The red supergiant population in the Perseus arm

TL;DR

This paper introduces a new, large catalogue of 197 cool supergiants in the Perseus arm, using a novel probabilistic method to distinguish them from red giants with high efficiency and low contamination.

Contribution

It develops an improved statistical method to identify red supergiants, resulting in the largest coherent catalogue of such stars in the Galaxy, with many new discoveries.

Findings

Catalogue of 197 cool supergiants, 191 newly identified

Method achieves high efficiency with low contamination

Comparison shows method is as effective as classical criteria

Abstract

We present a new catalogue of cool supergiants in a section of the Perseus arm, most of which had not been previously identified. To generate it, we have used a set of well-defined photometric criteria to select a large number of candidates (637) that were later observed at intermediate resolution in the the Infrared Calcium Triplet spectral range, using a long-slit spectrograph. To separate red supergiants from luminous red giants, we used a statistical method, developed in previous works and improved in the present paper. We present a method to assign probabilities of being a red supergiant to a given spectrum and use the properties of a population to generate clean samples, without contamination from lower-luminosity stars. We compare our identification with a classification done using classical criteria and discuss their respective efficiencies and contaminations as identification methods. We confirm that our method is as efficient at finding supergiants as the best classical methods, but with a far lower contamination by red giants than any other method. The result is a catalogue with 197 cool supergiants, 191 of which did not appear in previous lists of red supergiants. This is the largest coherent catalogue of cool supergiants in the Galaxy.