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Fukui A.,Japan National Astronomical Observatory | Gould A.,Ohio State University | Sumi T.,Osaka University | Bennett D.P.,University of Notre Dame | And 65 more authors.
Astrophysical Journal | Year: 2015

We report the discovery of a microlensing exoplanet OGLE-2012-BLG-0563Lb with the planet-star mass ratio of ∼1 ×10-3. Intensive photometric observations of a high-magnification microlensing event allow us to detect a clear signal of the planet. Although no parallax signal is detected in the light curve, we instead succeed at detecting the flux from the host star in high-resolution JHK-band images obtained by the Subaru/AO188 and Infrared Camera and Spectrograph instruments, allowing us to constrain the absolute physical parameters of the planetary system. With the help of spectroscopic information about the source star obtained during the high-magnification state by Bensby et al., we find that the lens system is located at 1.3 0.6 0.8 kpc from us, and consists of an M dwarf (0.34 0.12 0.20 M) orbited by a Saturn-mass planet (0.39 0.14 0.23 MJup) at the projected separation of 0.74 0.26 0.42 AU (close model) or 4.3 1.5 2.5 AU (wide model). The probability of contamination in the host star's flux, which would reduce the masses by a factor of up to three, is estimated to be 17%. This possibility can be tested by future high-resolution imaging. We also estimate the (J - Ks ) and (H - Ks ) colors of the host star, which are marginally consistent with a low metallicity mid-to-early M dwarf, although further observations are required for the metallicity to be conclusive. This is the fifth sub-Jupiter-mass (0.2 ≤ mp MJup <1) microlensing planet around an M dwarf with the mass well constrained. The relatively rich harvest of sub-Jupiters around M dwarfs is contrasted with a possible paucity of 1-2 Jupiter-mass planets around the same type of star, which can be explained by the planetary formation process in the core-accretion scheme. © 2015. The American Astronomical Society. All rights reserved.


Filgas R.,Max Planck Institute for Extraterrestrial Physics | Filgas R.,Czech Technical University | Greiner J.,Max Planck Institute for Extraterrestrial Physics | Schady P.,Max Planck Institute for Extraterrestrial Physics | And 25 more authors.
Astronomy and Astrophysics | Year: 2012

Aims. Using high-quality, broad-band afterglow data for GRB 091029, we test the validity of the forward-shock model for gamma-ray burst afterglows. Methods. We used multi-wavelength (NIR to X-ray) follow-up observations obtained with the GROND, BOOTES-3/YA and Stardome optical ground-based telescopes, and the UVOT and the XRT onboard the Swift satellite. The resulting data of excellent accuracy allow us to construct a multi-wavelength light curve with relative photometric errors as low as 1%, as well as the well-sampled spectral energy distribution covering 5 decades in energy. Results. The optical/NIR and the X-ray light curves of the afterglow of GRB 091029 are almost totally decoupled. The X-ray light curve shows a shallow rise with a peak at ∼7 ks and a decay slope of α ∼ 1.2 afterwards, while the optical/NIR light curve shows a much steeper early rise with a peak around 400 s, followed by a shallow decay with temporal index of α ∼ 0.6, a bump and a steepening of the decay afterwards. The optical/NIR spectral index decreases gradually by over 0.3 before this bump, and then slowly increases again, while the X-ray spectral index remains constant throughout the observations. Conclusions. To explain the decoupled light curves in the X-ray and optical/NIR domains, a two-component outflow is proposed. Several models are tested, including continuous energy injection, components with different electron energy indices and components in two different stages of spectral evolution. Only the last model can explain both the decoupled light curves with asynchronous peaks and the peculiar SED evolution. However, this model has so many unknown free parameters that we are unable to reliably confirm or disprove its validity, making the afterglow of GRB 091029 difficult to explain in the framework of the simplest fireball model. This conclusion provides evidence that a scenario beyond the simplistic assumptions is needed to be able to model the growing number of well-sampled afterglow light curves. © ESO, 2012.


Han C.,Chungbuk National University | Jung Y.K.,Chungbuk National University | Udalski A.,University of Warsaw | Sumi T.,Osaka University | And 70 more authors.
Astrophysical Journal | Year: 2013

Observations of accretion disks around young brown dwarfs (BDs) have led to the speculation that they may form planetary systems similar to normal stars. While there have been several detections of planetary-mass objects around BDs (2MASS 1207-3932 and 2MASS 0441-2301), these companions have relatively large mass ratios and projected separations, suggesting that they formed in a manner analogous to stellar binaries. We present the discovery of a planetary-mass object orbiting a field BD via gravitational microlensing, OGLE-2012-BLG-0358Lb. The system is a low secondary/primary mass ratio (0.080 ± 0.001), relatively tightly separated (0.87 AU) binary composed of a planetary-mass object with 1.9 ± 0.2 Jupiter masses orbiting a BD with a mass 0.022 M. The relatively small mass ratio and separation suggest that the companion may have formed in a protoplanetary disk around the BD host in a manner analogous to planets. © 2013. The American Astronomical Society. All rights reserved..


