The GAPS Programme at TNG : XXXII. The revealing non-detection of metastable He I in the atmosphere of the hot Jupiter WASP-80b

Context. Because of its proximity to an active K-type star, the hot Jupiter WASP-80b has been identified as a possible excellent target for detecting and measuring He I absorption in the upper atmosphere. Aims. Our aim was to look for, and eventually measure and model, metastable He I atmospheric absorption. Methods. We observed four primary transits of WASP-80b in the optical and near-infrared using the HARPS-N and GIANO-B high-resolution spectrographs attached to the Telescopio Nazionale Galileo telescope, focusing the analysis on the He I triplet. We further employed a three-dimensional hydrodynamic aeronomy model to understand the observational results. Results. We did not find any signature of planetary absorption at the position of the He I triplet with an upper limit of 0.7% (i.e. 1.11 planetary radii; 95% confidence level). We re-estimated the high-energy stellar emission, which we combined with a stellar photospheric model, to generate the input for the hydrodynamic modelling. We determined that, assuming a solar He to H abundance ratio, He I absorption should have been detected. Considering a stellar wind 25 times weaker than solar, we could reproduce the non-detection only by assuming a He to H abundance ratio about 16 times smaller than solar. Instead, considering a stellar wind ten times stronger than solar, we could reproduce the non-detection only with a He to H abundance ratio about ten times smaller than solar. We attempted to understand this result by collecting all past He I measurements and looking for correlations with high-energy stellar emission and planetary gravity, but without success. Conclusions. WASP-80b is not the only planet with an estimated sub-solar He to H abundance ratio, which suggests the presence of efficient physical mechanisms (e.g. phase separation, magnetic fields) capable of significantly modifying the He to H content in the upper atmosphere of hot Jupiters. The planetary macroscopic properties and the shape of the stellar spectral energy distribution are not sufficient for predicting the presence or absence of detectable metastable He in a planetary atmosphere, since the He abundance also appears to play a major role

Modeling of Absorption by Heavy Minor Species for the Hot Jupiter HD 209458b

The absorption of stellar radiation observed by HD 209458b in the resonant lines of O I and C II has not yet been satisfactorily explained. We apply a 2D hydrodynamic multi-fluid model that self-consistently describes the expanding planetary wind, driven by stellar XUV radiation and influenced by tidal forces and the surrounding stellar wind. According to this model, HD 209458b has a hydrogen-dominated plasmasphere, expanding beyond the Roche lobe, in the form of two supersonic streams that propagate toward and away from the star. The species heavier than hydrogen and helium are dragged in the escaping material streams and accelerated up to 50 km s-1. Our simulations show that, assuming solar abundances, O I and C II produce absorption due to the Doppler resonance mechanism at the level of 6%-10%, which is consistent with the observations. Most of this absorption takes place in the streams. The transit depth in the O I and C II lines is unaffected by the stellar wind, unless it is strong enough to form a compact bowshock around the planet and able to redirect all the escaping material to the tail. In this case, the absorption profile becomes asymmetric due to the prominent blueshifted attenuation. Thus, the spectroscopic measurements enable probing of the planetary wind character, as well as the strength of the stellar wind. The computed absorption at wavelengths of the Si III, Mg I, and Mg II lines at solar abundances appears to be much stronger, compared to the observations. This possibly indicates that Si and Mg may be under-abundant in the upper atmosphere of HD 209458b

Global 3D simulation of the upper atmosphere of HD189733b and absorption in metastable HeI and Ly{\alpha} lines

A 3D fully self-consistent multi-fluid hydrodynamic aeronomy model is applied to simulate the hydrogen-helium expanding upper atmosphere of the hot Jupiter HD189733b, and related absorption in the Lya line and the 10830 A line of metastable helium. We studied the influence of a high-energy stellar flux, stellar wind, and Lya cooling to reproduce the available observations. We found that to fit the width of the absorption profile in 10830 A line the escaping upper atmosphere of planet should be close to the energy limited escape achieved with a significantly reduced Lya cooling at the altitudes with HI density higher than 3*10^6 cm^-3. Based on the preformed simulations, we constrain the helium abundance in the upper atmosphere of HD189733b by a rather low value of He/H~0.005. We show that under conditions of a moderate stellar wind similar to that of the Sun the absorption of Lya line takes place mostly within the Roche lobe due to thermal broadening at a level of about 7%. At an order of magnitude stronger wind, a significant absorption of about 15% at high blue shifted velocities of up to 100 km/s is generated in the bowshock region, due to Doppler broadening. These blue shifted velocities are still lower than those (~200 km/s) detected in one of the observations. We explain the differences between performed observations, though not in all the details, by the stellar activity and the related fluctuations of the ionizing radiation (in case of 10830 A line), and stellar wind (in case of Lya line)

Status of Thomson scattering in ITER divertor

Detailed measurements of electron parameters in the ITER divertor will be used for monitoring inter- mode transitions (e.g., attached/detached conditions of the divertor plasma) and to study fast disturbances caused by ELMs. This paper describes the challenges of Thomson scattering implementation in ITER divertor and the evaluation of capabilities to adequately deal with project requirements from the point of view of the measured Te, ne range as well as interpretation of the expected Te, ne data