HST Imaging of MEGA Microlensing Candidates in M31
Crotts, Arlin P. S.; Kuijken, Konrad; Widrow, Lawrence M.; Baltz, Edward A.; de Jong, Jelte T. A.; Gyuk, Geza; Cseresnjes, Patrick; Bergier, Alex
United States, Netherlands, Canada
Abstract
We investigate HST/ACS and WFPC2 images at the positions of five candidate microlensing events from a large survey of variability in M31 (MEGA). Three closely match unresolved sources, and two produce only flux upper limits. All are confined to regions of the color-magnitude diagram where stellar variability is unlikely to be easily confused with microlensing. Red variable stars cannot explain these events (although background supernovae are possible for two). If these lenses arise in M31's halo, they are due to masses 0.15<m/Msolar<0.49 (95% certainty, for a δ-function mass distribution), with brown dwarfs for disk lenses and stellar masses for bulge lenses.
Based on observations made with the NASA/ESA Hubble Space Telescope (HST), obtained at STScI, which is operated by AURA, Inc., under NASA contract NAS 5-26555. These observations are associated with program 10273. Also based on observations made with the Isaac Newton Telescope (INT) operated on La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de Los Muchachos of the Instituto de Astrofísica de Canarias and at the Kitt Peak National Observatory (KPNO), NOAO, which is operated by AURA, Inc., under cooperative agreement with the NSF.