Planets Around The Evolved Stars 24 Bootis And Gamma Libra: A 30 D-Period Planet And A Double Giant-Planet System In Possible 7:3 Mmr

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-circle dot, a radius of 10.64 R-circle dot, 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. gamma Lib (K0 III) is also a metal-poor giant with a mass of 1.47 M-circle dot, a radius of 11.1 R-circle dot, 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 gamma Lib system sets the minimum orbital inclination angle to be about 70 degrees 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.