Population of red supergiants in dwarf irregular galaxies
February 21st, 2017
The identification and investigation of red supergiants (RSGs) in the Local Group and beyond are extremely important for understanding massive star evolution and mass-loss. Star-forming dwarf irregular (dIrr) galaxies serve as ideal laboratories for investigating physics of red supergiants within the context of different metallicities of host galaxies. Also, RSGs may be used as tracers for abundance determinations and star formation history of dIrrs. I will present a systematic survey of RSGs and luminous blue variables (LBVs) in nearby dIrr galaxies with the goal to complete the census of these objects in the Local Group. Using the fact that RSGs and LBVs are bright in mid-infrared colors due to dust, we applied a technique that allows us to select dusty massive stars based on their [3.6] and [4.5] Spitzer photometry. I applied our criteria to 7 dIrr galaxies: Pegasus, Phoenix, Sextans A, Sextans B, WLM, IC 10 and IC 1613 selecting 124 point sources, which we observed with the VLT/FORS2, GTC/OSIRIS and duPont/WFCCD spectrographs. In total, we identified 28 RSGs (21 are new discoveries) and 2 new emission line objects in these galaxies. These new discoveries are statistically significant and this sample increased the number of spectroscopically confirmed RSGs in dIrrs by 50%. Moreover, for the newly identified RSGs we measured the fundamental physical parameters by fitting their observational spectral energy distributions with MARCS stellar atmosphere models. This work serves as a basis for further investigation (also in a framework of my activity in IAC) of the newly discovered dusty massive stars and their host galaxies.