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신인구,Y.-H. Ryu,A. Udalski,M. Albrow,S.-M. Cha,J.-Y. Choi,S.-J. Chung,C. Han,K.-H. Hwang,Y. K. Jung,D.-J. Kim,S.-L. Kim,C.-U. Lee,Y. Lee,B.-G. Park,H. Park,R. W. Pogge,J. C. Yee,P. Pietrukowicz,P. Mroz 한국천문학회 2016 Journal of The Korean Astronomical Society Vol.49 No.3
We report the characterization of a massive $(m_p=3.9\pm 1.4 M_{\rm jup})$ microlensing planet (OGLE-2015-BLG-0954Lb) orbiting an M dwarf host ($M=0.33\,\pm 0.12 M_\odot$) at a distance toward the Galactic bulge of $0.6^{+0.4}_{-0.2}\,$kpc, which is extremely nearby by microlensing standards. The planet-host projected separation is $a_\perp \sim 1.2\,\au$. The characterization was made possible by the wide-field ($4\,\rm deg^2$) high cadence ($\Gamma = 6\,\rm hr^{-1}$) monitoring of the Korea Microlensing Telescope Network (KMTNet), which had two of its three telescopes in commissioning operations at the time of the planetary anomaly. The source crossing time $t_*=16\,$min is among the shortest ever published. The high-cadence, wide-field observations that are the hallmark of KMTNet are the only way to routinely capture such short crossings. High-cadence resolution of short caustic crossings will preferentially lead to mass and distance measurements for the lens. This is because the short crossing time typically implies a nearby lens, which enables the measurement of additional effects (bright lens and/or microlens parallax). When combined with the measured crossing time, these effects can yield planet/host masses and distance.
MOA-2010-BLG-328Lb: A SUB-NEPTUNE ORBITING VERY LATE M DWARF?
Furusawa, K.,Udalski, A.,Sumi, T.,Bennett, D. P.,Bond, I. A.,Gould, A.,Jørgensen, U. G.,Snodgrass, C.,Prester, D. Dominis,Albrow, M. D.,Abe, F.,Botzler, C. S.,Chote, P.,Freeman, M.,Fukui, A.,Harris, P IOP Publishing 2013 The Astrophysical journal Vol.779 No.2
<P>We analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of M-h = 0.11 +/- 0.01 M-circle dot and M-p = 9.2 +/- 2.2 M-circle dot, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at D-L = 0.81 +/- 0.10 kpc with projected separation r(perpendicular to) = 0.92 +/- 0.16 AU. Because of the host's a priori unlikely close distance, as well as the unusual nature of the system, we consider the possibility that the microlens parallax signal, which determines the host mass and distance, is actually due to xallarap (source orbital motion) that is being misinterpreted as parallax. We show a result that favors the parallax solution, even given its close host distance. We show that future high-resolution astrometric measurements could decisively resolve the remaining ambiguity of these solutions.</P>
CAN THE MASSES OF ISOLATED PLANETARY-MASS GRAVITATIONAL LENSES BE MEASURED BY TERRESTRIAL PARALLAX?
Freeman, M.,Philpott, L. C.,Abe, F.,Albrow, M. D.,Bennett, D. P.,Bond, I. A.,Botzler, C. S.,Bray, J. C.,Cherrie, J. M.,Christie, G. W.,Dionnet, Z.,Gould, A.,Han, C.,Heyrovský,, D.,McCormick, J. IOP Publishing 2015 The Astrophysical journal Vol.799 No.2
<P>Recently Sumi et al. reported evidence for a large population of planetary-mass objects ( PMOs) that are either unbound or orbit host stars in orbits >= 10 AU. Their result was deduced from the statistical distribution of durations of gravitational microlensing events observed by the MOA collaboration during 2006 and 2007. Here we study the feasibility of measuring the mass of an individual PMO through microlensing by examining a particular event, MOA-2011-BLG-274. This event was unusual as the duration was short, the magnification high, the source-size effect large, and the angular Einstein radius small. Also, it was intensively monitored from widely separated locations under clear skies at low air masses. Choi et al. concluded that the lens of the event may have been a PMO but they did not attempt a measurement of its mass. We report here a re-analysis of the event using re-reduced data. We confirm the results of Choi et al. and attempt a measurement of the mass and distance of the lens using the terrestrial parallax effect. Evidence for terrestrial parallax is found at a 3 sigma level of confidence. The best fit to the data yields the mass and distance of the lens as 0.80 +/- 0.30 M-J and 0.80 +/- 0.25 kpc respectively. We exclude a host star to the lens out to a separation similar to 40 AU. Drawing on our analysis of MOA-2011-BLG-274 we propose observational strategies for future microlensing surveys to yield sharper results on PMOs including those down to super-Earth mass.</P>
A brown dwarf orbiting an M-dwarf: MOA 2009–BLG–411L
