Abstract
Context.The search of close (a≲ 5 au) giant planet (GP) companions with radial velocity (RV) around young stars and the estimate of their occurrence rates is important to constrain the migration timescales. Furthermore, this search will allow the giant planet occurrence rates to be computed at all separations via the combination with direct imaging techniques. The RV search around young stars is a challenge as they are generally faster rotators than older stars of similar spectral types and they exhibit signatures of magnetic activity (spots) or pulsation in their RV time series. Specific analyses are necessary to characterize, and possibly correct for, this activity.Aims.Our aim is to search for planets around young nearby stars and to estimate the GP occurrence rates for periods up to 1000 days.Methods.We used the SOPHIEspectrograph on the 1.93 m telescope at the Haute-Provence Observatory to observe 63 A−Myoung (<400 Myr) stars. We used our Spectroscopic data via Analysis of the Fourier Interspectrum Radial velocities software to compute the RVs and other spectroscopic observables. We then combined this survey with the HARPSYNS survey to compute the companion occurrence rates on a total of 120 youngA−Mstars.Results.We report one new trend compatible with a planetary companion on HD 109647. We also report HD 105693 and HD 112097 as binaries, and we confirm the binarity of HD 2454, HD 13531, HD 17250 A, HD 28945, HD 39587, HD 131156, HD 142229, HD 186704 A, and HD 195943. We constrained for the first time the orbital parameters of HD 195943 B. We refute the HD 13507 single brown dwarf (BD) companion solution and propose a double BD companion solution. Two GPs were previously reported from this survey in the HD 113337 system. Based on our sample of 120 young stars, we obtain a GP occurrence rate of 1−0.3+2.2% for periods lower than 1000 days, and we obtain an upper limit on BD occurrence rate of 0.9−0.9+2% in the same period range. We report a possible lack of close (P∈ [1;1000] days) GPs around young FK stars compared to their older counterparts, with a confidence level of 90%.
Highlights
More than four thousand exoplanets and brown dwarfs (BDs) have been detected and most of them have been found by transit or radial velocity (RV) techniques1
We used the method presented in Grandjean et al (2020) to correct the RVs of the SOPHIE stars from their jitter and from their companion signal: for the stars for which the RVs are dominated by spots, we corrected the RVs from the (BVS, RV) correlation using the Melo et al (2007) method
If the p-value of our non-detection of hot Jupiters (HJs) around young stars is below 10% for a given occurrence rate on main sequence (MS) stars found in the literature, it indicates that the occurrence rate might be different between young and MS stars with a confidence level of 90%
Summary
More than four thousand exoplanets and brown dwarfs (BDs) have been detected and most of them have been found by transit or radial velocity (RV) techniques. There is a positive correlation with host star mass This correlation was observed for evolved stars in RV (Bowler et al 2009; Johnson et al 2010; Jones et al 2016) and for wide orbit planets around young stars in direct imaging (Lannier et al 2016; Baron et al 2019). These observations are consistent with the predictions of core accretion models (Kennedy & Kenyon 2008).
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