Journal Article

Rapidly rotating lenses: repeating features in the light curves of short-period binary microlenses

Matthew T. Penny, Eamonn Kerins and Shude Mao

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 417, issue 3, pages 2216-2229
Published in print November 2011 | ISSN: 0035-8711
Published online October 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19403.x
Rapidly rotating lenses: repeating features in the light curves of short-period binary microlenses

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Microlensing is most sensitive to binary lenses with relatively large orbital separations, and as such, typical binary microlensing events show little or no orbital motion during the event. However, despite the strength of binary microlensing features falling off rapidly as the lens separation decreases, we show that it is possible to detect repeating features in the light curve of binary microlenses that complete several orbits during the microlensing event. We investigate the light-curve features of such rapidly rotating lens (RRL) events. We derive analytical limits on the range of parameters where these effects are detectable, and confirm these numerically. Using a population synthesis Galactic model, we estimate the RRL event rate for a ground-based and a space-based microlensing survey to be 0.32fb and 7.8fb events per year, respectively, assuming year-round monitoring, where fb is the binary fraction. We detail how RRL event parameters can be quickly estimated from their light curves, and suggest a method to model RRL events using timing measurements of light-curve features. Modelling RRL light curves will yield the lens orbital period and possibly measurements of all orbital elements, including the inclination and eccentricity. Measurement of the period from the light curve allows a mass–distance relation to be defined, which when combined with a measurement of microlens parallax or finite-source effects can yield a mass measurement to a twofold degeneracy. With sub-per cent accuracy photometry, it is possible to detect planetary companions, but the likelihood of this is very small.

Keywords: gravitational lensing: micro; celestial mechanics; binaries: general; planetary systems; Galaxy: bulge

Journal Article.  12010 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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