Searching for Low Mass Stars in the Halo

Abstract

From microlensing events detected at high galactic latitude as well as from direct measurements of the halo stellar density, estimations of a potential contribution of low mass stars to the mass budget is questioned. Up to now no clear answer has been found for one main reason: the difficulty to observe them in a sufficient volume, which requires deep detection limit and/or wide field of view. While the HST fulfills the first requirement, its field of view is small therefore the problem requires to observe a very large number of WFC2 fields. Wide field CCD mosaics on large ground based telescopes offer a promissing alternative, provided that image quality is sufficient to allow reliable star/galaxy separation.