2021AJ....162..138R -
Astron. J., 162, 138-138 (2021/October-0)
HST PanCET program: a complete Near-UV to infrared transmission spectrum for the hot Jupiter WASP-79b.
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. and BUCHHAVE L.A.
Abstract (from CDS):
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 = 0.3-34x 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.
Abstract Copyright:
© 2021. The American Astronomical Society. All rights reserved.
Journal keyword(s):
Exoplanet atmospheres - Exoplanet atmospheric composition - Observational astronomy - Hot Jupiters - Transmission spectroscopy
Simbad objects:
7
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