NLTE Spectral Line Formation in a Three-Dimensional Atmosphere with Velocity Fields

1985 ◽  
pp. 215-224 ◽  
Author(s):  
Åke Nordlund
Keyword(s):  
Spectral Line ◽  
Three Dimensional ◽  
Velocity Fields ◽  
Line Formation ◽  
Spectral Line Formation

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 Neutral oxygen spectral line formation revisited with new collisional data: large departures from LTE at low metallicity

2009 ◽  
Vol 500 (3) ◽  
pp. 1221-1238 ◽  
Author(s):  
D. Fabbian ◽  
M. Asplund ◽  
P. S. Barklem ◽  
M. Carlsson ◽  
D. Kiselman
Keyword(s):  
Spectral Line ◽  
Line Formation ◽  
Spectral Line Formation ◽  
Low Metallicity

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 Effects of line-blocking on the non-LTE Fe I spectral line formation

2005 ◽  
Vol 442 (2) ◽  
pp. 643-650 ◽  
Author(s):  
R. Collet ◽  
M. Asplund ◽  
F. Thévenin
Keyword(s):  
Spectral Line ◽  
Line Formation ◽  
Spectral Line Formation
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