IRTF Observations of White Dwarfs with Possible Near-Infrared Excess

TL;DR

This study uses near-infrared observations to verify excess flux in white dwarfs, confirming some cases of excess and identifying new binary systems, with implications for understanding magnetic and peculiar atmospheres.

Contribution

It provides improved near-infrared data that confirm or refute previous excess detections and identifies new binary systems among white dwarfs.

Findings

Confirmed near-infrared excess in three metal-rich white dwarfs.

Ruled out excess in nine white dwarfs with better data.

Identified or suggested ten new binary systems, including white dwarf-red dwarf pairs and double degenerates.

Abstract

Near-infrared photometry and spectroscopy is obtained for a heterogeneous sample of nearby white dwarfs with possible excess flux as identified primarily in the Two Micron All Sky Survey. Among the sample of 43 stars are a number of white dwarfs that are either metal-rich, magnetic, or binary suspects. With a few notable exceptions in four (or possibly five) distinct categories, the newly obtained JHK photometric data fail to corroborate the putative excesses, with K_IRTF - K_2MASS = +0.31 mag. Where available, GALEX photometric data are used to better constrain the overall spectral energy distribution of the white dwarfs, enabling any excess near-infrared flux to stand out more readily against the expected stellar photosphere. With superior data, a near-infrared photometric excess is confirmed at three metal-rich white dwarfs and ruled out at nine others. Several new binaries are confirmed or suggested; five white dwarf - red dwarf pairs and five double degenerates. Four apparently single magnetic white dwarfs -- two DA and two DQp -- display modest to strong near-infrared excess (relative to non-magnetic models), which may be better described as two effective temperatures owing to a redistribution of energy in highly magnetic or peculiar atmospheres.