ACCESS: Ground-based Optical Transmission Spectroscopy of the Hot Jupiter WASP-4b

Abstract

We present an optical transmission spectrum of the atmosphere of WASP-4b obtained through observations of four transits with Magellan/IMACS. Using a Bayesian approach to atmospheric retrieval, we find no evidence for scattering or absorption features in our transit spectrum. Our models include a component to model the transit light source effect (spectral contamination from unocculted spots on the stellar photosphere), which we show can have a marked impact on the observed transmission spectrum for reasonable spot covering fractions (< 5%); this is the first such analysis for WASP-4b. We are also able to fit for the size and temperature contrast of spots observed during the second and third transits, finding evidence for both small, cool and large, warm spot-like features on the photosphere. Finally, we compare our results to those published by Huitson et al. (2017) using Gemini/GMOS and May et al. (2018) using IMACS, and find that our data are in agreement.

31 pages, 19 figures, 8 tables. Accepted for publication in AJ

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Cited by in corpus (14)

• The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars
• Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights From Microphysical Cloud Modeling
• ACCESS & LRG-BEASTS: a precise new optical transmission spectrum of the ultrahot Jupiter WASP-103b
• Near-Infrared Transmission Spectroscopy of HAT-P-18b with NIRISS: Disentangling Planetary and Stellar Features in the Era of JWST
• The GTC exoplanet transit spectroscopy survey XI. Possible detection of Rayleigh scattering in the atmosphere of the Saturn-mass planet WASP-69b
• LRG-BEASTS: sodium absorption and Rayleigh scattering in the atmosphere of WASP-94A b using NTT/EFOSC2
• ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of ${\mathrm{H}}_2\mathrm{O}$, but no evidence of Na or K
• ACCESS: Confirmation of a Clear Atmosphere for WASP-96b and a Comparison of Light Curve Detrending Techniques
• ACCESS: An optical transmission spectrum of the high-gravity, hot Jupiter HAT-P-23b
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• ACCESS: Tentative detection of H${}_2$O in the ground-based optical transmission spectrum of the low-density hot Saturn HATS-5b
• An Hα Transit of HD 189733b to Assess Stellar Activity Across the Transit Chord Close to JWST Observations
• SPECtrophotometer for TRansmission spectroscopy of exoplanets (SPECTR)
• Characterizing the WASP-4 system with TESS and radial velocity data: Constraints on the cause of the hot Jupiter's changing orbit and evidence of an outer planet