In the process of analyzing an observed light curve, one often confronts various scenarios that can mimic the planetary signals causing difficulties in the accurate interpretation of the lens system. ...In this paper, we present the analysis of the microlensing event OGLE-2016-BLG-0733. The light curve of the event shows a long-term asymmetric perturbation that would appear to be due to a planet. From the detailed modeling of the lensing light curve, however, we find that the perturbation originates from the binarity of the source rather than the lens. This result demonstrates that binary sources with roughly equal-luminosity components can mimic long-term perturbations induced by planets with projected separations near the Einstein ring. The result also represents the importance of the consideration of various interpretations in planet-like perturbations and of high-cadence observations for ensuring the unambiguous detection of the planet.
A planetary microlensing signal is generally characterized by a short-term perturbation to the standard single lensing light curve. A subset of binary-source events can produce perturbations that ...mimic planetary signals, thereby introducing an ambiguity between the planetary and binary-source interpretations. In this paper, we present the analysis of the microlensing event MOA-2012-BLG-486, for which the light curve exhibits a short-lived perturbation. Routine modeling not considering data taken in different passbands yields a best-fit planetary model that is slightly preferred over the best-fit binary-source model. However, when allowed for a change in the color during the perturbation, we find that the binary-source model yields a significantly better fit and thus the degeneracy is clearly resolved. This event not only signifies the importance of considering various interpretations of short-term anomalies, but also demonstrates the importance of multi-band data for checking the possibility of false-positive planetary signals.
ABSTRACT Simultaneous observations of microlensing events from multiple locations allow for the breaking of degeneracies between the physical properties of the lensing system, specifically by ...exploring different regions of the lens plane and by directly measuring the "microlens parallax." We report the discovery of a 30-65MJ brown dwarf orbiting a K dwarf in the microlensing event OGLE-2015-BLG-1319. The system is located at a distance of ∼5 kpc toward the Galactic Bulge. The event was observed by several ground-based groups as well as by Spitzer and Swift, allowing a measurement of the physical properties. However, the event is still subject to an eight-fold degeneracy, in particular the well-known close-wide degeneracy, and thus the projected separation between the two lens components is either ∼0.25 au or ∼45 au. This is the first microlensing event observed by Swift, with the UVOT camera. We study the region of microlensing parameter space to which Swift is sensitive, finding that though Swift could not measure the microlens parallax with respect to ground-based observations for this event, it can be important for other events. Specifically, it is important for detecting nearby brown dwarfs and free-floating planets in high magnification events.
We report the discovery of a massive planet, OGLE-2008-BLG-355Lb. The light curve analysis indicates a planet:host mass ratio of q = 0.0118 + or - 0.0006 at a separation of 0.877 + or - 0.010 ...Einstein radii. We do not measure a significant microlensing parallax signal and do not have high angular resolution images that could detect the planetary host star. Therefore, we do not have a direct measurement of the host star mass. A Bayesian analysis, assuming that all host stars have equal probability to host a planet with the measured mass ratio, implies a host star mass of M sub(h) = 0.37 super(+0.30) sub(-0.17) M sub(odot) and a companion of mass M sub(P) = 4.6 super(+3.7) sub(-2.2)M sub(J), at a projected separation of rbottom = 1.70 super(+0.29) sub(-0.30) AU. The implied distance to the planetary system is D sub(L) = 6.8+ or -1.1 kpc. A planetary system with the properties preferred by the Bayesian analysis may be a challenge to the core accretion model of planet formation, as the core accretion model predicts that massive planets are far more likely to form around more massive host stars. This core accretion model prediction is not consistent with our Bayesian prior of an equal probability of host stars of all masses to host a planet with the measured mass ratio. Thus, if the core accretion model prediction is right, we should expect that follow-up high angular resolution observations will detect a host star with a mass in the upper part of the range allowed by the Bayesian analysis. That is, the host would probably be a K or G dwarf.
We report the discovery of a binary composed of two brown dwarfs, based on the analysis of the microlensing event OGLE-2016-BLG-1469. Thanks to the detection of both finite-source and ...microlens-parallax effects, we are able to measure both the masses and , and the distance , as well as the projected separation au. This is the third brown-dwarf binary detected using the microlensing method, demonstrating the usefulness of microlensing in detecting field brown-dwarf binaries with separations of less than 1 au.
We present the analysis of the binary-microlensing event OGLE-2014-BLG-0289. The event light curve exhibits five very unusual peaks, four of which were produced by caustic crossings and the other by ...a cusp approach. It is found that the quintuple-peak features of the light curve provide tight constraints on the source trajectory, enabling us to precisely and accurately measure the microlensing parallax π E . Furthermore, the three resolved caustics allow us to measure the angular Einstein radius θ E . From the combination of π E and θ E , the physical lens parameters are uniquely determined. It is found that the lens is a binary composed of two M dwarfs with masses M 1 = 0.52 0.04 M and M 2 = 0.42 0.03 M separated in projection by a = 6.4 0.5 au . The lens is located in the disk with a distance of D L = 3.3 0.3 kpc . The reason for the absence of a lensing signal in the Spitzer data is that the time of observation corresponds to the flat region of the light curve.
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.
ABSTRACT Spitzer microlensing parallax observations of OGLE-2015-BLG-1212 decisively break a degeneracy between planetary and binary solutions that is somewhat ambiguous when only ground-based data ...are considered. Only eight viable models survive out of an initial set of 32 local minima in the parameter space. These models clearly indicate that the lens is a stellar binary system possibly located within the bulge of our Galaxy, ruling out the planetary alternative. We argue that several types of discrete degeneracies can be broken via such space-based parallax observations.
We report the analysis of the first resolved caustic-crossing binary-source microlensing event OGLE-2016-BLG-1003. The event is densely covered by round-the-clock observations of three surveys. The ...light curve is characterized by two nested caustic-crossing features, which is unusual for typical caustic-crossing perturbations. From the modeling of the light curve, we find that the anomaly is produced by a binary source passing over a caustic formed by a binary lens. The result proves the importance of high-cadence and continuous observations, and the capability of second-generation microlensing experiments to identify such complex perturbations that are previously unknown. However, the result also raises the issues of the limitations of current analysis techniques for understanding lens systems beyond two masses and of determining the appropriate multiband observing strategy of survey experiments.
We report the discovery of a planetary system in which a super-Earth orbits a late M-dwarf host. The planetary system was found from the analysis of the microlensing event OGLE-2017-BLG-0482, wherein ...the planet signal appears as a short-term anomaly to the smooth lensing light curve produced by the host. Despite its weak signal and short duration, the planetary signal was firmly detected from the dense and continuous coverage by three microlensing surveys. We find a planet/host mass ratio of q ∼ 1.4 × 10−4. We measure the microlens parallax from the long-term deviation in the observed lensing light curve, but the angular Einstein radius cannot be measured because the source trajectory did not cross the planet-induced caustic. Using the measured event timescale and the microlens parallax, we find that the masses of the planet and the host are and , respectively, and the projected separation between them is au. The estimated distance to the lens is kpc. The discovery of the planetary system demonstrates that microlensing provides an important method to detect low-mass planets orbiting low-mass stars.
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