THE INFLUENCE OF CHEMI-IONIZATION AND RECOMBINA- TION PROCESSES ON SPECTRAL LINE SHAPES IN STELLAR ATMOSPHERES (original) (raw)
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Symmetric Atom–Atom and Ion–Atom Processes in Stellar Atmospheres
We present the results of the influence of two groups of collisional processes (atom–atom and ion–atom) on the optical and kinetic properties of weakly ionized stellar atmospheres layers. The first type includes radiative processes of the photodissociation/association and radiative charge exchange, the second one the chemi-ionisation/recombination processes with participation of only hydrogen and helium atoms and ions. The quantitative estimation of the rate coefficients of the mentioned processes were made. The effect of the radiative processes is estimated by comparing their intensities with those of the known concurrent processes in application to the solar photosphere and to the photospheres of DB white dwarfs. The investigated chemi-ionisation/recombination processes are considered from the viewpoint of their influence on the populations of the excited states of the hydrogen atom (the Sun and an M-type red dwarf) and helium atom (DB white dwarfs). The effect of these processes on the populations of the excited states of the hydrogen atom has been studied using the general stellar atmosphere code, which generates the model. The presented results demonstrate the undoubted influence of the considered radiative and chemi-ionisation/recombination processes on the optical properties and on the kinetics of the weakly ionized layers in stellar atmospheres.
Proceedings of The International Astronomical Union, 2003
Results of our investigations of the influence of radiation, chemi-ionization and chemi-recombination processes in atom-atom and ion-atom collisions (in the case of the symmetric atom-atom and ion-atom systems) in stellar hydrogen and helium plasmas are presented. The considered ion-atom radiation processes influence significantly on the optical characteristics of stellar plasma, and the considered chemi-ionization/recombination processes on the excited atomic energy level populations, as well as on the electron density. The consequence of the obtained results is that they should be taken into account for the modeling of photosohere and lower chromosphere of the Sun and similar star (hydrogen case) and white dwarfs atmospheres (helium case).
In this paper we have presented some of our preliminary results illustrating the influence of a group of symmetrical chemical ionization and chemical recombination processes on the populations of hydrogen-atom Rydberg states in low-temperature layers of stellar photospheres and a part of chromospheres. These processes are H Ã (n) þ H(1s) ! H þ 2 þ e=H(1s) þ H þ e and H 2 þ e ! H (n) þ H(1s), H(1s) þ H þ e ! H (n) þ H(1s), where H Ã (n) is the hydrogen atom in a Rydberg state with the principal quantum number n ) 1, and H þ 2 is the hydrogen molecular ion in a weakly bound rovibrational state. The mentioned processes have been considered within the framework of the semiclassical approximation, developed in several previous papers. Their influence on the populations of hydrogen-atom Rydberg states has been investigated by direct inclusion in a computer code for stellar atmosphere modelling. Here we present some of our preliminary results for the M dwarf atmospheres. Our results show that the influence of these processes is significant for the considered stellar atmospheres, so that they should be taken into account for their modelling.
The non-symmetric ion-atom radiative processes in the stellar atmospheres
Monthly Notices of the Royal Astronomical Society, 2013
The aim of this research is to show that the processes of absorption charge exchange and photoassociation in A + B + collisions together with the processes of AB + photodissociation in the case of strongly non-symmetric ion-atom systems, significantly influence the opacity of stellar atmospheres in ultraviolet (UV) and extreme UV (EUV) region. In this work, the significance of such processes for solar atmosphere is studied. In the case of the solar atmosphere the absorption processes with A = H and B = Mg and Si are treated as dominant ones, but the cases A = H and B = Al and A = He and B = H are also taken into consideration. The choice of just these species is caused by the fact that, of the species relevant for the used solar atmosphere model, it was only for them that we could determine the necessary characteristics of the corresponding molecular ions, i.e. the molecular potential curves and dipole matrix elements. It is shown that the efficiency of the examined non-symmetric processes within the rather wide corresponding quasi-molecular absorption bands in the far-UV and EUV regions is comparable and sometimes even greater than the intensity of the known symmetric ion-atom absorption processes, which are included now in the models of the solar atmosphere. Consequently, the presented results suggest that the non-symmetric ion-atom absorption processes also have to be included ab initio in the corresponding models of the stellar atmospheres.
