KMT-2018-BLG-0029Lb: A Very Low Mass-Ratio Spitzer Microlens Planet

Creators: Gould, Andrew; Ryu, Yoon-Hyun; Calchi Novati, Sebastiano; Zang, Weicheng; Albrow, Michael D.; Chung, Sun-Ju; Han, Cheongho; Hwang, Kyu-Ha; Jung, Youn Kil; Shin, In-Gu; Shvartzvald, Yossi; Yee, Jennifer C.; Cha, Sang-Mok; Kim, Dong-Jin; Kim, Hyoun-Woo; Kim, Seung-Lee; Lee, Chung-Uk; Lee, Dong-Joo; Lee, Yongseok; Park, Byeong-Gon; Pogge, Richard W.; Beichman, Charles; Bryden, Geoff; Carey, Sean; Gaudi, B. Scott; Henderson, Calen B.; Zhu, Wei; Fouqué, Pascal; Penny, Matthew T.; Petric, Andreea; Burdullis, Todd; Mao, Shude; KMTNet Collaboration; Spitzer Team; CFHT Microlensing Collaboration

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Abstract

At q = 1.81 ± 0.20 × 10⁻⁵, KMT-2018-BLG-0029Lb has the lowest planet-host mass ratio q of any microlensing planet to date by more than a factor of two. Hence, it is the first planet that probes below the apparent "pile-up" at q = 5–10 ×10⁻⁵. The event was observed by Spitzer, yielding a microlens-parallax π_E measurement. Combined with a measurement of the Einstein radius θ_E from finite-source effects during the caustic crossings, these measurements imply masses of the host M_(host) = 1.14^(+0.10)_(−0.12)M⊙ and planet M_(planet) = 7.59^(+0.75)_(−0.69)M⊕, system distance D_L = 3.38^(+0.22)_(−0.26) 3.38^(+0.22)_(−0.26) kpc and projected separation a⊥ = 4.27^(+0.21)_(−0.23) 4.27^(+0.21)_(−0.23) AU. The blended light, which is substantially brighter than the microlensed source, is plausibly due to the lens and could be observed at high resolution immediately.

Additional Information

© 2020 Korean Astronomical Society. Published under Creative Commons license CC BY-SA 4.0. Received 27 Jun 2019 Accepted 31 Dec 2019. Print publication date 29 Feb 2020. We thank the anonymous referee for an especially valuable report that helped greatly to clarify the issues presented here. Work by AG was supported by AST-1516842 from the US NSF and by JPL grant 1500811. AG received support from the European Research Council under the European Unions Seventh Framework Programme (FP 7) ERC Grant Agreement n. [321035]. Work by CH was supported by the grant (2017R1A4A1015178) of the National Research Foundation of Korea. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. We are very grateful to the instrumentation and operations teams at CFHT who fixed several failures of MegaCam in the shortest time possible, allowing its return onto the telescope and these crucial observations. WZ and SM acknowledge support by the National Science Foundation of China (Grant No. 11821303 and 11761131004). MTP was supported by NASA grants NNX14AF63G and NNG16PJ32C, as well as the Thomas Jefferson Chair for Discovery and Space Exploration. This research uses data obtained through the Telescope Access Program (TAP), which has been funded by the National Astronomical Observatories of China, the Chinese Academy of Sciences, and the Special Fund for Astronomy from the Ministry of Finance.

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