Hubble PanCET: an isothermal day-side atmosphere for the bloated gas-giant HAT-P-32Ab

We present a thermal emission spectrum of the bloated hot Jupiter HAT-P-32Ab from a single eclipse observation made in spatial scan mode with the Wide Field Camera 3 (WFC3) aboard the Hubble Space Telescope (HST). The spectrum covers the wavelength regime from 1.123 to 1.644 μm which is binned into 14 eclipse depths measured to an averaged precision of 104 parts-per million. The spectrum is unaffected by a dilution from the close M-dwarf companion HAT-P-32B, which was fully resolved. We complemented our spectrum with literature results and performed a comparative forward and retrieval analysis with the 1D radiative-convective ATMO model. Assuming solar abundance of the planet atmosphere, we find that the measured spectrum can best be explained by the spectrum of a blackbody isothermal atmosphere with Tp = 1995 ± 17 K, but can equally well be described by a spectrum with modest thermal inversion. The retrieved spectrum suggests emission from VO at the WFC3 wavelengths and no evidence of the 1.4 μm water feature. The emission models with temperature profiles decreasing with height are rejected at a high confidence. An isothermal or inverted spectrum can imply a clear atmosphere with an absorber, a dusty cloud deck or a combination of both. We find that the planet can have continuum of values for the albedo and recirculation, ranging from high albedo and poor recirculation to low albedo and efficient recirculation. Optical spectroscopy of the planet\u27s day-side or thermal emission phase curves can potentially resolve the current albedo with recirculation degeneracy

A REMARKABLE AURORAL EVENT ON JUPITER OBSERVED IN THE ULTRAVIOLET WITH THE HUBBLE-SPACE-TELESCOPE

Two sets of ultraviolet images of the Jovian north aurora were obtained with the Faint Object Camera on board the Hubble Space Telescope. The first series shows an intense discrete are in near corotation with the planet. The maximum apparent molecular hydrogen emission rate corresponds to an electron precipitation of similar to 1 watt per square meter, which is about 30,000 times larger than the solar heating by extreme ultraviolet radiation. Such a particle heating rate of the auroral upper atmosphere of Jupiter should cause a large transient temperature increase and generate strong thermospheric winds. Twenty hours after initial observation, the discrete are had decreased in brightness by more than one order of magnitude. The time scale and magnitude of the change in the ultraviolet aurora leads us to suggest that the discrete Jovian auroral precipitation is related to large-scale variations in the current system, as is the case for Earth's discrete aurorae

Jovian auroral spectroscopy with FUSE: analysis of self-absorption and implications for electron precipitation

High-resolution (similar to 0.22 Angstrom) spectra of the north jovian aurora were obtained in the 905-1180 Angstrom window with the Far Ultraviolet Spectroscopic Explorer (FUSE) on October 28, 2000. The FUSE instrument resolves the rotational structure of the H-2 spectra and the spectral range allows the study of self-absorption. Below 1100 Angstrom, transitions connecting to the upsilon" less than or equal to 2 levels of the H-2 ground state are partially or totally absorbed by the overlying H2 molecules. The FUSE spectra provide information on the overlying H2 column and on the vibrational distribution of H-2. Transitions from high-energy H-2 Rydberg states and treatment of self-absorption are considered in our synthetic spectral generator. We show comparisons between synthetic and observed spectra in the 920-970, 1030-1080, and 1090-1180 Angstrom spectral windows. In a first approach (single-layer model), the synthetic spectra are venerated in a thin emitting layer and the emerging photons are absorbed by a layer located above the source. It is found that the parameters of the single-layer model best fitting the three spectral windows are 850, 800, and 800 K respectively for the H-2 gas temperature and 1.3 x 10(18), 1.5 x 10(20), and 1.3 x 10(20) cm(-2) for the H-2 self-absorbing vertical column respectively. Comparison between the H-2 column and a 1-D atmospheric model indicates that the short-wavelength FUV auroral emission originates from just above the homopause. This is confirmed by the high H-2 rovibrational temperatures, close to those deduced from spectral analyses of H-3(+) auroral emission. In a second approach, the synthetic spectral generator is coupled with a vertically distributed 3 energy degradation model, where the only input is the energy distribution of incoming electrons (multi-layer model). The model that best fits globally the three FUSE spectra is a sum of Maxwellian functions, with characteristic energies ranging from 1 to 100 keV, giving rise to an emission peak located at 5 mubar, that is similar to 100 km below the methane homopause. This multi-layer model is also applied to a re-analysis of the Hopkins Ultraviolet Telescope (HUT) auroral spectrum and accounts for the H2 self-absorption as well as the methane absorption. It is found that no additional discrete soft electron precipitation is necessary to fit either the FUSE or the HUT observations. (C) 2004 Elsevier Inc. All rights reserved