Astronomy and Astrophysics – Astrophysics
Scientific paper
2003-04-25
Astronomy and Astrophysics
Astrophysics
25 pages, Invited Review, to appear in "Gravitational Lensing: A Unique Tool For Cosmology", Aussois 2003, eds. D. Valls-Gabau
Scientific paper
We describe a few recent microlensing results from the MACHO Collaboration. The aim of the MACHO Project was the identification and quantitative description of dark and luminous matter in the Milky Way using microlensing toward the Magellanic Clouds and Galactic bulge. We start with a discussion of the HST follow-up observations of the microlensing events toward the LMC detected in the first 5 years of the experiment. Using color-magnitude diagrams we attempt to distinguish between two possible locations of the microlensing sources: 1) in the LMC or 2) behind the LMC. We conclude that unless the extinction is extremely patchy, it is very unlikely that most of the LMC events have sources behind the LMC. During an examination of the HST images of the 13 LMC events we found a very red object next to the source star of event LMC-5. Astrometry, microlensing parallax fit, and a spectrum suggest that in this case we directly image the lens - a low-mass disk star. Then we focus on the majority of events observed by the MACHO Project, which are detected toward the Galactic bulge. We argue that the microlensing optical depth toward the bulge is best measured using events that have clump giant sources, which are almost unaffected by blending. From this sample we derive a low optical depth toward the Galactic bulge of (1.4 +/- 0.3) x 10^{-6}, in good agreement with other observational constraints and with theoretical models. The presence of many long-duration events among the bulge candidates allows us to investigate the microlensing parallax effect. Events with the strongest parallax signal are probably due to massive remnants. Events MACHO-96-BLG-5 and MACHO-98-BLG-6 might have been caused by the 6-solar-mass black holes.
Alcock Charles
Allsman R. A.
Alves David R.
Axelrod Tim S.
Becker Andrew C.
No associations
LandOfFree
Recent Microlensing Results from the MACHO Project does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Recent Microlensing Results from the MACHO Project, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Recent Microlensing Results from the MACHO Project will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-698719