which appear massive enough to have begun crystallization, and six sources of unidentified variable type.