Near-IR CO and CN in classical Cepheids

TL;DR

This study uses near-infrared spectroscopy of 12 Galactic classical Cepheids to analyze CNO molecular features, revealing insights into stellar composition, temperature, and evolutionary processes, and connecting these to period-colour-metallicity relations.

Contribution

It provides new near-infrared spectral measurements of CO and CN in Cepheids, linking molecular features to stellar parameters and chemical evolution.

Findings

CN affected by dredge-up of processed material

Temperature estimates consistent with spectral features

Connection established between CO measurements and period-colour-metallicity relation

Abstract

We present medium resolution near-infrared spectral measurements of the carbon monoxide (CO) and the cyano radical (CN) features in 12 Galactic classical Cepheids. The pulsation periods of our sample range from 5.5 to 69 days, and the stars studied each had five or more near-IR spectral observations. The CO and CN measurements were used to probe CNO abundances of these stars, and elemental abundance values from the literature were used to identify the trends of [C/N] and [O/N] with CN and CO. To put these measurements in context, we performed stellar atmosphere fitting to obtain estimates of stellar parameters, with a primary focus on effective temperature. Our measurements and temperature estimates show that CN is significantly affected by dredge-up of processed material. We provide discussion as to the potential nature of the recently confirmed classical Cepheid, ET~Vul, and connect our near-infrared CO measurements to the mid-infrared period-colour-metallicity relation.