HST spectral light curve of HAT-P-41

The planet was observed in transit with Hubble STIS and WFC3 as part of the Hubble Panchromatic Comparative Exoplanet Treasury (PanCET) program, and we combine those data with warm Spitzer transit observations. We extract transit depths from each of the data sets, presenting the STIS transit spectrum (0.29-0.93{mu}m) for the first time.

We retrieve the transit spectrum both with a free-chemistry retrieval suite (AURA) and a complementary chemical equilibrium retrieval suite (PLATON) to constrain the atmospheric properties at the day-night terminator. Both methods provide an excellent fit to the observed spectrum. Both AURA and PLATON retrieve a metal-rich atmosphere for almost all model assumptions (most likely O/H ratio of log_10_Z/Z{odot}=1.46_-0.68_^+0.53^ and log_10_Z/Z{odot}=2.33_-0.25_^+0.23^, respectively); this is driven by a 4.9{sigma} detection of H_2_O as well as evidence of gas absorption in the optical (>2.7{sigma} detection) due to Na, AlO, and/or VO/TiO, though no individual species is strongly detected.