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Title: Self-lensing Models of the Large Magellanic Cloud

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 halomore » 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 0.47x10{sup -8} and 7.84x10{sup -8}, with 2.44x10{sup -8} being the value for the set of LMC parameters most consistent with current observations. (c) 2000 The American Astronomical Society.« less

Authors:
; ;
Publication Date:
OSTI Identifier:
20217419
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 535; Journal Issue: 1; Other Information: PBD: 20 May 2000; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; GALAXIES; GRAVITATIONAL LENSES; MATHEMATICAL MODELS; INTERSTELLAR SPACE; MONTE CARLO METHOD; EXPERIMENTAL DATA; THEORETICAL DATA

Citation Formats

Gyuk, G., Dalal, N., and Griest, K. Self-lensing Models of the Large Magellanic Cloud. United States: N. p., 2000. Web. doi:10.1086/308834.
Gyuk, G., Dalal, N., & Griest, K. Self-lensing Models of the Large Magellanic Cloud. United States. doi:10.1086/308834.
Gyuk, G., Dalal, N., and Griest, K. Sat . "Self-lensing Models of the Large Magellanic Cloud". United States. doi:10.1086/308834.
@article{osti_20217419,
title = {Self-lensing Models of the Large Magellanic Cloud},
author = {Gyuk, G. and Dalal, N. and Griest, K.},
abstractNote = {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 0.47x10{sup -8} and 7.84x10{sup -8}, with 2.44x10{sup -8} being the value for the set of LMC parameters most consistent with current observations. (c) 2000 The American Astronomical Society.},
doi = {10.1086/308834},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 1,
volume = 535,
place = {United States},
year = {2000},
month = {5}
}