OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star
Abstract
Microlensing is the only known direct method to measure the masses of stars that lack visible companions. In terms of microlensing observables, the mass is given by M=(c2/4G)rEθE and so requires the measurement of both the angular Einstein radius θE and the projected Einstein radius rE. Simultaneous measurement of these two parameters is extremely rare. Here we analyze OGLE-2003-BLG-238, a spectacularly bright (Imin=10.3), high-magnification (Amax=170) microlensing event. Pronounced finite-source effects permit a measurement of θE=650μas. Although the timescale of the event is only tE=38days, one can still obtain weak constraints on the microlens parallax: 4.4AU<rE<18AU at the 1 σ level. Together these two parameter measurements yield a range for the lens mass of 0.36Msolar<M<1.48Msolar. As was the case for MACHO-LMC-5, the only other single star (apart from the Sun) whose mass has been determined from its gravitational effects, this estimate is rather crude. It does, however, demonstrate the viability of the technique. We also discuss future prospects for single-lens mass measurements.
Based in part on observations obtained with the 1.3 m Warsaw Telescope at the Las Campanas Observatory of the Carnegie Institution of Washington and the Danish 1.54 m telescope at ESO, La Silla, Chile, operated by Instrumentcenter for Jordbaseret Astronomisk Forskning (IJAF) and financed by Statens Naturvidenskabelige Forskningsråd (SNF).- Publication:
-
The Astrophysical Journal
- Pub Date:
- December 2004
- DOI:
- 10.1086/425678
- arXiv:
- arXiv:astro-ph/0404394
- Bibcode:
- 2004ApJ...617.1307J
- Keywords:
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- Cosmology: Gravitational Lensing;
- Stars: Fundamental Parameters;
- Astrophysics
- E-Print:
- Submitted to ApJ, 23 pages including 3 figures