Solar Magnetic Fields and Velocities

1970 ◽  
Vol 1 (8) ◽  
pp. 363-364 ◽  
Author(s):  
R. G. Giovanelli
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Temperature Increase ◽  
Spectral Lines ◽  
Solar Magnetic Fields ◽  
Similar Increase ◽  
Physical Conditions ◽  
High Ionization ◽  
Reduced Intensity ◽  
The Continuum

It has long been known that Fraunhofer lines show variations in intensity from place to place over the Sun’s surface, these being particularly noticeable in spectroheliograms obtained in the strong chromospheric lines. An early account of the weaker Unes was given by d’Azam-buja. McMath, Mohler, Pierce and Goldberg attributed intensity increases in (or decreases in depth of) metallic spectral lines to local temperature increases. Sheeley used high-resolution spectra to study these line weakenings further, finding them where, and only where, strong non-spot magnetic fields occurred. He also reported that in many cases the continuum in such regions was of reduced intensity, suggesting that fields often occur in the dark lanes and pores in the granulation. Spectroheliograms obtained in the cores of the weakened lines (e.g., Fel 6302.5Å) by Chapman and Sheeley showed that the bright network which these weakenings form appears as a sequence of sharp, bright points in the cores of the fainter lines and the wings of stronger lines but is more diffuse in the cores of stronger lines. They found the bright network in Zeeman-insensitive Unes (e.g., 5123.7A) also, indicating that it is due, at least in part, to variations in physical conditions. Lines of low ionization and excitation are weakened more than those of high ionization and excitation, and they attributed this to a temperature increase by 100-200 °K in the region of formation of the line cores ; a similar increase of 250 °K was found by Harvey and Livingston.

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.

Configuration and Evolution of Solar Magnetic Fields

1970 ◽  
Vol 1 (8) ◽  
pp. 371-372 ◽  
Author(s):  
D. Schatz
Keyword(s):  
Active Region ◽  
Magnetic Fields ◽  
Wavelength Range ◽  
Time Resolution ◽  
Large Time ◽  
Field Configuration ◽  
High Time Resolution ◽  
Solar Magnetic Fields ◽  
Line Centre ◽  
The Continuum

Observations were made on 1970 February 9 using the Culgoora magnetograph to study the configuration and evolution of magnetic fields in a solar active region with high time resolution. The region observed was located at N20 E25 at the beginning of the observations which commenced at February 8, 22h 59m U.T. and finished at February 9, 07h 24 m. The magnetic fields were observed in the light of Cal 6102.7Å. Over a wavelength range corresponding to an intensity from 1/8 to 1/2 of the way up from line centre to the continuum on the blue side of the Une there is no apparent change in the field configuration, and the observations were made at a wavelength corresponding to the mid-point of this range. Exposures were made approximately every two minutes, with occasional large time gaps for instrumental adjustments.

scholarly journals Modeling surface magnetic fields in stars with radiative envelopes

2013 ◽  
Vol 9 (S302) ◽  
pp. 290-299
Author(s):  
Oleg Kochukhov
Keyword(s):  
Magnetic Field ◽  
High Resolution ◽  
Magnetic Fields ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Doppler Imaging ◽  
Magnetic Field Mapping ◽  
Ap Stars ◽  
Surface Fields ◽  
The Magnetic Field

AbstractStars with radiative envelopes, specifically the upper main sequence chemically peculiar (Ap) stars, were among the first objects outside our solar system for which surface magnetic fields have been detected. Currently magnetic Ap stars remains the only class of stars for which high-resolution measurements of both linear and circular polarization in individual spectral lines are feasible. Consequently, these stars provide unique opportunities to study the physics of polarized radiative transfer in stellar atmospheres, to analyze in detail stellar magnetic field topologies and their relation to starspots, and to test different methodologies of stellar magnetic field mapping. Here I present an overview of different approaches to modeling the surface fields in magnetic A- and B-type stars. In particular, I summarize the ongoing efforts to interpret high-resolution full Stokes vector spectra of these stars using magnetic Doppler imaging. These studies reveal an unexpected complexity of the magnetic field geometries in some Ap stars.

scholarly journals The Magnetic Fields of Single White Dwarfs

1979 ◽  
Vol 53 ◽  
pp. 297-312
Author(s):  
J.D. Landstreet
Keyword(s):  
Magnetic Fields ◽  
White Dwarfs ◽  
Binary Systems ◽  
Zeeman Splitting ◽  
Spectral Lines ◽  
Close Binary ◽  
Linear Component ◽  
Optical Flux ◽  
Absorption Features ◽  
The Continuum

