摘要：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 occurrencefpis 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 offp.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-hemispherefp.Results.We report the detection of two new giant planets around HD 220197 and HD 233832. The first companion has Msini= 0.20−0.04+0.07MJupand an orbital period of 1728−80+162days, and for the second companion, we find two solutions of equal statistical weight with periods of 2058−40+47and 4047−117+91days and minimum masses of 1.78−0.06+0.08and 2.72−0.23+0.23MJup, respectively. Joining our two detections with the three from the southern survey, we obtain a preliminary and conservative estimate of the global frequency offp= 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.
关键词：Key wordsentechniques: radial velocitiesmethods: data analysisplanetary systemsstars: abundancesstars: individual: HD 220197stars: individual: HD 233832
