Photospheric diagnostics of core helium burning in giant stars

TL;DR

This study demonstrates that infrared spectra alone can accurately distinguish core helium burning red clump stars from red giant branch stars, enabling better distance measurements and stellar evolution insights without relying solely on asteroseismology.

Contribution

The paper introduces a spectroscopic method to identify core helium burning stars with high accuracy, reducing dependence on asteroseismology for stellar classification.

Findings

Spectra can predict asteroseismic parameters with high precision.

Spectroscopic classification achieves less than 2% contamination.

Enables large-scale identification of standard candles.

Abstract

Core helium burning primary red clump (RC) stars are evolved red giant stars which are excellent standard candles. As such, these stars are routinely used to map the Milky Way or determine the distance to other galaxies among other things. However distinguishing RC stars from their less evolved precursors, namely red giant branch (RGB) stars, is still a difficult challenge and has been deemed the domain of asteroseismology. In this work, we use a sample of 1,676 RGB and RC stars which have both single epoch infrared spectra from the APOGEE survey and asteroseismic parameters and classification to show that the spectra alone can be used to (1) predict asteroseismic parameters with precision high enough to (2) distinguish core helium burning RC from other giant stars with less than 2% contamination. This will not only allow for a clean selection of a large number of standard candles across our own and other galaxies from spectroscopic surveys, but also will remove one of the primary roadblocks for stellar evolution studies of mixing and mass loss in red giant stars.