The Initial-Final Mass Relation for Hydrogen-Deficient White Dwarfs

TL;DR

This paper derives the initial-final mass relation for hydrogen-deficient white dwarfs, revealing a potential discrepancy with hydrogen-rich white dwarfs and discussing possible causes and uncertainties in the measurements.

Contribution

First semi-empirical derivation of the IFMR for non-DA white dwarfs, highlighting potential differences from DA white dwarfs and analyzing error correlations.

Findings

Non-DA white dwarfs may be less massive at a given initial mass.

Uncertainties in mass determinations can be asymmetric.

The IFMR shape is robust despite correlated errors.

Abstract

The initial-final mass relation (IFMR) represents the total mass lost by a star during the entirety of its evolution from the zero age main sequence to the white dwarf cooling track. The semi-empirical IFMR is largely based on observations of DA white dwarfs, the most common spectral type of white dwarf and the simplest atmosphere to model. We present a first derivation of the semi-empirical IFMR for hydrogen deficient white dwarfs (non-DA) in open star clusters. We identify a possible discrepancy between the DA and non-DA IFMRs, with non-DA white dwarfs $\approx 0.07 M_\odot$ less massive at a given initial mass. Such a discrepancy is unexpected based on theoretical models of non-DA formation and observations of field white dwarf mass distributions. If real, the discrepancy is likely due to enhanced mass loss during the final thermal pulse and renewed post-AGB evolution of the star. However, we are dubious that the mass discrepancy is physical and instead is due to the small sample size, to systematic issues in model atmospheres of non-DAs, and to the uncertain evolutionary history of Procyon B (spectral type DQZ). A significantly larger sample size is needed to test these assertions. In addition, we also present Monte Carlo models of the correlated errors for DA and non-DA white dwarfs in the initial-final mass plane. We find the uncertainties in initial-final mass determinations for individual white dwarfs can be significantly asymmetric, but the recovered functional form of the IFMR is grossly unaffected by the correlated errors.