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Register a new userOGLE-2015-BLG-1649Lb: A gas giant planet around a low-mass dwarf
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We report the discovery of an exoplanet in microlensing event OGLE-2015-BLG-1649. The planet/host-star mass ratio is $q =7.2 times 10^{-3}$ and the projected separation normalized by the Einstein radius is $s = 0.9$. The upper limit of the lens flux is obtained from adaptive optics observations by IRCS/Subaru, which excludes the probability of a G-dwarf or more massive host star and helps to put a tighter constraint on the lens mass as well as commenting on the formation scenarios of giant planets orbiting low-mass stars. We conduct a Bayesian analysis including constraints on the lens flux to derive the probability distribution of the physical parameters of the lens system. We thereby find that the masses of the host star and planet are $M_{L} = 0.34 pm 0.19 M_{odot}$ and $M_{p} = 2.5^{+1.5}_{-1.4} M_{Jup}$, respectively. The distance to the system is $D_{L} = 4.23^{+1.51}_{-1.64}$kpc. The projected star-planet separation is $a_{perp} = 2.07^{+0.65}_{-0.77}$AU. The lens-source relative proper motion of the event is quite high, at $sim 7.1 , {rm mas/yr}$. Therefore, we may be able to determine the lens physical parameters uniquely or place much stronger constraints on them by measuring the color-dependent centroid shift and/or the image elongation with additional high resolution imaging already a few years from now.
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We report the discovery of an extrasolar planet detected from the combined data of a microlensing event OGLE-2015-BLG-0051/KMT-2015-BLG-0048 acquired by two microlensing surveys. Despite that the short planetary signal occurred in the very early Bulge season during which the lensing event could be seen for just about an hour, the signal was continuously and densely covered. From the Bayesian analysis using models of the mass function, matter and velocity distributions combined with the information of the angular Einstein radius, it is found that the host of the planet is located in the Galactic bulge. The planet has a mass $0.72_{-0.07}^{+0.65} M_{rm J}$ and it is orbiting a low-mass M-dwarf host with a projected separation $d_perp=0.73 pm 0.08$ AU. The discovery of the planet demonstrates the capability of the current high-cadence microlensing lensing surveys in detecting and characterizing planets.
We report the analysis of planetary microlensing event OGLE-2018-BLG-1185, which was observed by a large number of ground-based telescopes and by the $Spitzer$ Space Telescope. The ground-based light curve indicates a low planet-host star mass ratio of $q = (6.9 pm 0.2) times 10^{-5}$, which is near the peak of the wide-orbit exoplanet mass-ratio distribution. We estimate the host star and planet masses with a Bayesian analysis using the measured angular Einstein radius under the assumption that stars of all masses have an equal probability to host this planet. The flux variation observed by $Spitzer$ was marginal, but still places a constraint on the microlens parallax. Imposing a conservative constraint that this flux variation should be $Delta f_{rm Spz} < 4$ instrumental flux units indicates a host mass of $M_{rm host} = 0.37^{+0.35}_{-0.21} M_odot$ and a planet mass of $m_{rm p} = 8.4^{+7.9}_{-4.7} M_oplus$. A Bayesian analysis including the full parallax constraint from $Spitzer$ suggests smaller host star and planet masses of $M_{rm host} = 0.091^{+0.064}_{-0.018} M_odot$ and $m_{rm p} = 2.1^{+1.5}_{-0.4} M_oplus$, respectively. Future high-resolution imaging observations with $HST$ or ELTs could distinguish between these two scenarios and help to reveal the planetary system properties in more detail.
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 $q=(1.58pm0.15)times10^{-3}$. By conducting a Bayesian analysis, we estimate that the host star is an M-dwarf star with a mass of $M_{rm L}=0.29_{-0.16}^{+0.33} M_{odot}$ located at $D_{rm L}=6.7_{-1.2}^{+1.1} {rm kpc}$ away from the Earth and the companions mass is $m_{rm P}=0.47_{-0.26}^{+0.54} M_{rm Jup}$. The projected planet-host separation is $a_{perp}=1.6_{-0.3}^{+0.4} {rm AU}$. 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 an another example of a possible pileup of sub-Jupiters $(0.2 < m_{rm P}/M_{rm Jup} < 1)$ in contrast to a lack of Jupiters ($sim 1 - 2 M_{rm Jup}$) 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 report the discovery and the analysis of the short (tE < 5 days) planetary microlensing event, OGLE-2015-BLG-1771. The event was discovered by the Optical Gravitational Lensing Experiment (OGLE), and the planetary anomaly (at I ~ 19) was captured by The Korea Microlensing Telescope Network (KMTNet). The event has three surviving planetary models that explain the observed light curves, with planet-host mass ratio q ~ 5.4 * 10^{-3}, 4.5 * 10^{-3} and 4.5 * 10^{-2}, respectively. The first model is the best-fit model, while the second model is disfavored by Deltachi^2 ~ 3. The last model is strongly disfavored by Deltachi^2 ~ 15 but not ruled out. A Bayesian analysis using a Galactic model indicates that the first two models are probably composed of a Saturn-mass planet orbiting a late M dwarf, while the third one could consist of a super-Jovian planet and a mid-mass brown dwarf. The source-lens relative proper motion is mu_rel ~ 9 mas/yr, so the source and lens could be resolved by current adaptive-optics (AO) instruments in 2021 if the lens is luminous.
We report the discovery of a $Spitzer$ microlensing planet OGLE-2018-BLG-0596Lb, with preferred planet-host mass ratio $q sim 2times10^{-4}$. The planetary signal, which is characterized by a short $(sim 1~{rm day})$ bump on the rising side of the lensing light curve, was densely covered by ground-based surveys. We find that the signal can be explained by a bright source that fully envelops the planetary caustic, i.e., a Hollywood geometry. Combined with the source proper motion measured from $Gaia$, the $Spitzer$ satellite parallax measurement makes it possible to precisely constrain the lens physical parameters. The preferred solution, in which the planet perturbs the minor image due to lensing by the host, yields a Uranus-mass planet with a mass of $M_{rm p} = 13.9pm1.6~M_{oplus}$ orbiting a mid M-dwarf with a mass of $M_{rm h} = 0.23pm0.03~M_{odot}$. There is also a second possible solution that is substantially disfavored but cannot be ruled out, for which the planet perturbs the major image. The latter solution yields $M_{rm p} = 1.2pm0.2~M_{oplus}$ and $M_{rm h} = 0.15pm0.02~M_{odot}$. By combining the microlensing and $Gaia$ data together with a Galactic model, we find in either case that the lens lies on the near side of the Galactic bulge at a distance $D_{rm L} sim 6pm1~{rm kpc}$. Future adaptive optics observations may decisively resolve the major image/minor image degeneracy.
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