We detect a Neptune mass ratio (q 8 x 10 super(-5)) planetary companion to the lens star in the extremely high magnification (A 6 800) microlensing event OGLE-2005-BLG-169. If the parent is a ...main-sequence star, it has mass M 6 0.5 M sub( ), implying a planet mass of 613 M sub( )and projected separation of 62.7 AU. When intensely monitored over their peak, high-magnification events similar to OGLE-2005-BLG-169 have nearly complete sensitivity to Neptune mass ratio planets with projected separations of 0.6-L6 Einstein radii, corresponding to 1.6-4.3 AU in the present case. Only two other such events were monitored well enough to detect Neptunes, and so this detection by itself suggests that Neptune mass ratio planets are common. Moreover, another Neptune was recently discovered at a similar distance from its parent star in a low-magnification event, which are more common but are individually much less sensitive to planets. Combining the two detections yields 90% upper and lower frequency limits f = 0.38 + D.31 -0.22 over just 0.4 decades of planet-star separation. In particular,/> 16% at 90% confidence. The parent star hosts no Jupiter-mass companions with projected separations within a factor 5 of that of the detected planet. The lens-source relative proper motion is k 6 7-10 mas yr super(-1), implying that if the lens is sufficiently bright, I 23.8, it will be detectable by the Hubble Space Telescope by 3 years after peak. This would permit a more precise estimate of the lens mass and distance and, so, the mass and projected separation of the planet. Analogs of OGLE-2005-BLG-169Lb orbiting nearby stars would be difficult to detect by other methods of planet detection, including radial velocities, transits, and astrometry.
Global 'second-generation' microlensing surveys aim to discover and characterize extrasolar planets and their frequency, by means of round-the-clock high-cadence monitoring of a large area of the ...Galactic bulge, in a controlled experiment. We report the discovery of a giant planet in microlensing event MOA-2011-BLG-322. This moderate-magnification event, which displays a clear anomaly induced by a second lensing mass, was inside the footprint of our second-generation microlensing survey, involving MOA, OGLE and the Wise Observatory. The event was observed by the survey groups, without prompting alerts that could have led to dedicated follow-up observations. Fitting a microlensing model to the data, we find that the time-scale of the event was t
E = 23.2 ± 0.8 d, and the mass ratio between the lens star and its companion is q = 0.028 ± 0.001. Finite-source effects are marginally detected, and upper limits on them help break some of the degeneracy in the system parameters. Using a Bayesian analysis that incorporates a Galactic structure model, we estimate the mass of the lens at
, at a distance of 7.56 ± 0.91 kpc. Thus, the companion is likely a planet of mass
, at a projected separation of
au, rather far beyond the snow line. This is the first pure-survey planet reported from a second-generation microlensing survey, and shows that survey data alone can be sufficient to characterize a planetary model. With the detection of additional survey-only planets, we will be able to constrain the frequency of extrasolar planets near their systems' snow lines.
Searches for extrasolar planets have uncovered an astonishing diversity of planetary systems, yet the frequency of solar system analogs remains unknown. The gravitational microlensing planet search ...method is potentially sensitive to multiple-planet systems containing analogs of all the solar system planets except Mercury. We report the detection of a multiple-planet system with microlensing. We identify two planets with masses of ~0.71 and ~0.27 times the mass of Jupiter and orbital separations of ~2.3 and ~4.6 astronomical units orbiting a primary star of mass ~0.50 solar mass at a distance of ~1.5 kiloparsecs. This system resembles a scaled version of our solar system in that the mass ratio, separation ratio, and equilibrium temperatures of the planets are similar to those of Jupiter and Saturn. These planets could not have been detected with other techniques; their discovery from only six confirmed microlensing planet detections suggests that solar system analogs may be common.
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BFBNIB, NMLJ, NUK, PNG, SAZU, UL, UM, UPUK
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 describe observations carried out by the MOA group of the Galactic bulge during 2000 that were designed to detect efficiently gravitational microlensing of faint stars in which the magnification ...is high and/or of short duration. These events are particularly useful for studies of extrasolar planets and faint stars. Approximately 17 deg2 were monitored at a sampling rate of up to six times per night. The images were analysed in real time using a difference imaging technique. 20 microlensing candidates were detected, of which eight were alerted to the microlensing community whilst in progress. Approximately half of the candidates had high magnifications (≳10), at least one had very high magnification (≳50), and one exhibited a clear parallax effect. The details of these events are reported here, together with details of the on-line difference imaging technique. Some nova-like events were also observed and these are described, together with one asteroid.
Since 1995, more than 500 exoplanets have been detected using different techniques, of which 12 were detected with gravitational microlensing. Most of these are gravitationally bound to their host ...stars. There is some evidence of free-floating planetary-mass objects in young star-forming regions, but these objects are limited to massive objects of 3 to 15 Jupiter masses with large uncertainties in photometric mass estimates and their abundance. Here, we report the discovery of a population of unbound or distant Jupiter-mass objects, which are almost twice (1.8(+1.7)(-0.8)) as common as main-sequence stars, based on two years of gravitational microlensing survey observations towards the Galactic Bulge. These planetary-mass objects have no host stars that can be detected within about ten astronomical units by gravitational microlensing. However, a comparison with constraints from direct imaging suggests that most of these planetary-mass objects are not bound to any host star. An abrupt change in the mass function at about one Jupiter mass favours the idea that their formation process is different from that of stars and brown dwarfs. They may have formed in proto-planetary disks and subsequently scattered into unbound or very distant orbits.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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 discovery of a Neptune-mass planet OGLE-2007-BLG-368Lb with a planet-star mass ratio of q = 9.5 +- 2.1 x 10{sup -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 M{sub l} = 0.64{sup +0.21}{sub -0.26} M{sub sun} and D{sub l} = 5.9{sup +0.9}{sub -1.4} kpc, respectively, so the mass and separation of the planet are M{sub p} = 20{sup +7}{sub -8} M{sub +} and a = 3.3{sup +1.4}{sub -0.8} AU, 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{sub pl}/dlog q {proportional_to} q {sup -0.7+}-{sup 0.2} with a 95% confidence level upper limit of n < -0.35 (where dN{sub pl}/dlog q {proportional_to} q{sup n} ). 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.
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