ACCESS: A Visual to Near-infrared Spectrum of the Hot Jupiter WASP-43b with Evidence of ${\mathrm{H}}_2\mathrm{O}$, 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 5,300 à -9,000 à and an average photometric precision of 708 ppm in 230 à bins. We perform an atmospheric retrieval of our transmission spectrum combined with literature HST/WFC3 observations to search for the presence of clouds/hazes as well as Na, K, H$\hat{I}\pm$, and ${\mathrm{H}}_2\mathrm{O}$ planetary absorption and stellar spot contamination over a combined spectral range of 5,318 à -16,420 à . We do not detect a statistically significant presence of Na I or K I alkali lines, or H$\hat{I}\pm$ 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 ${\mathrm{H}}_2\mathrm{O}$. This model yields a log-evidence of $8.26\pm 0.42$ 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 $f_{\text{het}}=0.27_{-0.16}^{+0.42}$ and temperature contrast $\hat{I}”T=132\text{ K}\pm 132\text{ K}$. Within the planet's atmosphere, we recover a log ${\mathrm{H}}_2\mathrm{O}$ volume mixing ratio of $-2.78_{-1.47}^{+1.38}$, which is consistent with previous ${\mathrm{H}}_2\mathrm{O}$ abundance determinations for this planet.

27 pages, 18 figures, 7 tables. Accepted for publication in AJ. Updated affiliations