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arXiv · 1812.07177

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

Alex Bixel·Benjamin V. Rackham·Dániel Apai·Néstor Espinoza·Mercedes López-Morales·David J. Osip·Andrés Jordán·Chima McGruder·Ian Weaver
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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.

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Alex Bixel, Benjamin V. Rackham, Dániel Apai, Néstor Espinoza, Mercedes López-Morales, David J. Osip, Andrés Jordán, Chima McGruder, Ian Weaver. 2018-12-18. ACCESS: Ground-based Optical Transmission Spectroscopy of the Hot Jupiter WASP-4b. https://doi.org/10.3847/1538-3881%2Faaf9a3

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