The HUSTLE Program: The UV to Near-infrared HST WFC3/UVIS G280 Transmission Spectrum of WASP-127b

Abstract Ultraviolet wavelengths offer unique insights into aerosols in exoplanetary atmospheres. However, only a handful of exoplanets have been observed in the ultraviolet to date. Here, we present the ultraviolet-visible transmission spectrum of the inflated hot Jupiter WASP-127b. We observed one transit of WASP-127b with WFC3/UVIS G280 as part of the Hubble Ultraviolet-optical Survey of Transiting Legacy Exoplanets, obtaining a transmission spectrum from 200 to 800 nm. Our reductions yielded a broadband transit depth precision of 91 ppm and a median precision of 240 ppm across 59 spectral channels. Our observations are suggestive of a high-altitude cloud layer with forward modeling showing they are composed of submicron particles and retrievals indicating a high-opacity patchy cloud. While our UVIS/G280 data only offer weak evidence for Na, adding archival Hubble Space Telescope (HST) WFC3/IR and STIS observations raises the overall Na detection significance to 4.1 σ . Our work demonstrates the capabilities of HST WFC3/UVIS G280 observations to probe the aerosols and atmospheric composition of transiting hot Jupiters with comparable precision to HST STIS.