Search

We simulate with a global 3D aeronomy code two warm Neptunes in the TOI-421 system and show that both planets experience significant escape of their upper atmospheres. The double shock structures, generated around the planets in course of their interaction with the stellar wind (SW) plasma flow are revealed. The calculations of stellar Ly α transit absorption by the planets reveal that it reaches a detectable level only for a moderate or strong SW, with a sufficiently high density. In this case, the energetic neutral atoms provide significant absorption at the high velocity blue wing of the Ly α line, whereas the corresponding transit light curves exhibit an early ingress and extended egress features. With the same code, we also modelled the absorption at the position of the 10 830 Å line of the metastable helium, showing that it can be detected only for the farthest planet of the considered two, if the helium abundance is comparable to the solar value. [ABSTRACT FROM AUTHOR]

The signs of an expanding atmosphere of HD209458b have been observed with far-ultraviolet transmission spectroscopy and in the measurements of transit absorption by metastable He  i. These observations are interpreted using the hydrodynamic and Monte Carlo numerical simulations of various degree of complexity and consistency. At the same time, no attempt has been made to model atmospheric escape of a magnetized HD209458b, to see how the planetary magnetic field might affect the measured transit absorption lines. This paper presents the global 3D MHD self-consistent simulations of the expanding upper atmosphere of HD209458b interacting with the stellar wind, and models the observed H  i (Ly α), O  i (1306 Å), C  ii (1337 Å), and He  i (10 830 Å) transit absorption features. We find that the planetary dipole magnetic field with the equatorial surface value of Bp = 1 G profoundly changes the character of atmospheric material outflow and the related absorption. We also investigate the formation of planetary magnetosphere in the stellar wind and show that its size is more determined by the escaping atmosphere flow rather than by the strength of magnetic field. Fitting of the simulation results to observations enables constraining the stellar XUV flux and He abundance at F XUV ∼ 10 erg cm2 s–1 (at 1 au) and He/H ≈ 0.02, respectively, as well as setting an upper limit for the dipole magnetic field of Bp < 0.1 G on the planetary surface at the equator. This implies that the magnetic dipole moment µP of HD209458b should be less than 6 per cent of the Jovian value. [ABSTRACT FROM AUTHOR]

Transmission spectroscopy of WASP-107b revealed 7–8 per cent absorption at the position of metastable He  i triplet at 10 830 Å in the velocity range of [−20; 10] km s−1. This absorption is stronger than that measured in other exoplanets. With a dedicated 3D self-consistent hydrodynamic multifluid model, we simulated the expanding upper atmosphere of WASP-107b and reproduced within the observations accuracy the measured He  i absorption profiles, constraining the stellar X-ray and UV radiation (XUV) flux to 6–10 erg cm−2 s−1 at 1 au, and the upper atmosphere helium abundance He/H to 0.075–0.15. The radiation pressure acting on the metastable He  i atoms was shown to be an important factor influencing the absorption profiles. Its effect is counterbalanced by the collisional depopulation of the He  i metastable state. Altogether, the observed He  i absorption in WASP-107b can be interpreted with the expected reasonable parameters of the stellar–planetary system and appropriate account of the electron and atom impact processes. [ABSTRACT FROM AUTHOR]

Warm Neptune GJ3470b has been recently observed in 23S-23P transition of metastable helium, yielding absorption of about 1 per cent in Doppler velocity range of [−40; 10] km s−1. Along with previous detection of absorption in Ly α with depth of 20–40 per cent in the blue and red wings of the line, it offers a complex target for simulation and testing of the current models. Obtained results suggest that absorption in both these lines comes from interaction of expanding upper planetary atmosphere with stellar plasma wind, allowing to constrain the stellar plasma parameters and the helium abundance in planet atmosphere. [ABSTRACT FROM AUTHOR]

