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MICROLENSING BINARIES DISCOVERED THROUGH HIGH-MAGNIFICATION CHANNEL
Shin, I.-G.,Choi, J.-Y.,Park, S.-Y.,Han, C.,Gould, A.,Sumi, T.,Udalski, A.,Beaulieu, J.-P.,Dominik, M.,Allen, W.,Bos, M.,Christie, G. W.,Depoy, D. L.,Dong, S.,Drummond, J.,Gal-Yam, A.,Gaudi, B. S.,Hun IOP Publishing 2012 The Astrophysical journal Vol.746 No.2
<P>Microlensing can provide a useful tool to probe binary distributions down to low-mass limits of binary companions. In this paper, we analyze the light curves of eight binary-lensing events detected through the channel of high-magnification events during the seasons from 2007 to 2010. The perturbations, which are confined near the peak of the light curves, can be easily distinguished from the central perturbations caused by planets. However, the degeneracy between close and wide binary solutions cannot be resolved with a 3 sigma confidence level for three events, implying that the degeneracy would be an important obstacle in studying binary distributions. The dependence of the degeneracy on the lensing parameters is consistent with a theoretical prediction that the degeneracy becomes severe as the binary separation and the mass ratio deviate from the values of resonant caustics. The measured mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is q similar to 0.1, making the companion of the lens a strong brown dwarf candidate.</P>
Choi, J.-Y.,Shin, I.-G.,Park, S.-Y.,Han, C.,Gould, A.,Sumi, T.,Udalski, A.,Beaulieu, J.-P.,Street, R.,Dominik, M.,Allen, W.,Almeida, L. A.,Bos, M.,Christie, G. W.,Depoy, D. L.,Dong, S.,Drummond, J.,Ga IOP Publishing 2012 The Astrophysical journal Vol.751 No.1
<P>We present the analysis of the light curves of nine high-magnification single-lens gravitational microlensing events with lenses passing over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176, MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436, MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300, and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all of the events, we measure the linear limb-darkening coefficients of the surface brightness profile of source stars by measuring the deviation of the light curves near the peak affected by the finite-source effect. For seven events, we measure the Einstein radii and the lens-source relative proper motions. Among them, five events are found to have Einstein radii of less than 0.2 mas, making the lenses very low mass star or brown dwarf candidates. For MOA-2011-BLG-274, especially, the small Einstein radius of theta(E) similar to 0.08 mas combined with the short timescale of t(E) similar to 2.7 days suggests the possibility that the lens is a free-floating planet. For MOA-2009-BLG-174, we measure the lens parallax and thus uniquely determine the physical parameters of the lens. We also find that the measured lens mass of similar to 0.84M(circle dot) is consistent with that of a star blended with the source, suggesting that the blend is likely to be the lens. Although we did not find planetary signals for any of the events, we provide exclusion diagrams showing the confidence levels excluding the existence of a planet as a function of the separation and mass ratio.</P>
MOA-2010-BLG-523: “FAILED PLANET” = RS CVn STAR
Gould, A.,Yee, J. C.,Bond, I. A.,Udalski, A.,Han, C.,Jørgensen, U. G.,Greenhill, J.,Tsapras, Y.,Pinsonneault, M. H.,Bensby, T.,Allen, W.,Almeida, L. A.,Bos, M.,Christie, G. W.,DePoy, D. L.,Dong, Subo IOP Publishing 2013 The Astrophysical journal Vol.763 No.2
<P>The Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A(max) similar to 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge.</P>
MOA-2013-BLG-220Lb: MASSIVE PLANETARY COMPANION TO GALACTIC-DISK HOST
Yee, J. C.,Han, C.,Gould, A.,Skowron, J.,Bond, I. A.,Udalski, A.,Hundertmark, M.,Monard, L. A. G.,Porritt, I.,Nelson, P.,Bozza, V.,Albrow, M. D.,Choi, J.-Y.,Christie, G. W.,DePoy, D. L.,Gaudi, B. S.,H IOP Publishing 2014 The Astrophysical journal Vol.790 No.1
<P>We report the discovery of MOA-2013-BLG-220Lb, which has a super-Jupiter mass ratio q = 3.01 +/- 0.02 x 10(-3) relative to its host. The proper motion, mu = 12.5 +/- 1 mas yr(-1), is one of the highest for microlensing planets yet discovered, implying that it will be possible to separately resolve the host within similar to 7 yr. Two separate lines of evidence imply that the planet and host are in the Galactic disk. The planet could have been detected and characterized purely with follow-up data, which has important implications for microlensing surveys, both current and into the Large Synoptic Survey Telescope (LSST) era.</P>
Shin, I.-G.,Udalski, A.,Han, C.,Gould, A.,Dominik, M.,Fouqué,, P.,Kubiak, M.,Szymań,ski, M. K.,Pietrzyń,ki, G.,Soszyń,ski, I.,Ulaczyk, K.,Wyrzykowski, Ł.,DePoy, D. L.,Dong, S.,Gau IOP Publishing 2011 The Astrophysical journal Vol.735 No.2
<P>We present the result of the analysis of the gravitational binary-lensing event OGLE-2005-BLG-018. The light curve of the event is characterized by two adjacent strong features and a single weak feature separated from the strong features. The light curve exhibits noticeable deviations from the best-fit model based on standard binary parameters. To explain the deviation, we test models including various higher-order effects of the motions of the observer, source, and lens. From this, we find that it is necessary to account for the orbital motion of the lens in describing the light curve. From modeling the light curve considering the parallax effect and Keplerian orbital motion, we are able to not only measure the physical parameters but also to find a complete orbital solution of the lens system. It is found that the event was produced by a binary lens located in the Galactic bulge with a distance of 6.7 +/- 0.3 kpc from the Earth. The individual lens components with masses 0.9 +/- 0.3 M-circle dot and 0.5 +/- 0.1 M-circle dot are separated with a semi-major axis of a = 2.5 +/- 1.0 AU and orbiting each other with a period P = 3.1 +/- 1.3 yr. This event demonstrates that it is possible to extract detailed information about binary lens systems from well-resolved lensing light curves.</P>