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Jeong J.,Chungbuk National University | Park H.,Chungbuk National University | Han C.,Chungbuk National University | Gould A.,Ohio State University | And 99 more authors.
Astrophysical Journal | Year: 2015

We reanalyze microlensing events in the published list of anomalous events that were observed from the Optical Gravitational Lensing Experiment (OGLE) lensing survey conducted during the 2004-2008 period. In order to check the existence of possible degenerate solutions and extract extra information, we conduct analyses based on combined data from other survey and follow-up observation and consider higher-order effects. Among the analyzed events, we present analyses of eight events for which either new solutions are identified or additional information is obtained. We find that the previous binary-source interpretations of five events are better interpreted by binary-lens models. These events include OGLE-2006-BLG-238, OGLE-2007-BLG-159, OGLE-2007-BLG-491, OGLE-2008-BLG-143, and OGLE-2008-BLG-210. With additional data covering caustic crossings, we detect finite-source effects for six events including OGLE-2006-BLG-215, OGLE-2006-BLG-238, OGLE-2006-BLG-450, OGLE-2008-BLG-143, OGLE-2008-BLG-210, and OGLE-2008-BLG-513. Among them, we are able to measure the Einstein radii of three events for which multi-band data are available. These events are OGLE-2006-BLG-238, OGLE-2008-BLG-210, and OGLE-2008-BLG-513. For OGLE-2008-BLG-143, we detect higher-order effects induced by the changes of the observer's position caused by the orbital motion of the Earth around the Sun. In addition, we present degenerate solutions resulting from the known close/wide or ecliptic degeneracy. Finally, we note that the masses of the binary companions of the lenses of OGLE-2006-BLG-450 and OGLE-2008-BLG-210 are in the brown-dwarf regime. © 2015. The American Astronomical Society. All rights reserved.

Yee J.C.,Ohio State University | Shvartzvald Y.,Tel Aviv University | Gal-Yam A.,Weizmann Institute of Science | Bond I.A.,Massey University | And 76 more authors.
Astrophysical Journal | Year: 2012

Because of the development of large-format, wide-field cameras, microlensing surveys are now able to monitor millions of stars with sufficient cadence to detect planets. These new discoveries will span the full range of significance levels including planetary signals too small to be distinguished from the noise. At present, we do not understand where the threshold is for detecting planets. MOA-2011-BLG-293Lb is the first planet to be published from the new surveys, and it also has substantial follow-up observations. This planet is robustly detected in survey+follow-up data (Δχ2 5400). The planet/host mass ratio is q = (5.3 ± 0.2) × 10-3. The best-fit projected separation is s = 0.548 ± 0.005 Einstein radii. However, due to the s↔s -1 degeneracy, projected separations of s -1 are only marginally disfavored at Δχ2 = 3. A Bayesian estimate of the host mass gives ML = 0.43+0.27 - 0.17 M, with a sharp upper limit of ML < 1.2 M from upper limits on the lens flux. Hence, the planet mass is mp = 2.4+1.5 - 0.9 M Jup, and the physical projected separation is either r ≃ 1.0AU or r ≃ 3.4AU. We show that survey data alone predict this solution and are able to characterize the planet, but the Δχ2 is much smaller (Δχ2 500) than with the follow-up data. The Δχ2 for the survey data alone is smaller than for any other securely detected planet. This event suggests a means to probe the detection threshold, by analyzing a large sample of events like MOA-2011-BLG-293, which have both follow-up data and high-cadence survey data, to provide a guide for the interpretation of pure survey microlensing data. © © 2012. The American Astronomical Society. All rights reserved..

Miyake N.,Nagoya University | Sumi T.,Nagoya University | Dong S.,Institute for Advanced Study | Street R.,Las Cumbres Observatory Global Telescope Network | And 131 more authors.
Astrophysical Journal | Year: 2011

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) × 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, θe, along with a standard Galactic model indicates a host star mass of Ml = 0.38 +0.34 -0.18 M⊙ and a planet mass of M p = 50+44 -24 M>, which is half the mass of Saturn. This analysis also yields a planet-star three-dimensional separation of a = 2.4+1.2 -0.6 AU and a distance to the planetary system of Dl = 6.1+1.1 -1.2 kpc. This separation is ∼2 times the distance of the snow line, a separation similar to most of the other planets discovered by microlensing.

