scholarly journals FBILI method for the two-level atom line formation in media with low velocity fields

2014 ◽  
pp. 53-67
Author(s):  
I. Pirkovic ◽  
O. Atanackovic
Keyword(s):  
Finite Thickness ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Benchmark Problems ◽  
Line Formation ◽  
Convergence Properties ◽  
Low Velocity ◽  
Level Atom ◽  
Line Transfer ◽  
Transfer Problems

In this paper we generalized the fast convergent Forth-and-Back Implicit Lambda Iteration (FBILI) method to the solution of the two-level atom line transfer problems in media with low velocity fields using the observer?s reference frame. In order to test the accuracy and the convergence properties of the method we solved several astrophysically important benchmark problems of the NLTE line formation: in a plan-parallel differentially expanding medium of finite thickness, and in spherically symmetric stellar atmospheres, both static and expanding. We compared our solutions with those obtained by other authors using different numerical methods.

scholarly journals Iteration factors in the line formation problem with frequency dependent source function

2010 ◽  
pp. 81-89 ◽  
Author(s):  
O. Kuzmanovska-Barandovska
Keyword(s):  
Source Function ◽  
Transfer Problem ◽  
Pure Line ◽  
Line Formation ◽  
Convergence Properties ◽  
Frequency Dependent ◽  
Variable Property ◽  
Level Atom ◽  
Back Ground ◽  
Line Transfer

In this paper some iteration factors families introduced previously to solve the pure line transfer problem are generalized to the case when the back- ground continuum is taken into account. The convergence properties of these factors are discussed when they are applied to the solution of the two-level atom line transfer problem in a constant and variable property media.

scholarly journals Tomography of cool giant and supergiant star atmospheres

2018 ◽  
Vol 610 ◽  
pp. A29 ◽  
Author(s):  
K. Kravchenko ◽  
S. Van Eck ◽  
A. Chiavassa ◽  
A. Jorissen ◽  
B. Freytag ◽  
...  
Keyword(s):  
Spectral Line ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Line Of Sight ◽  
Line Formation ◽  
Tomographic Method ◽  
1D Model ◽  
Supergiant Star

Context. Cool giant and supergiant star atmospheres are characterized by complex velocity fields originating from convection and pulsation processes which are not fully understood yet. The velocity fields impact the formation of spectral lines, which thus contain information on the dynamics of stellar atmospheres. Aim. The tomographic method allows to recover the distribution of the component of the velocity field projected on the line of sight at different optical depths in the stellar atmosphere. The computation of the contribution function to the line depression aims at correctly identifying the depth of formation of spectral lines in order to construct numerical masks probing spectral lines forming at different optical depths. Methods. The tomographic method is applied to one-dimensional (1D) model atmospheres and to a realistic three-dimensional (3D) radiative hydrodynamics simulation performed with CO5BOLD in order to compare their spectral line formation depths and velocity fields. Results. In 1D model atmospheres, each spectral line forms in a restricted range of optical depths. On the other hand, in 3D simulations, the line formation depths are spread in the atmosphere mainly because of temperature and density inhomogeneities. Comparison of cross-correlation function profiles obtained from 3D synthetic spectra with velocities from the 3D simulation shows that the tomographic method correctly recovers the distribution of the velocity component projected on the line of sight in the atmosphere.

scholarly journals Nonradial Oscillations: The Cause of Macroturbulence in Late-Type Stars?

1980 ◽  
Vol 58 ◽  
pp. 307-312
Author(s):  
Myron A. Smith
Keyword(s):  
Fundamental Problem ◽  
Velocity Fields ◽  
Stellar Atmospheres ◽  
Line Formation ◽  
Line Broadening ◽  
Late Type ◽  
Solar Granulation ◽  
Short Period ◽  
The Many ◽  
Primary Velocity

A fundamental problem in contemporary stellar atmospheres research concerns the cause of what the spectroscoplst calls “macroturbulence.” Even in so well studied a star as the Sun, it is unclear as to which of the many resolved velocity fields is most responsible for the broadening of the disk-integrated spectrum. There are several uncertainties attached to the identification of this primary velocity field. To cite one, Beckers (1980) indicates in a recent review that the two principal contributors to macroturbulence, convective granulation and the five-minute nonradial oscilltion pattern, each add only an r.m. s. velocity of 1/2 km s at τ5000 = 0.1. According to him, even when they are put together with related unresolved patterns [e.g. subgranulation and short period (<30) oscilltions] the sum of all known velocities seems to fall short of macroturbulence obtained from line broadening studies [~ 3 km s-1; radial-tangential model (Gray 1977, Smith 1978)]. The most recent models of the solar granulation field (Keil 1980) suggest somewhat higher velocities, e.g. 1.1 km s-1 at τ5000 = 0.1, when revised corrections for terrestrial seeing are taken into account. Nonetheless, such corrections must be added to both the convection and oscillation amplitudes, so it is still not clear whether one of these fields dominates the line formation.

