ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of H 2 O, but No Evidence of Na or K

Abstract

We present a new ground-based visual transmission spectrum of the hot Jupiter WASP-43b, obtained as part of the ACCESS Survey. The spectrum was derived from four transits observed between 2015 and 2018, with combined wavelength coverage between 5300 and 9000 Å and an average photometric precision of 708 ppm in 230 Å bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature Hubble Space Telescope /WFC3 observations to search for the presence of clouds/hazes as well as Na, K, H α , and H 2 O planetary absorption and stellar spot contamination over a combined spectral range of 5318–16420 Å. We do not detect a statistically significant presence of Na i or K i alkali lines, or H α in the atmosphere of WASP-43b. We find that the observed transmission spectrum can be best explained by a combination of heterogeneities on the photosphere of the host star and a clear planetary atmosphere with H 2 O. This model yields a log evidence of 8.26 ± 0.42 higher than a flat (featureless) spectrum. In particular, the observations marginally favor the presence of large, low-contrast spots over the four ACCESS transit epochs with an average covering fraction and temperature contrast Δ T  = 132 K ± 132 K. Within the planet’s atmosphere, we recover a log H 2 O volume mixing ratio of , which is consistent with previous H 2 O abundance determinations for this planet.