Abstract

The emergent spectra of close-in, giant exoplanets ("hot Jupiters") are expected to be distinct from those of self-luminous objects with similar effective temperatures because hot Jupiters are primarily heated from above by their host stars rather than internally from the release of energy from their formation. Theoretical models predict a continuum of dayside spectra for hot Jupiters as a function of irradiation level, with the coolest planets having absorption features in their spectra, intermediate-temperature planets having emission features due to thermal inversions, and the hottest planets having blackbody-like spectra due to molecular dissociation and continuum opacity from the H- ion. Absorption and emission features have been detected in the spectra of a number of individual hot Jupiters, and population-level trends have been observed in photometric measurements. However, there has been no unified, population-level study of the thermal emission spectra of hot Jupiters such as has been done for cooler brown dwarfs and transmission spectra of hot Jupiters. Here we show that hot Jupiter secondary eclipse spectra centered around a water absorption band at 1.4 microns follow a common trend in water feature strength with temperature. The observed trend is broadly consistent with model predictions for how the thermal structures of solar-composition planets vary with irradiation level. Nevertheless, the ensemble of planets exhibits some degree of scatter around the mean trend for solar composition planets. The spread can be accounted for if the planets have modest variations in metallicity and/or elemental abundance ratios, which is expected from planet formation models. (abridged abstract)

Highlights

  • We performed a statistical analysis of 19 hot Jupiter secondary eclipse spectra obtained with the Wide Field Camera 3 (WFC3) instrument on the Hubble Space Telescope (HST) using the G141 grism between 1.1 and 1.7 μm

  • Melville et al (2020)[23] examined the spectra of a different subset of 12 hot Jupiters but only analyzed them in the context of models with fixed temperature-pressure (T-P) profiles, with no feedback between the T-P profile and the chemistry. We expand on these studies by doubling the sample of hot Jupiter secondary eclipse spectra and comparing the spectra to a grid of models with fully consistent T-P profiles to understand in detail what drives their feature strengths

  • The exact temperatures of the transitions between these regimes, as well as the strength of absorption and emission features present in the models, depend on the parameters of each set of models. For both the models and the population of 19 observed hot Jupiters, we examined the degree of absorption or emission observed in the water feature at 1.4 μm, the primary feature in the HST/WFC3+G141 bandpass

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Summary

Introduction

We performed a statistical analysis of 19 hot Jupiter secondary eclipse spectra obtained with the Wide Field Camera 3 (WFC3) instrument on the Hubble Space Telescope (HST) using the G141 grism between 1.1 and 1.7 μm.

Results
Conclusion

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