The aim of this work is to draw attention to the processes of radiative charge exchange in non-symmetric ion-atom collisions as a factor of influence on the opacity of stellar atmospheres in VUV region. For that purpose calculations of the spectral absorption coefficients for several ion–atom systems, namely He + H + and H + X + , where X = Na and Li, have been performed. On chosen examples it has been established that the examined processes generate rather wide molecular absorption bands in the VUV region, which should be taken into account for the interpretation of data obtained from laboratory measurements or astrophysical observations. This paper discusses the potential significance of the considered radiative processes for DB white dwarfs and solar atmospheres, as well as for the atmospheres of the so-called lithium stars.
Monthly Notices of the Royal Astronomical Society, 2016
In this paper, the rate coefficients of the chemi-ionization processes in H(1s) + H*(n, l) and He(1s 2) + He * (n, l) collisions (where the principal quantum number n 1) are determined for the first time, taking into account the influence of the corresponding (n − n)-mixing processes. It is demonstrated that the inclusion of (n − n) mixing in the calculation influences the values of chemi-ionization rate coefficients significantly, particularly in the lower part of the block of Rydberg states. The interpretation of this influence is based on two existing methods of describing inelastic processes in symmetrical atom-Rydberg-atom collisions. The calculations of the chemi-ionization rate coefficients are performed for the temperature region that is characteristic of solar and DB white-dwarf atmospheres.
Astronomical and Astrophysical Transactions
The aim of this work is to draw attention to the processes of radiative charge exchange in non-symmetric ion-atom collisions as a factor of influence on the opacity of stellar atmospheres in VUV region. For that purpose calculations of the spectral absorption coefficients for several ion-atom systems, namely: He + H$^{+}$ and H + X$^{+}$, where X = Na and Li have been performed. On chosen examples it has been established that the examined processes generate rather wide molecular absorption bands in the VUV region, which should be taken into account for the interpretation of data obtained from laboratory measurements or astrophysical observations. In this paper the potential significance is discussed of the considered radiative processes for DB white dwarfs and solar atmospheres, as well as for the atmospheres of the so-called lithium stars.
Astronomy and Astrophysics, 2003
We study the influence of a group of chemi-ionization and chemi-recombination processes on the populations of higher states of hydrogen in the layers of a stellar atmosphere. The group of processes includes ionization: H * (n) + H(1s) =⇒ H + 2 +e , H * (n)+H(1s) =⇒ H(1s)+H + +e, and inverse recombination: , where H * (n) is the hydrogen atom in a state with the principal quantum number n 1, and H + 2 is the hydrogen molecular ion in a weakly bound rho-vibrational state of the ground state. These processes have been treated within the framework of the semi-classical approximation, developed in several previous papers, and have been included in the general stellar atmosphere code . We present results for an M dwarf atmosphere with T eff = 3800 K and find that the inclusion of chemi-ionization and chemi-recombination processes is significant in the low temperature parts of the atmosphere.
CHEMI-IONIZATION IN SOLAR PHOTOSPHERE: INFLUENCE ON THE HYDROGEN ATOM EXCITED STATES POPULATION
The Astrophysical Journal Supplement Series, 2011
In this paper, the influence of chemi-ionization processes in H * (n ≥ 2)+H(1s) collisions, as well as the influence of inverse chemi-recombination processes on hydrogen atom excited-state populations in solar photosphere, are compared with the influence of concurrent electron-atom and electron-ion ionization and recombination processes. It has been found that the considered chemiionization/recombination processes dominate over the relevant concurrent processes in almost the whole solar photosphere. Thus, it is shown that these processes and their importance for the non-LTE modeling of the solar atmosphere should be investigated further.