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

Albrow, M. D. and Beichman, C. and Henderson, C. B. and Calchi Novati, S. (2018) OGLE-2017-BLG-0173Lb: Low-mass-ratio Planet in a "Hollywood" Microlensing Event. Astronomical Journal, 155 (1). Art. No. 20. ISSN 1538-3881. doi:10.3847/1538-3881/aa992f.

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We present microlensing planet OGLE-2017-BLG-0173Lb, with planet–host mass ratio of either q ≃ 2.5 x 10^(-5) or q ≃ 6.5 x 10^(-5), the lowest or among the lowest ever detected. The planetary perturbation is strongly detected, Δχ^2 ~ 10000, because it arises from a bright (therefore, large) source passing over and enveloping the planetary caustic: a so-called "Hollywood" event. The factor ~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 Δχ^2 = 10000 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 x 10(-6). This formalism also enables an analytic understanding of the factor ~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⊙, D_L = 4.8^(+1.5)_(-1.8) kpc, and a⊥ = 3.8 ± 1.6 au, respectively. The two estimates of the planet mass are m_p = 3.3^(+3.8)_(-2.1) M⊕ and m_p = 8^(+11)_(-6) M⊕. The measured lens-source relative proper motion µ = 6 mas yr^(-1) 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 one to measure the host mass but probably will not be able to resolve the planet–host mass-ratio degeneracy.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Albrow, M. D.0000-0003-3316-4012
Beichman, C.0000-0002-5627-5471
Henderson, C. B.0000-0001-8877-9060
Calchi Novati, S.0000-0002-7669-1069
Additional Information:© 2017 The American Astronomical Society. Received 2017 August 28; revised 2017 September 25; accepted 2017 November 5; published 2017 December 15. Work by W.Z., Y.K.J., and A.G. was supported by AST-1516842 from the US NSF. W.Z., I.G.S., and A.G. were supported by JPL grant 1500811. Work by C.H. was supported by the grant (2017R1A4A1015178) of National Research Foundation of Korea. This research has made use of the KMTNet system operated by the Korea Astronomy and Space Science Institute (KASI) and the data were obtained at three host sites of CTIO in Chile, SAAO in South Africa, and SSO in Australia. The OGLE project has received funding from the National Science Centre, Poland, grant MAESTRO 2014/14/A/ST9/00121 to AU. Work by Y.S. was supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, California Institute of Technology, administered by Universities Space Research Association through a contract with NASA. The United Kingdom Infrared Telescope (UKIRT) is supported by NASA and operated under an agreement among the University of Hawaii, the University of Arizona, and Lockheed Martin Advanced Technology Center; operations are enabled through the cooperation of the Joint Astronomy Centre of the Science and Technology Facilities Council of the U.K.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
National Research Foundation of Korea2017R1A4A1015178
National Science Centre (Poland)2014/14/A/ST9/00121
NASA Postdoctoral ProgramUNSPECIFIED
Subject Keywords:gravitational lensing: micro – planetary systems
Issue or Number:1
Record Number:CaltechAUTHORS:20171214-131045847
Persistent URL:
Official Citation:K.-H. Hwang et al 2018 AJ 155 20
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:83925
Deposited By: Tony Diaz
Deposited On:14 Dec 2017 21:23
Last Modified:15 Nov 2021 20:15

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