1994/09/26 by Andrew Gould · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Gamma-ray bursts and supernovae #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/175893
published as Astrophys.J. 447 (1995) 491 · 11 pages, no figures, PostScript file, or request PostScript file to [email protected], OSU-TA-21/94
arxiv created 1994/09/26 · openalex publication_date 1995/07/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
I propose a radical revision in the search strategy for massive compact objects (MACHOS) toward the Galactic bulge: monitor a large portion ∼80 deg<SUP>2</SUP> of the bulge and tune the search primarily to microlensing events of bright M<SUB>1</SUB> ≲ 0.5 stars. There are three reasons for making this change. First, microlensing events of intrinsically bright sources have much smaller systematic uncertainties relative to the typical events now being monitored. Second, it is far more often possible to measure the proper motion of a MACHO when the source is intrinsically bright. By employing a small second telescope to follow up the events detected with low dimensionless impact parameter β ≲ 0.2, one could measure the proper motion μ of ∼20 yr<SUP>-1</SUP> events and significantly constrain μ for a similar number. Third, if the events were followed from a MACHO parallax satellite, it would be possible to measure individual masses, distances, and transverse velocities for the events with proper motions. Satellite parallaxes can in general be obtained only if the source is fairly bright. In addition, if a fraction ξ of the bulge is composed of low-mass objects in the range 10<SUP>-3</SUP> ≲ M<SUB>low</SUB>/M<SUB>sun</SUB> ≲ 10<SUP>-1</SUP>, then mass measurements could be made for ∼30(ξ/0.1) (0.01 M<SUB>sun</SUB> <M<SUB>low</SUB><SUP>-1</SUP>) yr<SUP>-1</SUP> of these, thus allowing a direct measurement of the mass function in the sub-stellar range. In the absence of a parallax satellite, ground-based observations could significantly constrain (but not measure) MACHO parallaxes. These constraints, when combined with the proper-motion measurements, would in turn constrain the mass, distance, and transverse speed of the MACHOS.