Discovery of an Extrasolar Planetary System

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

J. Skowron, Y.-H. Ryu, K.-H. Hwang, (and) A. Udalski, P. Mróz, S. Kozłowski, I. Soszyński, P. Pietrukowicz, M. K. Szymański, R. Poleski, K. Ulaczyk, M. Pawlak, K. Rybicki, P. Iwanek (OGLE Collaboration) M. D. Albrow, S.-J. Chung, A. Gould, C. Han, Y. K. Jung, I.-G. Shin, Y. Shvartzvald, J. C. Yee, W. Zang, W. Zhu, S.-M. Cha, D.-J. Kim, H.-W. Kim, S.-L. Kim, C.-U. Lee, D.-J. Lee, Y. Lee, B.-G. Park, R. W. Pogge (KMTNET Collaboration)
2018, Acta Astron., 68, 43 arXiv:1802.10067

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+0.30-0.15 M at a distance DL = 5.9+1.3-1.95 kpc. The lens-source relative proper motion is relatively fast, μ =9 mas yr-1, 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.

Zoomed Light Curve of the Microlensing Event MOA-2011-BLG-028

The Light Curve of the Microlensing Event OGLE-2017-BLG-0373. Two degenerate models are overplotted. Insets show source-lens relative trajectories. Data come from OGLE-IV survey (field no. BLG507.12), and KMTNet (CTIO and SAAO telescopes, fields no. BLG01 and BLG41).

OGLE-2017-BLG-0373 position in the Galactic bulge

Position of the planet within the Galactic bulge. North is up, East is to the left. Image size is 2' × 2'. The sky coordinates of the planetary system are (α,δ)J2000 = (17:57:19.06, -31:57:06.2) and (l,b) = (358.69, -3.71).

Estimation of the physical parameters of OGLE-2017-BLG-0373

Estimation of the physical parameters of OGLE-2017-BLG-0373

Data for download

Finding chart with marked stars

Light curves

Neighboring stars photometry

OGLE Early Warning System discovery page: OGLE-2017-BLG-0373.

PLEASE cite the following paper when using the data or referring to these OGLE results:
    Skowron et al., 2018, Acta Astron., 68, 3 arXiv:1802.10067

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