Checking It Twice: Using [C/N]-Masses and Asteroseismic Masses as a Diagnostic of Mass Loss and Transfer on the RGB

TL;DR

This study uses [C/N] ratios and asteroseismic masses to investigate mass loss and transfer in red giants, revealing metallicity-dependent mass loss trends and identifying potential mass transfer candidates.

Contribution

It introduces a mass- and metallicity-dependent Reimers' eta calibration and identifies outlier stars likely affected by mass transfer, advancing understanding of stellar evolution.

Findings

Mass loss decreases with metallicity and mass, contradicting Reimers' formula.

Identified 207 stars as potential mass transfer candidates.

Proposed a new calibration for Reimers' eta based on empirical trends.

Abstract

The surface [C/N] of red giants is correlated with birth mass, but not directly impacted by mass loss. Exploiting this, we compare asteroseismic masses of red giants with the same [C/N] and but different evolutionary states. We find bulk differences between stars at the beginning of the red giant branch and in the subsequent evolutionary phase, the red clump, providing a direct constraint on the strength of net RGB mass loss in field stars. We find that net mass loss decreases with metallicity and mass, matching recent studies for field giants, but contradicting expectations from the widely used Reimers' mass loss formula. We propose a mass- and metallicity-dependent Reimers' $\eta$ calibration that reproduces the empirical trends that we see. In addition, we identify 207 stars (3.33% of our sample) that are clear outliers from their population in these birth mass bins, which we believe are likely candidates for mass transfer events. These stars do not show any obvious discrepancies in abundances or binary properties from their counterparts. This population should be accounted for in Galactic archaeological studies. Further follow-up is required to quantify their occurrence rate and origin.