The large radii of many hot Jupiters can only be matched by models that have hot interior adiabats, and recent theoretical work has shown that the interior evolution of hot Jupiters has a significant ...impact on their atmospheric structure. Due to its inflated radius, low gravity, and ultra-hot equilibrium temperature, WASP-76b is an ideal case study for the impact of internal evolution on observable properties. Hot interiors should most strongly affect the non-irradiated side of the planet, and thus full phase curve observations are critical to ascertain the effect of the interior on the atmospheres of hot Jupiters. In this work, we present the first Spitzer phase curve observations of WASP-76b. We find that WASP-76b has an ultra-hot day side and relatively cold nightside with brightness temperatures of \(2471 \pm 27~\mathrm{K}\)/\(1518 \pm 61~\mathrm{K}\) at \(3.6~\micron\) and \(2699 \pm 32~\mathrm{K}\)/\(1259 \pm 44~\mathrm{K}\) at \(4.5~\micron\), respectively. These results provide evidence for a dayside thermal inversion. Both channels exhibit small phase offsets of \(0.68 \pm 0.48^{\circ}\) at \(3.6~\micron\) and \(0.67 \pm 0.2^{\circ}\) at \(4.5~\mu\mathrm{m}\). We compare our observations to a suite of general circulation models that consider two end-members of interior temperature along with a broad range of frictional drag strengths. Strong frictional drag is necessary to match the small phase offsets and cold nightside temperatures observed. From our suite of cloud-free GCMs, we find that only cases with a cold interior can reproduce the cold nightsides and large phase curve amplitude at \(4.5~\micron\), hinting that the hot interior adiabat of WASP-76b does not significantly impact its atmospheric dynamics or that clouds blanket its nightside.
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 \(\mu\)m 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.
We present a comprehensive analysis of the 0.3--5\,\(\mu\)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\,\(\mu\)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 \(\log_{10}{Z/Z_{\odot}} = 1.46^{+0.53}_{-0.68}\) and \(\log_{10}{Z/Z_{\odot}} = 2.33^{+0.23}_{-0.25}\), 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. 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.
Know thy star, know thy planetary atmosphere. Every exoplanet with atmospheric measurements orbits around a star, and the stellar environment directly affects the planetary atmosphere. Here we ...present the emission spectrum of ultra-hot Jupiter KELT-20b which provides an observational link between host star properties and planet atmospheric thermal structure. It is currently the only planet with thermal emission measurements in the \(T_{eq}\sim\)2200K range that orbits around an early A-type star. By comparing it with other similar ultra-hot Jupiters around FGK stars, we can better understand how different host star types influence planetary atmospheres. The emission spectrum covers 0.6 to 4.5 \(\mu m\) with data from TESS, HST WFC3/G141, and Spitzer 4.5 \(\mu m\) channel. KELT-20b has a 1.4 \(\mu m\) water feature strength metric of S\(_{H_2O}\) = -0.097\(\pm\)0.02 and a blackbody brightness temperature difference of 528K between WFC3/G141 (T\(_b\)=2402\(\pm\)14K) and Spitzer 4.5 \(\mu m\) channel (T\(_b\)=2930\(\pm59\)K). These very large H\(_2\)O and CO emission features combined with the A-type host star make KELT-20b a unique planet among other similar hot Jupiters. The abundant FUV, NUV, and optical radiation from its host star (T\(_{eff}=8720\pm250\)K) is expected to be the key that drives its strong thermal inversion and prominent emission features based on previous PHOENIX models calculations.
