Testing White Dwarf Age Estimates using Wide Double White Dwarf Binaries from Gaia EDR3

TL;DR

This study validates white dwarf age estimation methods using a large sample of wide WD+WD binaries from Gaia EDR3, revealing the reliability of WD ages and identifying cases of prior mergers or unresolved companions.

Contribution

It provides the first large-scale validation of WD age estimates using Gaia data, highlighting the impact of mergers and companions on age accuracy.

Findings

21-36% of more massive WDs have shorter cooling ages, indicating prior mergers or companions.

25% of high-fidelity WD pairs have reliable age uncertainties for certain mass and temperature ranges.

White dwarf ages are generally reliable, with specific cases where age estimates are less accurate.

Abstract

White dwarf (WD) stars evolve simply and predictably, making them reliable age indicators. However, self-consistent validation of the methods for determining WD total ages has yet to be widely performed. This work uses 1565 wide ( > 100 au) WD+WD binaries and 24 new triples containing at least two WDs to test the accuracy and validity of WD total age determinations. For these 1589 wide double-WD binaries and triples, we derive total ages of each WD using photometric data from all-sky surveys, in conjunction with Gaia parallaxes and current hydrogen-atmosphere WD models. Ignoring initial-to-final-mass relations and considering only WD cooling ages, we find that roughly 21-36% of the more massive WDs in a system have a shorter cooling age. Since more massive WDs should be born as more massive main-sequence stars, we attribute this unphysical disagreement as evidence of prior mergers or the presence of an unresolved companion, suggesting that roughly 21-36% of wide WD+WD binaries were once triples. Among the 423 wide WD+WD pairs that pass high-fidelity cuts, we find that 25% total age uncertainties are generally appropriate for WDs with masses > 0.63 Msun and temperatures < 12,000 K, and provide suggested inflation factors for age uncertainties for higher-mass WDs. Overall, WDs return reliable stellar ages, but we detail cases where total ages are least reliable, especially for WDs < 0.63 Msun.