An Earth-mass Planet in a Time of Covid-19: KMT-2020-BLG-0414Lb
Creators: name: Zang, Weicheng
name: Han, Cheongho
name: Kondo, Iona
name: Yee, Jennifer C.
name: Lee, Chung-Uk
name: Gould, Andrew
name: Mao, Shude
name: de Almeida, Leandro
name: Shvartzvald, Yossi
name: Zhang, Xiangyu
name: Albrow, Michael D.
name: Chung, Sun-Ju
name: Hwang, Kyu-Ha
name: Jung, Youn Kil
name: Ryu, Yoon-Hyun
name: Shin, In-Gu
name: Cha, Sang-Mok
name: Kim, Dong-Jin
name: Kim, Hyoun-Woo
name: Kim, Seung-Lee
name: Lee, Dong-Joo
name: Lee, Yongseok
name: Park, Byeong-Gon
name: Pogge, Richard W.
name: Drummond, John
name: Tan, Thiam-Guan
name: Júnior, José Dias do Nascimento
name: Maoz, Dan
name: Penny, Matthew T.
name: Zhu, Wei
name: Bond, Ian A.
name: Abe, Fumio
name: Barry, Richard
name: Bennett, David P.
name: Bhattacharya, Aparna
name: Donachie, Martin
name: Fujii, Hirosane
name: Fukui, Akihiko
name: Hirao, Yuki
name: Itow, Yoshitaka
name: Kirikawa, Rintaro
name: Koshimoto, Naoki
name: Li, Man Cheung Alex
name: Matsubara, Yutaka
name: Muraki, Yasushi
name: Miyazaki, Shota
name: Ranc, Clément
name: Rattenbury, Nicholas J.
name: Satoh, Yuki
name: Shoji, Hikaru
name: Sumi, Takahiro
name: Suzuki, Daisuke
name: Tanaka, Yuzuru
name: Tristram, Paul J.
name: Yamawaki, Tsubasa
name: Yonehara, Atsunori
name: Petric, Andreea
name: Burdullis, Todd
name: Fouqué, Pascal
Publisher: name: arXiv
Year: 2021
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Astrophysics of Galaxies (astro-ph.GA)
subject: High Energy Astrophysical Phenomena (astro-ph.HE)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio $q_2 = 0.9$--$1.2 \times 10^{-5} = 3$--$4~q_{\oplus}$ at $1σ$, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries ($4 \lesssim q/q_\oplus \lesssim 6$), it fills out the previous empty sector at the bottom of the triangular $(\log s, \log q)$ diagram, where $s$ is the planet-host separation in units of the angular Einstein radius $θ_{\rm E}$. Hence, these discoveries call into question the existence, or at least the strength, of the break in the mass-ratio function that was previously suggested to account for the paucity of very low-$q$ planets. Due to the extreme magnification of the event, $A_{\rm max}\sim 1450$ for the underlying single-lens event, its light curve revealed a second companion with $q_3 \sim 0.05$ and $|\log s_3| \sim 1$, i.e., a factor $\sim 10$ closer to or farther from the host in projection. The measurements of the microlens parallax $π_{\rm E}$ and the angular Einstein radius $θ_{\rm E}$ allow estimates of the host, planet, and second companion masses, $(M_1, M_2, M_3) \sim (0.3M_{\odot}, 1.0M_{\oplus}, 17M_{J})$, the planet and second companion projected separations, $(a_{\perp,2}, a_{\perp,3}) \sim (1.5, 0.15~{\rm or}~15)$~au, and system distance $D_{\rm L} \sim 1$ kpc. The lens could account for most or all of the blended light ($I \sim 19.3$) and so can be studied immediately with high-resolution photometric and spectroscopic observations that can further clarify the nature of the system. The planet was found as part of a new program of high-cadence follow-up observations of high-magnification events. The detection of this planet, despite the considerable difficulties imposed by Covid-19 (two KMT sites and OGLE were shut down), illustrates the potential utility of this program.
description: 23 pages, 5 figures; to be submitted to RAA