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Shin, I.-G.,Udalski, A.,Yee, J. C.,Novati, S. Calchi,Han, C.,Skowron, J.,Mró,z, P.,Soszyń,ski, I.,Poleski, R.,Szymań,ski, M. K.,Kozłowski, S.,Pietrukowicz, P.,Ulaczyk, K.,Pawlak, M.,Al American Astronomical Society 2017 The Astronomical journal Vol.154 No.5
<P>The microlens parallax is a crucial observable for conclusively identifying the nature of lens systems in microlensing events containing or composed of faint (even dark) astronomical objects such as planets, neutron stars, brown dwarfs, and black holes. With the commencement of a new era of microlensing in collaboration with space-based observations, the microlens parallax can be routinely measured. In addition, space-based observations can provide opportunities to verify the microlens parallax measured from ground-only observations and to find a unique solution to the lensing light-curve analysis. Furthermore, since most space-based observations cannot cover the full light curves of lensing events, it is also necessary to verify the reliability of the information extracted from fragmentary space-based light curves. We conduct a test based on the microlensing event OGLE-2016-BLG-0168, created by a binary lens system consisting of almost equal mass M-dwarf stars, to demonstrate that it is possible to verify the microlens parallax and to resolve degeneracies using the space-based light curve even though the observations are fragmentary. Since space-based observatories will frequently produce fragmentary light curves due to their short observing windows, the methodology of this test will be useful for next-generation microlensing experiments that combine space-based and ground-based collaboration.</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>
Udalski, A.,Yee, J. C.,Gould, A.,Carey, S.,Zhu, W.,Skowron, J.,Kozłowski, S.,Poleski, R.,Pietrukowicz, P.,Pietrzyń,ski, G.,Szymań,ski, M. K.,Mró,z, P.,Soszyń,ski, I.,Ulaczyk, K.,W IOP Publishing 2015 The Astrophysical journal Vol.799 No.2
<P>We combine Spitzer and ground-based observations to measure the microlens parallax vector pi(E), and thus the mass and distance of OGLE-2014-BLG-0124L, making it the first microlensing planetary system with a space-based parallax measurement. The planet and star have masses of m similar to 0.5M(jup) and M similar to 0.7M(circle dot) and are separated by a(perpendicular to) similar to 3.1AU in projection. The main source of uncertainty in all of these numbers (approximately 30%, 30%, and 20%) is the relatively poor measurement of the Einstein radius theta(E), rather than uncertainty in pE, which is measured with 2.5% precision. This compares to 22% based on OGLE data alone, implying that the Spitzer data provide not only a substantial improvement in the precision of the pE measurement, but also the first independent test of a ground-based pE measurement.</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>
Zhu (祝伟,), Wei,Udalski, A.,Gould, A.,Dominik, M.,Bozza, V.,Han, C.,Yee, J. C.,Novati, S. Calchi,Beichman, C. A.,Carey, S.,Poleski, R.,Skowron, J.,Kozłowski, S.,Mró,z, P.,Pietrukowicz, P.,P IOP Publishing 2015 The Astrophysical journal Vol.805 No.1
<P>We report the first mass and distance measurements of a caustic-crossing binary system OGLE-2014-BLG-1050 L using the space-based microlens parallax method. Spitzer captured the second caustic. crossing of the event, which occurred similar to 10 days before that seen from Earth. Due to the coincidence that the source-lens relative motion was almost parallel to the direction of the binary-lens axis, the fourfold degeneracy, which was known before only to occur in single-lens events, persists in this case, leading to either a lower-mass (0.2 and 0.07 M-circle dot) binary at similar to 1.1 kpc or a higher-mass (0.9 and 0.35 M-circle dot) binary at similar to 3.5 kpc. However, the latter solution is strongly preferred for reasons including blending and lensing probability. OGLE-2014-BLG-1050 L demonstrates the power of microlens parallax in probing stellar and substellar binaries.</P>
A VENUS-MASS PLANET ORBITING A BROWN DWARF: A MISSING LINK BETWEEN PLANETS AND MOONS
Udalski, A.,Jung, Y. K.,Han, C.,Gould, A.,Kozłowski, S.,Skowron, J.,Poleski, R.,Soszyń,ski, I.,Pietrukowicz, P.,Mró,z, P.,Szymań,ski, M. K.,Wyrzykowski, Ł.,Ulaczyk, K.,Pietrzyń,sk IOP Publishing 2015 The Astrophysical journal Vol.812 No.1
<P>The co-planarity of solar system planets led Kant to suggest that they formed from an accretion disk, and the discovery of hundreds of such disks around young stars as well as hundreds of co-planar planetary systems by the Kepler satellite demonstrate that this formation mechanism is extremely widespread. Many moons in the solar system, such as the Galilean moons of Jupiter, also formed out of the accretion disks that coalesced into the giant planets. Here we report the discovery of an intermediate system, OGLE-2013-BLG-0723LB/Bb, composed of a Venus-mass planet orbiting a brown dwarf, which may be viewed either as a scaled-down version of a planet plus a star or as a scaled-up version of a moon plus a planet orbiting a star. The latter analogy can be further extended since they orbit in the potential of a larger, stellar body. For ice-rock companions formed in the outer parts of accretion disks, like Uranus and Callisto, the scaled masses and separations of the three types of systems are similar, leading us to suggest that the formation processes of companions within accretion disks around stars, brown dwarfs, and planets are similar.</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>
Han, C.,Udalski, A.,Choi, J.-Y.,Yee, J. C.,Gould, A.,Christie, G.,Tan, T.-G.,Szymań,ski, M. K.,Kubiak, M.,Soszyń,ski, I.,Pietrzyń,ski, G.,Poleski, R.,Ulaczyk, K.,Pietrukowicz, P.,Kozłow IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.762 No.2
<P>We report the discovery of a planetary system from observation of the high-magnification microlensing event OGLE-2012-BLG-0026. The lensing light curve exhibits a complex central perturbation with multiple features. We find that the perturbation was produced by two planets located near the Einstein ring of the planet host star. We identify four possible solutions resulting from the well-known close/wide degeneracy. By measuring both the lens parallax and the Einstein radius, we estimate the physical parameters of the planetary system. According to the best-fit model, the two planet masses are similar to 0.11 M-J and 0.68 M-J and they are orbiting a G-type main-sequence star with a mass similar to 0.82 M-circle dot. The projected separations of the individual planets are beyond the snow line in all four solutions, being similar to 3.8 AU and 4.6 AU in the best-fit solution. The deprojected separations are both individually larger and possibly reversed in order. This is the second multi-planet system with both planets beyond the snow line discovered by microlensing. This is the only such system (other than the solar system) with measured planet masses without sin i degeneracy. The planetary system is located at a distance 4.1 kpc from the Earth toward the Galactic center. It is very likely that extra light from stars other than the lensed star comes from the lens itself. If this is correct, it will be possible to obtain detailed information about the planet host star from follow-up observation.</P>
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>