Extrasolar planets and brown dwarfs around AF-type stars

Abstract

Context. The impact of the stellar mass on the giant planet properties is still to be fully understood. Main-Sequence (MS) stars more massive than the Sun remain relatively unexplored in radial velocity (RV) surveys, due to their characteristics that hinder classical RV measurements. Aims. Our aim is to characterize the close (up to ∼2 au) giant planet (GP) and brown dwarf (BD) population around AF MS stars and compare this population to stars with different masses. Methods. We used the SOPHIE spectrograph located on the 1.93m telescope at Observatoire de Haute-Provence to observe 125 northern, MS AF dwarfs. We used our dedicated SAFIR software to compute the RV and other spectroscopic observables. We characterized the detected substellar companions and computed the GP and BD occurrence rates combining the present SOPHIE survey and a similar HARPS survey. Results. We present new data on two known planetary systems around the F5-6V dwarfs HD 16232 and HD 113337. For the latter, we report an additional RV variation that might be induced by a second GP on a wider orbit. We also report the detection of fifteen binaries or massive substellar companions with high-amplitude RV variations or long-term RV trends. Based on 225 targets observed with SOPHIE and/or HARPS, we constraint the BD frequency within 2-3 au around AF stars to be below 4% (1σ). For Jupiter-mass GP within 2-3 au (periods ≤ 10 3 days), we found the occurrence rate to be 3.7 +3 −1 % around AF stars with masses < 1.5 M , and to be ≤ 6% (1σ) around AF stars with masses > 1.5 M . For periods smaller than 10 days, we find the GP occurrence rate to be below 3 or 4.5% (1σ), respectively. Our results are compatible with the GP frequency reported around FGK dwarfs and are compatible with a possible increase of GP orbital periods with the stellar mass as predicted by formation models. Description of the SOPHIE survey SampleOur SOPHIE sample is made of 125 AF MS dwarf stars with spectral types in the range A0V to F9V. We detail the physical properties of our sample in Appendix A. We selected our targets using the same selection process as for our HARPS survey (see more details in Lagrange et al., 2009, Paper IX and Appendix B). Briefly, our selection relies on the following criteria: i) the spectral type; ii) the distance to the Sun, and iii) the exclusion of known SB2 binary, chemically peculiar stars, or confirmed δ Scuti or γ Doradus pulsators. We ended up with 125 targets with B − V in the range -0.02 to 0.56, v sin i in the range 3 to 250 km.s −1 , and masses in the range 1 to 2.5 M (Fig. 1). Note that the exclusion of known pulsators results in a visible dichotomy between our ∼Aand ∼F-type targets. ObservationsWe observed our 125 SOPHIE targets mainly between November 2006 and April 2014. We made some additional observations later (2015)(2016) to complete our survey for the targets with the less data and to further monitor the most interesting targets. We acquired the SOPHIE spectra in high-resolution mode (R ∼75000), in the 3872-6943 Å wavelength range. As...

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