The Hubble PanCET Program: Transit and Eclipse Spectroscopy of the Strongly Irradiated Giant Exoplanet WASP-76b

Abstract

Ultra-hot Jupiters with equilibrium temperature greater than 2000K are uniquely interesting targets as they provide us crucial insights into how atmospheres behave under extreme conditions. This class of giant planets receives intense radiation from their host star and usually has strongly irradiated and highly inflated atmospheres. At such high temperature, cloud formation is expected to be suppressed and thermal dissociation of water vapor could occur. We observed the ultra-hot Jupiter WASP-76b with 7 transits and 5 eclipses using the Hubble Space Telescope (HST) and Spitzer for a comprehensive study of its atmospheric chemical and physical processes. We detect TiO and H 2 O absorption in the optical and near-infrared transit spectrum. Additional absorption by a number of neutral and ionized heavy metals like Fe, Ni, Ti, and SiO help explain the short wavelength transit spectrum. The secondary eclipse spectrum shows muted water feature but a strong CO emission feature in Spitzer's 4.5 µm band indicating an inverted temperature pressure profile. We analyzed both the transit and emission spectrum with a combination of self-consistent PHOENIX models and retrieval models (ATMO & PLATON). Both spectra are well fitted by the self-consistent PHOENIX forward atmosphere model in chemical and radiative equilibrium at solar metallicity, adding to the growing evidence that both TiO/VO and NUV heavy metals opacity are prominent NUV-optical opacity sources in the stratospheres of ultra-hot Jupiters.

The Hubble PanCET program: Transit and Eclipse Spectroscopy of the Hot Jupiter WASP-74b

“…With the many recent studies of hot Jupiter atmospheres, we are starting to see a highly diverse landscape of atmospheric chemical composition and thermal structure. Some ultra-hot (T eq >2000K) Jupiters have shown significant gaseous heavy metal absorption (Fu et al 2021;Lothringer et al 2020) while other cooler hot Jupiters exhibit high metallicity (Colón et al 2020;Sheppard et al 2021;Lewis et al 2020) and aerosols coverage (Alam et al 2020). We have also detected absorption and emission features of various chemical species such as water, sodium, CO/CO 2 , metals and metal oxides (TiO and VO) (Evans et al 2017;Fu et al 2021;Kreidberg et al 2018).…”

“…The HST WFC3 data reduction pipeline is exactly the same as detailed in Fu et al (2021) for both transit and eclipse. We used a combination of the BATMAN lightcurve model (Kreidberg 2015) with the RECTE charge trapping systematics model (Zhou et al 2017) for lightcurve detrending.…”

“…Some ultra-hot (T eq >2000K) Jupiters have shown significant gaseous heavy metal absorption (Fu et al 2021;Lothringer et al 2020) while other cooler hot Jupiters exhibit high metallicity (Colón et al 2020;Sheppard et al 2021;Lewis et al 2020) and aerosols coverage (Alam et al 2020). We have also detected absorption and emission features of various chemical species such as water, sodium, CO/CO 2 , metals and metal oxides (TiO and VO) (Evans et al 2017;Fu et al 2021;Kreidberg et al 2018). With this ever growing library of exoplanet atmosphere spectra, we are starting to understand the chemical and physical processes taking place in these hot Jupiters.…”

The Hubble PanCET program: Emission spectrum of hot Jupiter HAT-P-41b

“…Notably, water features at 1.4 µm (Fu et al 2017) has been the most robustly detected in both absorption (Kreidberg et al 2014) and emission (Fu et al 2022;Evans et al 2017). The presence of H-continuum opacity was inferred in multiple ultra-hot Jupiters (Arcangeli et al 2019;Fu et al 2021a). In the longer wavelength, the CO/CO 2 features were indicated by the deviations of Spitzer photometric points in 3.6 µm and 4.5 µm channels from the blackbody approximation (Garhart et al 2020;Fu et al 2021b).…”

“…The forward scanning rate is 0.065 arcsec s −1 and the exposure time is 81 seconds. The data reduction process starts with applying the standard flat field, background subtraction and bad pixels, cosmic rays removal on the ima frames (Fu et al 2021a). Then we extract the non-destructive reads from each frame (Deming et al 2013).…”