Giant planets at HD 220197 and HD 233832

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Giant planets at HD 220197 and HD 233832

Post by Sirius_Alpha on 19th November 2018, 11:47 pm

The GAPS Programme with HARPS-N at TNG XVIII. Two new giant planets around the metal-poor stars HD 220197 and HD 233832

Statistical studies of exoplanets have shown that giant planets are more commonly hosted by metal-rich dwarf stars than low-metallicity ones, while such a correlation is not 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. 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. High-precision HARPS-N observations of 42 metal-poor stars are used to search for planetary signals to be fitted using differential evolution MCMC single-Keplerian models. We then join our detections to the results of the previous HARPS survey on 88 metal-poor stars to provide a preliminar estimate of the two-hemisphere fp. We report the detection of two new giant planets around HD 220197 and HD 233832. The first companion has Msini=0.20+0.07−0.04 MJup and orbital period of 1728+162−80 days, and for the second companion we find two solutions of equal statistical weight having periods 2058+47−40 and 4047+91−117 days and minimum masses of 1.78+0.08−0.06 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 global frequency of fp=3.84+2.45−1.06% for giant planets around metal-poor stars. The two new giant planets orbit dwarf stars at the metal-rich end of the HARPS-N metal-poor sample, corroborating previous results suggesting that giant planet frequency still is a rising function of host star [Fe/H]. We also note that all detections in the overall sample are giant long-period planets.

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