A Near-Infrared Spectroscopic Study of the Accreting Magnetic White Dwarf SDSS J121209.31+013627.7 and its Substellar Companion

Abstract

The nature of the excess near-infrared emission associated with the magnetic white dwarf commonly known as SDSS 1212 is investigated primarily through spectroscopy, and also via photometry. The inferred low mass secondary in this system has been previously detected by the emission and variation of H$\alpha$, and the $1-2.5$ $\mu$m spectral data presented here are consistent with the presence of a late L or early T dwarf. The excess flux seen beyond 1.5 $\mu$m in the phase-averaged spectrum is adequately modeled with an L8 dwarf substellar companion and cyclotron emission in a 7 MG magnetic field. This interesting system manifests several observational properties typical of polars, and is most likely an old interacting binary with a magnetic white dwarf and a substellar donor in an extended low state.

28 pages, 5 figures, Accepted to ApJ

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• X-ray orbital modulation of a white dwarf accreting from an L dwarf: The system SDSS J121209.31+013627.7
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• New X-ray detections of magnetic period-bounce cataclysmic variables from XMM-Newton and SRG/eROSITA
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• Cataclysmic variables around the period-bounce: An eROSITA-enhanced multi-wavelength catalog
• Circular Polarimetry of Suspect Wind-accreting Magnetic pre-Polars
• The magnetic system SMSS J1606-1000 as a period bouncer
• Measurement of stellar and substellar winds using white dwarf hosts
• eROSITA-selection of new period-bounce Cataclysmic Variables: First follow-up confirmation using TESS and SDSS