scholarly journals Hydrogen Line Profiles

1995 ◽  
Vol 10 ◽  
pp. 411-414 ◽  
Author(s):  
I. Hubeny
Keyword(s):  
Transfer Problem ◽  
Current Status ◽  
Line Profiles ◽  
Line Broadening ◽  
Hydrogen Line ◽  
Radiative Transfer Problem ◽  
Frequency Redistribution ◽  
Sufficient Detail ◽  
High Degree ◽  
Complete Frequency

Observed hydrogen line profiles are an enormously important source of diagnostic information about virtually all kinds of astronomical bodies. Therefore, it is important to understand the hydrogen line formation in sufficient detail to be able to achieve a high degree of reliability by analyzing observed hydrogen line profiles.Calculation of the predicted hydrogen line profiles involves two basic ingredients, (i) intrinsic line profiles, or line broadening - ”atomic physics” part, and (ii) the radiative transfer problem - ”astrophysics” part. There is not enough space to discuss here the current status of the astrophysical part of the problem. Fortunately, this topic is covered by many reviews. There are two major problems here, (a) departures from local thermodynamic equilibrium (LTE) - the so-called non-LTE description (e.g. Mihalas 1978; Hubenyet al.1994); and (b) departures from complete frequency redistribution (Cooperet al.1989; Hubeny and Lites 1994).

scholarly journals ∊ Aur in eclipse: Post-AGB primary and disk-shaped secondary

2011 ◽  
Vol 7 (S283) ◽  
pp. 454-455
Author(s):  
Chinnathambi Muthumariappan ◽  
Mudumba Parthasarathy ◽  
Kanniah Jayakumar ◽  
Manickam Appakutty
Keyword(s):  
High Resolution ◽  
Binary System ◽  
Radiative Transfer ◽  
Transfer Problem ◽  
Line Profiles ◽  
Radiative Transfer Problem ◽  
Eclipsing Binary ◽  
Preliminary Results ◽  
Spectroscopic Monitoring

AbstractWe present physical and chemcal properties of the disk in the eclipsing binary system ∊ Aur by solving 2D radiative transfer problem. We also present preliminary results of our high resolution spectroscopic monitoring of K I, Na, and Hα line profiles variation during the totality phase of the recent eclipse of ∊ Aur.

scholarly journals Semi-empirical model atmospheres for the chromosphere of the sunspot penumbra and umbral flashes

2019 ◽  
Vol 627 ◽  
pp. A46 ◽  
Author(s):  
Souvik Bose ◽  
Vasco M. J. Henriques ◽  
Luc Rouppe van der Voort ◽  
Tiago M. D. Pereira
Keyword(s):  
Transition Region ◽  
Empirical Model ◽  
Solar Chromosphere ◽  
Line Profiles ◽  
Frequency Redistribution ◽  
Lower Transition ◽  
Semi Empirical ◽  
Complete Frequency ◽  
Imaging Spectrograph ◽  
Sunspot Penumbra

Context. The solar chromosphere and the lower transition region are believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution (CRD) in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmospheres that reproduce the features of the Mg II h&k line profiles that sample the middle chromosphere with focus on a sunspot. Methods. We used spectropolarimetric observations of the Ca II 8542 Å spectra obtained with the Swedish 1 m Solar Telescope and used NICOLE inversions to obtain semi-empirical model atmospheres for different features in and around a sunspot. These were used to synthesize Mg II h&k spectra using the RH1.5D code, which we compared with observations taken with the Interface Region Imaging Spectrograph (IRIS). Results. Comparison of the synthetic profiles with IRIS observations reveals that there are several areas, especially in the penumbra of the sunspot, where most of the observed Mg II h&k profiles are very well reproduced. In addition, we find that supersonic hot down-flows, present in our collection of models in the umbra, lead to synthetic profiles that agree well with the IRIS Mg II h&k profiles, with the exception of the line core. Conclusions. We put forward and make available four semi-empirical model atmospheres. Two for the penumbra, reflecting the range of temperatures obtained for the chromosphere, one for umbral flashes, and a model representative of the quiet surroundings of a sunspot.

scholarly journals Diffuse Galactic Light in the UV and Visible

1990 ◽  
Vol 139 ◽  
pp. 127-138
Author(s):  
A. N. Witt
Keyword(s):  
Radiative Transfer ◽  
Interstellar Medium ◽  
Transfer Problem ◽  
Coherent Scattering ◽  
Space Mission ◽  
Radiative Transfer Problem ◽  
The Galaxy ◽  
The Subject ◽  
High Degree ◽  
Galactic Distribution

The diffuse galactic light, resulting from the coherent scattering of galactic starlight by dust grains contained in the general interstellar medium, has been the subject of active investigation for nearly 60 years. The separation of the diffuse galactic light from the other sources contributing to the light from the night sky has proven difficult, and different attempts at measuring the intensity and galactic distribution of the diffuse galactic light, both in the visible and the UV, are reviewed here. The interpretation of such measurements in terms of average scattering properties of interstellar grains is subject to additional uncertainties, stemming from the high degree of idealization imposed on the galaxy models used to study the radiative transfer problem. In the visible, the observations are more nearly definitive and the model problems less severe; reasonably consistent scattering properties have therefore been derived for this spectral region. In the UV, the situation is considerably less satisfactory, mainly due to a lack of sufficiently extensive, reliable measurements of the diffuse galactic light intensity at λ < 200 nm. A dedicated space mission may be the required solution. The radiative transfer in the UV presents serious difficulties due to the increasing opacity of the interstellar medium with shorter wavelengths and the resulting growing importance of the local galactic structure.

Effects of Ambipolar Diffusion on Prominence Thread Models

1994 ◽  
Vol 144 ◽  
pp. 315-321 ◽  
Author(s):  
M. G. Rovira ◽  
J. M. Fontenla ◽  
J.-C. Vial ◽  
P. Gouttebroze
Keyword(s):  
Energy Balance ◽  
Transition Region ◽  
Ambipolar Diffusion ◽  
Line Profiles ◽  
Balance Equations ◽  
Model Calculations ◽  
Partial Frequency ◽  
Frequency Redistribution ◽  
Partial Frequency Redistribution ◽  
Theoretical Structure

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.

Hydrogen line profiles at low densities

1984 ◽  
Vol 9 (4) ◽  
pp. 697-704 ◽  
Author(s):  
C. Stehlé ◽  
N. Feautrier
Keyword(s):  
Line Profiles ◽  
Hydrogen Line
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