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Register a new userSystematic KMTNet Planetary Anomaly Search, Paper II: Five New $q<2times 10^{-4}$ Mass-ratio Planets
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We apply the automated AnomalyFinder algorithm of Paper I (Zang et al. 2021b) to 2018-2019 light curves from the $simeq 13,{rm deg}^2$ covered by the six KMTNet prime fields, with cadences $Gamma geq 2,{rm hr}^{-1}$. We find a total of 10 planets with mass ratios $q<2times 10^{-4}$, including five newly discovered planets, one planet that was reported in Paper I, and recovery of four previously discovered planets. One of the new planets, OGLE-2018-BLG-0977Lb, is in a planetary-caustic event, while the other four (OGLE-2018-BLG-0506Lb, OGLE-2018-BLG-0516Lb, OGLE-2019-BLG-1492Lb, and KMT-2019-BLG-0253) are revealed by a ``dip in the light curve as the source crosses the host-planet axis on the opposite side of the planet. These subtle signals were missed in previous by-eye searches. The planet-host separations (scaled to the Einstein radius), $s$, and planet-host mass ratios, $q$, are, respectively, $(s,qtimes 10^5) = (0.88, 4.1)$, $(0.96pm 0.10, 8.3)$, $(0.94pm 0.07, 13)$, $(0.97pm 0.07, 18)$, and $(0.97pm0.04,4.1)$, where the ``$pm$ indicates a discrete degeneracy. The ten planets are spread out over the range $-5<log q < -3.7$. Together with the two planets previously reported with $qsim 10^{-5}$ from the 2018-2019 non-prime KMT fields, this result suggests that planets toward the bottom of this mass-ratio range may be more common than previously believed.
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In order to exhume the buried signatures of ``missing planetary caustics in the KMTNet data, we conducted a systematic anomaly search to the residuals from point-source point-lens fits, based on a modified version of the KMTNet EventFinder algorithm. This search reveals the lowest mass-ratio planetary caustic to date in the microlensing event OGLE-2019-BLG-1053, for which the planetary signal had not been noticed before. The planetary system has a planet-host mass ratio of $q = (1.25 pm 0.13) times 10^{-5}$. A Bayesian analysis yields estimates of the mass of the host star, $M_{rm host} = 0.61_{-0.24}^{+0.29}~M_odot$, the mass of its planet, $M_{rm planet} = 2.48_{-0.98}^{+1.19}~M_{oplus}$, the projected planet-host separation, $a_perp = 3.4_{-0.5}^{+0.5}$ au, and the lens distance of $D_{rm L} = 6.8_{-0.9}^{+0.6}$ kpc. The discovery of this very low mass-ratio planet illustrates the utility of our method and opens a new window for a large and homogeneous sample to study the microlensing planet-host mass-ratio function down to $q sim 10^{-5}$.
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Photometry of stars from the K2 extension of NASAs Kepler mission is afflicted by systematic effects caused by small (few-pixel) drifts in the telescope pointing and other spacecraft issues. We present a method for searching K2 light curves for evidence of exoplanets by simultaneously fitting for these systematics and the transit signals of interest. This method is more computationally expensive than standard search algorithms but we demonstrate that it can be efficiently implemented and used to discover transit signals. We apply this method to the full Campaign 1 dataset and report a list of 36 planet candidates transiting 31 stars, along with an analysis of the pipeline performance and detection efficiency based on artificial signal injections and recoveries. For all planet candidates, we present posterior distributions on the properties of each system based strictly on the transit observables.
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