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 Optical Gravitational Lensing Experiment (OGLE) and Microlensing Observations in Astrophysics (MOA) photometric surveys. The light curve modeling indicates that the planet-to-host mass ratios are and , 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 the masses of both planets: (OGLE-2013-BLG-0132Lb) and (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.
We report the discovery of a sub-Jupiter-mass planet orbiting beyond the snow line of an M dwarf most likely in the Galactic disk as part of the joint Spitzer and ground-based monitoring of planetary ...microlensing anomalies toward the Galactic bulge. Most of the microlensing parameters are strongly constrained by the light-curve modeling, and in particular there is a Spitzer-based measurement of the microlens parallax, πE. However, there are no caustic crossings, so the angular Einstein radius has only an upper limit based on the light-curve modeling alone. Additionally, the analysis leads us to identify eight degenerate configurations: the fourfold microlensing parallax degeneracy being doubled by a degeneracy in the caustic structure present at the level of the ground-based solutions. To calculate the physical parameters, and at the same time to break the parallax degeneracy, we make use of a series of arguments: the χ2 hierarchy, the Rich argument (stating that the small-parallax solution is more likely), and a prior Galactic model. The preferred configuration, favored by a likelihood ratio of at least 4000, is for a host at with mass , orbited by a Saturn-like planet with at projected separation , about 2.1 times beyond the system snow line. Therefore, it adds to the growing population of sub-Jupiter planets orbiting beyond the snow line of M dwarfs discovered by microlensing. Based on the rules of the real-time protocol for the selection of events to be followed up with Spitzer, this planet will not enter the sample for measuring the Galactic distribution of planets.
We 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 . 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.
We present the analysis of the simultaneous high-resolution images from the Hubble Space Telescope and Keck adaptive optics system of the planetary event OGLE-2012-BLG-0950 that determine that the ...system consists of a 0.58 0.04 host star orbited by a 39 8 planet at a projected separation of 2.54 0.23 au. The planetary system is located at a distance of 2.19 0.23 kpc from Earth. This is the second microlens planet beyond the snow line with a mass measured to be in the mass range 20-80 . The runaway gas accretion process of the core accretion model predicts fewer planets in this mass range. This is because giant planets are thought to be growing rapidly at these masses, and they rarely complete growth at this mass. So this result suggests that the core accretion theory may need revision. This analysis also demonstrates the techniques that will be used to measure the masses of planets and their host stars by the WFIRST exoplanet microlensing survey: one-dimensional microlensing parallax combined with the separation and brightness measurement of the unresolved source and host stars to yield multiple redundant constraints on the masses and distance of the planetary system.
We present the result of microlensing event MOA-2016-BLG-290, which received observations from the two-wheel Kepler (K2), Spitzer, as well as ground-based observatories. A joint analysis of data from ...K2 and the ground leads to two degenerate solutions of the lens mass and distance. This degeneracy is effectively broken once the (partial) Spitzer light curve is included. Altogether, the lens is found to be an extremely low-mass star or brown dwarf ( ) located in the Galactic bulge ( kpc). MOA-2016-BLG-290 is the first microlensing event for which we have signals from three well-separated (∼1 au) locations. It demonstrates the power of two-satellite microlensing experiment in reducing the ambiguity of lens properties, as pointed out independently by S. Refsdal and A. Gould several decades ago.
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.
We present the analysis of the event OGLE-2017-BLG-1186 from the 2017 Spitzer microlensing campaign. This is a remarkable microlensing event because its source is photometrically bright and variable, ...which makes it possible to perform an asteroseismic analysis using ground-based data. We find that the source star is an oscillating red giant with average timescale of ∼9 d. The asteroseismic analysis also provides us source properties including the source angular size (∼27 μas) and distance (∼11.5 kpc), which are essential for inferring the properties of the lens. When fitting the light curve, we test the feasibility of Gaussian processes (GPs) in handling the correlated noise caused by the variable source. We find that the parameters from the GP model are generally more loosely constrained than those from the traditional χ(exp 2) minimization method. We note that this event is the first microlensing system for which asteroseismology and GPs have been used to account for the variable source. With both finite-source effect and microlens parallax measured, we find that the lens is likely a ∼0.045 Mʘ brown dwarf at distance ∼9.0 kpc, or a ∼0.073 Mʘ ultracool dwarf at distance ∼9.8 kpc. Combining the estimated lens properties with a Bayesian analysis using a Galactic model, we find a ∼ 35 per cent probability for the lens to be a bulge object and ∼ 65 per cent to be a background disc object.
We report on the discovery and analysis of the short-timescale binary-lens microlensing event, MOA-2015-BLG-337. The lens system could be a planetary system with a very low-mass host, around the ...brown dwarf (BD)/planetary-mass boundary, or a BD binary. We found two competing models that explain the observed light curves with companion/host mass ratios of q ∼ 0.01 and ∼0.17, respectively. A significant finite source effect in the best-fit planetary model (q ∼ 0.01) reveals a small angular Einstein radius of θE 0.03 mas, which favors a low-mass lens. We obtain the posterior probability distribution of the lens properties from a Bayesian analysis. The results for the planetary models strongly depend on a power-law index in planetary-mass regime, pl, in the assumed mass function. In summary, there are two solutions of the lens system: (1) a BD/planetary-mass boundary object orbited by a super-Neptune (the planetary model with pl = 0.49) and (2) a BD binary (the binary model). If the planetary models are correct, this system can be one of a new class of planetary system, having a low host mass and also a planetary-mass ratio (q < 0.03) between the companion and its host. The discovery of the event is important for the study of planetary formation in very low-mass objects. In addition, it is important to consider all viable solutions in these kinds of ambiguous events in order for the future comprehensive statistical analyses of planetary/binary microlensing events.
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.
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