The absorption of stellar radiation observed at transits of HD 209458b in resonant lines of O  i and C  ii has not yet been satisfactorily modelled. In our previous two-dimensional (2D) simulations, we have shown that the hydrogen-dominated upper atmosphere of HD 209458b, heated by extreme ultraviolet radiation, expands supersonically beyond the Roche lobe and drags heavier species along with it. Assuming solar abundances, O  i and C  ii particles accelerated by tidal forces to velocities up to 50  |${\rm km}\,{\rm s}^{-1}$| should produce the absorption due to Doppler resonance at the level of 6–10 per  cent, consistent with the observations. Since the 2D geometry does not take into account the Coriolis force in a planet reference frame, the question remains to what extent the spiralling of escaping planetary material and actually achieved velocity may influence the conclusions made on the basis of 2D modelling. In this paper, we apply for the first time in studies of HD 209458b a global 3D hydrodynamic multifluid model. The results confirm our previous findings that the velocity of the planetary flow is sufficiently high to match the widths of O  i and C  ii resonant lines. To match the absorption in those lines, including H  i , with observations, the mass-loss rate of HD 209458b should be about |$2.5\times10^{11}\,{\rm g\,s^{-1}}$|⁠ , which is 3.5 times larger than that revealed by the 2D model. The other novel finding is that matching of the absorption measured in Mg  ii and S  iii lines requires at least 10 times lower abundances of these elements than the solar values. [ABSTRACT FROM AUTHOR]

We present a 3D fully self-consistent multifluid hydrodynamic aeronomy model to study the structure of a hydrogen-dominated expanding upper atmosphere around the hot Jupiter HD 209458b and the warm Neptune GJ 436b. In comparison to previous studies with 1D and 2D models, this work finds such 3D features as zonal flows in upper atmosphere reaching up to 1 km s−1, the tilting of the planetary outflow by Coriolis force by up to 45 degrees and its compression around equatorial plane by tidal forces. We also investigated in detail the influence of helium (He) on the structure of the thermosphere. It is found that by decrease of the barometric scale height, the He presence in the atmosphere strongly affects the H2dissociation front and the temperature maximum. [ABSTRACT FROM AUTHOR]

Possible reasons for the non-detection of absorption in the metastable He  i (23S) line at transit observations of warm Neptune GJ436b, in spite of the well-pronounced strong absorption features measured earlier in Lyα for this planet, are investigated. We perform numeric simulations of the escaping upper atmosphere of this planet and its He  i (23S) triplet absorption with a global 3D multifluid, self-consistent hydrodynamic model. By fitting the model parameters to the lowest detection level of absorption measurements, we constrain an upper limit for the He/H abundance three times smaller than the solar value. We demonstrate that neither the significant changes of the stellar wind related to possible stellar coronal mass ejections (CMEs), or possible variations in the stellar ionization radiation, nor the presence of heavy trace elements have a crucial effect on the absorption at the 10   830 Å line of He  i (23S) triplet. The main reason of weak signature is that the region populated by the absorbing metastable helium is rather small (<3 R p), as well as the small size of the planet itself in comparison to the host star. We show that the radiation pressure force acting on the He  i (23S) atoms spreads them along the line of sight and around the planet, thus further reducing peak absorption. [ABSTRACT FROM AUTHOR]

We present two-dimensional multifluid numerical modelling of the upper atmosphere of the hot Jupiter WASP-12b. The model includes hydrogen chemistry, and self-consistently describes the expansion of the planetary upper atmosphere and mass-loss due to intensive stellar irradiation, assuming a weakly magnetized planet. We simulate the planetary upper atmosphere and its interaction with the stellar wind (SW) with and without the inclusion of tidal force and consider different XUV irradiation conditions and SW parameters. With the inclusion of tidal force, even for a fast SW, the escaping planetary material forms two streams, propagating towards and away from the star. The atmospheric escape and related mass-loss rate reaching the value of 1012 g s−1 appear to be mostly controlled by the stellar gravitational pull. We computed the column density and dynamics of Mg  ii ions considering three different sets of SW parameters and XUV fluxes. The simulations enable to compute the absorption at the position of the Mg h line and to reproduce the times of ingress and egress. In case of a slow SW and without accounting for tidal force, the high orbital velocity leads to the formation of a shock approximately in the direction of the planetary orbital motion. In this case, mass-loss is proportional to the stellar XUV flux. At the same time, ignoring of tidal effects for WASP-12b is a strong simplification, so the scenario with a shock, altogether is an unrealistic one. [ABSTRACT FROM AUTHOR]