Bachelet, E.,Fouqué,, P.,Han, C.,Gould, A.,Albrow, M. D.,Beaulieu, J.-P.,Bertin, E.,Bond, I. A.,Christie, G. W.,Heyrovský,, D.,Horne, K.,Jørgensen, U. G.,Maoz, D.,Mathiasen, M.,Matsunaga, EDP Sciences 2012 Astronomy and astrophysics Vol.547 No.-
OGLE-2016-BLG-1469L: Microlensing Binary Composed of Brown Dwarfs
Han, C.,Udalski, A.,Sumi, T.,Gould, A.,Albrow, M. D.,Chung, S.-J.,Jung, Y. K.,Ryu, Y.-H.,Shin, I.-G.,Yee, J. C.,Zhu, W.,Cha, S.-M.,Kim, S.-L.,Kim, D.-J.,Lee, C.-U.,Lee, Y.,Park, B.-G.,Soszyń,ski, American Astronomical Society 2017 The Astrophysical journal Vol.843 No.1
<P>We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the microlensing event OGLE-2016-BLG-1469. Thanks to the detection of both finite-source and microlens-parallax effects, we are able to measure both the masses M-1 similar to 0.05M(circle dot) and. M-2 similar to 0.01M(circle dot), and the. distance D-L similar to 4.5 kpc, as well as the projected separation a(perpendicular to) similar to 0.33 au. This is the third brown-dwarf binary detected using the microlensing method, demonstrating the usefulness of microlensing in detecting field brown-dwarf binaries with separations of less than 1 au.</P>
Han, C.,Udalski, A.,Gould, A.,Bond, I. A.,Albrow, M. D.,Chung, S.-J.,Jung, Y. K.,Ryu, Y.-H.,Shin, I.-G.,Yee, J. C.,Zhu, W.,Cha, S.-M.,Kim, S.-L.,Kim, D.-J.,Lee, C.-U.,Lee, Y.,Park, B.-G.,Skowron, J.,M American Astronomical Society 2017 The Astronomical journal Vol.154 No.4
<P>We report the discovery of a planet-mass companion to the microlens OGLE-2016-BLG-0263L. Unlike most low-mass companions that were detected through perturbations to the smooth and symmetric light curves produced by the primary, the companion was discovered through the channel of a repeating event, in which the companion itself produced its own single-mass light curve after the event produced by the primary had ended. Thanks to the continuous coverage of the second peak by high-cadence surveys, the possibility of the repeating nature due to source binarity is excluded with a 96% confidence level. The mass of the companion estimated by a Bayesian analysis is Mp = 4.1(-2.5)(+6.5) M-j. The projected primary-companion separation is a(perpendicular to) = 6.5(-1.9)(+1.3) au. The ratio of the separation to the snow-line distance of a(perpendicular to/)a(s1) similar to 15.4 corresponds to the region beyond Neptune, the outermost planet of the solar system. We discuss the importance of high-cadence surveys in expanding the range of microlensing detections of low-mass companions and future space-based microlensing surveys.</P>
A SUB-SATURN MASS PLANET, MOA-2009-BLG-319Lb
Miyake, N.,Sumi, T.,Dong, Subo,Street, R.,Mancini, L.,Gould, A.,Bennett, D. P.,Tsapras, Y.,Yee, J. C.,Albrow, M. D.,Bond, I. A.,Fouqué,, P.,Browne, P.,Han, C.,Snodgrass, C.,Finet, F.,Furusawa, K IOP Publishing 2011 The Astrophysical journal Vol.728 No.2
<P>We report the gravitational microlensing discovery of a sub-Saturn mass planet, MOA-2009-BLG-319Lb, orbiting a K-or M-dwarf star in the inner Galactic disk or Galactic bulge. The high-cadence observations of the MOA-II survey discovered this microlensing event and enabled its identification as a high-magnification event approximately 24 hr prior to peak magnification. As a result, the planetary signal at the peak of this light curve was observed by 20 different telescopes, which is the largest number of telescopes to contribute to a planetary discovery to date. The microlensing model for this event indicates a planet-star mass ratio of q = (3.95 +/- 0.02) x 10(-4) and a separation of d = 0.97537 +/- 0.00007 in units of the Einstein radius. A Bayesian analysis based on the measured Einstein radius crossing time, t(E), and angular Einstein radius,theta(E), along with a standard Galactic model indicates a host star mass of M-L = 0.38(-0.18)(+0.34) M-circle dot and a planet mass of M-p = 50(-24)(+44)M(circle plus), which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4(-0.6)(+1.2) AU and a distance to the planetary system of D-L = 6.1(-1.2)(+1.1) kpc. This separation is similar to 2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing.</P>
OGLE-2016-BLG-0613LABb: A Microlensing Planet in a Binary System
Han, C.,Udalski, A.,A., Gould,Lee, C.-U.,Shvartzvald, Y.,Zang, W. C.,Mao, S.,Kozłowski, S.,Albrow, M. D.,Chung, S.-J.,Hwang, K.-H.,Jung, Y. K.,Kim, D.,Kim, H.-W.,Ryu, Y.-H.,Shin, I.-G.,Yee, J. C.,Zhu, American Astronomical Society 2017 The Astronomical journal Vol.154 No.6
