A Gaia DR2 view of white dwarfs in the Hyades

TL;DR

This study uses Gaia DR2 data to analyze white dwarf members of the Hyades, deriving their masses and cooling ages, and exploring the initial-final mass relation with implications for cluster age and stellar evolution.

Contribution

It provides precise measurements of white dwarf masses and ages in the Hyades, compares them with evolutionary models, and investigates the initial-final mass relation and cluster age.

Findings

White dwarf masses are consistent across models with 1-3% precision.

Cooling ages are generally larger than spectroscopic estimates.

The initial-final mass relation slope is steeper than global estimates, but uncertain due to age errors.

Abstract

We have exploited the very precise parallaxes, proper motions and photometry of \textit{Gaia}\, Data Release~2 to study white dwarf members of the Hyades star cluster. Gaia photometry and parallaxes for the eight DA white dwarfs confirmed members have been then used to compute absolute magnitudes and colours. These were compared to three independent sets of white dwarf evolutionary tracks, to derive cooling times and white dwarf (final) masses. All sets of models provide the same mass values, with only small differences in the cooling ages. The precision in the derived masses and cooling ages is typically 1-3%. Our derived masses are generally consistent with spectroscopic estimates from the literature, whilst cooling ages are generally larger. The recent estimate of the cluster age from the Gaia Data Release~2 main sequence turn off colour-magnitude-diagram (790Myr) has been employed to derive progenitor (initial) masses. We find a slope of the initial-final mass relation for the Hyades white dwarfs (masses between ~0.67 and ~0.84 Mo) steeper than that derived for the same mass range from global estimates --averaged over the whole spectrum of white dwarf masses-- irrespectively of the cooling models adopted. However, when considering the error in this age estimate (+160 -100 Myr), a definitive conclusion on this issue cannot be reached yet. The lower limit of 690Myr (closer to the classical Hyades age of 600-650Myr) would provide a slope of the initial-final mass relation closer to the global determinations. We also find hints of an intrinsic spread of the cluster initial-final mass relation for the cluster.