Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Weicheng Zang
Kyu-Ha Hwang
Andrzej Udalski
Tianshu Wang
Wei Zhu
Takahiro Sumi
Jennifer C. Yee
Andrew Gould
Shude Mao
Xiangyu Zhang
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Abstract： 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 $q \sim 10^{-5}$.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Weicheng Zang
Yossi Shvartzvald
Andrzej Udalski
Jennifer C. Yee
Chung-Uk Lee
Takahiro Sumi
Xiangyu Zhang
Hongjing Yang
Shude Mao
Sebastiano Calchi Novati
Andrew Gould
Wei Zhu
Charles A. Beichman
Geoffery Bryden
Sean Carey
B. Scott Gaudi
Calen B. Henderson
Przemek Mróz
Jan Skowron
Radoslaw Poleski
Abstract： We report the discovery and analysis of a 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 microlensing parallax vector $\vec{\pi}_{\rm E}$, is strongly constrained by the Spitzer data. However, the 2019 Spitzer baseline data reveal systematics in the Spitzer photometry, so there is ambiguity in the magnitude of the parallax. In our preferred interpretation, a full Bayesian analysis using a Galactic model indicates that the planetary system is composed of an $M_{\rm planet} = 0.26_{-0.11}^{+0.22}~M_{J}$ planet orbiting an $M_{\rm host} = 0.093_{-0.038}^{+0.082}~M_{\odot}$, at a distance of $D_{\rm L} = 3.71_{-1.70}^{+3.24}$ kpc. An alternate interpretation of the data shifts the localization of the minima along the arc-shaped microlens parallax constraints. This, in turn, yields a more massive host with median mass of $0.13 {M_{\odot}}$ at a distance of 6.3 kpc. This analysis demonstrates the robustness of the osculating circles formalism, but shows that further investigation is needed to assess how systematics affect the specific localization of the microlens parallax vector and, consequently, the inferred physical parameters.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hongjing Yang
Weicheng Zang
Andrew Gould
Jennifer C. Yee
Kyu-Ha Hwang
Grant Christie
Takahiro Sumi
Jiyuan Zhang
Shude Mao
Michael D. Albrow
Sun-Ju Chung
Cheongho Han
Youn Kil Jung
Yoon-Hyun Ryu
In-Gu Shin
Yossi Shvartzvald
Sang-Mok Cha
Dong-Jin Kim
Hyoun-Woo Kim
Seung-Lee Kim
Abstract： Follow-up observations of high-magnification gravitational microlensing events can fully exploit their intrinsic sensitivity to detect extrasolar planets, especially those with small mass ratios. To make followup more uniform and efficient, we develop a system, HighMagFinder, based on the real-time data from the Korean Microlensing Telescope Network (KMTNet) to automatically alert possible ongoing high-magnification events. We started a new phase of follow-up observations with the help of HighMagFinder in 2021. Here we report the discovery of two planets in high-magnification microlensing events, KMT-2021-BLG-0171 and KMT-2021-BLG-1689, which were identified by the HighMagFinder. We find that both events suffer the ``central-resonant'' caustic degeneracy. The planet-host mass-ratio is $q\sim4.7\times10^{-5}$ or $q\sim 2.2\times10^{-5}$ for KMT-2021-BLG-0171, and $q\sim2.5\times10^{-4}$ or $q\sim 1.8\times10^{-4}$ for KMT-2021-BLG-1689. Together with two events reported by Ryu et al. (2022), four cases that suffer such degeneracy have been discovered in the 2021 season alone, indicating that the degenerate solutions may have been missed in some previous studies. We also propose a new factor for weighting the probability of each solution from the phase-space. The resonant interpretations for the two events are disfavored under this consideration. This factor can be included in future statistical studies to weight degenerate solutions.
Peer Review Status:Awaiting Review
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