Using the chromatic Rossiter-McLaughlin effect to probe the broadband signature in the optical transmission spectrum of HD 189733b

Context. Transmission spectroscopy is a powerful technique for probing exoplanetary atmospheres. A successful ground-based observational method uses a differential technique that uses high-dispersion spectroscopy, but it only preserves narrow features in transmission spectra. Broadband features, such as the remarkable Rayleigh-scattering slope from possible hazes in the atmosphere of HD 189733b as observed by the Hubble Space Telescope, cannot be probed in this way.