2010ApJ...708..411K

The formation scenarios for single low-mass (M < 0.45 M_☉) white dwarfs (WDs) 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 WDs may have planets. Here, we present a Spitzer IRAC search for substellar and planetary mass companions to 14 low-mass WDs. 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 WDs. We conclude that a significant fraction of the low-mass WDs in our sample do not have stellar or massive brown dwarf companions.