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    OGLE-2017-BLG-0373Lb: A Jovian Mass-Ratio Planet Exposes A New Accidental Microlensing Degeneracy

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    Author
    Skowron J
    Ryu Y-H
    Hwang K-H
    Udalski A
    Mróz P
    Kozłowski S
    Soszyński I
    Pietrukowicz P
    Szymański MK
    Poleski R
    Ulaczyk K
    Pawlak M
    Rybicki K
    Iwanek P
    Albrow MD
    Chung S-J
    Gould A
    Han C
    Jung YK
    Shin I-G
    Shvartzvald Y
    Yee JC
    Zang W
    Zhu RW
    Cha S-M
    Kim D-J
    Kim H-W
    Kim S-L
    Lee C-U
    Lee D-J
    Lee Y
    Park B-G
    Pogge RW
    Date
    2018
    Permanent Link
    http://hdl.handle.net/10092/15188

    We report the discovery of microlensing planet OGLE-2017-BLG-0373Lb. We show that while the planet-host system has an unambiguous microlens topology, there are two geometries within this topology that fit the data equally well, which leads to a factor 2.5 difference in planet-host mass ratio, i.e., $q=1.5\times 10^{-3}$ versus $q=0.6\times 10^{-3}$. We show that this is an "accidental degeneracy" in the sense that it is due to a gap in the data. We dub it "the caustic-chirality degeneracy". We trace the mathematical origins of this degeneracy, which should enable similar degenerate solutions to be easily located in the future. A Bayesian estimate, based on a Galactic model, yields a host mass $M=0.25^{+0.30}_{-0.15} M_\odot$ at a distance $D_L=5.9^{+1.3}_{-1.95}$ kpc. The lens-source relative proper motion is relatively fast, $\mu=9$ mas/yr, which implies that the host mass and distance can be determined by high-resolution imaging after about 10 years. The same observations could in principle resolve the discrete degeneracy in $q$, but this will be more challenging.

    Subjects
    astro-ph.EP
     
    gravitational lensing: micro
     
    Field of Research::02 - Physical Sciences::0201 - Astronomical and Space Sciences::020108 - Planetary Science (excl. Extraterrestrial Geology)
     
    Field of Research::02 - Physical Sciences::0201 - Astronomical and Space Sciences::020102 - Astronomical and Space Instrumentation
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    • Science: Journal Articles [906]

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