An atlas of cool supergiants from the Magellanic Clouds and typical interlopers. A guide for the classification of luminous red stars

TL;DR

This paper provides an extensive spectral atlas and a modernized classification guide for late-type stars, especially cool supergiants, based on over 1500 optical spectra from the Magellanic Clouds.

Contribution

It introduces a comprehensive spectral atlas and a systematic, modernized classification method for luminous late-type stars using CCD spectra.

Findings

Over 1500 spectra of late-type stars analyzed

Classification of 71% supergiants, 13% giants, and others

A detailed, modern spectral classification guide provided

Abstract

We present an atlas composed of more than 1500 spectra of late-type stars (spectral types from G to M) observed simultaneously in the optical and calcium triplet spectral ranges. These spectra were obtained as part of a survey to search for cool supergiants in the Magellanic Clouds and were taken over four epochs. We provide the spectral and luminosity classification for each spectrum (71% are supergiants, 13% are giants or luminous giants, 4% are carbon or S stars, and the remaining 12% are foreground stars of lesser luminosities). We also provide a detailed guide for the spectral classification of luminous late-type stars, the result of the extensive classification work done for the atlas. Although this guide is based on classical criteria, we have put them together and re-elaborated them for modern CCD-spectra as these criteria were scattered among many different works and mainly conceived for use with photographic plate spectra. The result is a systematic, well-tested process for identifying and classifying luminous late-type stars, illustrated with CCD spectra of standard stars and the classifications of our own catalogue.