Planets around the evolved stars 24 Boötis and γ Libra: A 30 d-period planet and a double giant-planet system in possible 7:3 MMR. (25th May 2018)

• Record Type: Journal Article
• Authors: Takarada, Takuya; Sato, Bun'ei; Omiya, Masashi; Harakawa, Hiroki; Nagasawa, Makiko; Izumiura, Hideyuki; Kambe, Eiji; Takeda, Yoichi; Yoshida, Michitoshi; Itoh, Yoichi; Ando, Hiroyasu; Kokubo, Eiichiro; Ida, Shigeru
• Is Part Of: Publications of the Astronomical Society of Japan. Volume 70:Number 4(2018:Aug.)
• Publication Date: 2018-05-25
• Subjects: stars: individual (24 Boötis, γ Libra) -- stars: planetary systems -- techniques: radial velocities; Astronomy -- Periodicals; 520.5
• DOI: 10.1093/pasj/psy052
• Languages: English
• ISSNs: 0004-6264

Abstract

Abstract: We report the detection of planets around two evolved giant stars from radial velocity measurements at Okayama Astrophysical observatory. 24 Boo (G3 IV) has a mass of $0.99\, M_{\odot }$, a radius of $10.64\, R_{\odot }$, and a metallicity of [Fe/H] = −0.77. The star hosts one planet with a minimum mass of 0.91 M Jup and an orbital period of 30.35 d. The planet has one of the shortest orbital periods among those ever found around evolved stars using radial-velocity methods. The stellar radial velocities show additional periodicity with 150 d, which can probably be attributed to stellar activity. The star is one of the lowest-metallicity stars orbited by planets currently known. γ Lib (K0 III) is also a metal-poor giant with a mass of $1.47\, M_{\odot }$, a radius of $11.1\, R_{\odot }$, and [Fe/H] = −0.30. The star hosts two planets with minimum masses of 1.02 M Jup and 4.58 M Jup, and periods of 415 d and 964 d, respectively. The star has the second-lowest metallicity among the giant stars hosting more than two planets. Dynamical stability analysis for the γ Lib system sets the minimum orbital inclination angle to be about 70° and suggests that the planets are in 7:3 mean-motion resonance, though the current best-fitting orbits for the radial-velocity data are not totally regular.