We present evidence for a correlation between the observed properties of hot
Jupiter emission spectra and the activity levels of the host stars measured
using Ca II H & K emission lines. We find that planets with dayside emission
spectra that are well-described by standard 1D atmosphere models with water in
absorption (HD 189733, TrES-1, TrES-3, WASP-4) orbit chromospherically active
stars, while planets with emission spectra that are consistent with the
presence of a strong high-altitude temperature inversion and water in emission
orbit quieter stars. We estimate that active G and K stars have Lyman alpha
fluxes that are typically a factor of 4-7 times higher than quiet stars with
analogous spectral types, and propose that the increased UV flux received by
planets orbiting active stars destroys the compounds responsible for the
formation of the observed temperature inversions. In this paper we also derive
a model-independent method for differentiating between these two atmosphere
types using the secondary eclipse depths measured in the 3.6 and 4.5 micron
bands on the Spitzer Space Telescope, and argue that the observed correlation
is independent of the inverted/non-inverted paradigm for classifying hot
Jupiter atmospheres.Comment: 9 pages, 5 figures, accepted for publication in ApJ. The updated
paper includes spectra for ten additional systems and a new section
discussing the connection between chromospheric activity and UV flu
