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Register a new userOGLE-2018-BLG-1185b : A Low-Mass Microlensing Planet Orbiting a Low-Mass Dwarf
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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.
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We report the discovery and analysis of a sub-Saturn-mass planet in the microlensing event OGLE-2018-BLG-0799. The planetary signal was observed by several ground-based telescopes, and the planet-host mass ratio is $q = (2.65 pm 0.16) times 10^{-3}$. The ground-based observations yield a constraint on the angular Einstein radius $theta_{rm E}$, and the microlens parallax $pi_{rm E}$ is measured from the joint analysis of the Spitzer and ground-based observations, which suggests that the host star is most likely to be a very low-mass dwarf. A full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $M_{rm planet} = 0.22_{-0.06}^{+0.19}~M_{J}$ planet orbiting an $M_{rm host} = 0.080_{-0.020}^{+0.080}~M_odot$, at a distance of $D_{rm L} = 4.42_{-1.23}^{+1.73}$ kpc. The projected planet-host separation is $r_perp = 1.27_{-0.29}^{+0.45}$ AU, implying that the planet is located beyond the snowline of the host star. However, because of systematics in the Spitzer photometry, there is ambiguity in the parallax measurement, so the system could be more massive and farther away.
We aim to find missing microlensing planets hidden in the unanalyzed lensing events of previous survey data. For this purpose, we conduct a systematic inspection of high-magnification microlensing events, with peak magnifications $A_{rm peak}gtrsim 30$, in the data collected from high-cadence surveys in and before the 2018 season. From this investigation, we identify an anomaly in the lensing light curve of the event KMT-2018-BLG-1025. The analysis of the light curve indicates that the anomaly is caused by a very low mass-ratio companion to the lens. We identify three degenerate solutions, in which the ambiguity between a pair of solutions (solutions B) is caused by the previously known close--wide degeneracy, and the degeneracy between these and the other solution (solution A) is a new type that has not been reported before. The estimated mass ratio between the planet and host is $qsim 0.8times 10^{-4}$ for the solution A and $qsim 1.6times 10^{-4}$ for the solutions B. From the Bayesian analysis conducted with measured observables, we estimate that the masses of the planet and host and the distance to the lens are $(M_{rm p}, M_{rm h}, D_{rm L})sim (6.1~M_oplus, 0.22~M_odot, 6.7~{rm kpc})$ for the solution A and $sim (4.4~M_oplus, 0.08~M_odot, 7.5~{rm kpc})$ for the solutions B. The planet mass is in the category of a super-Earth regardless of the solutions, making the planet the eleventh super-Earth planet, with masses lying between those of Earth and the Solar systems ice giants, discovered by microlensing.
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 $qsim 1.4times 10^{-4}$. We measure the microlens parallax $pi_{rm E}$ from the long-term deviation in the observed lensing light curve, but the angular Einstein radius $theta_{rm E}$ 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 $M_{rm p}=9.0_{-4.5}^{+9.0} M_oplus$ and $M_{rm host}=0.20_{-0.10}^{+0.20} M_odot$, respectively, and the projected separation between them is $a_perp=1.8_{-0.7}^{+0.6}$ au. The estimated distance to the lens is $D_{rm L}=5.8_{-2.1}^{+1.8}$ kpc. The discovery of the planetary system demonstrates that microlensing provides an important method to detect low-mass planets orbiting low-mass stars.
We report a multiplanetary system found from the analysis of microlensing event OGLE-2018-BLG-1011, for which the light curve exhibits a double-bump anomaly around the peak. We find that the anomaly cannot be fully explained by the binary-lens or binary-source interpretations and its description requires the introduction of an additional lens component. The 3L1S (3 lens components and a single source) modeling yields three sets of solutions, in which one set of solutions indicates that the lens is a planetary system in a binary, while the other two sets imply that the lens is a multiplanetary system. By investigating the fits of the individual models to the detailed light curve structure, we find that the multiple-planet solution with planet-to-host mass ratios $sim 9.5times 10^{-3}$ and $sim 15times 10^{-3}$ are favored over the other solutions. From the Bayesian analysis, we find that the lens is composed of two planets with masses $1.8^{+3..4}_{-1.1}~M_{rm J}$ and $2.8^{+5.1}_{-1.7}~M_{rm J}$ around a host with a mass $0.18^{+0.33}_{-0.10}~M_odot$ and located at a distance $7.1^{+1.1}_{-1.5}~{rm kpc}$. The estimated distance indicates that the lens is the farthest system among the known multiplanetary systems. The projected planet-host separations are $a_{perp,2}=1.8^{+2.1}_{-1.5}~{rm au}$ ($0.8^{+0.9}_{-0.6}~{rm au}$) and $a_{perp,3}=0.8^{+0.9}_{-0.6}~{rm au}$, where the values of $a_{perp,2}$ in and out the parenthesis are the separations corresponding to the two degenerate solutions, indicating that both planets are located beyond the snow line of the host, as with the other four multiplanetary systems previously found by microlensing.
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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