A Jupiter-mass planet around the K0 giant HD 208897^⋆

¹ Ankara University, Department of Astronomy and Space Sciences, 06100 Ankara Turkey,
e-mail: mesutyilmaz@ankara.edu.tr
² Tokyo Institute of Technology, Ookayama, Meguro-ku, Tokyo 152-8550, Japan
³ Kazan Federal University, Department of Astronomy and Satellite Geodesy, 420008 Kazan, Russia
⁴ Okayama Astrophysical Observatory, Honjo 3037-5, Kamogata, Asakuchi, Okayama 719-0232, Japan
⁵ Ege University, Department of Astronomy and Space Sciences, 35100 Bornova, İzmir, Turkey
⁶ Academy of Sciences of Tatarstan, Bauman Str, 20, 420111 Kazan, Russia
⁷ Main (Pulkovo) Astronomical Observatory, Russian Academy of Sciences, 196140 Saint-Petersburg, Russia

Received: 17 May 2017
Accepted: 26 July 2017

Abstract

For over 10 years, we have carried out a precise radial velocity (RV) survey to find substellar companions around evolved G, K-type stars to extend our knowledge of planet formation and evolution. We performed high precision RV measurements for the giant star HD 208897 using an iodine (I₂) absorption cell. The measurements were made at TÜBİTAK National Observatory (TUG; RTT150) and Okayama Astrophysical Observatory (OAO). For the origin of the periodic variation seen in the RV data of the star, we adopted a Keplerian motion caused by an unseen companion. We found that the star hosts a planet with a minimum mass of m₂sini = 1.40 M_J, which is relatively low compared to those of known planets orbiting evolved intermediate-mass stars. The planet is in a nearly circular orbit with a period of P = 353 days at about 1 AU distance from the host star. The star is metal rich and located at the early phase of ascent along the red giant branch. The photometric observations of the star at Ankara University Kreiken Observatory (AUKR) and the Hipparcos photometry show no sign of variation with periods associated with the RV variation. Neither bisector velocity analysis nor analysis of the Ca II and Hα lines shows any correlation with the RV measurements.