Sumi T.,Nagoya University | Bennett D.P.,University of Notre Dame | Bond I.A.,Massey University | Udalski A.,University of Warsaw | And 106 more authors.
Astrophysical Journal | Year: 2010

We present the discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q = [9.5 2.1] × 10-5 via gravitational microlensing. The planetary deviation was detected in real-time thanks to the high cadence of the Microlensing Observations in Astrophysics survey, real-time light-curve monitoring and intensive follow-up observations. A Bayesian analysis returns the stellar mass and distance at Ml = 0.64+0.21 -0.26 M· and Dl = 5.9 +0.9 -1.4 kpc, respectively, so the mass and separation of the planet are Mp = 20+7 -8 M ⊕ and a = 3.3+1.4 -0.8AU, respectively. This discovery adds another cold Neptune-mass planet to the planetary sample discovered by microlensing, which now comprises four cold Neptune/super-Earths, five gas giant planets, and another sub-Saturn mass planet whose nature is unclear. The discovery of these 10 cold exoplanets by the microlensing method implies that the mass ratio function of cold exoplanets scales as dN pl/dlog qαq -0.70.2 with a 95% confidence level upper limit of n < -0.35 (where dN pl/dlog qαqn ). As microlensing is most sensitive to planets beyond the snow-line, this implies that Neptune-mass planets are at least three times more common than Jupiters in this region at the 95% confidence level. © 2010. The American Astronomical Society. All rights reserved..

Batista V.,University Pierre and Marie Curie | Gould A.,Microlensing Follow Up Network I EFUN | Gould A.,Ohio State University | Dieters S.,University Pierre and Marie Curie | And 164 more authors.
Astronomy and Astrophysics | Year: 2011

Aims. We report the discovery of a planet with a high planet-to-star mass ratio in the microlensing event MOA-2009-BLG-387, which exhibited pronounced deviations over a 12-day interval, one of the longest for any planetary event. The host is an M dwarf, with a mass in the range 0.07 M ⊙ < Mhost < 0.49 M1 at 90% confidence. The planet-star mass ratio q = 0.0132 ± 0.003 has been measured extremely well, so at the best-estimated host mass, the planet mass is mp = 2.6 Jupiter masses for the median host mass, M = 0.19 M ⊙. Methods. The host mass is determined from two "higher order" microlensing parameters. One of these, the angular Einstein radius θE = 0.31 ± 0.03 mas has been accurately measured, but the other (the microlens parallax πE, which is due to the Earth's orbital motion) is highly degenerate with the orbital motion of the planet. We statistically resolve the degeneracy between Earth and planet orbital effects by imposing priors from a Galactic model that specifies the positions and velocities of lenses and sources and a Kepler model of orbits. Results. The 90% confidence intervals for the distance, semi-major axis, and period of the planet are 3.5 kpc < DL < 7.9 kpc, 1.1 AU < a < 2.7 AU, and 3.8 yr < P < 7.6 yr, respectively. © 2011 ESO.

Gould A.,Ohio State University | Dong S.,Institute for Advanced Study | Gaudi B.S.,Ohio State University | Udalski A.,Optical Gravitational Lens Experiment OGLE | And 169 more authors.
Astrophysical Journal | Year: 2010

We present the first measurement of the planet frequency beyond the "snow line," for the planet-to-star mass-ratio interval-4.5 < logq <-2, corresponding to the range of ice giants to gas giants. We find d 2Np1/dlog q d log s= (0.36 ± 0.15) dex dlog q d logs at the mean mass ratio q = 5 × 10-4 with no discernible deviation from a flat (öpik's law) distribution in logprojected separation s. The determination is based on a sample of six planets detected from intensive follow-up observations of high-magnification (A > 200) microlensing events during 2005-2008. The sampled host stars have a typical mass Mhost ∼ 0.5 M⊙, and detection is sensitive to planets over a range of planet-star-projected separations (s max -1Re, s maxRE), where Re ∼ 3.5 AU(Mhost/M⊙) 1/2 is the Einstein radius and smax ∼ (q/10 -43)1/3. This corresponds to deprojected separations roughly three times the "snow line." We show that the observations of these events have the properties of a "controlled experiment," which is what permits measurement of absolute planet frequency. High-magnification events are rare, but the survey-plus-follow-up high-magnification channel is very efficient: half of all high-mag events were successfully monitored and half of these yielded planet detections. The extremely high sensitivity of high-mag events leads to a policy of monitoring them as intensively as possible, independent of whether they show evidence of planets. This is what allows us to construct an unbiased sample. The planet frequency derived from microlensing is a factor 8 larger than the one derived from Doppler studies at factor ∼25 smaller star-planet separations (i.e., periods 2-2000 days). However, this difference is basically consistent with the gradient derived from Doppler studies (when extrapolated well beyond the separations from which it is measured). This suggests a universal separation distribution across 2 dex in planet-star separation, 2 dex in mass ratio, and 0.3 dex in host mass. Finally, if all planetary systems were "analogs" of the solar system, our sample would have yielded 18.2 planets (11.4 "Jupiters," 6.4 "Saturns," 0.3 "Uranuses," 0.2 "Neptunes") including 6.1 systems with two or more planet detections. This compares to six planets including one twoplanet system in the actual sample, implying a first estimate of 1/6 for the frequency of solar-like systems.

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