A consistent retrieval analysis of 10 Hot Jupiters observed in transmission

A consistent retrieval analysis of 10 Hot Jupiters observed in transmission

Authors:

Barstow et al

Abstract:

We present a consistent optimal estimation retrieval analysis of ten hot Jupiter exoplanets, each with transmission spectral data spanning the visible to near-infrared wavelength range. Using the NEMESIS radiative transfer and retrieval tool, we calculate a range of possible atmospheric states for WASP-6b, WASP-12b, WASP-17b, WASP-19b, WASP-31b, WASP-39b, HD 189733b, HD 209458b, HAT-P-1b and HAT-P-12b. We find that the spectra of all ten planets are consistent with the presence of some atmospheric aerosol; WASP-6b, WASP-12b, WASP-17b, WASP-19b, HD 189733b and HAT-P-12b are all fit best by Rayleigh scattering aerosols, whereas WASP-31b, WASP-39b and HD 209458b are better represented by a grey cloud model. HAT-P-1b has solutions that fall into both categories. WASP-6b, HAT-P-12b, HD 189733b and WASP-12b must have aerosol extending to low atmospheric pressures (below 0.1 mbar). In general, planets with equilibrium temperatures between 1300 and 1700 K are best represented by deeper, grey cloud layers, whereas cooler or hotter planets are better fit using high Rayleigh scattering aerosol. We find little evidence for the presence of molecular absorbers other than H2O. Retrieval methods can provide a consistent picture across a range of hot Jupiter atmospheres with existing data, and will be a powerful tool for the interpretation of James Webb Space Telescope observations.

Hot Jupiter WASP-31b may Have Cloud Deck, Potassium and Exhibit Raleigh Scattering

HST hot-Jupiter transmission spectral survey: detection of potassium in WASP-31b along with a cloud deck and Rayleigh scattering

Authors:

Sing et al

Abstract:

We present Hubble Space Telescope optical and near-IR transmission spectra of the transiting hot-Jupiter WASP-31b. The spectrum covers 0.3-1.7 μm at a resolution R∼70, which we combine with Spitzer photometry to cover the full-optical to IR. The spectrum is dominated by a cloud-deck with a flat transmission spectrum which is apparent at wavelengths >0.52μm. The cloud deck is present at high altitudes and low pressures, as it covers the majority of the expected optical Na line and near-IR H2O features. While Na I absorption is not clearly identified, the resulting spectrum does show a very strong potassium feature detected at the 4.2-σ confidence level. Broadened alkali wings are not detected, indicating pressures below ∼10 mbar. The lack of Na and strong K is the first indication of a sub-solar Na/K abundance ratio in a planetary atmosphere (ln[Na/K]=−3.3±2.8), which could potentially be explained by Na condensation on the planet's night side, or primordial abundance variations. A strong Rayleigh scattering signature is detected at short wavelengths, with a 4-σ significant slope. Two distinct aerosol size populations can explain the spectra, with a smaller sub-micron size grain population reaching high altitudes producing a blue Rayleigh scattering signature on top of a larger, lower-lying population responsible for the flat cloud deck at longer wavelengths. We estimate that the atmospheric circulation is sufficiently strong to mix micron size particles upward to the required 1-10 mbar pressures, necessary to explain the cloud deck. These results further confirm the importance of clouds in hot-Jupiters, which can potentially dominate the overall spectra and may alter the abundances of key gaseous species.