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Kojima-1Lb is a mildly cold Neptune around the brightest microlensing host star


Fukui, A and Suzuki, D and Koshimoto, N and Bachelet, E and Vanmunster, T and Storey, D and Maehara, H and Yanagisawa, K and Yamada, T and Yonehara, A and Hirano, T and Bennett, DP and Bozza, V and Mawet, D and Penny, MT and Awiphan, S and Oksanen, A and Heintz, TM and Oberst, TE and Bejar, VJS and Casasayas-Barris, N and Chen, G and Crouzet, N and Hidalgo, D and Klagyivik, P and Murgas, F and Narita, N and Palle, E and Parviainen, H and Watanabe, N and Kusakabe, N and Mori, M and Terada, Y and de Leon, JP and Hernandez, A and Luque, R and Monelli, M and Montanes-Rodriguez, P and Prieto-Arranz, J and Murata, KL and Shugarov, S and Kubota, Y and Otsuki, C and Shionoya, A and Nishiumi, T and Nishide, A and Fukagawa, M and Villanueva, J and Street, RA and Tsapras, Y and Hundertmark, M and Kuzuhara, M and Fujita, M and Beichman, C and Beaulieu, J-P and Alonso, R and Reichart, DE and Kawai, N and Tamura, M, Kojima-1Lb is a mildly cold Neptune around the brightest microlensing host star, Astronomical Journal, 158, (5) Article 206. ISSN 0004-6256 (2019) [Refereed Article]

Copyright Statement

2019. The American Astronomical Society. All rights reserved

DOI: doi:10.3847/1538-3881/ab487f


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 MO) located at 505 +- 47 pc, and the companion (Kojima-1Lb) is a Neptune-mass planet (20.0 +- 2.0 MO) 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 (Ks = 13.7), offering a great opportunity to spectroscopically characterize this system, even with current facilities.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:Beaulieu, J-P (Dr Jean-Philippe Beaulieu)
ID Code:152295
Year Published:2019
Web of Science® Times Cited:14
Deposited By:Plant Science
Deposited On:2022-08-16
Last Modified:2022-11-24

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