Two Massive White Dwarfs from NGC 2323 and the Initial-Final Mass Relation for Progenitors of 4 to 6.5 M$_\odot$

TL;DR

This study investigates the initial-final mass relation for white dwarfs in NGC 2323, finding a mostly linear relation for progenitors of 3-6.5 solar masses and highlighting the importance of uniform analysis and cluster age assumptions.

Contribution

It provides a uniform analysis of high-mass white dwarfs and refines the initial-final mass relation, reducing scatter and examining the impact of different cluster age models.

Findings

The initial-final mass relation is mostly linear for progenitors of 3-6.5 M_sun.

Uniform spectral analysis reduces scatter in the relation.

The slope of the IFMR depends on the adopted cluster age model.

Abstract

We have observed a sample of 10 white dwarf candidates in the rich open cluster NGC 2323 (M50) with the Keck Low-Resolution Imaging Spectrometer. The spectroscopy shows eight to be DA white dwarfs, with six of these having high S/N appropriate for our analysis. Two of these white dwarfs are consistent with singly evolved cluster membership, and both are high mass $\sim$1.07 M$_\odot$, and give equivalent progenitor masses of 4.69 M$_\odot$. To supplement these new high-mass white dwarfs and analyze the initial-final mass relation (IFMR), we have also looked at 30 white dwarfs from publicly available data that are mostly all high-mass ($\gtrsim$0.9 M$_\odot$). These original published data exhibited significant scatter, and to test if this scatter is true or simply the result of systematics, we have uniformly analyzed the white dwarf spectra and have adopted thorough photometric techniques to derive uniform cluster parameters for their parent clusters. The resulting IFMR scatter is significantly reduced, arguing that mass-loss rates are not stochastic in nature and that within the ranges of metallicity and mass analyzed in this work mass loss is not highly sensitive to variations in metallicity. Lastly, when adopting cluster ages based on Y$^2$ isochrones, the slope of the high-mass IFMR remains steep and consistent with that found from intermediate-mass white dwarfs, giving a linear IFMR from progenitor masses between 3 to 6.5 M$_\odot$. In contrast, when adopting the slightly younger cluster ages based on PARSEC isochrones, the high-mass IFMR has a moderate turnover near an initial mass of 4 M$_\odot$.