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Detection of Rotation in a Binary Microlens: Planet Photometry of MACHO 97-BLG-41

Citation

Albrow, MD and Beaulieu, JP and Caldwell, JAR and Dominik, M and Gaudi, BS and Gould, A and Greenhill, JG and Hill, KM and Kane, S and Martin, R and Menzies, J and Naber, RM and Pollard, KR and Sackett, PD and Sahu, KC and Vermaak, P and Watson, RD and Willams, A and Bond, HE and van Bemmel, IM, Detection of Rotation in a Binary Microlens: Planet Photometry of MACHO 97-BLG-41, The Astrophysical Journal , 534, (2) pp. 894-906. ISSN 0004-637X (2000) [Refereed Article]

DOI: doi:10.1086/308798

Abstract

We analyze PLANET collaboration data for MACHO 97-BLG-41, the only microlensing event observed to date in which the source transits two disjoint caustics. The PLANET data, consisting of 46 V-band and 325 I-band observations from five southern observatories, span a period from the initial alert until the end of the event. Our data are incompatible with a static binary lens, but are well fitted by a rotating binary lens of mass ratio q = 0.34 and angular separation d ≈ 0.5 (in units of the Einstein ring radius), in which the binary separation changes in size by δd = -0.070 ± 0.009 and in orientation by δθ = 5°.61 ± 0°.36 during the 35.17 days between the separate caustic transits. We use this measurement, combined with other observational constraints, to derive the first kinematic estimate of the mass, distance, and period of a binary microlens. The relative probability distributions for these parameters peak at a total lens mass M ∼ 0.3 M⊙ (M-dwarf binary system), lens distance DL ∼ 5.5 kpc, and binary period P ∼ 1.5 yr. The robustness of our model is demonstrated by its striking agreement with MACHO/ GMAN data that cover several sharp features in the light curve not probed by the PLANET observations, and which did not enter our modeling procedure in any way. Available data sets thus indicate that the light curve of MACHO 97-BLG-41 can be modeled as a source crossing two caustics of a physically realistic rotating binary. Thus, contrary to a recent suggestion, the additional effects of a postulated planetary companion to the binary lens are not required.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Greenhill, JG (Dr John Greenhill)
UTAS Author:Hill, KM (Dr Kym Hill)
UTAS Author:Kane, S (Dr Stephen Kane)
UTAS Author:Watson, RD (Dr Bob Watson)
ID Code:18577
Year Published:2000
Web of Science® Times Cited:134
Deposited By:Physics
Deposited On:2000-08-01
Last Modified:2011-11-29
Downloads:0

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