Jennifer C. Yee, Harvard-Smithsonian Center for Astrophysics
Weicheng Zang, Tsinghua University
Andrzej Udalski, Uniwersytet Warszawski
Yoon Hyun Ryu, Korea Astronomy and Space Science Institute
Jonathan Green, Kumeu Observatory
Steve Hennerley, Kumeu Observatory
Andrew Marmont, Kumeu Observatory
Takahiro Sumi, Osaka University
Shude Mao, Tsinghua University
Mariusz Gromadzki, Uniwersytet Warszawski
Przemek Mróz, Uniwersytet Warszawski
Jan Skowron, Uniwersytet Warszawski
Radoslaw Poleski, Uniwersytet Warszawski
Michal K. Szymanski, Uniwersytet Warszawski
Igor Soszynski, Uniwersytet Warszawski
Pawel Pietrukowicz, Uniwersytet Warszawski
Szymon Kozlowski, Uniwersytet Warszawski
Krzysztof Ulaczyk, Faculty of Science, Engineering and Medicine
Krzysztof A. Rybicki, Uniwersytet Warszawski
Patryk Iwanek, Uniwersytet Warszawski
Marcin Wrona, Uniwersytet Warszawski
Michael D. Albrow, University of Canterbury
Sun Ju Chung, Korea Astronomy and Space Science Institute
Andrew Gould, Max Planck Institute for Astronomy
Cheongho Han, Chungbuk National University
Kyu Ha Hwang, Korea Astronomy and Space Science Institute
Youn Kil Jung, Korea Astronomy and Space Science Institute
Hyoun Woo Kim, Korea Astronomy and Space Science Institute
In Gu Shin, Korea Astronomy and Space Science Institute
Yossi Shvartzvald, Weizmann Institute of Science Israel
Sang Mok Cha, Korea Astronomy and Space Science Institute
Dong Jin Kim, Korea Astronomy and Space Science Institute
Seung Lee Kim, Korea Astronomy and Space Science Institute

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We report the analysis of OGLE-2019-BLG-0960, which contains the smallest mass-ratio microlensing planet found to date (q = 1.2-1.6 × 10-5 at 1s). Although there is substantial uncertainty in the satellite parallax measured by Spitzer, the measurement of the annual parallax effect combined with the finite source effect allows us to determine the mass of the host star (M L = 0.3-0.6 M o?), the mass of its planet (m p = 1.4-3.1 M ?), the projected separation between the host and planet (a ? = 1.2-2.3 au), and the distance to the lens system (D L = 0.6-1.2 kpc). The lens is plausibly the blend, which could be checked with adaptive optics observations. As the smallest planet clearly below the break in the mass-ratio function, it demonstrates that current experiments are powerful enough to robustly measure the slope of the mass-ratio function below that break. We find that the cross-section for detecting small planets is maximized for planets with separations just outside of the boundary for resonant caustics and that sensitivity to such planets can be maximized by intensively monitoring events whenever they are magnified by a factor A > 5. Finally, an empirical investigation demonstrates that most planets showing a degeneracy between (s > 1) and (s < 1) solutions are not in the regime (log s| » 0) for which the "close"/"wide"degeneracy was derived. This investigation suggests that there is a link between the "close"/"wide"and "inner/outer"degeneracies and also that the symmetry in the lens equation goes much deeper than symmetries uncovered for the limiting cases.

Publication Source (Journal or Book title)

Astronomical Journal