40 research outputs found
A Super-Jupiter orbiting a late-type star: A refined analysis of microlensing event OGLE-2012-BLG-0406
No full textpeer reviewedWe present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a planet orbiting a early M-type star. The distance to the lens is \ kpc and the projected separation between the host star and its planet at the time of the event is AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens
OGLE-2015-BLG-1649Lb : A gas giant planet around a low-mass dwarf
No full textPublisher Copyright: © 1999. The American Astronomical Society. All rights reserved.We report the discovery of an exoplanet from the analysis of the gravitational microlensing event OGLE-2015BLG-1649 that challenges the core accretion model of planet formation and appears to support the disk instability model. The planet/host-star mass ratio is q = 7.2 × 10−3 and the projected separation normalized to the angular Einstein radius is s = 0.9. We conducted high-resolution follow-up observations using the Infrared Camera and Spectrograph (IRCS) camera on the Subaru telescope and are able to place an upper limit on the lens flux. From these measurements we are able to exclude all host stars greater than or equal in mass to a G-type dwarf. We conducted a Bayesian analysis with these new flux constraints included as priors resulting in estimates of the masses of the host star and planet. These are ML = 0.34 ± 0.19 M☉ and Mp = 2.5-1.4+1.5 MJup, respectively. The distance to the system is DL = 4.23-1.64+1.51 kpc. The projected star–planet separation is a⊥ = 2.07-0.77+0.65 au. The estimated relative lens-source proper motion, ∼7.1 mas yr−1, is fairly high and thus the lens can be better constrained if additional follow-up observations are conducted several years after the event
MOA-2011-BLG-262Lb : a sub-earth-mass moon orbiting a gas giant primary or a high velocity planetary system in the galactic bulge
No full textD.P.B. was supported by grants NASA-NNX12AF54G, JPL-RSA 1453175 and NSF AST-1211875. This MOA project is supported by the grants JSPS18253002 and JSPS20340052. T.S. acknowledges the financial support from the JSPS, JSPS23340044, JSPS24253004. This work was partially supported by a NASA Keck PI Data Award, administered by the NASA Exoplanet Science Institute. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. B.S.G. and A.G. were supported by NSF grant AST 110347. B.S.G., A.G., R.P.G. were supported by NASA grant NNX12AB99G. S.D. was partly supported through a Ralph E. and Doris M. Hansmann Membership at the IAS and by NSF grant AST-0807444. Work by J.C.Y. was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. The OGLE project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement No. 246678 to A.U. D.H. was supported by Czech Science Foundation grant GACR P209/10/1318. D.M.B., M.D., K.H., C.S., R.A.S., M.H. and Y.T. are supported by NPRP grant NPRP-09-476-1-78 from the Qatar National Research Fund (a member of the Qatar Foundation).We present the first microlensing candidate for a free-floating exoplanet-exomoon system, MOA-2011-BLG-262, with a primary lens mass of M host ~ 4 Jupiter masses hosting a sub-Earth mass moon. The argument for an exomoon hinges on the system being relatively close to the Sun. The data constrain the product MLπrel where ML is the lens system mass and πrel is the lens-source relative parallax. If the lens system is nearby (large πrel), then ML is small (a few Jupiter masses) and the companion is a sub-Earth-mass exomoon. The best-fit solution has a large lens-source relative proper motion, μrel = 19.6 ± 1.6 mas yr–1, which would rule out a distant lens system unless the source star has an unusually high proper motion. However, data from the OGLE collaboration nearly rule out a high source proper motion, so the exoplanet+exomoon model is the favored interpretation for the best fit model. However, there is an alternate solution that has a lower proper motion and fits the data almost as well. This solution is compatible with a distant (so stellar) host. A Bayesian analysis does not favor the exoplanet+exomoon interpretation, so Occam's razor favors a lens system in the bulge with host and companion masses of M host = 0.12 +0.19-0.06 MΘ and mcomp = 18+28-10M⊕, at a projected separation of a⊥ = 0.84+0.25−0.14 AU. The existence of this degeneracy is an unlucky accident, so current microlensing experiments are in principle sensitive to exomoons. In some circumstances, it will be possible to definitively establish the mass of such lens systems through the microlensing parallax effect. Future experiments will be sensitive to less extreme exomoons.Peer reviewe
Pathway to the Galactic distribution of planets : combined Spitzer and ground-based microlens parallax measurements of 21 single-lens events
