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

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2018
Authors
Skowron J
Ryu Y-H
Hwang K-H
Udalski A
Mróz P
Kozłowski S
Soszyński I
Pietrukowicz P
Szymański MK
Poleski R
Abstract

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=1.5×10−3 versus q=0.6×10−3. 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=0.25−0.15+0.30M⊙ at a distance DL=5.9−1.95+1.3 kpc. The lens-source relative proper motion is relatively fast, μ=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.

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astro-ph.EP, gravitational lensing: micro
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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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