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 μ m. Combining these transits with previous observations, we construct a complete 0.3–5.0 μ m transmi...
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Published in | The Astronomical journal Vol. 162; no. 4; pp. 138 - 157 |
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Main Authors | , , , , , , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Madison
The American Astronomical Society
01.10.2021
IOP Publishing |
Subjects | |
Online Access | Get full text |
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Summary: | 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
μ
m. Combining these transits with previous observations, we construct a complete 0.3–5.0
μ
m 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 H
2
O (at 4.0
σ
confidence) while providing moderate evidence of H
−
bound–free opacity (3.3
σ
) and strong evidence of stellar contamination from unocculted faculae (4.7
σ
). The retrieved H
2
O 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(
X
H
−
) ≈ −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. |
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Bibliography: | The Solar System, Exoplanets, and Astrobiology AAS28002 |
ISSN: | 0004-6256 1538-3881 1538-3881 |
DOI: | 10.3847/1538-3881/ac0e99 |