The K2-Esprint Project. V. A short-period giant planet orbiting a subgiant star

Van Eylen, Vincent and Albrecht, Simon and Gandolfi, Davide and Dai, Fei and Winn, Joshua and Hirano, Teriyuki and Narita, Norio and Bruntt, Hans and Prieto-Arranz, Jorge and Bejar, Víctor and Nowak, Grzegorz and Lund, Mikkel and Palle, Enric and Ribas, Ignasi and Sanchis-Ojeda, Roberto and Yu, Liang and Arriagada, Pamela and Butler, R. Paul and Crane, Jeffrey D. and Handberg, Rasmus and Deeg, Hans and Jessen-Hansen, Jens and Johnson, John A. and Nespral, David and Rogers, Leslie and Ryu, Tsuguru and Schectman, Stephen and Shrotriya, Tushar and Slumstrup, Ditte and Takeda, Yoichi and Teske, Johanna and Thompson, Ian and Vanderburg, Andrew and Wittenmyer, Robert (2016) The K2-Esprint Project. V. A short-period giant planet orbiting a subgiant star. The Astronomical Journal, 152 (5). ISSN 0004-6256

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We report on the discovery and characterization of the transiting planet K2-39b (EPIC 206247743b). With an
orbital period of 4.6 days, it is the shortest-period planet orbiting a subgiant star known to date. Such planets are rare, with only a handful of known cases. The reason for this is poorly understood but may reflect differences in planet occurrence around the relatively high-mass stars that have been surveyed, or may be the result of tidal
destruction of such planets. K2-39 (EPIC 206247743) is an evolved star with a spectroscopically derived stellar
radius and mass of

3.88 -0.42 to +0.48 Ro and

1.53 -0.12 to + 0.13 Mo, respectively,

and a very close-in transiting planet, with a/R* = 3.4.

Radial velocity (RV) follow-up using the HARPS, FIES, and PFS instruments leads to a planetary mass of

50.3 -9.4 to +9.7 MÅ.

In combination with a radius measurement of 8.3 +/- 1.1 RÅ, this results in a mean planetary density of

0.50 -0.17 to +0.29 g cm−3.

We furthermore discover a long-term RV trend, which may be caused by a long period planet or stellar companion. Because K2-39b has a short orbital period, its existence makes it seem unlikely that tidal destruction is wholly responsible for the differences in planet populations around subgiant and main-sequence stars. Future monitoring of the transits of this system may enable the detection of period decay and constrain the tidal dissipation rates of subgiant stars.

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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Additional Information: Access to Published version allowed due to publisher copyright policy.
Faculty / Department / School: Current - Faculty of Health, Engineering and Sciences - School of Agricultural, Computational and Environmental Sciences
Date Deposited: 28 Mar 2017 06:19
Last Modified: 10 May 2017 23:49
Uncontrolled Keywords: planets and satellites; detection; dynamical evolution and stability; stars; fundamental parameters; K2-39
Fields of Research : 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020110 Stellar Astronomy and Planetary Systems
Socio-Economic Objective: E Expanding Knowledge > 97 Expanding Knowledge > 970102 Expanding Knowledge in the Physical Sciences
Identification Number or DOI: 10.3847/0004-6256/152/5/143

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