Three planets around HD 27894
A close-in pair with a 2:1 period ratio and an eccentric Jovian planet at 5.4 AU⋆
1 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117, Heidelberg, Germany
2 Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
3 Main Astronomical Observatory, National Academy of Sciences of the Ukraine, Ukraine
4 Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
5 Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong
6 Department of Physics, The University of Hong Kong, Pokfulman Road, Hong Kong
7 European Southern Observatory (ESO), Alonso de Cordova 3107, Vitacura, Santiago de Chile, Chile
8 UCO/Lick Observatory, University of California, Santa Cruz, CA, 95064, USA
Received: 25 April 2017
Accepted: 30 May 2017
Aims. Our new program with HARPS aims to detect mean motion resonant planetary systems around stars which were previously reported to have a single bona fide planet, often based only on sparse radial velocity data.
Methods. Archival and new HARPS radial velocities for the K2V star HD 27894 were combined and fitted with a three-planet self-consistent dynamical model. The best-fit orbit was tested for long-term stability.
Results. We find clear evidence that HD 27894 is hosting at least three massive planets. In addition to the already known Jovian planet with a period Pb≈ 18 days we discover a Saturn-mass planet with Pc≈ 36 days, likely in a 2:1 mean motion resonance with the first planet, and a cold massive planet (≈5.3 MJup) with a period Pd ≈ 5170 days on a moderately eccentric orbit (ed = 0.39).
Conclusions. HD 27894 is hosting a massive, eccentric giant planet orbiting around a tightly packed inner pair of massive planets likely involved in an asymmetric 2:1 mean motion resonance. HD 27894 may be an important milestone for probing planetary formation and evolution scenarios.
Key words: techniques: radial velocities / planetary systems / planets and satellites: dynamical evolution and stability
© ESO, 2017