A Correlation Between Stellar Activity and Hot Jupiter Emission Spectra

TL;DR

This study finds a correlation between stellar activity levels and hot Jupiter emission spectra, suggesting that increased UV flux from active stars influences atmospheric temperature inversions and water emission features.

Contribution

It introduces a new observational correlation linking stellar activity to hot Jupiter atmospheric properties and proposes a model-independent method to classify atmospheres based on Spitzer eclipse data.

Findings

Active stars have 4-7 times higher Lyman alpha flux than quiet stars.

Planets orbiting active stars show water in absorption, while those around quiet stars show water in emission.

The correlation is independent of the inverted/non-inverted atmosphere classification.

Abstract

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.