ABSTRACT We report the results of the statistical analysis of planetary signals discovered in MOA-II microlensing survey alert system events from 2007 to 2012. We determine the survey sensitivity as ...a function of planet-star mass ratio, q, and projected planet-star separation, s, in Einstein radius units. We find that the mass-ratio function is not a single power law, but has a change in slope at q ∼ 10−4, corresponding to ∼20 M⊕ for the median host-star mass of ∼0.6 . We find significant planetary signals in 23 of the 1474 alert events that are well-characterized by the MOA-II survey data alone. Data from other groups are used only to characterize planetary signals that have been identified in the MOA data alone. The distribution of mass ratios and separations of the planets found in our sample are well fit by a broken power-law model of the form for q > qbr and for q < qbr, where qbr is the mass ratio of the break. We also combine this analysis with the previous analyses of Gould et al. and Cassan et al., bringing the total sample to 30 planets. This combined analysis yields , n = −0.93 0.13, , and for qbr 1.7 × 10−4. The unbroken power-law model is disfavored with a p-value of 0.0022, which corresponds to a Bayes factor of 27 favoring the broken power-law model. These results imply that cold Neptunes are likely to be the most common type of planets beyond the snow line.
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. Our event rate and optical depth analysis uses 474 ...events with well-defined microlensing parameters. We find that the event rate is maximized at low latitudes and a longitude of l approximately 1degrees. 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.
We present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based
on observations obtained from 13 different telescopes. Intensive coverage of the anomalous
parts of the light ...curve was achieved by automated follow-up observations from the robotic
telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of
an anomalous microlensing event are well covered by follow-up data, allowing us to estimate
the physical parameters of the lens. The strong detection of second-order effects in the event
light curve necessitates the inclusion of longer-baseline survey data in order to constrain
the parallax vector. We find that the event was most likely caused by a stellar binary-lens
with masses M ͙(1) = 0.87 ± 0.12M(☉) and M ͙(2)= 0.77 ± 0.11M(☉). The distance to the lensing
system is 6.41 ± 0.14 kpc and the projected separation between the two components is
13.85 ± 0.16 au. Alternative interpretations are also considered.
We present the analysis of four candidate short-duration binary microlensing events from the 2006-2007 MOA Project short-event analysis. Three of these events are determined to be microlensing ...events, while the fourth is most likely caused by stellar variability. One of these events, MOA-bin-1, is due to a planet, and it is the first example of a planetary event in which the stellar host is only detected through binary microlensing effects. This is one of the most massive and widest separation planets found by microlensing. The scarcity of such wide-separation planets also has implications for interpretation of the isolated planetary mass objects found by this analysis. In particular, if the entire isolated planet sample found by Sumi et al. consists of planets bound in wide orbits around stars, we find that it is likely that the median orbital semimajor axis is <30 AU.
We present the MOA Collaboration light-curve data for the planetary microlensing event OGLE-2015-BLG-0954, which was previously announced in a paper by the KMTNet and OGLE Collaborations. The MOA ...data cover the caustic exit, which was not covered by the KMTNet or Optical Gravitational Lensing Experiment (OGLE) data, and they provide a more reliable measurement of the finite source effect. The MOA data also provide a new source color measurement that reveals a lens-source relative proper motion of rel = 11.8 0.8 mas yr−1, which compares to the value of rel = 18.4 1.7 mas yr−1 reported in the KMTNet-OGLE paper. This new MOA value for rel has an a priori probability that is a factor of 100 times larger than the previous value, and it does not require a lens system distance of DL < 1 kpc. Based on the corrected source color, we find that the lens system consists of a planet of mass orbiting a star at an orbital separation of and a distance of .
We present the discovery of a Neptune-mass planet orbiting a 0.8 + or - 0.3Mmiddot in circle star in the Galactic bulge. The planet manifested itself during the microlensing event ...MOA-2011-BLG-028/OGLE-2011-BLG-0203 as a low-mass companion to the lens star. The analysis of the light curve provides the measurement of the mass ratio (1.2 + or - 0.2) x 10 super(-4), which indicates that the mass of the planet is 12-60 Earth masses. The lensing system is located at 7.3 + or - 0.7 kpc away from the Earth near the direction of Baade's Window. The projected separation of the planet at the time of the microlensing event was 3.1-5.2 au. Although the microlens parallax effect is not detected in the light curve of this event, preventing the actual mass measurement, the uncertainties of mass and distance estimation are narrowed by the measurement of the source star proper motion on the OGLE-III images spanning eight years, and by the low amount of blended light seen, proving that the host star cannot be too bright and massive. We also discuss the inclusion of undetected parallax and orbital motion effects into the models and their influence onto the final physical parameters estimates.
We report the discovery and the analysis of the planetary microlensing event, OGLE-2013-BLG-1761. There are some degenerate solutions in this event because the planetary anomaly is only sparsely ...sampled. However, the detailed light-curve analysis ruled out all stellar binary models and shows the lens to be a planetary system. There is the so-called close/wide degeneracy in the solutions with the planet/host mass ratio of q ∼ (7.0 2.0) × 10−3 and q ∼ (8.1 2.6) × 10−3 with the projected separation in Einstein radius units of s = 0.95 (close) and s = 1.18 (wide), respectively. The microlens parallax effect is not detected, but the finite source effect is detected. Our Bayesian analysis indicates that the lens system is located away from us and the host star is an M/K dwarf with a mass of orbited by a super-Jupiter mass planet with a mass of at the projected separation of . The preference of the large lens distance in the Bayesian analysis is due to the relatively large observed source star radius. The distance and other physical parameters may be constrained by the future high-resolution imaging by large ground telescopes or HST. If the estimated lens distance is correct, then this planet provides another sample for testing the claimed deficit of planets in the Galactic bulge.
ABSTRACT We report the discovery of a planet by the microlensing method, OGLE-2012-BLG-0724Lb. Although the duration of the planetary signal for this event was one of the shortest seen for a ...planetary event, the anomaly was well covered thanks to high-cadence observations taken by the survey groups OGLE and MOA. By analyzing the light curve, this planetary system is found to have a mass ratio q = ( 1.58 0.15 ) × 10 − 3 . By conducting a Bayesian analysis, we estimate that the host star is an M dwarf with a mass of M L = 0.29 − 0.16 + 0.33 M ☉ located at D L = 6.7 − 1.2 + 1.1 kpc away from the Earth and the companion's mass is m P = 0.47 − 0.26 + 0.54 M Jup . The projected planet-host separation is a = 1.6 − 0.3 + 0.4 AU . Because the lens-source relative proper motion is relatively high, future high-resolution images would detect the lens host star and determine the lens properties uniquely. This system is likely a Saturn-mass exoplanet around an M dwarf, and such systems are commonly detected by gravitational microlensing. This adds another example of a possible pileup of sub-Jupiters ( 0.2 < m P / M Jup < 1 ) in contrast to a lack of Jupiters ( ∼ 1 - 2 M Jup ) around M dwarfs, supporting the prediction by core accretion models that Jupiter-mass or more massive planets are unlikely to form around M dwarfs.
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