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Register a new userKMT-2017-BLG-0165Lb: A Super-Neptune mass planet Orbiting a Sun-like Host Star
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We report the discovery of a low mass-ratio planet $(q = 1.3times10^{-4})$, i.e., 2.5 times higher than the Neptune/Sun ratio. The planetary system was discovered from the analysis of the KMT-2017-BLG-0165 microlensing event, which has an obvious short-term deviation from the underlying light curve produced by the host of the planet. Although the fit improvement with the microlens parallax effect is relatively low, one component of the parallax vector is strongly constrained from the light curve, making it possible to narrow down the uncertainties of the lens physical properties. A Bayesian analysis yields that the planet has a super-Neptune mass $(M_{2}=34_{-12}^{+15}~M_{oplus})$ orbiting a Sun-like star $(M_{1}=0.76_{-0.27}^{+0.34}~M_{odot})$ located at $4.5~{rm kpc}$. The blended light is consistent with these host properties. The projected planet-host separation is $a_{bot}={3.45_{-0.95}^{+0.98}}~{rm AU}$, implying that the planet is located outside the snowline of the host, i.e., $a_{sl}sim2.1~{rm AU}$. KMT-2017-BLG-0165Lb is the sixteenth microlensing planet with mass ratio $q<3times10^{-4}$. Using the fifteen of these planets with unambiguous mass-ratio measurements, we apply a likelihood analysis to investigate the form of the mass-ratio function in this regime. If we adopt a broken power law for the form of this function, then the break is at $q_{rm br}simeq0.55times10^{-4}$, which is much lower than previously estimated. Moreover, the change of the power law slope, $zeta>3.3$ is quite severe. Alternatively, the distribution is also suggestive of a pile-up of planets at Neptune-like mass ratios, below which there is a dramatic drop in frequency.
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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.
Although several thousands of exoplanets have now been detected and characterized, observational biases have led to a paucity of long-period, low-mass exoplanets with measured masses and a corresponding lag in our understanding of such planets. In this paper we report the mass estimation and characterization of the long-period exoplanet Kepler-538b. This planet orbits a Sun-like star (V = 11.27) with M_* = 0.892 +/- (0.051, 0.035) M_sun and R_* = 0.8717 +/- (0.0064, 0.0061) R_sun. Kepler-538b is a 2.215 +/- (0.040, 0.034) R_earth sub-Neptune with a period of P = 81.73778 +/- 0.00013 d. It is the only known planet in the system. We collected radial velocity (RV) observations with HIRES on Keck I and HARPS-N on the TNG. We characterized stellar activity by a Gaussian process with a quasi-periodic kernel applied to our RV and cross correlation function full width at half maximum (FWHM) observations. By simultaneously modeling Kepler photometry, RV, and FWHM observations, we found a semi-amplitude of K = 1.68 +/- (0.39, 0.38) m s^-1 and a planet mass of M_p = 10.6 +/- (2.5, 2.4) M_earth. Kepler-538b is the smallest planet beyond P = 50 d with an RV mass measurement. The planet likely consists of a significant fraction of ices (dominated by water ice), in addition to rocks/metals, and a small amount of gas. Sophisticated modeling techniques such as those used in this paper, combined with future spectrographs with ultra high-precision and stability will be vital for yielding more mass measurements in this poorly understood exoplanet regime. This in turn will improve our understanding of the relationship between planet composition and insolation flux and how the rocky to gaseous transition depends on planetary equilibrium temperature.
We announce the discovery of a microlensing planetary system, in which a sub-Saturn planet is orbiting an ultracool dwarf host. We detect the planetary system by analyzing the short-timescale ($t_{rm E}sim 4.4$~days) lensing event KMT-2018-BLG-0748. The central part of the light curve exhibits asymmetry due to the negative deviations in the rising part and the positive deviations in the falling part. We find that the deviations are explained by a binary-lens model with a mass ratio between the lens components of $qsim 2times 10^{-3}$. The short event timescale together with the small angular Einstein radius, $theta_{rm E}sim 0.11$~mas, indicate that the mass of the planet host is very small. The Bayesian analysis conducted under the assumption that the planet frequency is independent of the host mass indicates that the mass of the planet is $M_{rm p}=0.18^{+0.29}_{-0.10}~M_{rm J}$, and the mass of the host, $M_{rm h}= 0.087^{+0.138}_{-0.047}~M_odot$, is near the star/brown dwarf boundary, but the estimated host mass is sensitive to the assumption about the planet hosting probability. High-resolution follow-up observations would lead to revealing the nature of the planet host.
We report the discovery of a cold planet with a very low planet/host mass ratio of $q=(4.09pm0.27) times 10^{-5}$, which is similar to the ratio of Uranus/Sun ($q=4.37 times 10^{-5}$) in the Solar system. The Bayesian estimates for the host mass, planet mass, system distance, and planet-host projected separation are $M_{rm host}=0.76pm 0.40 M_odot$, $M_{rm planet}=10.3pm 5.5 M_oplus$, $D_{rm L} = 3.3pm1.3,{rm kpc}$, and $a_perp = 3.3pm 1.4,{rm au}$, respectively. The consistency of the color and brightness expected from the estimated lens mass and distance with those of the blend suggests the possibility that the most blended light comes from the planet host, and this hypothesis can be established if high resolution images are taken during the next (2020) bulge season. We discuss the importance of conducting optimized photometry and aggressive follow-up observations for moderately or very high magnification events to maximize the detection rate of planets with very low mass ratios.
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