THE K2-ESPRINT PROJECT. V. A SHORT-PERIOD GIANT PLANET ORBITING A SUBGIANT STAR

THE K2-ESPRINT PROJECT. V. A SHORT-PERIOD GIANT PLANET ORBITING A SUBGIANT STAR

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 und...

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Bibliographic Details
Main Authors: Van Eylen, Vincent, Albrecht, Simon, Gandolf, Davide, Hirano, Teriyuki, Narita, Norio, Bruntt, Hans, Prieto-Arranz, Jorge, Béjar, Víctor J. S., Nowak, Grzegorz, Lund, Mikkel N., Palle, Enric, Ribas, Ignasi, Sanchis-Ojeda, Roberto, Arriagada, Pamela, Butler, R. Paul, Crane, Jeffrey D., Handberg, Rasmus, Deeg, Hans, Jessen-Hansen, Jens, Johnson, John A., Nespra, David, Rogers, Leslie, Ryu, Tsuguru, Shectman, Stephen, Shrotriya, Tushar, Slumstrup, Ditte, Takeda, Yoichi, Teske, Johanna, Thompson, Ian, Vanderburg, Andrew, Wittenmyer, Robert, Dai, Fei, Yu, Liang, Winn, Joshua Nathan
Other Authors: Massachusetts Institute of Technology. Department of Physics
Format: Article
Language:en_US
Published: IOP Publishing 2017
Online Access:http://hdl.handle.net/1721.1/109573
https://orcid.org/0000-0002-8958-0683
https://orcid.org/0000-0002-4265-047X
https://orcid.org/0000-0003-1667-5427
Description
Summary: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 [subscript -0.42] [superscript +0.48] R [subscript ⊙] and 1.53[subscript-0.12] [superscript +0.13] M[subscript ⊙], respectively, and a very close-in transiting planet, with a/R [subscript asterisk]= 3.4 Radial velocity (RV) follow-up using the HARPS, FIES, and PFS instruments leads to a planetary mass of 50.3 [subscript -9.4] [superscript +9.7] M [subscript ⊙]. In combination with a radius measurement of 8.3 ± 1.1 R [subscript oplus], this results in a mean planetary density of 0.50 [subscript -0.17] [superscript +0.29] g cm [superscript -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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