In the present series of papers we propose a consistent description of the mass loss process. To study in a comprehensive way the effects of the intrinsic magnetic field of a close-orbit giant exoplanet (a so-called hot Jupiter) on atmospheric material escape and the formation of a planetary inner magnetosphere, we start with a hydrodynamic model of an upper atmosphere expansion in this paper. While considering a simple hydrogen atmosphere model, we focus on the self-consistent inclusion of the effects of radiative heating and ionization of the atmospheric gas with its consequent expansion in the outer space. Primary attention is paid to an investigation of the role of the specific conditions at the inner and outer boundaries of the simulation domain, under which different regimes of material escape (free and restricted flow) are formed. A comparative study is performed of different processes, such as X-ray and ultraviolet (XUV) heating, material ionization and recombination, cooling, adiabatic and Lyα cooling, and Lyα reabsorption. We confirm the basic consistency of the outcomes of our modeling with the results of other hydrodynamic models of expanding planetary atmospheres. In particular, we determine that, under the typical conditions of an orbital distance of 0.05 AU around a Sun-type star, a hot Jupiter plasma envelope may reach maximum temperatures up to ∼9000 K with a hydrodynamic escape speed of ∼9 km s–1, resulting in mass loss rates of ∼(4-7) · 1010 g s–1. In the range of the considered stellar-planetary parameters and XUV fluxes, that is close to the mass loss in the energy-limited case. The inclusion of planetary intrinsic magnetic fields in the model is a subject of the follow-up paper (Paper II). [ABSTRACT FROM AUTHOR]

Aims. We modeled the transit signatures in the Lyman-alpha (Ly-α) line of a putative Earth-sized planet orbiting in the habitable zone (HZ) of the M dwarf GJ 436. We estimated the transit depth in the Ly-α line for an exo-Earth with three types of atmospheres: a hydrogen-dominated atmosphere, a nitrogen-dominated atmosphere, and a nitrogen-dominated atmosphere with an amount of hydrogen equal to that of the Earth. For all types of atmospheres, we calculated in-transit absorption they would produce in the stellar Ly-α line. We applied it to the out-of-transit Ly-α observations of GJ 436 obtained by the Hubble Space Telescope (HST) and compared the calculated in-transit absorption with observational uncertainties to determine if it would be detectable. To validate the model, we also used our method to simulate the deep absorption signature observed during the transit of GJ 436b and showed that our model is capable of reproducing the observations. Methods. We used a direct simulation Monte Carlo (DSMC) code to model the planetary exospheres. The code includes several species and traces neutral particles and ions. It includes several ionization mechanisms, such as charge exchange with the stellar wind, photo- and electron impact ionization, and allows to trace particles collisions. At the lower boundary of the DSMC model we assumed an atmosphere density, temperature, and velocity obtained with a hydrodynamic model for the lower atmosphere. Results. We showed that for a small rocky Earth-like planet orbiting in the HZ of GJ 436 only the hydrogen-dominated atmosphere is marginally detectable with the Space Telescope Imaging Spectrograph (STIS) on board the HST. Neither a pure nitrogen atmosphere nor a nitrogen-dominated atmosphere with an Earth-like hydrogen concentration in the upper atmosphere are detectable. We also showed that the Ly-α observations of GJ 436b can be reproduced reasonably well assuming a hydrogen-dominated atmosphere, both in the blue and red wings of the Ly-α line, which indicates that warm Neptune-like planets are a suitable target for Ly-α observations. Terrestrial planets, on the other hand, can be observed in the Ly-α line if they orbit very nearby stars, or if several observational visits are available. [ABSTRACT FROM AUTHOR]

