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Kojima-1Lb Is a Mildly Cold Neptune around the Brightest Microlensing Host Star

Fukui, A. and Mawet, D. and Beichman, C. (2019) Kojima-1Lb Is a Mildly Cold Neptune around the Brightest Microlensing Host Star. Astronomical Journal, 158 (5). Art. No. 206. ISSN 1538-3881.

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We report the analysis of additional multiband photometry and spectroscopy and new adaptive optics (AO) imaging of the nearby planetary microlensing event TCP J05074264+2447555 (Kojima-1), which was discovered toward the Galactic anticenter in 2017 (Nucita et al.). We confirm the planetary nature of the light-curve anomaly around the peak while finding no additional planetary feature in this event. We also confirm the presence of apparent blending flux and the absence of significant parallax signal reported in the literature. The AO image reveals no contaminating sources, making it most likely that the blending flux comes from the lens star. The measured multiband lens flux, combined with a constraint from the microlensing model, allows us to narrow down the previously unresolved mass and distance of the lens system. We find that the primary lens is a dwarf on the K/M boundary (0.581 ± 0.033 M⊙) located at 505 ± 47 pc, and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 ± 2.0 M⊕) with a semimajor axis of 1.08^(+0.62)_(-0.18) au. This orbit is a few times smaller than those of typical microlensing planets and is comparable to the snow-line location at young ages. We calculate that the a priori detection probability of Kojima-1Lb is only ~35%, which may imply that Neptunes are common around the snow line, as recently suggested by the transit and radial velocity techniques. The host star is the brightest among the microlensing planetary systems (K_s = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities.

Item Type:Article
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URLURL TypeDescription Paper
Fukui, A.0000-0002-4909-5763
Mawet, D.0000-0002-8895-4735
Beichman, C.0000-0002-5627-5471
Additional Information:© 2019 The American Astronomical Society. Received 2019 May 24; revised 2019 September 16; accepted 2019 September 25; published 2019 October 31. We thank the anonymous referee for a lot of thoughtful comments. A.F. thanks T. Kimura and H. Kawahara for meaningful discussions on the formation and abundance of Neptunes around the snow line. A.F. also thanks A. Nucita and A. Mann for kindly providing data used in their papers. This article is based on observations made with the MuSCAT2 instrument, developed by ABC, at Telescopio Carlos Sánchez, operated on the island of Tenerife by the IAC in the Spanish Observatorio del Teide. We acknowledge ISAS/JAXA for the use of its facility through the inter-university research system. A.Y. is grateful to Mizuki Isogai, Akira Arai, and Hideyo Kawakita for their technical support on observations with the Araki telescope. D.S. acknowledges The Open University for the use of the COAST telescope. A.F. acknowledges the MOA collaboration/Osaka University for the use of the computing cluster. This work was partly supported by JSPS KAKENHI grant Nos. JP25870893, JP16K17660, JP17H02871, JP17H04574, JP18H01265, and JP18H05439; MEXT KAKENHI grant Nos. JP17H06362 and JP23103004; and JST PRESTO grant No. JPMJPR1775. This work was also partially supported by the Optical and Near-Infrared Astronomy Inter-University Cooperation Program of the MEXT of Japan and the JSPS and NSF under the JSPS-NSF Partnerships for International Research and Education. This work was partly financed by the Spanish Ministry of Economics and Competitiveness through grants ESP2013-48391-C4-2-R and AYA2015-69350-C3-2-P. Y.T. acknowledges the support of DFG priority program SPP 1992 "Exploring the Diversity of Extrasolar Planets" (WA 1047/11-1). S.Sh. acknowledges support from grants APVV-15-0458 and VEGA 2/0008/17.
Group:Infrared Processing and Analysis Center (IPAC), Astronomy Department
Funding AgencyGrant Number
Japan Society for the Promotion of Science (JSPS)JP25870893
Japan Society for the Promotion of Science (JSPS)JP16K17660
Japan Society for the Promotion of Science (JSPS)JP17H02871
Japan Society for the Promotion of Science (JSPS)JP17H04574
Japan Society for the Promotion of Science (JSPS)JP18H01265
Japan Society for the Promotion of Science (JSPS)JP18H05439
Japan Society for the Promotion of Science (JSPS)JP17H06362
Japan Society for the Promotion of Science (JSPS)JP23103004
Japan Science and Technology AgencyJPMJPR1775
Ministry of Education, Culture, Sports, Science and Technology (MEXT)UNSPECIFIED
Ministerio de Economía, Industria y Competitividad (MINECO)ESP2013-48391-C4-2-R
Ministerio de Economía, Industria y Competitividad (MINECO)AYA2015-69350-C3-2-P. Y.T
Deutsche Forschungsgemeinschaft (DFG)SPP 1992
Deutsche Forschungsgemeinschaft (DFG)WA 1047/11-1
Slovak Research and Development AgencyAPVV-15-0458
Russian Foundation for Basic ResearchVEGA 2/0008/17
Issue or Number:5
Record Number:CaltechAUTHORS:20191031-144059352
Persistent URL:
Official Citation:A. Fukui et al 2019 AJ 158 206
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99605
Deposited By: Tony Diaz
Deposited On:31 Oct 2019 23:22
Last Modified:31 Oct 2019 23:22

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