OGLE-2017-BLG-0173Lb: Low-mass-ratio Planet in a "Hollywood" Microlensing Event

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dc.contributor.authorHwang K-H
dc.contributor.authorUdalski A
dc.contributor.authorShvartzvald Y
dc.contributor.authorRyu Y-H
dc.contributor.authorAlbrow MD
dc.contributor.authorChung S-J
dc.contributor.authorGould A
dc.contributor.authorHan C
dc.contributor.authorJung YK
dc.contributor.authorShin I-G
dc.contributor.authorYee JC
dc.contributor.authorZhu W
dc.contributor.authorCha S-M
dc.contributor.authorKim D-J
dc.contributor.authorKim H-W
dc.contributor.authorKim S-L
dc.contributor.authorLee C-U
dc.contributor.authorLee D-J
dc.contributor.authorLee Y
dc.contributor.authorPark B-G
dc.contributor.authorPogge RW
dc.contributor.authorSkowron J
dc.contributor.authorMroz P
dc.contributor.authorPoleski R
dc.contributor.authorKozlowski S
dc.contributor.authorSoszynski I
dc.contributor.authorPietrukowicz P
dc.contributor.authorSzymanski MK
dc.contributor.authorUlaczyk K
dc.contributor.authorPawlak M
dc.contributor.authorBryden G
dc.contributor.authorBeichman C
dc.contributor.authorNovati SC
dc.contributor.authorGaudi BS
dc.contributor.authorHenderson CB
dc.contributor.authorJacklin S
dc.contributor.authorPenny MT
dc.contributor.authorCollaboration K
dc.contributor.authorCollaboration OGLE
dc.contributor.authorTeam UKIRTM
dc.date.accessioned2018-04-23T21:08:53Z
dc.date.available2018-04-23T21:08:53Z
dc.date.issued2018en
dc.date.updated2018-01-17T14:12:49Z
dc.description.abstractWe present microlensing planet OGLE-2017-BLG-0173Lb, with planet-host mass ratio either $q\simeq 2.5\times 10^{-5}$ or $q\simeq 6.5\times 10^{-5}$, the lowest or among the lowest ever detected. The planetary perturbation is strongly detected, $\Delta\chi^2\sim 10,000$, because it arises from a bright (therefore, large) source passing over and enveloping the planetary caustic: a so-called "Hollywood" event. The factor $\sim 2.5$ offset in $q$ arises because of a previously unrecognized discrete degeneracy between Hollywood events in which the caustic is fully enveloped and those in which only one flank is enveloped, which we dub "Cannae" and "von Schlieffen", respectively. This degeneracy is "accidental" in that it arises from gaps in the data. Nevertheless, the fact that it appears in a $\Delta\chi^2=10,000$ planetary anomaly is striking. We present a simple formalism to estimate the sensitivity of other Hollywood events to planets and show that they can lead to detections close to, but perhaps not quite reaching, the Earth/Sun mass ratio of $3\times 10^{-6}$. This formalism also enables an analytic understanding of the factor $\sim 2.5$ offset in $q$ between the Cannae and von Schlieffen solutions. The Bayesian estimates for the host-mass, system distance, and planet-host projected separation are $M=0.39^{+0.40}_{-0.24}\,M_\odot$, $D_L=4.8^{+1.5}_{-1.8}\,\kpc$, and $a_\perp=3.8\pm 1.6\,\au$. The two estimates of the planet mass are $m_p=3.3^{+3.8}_{-2.1}\,M_\oplus$ and $m_p=8^{+11}_{-6}\,M_\oplus$. The measured lens-source relative proper motion $\mu=6\,\masyr$ will permit imaging of the lens in about 15 years or at first light on adaptive-optics imagers on next-generation telescopes. These will allow to measure the host mass but probably cannot resolve the planet-host mass-ratio degeneracy.en
dc.identifier.doihttps://doi.org/10.3847/1538-3881/aa992f
dc.identifier.issn0004-6256
dc.identifier.issn1538-3881
dc.identifier.urihttp://hdl.handle.net/10092/15206
dc.language.isoen
dc.subjectgravitational lensing: microen
dc.subjectplanetary systemsen
dc.subject.anzsrcFields of Research::51 - Physical sciences::5101 - Astronomical sciences::510109 - Stellar astronomy and planetary systemsen
dc.subject.anzsrcField of Research::02 - Physical Sciences::0201 - Astronomical and Space Sciences::020102 - Astronomical and Space Instrumentationen
dc.titleOGLE-2017-BLG-0173Lb: Low-mass-ratio Planet in a "Hollywood" Microlensing Eventen
dc.typeJournal Articleen
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