Massive White Dwarfs in Young Star Clusters

TL;DR

This study used Gaia DR2 data and spectroscopy to identify and confirm massive white dwarf members in young star clusters, revealing a refined initial-final mass relation with no progenitors above approximately 6 solar masses.

Contribution

The paper provides a new, highly selected sample of high-mass white dwarfs in young clusters, refining the initial-final mass relation and clarifying cluster membership using Gaia astrometry and spectroscopy.

Findings

Some white dwarfs previously thought to be members are non-members.

Confirmed members have progenitor masses up to about 6 solar masses.

The refined initial-final mass relation shows no progenitors significantly above 6 solar masses.

Abstract

We have carried out a search for massive white dwarfs (WDs) in the direction of young open star clusters using the Gaia DR2 database. The aim of this survey was to provide robust data for new and previously known high-mass WDs regarding cluster membership, to highlight WDs previously included in the Initial Final Mass Relation (IFMR) that are unlikely members of their respective clusters according to Gaia astrometry and to select an unequivocal WD sample that could then be compared with the host clusters' turnoff masses. All promising WD candidates in each cluster CMD were followed up with spectroscopy from Gemini in order to determine whether they were indeed WDs and derive their masses, temperatures and ages. In order to be considered cluster members, white dwarfs were required to have proper motions and parallaxes within 2, 3, or 4-$\sigma$ of that of their potential parent cluster based on how contaminated the field was in their region of the sky, have a cooling age that was less than the cluster age and a mass that was broadly consistent with the IFMR. A number of WDs included in current versions of the IFMR turned out to be non-members and a number of apparent members, based on Gaia's astrometric data alone, were rejected as their mass and/or cooling times were incompatible with cluster membership. In this way, we developed a highly selected IFMR sample for high mass WDs that, surprisingly, contained no precursor masses significantly in excess of ${\sim}$6 $M_{\odot}$.