# Dix Planetary Science Seminar

Tuesday, June 11, 2019
4:00pm to 5:00pm
Abstract 1: We present the first comprehensive look at the $0.35-5$ $\mu$m transmission spectrum of the warm ($\sim 800$ K) Neptune HAT-P-11b derived from thirteen individual transits observed using the \emph{Hubble} and \emph{Spitzer Space Telescopes}. Along with the previously published molecular absorption feature in the $1.1-1.7$~$\mu$m bandpass, we detect a distinct absorption feature at 1.15~$\mu$m and a weak feature at 0.95~$\mu$m, indicating the presence of water and/or methane with a combined significance of 4.4 $\sigma$. We find that this planet's flat optical transmission spectrum and attenuated near-infrared molecular absorption features are best-matched by models incorporating a high altitude cloud layer. Atmospheric retrievals using the combined $0.35-1.7$~$\mu$m \emph{HST} transmission spectrum yield strong constraints on atmospheric cloud-top pressure and metallicity, but we are unable to match the relatively shallow \emph{Spitzer} transit depths without under-predicting the strength of the near-infrared molecular absorption bands. HAT-P-11b's \emph{HST} transmission spectrum is well-matched by predictions from our microphysical cloud models when sulphide condensates are removed, and that the physical properties of the condensates in these models are in good agreement with constraints obtained from retrievals using the Mie scattering formalism. Both forward models and retrievals indicate that HAT-P-11b most likely has a relatively low atmospheric metallicity ($<55 \; Z_{\odot}$ or $<28 \; Z_*$ with 95\% confidence), in contrast to the expected trend based on the solar system planets. Our work also demonstrates that the wide wavelength coverage provided by the addition of the \emph{HST} STIS data is critical for making these inferences.