The first magnetic field in a white dwarf was discovered nine years ago (Kemp et al. 1970). Since that time magnetic fields have been detected in a total of 12 single white dwarfs and four white dwarfs in close binary systems. These magnetic fields have been found both through the Zeeman splitting and shifting of spectral lines and through the continuum circular (and sometimes linear) polarisation which a field may produce in the optical flux of a star in which it occurs. The fields so far detected appear to range between 3 MG and more than 100 MG. For stars with fields less than about 40 MG, both the observed Zeeman shifts of spectral lines and the observed circular polarisation appear to be reasonably well understood. For stars with fields above this level, attempts so far to identify absorption features in the spectra and to account for the continuum polarisation have not been very successful; indeed, there is considerable dispute about the fundamental mechanism producing the continuum polarisation, especially the linear component.

scholarly journals First Results of Continuous IUE Observations of Algol

1992 ◽  
Vol 151 ◽  
pp. 285-288
Author(s):  
R. González-Riestra ◽  
A. Gimènez ◽  
E. F. Guinan
Keyword(s):  
Mass Transfer ◽  
High Resolution ◽  
Light Source ◽  
Orbital Period ◽  
Continuous Monitoring ◽  
Slow Stage ◽  
High Ionization ◽  
First Results ◽  
The Continuum

We present the first results of a continuous monitoring of Algol with IUE along 1.5 orbital period (4 1/3 days). A total of 32 high resolution spectra were obtained. Algol represents the final slow stage of mass transfer. The spectra show the presence of high ionization lines (NV, SiIV, CIV) due to the heating of the gas that impacts the accreting star. The depth of the primary eclipse is larger at shorter wavelengths and the shape of the continuum out of the eclipse is compatible with a B star, ruling out the presence of an extra light source at these wavelengths.

scholarly journals IFU investigation of possible Lyman continuum escape from Mrk 71/NGC 2366

2019 ◽  
Vol 623 ◽  
pp. A145 ◽  
Author(s):  
Genoveva Micheva ◽  
Edmund Christian Herenz ◽  
Martin M. Roth ◽  
Göran Östlin ◽  
Philipp Girichidis
Keyword(s):  
High Resolution ◽  
Velocity Dispersion ◽  
Physical Conditions ◽  
The North ◽  
Direct Observations ◽  
Lyman Continuum ◽  
High Ionization ◽  
Green Pea ◽  
Field Unit ◽  
Electron Density Map

Context. Mrk 71/NGC 2366 is the closest green pea (GP) analog and candidate Lyman Continuum (LyC) emitter. Recently, 11 LyC-leaking GPs have been detected through direct observations of the ionizing continuum, making this the most abundant class of confirmed LyC-emitters at any redshift. High resolution, multiwavelength studies of GPs can lead to an understanding of the method(s), through which LyC escapes from these galaxies. Aims. The proximity of Mrk 71/NCG 2366 offers unprecedented detail on the inner workings of a GP analog, and enables us to identify the mechanisms of LyC escape. Methods. We used 5825–7650 Å integral field unit PMAS observations to study the kinematics and physical conditions in Mrk 71. An electron density map was obtained from the [S II] ratio. A fortuitous second order contamination by the [O II] λ3727 doublet enabled the construction of an electron temperature map. Resolved maps of sound speed, thermal broadening, “true” velocity dispersion, and Mach number were obtained and compared to the high resolution magnetohydrodynamic SImulating the LifeCycle of molecular Clouds (SILCC) simulations. Results. Two regions of increased velocity dispersion indicative of outflows are detected to the north and south of the super star cluster, knot B, with redshifted and blueshifted velocities, respectively. We confirm the presence of a faint broad kinematical component, which is seemingly decoupled from the outflow regions, and is fainter and narrower than previously reported in the literature. Within uncertainties, the low- and high-ionization gasses move together. Outside of the core of Mrk 71, an increase in Mach numbers is detected, implying a decrease in gas density. Simulations suggest this drop in density can be as high as ∼4 dex, down to almost optically thin levels, which would imply a nonzero LyC escape fraction along the outflows even when assuming all of the detected H I gas is located in front of Mrk 71 in the line of sight. Conclusions. Our results strongly indicate that kinematical feedback is an important ingredient for LyC leakage in GPs.

Precision spectro-polarimeter for high-resolution observations of solar magnetic fields

2001 ◽  
Author(s):  
Bruce W. Lites ◽  
David F. Elmore ◽  
Kim V. Streander ◽  
David L. Akin ◽  
Tom Berger ◽  
...  
Keyword(s):  
High Resolution ◽  
Magnetic Fields ◽  
Solar Magnetic Fields

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.

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