Near-IR spectra of IPHAS extremely red Galactic AGB stars

TL;DR

This paper introduces a comprehensive library of 139 near-IR spectra of cool AGB stars, aiding in the comparison with models and understanding stellar populations, with a focus on very late-type, S-type, and carbon stars.

Contribution

The study provides a new spectral library of extremely red AGB stars, including rare types, and explores the correlation between photometric colours and stellar properties.

Findings

Spectral classification sequences for molecular features.

Identification of rare spectral features.

Strong correlation between (r'-H Alpha) colour and C/O ratio.

Abstract

We present a library of 139 near-IR spectra of cool asymptotic giant branch stars that will be useful for comparison with theoretical model atmosphere calculations and for modeling the integrated emission from intermediate-age stellar populations. The source list was selected from the `extremely red' region of the INT Photometric H Alpha Survey (IPHAS) colour-colour plane that is overwhelmingly dominated by very late-type stars. The spectral library also includes a large fraction of S-type and carbon stars. We present a number of spectral classification sequences highlighting the various molecular features identified and discuss a number of rare features with uncertain identifications in the literature. With its focus on particularly cool photospheres this catalogue serves as a companion to recent spectroscopic atlases of MK standards in the near-IR. Finally the relationship between IPHAS (r'-i') and (r'-H Alpha) colours and spectroscopically determined properties is discussed and a strong correlation between (r'-H Alpha) colour and the C/O abundance index for S-type and carbon stars is noted. This relation has the potential to separate O-rich, S-type and carbon stars in the Galaxy based on their photometry alone.