The Interpretation of Line Profiles

1977 ◽  
Vol 36 ◽  
pp. 191-215
Author(s):  
G.B. Rybicki
Keyword(s):  
Magnetic Fields ◽  
Atomic Physics ◽  
Velocity Fields ◽  
Spectral Lines ◽  
Inhomogeneous Structure ◽  
The Sun ◽  
Line Profiles ◽  
Physical Phenomena

Observations of the shapes and intensities of spectral lines provide a bounty of information about the outer layers of the sun. In order to utilize this information, however, one is faced with a seemingly monumental task. The sun’s chromosphere and corona are extremely complex, and the underlying physical phenomena are far from being understood. Velocity fields, magnetic fields, Inhomogeneous structure, hydromagnetic phenomena – these are some of the complications that must be faced. Other uncertainties involve the atomic physics upon which all of the deductions depend.

scholarly journals Summary-Introduction

1960 ◽  
Vol 12 ◽  
pp. 403-415
Author(s):  
A. B. Severny
Keyword(s):  
Magnetic Fields ◽  
Active Regions ◽  
Magnetic Activity ◽  
Velocity Fields ◽  
Spectral Lines ◽  
The Sun ◽  
Line Profiles ◽  
Doppler Shifts ◽  
State Of Affairs ◽  
Image Position

Speaking on localized velocity fields on the Sun, we mean the velocity fields in active regions on the disk. The experimental data used to picture these fields are based mainly on 1) the observations of Doppler shifts of spectral lines, 2) the form (asymmetry) of line profiles, 3) moving picture process in monochromatic, mainly Hα and H or K, light. However the big skin-time of solar plasma makes these data insufficient to get an adequate and complete idea about the motions in active regions, and we must also take into account the available observational data about magnetic fields in these regions. Somewhere the state of affairs permits one to disregard the possible influence of magnetic fields on the picture of velocity fields But these occasions are comparatively rare, because the main source of solar activity is closely, but in a not quite recognized way, connected with magnetic activity of the Sun. This is why we should in our talk consider as closely as possible both subjects—the motions in active regions and their magnetic fields. The best illustrations of the necessity of such a mode of consideration are the velocity fields in sunspots.

scholarly journals Ultra-weak magnetic fields in Am stars: β UMa and θ Leo

2014 ◽  
Vol 10 (S305) ◽  
pp. 67-72 ◽  
Author(s):  
A. Blazère ◽  
P. Petit ◽  
F. Lignières ◽  
M. Aurière ◽  
J. Ballot ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Large Fraction ◽  
Spectral Lines ◽  
Line Profiles ◽  
Circularly Polarized ◽  
Structure And Dynamics ◽  
Weak Magnetic Fields ◽  
Magnetic Origin ◽  
The One ◽  
Ap Stars

AbstractAn extremely weak circularly-polarized signature was recently detected in the spectral lines of the Am star Sirius A. With a prominent positive lobe, the shape of the phase-averaged Stokes V line profile is atypical of stellar Zeeman signatures, casting doubts on its magnetic origin. We report here on ultra-deep spectropolarimetric observations of two more bright Am stars: β Uma and θ Leo. Stokes V line signatures are detected in both objects, with a shape and amplitude similar to the one observed on Sirius A. We demonstrate that the amplitude of the Stokes V line profiles depend on various line parameters (Landé factor, wavelength, depth) as expected from a Zeeman signature, confirming that extremely weak magnetic fields are likely present in a large fraction of Am stars. We suggest that the strong asymmetry of the polarized signatures, systematically observed so far in Am stars and never reported in strongly magnetic Ap stars, bears unique information about the structure and dynamics of the thin surface convective shell of Am stars.

Theory of the Solar 22-Year Cycle

1971 ◽  
Vol 2 (1) ◽  
pp. 7-10 ◽  
Author(s):  
J. H. Piddington
Keyword(s):  
Magnetic Fields ◽  
Solar Surface ◽  
Velocity Fields ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Radio Bursts ◽  
X Rays ◽  
Plasma Velocity ◽  
Full Understanding ◽  
Satisfactory Theory

If there were no solar magnetic fields, then the most active feature observable on the Sun would be the hydrodynamic convection. There would be no sunspots, flares, prominences, plage, spicules, and no copious emissions of X-rays, energetic particles or radio bursts. These effects are all due to the presence of a changing pattern of magnetic fields which repeats every 22 years. While observations of electromagnetic phenomena are limited to the solar surface and atmosphere, a full understanding of these effects must include a satisfactory theory of the solar cycle and of the fields which evolve beneath the surface as a result of plasma velocity fields.

