The evolutionary state of short-period magnetic white dwarf binaries

Abstract

We present phase-resolved spectroscopy of two new short-period low accretion rate magnetic binaries, SDSSJ125044.42+154957.3 (Porb= 86 min) and SDSSJ151415.65+074446.5 (Porb= 89 min). Both systems were previously identified as magnetic white dwarfs from the Zeeman splitting of the Balmer absorption lines in their optical spectra. Their spectral energy distributions exhibit a large near-infrared excess, which we interpret as a combination of cyclotron emission and possibly a late-type companion star. No absorption features from the companion are seen in our optical spectra. We derive the orbital periods from a narrow, variable Hα emission line which we show to originate on the companion star. The high radial velocity amplitude measured in both systems suggests a high orbital inclination, but we find no evidence for eclipses in our data. The two new systems resemble the polar EF Eri in its prolonged low state and also SDSSJ121209.31+013627.7, a known magnetic white dwarf plus possible brown dwarf binary, which was also recovered by our method. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.