A Young Ultramassive White Dwarf in the AB Doradus Moving Group

Abstract

We use Gaia  Data Release 2 (DR2) kinematic data and white dwarf evolutionary models to determine that the young and ultramassive 1.28 ± 0.08 M ⊙ white dwarf GD 50 is a likely member of the AB Doradus moving group (ABDMG). Comparison with the Montréal white dwarf evolutionary models and the MESA Isochrones and Stellar Tracks (MIST) main-sequence lifetimes imply a total age of 117 ± 26 (±13 statistic, ±22 systematic) Myr, accounting for all possible C/O/Ne core compositions and using the Pleiad white dwarf LB 1497 as a comparison benchmark. This is the first white dwarf cosmochronology age for a nearby young moving group, and allows us to refine the age of the ABDMG at Myr by combining it with its independent isochronal age. GD 50 is the first white dwarf member of the ADMG and is located at only 31 pc from the Sun, making it an important benchmark to better understand the star formation history of the Solar neighborhood.