  Recently Knutson et al. (2010) have demonstrated a correlation between the
presence of temperature inversions in the atmospheres of hot Jupiters, and the
chromospheric activity levels of the host stars. Here we show that there is
also a correlation, with greater than 99.5% confidence, between the surface
gravity of hot Jupiters and the activity levels of the host stars, such that
high surface gravity planets tend be found around high activity stars. We also
find a less significant positive correlation between planet mass and
chromospheric activity, but no significant correlation is seen between planet
radius and chromospheric activity. We consider the possibility that this may be
due to an observational bias against detecting lower mass planets around higher
activity stars, but conclude that this bias is only likely to affect the
detection of planets much smaller than those considered here. Finally, we
speculate on physical origins for the correlation, including the possibility
that the effect of stellar insolation on planetary radii has been significantly
underestimated, that strong UV flux evaporates planetary atmospheres, or that
high mass hot Jupiters induce activity in their host stars, but do not find any
of these hypotheses to be particularly compelling.
