0000000000936931
AUTHOR
S. Dieters
A brown dwarf orbiting an M-dwarf:MOA 2009-BLG-411L
Context. Caustic crossing is the clearest signature of binary lenses in microlensing. In the present context, this signature is diluted by the large source star but a detailed analysis has allowed the companion signal to be extracted.Aims. MOA 2009-BLG-411 was detected on August 5, 2009 by the MOA-Collaboration. Alerted as a high-magnification event, it was sensitive to planets. Suspected anomalies in the light curve were not confirmed by a real-time model, but further analysis revealed small deviations from a single lens extended source fit.Methods. Thanks to observations by all the collaborations, this event was well monitored. We first decided to characterize the source star properties b…
A giant planet beyond the snow line in microlensing event OGLE-2011-BLG-0251
We present the analysis of the gravitational microlensing event OGLE-2011-BLG-0251. This anomalous event was observed by several survey and follow-up collaborations conducting microlensing observations towards the Galactic Bulge. Based on detailed modelling of the observed light curve, we find that the lens is composed of two masses with a mass ratio q=1.9 x 10^-3. Thanks to our detection of higher-order effects on the light curve due to the Earth's orbital motion and the finite size of source, we are able to measure the mass and distance to the lens unambiguously. We find that the lens is made up of a planet of mass 0.53 +- 0.21,M_Jup orbiting an M dwarf host star with a mass of 0.26 +- 0.…
Photometric observations of the radio bright B[e]/X-ray binary CI Cam
We present multiwavelength (optical, IR, radio) observations of CI Cam, the optical counterpart to the transient X-ray source XTE J0421+560. Pre-outburst quiescent observations reveal the presence of a dusty envelope around the system. Pronounced short term variability is observed at all wavebands from U-K, but no indication of prior flaring of a similar magnitude to the 1998 April outburst is found in these data.\ud \ud Data obtained during the 1998 April X-ray flare reveal pronounced optical-radio flaring. The optical flux was observed to quickly return to quiescent levels, while the radio flare was of much longer duration. The optical component is likely to result from a combination of f…
Characterizing Lenses and Lensed Stars of High-magnification Single-lens Gravitational Microlensing Events with Lenses Passing over Source Stars
We present the analysis of the light curves of 9 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 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 7 events, we measure the Einstein radii and the lens-source relative proper motions. Among the…
Microlensing Discovery of a Population of Very Tight, Very Low Mass Binary Brown Dwarfs
Although many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M [SUB]⊙[/SUB] and 0.034 M [SUB]⊙[/SUB], and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can …