Planetary companions around the metal-poor star HIP 11952

J. Setiawan¹, V. Roccatagliata^2,1, D. Fedele³, Th. Henning¹, A. Pasquali⁴, M. V. Rodríguez-Ledesma^1,5, E. Caffau⁴, U. Seemann^5,6 and R. J. Klement^7,1

¹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
e-mail: setiawan@mpia.de
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
⁴ Astronomisches Rechen-Institut, Zentrum für Astronomie, Mönchhofstrasse, 12-14, 69120 Heidelberg, Germany
⁵ Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany
⁶ European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching bei München, Germany
⁷ University of Würzburg, Department of Radiation Oncology, 97080 Würzburg, Germany

Received: 4 August 2011
Accepted: 27 February 2012

Abstract

Aims. We carried out a radial-velocity survey to search for planets around metal-poor stars. In this paper we report the discovery of two planets around HIP 11952, a metal-poor star with  [Fe/H]  =  −1.9 that belongs to our target sample.

Methods. Radial velocity variations of HIP 11952 were monitored systematically with FEROS at the 2.2 m telescope located at the ESO La Silla observatory from August 2009 until January 2011. We used a cross-correlation technique to measure the stellar radial velocities (RV).

Results. We detected a long-period RV variation of 290 d and a short-period one of 6.95 d. The spectroscopic analysis of the stellar activity reveals a stellar rotation period of 4.8 d. The Hipparcos photometry data shows intra-day variabilities, which give evidence for stellar pulsations. Based on our analysis, the observed RV variations are most likely caused by the presence of unseen planetary companions. Assuming a primary mass of 0.83 M_⊙, we computed minimum planetary masses of 0.78 M_Jup for the inner and 2.93 M_Jup for the outer planet. The semi-major axes are a₁ = 0.07 AU and a₂ = 0.81 AU, respectively.

Conclusions. HIP 11952 is one of very few stars with  [Fe/H]  < −1.0 which have planetary companions. This discovery is important to understand planet formation around metal-poor stars.