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OGLE-2016-BLG-0596Lb: A High-mass Planet from a High-magnification Pure-survey Microlensing Event
Mró,z, P.,Han, C.,Udalski, A.,Poleski, R.,Skowron, J.,Szymań,ski, M. K.,Soszyń,ski, I.,Pietrukowicz, P.,Kozłowski, S.,Ulaczyk, K.,Wyrzykowski, Ł.,Pawlak, M.,Albrow, M. D.,Cha, S.-M.,Ch American Institute of Physics 2017 The Astronomical journal Vol.153 No.4
<P>We report the discovery of a high mass ratio planet, q = 0.012, i.e., 13 times higher than the Jupiter/Sun ratio. The host mass has not yet been measured but can be determined or strongly constrained from adaptive optics imaging. The planet was discovered in a small archival study of high-magnification events in pure-survey microlensing data, which was unbiased by the presence of anomalies. The fact that it was previously unnoticed may indicate that more such planets lie in archival data and could be discovered by a similar systematic study. In order to understand the transition from predominantly survey+followup to predominately survey-only planet detections, we conduct the first analysis of these detections in the observational (s, q) plane. Here s is the projected separation in units of the Einstein radius. We find some evidence that survey+followup is relatively more sensitive to planets near the Einstein ring, but that there is no statistical difference in sensitivity by mass ratio.</P>
Han, C.,Udalski, A.,Bozza, V.,Szymań,ski, M. K.,Soszyń,ski, I.,Skowron, J.,Mró,z, P.,Poleski, R.,Pietrukowicz, P.,Kozłowski, S.,Ulaczyk, K.,Wyrzykowski, Ł.,Novati, S. Calchi,D’Ago, G. American Astronomical Society 2017 The Astrophysical journal Vol.843 No.2
<P>Due to the nature of the gravitational field, microlensing, in principle, provides an important tool for detecting faint and even dark brown dwarfs. However, the number of identified brown dwarfs is limited due to the difficulty of the lens mass measurement that is needed to check the substellar nature of the lensing object. In this work, we report a microlensing brown dwarf discovered from an analysis of the gravitational binary-lens event OGLE-2014-BLG1112. We identify the brown dwarf nature of the lens companion by measuring the lens mass from the detections of both microlens-parallax and finite-source effects. We find that the companion has a mass of. ' ( 3.03 +/- 0.78) 10(-2) M-circle dot and it is orbiting a solar-type primary star with a mass of 1.07 +/- 0.28 M-circle dot. The estimated projected separation between the lens components is 9.63 +/- 1.33 au and the distance to the lens is 4.84 +/- 0.67 kpc. We discuss the usefulness of space-based microlensing observations for detecting brown dwarfs through the channel of binary-lens events.</P>
OGLE-2014-BLG-0289: Precise Characterization of a Quintuple-peak Gravitational Microlensing Event
Udalski, A.,Han, C.,Bozza, V.,Gould, A.,Bond, I. A.,Mró,z, P.,Skowron, J.,Wyrzykowski, Ł.,Szymań,ski, M. K.,Soszyń,ski, I.,Ulaczyk, K.,Poleski, R.,Pietrukowicz, P.,Kozłowski, S.,Abe, F American Astronomical Society 2018 The Astrophysical journal Vol.853 No.1
<P>We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits five very unusual peaks, four of which were produced by caustic crossings and the other by a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax pi(E). Furthermore, the three resolved caustics allow us to measure the angular Einstein radius theta(E). From the combination of pE and qE, the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses M-1 = 0.52 +/- 0.04 M-circle dot and M-2 = 0.42 +/- 0.03 M-circle dot separated in projection by a(perpendicular to) = 6.4 +/- 0.5 au. The lens is located in the disk with a distance of D-L = 3.3 +/- 0.3 kpc. The reason for the absence of a lensing signal in the Spitzer data is that the time of observation corresponds to the flat region of the light curve.</P>
OGLE-2013-BLG-0578 L: A MICROLENSING BINARY COMPOSED OF A BROWN DWARF AND AN M DWARF
Park, H.,Udalski, A.,Han, C.,Poleski, R.,Skowron, J.,Kozłowski, S.,Wyrzykowski, Ł.,Szymań,ski, M. K.,Pietrukowicz, P.,Pietrzyń,ski, G.,Soszyń,ski, I.,Ulaczyk, K. IOP Publishing 2015 The Astrophysical journal Vol.805 No.2
<P>Determining the physical parameters of binary microlenses is hampered by the lack of information about the angular Einstein radius due to the difficulty involved in resolving caustic crossings. In this paper, we present an analysis of the binary microlensing event OGLE-2013-BLG-0578, for which the caustic exit was precisely predicted in advance from real-time analysis, enabling us to densely resolve the caustic crossing and to measure the Einstein radius. From the mass measurement of the lens system based on the Einstein radius, combined with additional information about the lens parallax, we determine that the lens is a binary composed of a late-type M dwarf primary and a substellar brown dwarf companion. This event demonstrates the capability of current real-time microlensing modeling and the usefulness of microlensing for detecting and characterizing faint or dark objects in the Galaxy.</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>
A Neptune-mass Free-floating Planet Candidate Discovered by Microlensing Surveys
Mró,z, Przemek,Ryu, Y.-H.,Skowron, J.,Udalski, A.,Gould, A.,Szymań,ski, M. K.,Soszyń,ski, I.,Poleski, R.,Pietrukowicz, P.,Kozłowski, S.,Pawlak, M.,Ulaczyk, K.,Albrow, M. D.,Chung, S.-J American Astronomical Society 2018 The Astronomical journal Vol.155 No.3
