scholarly journals The Radio Brightness of the Quiet Sun at 21 cm Wavelength Near Sunspot Maximum

1960 ◽  
Vol 13 (4) ◽  
pp. 700 ◽  
Author(s):  
NR Labrum
Keyword(s):  
Active Regions ◽  
Residual Effects ◽  
High Angular Resolution ◽  
Radio Brightness ◽  
Sunspot Maximum ◽  
One Dimensional ◽  
Quiet Sun ◽  
Limits Of Error ◽  
Very High ◽  
Intense Radiation

An investigation has been made of the radio emission from the quiet Sun at 21� 2 em wavelength in 1958 (near sunspot maximum). Two different methods have been used, both involving observations with very high angular resolution, to distinguish between the quiet-Sun component and the radiation from localized active regions. In one method, the Sun was scanned with a narrow pencil-beam; in the other, a fan-shaped aerial beam was used to give one-dimensional strip scans. In both cases it was necessary, when analysing the data, to take into account the residual effects of the very intense radiation from the localized sources. The two independent measurements gave results which agree within the limits of error. The apparent disk temperature was found to be approximately 140 000 oK, or twice the value for the same wavelength at sunspot minimum.

scholarly journals Solar Brightness Distribution at a Wavelength of 60 Centimetres. I. The Quiet Sun

1955 ◽  
Vol 8 (4) ◽  
pp. 487 ◽  
Author(s):  
G Swarup ◽  
R Parthasarathy
Keyword(s):  
Solar Cycle ◽  
Brightness Distribution ◽  
Central Meridian ◽  
The Sun ◽  
Two Dimensional ◽  
Radio Brightness ◽  
One Dimensional ◽  
Quiet Sun ◽  
Solar Brightness

A multiple-element interferometer has been employed to determine one-dimensional distributions of radio brightness over the quiet Sun at a wavelength of 60 cm for scanning directions varying from 90� to 60� with respect to the central meridian of the Sun. These observations have been compared with measurements by other workers at the same, or nearly the same, wavelength. The present observations are reasonably consistent with the two-dimensional brightness distribution derived recently by O'Brien and Tandberg-Hanssen with a two-aerial interferometer, but do not agree with the earlier results of Stanier at the same wavelength. The disagreement, largely the absence of the theoretically predicted limb-brightening in Stanier's results, may reflect actual changes in the Sun over the solar cycle. However, the possibility of localized disturbed regions affecting Stanier's results for the quiet Sun cannot be eliminated.

scholarly journals The Distribution of Radio Brightness over the Solar Disk at a Wavelength of 21 Centimetres. III. The Quiet Sun ? Two-Dimensional Observations

1955 ◽  
Vol 8 (4) ◽  
pp. 474 ◽  
Author(s):  
WN Christiansen ◽  
JA Warburton
Keyword(s):  
Solar Disk ◽  
Fourier Method ◽  
Brightness Distribution ◽  
Sunspot Activity ◽  
Polar Regions ◽  
Two Dimensional ◽  
Radio Brightness ◽  
One Dimensional ◽  
Quiet Sun ◽  
Coronal Electron

A distribution of solar radio brightness at a wavelength of 21 cm has been derived from observations made during the period of low sunspot activity from 1952 to 1954. The observations were made using two multiple interferometers arranged at right angles; this enabled the solar disk to be scanned in many different directions. The derived one-dimensional profiles of the quiet Sun for these various scanning directions were combined and a Fourier method adopted to derive a two-dimensional brightness distribution. The distribution shows marked limb-brightening in the equatorial zones but none in the polar regions. The contours of brightness are in general conformity with those expected from a solar atmosphere having a coronal electron density distribution of the kind proposed by van de Hulst for the period of minimum sunspot activity.

scholarly journals The Distribution Of Radio Brightness Over The Solar Disk At A Wavelength Of 21 Centimetres. I. A New Highly Directional Aerial System

1953 ◽  
Vol 6 (2) ◽  
pp. 190 ◽  
Author(s):  
WN Christiansen ◽  
JA Warburton
Keyword(s):  
Transmission Lines ◽  
Solar Disk ◽  
Brightness Distribution ◽  
Resolving Power ◽  
Radio Brightness ◽  
One Dimensional ◽  
Multiple Beams ◽  
Rotation Of The Earth ◽  
Very High ◽  
East West

A new aerial system of very high resolving power has been designed for use in determining the distribution of radio brightness across the solar disk at a wavelength of 21 cm. Thirty-two aerials with paraboloidal reflectors are evenly spaced in an east-west direction over a distance of about 700 ft., and are connected by a branching system of balanced open-wire transmission lines to a receiver. The aerial system produces multiple beams each 3' of arc wide and spaced 1.7� apart. The rotation of the Earth causes one after another of the aerial beams to scan the disk of the Sun. The record obtained from the radio receiver gives a one-dimensional brightness distribution over the solar disk.