No full textWe present microlens parallax measurements for 21 (apparently) isolated lenses observed toward the Galactic bulge that were imaged simultaneously from Earth and Spitzer, which was ~1 AU west of Earth in projection. We combine these measurements with a kinematic model of the Galaxy to derive distance estimates for each lens, with error bars that are small compared to the Sun's galactocentric distance. The ensemble therefore yields a well-defined cumulative distribution of lens distances. In principle, it is possible to compare this distribution against a set of planets detected in the same experiment in order to measure the Galactic distribution of planets. Since these Spitzer observations yielded only one planet, this is not yet possible in practice. However, it will become possible as larger samples are accumulated.Peer reviewe
MOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection
No full textpeer reviewedWe analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~140. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question
MOA-2010-BLG-523: "Failed Planet" = RS CVn Star
No full textpeer reviewedThe Galactic bulge source MOA-2010-BLG-523S exhibited short-term deviations from a standard microlensing light curve near the peak of an A [SUB]max[/SUB] ~ 265 high-magnification microlensing event. The deviations originally seemed consistent with expectations for a planetary companion to the principal lens. We combine long-term photometric monitoring with a previously published high-resolution spectrum taken near peak to demonstrate that this is an RS CVn variable, so that planetary microlensing is not required to explain the light-curve deviations. This is the first spectroscopically confirmed RS CVn star discovered in the Galactic bulge. Based on observations made with the European Southern Observatory telescopes, Program ID 85.B-0399(I)
Microlensing discovery of a population of very tight, very low mass binary brown dwarfs
No full textAlthough many models have been proposed, the physical mechanisms responsible for the formation of low-mass brown dwarfs (BDs) are poorly understood. The multiplicity properties and minimum mass of the BD mass function provide critical empirical diagnostics of these mechanisms. We present the discovery via gravitational microlensing of two very low mass, very tight binary systems. These binaries have directly and precisely measured total system masses of 0.025 M ☉ and 0.034 M ☉, and projected separations of 0.31 AU and 0.19 AU, making them the lowest-mass and tightest field BD binaries known. The discovery of a population of such binaries indicates that BD binaries can robustly form at least down to masses of ~0.02 M ☉. Future microlensing surveys will measure a mass-selected sample of BD binary systems, which can then be directly compared to similar samples of stellar binaries
MOA-2010-BLG-328Lb: a sub-Neptune orbiting very late M dwarf ?
No full textpeer reviewedWe analyze the planetary microlensing event MOA-2010-BLG-328. The best fit yields host and planetary masses of Mh = 0.11+/-0.01 M_{sun} and Mp = 9.2+/-2.2M_Earth, corresponding to a very late M dwarf and sub-Neptune-mass planet, respectively. The system lies at DL = 0.81 +/- 0.10 kpc with projected separation r = 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
MOA-2013-BLG-220Lb : massive planetary companion to galactic-disk host
No full textWork by J. C. Yee was supported in part by a Distinguished University Fellowship from The Ohio State University and in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. Work by CH was supported by the Creative Research Initiative Program (2009-0081561) of the National Research Foundation of Korea. Work by A.G. and B.S.G. was supported by NSF grant AST 1103471. Work by A.G., B.S.G., and R.W.P. was supported by NASA grant NNX12AB99G. T.S. acknowledges the support from the grant JSPS23340044 and JSPS24253004. The OGLE project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 246678 to AU. This publication was made possible by NPRP grant X-019-1-006 from the Qatar National Research Fund (a member of Qatar Foundation).We report the discovery of MOA-2013-BLG-220Lb, which has a super-Jupiter mass ratio q = 3.01 ± 0.02 × 10-3 relative to its host. The proper motion, μ = 12.5 ± 1 mas yr-1, is one of the highest for microlensing planets yet discovered, implying that it will be possible to separately resolve the host within ∼7 yr. Two separate lines of evidence imply that the planet and host are in the Galactic disk. The planet could have been detected and characterized purely with follow-up data, which has important implications for microlensing surveys, both current and into the Large Synoptic Survey Telescope (LSST) era.Peer reviewe
