Near-infrared spectroscopy of the very low mass companion to the hot DA white dwarf PG 1234+482

We present a near-infrared spectrum of the hot (T_eff ≈ 55 000 K) hydrogen atmosphere (DA) white dwarf PG 1234+482. We confirm that a very low mass companion is responsible for the previously recognized 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 Two-Micron All-Sky Survey HK photometry of the white dwarf prevent us from distinguishing whether the secondary is stellar or substellar, and assign a spectral type of L0±1 (M9–L1). Therefore, this is the hottest and youngest (≈ 10⁶ yr) DA white dwarf with a possible brown dwarf companion.