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OGLE-2015-BLG-1482L: The First Isolated Low-mass Microlens in the Galactic Bulge

Chung, S. and Beichman, C. and Calchi Novati, S. and Carey, S. (2017) OGLE-2015-BLG-1482L: The First Isolated Low-mass Microlens in the Galactic Bulge. Astrophysical Journal, 838 (2). Art. No. 154. ISSN 0004-637X. https://resolver.caltech.edu/CaltechAUTHORS:20170407-111737297

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Abstract

We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from Spitzer. The Spitzer data exhibit finite-source effects that are due to the passage of the lens close to or directly over the surface of the source star as seen from Spitzer. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the Spitzer light curves yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with a mass 0.10 ± 0.02 M_☉ or a brown dwarf with a mass 55 ± 9 M_J, which are located at D_(LS) = 0.80 ± 0.19 kpc and D_(LS) = 0.54 ± 0.08 kpc, respectively, where D_(LS) is the distance between the lens and the source, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The degeneracy between the two solutions is severe (Δx^2 = 0.3). The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from Spitzer, and this single data point gives rise to two solutions for ρ, the angular size of the source in units of the angular Einstein ring radius. Because the ρ degeneracy can be resolved only by relatively high-cadence observations around the peak, while the Spitzer cadence is typically ~ 1 day^(-1), we expect that events for which the finite-source effect is seen only in the Spitzer data may frequently exhibit this ρ degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is µ_(rel) = 9.0 ± 1.9 masyr^(-1), while for the brown dwarf it is 5.5 ± 0.5 (mas) yr^(-1). Hence, the degeneracy can be resolved within ~ 10 years from direct-lens imaging by using next-generation instruments with high spatial resolution.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3847/1538-4357/aa67faDOIArticle
http://iopscience.iop.org/article/10.3847/1538-4357/aa67fa/metaPublisherArticle
https://arxiv.org/abs/1703.05887arXivDiscussion Paper
ORCID:
AuthorORCID
Beichman, C.0000-0002-5627-5471
Calchi Novati, S.0000-0002-7669-1069
Carey, S.0000-0002-0221-6871
Additional Information:© 2017 American Astronomical Society. Received 2016 December 21. Accepted 2017 March 16. Published 2017 April 5. Work by S.-J.C. was supported by the KASI (Korea Astronomy and Space Science Institute) grant 2017-1-830-03. Work by W.Z. and A.G. was supported by JPL grant 1500811. Work by C.H. was supported by the Creative Research Initiative Program (2009-0081561) of the National Research Foundation of Korea. This research has made use of the KMTNet system operated by KASI, and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. The OGLE has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to A.U. The OGLE Team thanks Professors M. Kubiak, G. Pietrzynǹski, and Ł. Wyrzykowski for their contribution to the collection of the OGLE photometric data over the past years.
Group:Infrared Processing and Analysis Center (IPAC)
Funders:
Funding AgencyGrant Number
Korea Astronomy and Space Science Institute (KASI)2017-1-830-03
JPL1500811
National Research Foundation of Korea2009-0081561
National Science Centre (Poland)MAESTRO 2014/14/A/ST9/00121
Subject Keywords:brown dwarfs; gravitational lensing: micro; stars: fundamental parameters
Issue or Number:2
Record Number:CaltechAUTHORS:20170407-111737297
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170407-111737297
Official Citation:S.-J. Chung et al 2017 ApJ 838 154
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:75840
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:07 Apr 2017 19:15
Last Modified:24 Feb 2020 10:30

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