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

TL;DR

This study uses near-infrared spectroscopy and photometry to analyze the magnetic white dwarf SDSS J121209.31+013627.7, revealing a substellar companion likely an L8 dwarf and cyclotron emission, characteristic of polars.

Contribution

It provides the first spectral evidence of a substellar companion to a magnetic white dwarf in a polar system, combining spectroscopic and photometric data for detailed analysis.

Findings

Detection of a late L or early T dwarf companion

Modeling of excess flux with an L8 dwarf and cyclotron emission

System likely an old, low-state magnetic white dwarf binary

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.