A Spitzer Search for Substellar Companions to Low Mass White Dwarfs

TL;DR

This study used the Spitzer Space Telescope to search for substellar companions around 14 low-mass white dwarfs, finding no such companions but identifying some flux excesses due to background objects or stellar companions.

Contribution

First infrared survey targeting low-mass white dwarfs for substellar companions, providing constraints on their companion frequency and nature.

Findings

No substellar companions detected among the sample.

Some flux excesses explained by background sources or stellar companions.

Radial velocity data rule out stellar mass companions for most targets.

Abstract

The formation scenarios for single low-mass (M < 0.45 Msol) white dwarfs include enhanced mass loss from a metal-rich progenitor star or a common envelope phase of a solar-like star with a close-in massive planet or a brown dwarf. Both scenarios suggest that low-mass white dwarfs may have planets. Here, we present a Spitzer IRAC search for substellar and planetary mass companions to 14 low-mass white dwarfs. One of our targets, HS 1653+7753, displays near- and mid-infrared flux excess. However, follow-up MMT observations show that this excess is due to a nearby resolved source, which is mostly likely a background object. Another target, PG 2257+162, shows flux excess compatible with a late-type stellar companion. We do not detect substellar companions to any of the remaining targets. In addition, eight of these stars do not show any radial velocity variations, ruling out stellar mass companions including other white dwarfs. We conclude that a significant fraction of the low-mass white dwarfs in our sample do not have stellar or massive brown dwarf companions.