Han C.,Chungbuk National University | Udalski A.,University of Warsaw | Choi J.-Y.,Chungbuk National University | Yee J.C.,Ohio State University | And 34 more authors.
Astrophysical Journal Letters | Year: 2013

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 ∼0.11 M J and 0.68 MJ and they are orbiting a G-type main-sequence star with a mass ∼0.82 M⊙. The projected separations of the individual planets are beyond the snow line in all four solutions, being ∼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. © 2013. 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..


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..


PubMed | University of Notre Dame, Korea Astronomy and Space Science Institute, Turitea Observatory, Tel Aviv University and 23 more.
Type: Journal Article | Journal: Science (New York, N.Y.) | Year: 2014

Using gravitational microlensing, we detected a cold terrestrial planet orbiting one member of a binary star system. The planet has low mass (twice Earths) and lies projected at ~0.8 astronomical units (AU) from its host star, about the distance between Earth and the Sun. However, the planets 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.


Freeman M.,University of Auckland | Philpott L.C.,University of British Columbia | Abe F.,Nagoya University | Albrow M.D.,University of Canterbury | And 21 more authors.
Astrophysical Journal | Year: 2015

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 3σ level of confidence. The best fit to the data yields the mass and distance of the lens as 0.80 ± 0.30 MJ and 0.80 ± 0.25 kpc respectively. We exclude a host star to the lens out to a separation ∼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. © 2015. The American Astronomical Society. All rights reserved.


Janczak J.,Ohio State University | Fukui A.,Nagoya University | Dong S.,Ohio State University | Monard L.A.G.,Bronberg Observatory | And 65 more authors.
Astrophysical Journal | Year: 2010

We report the detection of sub-Saturn-mass planet MOA-2008-BLG-310Lb and argue that it is the strongest candidate yet for a bulge planet. Deviations from the single-lens fit are smoothed out by finite-source effects and therefore are not immediately apparent from the light curve. Nevertheless, we find that a model in which the primary has a planetary companion is favored over the single-lens model by Δχ2 ∼ 880 for an additional 3 degrees of freedom. Detailed analysis yields a planet/star mass ratio q = (3.3 ± 0.3) × 10-4 and an angular separation between the planet and star within 10% of the angular Einstein radius. The small angular Einstein radius, θE = 0.155 ± 0.011 mas, constrains the distance to the lens to be DL >6.0kpc if it is a star (M L >0.08 M). This is the only microlensing exoplanet host discovered so far that must be in the bulge if it is a star. By analyzing VLT NACO adaptive optics images taken near the baseline of the event, we detect additional blended light that is aligned to within 130mas of the lensed source. This light is plausibly from the lens, but could also be due to a companion to the lens or source, or possibly an unassociated star. If the blended light is indeed due to the lens, we can estimate the mass of the lens, ML = 0.67 0.14 M ⊙, planet mass m = 74 ± 17 M ⊕, and projected separation between the planet and host, 1.25 ± 0.10AU, putting it right on the "snow line." If not, then the planet has lower mass, is closer to its host and is colder. To distinguish among these possibilities on reasonable timescales would require obtaining Hubble Space Telescope images almost immediately, before the source-lens relative motion of causes them to separate substantially. © 2010. The American Astronomical Society.


Bennett D.P.,University of Notre Dame | Rhie S.H.,University of Notre Dame | Nikolaev S.,Lawrence Livermore National Laboratory | Gaudi B.S.,Ohio State University | And 73 more authors.
Astrophysical Journal | Year: 2010

We present a new analysis of the Jupiter+Saturn analog system, OGLE-2006-BLG-109Lb,c, which was the first double planet system discovered with the gravitational microlensing method. This is the only multi-planet system discovered by any method with measured masses for the star and both planets. In addition to the signatures of two planets, this event also exhibits a microlensing parallax signature and finite source effects that provide a direct measure of the masses of the star and planets, and the expected brightness of the host star is confirmed by Keck AO imaging, yielding masses of M * = 0.51+0.05?0.04 M⊙ Mb = 231 ± 19M, and Mc = 86 ± 7M. The Saturn-analog planet in this system had a planetary light-curve deviation that lasted for 11 days, and as a result, the effects of the orbital motion are visible in the microlensing light curve. We find that four of the six orbital parameters are tightly constrained and that a fifth parameter, the orbital acceleration, is weakly constrained. No orbital information is available for the Jupiter-analog planet, but its presence helps to constrain the orbital motion of the Saturn-analog planet. Assuming co-planar orbits, we find an orbital eccentricity of ε = 0.15+0.17?0.10 and an orbital inclination of i = 64° +4°?7° . The 95% confidence level lower limit on the inclination of i> 49° implies that this planetary system can be detected and studied via radial velocity measurements using a telescope of ≳30m aperture. © 2010. The American Astronomical Society.

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