HST hot-Jupiter transmission spectral survey: Haze in the atmosphere of WASP-6b

TL;DR

This study presents HST and Spitzer transmission spectra of WASP-6b, revealing atmospheric haze characterized by Rayleigh scattering and aerosol opacity, with implications for understanding hot Jupiter atmospheres near 1200 K.

Contribution

First detailed optical to near-infrared transmission spectrum of WASP-6b showing haze and aerosol effects, advancing atmospheric characterization of hot Jupiters.

Findings

Spectrum shows increasing radius with decreasing wavelength, indicating Rayleigh scattering.

Models with aerosols fit the data better than clear-atmosphere models.

WASP-6b exhibits atmospheric scattering similar to HD189733b at similar temperatures.

Abstract

We report Hubble Space Telescope (HST) optical to near-infrared transmission spectroscopy of the hot Jupiter WASP-6b, measured with the Space Telescope Imaging Spectrograph (STIS) and Spitzer's InfraRed Array Camera (IRAC). The resulting spectrum covers the range $0.29-4.5\,\mu$m. We find evidence for modest stellar activity of WASP-6b and take it into account in the transmission spectrum. The overall main characteristic of the spectrum is an increasing radius as a function of decreasing wavelength corresponding to a change of $\Delta (R_p/R_{\ast})=0.0071$ from 0.33 to $4.5\,\mu$m. The spectrum suggests an effective extinction cross-section with a power law of index consistent with Rayleigh scattering, with temperatures of $973\pm144$ K at the planetary terminator. We compare the transmission spectrum with hot-Jupiter atmospheric models including condensate-free and aerosol-dominated models incorporating Mie theory. While none of the clear-atmosphere models is found to be in good agreement with the data, we find that the complete spectrum can be described by models that include significant opacity from aerosols including Fe-poor Mg$_2$SiO$_4$, MgSiO$_3$, KCl and Na$_2$S dust condensates. WASP-6b is the second planet after HD189733b which has equilibrium temperatures near $\sim1200$ K and shows prominent atmospheric scattering in the optical.