HST PanCET program : a complete near-UV to infrared transmission spectrum for the Hot Jupiter WASP-79b
Abstract
We present a new optical transmission spectrum of the hot Jupiter WASP-79b. We observed three transits with the STIS instrument mounted on the Hubble Space Telescope (HST), spanning 0.3–1.0 μm. Combining these transits with previous observations, we construct a complete 0.3–5.0 μm transmission spectrum of WASP-79b. Both HST and ground-based observations show decreasing transit depths toward blue wavelengths, contrary to expectations from Rayleigh scattering or hazes. We infer atmospheric and stellar properties from the full near-UV to infrared transmission spectrum of WASP-79b using three independent retrieval codes, all of which yield consistent results. Our retrievals confirm previous detections of H2O (at 4.0σ confidence) while providing moderate evidence of H− bound–free opacity (3.3σ) and strong evidence of stellar contamination from unocculted faculae (4.7σ). The retrieved H2O abundance (∼1%) suggests a superstellar atmospheric metallicity, though stellar or substellar abundances remain consistent with present observations (O/H = 0.3–34× stellar). All three retrieval codes obtain a precise H− abundance constraint: log() ≈ −8.0 ± 0.7. The potential presence of H− suggests that James Webb Space Telescope observations may be sensitive to ionic chemistry in the atmosphere of WASP-79b. The inferred faculae are ∼500 K hotter than the stellar photosphere, covering ∼15% of the stellar surface. Our analysis underscores the importance of observing UV–optical transmission spectra in order to disentangle the influence of unocculted stellar heterogeneities from planetary transmission spectra.
Citation
Rathcke , A D , MacDonald , R J , Barstow , J K , Goyal , J M , Lopez-Morales , M , Mendonca , J M , Sanz-Forcada , J , Henry , G W , Sing , D K , Alam , M K , Lewis , N K , Chubb , K L , Taylor , J , Nikolov , N & Buchhave , L A 2021 , ' HST PanCET program : a complete near-UV to infrared transmission spectrum for the Hot Jupiter WASP-79b ' , Astronomical Journal , vol. 162 , no. 4 , 138 . https://doi.org/10.3847/1538-3881/ac0e99
Publication
Astronomical Journal
Status
Peer reviewed
ISSN
0004-6256Type
Journal article
Description
Funding: G.W.H. acknowledges long-term support from NASA, NSF, Tennessee State University, and the State of Tennessee through its Centers of Excellence Program. J.S.F. acknowledges support from the Spanish State Research Agency project AYA2016-79425-C3-2-P.Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.