Near-infrared spectroscopy of the very low mass companion to the hot DA white dwarf PG1234+482

TL;DR

This study presents near-infrared spectroscopy of the hot white dwarf PG 1234+482, confirming a very low mass companion likely to be a brown dwarf, and constrains its spectral type despite photometric uncertainties.

Contribution

First near-infrared spectrum of a very hot white dwarf with a low mass companion, constraining its spectral type despite photometric uncertainties.

Findings

Confirmed infrared excess due to a low mass companion.

Estimated the companion's spectral type as L0±1.

Identified the system as the hottest and youngest white dwarf with a possible brown dwarf companion.

Abstract

We present a near-infrared spectrum of the hot ($T_{\rm eff}$ $\approx$ 55,000 K) DA white dwarf PG 1234+482. We confirm that a very low mass companion is responsible for the previously recognised infrared photometric excess. We compare spectra of M and L dwarfs, combined with an appropriate white dwarf model, to the data to constrain the spectral type of the secondary. We find that uncertainties in the 2MASS $HK$ photometry of the white dwarf prevent us from distinguishing whether the secondary is stellar or substellar, and assign a spectral type of L0$\pm$1 (M9-L1).Therefore, this is the hottest and youngest ($\approx 10^6$ yr) DA white dwarf with a possible brown dwarf companion.