2019/10/16 by Yayaati Chachan, Heather A. Knutson, Peter Gao +16 · 55 citations
Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Astro and Planetary Science #Astrophysics and Star Formation Studies #Hubble space telescope #Metallicity #Molecular absorption #Neptune #Spectral line #Stellar, planetary, and galactic studies #Transmission (telecommunications) #Wavelength #astro-ph.EP
paper · pdf · open access · doi:10.3847/1538-3881/ab4e9a
published in The Astronomical Journal 158(6), 244 (Institute of Physics) · Accepted for publication in AJ. 33 pages, 23 figures
arxiv created 2019/10/16 · openalex created_date 2019/10/25 · openalex publication_date 2019/11/22 · arxiv updated 2019/12/02 · openalex updated_date 2026/08/05
We present the first comprehensive look at the 0.35-5 μm transmission spectrum of the warm (∼ 800 K) Neptune HAT-P-11b derived from thirteen individual transits observed using the Hubble and Spitzer Space Telescopes. Along with the previously published molecular absorption feature in the 1.1-1.7 μm bandpass, we detect a distinct absorption feature at 1.15 μm and a weak feature at 0.95 μm, indicating the presence of water and/or methane with a combined significance of 4.4 σ. We find that this planet's nearly 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 μm HST transmission spectrum yield strong constraints on atmospheric cloud-top pressure and metallicity, but we are unable to match the relatively shallow Spitzer transit depths without under-predicting the strength of the near-infrared molecular absorption bands. HAT-P-11b's HST transmission spectrum is well-matched by predictions from our microphysical cloud models. Both forward models and retrievals indicate that HAT-P-11b most likely has a relatively low atmospheric metallicity (<4.6 Z\odot and <86 Z\odot at the 2 σ and 3 σ levels respectively), 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 HST STIS data is critical for making these inferences.