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RED NOISE VERSUS PLANETARY INTERPRETATIONS IN THE MICROLENSING EVENT OGLE-2013-BLG-446
Bachelet, E.,Bramich, D. M.,Han, C.,Greenhill, J.,Street, R. A.,Gould, A.,D’Ago, G.,AlSubai, K.,Dominik, M.,Jaimes, R. Figuera,Horne, K.,Hundertmark, M.,Kains, N.,Snodgrass, C.,Steele, I. A.,Tsapras, IOP Publishing 2015 The Astrophysical journal Vol.812 No.2
<P>For all exoplanet candidates, the reliability of a claimed detection needs to be assessed through a careful study of systematic errors in the data to minimize the false positives rate. We present a method to investigate such systematics in microlensing data sets using the microlensing event OGLE-2013-BLG-0446 as a case study. The event was observed from multiple sites around the world and its high magnification (A(max) similar to 3000) allowed us to investigate the effects of terrestrial and annual parallax. Real-time modeling of the event while it was still ongoing suggested the presence of an extremely low-mass companion (similar to 3M(circle plus)) to the lensing star, leading to substantial follow-up coverage of the light curve. We test and compare different models for the light curve and conclude that the data do not favor the planetary interpretation when systematic errors are taken into account.</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>
Miyake, N.,Udalski, A.,Sumi, T.,Bennett, D. P.,Dong, S.,Street, R. A.,Greenhill, J.,Bond, I. A.,Gould, A.,Kubiak, M.,Szymań,ski, M. K.,Pietrzyń,ski, G.,Soszyń,ski, I.,Ulaczyk, K.,Wyrzyk IOP Publishing 2012 The Astrophysical journal Vol.752 No.2
<P>We report the extremely high-magnification (A > 1000) binary microlensing event OGLE-2007-BLG-514. We obtained good coverage around the double peak structure in the light curve via follow-up observations from different observatories. The binary lens model that includes the effects of parallax (known orbital motion of the Earth) and orbital motion of the lens yields a binary lens mass ratio of q = 0.321 +/- 0.007 and a projected separation of s = 0.072 +/- 0.001 in units of the Einstein radius. The parallax parameters allow us to determine the lens distance D-L = 3.11 +/- 0.39 kpc and total mass M-L = 1.40 +/- 0.18 M-circle dot; this leads to the primary and secondary components having masses of M-1 = 1.06 +/- 0.13 M-circle dot and M-2 = 0.34 +/- 0.04 M-circle dot, respectively. The parallax model indicates that the binary lens system is likely constructed by the main-sequence stars. On the other hand, we used a Bayesian analysis to estimate probability distributions by the model that includes the effects of xallarap (possible orbital motion of the source around a companion) and parallax (q = 0.270 +/- 0.005, s = 0.083 +/- 0.001). The primary component of the binary lens is relatively massive, with M-1 = 0.9(-0.3)(+4.6) M-circle dot and it is at a distance of D-L = 2.6(-0.9)(+3.8) kpc. Given the secure mass ratio measurement, the companion mass is therefore M-2 = 0.2(-0.1)(+1.2) M-circle dot. The xallarap model implies that the primary lens is likely a stellar remnant, such as a white dwarf, a neutron star, or a black hole.</P>
MOA-2007-BLG-197: Exploring the brown dwarf desert
Ranc, C.,Cassan, A.,Albrow, M. D.,Kubas, D.,Bond, I. A.,Batista, V.,Beaulieu, J.-P.,Bennett, D. P.,Dominik, M.,Dong, Subo,Fouqué,, P.,Gould, A.,Greenhill, J.,Jørgensen, U. G.,Kains, N.,Menzies, EDP Sciences 2015 Astronomy and astrophysics Vol.580 No.-
BINARY MICROLENSING EVENT OGLE-2009-BLG-020 GIVES VERIFIABLE MASS, DISTANCE, AND ORBIT PREDICTIONS
Skowron, J.,Udalski, A.,Gould, A.,Dong, Subo,Monard, L. A. G.,Han, C.,Nelson, C. R.,McCormick, J.,Moorhouse, D.,Thornley, G.,Maury, A.,Bramich, D. M.,Greenhill, J.,Kozłowski, S.,Bond, I.,Poleski, R.,W IOP Publishing 2011 The Astrophysical journal Vol.738 No.1
<P>We present the first example of binary microlensing for which the parameter measurements can be verified (or contradicted) by future Doppler observations. This test is made possible by a confluence of two relatively unusual circumstances. First, the binary lens is bright enough (I = 15.6) to permit Doppler measurements. Second, we measure not only the usual seven binary-lens parameters, but also the 'microlens parallax' (which yields the binary mass) and two components of the instantaneous orbital velocity. Thus, we measure, effectively, six 'Kepler+1' parameters (two instantaneous positions, two instantaneous velocities, the binary total mass, and the mass ratio). Since Doppler observations of the brighter binary component determine five Kepler parameters (period, velocity amplitude, eccentricity, phase, and position of periapsis), while the same spectroscopy yields the mass of the primary, the combined Doppler + microlensing observations would be overconstrained by 6 + (5 + 1) - (7 + 1) = 4 degrees of freedom. This makes possible an extremely strong test of the microlensing solution. We also introduce a uniform microlensing notation for single and binary lenses, define conventions, summarize all known microlensing degeneracies, and extend a set of parameters to describe full Keplerian motion of the binary lenses.</P>