The resolved stellar populations of M32

PhD ceremony: Ms. A. Monachesi, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Title: The resolved stellar populations of M32

Promotor(s): prof. S.C. Trager

Faculty: Mathematics and Natural Sciences

The Local Group galaxy Messier 32 (M32) is a compact elliptical galaxy, satellite of M31. Given its proximity, M32 provides a unique window on the stellar composition of elliptical galaxies, since it can be studied by both its integrated spectrum and the photometry of its resolved stars. In this thesis we have obtained the most complete inventory yet possible of the resolved stellar populations of M32 and derived its star formation history (SFH) at 2 arcmin from its center. We have used very high resolution observations, obtained with the Hubble Space Telescope, to construct and analyze deep color-magnitude diagrams and to search for RR Lyrae variables to extract information about the stellar age and metallicity distributions in this galaxy.

We find that M32 has had an extended SFH and is composed of two main dominant populations at 2 arcmin from its center: a 2-5 Gyr old, metal-rich population, and a population older than 5 Gyr, with slightly subsolar metallicities. We do not expect a significant contribution from stars older than 10 Gyr, although there are a few ancient metal-poor stars present in M32. We also find a small contribution from a young population (< 2 Gyr), half of it metal-rich and half metal-poor. We associate the latter with blue straggler stars belonging to an old metal-poor population. The results obtained in this thesis significantly improve our knowledge on the stellar populations of M32 and provide an unprecedented rich data base to compare with unresolved stellar population models and to test their applicability to more distant galaxies.