Self‐lensing Models of the Large Magellanic Cloud
Open Access
- 20 May 2000
- journal article
- research article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 535 (1) , 90-103
- https://doi.org/10.1086/308834
Abstract
All of the proposed explanations for the microlensing events observed toward the LMC have difficulties. One of these proposed explanations, LMC self-lensing, which invokes ordinary LMC stars as the long sought-after lenses, has recently gained considerable popularity as a possible solution to the microlensing conundrum. In this paper, we carefully examine the full range of LMC self-lensing models, including for the first time the contribution of the LMC bar in both sources and lenses. In particular, we review the pertinent observations made of the LMC and show how these observations place limits on such self-lensing models. We find that, given current observational constraints, no purely LMC disk models are capable of producing optical depths as large as that reported in the MACHO collaboration 2 year analysis. We also introduce a new quantitative measure of the central concentration of the microlensing events and show that it discriminates well between disk/bar self-lensing and halo microlensing. Besides pure disk/bar, we also consider alternative geometries and present a framework which encompasses the previous studies of LMC self-lensing. We discuss which model parameters need to be pushed in order for such models to succeed. For example, like previous workers, we find that an LMC halo geometry may be able to explain the observed events. However, since all known LMC tracer stellar populations exhibit disklike kinematics, such models will have difficulty being reconciled with observations. For SMC self-lensing, we find predicted optical depths differing from previous results, but more than sufficient to explain all observed SMC microlensing. In contrast, for the LMC we find a self-lensing optical depth contribution between 0.47 × 10-8 and 7.84 × 10-8, with 2.44 × 10-8 being the value for the set of LMC parameters most consistent with current observations.Keywords
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This publication has 51 references indexed in Scilit:
- Discovery and Characterization of a Caustic Crossing Microlensing Event in the Small Magellanic CloudThe Astrophysical Journal, 1999
- The Relative Lens‐Source Proper Motion in MACHO 98‐SMC‐1The Astrophysical Journal, 1999
- Red Clump Morphology as Evidence against a New Intervening Stellar Population as the Primary Source of Microlensing toward the Large Magellanic CloudThe Astronomical Journal, 1998
- Red Clump Stars as a Tracer of Microlensing Optical DepthThe Astrophysical Journal, 1998
- First Detection of a Gravitational Microlensing Candidate toward the Small Magellanic CloudThe Astrophysical Journal, 1997
- Is the Large Magellanic Cloud Microlensing Due to an Intervening Dwarf Galaxy?The Astrophysical Journal, 1997
- The MACHO Project Large Magellanic Cloud Microlensing Results from the First Two Years and the Nature of the Galactic Dark HaloThe Astrophysical Journal, 1997
- A binary lensing event toward the LMC: Observations and dark matter implicationsNuclear Physics B - Proceedings Supplements, 1996
- The velocity dispersion of old stars in the Large Magellanic CloudThe Astrophysical Journal, 1986
- Methods for determining the masses of spherical systems. I - Test particles around a point massThe Astrophysical Journal, 1981