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.
@article{arxiv.1812.07177,
title = {ACCESS: Ground-based Optical Transmission Spectroscopy of the Hot Jupiter WASP-4b},
author = {Alex Bixel and Benjamin V. Rackham and Dániel Apai and Néstor Espinoza and Mercedes López-Morales and David J. Osip and Andrés Jordán and Chima McGruder and Ian Weaver},
journal= {arXiv preprint arXiv:1812.07177},
year = {2019}
}
Comments
31 pages, 19 figures, 8 tables. Accepted for publication in AJ