A Young Ultramassive White Dwarf in the AB Doradus Moving Group

TL;DR

This study identifies GD 50 as a young, ultramassive white dwarf member of the AB Doradus moving group, providing a new cosmochronology age estimate that refines the group's age and offers insights into local star formation history.

Contribution

First white dwarf cosmochronology age determination for a nearby young moving group, refining the age of AB Doradus and establishing GD 50 as its member.

Findings

GD 50 is a likely member of AB Doradus group.

The age of AB Doradus is refined to approximately 133 Myr.

GD 50's properties serve as benchmarks for local star formation studies.

Abstract

We use Gaia DR2 kinematic data and white dwarf evolutionary models to determine that the young and ultramassive white dwarf GD 50 is a likely member of the AB Doradus moving group. Comparison with the Montr\'eal white dwarf evolutionary models and the MIST main-sequence lifetimes imply a total age of 117 $\pm$ 26 ($\pm$ 13 statistic, $\pm$ 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 AB Doradus moving group at 133$_{-20}^{+15}$ Myr by combining it with its independent isochronal age. GD 50 is the first white dwarf member of the AB Doradus moving group 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.