The Hubble PanCET Program: A Metal-rich Atmosphere for the Inflated Hot Jupiter HAT-P-41b

Abstract

We present a comprehensive analysis of the 0.3--5\,$\hat{I}¼$m transit spectrum for the inflated hot Jupiter HAT-P-41b. 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 \textit{Spitzer} transit observations. We extract transit depths from each of the data sets, presenting the STIS transit spectrum (0.29--0.93\,$\hat{I}¼$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-$\ddot{I}ƒ$ detection of H${}_2$O as well as evidence of gas absorption in the optical ($>$2.7-$\ddot{I}ƒ$ detection) due to Na, AlO and/or VO/TiO, though no individual species is strongly detected. Both retrievals determine the transit spectrum to be consistent with a clear atmosphere, with no evidence of haze or high-altitude clouds. Interior modeling constraints on the maximum atmospheric metallicity (${\log }_{10}Z/Z_{\odot }<1.7$) favor the AURA results. The inferred elemental oxygen abundance suggests that HAT-P-41b has one of the most metal-rich atmospheres of any hot Jupiters known to date. Overall, the inferred high metallicity and high inflation make HAT-P-41b an interesting test case for planet formation theories.

Resubmitted to AAS Journals after revisions