Ultracool white dwarfs

For the first time, a large number of cool and ultracool WDs have distance and tangential velocities measurements available. Our targets have distances ranging from 21pc to >100pc, and include five stars within 30pc.

Contrary to expectations, all but two of them have tangential velocities smaller than 150km/s thus suggesting Galactic disc membership. The oldest WDs in this sample have WD cooling ages of 10Gyr, providing a firm lower limit to the age of the thick disc population. Many of our targets have uncharacteristically large radii, indicating that they are low-mass WDs.