ACCESS: An Optical Transmission Spectrum of the High-gravity Hot Jupiter HAT-P-23b

Abstract We present a new ground-based visible transmission spectrum of the high-gravity, hot Jupiter HAT-P-23b, obtained as part ACCESS project. derive from five transits observed between 2016 and 2018, with combined wavelength coverage 5200 Å 9269 in 200 bins, median precision 247 ppm per bin. HAT-P-23b’s relatively high surface gravity ( g ? 30 m s ?2 ), updated stellar planetary parameters Gaia DR2, gives five-scale-height signal 384 for hydrogen-dominated atmosphere. Bayesian models favor clear atmosphere planet tentative presence TiO, after simultaneously modeling contamination, using spots parameter constraints photometry. If confirmed, HAT-P-23b would be first example high-gravity gas giant at optical/near-IR wavelengths; therefore, we recommend expanding observations to UV IR confirm our results further characterize this planet. This result demonstrates how combining spectroscopy exoplanet atmospheres long-term photometric monitoring host stars can help disentangle activity signals.