The GAPS Programme with HARPS-N at TNG. XVIII. Two new giant planets around the metal-poor stars HD 220197 and HD 233832
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.
Astronomy and Astrophysics
- Pub Date:
- January 2019
- techniques: radial velocities;
- methods: data analysis;
- planetary systems;
- stars: abundances;
- stars: individual: HD 220197;
- stars: individual: HD 233832;
- Astrophysics - Earth and Planetary Astrophysics
- 15 pages, 8 figures, 5 tables, accepted for publication in A&