The Separation/Period Gap in the Distribution of Extrasolar Planets around Stars with MassesM≥ 1.2M⊙

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 agap in the radial distribution of planets, orbiting stars with masses M >= 1.2Msolar (the high-mass sample, HMS). No underabundance is found for planetsorbiting stars with smaller masses. The observational data also indicate thatwithin the HMS population it is preferentially the more massive planets with Msin(i) >= 0.8 M_J that are missing. Monte-Carlo simulations of planet formationand migration are presented that reproduce the observed shortage of planets inthe observed radius regime. A dependence on the disk depletion timescaletau_dep is found. The gap is more pronounced for tau_dep = 10^6 - 10^7 yrs thanfor tau_dep = 3*10^6 - 3*10^7 yrs. This might explain the observed trend withstellar mass if disks around stars with masses M* >= 1.2 Msolar have shorterdepletion timescales than those around less massive stars. Possible reasons forsuch a dependence are a decrease of disk size and an increase of stellar EUVflux with stellar mass.Comment: 12 pages, 2 figures, submitted to the Astrophysical Journa