Discovery of a Magnetic White Dwarf/Probable Brown Dwarf Short-Period Binary

Abstract

The magnetic white dwarf SDSS J121209.31+013627.7 exhibits a weak, narrow Halpha emission line whose radial velocity and strength are modulated on a period of ~90 minutes. Though indicative of irradiation on a nearby companion, no cool continuum component is evident in the optical spectrum, and IR photometry limits the absolute magnitude of the companion to M_J > 13.37. This is equivalent to an isolated L5 dwarf, with T_eff < 1700 K. Consideration of possible evolutionary histories suggests that, until ~0.6 Gyr ago, the brown dwarf orbited a ~1.5 M_sun main seqeunce star with P ~ 1 yr, a ~ 1 AU, thus resembling many of the gaseous superplanets being found in extrasolar planet searches. Common envelope evolution when the massive star left the main sequence reduced the period to only a few hours, and ensuing angular momentum loss has further degraded the orbit. The binary is ripe for additional observations aimed at better studying brown dwarfs and the effects of irradiation on their structure.

6 pages, 3 figures

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• Analysis of hydrogen-rich magnetic white dwarfs detected in the Sloan Digital Sky Survey
• White dwarfs in the UKIDSS Large Area Survey: The Substellar Companion Fraction
• New Close Binary Systems from the SDSS-I (Data Release Five) and the Search for Magnetic White Dwarfs in Cataclysmic Variable Progenitor Systems
• Close detached white dwarf + brown dwarf binaries: further evidence for low values of the common envelope efficiency
• A Catalogue of Potential Post Common Envelope Binaries
• The nature of the close magnetic white dwarf + probable brown dwarf binary SDSS J121209.31+013627.7
• Two Additions to the New Class of Low Accretion-Rate Magnetic Binaries
• A Near-Infrared Spectroscopic Study of the Accreting Magnetic White Dwarf SDSS J121209.31+013627.7 and its Substellar Companion
• Mass Determination and Detection of the Onset of Chromospheric Activity for the Sub-Stellar Object in EF Eridani
• Magnetic white dwarfs in post-common-envelope binaries
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• Detection of a Variable Infrared Excess Around SDSS 121209.31+013627.7
• Variability, periodicity and contact binaries in WISE
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• Circular Polarimetry of Suspect Wind-accreting Magnetic pre-Polars
• GALEX and Optical Light Curves of WX LMi, SDSSJ103100.5+202832.2 and SDSSJ121209.31+013627.7
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