Three-dimensional hydrodynamical CO5BOLD model atmospheres of red giant stars VI. First chromosphere model of a late-type giant

Although observational data unequivocally point out to the presence of chromospheres in red giant stars, no attempts have been made so far to model them using 3D hydrodynamical model atmospheres. We therefore compute an exploratory 3D hydrodynamical model atmosphere for a cool red giant in order to study the dynamical and thermodynamic properties of its chromosphere, as well as the influence of the chromosphere on its observable properties. 3D radiation hydrodynamics simulations are carried out with the CO5BOLD model atmosphere code for a star with the atmospheric parameters (Teff=4010 K, log g=1.5, [M/H]=0.0), which are similar to those of the K-type giant star Aldebaran (alpha Tau). ... we compute the emergent continuum intensity maps at different wavelengths, spectral line profiles of Ca II K, the Ca II infrared triplet line at 854.2nm, and H alpha, as well as the spectral energy distribution (SED) of the emergent radiative flux. The initial model quickly develops a dynamical chromosphere characterised by propagating and interacting shock waves. The peak temperatures in the chromospheric shock fronts reach values on the order of up to 5000 K although the shock fronts remain quite narrow. Like for the Sun, the gas temperature distribution in the upper layers is composed of a cool component due to adiabatic cooling in the expanding post-shock regions and a hot component due to shock waves. For this red giant model, the hot component is a rather flat high-temperature tail, which nevertheless affects the resulting average temperatures significantly. The simulations show that the atmospheres of red giant stars are dynamic and intermittent. Consequently, many observable properties cannot be reproduced with one-dimensional static models but demand for advanced 3D HD modelling. Furthermore, including a chromosphere in the models might produce significant contributions to the emergent UV flux.Comment: 14 pages, 8 figures, A&A (2017, accepted

Konvekcijos ir nelokalaus spinduliuotės lauko įtaka spektro linijų formavimuisi žvaigždžių atmosferose

In the Thesis, the influence of convection and non-equilibrium radiative transfer on the structure of stellar atmospheres and spectral line properties is investigated. State-of-the-art three-dimensional hydrodynamical model atmospheres are used to study the role of convection in the formation of spectral lines of neutral iron in the metal-poor red giant HD 122563, as well as its impact on the formation of spectral lines of light elements (Li, Na, Mg, Al, K, Mg, Ca) in the atmospheres of red giant stars. The influence of convection on the spectral line properties increases with decreasing metallicity of the star: in red giants, abundance corrections for the light elements do not exceed 0.1 dex at solar metallicity while at [M/H] = –3.0 corrections reach up to –0.7 dex. Convection and non-equilibrium radiative transfer have a significant impact on the strength and shape of Li I 670.8 nm resonance doublet. The latter effect is most pronounced in solar metallicity red giants where 3D NLTE – 1D LTE abundance corrections reach up to +0.3 dex, while for the main sequence and subgiant stars these corrections do not exceed +0.2 dex. In the Thesis, methodical techniques and abundance corrections are provided which can be used in the future studies to determine 3D NLTE Li abundance in the atmospheres of main sequence, subgiant and red giant stars

The influence of convection and non-local radiative field on spectral line formation in stellar atmospheres

In the Thesis, the influence of convection and non-equilibrium radiative transfer on the structure of stellar atmospheres and spectral line properties is investigated. State-of-the-art three-dimensional hydrodynamical model atmospheres are used to study the role of convection in the formation of spectral lines of neutral iron in the metal-poor red giant HD 122563, as well as its impact on the formation of spectral lines of light elements (Li, Na, Mg, Al, K, Mg, Ca) in the atmospheres of red giant stars. The influence of convection on the spectral line properties increases with decreasing metallicity of the star: in red giants, abundance corrections for the light elements do not exceed 0.1 dex at solar metallicity while at [M/H] = –3.0 corrections reach up to –0.7 dex. Convection and non-equilibrium radiative transfer have a significant impact on the strength and shape of Li I 670.8 nm resonance doublet. The latter effect is most pronounced in solar metallicity red giants where 3D NLTE – 1D LTE abundance corrections reach up to +0.3 dex, while for the main sequence and subgiant stars these corrections do not exceed +0.2 dex. In the Thesis, methodical techniques and abundance corrections are provided which can be used in the future studies to determine 3D NLTE Li abundance in the atmospheres of main sequence, subgiant and red giant stars

The sense of the feasibility of the new nuclear power plant on the background of security of energy supply

The main idea of the paper is that security of energy supply is the background of evaluation of feasibility and competitiveness of the new nuclear power plant. The research is based on general hypothesis that on the basis of economic evaluation of the risk of interruption of energy supply it is possible to give correct justification of energy development scenario.Straipsnyje nagrinėjamas branduolinės energetikos ekonominis pagrįstumas ir konkurencingumas atsižvelgiant į energijos tiekimo patikimumo aspektą. Tyrimai grindžiami bendra moksline hipoteze; kad energijos tiekimo pertrūkių rizikos ekonominis vertinimas leistų palyginti įvairias energijos rūšis. Parodoma; kokiu pagrindu šiuos aspektus galima ekonomiškai vertinti; geriau argumentuojant vieno ar kito energetikos raidos scenarijaus pagrįstumą

Sense of the feasibility of the new nuclear power plant on the background of security of energy supply

The main idea of the paper is that security of energy supply is the background of evaluation of feasibility and competitiveness of the new nuclear power plant. The research is based on general hypothesis that on the basis of economic evaluation of the risk of interruption of energy supply it is possible to give correct justification of energy development scenario