A. Sozzetti, K. Biazzo, L. Malavolta, N. C. Santos, M. Damasso, A. F. Lanza, L. Affer, S. Benatti, A. Bignamini, A. S. Bonomo, F. Borsa, I. Carleo, R. Claudi, R. Cosentino, E. Covino, S. Desidera, M. Esposito, P. Giacobbe, E. GonzŠlez-Ńlvarez, R. Gratton, H. Avet, G. Leto, A. Maggio, J. Maldonado, L. Mancini, S. Masiero, G. Micela, E. Molinari, V. Nascimbeni, I. Pagano, G. Piotto, E. Poretti, M. Rainer, G. Scandariato, R. Smareglia, L. Di Fabrizio, J. P. S. Faria, A. F. Martinez Fiorenziano, M. Molinaro, M. Pedani
Context. Statistical studies of exoplanets have shown that giant planets are more commonly hosted by metal-rich dwarf stars than low-metallicity stars, while no such correlation is evident for lower mass planets. The search for giant planets around metal-poor stars and the estimate of their occurrence fp is an important element in providing support to models of planet formation.
Aims. We present results from the HARPS-N search for giant planets orbiting metal-poor (− 1.0 ≤[Fe/H] ≤−0.5 dex) stars in the northern hemisphere, complementing a previous HARPS survey on southern stars in order to update the estimate of fp.
Methods. High-precision HARPS-N observations of 42 metal-poor stars were used to search for planetary signals to be fitted using differential evolution Markov chain Monte Carlo single-Keplerian models. We then joined our detections to the results of the previous HARPS survey on 88 metal-poor stars to provide a preliminary estimate of the two-hemisphere fp.
Results. We report the detection of two new giant planets around HD 220197 and HD 233832. The first companion has Msin i = 0.20−0.04+0.07 MJup and an orbital period of 1728−80+162 days, and for the second companion, we find two solutions of equal statistical weight with periods of 2058−40+47 and 4047−117+91 days and minimum masses of 1.78−0.06+0.08 and 2.72−0.23+0.23 MJup, respectively. Joining our two detections with the three from the southern survey, we obtain a preliminary and conservative estimate of the global frequency of fp = 3.84 −1.06+2.45% for giant planets around metal-poor stars.
Conclusions. The two new giant planets orbit dwarf stars at the metal-rich end of the HARPS-N metal-poor sample. This corroborates previous results that suggested that giant planet frequency is still a rising function of the host star [Fe/H]. We also note that all detections in the overall sample are giant long-period planets.
techniques: radial velocities; methods: data analysis; planetary systems; stars: abundances; stars: individual: HD 220197; stars: individual: HD 233832
Astronomy and Astrophysics
Volume 621, Article Number A110, Number of pages 12