Breakthrough direct detections of planetary companions orbiting A-type stars confirm the existence of massive planets at relatively large separations , but dedicated surveys are required to estimate the frequency of similar planetary systems .
To measure the first estimation of the giant exoplanetary systems frequency at large orbital separation around A-stars , we have conducted a deep-imaging survey of young ( 8–400 Myr ) , nearby ( 19–84 pc ) A- and F-stars to search for substellar companions in the \sim 10–300 AU range .
The sample of 42 stars combines all A-stars observed in previous AO planet search surveys reported in the literature with new AO observations from VLT/NaCo and Gemini/NIRI .
It represents an initial subset of the International Deep Planet Survey ( IDPS ) sample of stars covering M- to B-stars .
The data were obtained with diffraction-limited observations in H - and K _ { \mathrm { s } } -band combined with angular differential imaging to suppress the speckle noise of the central stars , resulting in typical 5 \sigma detection limits in magnitude difference of 12 mag at 1 ^ { \prime \prime } , 14 mag at 2 ^ { \prime \prime } and 16 mag at 5 ^ { \prime \prime } which is sufficient to detect massive planets .
A detailed statistical analysis of the survey results is performed using Monte Carlo simulations .
Considering the planet detections , we estimate the fraction of A-stars having at least one massive planet ( 3–14 M _ { \mathrm { Jup } } ) in the range 5–320 AU to be inside 5.9–18.8 % at 68 % confidence , assuming a flat distribution for the mass of the planets .
By comparison , the brown dwarf ( 15–75 M _ { \mathrm { Jup } } ) frequency for the sample is 2.0–8.9 % at 68 % confidence in the range 5–320 AU .
Assuming power law distributions for the mass and semimajor axis of the planet population , the AO data are consistent with a declining number of massive planets with increasing orbital radius which is distinct from the rising slope inferred from radial velocity ( RV ) surveys around evolved A-stars and suggests that the peak of the massive planet population around A-stars may occur at separations between the ranges probed by existing RV and AO observations .
Finally , we report the discovery of three new close M-star companions to HIP 104365 and HIP 42334 .