Abstract

Context. Massive, main-sequence (MS) AF-type stars have so far remained unexplored in past radial velocities (RV) surveys due to their small number of spectral lines and high rotational velocities that prevent the classic RV computation method.
Aims: Our aim is to search for giant planets (GPs) around AF MS stars, to get primary statistical information on their occurrence rate and to compare the results with evolved stars and lower-mass MS stars.
Methods: We used the HARPS spectrograph located on the 3.6 m telescope at ESO La Silla Observatory to observe 108 AF MS stars with B-V in the range -0.04 to 0.58 and masses in the range 1.1 to 3.6 M_⊙. We used our SAFIR software developed to compute the RV and other spectroscopic observables of these early-type stars. We characterized the detected companions as well as the intrinsic stellar variability. We computed the detection limits and used them as well as the detected companions to derive the first estimates of the close-in brown dwarf (BD) and GP frequencies around AF stars.
Results: We report the detection of a m_psini = 4.51M_Jup planetary companion with an 826-day period to the F6V dwarf HD 111998. We also present new data on the two-planet system around the F6IV-V dwarf HD 60532. We also report the detections of 14 binaries with long-term RV trends and/or high-amplitude RV variations combined to a flat RV-bisector span diagram. We constrain the minimal masses and semi-major axes of these companions and check that these constraints are compatible with the stellar companions previously detected by direct imaging or astrometry for six of these targets. We get detection limits deep into the planetary domain with 70% of our targets showing detection limits between 0.1 and 10 M_Jup at all orbital periods in the 1- to 10³-day range. We derive BD (13 ≤m_psini ≤ 80 M_Jup) occurrence rates in the 1- to 10³-day period range of 2_-2⁺⁵% and 2.6_-2.6^+6.7% for stars with M_⋆ in the ranges 1.1 to 1.5 and 1.5 to 3 M_⊙, respectively. As for Jupiter-mass companions (1 ≤ m_psini≤ 13 M_Jup), we get occurrence rates in the 1- to 10³-day period range of 4_-0.9^+5.9% and 6.3_-6.3^+15.9% respectively for the same M_⋆ ranges. When considering the same Jupiter-mass companions but periods in the 1- to 100-day range only, we get occurrence rates of 2_-2^+5.2% and 3.9_-3.9^+9.9%. Given the present error bars, these results do not show a significant difference from companion frequencies derived in the same domains for solar-like MS stars.

Based on observations collected at the European southern Observatory, Chile, ESO 072.C-0636, 073.C-0733, 075.C-0689, 076.C-0279, 077.C-0295, 078.C-0209, 080.C-0664, 080.C-0712., 081.C-0774, 082.C-0412, 083.C-0794, 084.C-1039, 184.C-0815, 192.C-0224.RV and other observable data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/599/A57