A mass function constraint on extrasolar giant planet evaporation rates

The observed mass function for all known extrasolar giant planets (EGPs) varies approximately as M-1 for mass M between similar to 0.2 Jupiter masses (M-J) and similar to 5 M-J. In order to study evaporation effects for highly irradiated EGPs in this mass range, we have constructed an observational mass function for a subset of EGPs in the same mass range but with orbital radii <0.07 AU. Surprisingly, the mass function for such highly irradiated EGPs agrees quantitatively with the M-1 law, implying that the mass function for EGPs is preserved despite migration to small orbital radii. Unless there is a remarkable compensation of mass- dependent orbital migration for massdependent evaporation, this result places a constraint on orbital migration models and rules out the most extreme mass-loss rates in the literature. A theory that predicts more moderate mass loss gives a mass function that is closer to observed statistics but still disagrees for M < 1 M-J.