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

摘要

The nature of the excess near-infrared emission associated with the magneticwhite dwarf commonly known as SDSS 1212 is investigated primarily throughspectroscopy, and also via photometry. The inferred low mass secondary in thissystem 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 thepresence of a late L or early T dwarf. The excess flux seen beyond 1.5 $\mu$min the phase-averaged spectrum is adequately modeled with an L8 dwarfsubstellar companion and cyclotron emission in a 7 MG magnetic field. Thisinteresting system manifests several observational properties typical ofpolars, and is most likely an old interacting binary with a magnetic whitedwarf and a substellar donor in an extended low state.