scholarly journals Study of the effects of magnetic braking on the lithium abundances of the Sun and solar-type stars

2020 ◽  
Vol 496 (2) ◽  
pp. 1343-1354
Author(s):  
R Caballero Navarro ◽  
A García Hernández ◽  
A Ayala ◽  
J C Suárez
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Globular Clusters ◽  
Main Sequence ◽  
The Sun ◽  
Depletion Rate ◽  
Solar Type ◽  
Magnetic Braking ◽  
Physical Phenomena ◽  
The Impact

ABSTRACT The study of lithium (Li) surface abundance in the Sun and young stellar globular clusters which are seemingly anomalous in present-day scenarios, as well as the influence of rotation and magnetic braking (MB) on its depletion during pre-main sequence (PMS) and main sequence (MS). In this work, the effects of rotational mixing and of the rotational hydrostatic effects on Li abundances are studied by simulating several grids of PMS and MS rotating and non-rotating models. Those effects are combined with the additional impact of the MB (with magnetic field intensities ranging between 3.0 and 5.0 G). The data obtained from simulations are confronted by comparing different stellar parameters. The results show that the surface Li abundance for the Sun-like models at the end of the PMS and throughout the MS decreases when rotational effects are included, that is the Li depletion rate for rotating models is higher than for non-rotating ones. This effect is attenuated when the MB produced by a magnetic field is present. This physical phenomena impacts also the star effective temperature (Teff) and its location in the HR diagram. The impact of MB in Li depletion is sensitive to the magnetic field intensity: the higher it is, the lower the Li destruction. A direct link between the magnetic fields and the convective zone (CZ) size is observed: stronger magnetic fields produce shallower CZ’s. This result suggests that MB effect must be taken into consideration during PMS if we aim to reproduce Li abundances in young clusters.

The Magnetic Sun from Different Views: A Comparison of the Mean and Background Magnetic Field Observations made in Different Observatories and in Different Spectral Lines

2000 ◽  
Vol 179 ◽  
pp. 209-212
Author(s):  
M. L. Demidov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Solar Observatory ◽  
Spectral Lines ◽  
The Sun ◽  
Background Magnetic Field ◽  
The Mean ◽  
Selection Of ◽  
Made In

AbstractA comparison is made of observational data on the mean magnetic field of the Sun from several observatories (a selection of published information and new measurements). Results of correlation and regression analyses of observations of background magnetic fields at the STOP telescope of the Sayan solar observatory in different spectral lines are also presented. Results obtained furnish an opportunity to obtain more unbiased information about large-scale magnetic fields of the Sun and, in particular, about manifestations of strong (kilogauss) magnetic fields in them.

scholarly journals Zeeman Doppler Imaging

1993 ◽  
Vol 138 ◽  
pp. 247-257
Author(s):  
William Wehlau ◽  
John Rice
Keyword(s):  
Integral Equation ◽  
Magnetic Fields ◽  
Model Atmosphere ◽  
Stellar Atmosphere ◽  
Spectral Lines ◽  
Doppler Imaging ◽  
Analytic Approximation ◽  
Line Profiles ◽  
Surface Mapping ◽  
Stellar Magnetic Fields

AbstractThe mapping of stellar surfaces using the observed profiles of spectral lines is described. The problem is expressed in terms of an integral equation to be solved, using Tikhonov’s method. The local line profiles may be given either by an analytic approximation or by the solution of the equation of transfer with a model atmosphere. The model atmospheres commonly used may not correctly represent the stellar atmosphere which may lead to errors in the derived surface maps. Tests of mapping programs and applications to real stars show the capabilities and limitations of surface mapping. Mapping stellar magnetic fields places more severe demands on the data and computational programs than mapping the abundance distributions.

scholarly journals Coronal Magnetic Fields

1986 ◽  
Vol 7 ◽  
pp. 447-456
Author(s):  
R. Pallavicini
Keyword(s):  
Magnetic Fields ◽  
Transition Region ◽  
Solar Physics ◽  
Zeeman Effect ◽  
Spectral Lines ◽  
The Sun ◽  
Direct Measurements ◽  
Future Space ◽  
Coronal Magnetic Fields ◽  
Polarization Characteristics

