# JKAS - Journal of the Korean Astronomical Society

## The Korean Astronomical Society

JKAS is a bimonthly publication of the Korean Astronomical Society. We aim at promoting the original work of researchers in all branches of astronomy and astrophysics. We cover all categories of work, including observation, theory, methodology, instrumentation, software, and data bases. We welcome proposals for review articles or special issues.

JKAS was launched in 1968 to provide a peer-reviewed scientific journal to the Korean community of astronomers. As there were only a few professional astronomers in Korea back then, JKAS initially published one issue per year, with each issue containing a handful of papers written either in Korean or English. The first-ever JKAS paper was written by Chou & Kitamura and discussed the photometric orbit of the eclipsing binary DI Pegasi. Over time, the Korean astronomy community grew, and so did the number of papers. In 1986, JKAS became English-only, with Korean language papers spun off to the Publications of the Korean Astronomical Society (PKAS). Around 2004/2005, the astronomical societies of Korea, Japan, China, and India discussed a merger of their national astronomy journals, including JKAS, into a unified Asian journal; eventually, this proposal was rejected In the past decade, efforts were made to make JKAS fit for the 21st century. In 2009, JKAS was added to the ISI/Thomson Reuters Science Citation Index Expanded database and received an impact factor, thus – at last – joining the family of globally recognized quality scientific journals. Nowadays, JKAS receives about 40 to 50 papers per year out of which 20 to 30 are accepted and published.

Journal of the Korean Astronomical Society - Vol. 53 , No. 1

53: 9 - 26, 2020 February

https://doi.org/10.5303/JKAS.2020.53.1.9

## KMT-2018-BLG-0029LB: A VERY LOW MASS-RATIO SPITZER MICROLENS PLANET

ANDREW GOULD, YOON-HYUN RYU, SEBASTIANO CALCHI NOVATI, WEICHENG ZANG, MICHAEL D. ALBROW, SUN-JU CHUNG, CHEONGHO HAN, KYU-HA HWANG, YOUN KIL JUNG, IN-GU SHIN, YOSSI SHVARTZVALD, JENNIFER C. YEE, SANG-MOK CHA, DONG-JIN KIM, HYOUN-WOO KIM, SEUNG-LEE KIM, CHUNG-UK LEE, DONG-JOO LEE, YONGSEOK LEE, BYEONG-GON PARK, RICHARD W. POGGE, CHARLES BEICHMAN, GEOFF BRYDEN, SEAN CAREY, B. SCOTT GAUDI, CALEN B. HENDERSON, WEI ZHU, PASCAL FOUQUÉ, MATTHEW T. PENNY, ANDREEA PETRIC, TODD BURDULLIS, SHUDE MAO

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 πE measurement. Combined with a measurement of the Einstein radius θE from finite-source effects during the caustic crossings, these measurements imply masses of the host Mhost = ${1.14}_{-0.12}^{+0.10}$M and planet Mplanet = ${7.59}_{-0.69}^{+0.75}$M, system distance DL = ${3.38}_{-0.26}^{+0.22}$ kpc and projected separation a⊥ = ${4.27}_{-0.23}^{+0.21}$ 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.

Key words: gravitational lensing: micro, planetary systems

Received June 27, 2019; accepted December 31, 2019