173 research outputs found
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
Galactic microlensing : binary-lens light curve morphologies and results from the Rosetta spacecraft bulge survey
No full textFor 20 years now, gravitational microlensing observations towards the Galactic bulge have provided us with a wealth of information about the stellar and planetary content of our Galaxy, which is inaccessible via other current methods. This thesis summarises work on two research topics that arose in the context of exoplanetary microlensing, but we take a step back and consider ways of increasing our understanding of more fundamental phenomena: firstly, stellar microlenses in our Galaxy that were stereoscopically observed and, secondly, the morphological variety of binary-lens light curves.
In autumn 2008, the ESA Rosetta spacecraft surveyed the Galactic bulge for microlensing events. With a baseline of ∼1.6 AU between the spacecraft and ground observations, significant parallax effects can be expected. We develop a photometry pipeline to deal with a severely undersampled point spread function in the crowded fields of the Galactic bulge, making use of complementary ground observations. Comparison of Rosetta and OGLE light curves provides the microlens parallax π[subscript{E}] , which constrains the mass and distance of the observed lenses. The lens mass could be fully determined if future proper motion measurements were obtained, whereas the lens distance additionally requires the determination of the source distance.
In the second project, we present a detailed study of microlensing light curve morphologies. We provide a complete morphological classification for the case of the equal-mass binary lens, which makes use of the realisation that any microlensing peak can be categorised as one of only four types: cusp-grazing, cusp-crossing, fold-crossing or fold-grazing. As a means for this classification, we develop a caustic feature notation, which can be universally applied to binary lens caustics. Ultimately, this study aims to refine light curve modelling approaches by providing an optimal choice of initial parameter sets, while ensuring complete coverage of the relevant parameter space
OGLE-2015-BLG-1459L: The Challenges of Exo-moon Microlensing
No full textWe show that dense OGLE and KMTNet I-band survey data require four bodies (sources plus lenses) to explain the microlensing light curve of OGLE-2015-BLG-1459. However, these can equally well consist of three lenses and one source (3L1S), two lenses and two sources (2L2S), or one lens and three sources (1L3S). In the 3L1S and 2L2S interpretations, the host is a brown dwarf and the dominant companion is a Neptune-class planet, with the third body (in the 3L1S case) being a Mars-class object that could have been a moon of the planet. In the 1L3S solution, the light curve anomalies are explained by a tight (five stellar radii) low- luminosity binary source that is offset from the principal source of the event by ̃ 0.17 {au}. These degeneracies are resolved in favor of the 1L3S solution by color effects derived from comparison to MOA data, which are taken in a slightly different (R/I) passband. To enable current and future (WFIRST) surveys to routinely characterize exo-moons and distinguish among such exotic systems requires an observing strategy that includes both a cadence faster than 9 minute-1 and observations in a second band on a similar timescale
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
Spitzer as a microlens parallax satellite : mass and distance measurements of the binary lens system OGLE-2014-BLG-1050L
No full textWe 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 ~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 MΘ) binary at ~1.1 kpc or a higher-mass (0.9 and 0.35 MΘ) binary at ~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.Peer reviewe
The "666" collaboration on OGLE transits. I. Accurate radius of the planets OGLE-TR-10b and OGLE-TR-56b with VLT deconvolution photometry
No full textpeer reviewedTransiting planets are essential to study the structure and evolution of extra-solar planets. For that purpose, it is important to measure precisely the radius of these planets. Here we report new high-accuracy photometry of the transits of OGLE-TR-10 and OGLE-TR-56 with VLT/FORS1. One transit of each object was covered in Bessel V and R filters, and treated with the deconvolution-based photometry algorithm DECPHOT, to ensure accurate millimagnitude light curves. Together with earlier spectroscopic measurements, the data imply a radius of 1.22{[SUP]+0.12[/SUP][SUB]-0.07[/SUB]} R[SUB]J[/SUB] for OGLE-TR-10b and 1.30 ± 0.05 R[SUB]J[/SUB] for OGLE-TR-56b. A re-analysis of the original OGLE photometry resolves an earlier discrepancy about the radius of OGLE-TR-10. The transit of OGLE-TR-56 is almost grazing, so that small systematics in the photometry can cause large changes in the derived radius. Our study confirms both planets as inflated hot Jupiters, with large radii comparable to that of HD 209458b and at least two other recently discovered transiting gas giants. Based on data collected with the FORS1 imager at the VLT-Kueyen telescope (Paranal Observatory, ESO, Chile) in the programme 177.C-0666E
Reanalyses of anomalous gravitational microlensing events in the OGLE-III early warning system database with combined data
No full textWork by C.H. was supported by the Creative Research Initiative Program (2009-0081561) of the National Research Foundation of Korea. 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. The MOA project is supported by the grants JSPS18253002 and JSPS20340052. T.S. acknowledges the financial support from the JSPS, JSPS23340044 and JSPS24253004. D.P.B. was supported by grants NASA-NNX12AF54G, JPL-RSA 1453175, and NSF AST-1211875. B.S.G. and A.G. were supported by NSF grant AST 110347. B.S.G., A.G., and R.P.G. were supported by NASA grant NNX12AB99G.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.Peer reviewe
Results Fromthe Optical Gravitationallensing Experiment (ogle)
No full text. The analysis of the first three years of the OGLE data revealed 12 microlensing events of the Galactic bulge stars, with the characteristic time scales in the range 8:6 ! t 0 ! 80 days, where t 0 = RE =V . A complete sample of nine events gave the optical depth to gravitational microlensing larger than (3:3 \Sigma 1:2) \Theta 10 \Gamma6 , in excess of current theoretical estimates, indicating a much higher efficiency for microlensing by either bulge or disk lenses. The lenses are likely to be ordinary stars in the Galactic bar, which has its long axis elongated towards us. At this time we have no evidence that the OGLE events are related to dark matter. The OGLE color magnitude diagrams reveal the presence of the Galactic bar and a low density inner disk region ¸ 4 kpc in radius. A catalogue of a few thousand variable stars is in preparation. 2 B. Paczy'nski ET AL. 1. INTRODUCTION The OGLE project (Optical Gravitational Lensing Experiment) is a collaboration between the Warsaw ..
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