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Confirmation of the stellar binary microlensing event, Macho 97-BLG-28


Blackman, JW and Beaulieu, J-P and Cole, AA and Vandorou, A and Koshimoto, N and Bachelet, E and Batista, V and Bhattacharya, A and Bennett, DP, Confirmation of the stellar binary microlensing event, Macho 97-BLG-28, Astrophysical Journal, 890, (1) Article 87. ISSN 0004-637X (2020) [Refereed Article]

Copyright Statement

Copyright 2020 The American Astronomical Society

DOI: doi:10.3847/1538-4357/ab68da


The high-magnification microlensing event MACHO-97-BLG-28 was previously determined to be a binary system composed of either two M dwarfs or an M dwarf and a brown dwarf. We present a revised light-curve model using additional data from the Mt. Stromlo 74'' telescope, model estimates of stellar limb darkening, and fitting of the blend separately for each telescope and passband. We find a lensing system with a larger mass ratio, q = 0.28 ± 0.01, and smaller projected separation, s = 0.61 ± 0.01, than those presented in the original study. We revise the estimate of the lens–source relative proper motion to μrel = 2.8 ± 0.5 mas yr−1, which indicates that 16.07 yr after the event maximum the lens and source should have separated by 46 ± 8 mas. We revise the radius of the source star using more recent reddening maps and angular diameter–color relations to R* = (10.3 ± 1.9) R. K- and J-band adaptive optics images of the field taken at this epoch using the NIRC2 imager on the Keck telescope show that the source and lens are still blended, consistent with our light-curve model. With no statistically significant excess flux detection we constrain the mass, ML = 0.24+0.28-0.12 M, and distance, DL = 7.0 ± 1.0 kpc, of the lensing system. This supports the interpretation of this event as a stellar binary in the Galactic bulge. This lens mass gives a companion mass of M = 0.07+0.08-0.04 M, close to the boundary between being a star and a brown dwarf.

Item Details

Item Type:Refereed Article
Keywords:Exoplanets, gravitational microlensing, proper motions
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Stellar astronomy and planetary systems
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Blackman, JW (Mr Joshua Blackman)
UTAS Author:Beaulieu, J-P (Dr Jean-Philippe Beaulieu)
UTAS Author:Cole, AA (Associate Professor Andrew Cole)
UTAS Author:Vandorou, A ( Aikaterini Vandorou)
ID Code:139067
Year Published:2020
Web of Science® Times Cited:2
Deposited By:Physics
Deposited On:2020-05-25
Last Modified:2020-08-12

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