<P>We present the analysis of OGLE-2016-BLG-0613, for which the lensing light curve appears to be that of a typical binary-lens event with two caustic spikes but with a discontinuous feature on the trough between the spikes. We find that the discontinuous feature was produced by a planetary companion to the binary lens. We find four degenerate triplelens solution classes, each composed of a pair of solutions according to the well-known wide/close planetary degeneracy. One of these solution classes is excluded due to its relatively poor fit. For the remaining three pairs of solutions, the most-likely primary mass is about M-1 similar to 0.7M(circle dot) , while the planet is a super Jupiter. In all cases, the system lies in the Galactic disk, about halfway toward the Galactic bulge. However, in one of these three solution classes, the secondary of the binary system is a low- mass brown dwarf, with relative mass ratios (1: 0.03: 0.003), while in the two others the masses of the binary components are comparable. These two possibilities can be distinguished in about 2024 when the measured lens-source relative proper motion will permit separate resolution of the lens and source.</P>
DISCOVERY AND MASS MEASUREMENTS OF A COLD, 10 EARTH MASS PLANET AND ITS HOST STAR
Muraki, Y.,Han, C.,Bennett, D. P.,Suzuki, D.,Monard, L. A. G.,Street, R.,Jorgensen, U. G.,Kundurthy, P.,Skowron, J.,Becker, A. C.,Albrow, M. D.,Fouqué,, P.,Heyrovský,, D.,Barry, R. K.,Beau IOP Publishing 2011 The Astrophysical journal Vol.741 No.1
<P>We present the discovery and mass measurement of the cold, low-mass planet MOA-2009-BLG-266Lb, performed with the gravitational microlensing method. This planet has a mass of m(p) = 10.4 +/- 1.7 M-circle plus and orbits a star of mass M-star = 0.56 +/- 0.09 M-circle dot at a semimajor axis of a = 3.2(-0.5)(+1.9) AU and an orbital period of P = 7.6(-1.5)(+7.7) yrs. The planet and host star mass measurements are enabled by the measurement of the microlensing parallax effect, which is seen primarily in the light curve distortion due to the orbital motion of the Earth. But the analysis also demonstrates the capability to measure the microlensing parallax with the Deep Impact (or EPOXI) spacecraft in a heliocentric orbit. The planet mass and orbital distance are similar to predictions for the critical core mass needed to accrete a substantial gaseous envelope, and thus may indicate that this planet is a 'failed' gas giant. This and future microlensing detections will test planet formation theory predictions regarding the prevalence and masses of such planets.</P>
OGLE-2015-BLG-1482L: The First Isolated Low-mass Microlens in the Galactic Bulge
Chung, S.-J.,Zhu, W.,Udalski, A.,Lee, C.-U.,Ryu, Y.-H.,Jung, Y. K.,Shin, I.-G.,Yee, J. C.,Hwang, K.-H.,Gould, A.,Albrow, M.,Cha, S.-M.,Han, C.,Kim, D.-J.,Kim, H.-W.,Kim, S.-L.,Kim, Y.-H.,Lee, Y.,Park, American Astronomical Society 2017 The Astrophysical Journal Vol.838 No.2
<P>We analyze the single microlensing event OGLE-2015-BLG-1482 simultaneously observed from two ground-based surveys and from Spitzer. The Spitzer data exhibit finite-source effects that are. due to the passage of the lens close to or directly over. the surface of the source star as seen from Spitzer. Such finite-source effects generally yield measurements of the angular Einstein radius, which when combined with the microlens parallax derived from a comparison between the ground-based and the Spitzer light curves. yields the lens mass and lens-source relative parallax. From this analysis, we find that the lens of OGLE-2015-BLG-1482 is a very low-mass star with a. mass 0.10 +/- 0.02 M-circle dot or a brown dwarf with a. mass 55 +/- 9MJ, which are. located at D-LS = 0.80 +/- 0.19 kpc and D-LS = 0.54 +/- 0.08 kpc, respectively,. where DLS is the distance between the lens and the source, and thus it is the first isolated low-mass microlens that has been decisively located in the Galactic bulge. The degeneracy between the two solutions is severe ( Delta chi(2) = 0.3). The fundamental reason for the degeneracy is that the finite-source effect is seen only in a single data point from Spitzer, and this single data point gives rise to two solutions for rho, the angular size of the source in units of the angular Einstein ring radius. Because the rho degeneracy can be resolved only by relatively high-cadence observations around the peak, while the Spitzer cadence is typically similar to 1 day(-1), we expect that events for which the finite-source effect is seen only in the Spitzer data may frequently exhibit this rho degeneracy. For OGLE-2015-BLG-1482, the relative proper motion of the lens and source for the low-mass star is mu(rel) = 9.0 +/- 1.9 mas yr(-1), while for the brown dwarf it is 5.5 +/- 0.5 mas yr(-1). Hence, the degeneracy can be resolved within similar to 10 years from direct-lens imaging by using next-generation instruments with high spatial resolution.</P>