The separation/period gap in the distribution of extrasolar planets around stars with masses M ≥ 1.2 M⊙

The evidence for a shortage of exosolar planets with semimajor axes -1.1 <= log (a/AU) <= -0.2 is investigated. It is shown that this valley results from a gap in the radial distribution of planets orbiting stars with masses M-* >= 1.2M(circle dot) (the high-mass sample, HMS). No underabundance is found for planets orbiting stars with smaller masses. The observational data also indicate that within the HMS population, it is preferentially the more massive planets with M sin (i) >= 0.8 M-J that are missing. Monte Carlo simulations of planet formation and migration are presented that reproduce the observed shortage of planets in the observed radius regime. A dependence on the disk depletion timescale tau dep is found. The gap is more pronounced for tau(dep) -10(6)-10(7) yr than for tau(dep) -3 x 10(6)-3 x 10(7) yr. This might explain the observed trend with stellar mass if disks around stars with masses M-* >= 1.2 M-circle dot have shorter depletion timescales than those around less massive stars. Possible reasons for such a dependence are a decrease of disk size and an increase of stellar EUV flux with stellar mass.