IAASARS, National Observatory of Athens,
e-mail: email@example.com; firstname.lastname@example.org
2 Section of Astrophysics, Astronomy & Mechanics, Department of Physics, University of Athens, 15783 Athens, Greece
3 ESO – European Organisation for Astronomical Research in the Southern Hemisphere, 3107 Alonso de Cordova, Vitacura, Santiago de Chile, Chile
4 Instituto de Astrofísica de Canarias, avenida Vía Láctea, , 38205, La Laguna, Tenerife, Spain
5 Departamento de Astrofísica, Universidad de La Laguna, 38205, La Laguna, Tenerife, Spain
6 Grantecan S. A., Centro de Astrofísica de La Palma, Cuesta de San José, 38712 Breña Baja, La Palma, Spain
7 Department of Astrophysical Science, Princeton University, 4 Ivy Lane, Peyton Hall, Princeton NJ 08544, USA
8 Las Campanas Observatory, Carnegie Observatories, 601 Casilla, La Serena, Chile
Received: 18 September 2013
Accepted: 16 December 2013
Context. The role of episodic mass loss in massive-star evolution is one of the most important open questions of current stellar evolution theory. Episodic mass loss produces dust and therefore causes evolved massive stars to be very luminous in the mid-infrared and dim at optical wavelengths.
Aims. We aim to increase the number of investigated luminous mid-IR sources to shed light on the late stages of these objects. To achieve this we employed mid-IR selection criteria to identity dusty evolved massive stars in two nearby galaxies.
Methods. The method is based on mid-IR colors, using 3.6 μm and 4.5 μm photometry from archival Spitzer Space Telescope images of nearby galaxies and J-band photometry from 2MASS. We applied our criteria to two nearby star-forming dwarf irregular galaxies, Sextans A and IC 1613, selecting eight targets, which we followed-up with spectroscopy.
Results. Our spectral classification and analysis yielded the discovery of two M-type supergiants in IC 1613, three K-type supergiants and one candidate F-type giant in Sextans A, and two foreground M giants. We show that the proposed criteria provide an independent way for identifying dusty evolved massive stars that can be extended to all nearby galaxies with available Spitzer/IRAC images at 3.6 μm and 4.5 μm.
Key words: stars: massive / stars: late-type / galaxies: individual: IC 1613 / galaxies: individual: Sex A
Based on observations made with the Gran Telescopio Canarias (GTC), installed in the Spanish Observatorio de El Roque de Los Muchachos of the Instituto de Astrofísica de Canarias, on the island of La Palma, and the 2.5 m du Pont telescope in operation at Las Campanas Observatory, Chile.
Spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/562/A75
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