Photometry of Resolved Stellar Populations in Local Group Galaxies

Sammanfattning: This thesis presents results from two projects using photometric observations to investigate stellar populations in Local Group galaxies. In the first project, Strömgren photometry is used to study stellar populations in dwarf spheroidal galaxies. It is demonstrated that the Strömgren c1 and m1 colour indices can be efficiently used to identify RGB members in dwarf spheroidal galaxies, and derive accurate, age-independent, metallicities for individual stars. The method is applied on the Draco dwarf spheroidal galaxy. The metallicity distribution function is presented and spatial metallicity gradients are studied. In the second project, deep HST/ACS observations are used to investigate the nature of several substructures in the outer regions of M31. The individual colour-magnitude diagrams for five substructures are presented and compared. A detailed investigation of one of the substructures, the G1 clump, is performed and stellar ages and metallicities are derived. Possible scenarios for the origin of the G1 clump are discussed based on these results.