An Earth-mass planet in a time of COVID-19: KMT-2020-BLG-0414Lb
Maoz, Dan; Tan, Thiam-Guan; Han, Cheongho; Lee, Chung-Uk; Zang, Weicheng; Albrow, Michael D.; Chung, Sun-Ju; Gould, Andrew; Hwang, Kyu-Ha; Jung, Youn Kil; Ryu, Yoon-Hyun; Shvartzvald, Yossi; Shin, In-Gu; Yee, Jennifer C.; Cha, Sang-Mok; Kim, Dong-Jin; Kim, Seung-Lee; Lee, Dong-Joo; Lee, Yongseok; Park, Byeong-Gon; Pogge, Richard W.; Fukui, Akihiko; Penny, Matthew T.; Kim, Hyoun-Woo; Zhu, Wei; Sumi, Takahiro; Mao, Shude; Zhang, Xiangyu; Bond, Ian A.; Abe, Fumio; Barry, Richard; Bennett, David P.; Bhattacharya, Aparna; Donachie, Martin; Fujii, Hirosane; Hirao, Yuki; Itow, Yoshitaka; Kirikawa, Rintaro; Kondo, Iona; Koshimoto, Naoki; Matsubara, Yutaka; Muraki, Yasushi; Miyazaki, Shota; Olmschenk, Greg; Ranc, Clément; Rattenbury, Nicholas J.; Satoh, Yuki; Shoji, Hikaru; Suzuki, Daisuke; Tanaka, Yuzuru; Tristram, Paul J.; Yamawaki, Tsubasa; Yonehara, Atsunori; Silva, Stela Ishitani; Petric, Andreea; Fouqué, Pascal; Burdullis, Todd; Alex Li, Man Cheung; de Almeida, Leandro; Drummond, John; Nascimento Júnior, José Dias do
China, India, South Korea, Japan, United States, Germany, Brazil, Israel, New Zealand, Australia, Canada, Spain, France
Abstract
We report the discovery of KMT-2020-BLG-0414Lb, with a planet-to-host mass ratio q 2 = 0.9-1.2 × 10-5 = 3-4 ⊕ at 1σ, which is the lowest mass-ratio microlensing planet to date. Together with two other recent discoveries (4 ≲ q/q ⊕ ≲ 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 θE. 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 max ~ 1450 for the underlying single-lens event, its light curve revealed a second companion with q 3 ~ 0.05 and |log s 3| ~ 1, i.e., a factor ~ 10 closer to or farther from the host in projection. The measurements of the microlens parallax π E and the angular Einstein radius θE allow estimates of the host, planet and second companion masses, (M 1, M 2, M 3) ~ (0.3 M ⊙, 1.0 M ⊕, 17 MJ ), the planet and second companion projected separations, (a ⊥,2, a ⊥,3) ~ (1.5, 0.15 or 15) au, and system distance D L ~ 1 kpc. The lens could account for most or all of the blended light (I ~ 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.