Near-infrared spectroscopic study of the accreting magnetic white dwarf SDSS J121209.31+013627.7 and its substellar companion

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 Hα, and the 1-2.5 μm spectral data presented here are consistent with the presence of a late L or early T dwarf. The excess flux seen beyond 1.5 μm 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