Characterizing Lenses and Lensed Stars of High-Magnification Single-Lens Gravitational Microlensing Events With Lenses Passing Over Source Stars

Abstract

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. 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 θ E ∼ 0.08 mas combined with the short timescale of t E ∼ 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 ∼0.84 M 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.

Measuring limb darkening of stars in high-magnification microlensing events by the Finite Element Method

“…In this case, the magnification is obtained from the convolution of equation (1) and surface brightness of the source. In the observations, the high magnification events alerted well before the peak so that a network of follow-up telescopes can perform high cadence observation (Alcock et al 1997;Choi et al 2012). From the measurement of the light curve around the peak, they can calculate the angular size of the source, θ in units of θE (i.e.…”

“…The other new method is the high-magnification gravitational microlensing events (Albrow et al 2001;An et al 2002;Yoo et al 2004;Choi et al 2012;Rahvar 2015) which is the subject of our study and can be used as a probe to scan the intensity profile of distant stars. Gravitational microlensing happens when a massive astronomical object E-mail: lgolchin@physics.sharif.edu † E-mail: rahvar@sharif.edu inside the Milky Galaxy intervenes a background star and bends its light toward the observer.…”

Eclipsing negative-parity image of gravitational microlensing by a giant-lens star

“…Moreover, the colour and magnitude of the source star also can be obtained in the high magnification events (Choi et al 2012) if the observation is performed in two different filters at the peak of light curve. In this case we can ignore the contribution of the blending effect in the colour and magnitude of the source star.…”

OGLE-2014-BLG-0289: Precise Characterization of a Quintuple-peak Gravitational Microlensing Event

“…The angular Einstein radius can be measured by detecting light curve deviations caused by finite-source effects (Gould 1994;Nemiroff & Wickramasinghe 1994). For lensing events produced by single masses, finite-source effects can be detected when a lens crosses the surface of a source star (Pratt et al 1996;Choi et al 2012). However, the ratio of the angular source radius * q to the angular Einstein radius is of order 10 −3 for a main-sequence source star and of order 10 −2 even for a giant star.…”