Precise radial velocities of giant stars
IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a ~13.6 au eccentric binary system⋆,⋆⋆,⋆⋆⋆
1 Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
2 Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, 40000 Hong Kong, PR China
3 Physics Department, California Polytechnic State University, San Luis Obispo, CA 93407, USA
4 Institute for Astronomy, ETH Zurich, Wolfgang-Pauli-Strasse 27, 8093 Zurich, Switzerland
5 Steward Observatory, Department of Astronomy, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
6 Department of Astronomy, Yale University, New Haven, CT 06511, USA
7 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
8 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
9 Univ. Grenoble Alpes, IPAG, CNRS, IPAG, 38000 Grenoble, France
10 Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
11 Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
12 Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, PR China
Received: 25 April 2016
Accepted: 30 July 2016
Context. For over 12 yr, we have carried out a precise radial velocity (RV) survey of a sample of 373 G- and K-giant stars using the Hamilton Échelle Spectrograph at the Lick Observatory. There are, among others, a number of multiple planetary systems in our sample as well as several planetary candidates in stellar binaries.
Aims. We aim at detecting and characterizing substellar and stellar companions to the giant star HD 59686 A (HR 2877, HIP 36616).
Methods. We obtained high-precision RV measurements of the star HD 59686 A. By fitting a Keplerian model to the periodic changes in the RVs, we can assess the nature of companions in the system. To distinguish between RV variations that are due to non-radial pulsation or stellar spots, we used infrared RVs taken with the CRIRES spectrograph at the Very Large Telescope. Additionally, to characterize the system in more detail, we obtained high-resolution images with LMIRCam at the Large Binocular Telescope.
Results. We report the probable discovery of a giant planet with a mass of mp sin i = 6.92-0.24+0.18 MJup orbiting at ap = 1.0860-0.0007+0.0006 au from the giant star HD 59686 A. In addition to the planetary signal, we discovered an eccentric (eB = 0.729-0.003+0.004) binary companion with a mass of mB sin i = 0.5296-0.0008+0.0011 M⊙ orbiting at a close separation from the giant primary with a semi-major axis of aB = 13.56-0.14+0.18 au.
Conclusions. The existence of the planet HD 59686 Ab in a tight eccentric binary system severely challenges standard giant planet formation theories and requires substantial improvements to such theories in tight binaries. Otherwise, alternative planet formation scenarios such as second-generation planets or dynamical interactions in an early phase of the system’s lifetime need to be seriously considered to better understand the origin of this enigmatic planet.
Key words: planetary systems / planets and satellites: formation / planets and satellites: fundamental parameters / planets and satellites: gaseous planets / planets and satellites: detection / planets and satellites: general
RV data (Table A.1) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/595/A55
© ESO, 2016