Letter to the Editor

A new method to identify subclasses among AGB stars using Gaia and 2MASS photometry

¹ University of Vienna, Department of Astrophysics, Tuerkenschanzstrasse 17, 1180 Vienna, Austria
e-mail: thomas.lebzelter@univie.ac.at
² Department of Astronomy, University of Geneva, Ch. des Maillettes 51, 1290 Versoix, Switzerland
³ Dipartimento di Fisica e Astronomia Galileo Galilei, Università di Padova, Vicolo dell’Osservatorio 3, 35122 Padova, Italy
⁴ Research School of Astronomy and Astrophysics, Australian National University, Canberra, ACT 2611, Australia

Received: 11 June 2018
Accepted: 10 August 2018

Abstract

Aims. We explore the wealth of high-quality photometric data provided by data release 2 (DR2) of the Gaia mission for long-period variables (LPVs) in the Large Magellanic Cloud (LMC). Our goal is to identify stars of various types and masses along the asymptotic giant branch.

Methods. For this endeavour, we developed a new multi-band approach combining Wesenheit functions W_RP,BP−RP and W_Ks,J−Ks in the Gaia BP, RP, and 2MASS J, K_s spectral ranges, respectively, and use a new diagram, (W_RP,BP−RP − W_Ks,J−Ks) versus K_s, to distinguish between different kinds of stars in our sample of LPVs. We used stellar population synthesis models to validate our approach.

Results. We demonstrate the ability of the new diagram to discriminate between O- and C-rich objects, and to identify low-mass, intermediate-mass, and massive O-rich red giants, as well as extreme C-rich stars. Stellar evolution and population synthesis models guide the interpretation of the results, highlighting the diagnostic power of the new tool to discriminate between stellar initial masses, chemical properties, and evolutionary stages.