Velocity fields in stellar atmospheres and the concept of microturbulence

1973 ◽  
Vol 15 ◽  
pp. 39-60 ◽  
Author(s):  
Gordon Worrall ◽  
Alistair M. Wilson
Keyword(s):  
Velocity Fields ◽  
Stellar Atmospheres

POLARIZED LINE FORMATION IN NON-MONOTONIC VELOCITY FIELDS

2016 ◽  
Vol 833 (1) ◽  
pp. 32 ◽  
Author(s):  
M. Sampoorna ◽  
K. N. Nagendra
Keyword(s):  
Velocity Fields ◽  
Line Formation

scholarly journals Formation Depths of Spectral Lines in Cepheids

1995 ◽  
Vol 155 ◽  
pp. 373-374
Author(s):  
Michael D. Albrow ◽  
P. L. Cottrell
Keyword(s):  
Spectral Line ◽  
Velocity Fields ◽  
Radial Velocities ◽  
Spectral Lines ◽  
Line Formation ◽  
Ionisation Potential ◽  
Velocity Gradients ◽  
Different Levels ◽  
Line Depth

There has been a number of observational programmes that have endeavoured to investigate the atmospheric velocity fields in Cepheids (e.g., Sanford 1956, Wallerstein et al. 1992, Butler 1993). These studies measured the radial velocities of lines of different strength, excitation and ionisation potential as these provide an indication of line formation at different levels in the atmosphere. From these measurements, the presence of velocity gradients can be inferred, but determination of the magnitude of such gradients requires knowledge of the spectral line depth of formation. Through dynamical modelling we are endeavouring to ascertain what is actually being measured in the above observational programmes.

scholarly journals Cobalt-Hydrogen Atomic and Ionic Collisional Data

Atoms ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 34
Author(s):  
Svetlana A. Yakovleva ◽  
Andrey K. Belyaev ◽  
Maria Bergemann
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Ion Pair ◽  
Pair Formation ◽  
Stellar Atmospheres ◽  
Rate Coefficients ◽  
Line Formation ◽  
Non Local ◽  
Excitation Processes ◽  
Inelastic Processes ◽  
Ionized Systems

Rate coefficients for inelastic processes in low-energy Co + H, Co + + H − , Co + + H , and Co 2 + + H − collisions are estimated using the quantum simplified model. Considerations include 44 triplet and 55 quintet molecular states of CoH, as well as 91 molecular states of CoH + . The estimations provide the rate coefficients for the 4862 partial processes (mutual neutralization, ion-pair formation, excitation, and de-excitation) in the neutral CoH system, and for the 8190 partial processes in the ionized CoH + system, 13 , 052 processes in total. At T = 6000 K, the rate coefficients with the largest values around 6 × 10 − 8 cm 3 s − 1 correspond to the mutual neutralization processes into the Co ( e 2 F ) + H and Co + ( g 5 F ) + H final channels in the neutral and ionized systems, respectively. Among the excitation and de-excitation processes in Co + H and in Co + + H collisions, at T = 6000 K, the largest rate coefficients have values around 7 × 10 − 9 cm 3 s − 1 and correspond to the processes Co ( y 2 S ∘ ) + H → Co ( e 2 F ; v 4 D ∘ ) + H and Co + ( h 3 P ) + H → Co + ( g 3 P ; g 5 P ; g 5 F ) + H , respectively. The calculations single out inelastic processes important for non-local thermodynamic equilibrium (NLTE) modelling of Co I and Co II spectra in stellar atmospheres. The test NLTE calculations are carried out, and it is found that the new collision rates have a strong effect on the line formation and NLTE abundance corrections.

scholarly journals Mg line formation in late-type stellar atmospheres

2015 ◽  
Vol 579 ◽  
pp. A53 ◽  
Author(s):  
Y. Osorio ◽  
P. S. Barklem ◽  
K. Lind ◽  
A. K. Belyaev ◽  
A. Spielfiedel ◽  
...  
Keyword(s):  
Stellar Atmospheres ◽  
Line Formation ◽  
Late Type
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