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News Article | May 8, 2017
Site: phys.org

The planets were discovered by researchers working as part of the Optical Gravitational Lensing Experiment (OGLE) group and the Microlensing Observations in Astrophysics (MOA) collaboration. OGLE uses the 1.3-m Warsaw Telescope located at Las Campanas Observatory in Chile, while MOA utilizes the 1.8-m MOA-II telescope at the Mount John University Observatory, located in New Zealand. The main goal of these two microlensing surveys is to study the planet formation around late-type stars. Gravitational microlensing is an invaluable method of detecting new extrasolar planets circling their parent stars relatively closely. This technique is sensitive to planets orbiting beyond the so-called "snow line" around relatively faint host stars like M dwarfs or brown dwarfs. It is a location in the proto-planetary disk where the water ice may condense and where gas giant planets are believed to be formed. Therefore, understanding the distribution of exoplanets in this region could offer important clues to how planets form. Recently, OGLE and MOA scientists led by Przemek Mróz of the Warsaw University Observatory in Poland, have found planetary anomalies in two faint microlensing events designated OGLE-2013-BLG-0132 and OGLE-2013-BLG-1721. "Both events showed clear deviations from the simple point-source point-lens model, caused by the presence of a second body with well-measured planet-to-host mass ratios of (5.15 ± 0.28) x 10-4 and (13.18 ± 0.72) x 10-4, respectively," the researchers wrote in the paper. The newly discovered planets received designation OGLE-2013-BLG-0132b and OGLE-2013-BLG-1721b. Both planets likely belong to a group of sub-Jupiter-mass planets orbiting M dwarfs beyond the snow line distance. According to the research, OGLE-2013-BLG-0132b has a mass of about 0.29 Jupiter masses and orbits its parent star at a distance of 3.6 AU. The planet's host is located about 12,700 light years away and has a mass of approximately 0.54 solar masses. With a mass of about 0.64 Jupiter masses, OGLE-2013-BLG-1721b is circling its host (0.46 solar masses) at a distance of 2.6 AU. This planetary system is located some 20,500 light years away from the Earth. The researchers estimated the masses of the planets using the Bayesian analysis as both events were short and faint, which prevented them from measuring a reliable parallax signal. "Both events were too short and too faint to measure a reliable parallax signal and hence the lens mass. We therefore used a Bayesian analysis to estimate masses of both planets," the paper reads. The team noted that in order to uncover more properties of the two newly discovered planetary systems, follow-up high-resolution imaging observations should be conducted in the future. In particular, the Near InfRared Camera (NIRCam) on the James Webb Space Telescope (JWST) that will be launched into space in late 2018, could reveal important insights about these new Saturn-mass exoworlds. More information: OGLE-2013-BLG-0132Lb and OGLE-2013-BLG-1721Lb: Two Saturn-mass Planets Discovered around M-dwarfs, arXiv:1705.01058 [astro-ph.EP] arxiv.org/abs/1705.01058 Abstract We present the discovery of two planetary systems consisting of a Saturn-mass planet orbiting an M-dwarf, which were detected in faint microlensing events OGLE-2013-BLG-0132 and OGLE-2013-BLG-1721. The planetary anomalies were covered with high cadence by OGLE and MOA photometric surveys. The light curve modeling indicates that planet-host mass ratios are (5.15±0.28)×10−4 and (13.18±0.72)×10−4, respectively. Both events were too short and too faint to measure a reliable parallax signal and hence the lens mass. We therefore used a Bayesian analysis to estimate masses of both planets: 0.29+0.16−0.13 MJup (OGLE-2013-BLG-0132Lb) and 0.64+0.35−0.31 M (OGLE-2013-BLG-1721Lb). Thanks to a high relative proper motion, OGLE-2013-BLG-0132 is a promising candidate for the high-resolution imaging follow-up. Both planets belong to an increasing sample of sub-Jupiter-mass planets orbiting M-dwarfs beyond the snow line.

Park H.,Chungbuk National University | Han C.,Chungbuk National University | Gould A.,Ohio State University | Udalski A.,University of Warsaw | And 59 more authors.
Astrophysical Journal | Year: 2014

Characterizing a microlensing planet is done by modeling an observed lensing light curve. In this process, it is often confronted that solutions of different lensing parameters result in similar light curves, causing difficulties in uniquely interpreting the lens system, and thus understanding the causes of different types of degeneracy is important. In this work, we show that incomplete coverage of a planetary perturbation can result in degenerate solutions even for events where the planetary signal is detected with a high level of statistical significance. We demonstrate the degeneracy for an actually observed event OGLE-2012-BLG-0455/MOA-2012-BLG-206. The peak of this high-magnification event (A max 400) exhibits very strong deviation from a point-lens model with Δχ2 ≳ 4000 for data sets with a total of 6963 measurements. From detailed modeling of the light curve, we find that the deviation can be explained by four distinct solutions, i.e., two very different sets of solutions, each with a twofold degeneracy. While the twofold (so-called close/wide) degeneracy is well understood, the degeneracy between the radically different solutions is not previously known. The model light curves of this degeneracy differ substantially in the parts that were not covered by observation, indicating that the degeneracy is caused by the incomplete coverage of the perturbation. It is expected that the frequency of the degeneracy introduced in this work will be greatly reduced with the improvement of the current lensing survey and follow-up experiments and the advent of new surveys. © 2014. The American Astronomical Society. All rights reserved.

Sumi T.,Osaka University | Bennett D.P.,University of Notre Dame | Bond I.A.,Massey University | Abe F.,Nagoya University | And 17 more authors.
Astrophysical Journal | Year: 2013

We present measurements of the microlensing optical depth and event rate toward the Galactic Bulge (GB) based on two years of the MOA-II survey. This sample contains ∼1000 microlensing events, with an Einstein radius crossing time of t E ≤ 200 days in 22 bulge fields covering ∼42 deg2 between -5° < l < 10°and -7°< b < -1°. Our event rate and optical depth analysis uses 474 events with well-defined microlensing parameters. In the central fields with |l| < 5°, we find an event rate of Γ = [2.39 ± 1.1]e [0.60 ± 0.05](3-|b|) × 10-5 star-1 yr-1 and an optical depth (for events with t E ≤ 200 days) of τ200 = [2.35 ± 0.18]e [0.51 ± 0.07](3-|b|) × 10-6 for the 427 events, using all sources brighter than Is ≤ 20 mag. The distribution of observed fields is centered at (l, b) = (0.°38, -3.°72). We find that the event rate is maximized at low latitudes and a longitude of l ≈ 1°. For the 111 events in 3.2 deg2 of the central GB at |b| ≤ 3.°0 and 0.°0 ≤ l ≤ 2.°0, centered at (l, b) = (0.°97, -2.°26), we find star-1 yr-1 and . We also consider a red clump giant (RCG) star sample with Is < 17.5, and we find that the event rate for the RCG sample is slightly lower than but consistent with the all-source event rate. The main difference is the lack of long duration events in the RCG sample due to a known selection effect. Our results are consistent with previous optical depth measurements, but they are somewhat lower than previous all-source measurements, and slightly higher than previous RCG optical depth measurements. This suggests that the previously observed difference in optical depth measurements between all-source and RCG samples may largely be due to statistical fluctuations. These event rate measurements toward the central GB are necessary to predict the microlensing event rate and to optimize the survey fields in future space missions such as Wide Field Infrared Space Telescope. © 2013. The American Astronomical Society. All rights reserved..

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