Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-02-25
Mon.Not.Roy.Astron.Soc. 365 (2006) 1099-1108
Astronomy and Astrophysics
Astrophysics
9 pages, submitted to MNRAS
Scientific paper
10.1111/j.1365-2966.2005.09636.x
The Andromeda Galaxy Stellar Robotic Microlensing Project (The Angstrom Project) aims to use stellar microlensing events to trace the structure and composition of the inner regions of the Andromeda Galaxy (M31). We present microlensing rate and timescale predictions and spatial distributions for stellar and sub-stellar lens populations in combined disk and barred bulge models of M31. We show that at least half of the stellar microlenses in and around the bulge are expected to have characteristic durations between 1 and 10 days, rising to as much as 80% for brown-dwarf dominated mass functions. These short-duration events are mostly missed by current microlensing surveys that are looking for Macho candidates in the M31 dark matter halo. Our models predict that an intensive monitoring survey programme such as Angstrom, which will be able to detect events of durations upwards of a day, could detect around 30 events per season within ~5 arcminutes of the M31 centre, due to ordinary low-mass stars and remnants. This yield increases to more than 60 events for brown-dwarf dominated mass functions. The overall number of events and their average duration are sensitive diagnostics of the bulge mass, in particular the contribution of low-mass stars and brown dwarfs. The combination of an inclined disk, an offset bar-like bulge, and differences in the bulge and disk luminosity functions results in a four-way asymmetry in the number of events expected in each quadrant defined by the M31 disk axes. The asymmetry is sensitive to the bar prolongation, orientation and mass.
Darnley Matt J.
Duke J.
Gould Andrew
Han Cheongho
Jeon Young-Beom
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