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 Diagnostic methods based on scattering polarization and the joint action of the Hanle and Zeeman effects

2008 ◽  
Vol 4 (S259) ◽  
pp. 623-632
Author(s):  
Javier Trujillo Bueno
Keyword(s):  
Magnetic Fields ◽  
Solar Physics ◽  
Energy Levels ◽  
Zeeman Effect ◽  
Polarized Light ◽  
Thomson Scattering ◽  
Stellar Atmospheres ◽  
Diagnostic Methods ◽  
Spectral Lines ◽  
Polarized Radiation

AbstractPolarized light provides the most reliable source of information at our disposal for diagnosing the physical properties of astrophysical plasmas, including the magnetic fields of the solar atmosphere. The interaction between radiation and hydrogen plus free electrons through Rayleigh and Thomson scattering gives rise to the polarization of the stellar continuous spectrum, which is very sensitive to the medium's thermal and density structure. Anisotropic radiative pumping processes induce population imbalances and quantum coherences among the sublevels of degenerate energy levels (that is, atomic level polarization), which produce polarization in spectral lines without the need of a magnetic field. The Hanle effect caused by the presence of relatively weak magnetic fields modifies the atomic polarization of the upper and lower levels of the spectral lines under consideration, allowing us to detect magnetic fields to which the Zeeman effect is blind. After discussing the physical origin of the polarized radiation in stellar atmospheres, this paper highlights some recent developments in polarized radiation diagnostic methods and a few examples of their application in solar physics.

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 Small Scale Solar Magnetic Fields: Theory

1977 ◽  
Vol 4 (2) ◽  
pp. 241-250 ◽  
Author(s):  
N. O. Weiss
Keyword(s):  
Magnetic Fields ◽  
Field Strength ◽  
Solar Physics ◽  
Small Scale ◽  
The Sun ◽  
Solar Magnetic Fields ◽  
Solar Granulation ◽  
The Past ◽  
Maximum Field Strength ◽  
Maximum Field

One of the most exciting developments in solar physics over the past eight years has been the success of ground based observers in resolving features with a scale smaller than the solar granulation. In particular, they have demonstrated the existence of intense magnetic fields, with strengths of up to about 1600G. Harvey (1976) has just given an excellent summary of these results.In solar physics, theory generally follows observations. Inter-granular magnetic fields had indeed been expected but their magnitude came as a surprise. Some problems have been discussed in previous reviews (Schmidt, 1968, 1974; Weiss, 1969; Parker, 1976d; Stenflo, 1976) and the new observations have stimulated a flurry of theoretical papers. This review will be limited to the principal problems raised by these filamentary magnetic fields. I shall discuss the interaction of magnetic fields with convection in the sun and attempt to answer such questions as: what is the nature of the equilibrium in a flux tube? how are the fields contained? what determines their stability? how are such strong fields formed and maintained? and what limits the maximum field strength?

scholarly journals Magnetic fields of rapidly oscillating Ap stars

1993 ◽  
Vol 139 ◽  
pp. 132-132
Author(s):  
G. Mathys
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Zeeman Effect ◽  
Rotation Frequency ◽  
Spectral Lines ◽  
Driving Mechanism ◽  
Line Splitting ◽  
Ap Stars ◽  
The Magnetic Field

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.

scholarly journals WHY IS NON-THERMAL LINE BROADENING OF SPECTRAL LINES IN THE LOWER TRANSITION REGION OF THE SUN INDEPENDENT OF SPATIAL RESOLUTION?

2015 ◽  
Vol 799 (1) ◽  
pp. L12 ◽  
Author(s):  
B. De Pontieu ◽  
S. McIntosh ◽  
J. Martinez-Sykora ◽  
H. Peter ◽  
T. M. D. Pereira
Keyword(s):  
Transition Region ◽  
Spatial Resolution ◽  
Spectral Lines ◽  
The Sun ◽  
Line Broadening ◽  
Lower Transition ◽  
Thermal Line

scholarly journals Investigations of space magnetism at the Crimean Astrophysical Observatory. II. Direct spectropolarimetric measurements of stellar magnetic fields

2020 ◽  
Vol 1 (2) ◽  
pp. 26-36
Author(s):  
Sergei Plachinda ◽  
Varvara Butkovskaya
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Spectral Lines ◽  
Crimean Astrophysical Observatory ◽  
Scientific School ◽  
Pulsation Period ◽  
Echelle Spectrograph ◽  
Direct Measurements ◽  
Stellar Magnetic Fields ◽  
The Magnetic Field

