Carbon and Oxygen Isotopic Ratios. II. Semiregular Variable M Giants

TL;DR

This study measures carbon and oxygen isotopic ratios in 51 semiregular and irregular variable M giants, linking isotopic data to stellar masses and evolutionary stages, and evaluating model atmosphere applicability.

Contribution

It provides new isotopic ratio measurements for a significant sample of variable M giants and explores their implications for stellar mass, evolution, and atmospheric modeling.

Findings

Isotopic ratios enable mass estimation of SRb stars.

SRb stars are progenitors of Mira variables.

Model atmospheres are valid within certain parameters.

Abstract

Carbon and oxygen isotopic ratios are reported for a sample of 51 SRb- and Lb-type variable asymptotic giant branch stars. Vibration-rotation first- and second-overtone CO lines in 1.5-2.5 mum spectra were measured to derive isotopic ratios for 12C/13C, 16O/17O, and 16O/18O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Using the oxygen isotopic ratios, the masses of the SRb stars can be derived. Combining the masses with Gaia luminosities, the SRb stars are shown to be antecedents of the Mira variables. The limiting parameters where plane-parallel, hydrostatic equilibrium model atmospheres can be used for abundance analysis of M giants are explored.