We investigate the interaction between themagnetized stellarwind plasma and the partially ionized hydrodynamic hydrogen outflow from the escaping upper atmosphere of non-magnetized or weakly magnetized hot Jupiters. We use the well-studied hot Jupiter HD 209458b as an example for similar exoplanets, assuming a negligible intrinsic magnetic moment. For this planet, the stellar wind plasma interaction forms an obstacle in the planet's upper atmosphere, in which the position of the magnetopause is determined by the condition of pressure balance between the stellar wind and the expanded atmosphere, heated by the stellar extreme ultraviolet radiation.We show that the neutral atmospheric atoms penetrate into the region dominated by the stellar wind, where they are ionized by photoionization and charge exchange, and then mixed with the stellar wind flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced magnetic field forms in front of the planetary obstacle, which appears to be much stronger compared to those produced by the solar wind interaction with Venus and Mars. Depending on the stellar wind parameters, because of the induced magnetic field, the planetary obstacle can move up to ≈0.5-1 planetary radii closer to the planet. Finally, we discuss how estimations of the intrinsic magnetic moment of hot Jupiters can be inferred by coupling hydrodynamic upper planetary atmosphere andMHDstellar wind interaction models together with UV observations. In particular, we find that HD 209458b should likely have an intrinsic magnetic moment of 10-20 per cent that of Jupiter. [ABSTRACT FROM AUTHOR]

Giant exoplanets at close orbits, or so-called hot Jupiters, are supposed to have an intensive escape of upper atmospheric material heated and ionized by the radiation of a host star. An interaction between outflowing atmospheric plasma and the intrinsic planetary magnetic dipole field leads to the formation of a crucial feature of a hot Jupiter's magnetosphere—an equatorial current-carrying magnetodisk. The presence of a magnetodisk has been shown to influence the topology of a hot Jupiter's magnetosphere and to change a standoff distance of the magnetopause. In this paper, the basic features of the formation of a hot Jupiter's magnetodisk are studied by means of a laboratory experiment. A localized central source produces plasma that expands outward from the surface of the dipole and inflates the magnetic field. The observed structure of magnetic fields, electric currents, and plasma density indicates the formation of a relatively thin current disk extending beyond the Alfvénic point. At the edge of the current disk, an induced magnetic field was found to be several times larger than the field of the initial dipole. [ABSTRACT FROM AUTHOR]

This paper presents the results of laboratory experiments with laser plasma flow around a magnetic dipole which model the extreme compression of the Earthś magnetosphere by the plasma generated by high-power coronal mass ejections. Data on the formation of an artificial magnetosphere, the boundary-layer structure, and the size of the magnetosphere as a function of the magnetic moment are given. It is shown that in the presence of a conducting dipole shell modeling the ionosphere, conditions are created for the flow of intense longitudinal currents in the polar regions. It is established that the longitudinal currents have little effect on the position of the plasma stagnation point and the transition layer but make a significant contribution to the disturbance of the magnetic field in the magnetosphere. [ABSTRACT FROM AUTHOR]

The ion composition of a plasma flow obtained by intense irradiation of a solid target is determined by methods of probing diagnostics and measuring the secondary emission rate. As the ions fly through a dense gas jet, C 5+ ions are found to recharge to C 4+ ions and then to C 3+ ions. The fraction of high-charge ions in the initial plasma flow and their concentration in the region of interaction with the jet are calculated. The concentration of atoms in the gas jet is estimated on the basis of the integral change in the charge value. Results necessary for analyzing the conditions of experiments on effective charge-transfer pumping and laser generation in the far ultraviolet spectral range are obtained. [ABSTRACT FROM AUTHOR]

The paper deals with the physical and electrotechnical principles of the promising method of direct conversion of the kinetic energy of an expanding plasma cloud to electrical energy by inductive generation of currents in short–circuited load coils that enclose the plasma and are oriented across the external magnetic field. An analysis of plasma deceleration by a magnetic field and transfer of plasma energy to an inductive load gave a solution of the problem in general form and the dimensionless parameters of the problem that determine the deceleration radius, the coil current, and the theoretical conversion efficiency. The role of the basic physical effects, including parasitic ones (plasma instabilities and Joule heating), influencing the real efficiency is assessed. A comparison of the results with data of experiments with laser–produced plasma clouds on a KI–1 facility and with available numerical results shows that in the optimized version of the method for conversion of inertial confinement fusion energy, a 30% efficiency can be achieved. [ABSTRACT FROM AUTHOR]