Carbon star formation as seen through the non-monotonic initial-final mass relation

TL;DR

This paper identifies a non-monotonic feature in the initial-final mass relation of stars, linking it to carbon star formation and providing insights into stellar evolution and galactic chemical enrichment.

Contribution

It reveals a kink in the initial-final mass relation associated with carbon star formation, based on analysis of white dwarfs in old open clusters.

Findings

Detected a kink in the IFMR at initial masses 1.65-2.10 M_sun.

Peak WD mass of 0.70-0.75 M_sun corresponds to stars of 1.8-1.9 M_sun.

Kink indicates the transition between low-mass and intermediate-mass star evolution.

Abstract

The initial-final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved. A new analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR, located over a range of initial masses, $1.65 \lesssim M_{\rm i}/M_{\odot} \lesssim 2.10$. The kink's peak in WD mass of $\approx 0.70-0.75 \, M_{\odot}$ is produced by stars with $M_{\rm i} \simeq 1.8 - 1.9 \, M_{\odot}$, corresponding to ages of about $1.8 - 1.7 $ Gyr. Interestingly, this peak coincides with the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their impact on the spectrophotometric properties of galaxies.