Pursuing Local Group blue massive stars with WSO-ISSIS

Abstract

The Local Group galaxies enable us to study the impact of metallicity on the structure and evolution of mas- sive stars through spectroscopic analyses. However, color- based target selection for spectroscopy (in absence of known spectral types), though relatively successful, usually pro- duces lists dominated by B-type modest-mass stars. We have developed a friends of friends code to find OB associations in Local Group galaxies (Garcia et al. in Astron. Astrophys. 502:1015, 2009; Bull. Soc. R. Sci. Liege 80:381, 2011a). The interpretation of the association's color-magnitude di- agrams (CMDs) and the automatic determination of evo- lutionary masses for the members, allow a more insightful choice of candidates for spectroscopy and to spot out po- tential advanced evolutionary stages (Garcia et al. in As- tron. Astrophys. 523:A23, 2010). We show our results on the dwarf irregular IC 1613 as illustration of the potential of the method. Because of its large field of view and high spatial reso- lution at ultraviolet (UV) wavelengths, ISSIS at the WSO is a powerful discovery machine of resolved blue massive stars in nearby galaxies. Our code can be easily modified to choose candidate OB stars based on ISSIS magnitudes on the UV, where hot young massive stars are intrinsically brighter and their color degeneracy is broken. The combina- tion of our algorithm and ISSIS's panchromatic photometry can readily produce a list of the most massive stars of the Local Group.