A First Look at White Dwarf-M Dwarf Pairs in the Sloan Digital Sky Survey

We have identified 109 white dwarf (WD)–M dwarf pairs in the Sloan Digital Sky Survey (SDSS) with g < 20th magnitude. For each system we determined the temperature of the WD primary and the spectral type of the M dwarf secondary. Using Hα emission as a proxy for the chromospheric activity level of the M dwarf, we investigated correlations between the activity level and properties of the system. Compared with field M dwarfs previously observed in the Palomar/MSU Survey, we see a slightly higher active fraction of early-type stars, with activity levels similar to the field. We have conducted follow-up observations at the ARC 3.5 m telescope to obtain radial velocity information and to search for short-period binaries that may be on the verge of interacting. We report on one system with a 4.1 hr period and several additional systems with significant velocity variations.