Han, C.,Udalski, A.,Gould, A.,Zhu, Wei,Szymań,ski, M. K.,Soszyń,ski, I.,Skowron, J.,Mró,z, P.,Poleski, R.,Pietrukowicz, P.,Kozłowski, S.,Ulaczyk, K.,Pawlak, M.,Yee, J. C.,Beichman, C. American Astronomical Society 2017 The Astrophysical journal Vol.834 No.1
<P>In this paper, we present an analysis of the binary gravitational microlensing event OGLE-2015-BLG-0196. The event lasted for almost a year, and the light curve exhibited significant deviations from the lensing model based on the rectilinear lens-source relative motion, enabling us to measure the microlens parallax. The ground-based microlens parallax is confirmed by the data obtained from space-based microlens observations using the Spitzer telescope. By additionally measuring the angular Einstein radius from the analysis of the resolved caustic crossing, the physical parameters of the lens are determined up to the twofold degeneracy, u(0) < 0 and u(0) > 0, solutions caused by the well-known 'ecliptic' degeneracy. It is found that the binary lens is composed of two M dwarf stars with similar masses, M-1 = 0.38 +/- 0.04M(circle plus) (0.50 +/- 0.05M(circle plus)) and M-2 = 0.38 +/- 0.04M(circle plus) (0.55 +/- 0.06M(circle plus)), and the distance to the lens is D-L = 2.77. +/- 0.23 kpc (3.30 +/- 0.29 kpc). Here the physical parameters outside and inside the parentheses are for the u(0) < 0 and u(0) > 0 solutions, respectively.</P>
OGLE-2014-BLG-0257L: A MICROLENSING BROWN DWARF ORBITING A LOW-MASS M DWARF
Han, C.,Jung, Y. K.,Udalski, A.,Gould, A.,Bozza, V.,Szymań,ski, M. K.,Soszyń,ski, I.,Poleski, R.,Kozłowski, S.,Pietrukowicz, P.,Skowron, J.,Ulaczyk, K.,Wyrzykowski, Ł. American Astronomical Society 2016 The Astrophysical Journal Vol.822 No.2
<P>In this paper, we report the discovery of a binary composed of a brown dwarf (BD) and a low-mass M dwarf from observation of the microlensing event OGLE-2014-BLG-0257. The resolution of the very brief caustic crossing combined with the detection of subtle continuous deviation in the lensing light curve induced by the Earth's orbital motion enable us to precisely measure both the Einstein radius theta(E) and the lens parallax pi(E), which are the two quantities needed to unambiguously determine the mass and distance to the lens. It is found that the companion is a substellar BD with a mass of 0.036 +/- 0.005 M-circle dot (37.7 +/- 5.2 M-J) and it is orbiting an M dwarf with a mass of 0.19 +/- 0.02 M-circle dot. The binary is located at a distance of 1.25 +/- 0.13 kpc toward the Galactic bulge and the projected separation between the binary components is 0.61 +/- 0.07 au. The separation scaled by the mass of the host is 3.2 au/M-circle dot. Based on the assumption that separations scale with masses, the discovered BD is located in the BD desert. With the growing sample of BDs in various environments, microlensing will provide a powerful probe of BDs in the Galaxy.</P>
GRAVITATIONAL BINARY-LENS EVENTS WITH PROMINENT EFFECTS OF LENS ORBITAL MOTION
Park, H.,Udalski, A.,Han, C.,Gould, A.,Beaulieu, J.-P.,Tsapras, Y.,Szymań,ski, M. K.,Kubiak, M.,Soszyń,ski, I.,Pietrzyń,ski, G.,Poleski, R.,Ulaczyk, K.,Pietrukowicz, P.,Kozłowski, S.,Sk IOP Publishing 2013 The Astrophysical journal Vol.778 No.2
<P>Gravitational microlensing events produced by lenses composed of binary masses are important because they provide a major channel for determining physical parameters of lenses. In this work, we analyze the light curves of two binary-lens events, OGLE-2006-BLG-277 and OGLE-2012-BLG-0031, for which the light curves exhibit strong deviations from standard models. From modeling considering various second-order effects, we find that the deviations are mostly explained by the effect of the lens orbital motion. We also find that lens parallax effects can mimic orbital effects to some extent. This implies that modeling light curves of binary-lens events not considering orbital effects can result in lens parallaxes that are substantially different from actual values and thus wrong determinations of physical lens parameters. This demonstrates the importance of routine consideration of orbital effects in interpreting light curves of binary-lens events. It is found that the lens of OGLE-2006-BLG-277 is a binary composed of a low-mass star and a brown dwarf companion.</P>
A terrestrial planet in a ~1-AU orbit around one member of a ∼15-AU binary
Gould, A.,Udalski, A.,Shin, I.-G.,Porritt, I.,Skowron, J.,Han, C.,Yee, J. C.,Kozłowski, S.,Choi, J.-Y.,Poleski, R.,Wyrzykowski, Ł.,Ulaczyk, K.,Pietrukowicz, P.,Mró,z, P.,Szymań,ski, M. K.,K American Association for the Advancement of Scienc 2014 Science Vol.345 No.6192
<P>Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earth's) and lies projected at similar to 0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planet's temperature is much lower, <60 Kelvin, because the host star is only 0.10 to 0.15 solar masses and therefore more than 400 times less luminous than the Sun. The host itself orbits a slightly more massive companion with projected separation of 10 to 15 AU. This detection is consistent with such systems being very common. Straightforward modification of current microlensing search strategies could increase sensitivity to planets in binary systems. With more detections, such binary-star planetary systems could constrain models of planet formation and evolution.</P>