It is unfortunate that coronal magnetic fields cannot be easily measured, even in the case of the Sun. Except for a few measurements of magnetic fields in the transition region above sunspots, made using the conventional Zeeman effect, and except for the possibility of inferring the direction – not the intensity – of coronal magnetic fields using optical forbidden lines, direct measurements of coronal fields are virtually non-existent. The most promising method appears to be the use of the Hanle effect, i.e. the modification of polarization characteristics of spectral lines induced by magnetic fields. This method has been proposed for future space missions in solar physics, for instance for the European satellite SOHO, but its feasibility depends on the strength of the fields to be measured, which in any case must be higher than a few tens of Gauss.

scholarly journals On the manifestation in the Sun-as-a-star magnetic field measurements of the quiet and active regions

2010 ◽  
Vol 6 (S273) ◽  
pp. 56-60 ◽  
Author(s):  
Mikhail Demidov
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Active Regions ◽  
Field Measurements ◽  
Solar Observatory ◽  
Spectral Lines ◽  
The Sun ◽  
Time Data ◽  
Full Disk

AbstractThe best way to test the stellar magnetic field mapping codes is to apply them, with some changes, to the Sun, where high-precision disk-integrated and disk-resolved observations are available for a long time. Data sets of the full-disk magnetograms and the solar mean magnetic fields (SMMF) measurements are provided, for example, by the J.M.Wilcox Solar observatory (WSO) and by the Sayan Solar observatory (SSO). In the second case the measurements in the Stokes-meter mode simultaneously in many spectral lines are available. This study is devoted to analysis of the SSO quasi-simultaneous full-disk magnetograms and SMMF measurements. Changes of the SMMF signal with rotation of the surface large-scale magnetic fields are demonstrated. Besides, by deleting of selected pixels with active regions (AR) from the maps their contribution to the integrated SMMF signal is evaluated. It is shown that in some cases the role of AR can be rather significant.

Facular Models, the K-Line, and Magnetic Fields

1977 ◽  
Vol 4 (2) ◽  
pp. 261-264
Author(s):  
G. A. Chapman
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Atomic Physics ◽  
Solar Magnetic Field ◽  
Good Description ◽  
Velocity Fields ◽  
Small Scale ◽  
Solar Magnetic Fields ◽  
Spectroscopic Observations ◽  
Spatially Resolved

Photospheric faculae are now believed to be closely associated with the small-scale solar magnetic field. In order to obtain reliable observations of solar magnetic fields, one needs to have a good description of faculae, which is presently lacking. The problem in obtaining good observational data is severe because faculae are usually not spatially resolved, particularly so in the case of spectroscopic observations. Proper use of spectroscopic observations also requires some knowledge of solar velocity fields and atomic physics in the case of a non LTE analysis. Many of these problems can be avoided by making use of the wings of the Ca II K-line. The wing of this line is unaffected by magnetic and velocity effects. The formation of the line has become increasingly well understood and most of the wing (with the exception of the inner 1 - 2 Å) is formed in LTE. The line is so strong that its formation spans the whole depth of the photosphere.

scholarly journals Power Spectrum Analysis of Time Series in Positions and Intensities of Solar EUV Lines Observed with 0S0-8

1977 ◽  
Vol 43 ◽  
pp. 12-12c
Author(s):  
R. Grant Athay ◽  
O.R. White
Keyword(s):  
Time Series ◽  
Spectral Lines ◽  
The Sun ◽  
Line Profiles ◽  
Central Wavelength ◽  
University Of Colorado ◽  
Repeat Time ◽  
The University ◽  
Analysis Of Time Series ◽  
Extract Information

Several hundred hours of observing time with the University of Colorado spectrometer on 0S0-8 was devoted to rapidly repeated scans of one or two spectral lines while the instrument was pointed at a fixed location on the solar disk. These repeated line scans provide time series of line profiles at a given location on the sun from which we extract information on the line intensity, central wavelength and width. The data reported here are for the λ1816.93 and λ1817.45 lines of SiII. These lines are members of the same multiplet and have a gf ratio of 10:1. The lines were scanned with a slit or 1 x 20 arc second size projected on the sun. About half of the experiments were conducted by scanning only the 1816.93 line with a repeat time of about 15 seconds and about half included alternate scans of line λ1816.93 then λ1817.45 with a repeat time for each line of about 28 seconds.

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