A research on stellar magnetism in Crimea was initiated by pioneer works of A.B. Severny, V.E. Stepanov, and D.N. Rachkovsky. Today, the study of stellar magnetic fields is a key field of research at the Crimean Astrophysical Observatory (CrAO). The 2.6 m Shajn telescope equipped with the echelle spectrograph ESPL, CCD, and Stokesmeter (a circular polarization analyzer) allows us to study the magnetic field of bright stars up to 5m–6m. The Single Line (SL) technique is developed for measuring magnetic fields at CrAO. This technique is based on the calculation of the Zeeman effect in individual spectral lines. A key advantage of the SL technique is its ability to detect local magnetic fields on the surface of stars. Many results in the field of direct measurements of stellar magnetic fields were obtained at CrAO for the first time. In particular, the magnetic field on supergiants (ǫ Gem), as well as on a number of subgiants, giants, and bright giants was first detected. This, and investigations of other authors, confirmed the hypothesis that a magnetic field is generated at all the stages of evolution of late-type stars, including the stage of star formation. The emergence of large magnetic flux tubes at the surface of stars of V-IV-III luminosity classes (61 Cyg A, β Gem, β Aql) was first registered. In subgiants, the magnetic field behavior with the activity cycle was first established for β Aql. Using the long-term Crimean spectroscopic and spectropolarimetric observations of α Lyr, the 22-year variability cycle of the star, supposedly associated with meridional flows, is confirmed. Magnetic field variability with the pulsation period was first detected for different types of pulsating variables: the classical Cepheid β Aql, the low-amplitude β Cep-type variable γ Peg, and others. In this review we cover more than a half-century history of the formation of the Crimean scientific school for high-precision direct measurements of stellar magnetic fields.

6. The future of solar physics

2020 ◽  
pp. 149-154
Author(s):  
Philip Judge
Keyword(s):  
Solar Wind ◽  
Magnetic Fields ◽  
Coronal Mass Ejections ◽  
Solar Physics ◽  
Solar Telescope ◽  
The Sun ◽  
New Era ◽  
The Future ◽  
To Come ◽  
Orbiter Mission

Solar physics is a historically data-starved science, but about to becomes less so. ‘The future of solar physics’ looks at new facilities, either online or about to come online, such as the Daniel K. Inouye Solar Telescope on Maui. This aims to see, through measurements of coronal magnetic fields and plasma, how the Sun’s magnetic fields generate flares, coronal mass ejections, and the solar wind. Other major missions include NASA’s Parker Solar Probe and the European Solar Orbiter mission, spacecraft intended to orbit the Sun in new ways and from different viewpoints on Earth. Supported by increasingly powerful computers, these missions are ushering in a new era.

scholarly journals Zeeman effects for fine structure components of thallium spectral lines

1930 ◽  
Vol 129 (809) ◽  
pp. 48-70 ◽  
Keyword(s):  
Fine Structure ◽  
Magnetic Fields ◽  
Atomic Structure ◽  
Zeeman Effect ◽  
Spectral Lines ◽  
Correct Classification ◽  
Vector Coupling ◽  
Atomic Nuclei ◽  
Extensive Analysis ◽  
Quantum Vector

For many years the study of the Zeeman effect with various types of spectra lines has been a very successful method of investigating the electronic features of atomic structure. More recently it has proved to be a successful means of investigating some of the characteristics of atomic nuclei. Certain considerations now being brought forward, associate the fine structure of spectral lines with the spin of the nuclei of the atoms in which the radiation originates. As spectral lines with fine structure components having separations of a considerable magnitude have been found in the spectra of thallium and other elements, it is evident that in a study of the Zeeman effects for these components with magnetic fields of various strengths, a very promising filed of investigation has been created. In the investigation top be described initially to securing Zeeman effects for certain prominent lines in the spark spectrum of thallium in order to obtain information which would lead to their correct classification. While this work was in progress, other investigators, utilising the information at hand concerning the spectra of Hg I and Pb III, were able to assign classifications to a few of the wave-lengths of thallium II in question. These results are now embodied in the publication of a more extensive analysis by McLennan, McLay and Crawford ( loc. cit .). It was thought well, however, to continue the Zeeman effect investigation having in mind either the confirmation of their classification or the extension of the information available regarding the Zeeman effect with elements of high atomic number. In general, the spectra of such atoms indicate interesting quantum vector coupling types.

scholarly journals roAp stars

1995 ◽  
Vol 10 ◽  
pp. 338-340
Author(s):  
D. Kurtz ◽  
P. Martinez
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Field Strength ◽  
Magnetic Field Strength ◽  
Rotation Axis ◽  
Zeeman Effect ◽  
Spectral Lines ◽  
Effective Magnetic Field ◽  
Surface Magnetic Field ◽  
Ap Stars

Among the A stars there is a subclass of peculiar stars, the Ap stars, which show strongly enhanced spectral lines of the Fe peak, rare earth and lanthanide elements. These stars have global surface magnetic fields several orders of magnitude larger than that of the Sun, 0.3 to 30 kGauss is the measured range. For stars with the strongest magnetic fields, the spectral lines are split by the Zeeman Effect and the surface magnetic field strength can be measured. Generally, though, the magnetic fields are not strong enough for the magnetic splitting to exceed other sources of line broadening. In these cases residual polarization differences between the red and blue wings of the spectral lines give a measure of the effective magnetic field strength - the integral of the longitudinal component of the global magnetic field over the visible hemisphere, weighted by limb-darkening. In the Ap stars the effective magnetic field strengths vary with rotation. This is well understood in terms of the oblique rotator model in which the magnetic axis is oblique to the rotation axis, so that the magnetic field is seen from varying aspect with rotation.

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.

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