A new estimate of the frequency of giant planets around metal-poor stars with HARPS-N

Monday 2 July, 10:15

The study of exoplanetary frequency in relation to the physical properties of their host stars has so far revealed interesting correlations such as the one between occurrence rate of giant planets and stellar metallicity ([Fe/H]). Giant planets are more common around metal-rich stars, their frequency rising from 2.36% around metal-poor stars to 5% around solar-metallicity stars and to 25% around stars having twice the metallicity of the Sun. Recent work also show that stars hosting hot Jupiters have higher metallicities than stars orbited by long-period giant planets. Further study on the relation between star metallicity and giant planet occurrence rate, and especially the search for the metallicity limit under which no giant planets are formed, is key in helping discriminate between competing planetary formation models.
We present the results of HARPS-N observations on metal-poor stars within the Large Programme GAPS to search for new giant planetary companions. We report the detection of two long-period giant planetary companions around primaries with [Fe/H] around four and seven times lower than that of the Sun. Our results are input for the numerical study of the global survey detection limits and for new assessment of the frequency of gas giants around low-metallicity stars.
The new giant planets found are good candidates for further observation and characterization by astrometric measurements such as those provided by Gaia, and the updated estimate on planetary frequencies can usefully inform and help coordinating new observational efforts.

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