1 Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
2 Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Portugal
3 INAF – Osservatorio Astronomico di Torino, strada dell’Osservatorio 20, 10025 Pino Torinese, Italy
4 Observatoire de Genve, Université de Genève, 51 Ch. des Maillettes, 1290 Sauverny, Switzerland
5 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
6 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
Received: 15 December 2011
Accepted: 11 May 2012
Context. The discovery of about 700 extrasolar planets, so far, has lead to the first statistics concerning extrasolar planets. The presence of giant planets seems to depend on stellar metallicity and mass. For example, they are more frequent around metal-rich stars, with an exponential increase in planet occurrence rates with metallicity.
Aims. We analyzed two samples of metal-poor stars (−2.0 ≤ [Fe/H] ≤ 0.0) to see if giant planets are indeed rare around these objects. Radial velocity datasets were obtained with two different spectrographs (HARPS and HIRES). Detection limits for these data, expressed in minimum planetary mass and period, are calculated. These produce trustworthy numbers for the planet frequency.
Methods. A general Lomb-Scargle (GLS) periodogram analysis was used together with a bootstrapping method to produce the detection limits. Planet frequencies were calculated based on a binomial distribution function within metallicity bins.
Results. Almost all hot Jupiters and most giant planets should have been found in these data. Hot Jupiters around metal-poor stars have a frequency lower than 1.0% at one sigma. Giant planets with periods up to 1800 days, however, have a higher frequency of fp = 2.63-0.8+2.5%. Taking into account the different metallicities of the stars, we show that giant planets appear to be very frequent (fp = 4.48-1.38+4.04%) around stars with [Fe/H] > − 0.7, while they are rare around stars with [Fe/H] ≤ − 0.7 ( ≤ 2.36% at one sigma).
Conclusions. Giant planet frequency is indeed a strong function of metallicity, even in the low-metallicity tail. However, the frequencies are most likely higher than previously thought.
Key words: techniques: radial velocities / planetary systems / planets and satellites: formation / stars: abundances / stars: statistics
The data presented herein are based on observations collected at the La Silla Parana Observatory, ESO (Chile) with the HARPS spectrograph at the 3.6-m telescope (ESO runs ID 72.C-0488, 082.C-0212, and 085.C-0063) and at the W. M. Keck Observatory that is operated as a scientific partnership among the California Institute of Technology, the University of California and the National Aeronautics and Space Administration. This Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Full Table 1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (220.127.116.11) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/543/A45
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2012