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, SDSS J125044.42+154957.3 (P_(orb)= 86 min) and SDSS J151415.65+074446.5 (P_(orb)= 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 SDSS J121209.31+013627.7, a known magnetic white dwarf plus possible brown dwarf binary, which was also recovered by our method.

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