Studies of Two Post Common Envelope Binary Stars

Abstract: New time series photometry of the short period ($P<0.2$~d) binary stars ZTF~J032906.36+070408.3 (ZTF~0329) and ATO~J090.7238+00.5996 (ATL~0602) is presented. The primary (hotter) stars in both systems are white dwarfs, while the cooler stars are M dwarfs. Archival photometry and new and archival spectra are used to derive the temperatures of the components in the two binaries. Both are single-lined binaries. Velocity curves are fitted to radial velocity measurements of the red dwarfs and used to place lower limits on the masses of the white dwarfs. New and archival time series photometry show evolution in the shapes of the light curves of both stars. Spectra of ZTF~0329 show an excess of radiation in the $R_C$ band which is ascribed to electron cyclotron radiation, suggesting that the star is a low accretion rate polar. Satisfactory model fits to the multi-filter light curves of ATL~0602 require the presence of cool spots on the red component of the binary. The latter star exhibits a variety of velocities associated with Balmer and Ca~II emission lines within individual spectra.