1 Department of Electrical Engineering and Center of Astro-Engineering UC, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago Chile
2 Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Casilla 36-D Las Condes, Santiago, Chile
3 Departamento de Astronomía, Universidad de Concepción, Casilla 160- C Concepción, Chile
4 Department of Astronomy, Cornell University, 610 Space Sciences Building, Ithaca NY14853-6801, USA
5 European Southern Observatory, Casilla 19001 Santiago, Chile
Received: 27 December 2013
Accepted: 22 April 2014
Context. More than 50 exoplanets have been found around giant stars, revealing different properties when compared to planets orbiting solar-type stars. In particular, they are super-Jupiters and are not found orbiting interior to ~0.5 AU.
Aims. We are conducting a radial velocity study of a sample of 166 giant stars aimed at studying the population of close-in planets orbiting giant stars and how their orbital and physical properties are influenced by the post-MS evolution of the host star.
Methods. We have collected multiepoch spectra for all of the targets in our sample. We have computed precision radial velocities from FECH/CHIRON and FEROS spectra, using the I2 cell technique and the simultaneous calibration method, respectively.
Results. We present the discovery of a massive planet around the giant star HIP 105854. The best Keplerian fit to the data leads to an orbital distance of 0.81 ± 0.03 AU, an eccentricity of 0.02 ± 0.03 and a projected mass of 8.2 ± 0.2 MJ. With the addition of this new planet discovery, we performed a detailed analysis of the orbital properties and mass distribution of the planets orbiting giant stars. We show that there is an overabundance of planets around giant stars with a ~ 0.5 − 0.9 AU, which might be attributed to tidal decay. Additionally, these planets are significantly more massive than those around MS and subgiant stars, suggesting that they grow via accretion either from the stellar wind or by mass transfer from the host star. Finally, we show that planets around evolved stars have lower orbital eccentricities than those orbiting solar-type stars, which suggests that they are either formed in different conditions or that their orbits are efficiently circularized by interactions with the host star.
Key words: planetary systems / techniques: radial velocities / stars: evolution
Based on observations collected at La Silla – Paranal Observatory under programs IDs 085.C-0557, 087.C.0476, 089.C-0524 and 090.C-0345.
The RV Table is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (188.8.131.52) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/566/A113
© ESO, 2014