scholarly journals The Distribution of Radio Brightness over the Solar Disk at a Wavelength of 21 Centimetres. II. The Quiet Sun ? One-dimensional Observations

1953 ◽  
Vol 6 (3) ◽  
pp. 262 ◽  
Author(s):  
WN Christiansen ◽  
JA Warburton
Keyword(s):  
Brightness Distribution ◽  
Lower Envelope ◽  
Solar Model ◽  
Radio Brightness ◽  
Preliminary Calculation ◽  
One Dimensional ◽  
Quiet Sun ◽  
Dimensional Distribution ◽  
Small Change ◽  
Shape And Size

Daily records of one-dimensional distribution of radio brightness over the Sun are obtained in the way described in Part I of this series (Christiansen and Warburton 1953). When superimposed, these records show a well-marked lower envelope which remains substantially the same, in shape and size, over a period of months. This envelope gives the brightness distribution over the "quiet" Sun. The direction of scan, with respect to the position of. the solar axis, changes during a year by more than 50�. The very small change in shape of the envelope during this period suggests that for purposes of preliminary calculation the brightness distribution may be assumed to be circularly symmetrical. The radial distribution of brightness, calculated on this basis, is found to show marked limb-brightening and to be consistent with the calculated brightness distribution for a simple solar model in which the assumed values of temperature and density are close to those commonly accepted.

Interpretation of the Filament Depression at Millimetric and Centimetric Wavelengths

1979 ◽  
Vol 44 ◽  
pp. 131-134
Author(s):  
A. Raoult ◽  
P. Lantos ◽  
E. Fürst
Keyword(s):  
Radio Telescope ◽  
Active Regions ◽  
Simple Shape ◽  
Quiet Sun ◽  
Unstable Process

The depressions at centimetric and millimetric wavelengths associated with the filaments are studied using already published maps as well as unpublished observations from the Effelsberg 100 m radio telescope of the M.P.I., Bonn. The study has been restricted to large Ha quiescent prominences of relatively simple shape, situated far from the limb and from active regions. The data has been reduced employing one method whose main characteristics are choice of a local quiet sun definition and avoidance of the unstable process of deconvolution.

Small-Angle Electron Scattering (SAES) of Polymers

1985 ◽  
Vol 43 ◽  
pp. 78-79
Author(s):  
Ralph Oralor ◽  
Pamela Lloyd ◽  
Satish Kumar ◽  
W. W. Adams
Keyword(s):  
Electron Scattering ◽  
Small Angle ◽  
Angular Resolution ◽  
Structural Features ◽  
Objective Lens ◽  
High Angular Resolution ◽  
Push Button ◽  
First Case ◽  
Diffraction Mode ◽  
Very High

Small angle electron scattering (SAES) has been used to study structural features of up to several thousand angstroms in polymers, as well as in metals. SAES may be done either in (a) long camera mode by switching off the objective lens current or in (b) selected area diffraction mode. In the first case very high camera lengths (up to 7Ø meters on JEOL 1Ø ØCX) and high angular resolution can be obtained, while in the second case smaller camera lengths (approximately up to 3.6 meters on JEOL 1Ø ØCX) and lower angular resolution is obtainable. We conducted our SAES studies on JEOL 1ØØCX which can be switched to either mode with a push button as a standard feature.

scholarly journals High Angular Resolution Stokes V Spectra in Penumbrae

1993 ◽  
Vol 141 ◽  
pp. 192-195
Author(s):  
J. Sánchez Almeida ◽  
V. Martínez Pillet ◽  
J. Trujillo Bueno ◽  
B.W. Lites
Keyword(s):  
Angular Resolution ◽  
Small Scale ◽  
High Angular Resolution ◽  
Quiet Sun ◽  
Continuum Intensity

AbstractStokes I and V profiles of Fel 630.1 nm and Fel 630.2 nm observed in a sunspot with an angular resolution ≥0.5” are analyzed. We find asymmetric V-profiles whose shapes are in agreement with previous determinations having lower angular resolution (~5”). We also find a correlation between penumbral small scale variations of continuum intensity and velocity. Although it involves smaller velocities, such correlation resembles that existing in the quiet sun as a consequence of convection.

scholarly journals TOPoS

2018 ◽  
Vol 620 ◽  
pp. A187 ◽  
Author(s):  
P. François ◽  
E. Caffau ◽  
P. Bonifacio ◽  
M. Spite ◽  
F. Spite ◽  
...  
Keyword(s):  
Thermodynamic Equilibrium ◽  
Neutron Capture ◽  
Local Thermodynamic Equilibrium ◽  
Early Evolution ◽  
One Dimensional ◽  
Giant Stars ◽  
Medium Resolution ◽  
Calcium Iron ◽  
Significant Spread ◽  
Very High

Context. Extremely metal-poor stars are keys to understand the early evolution of our Galaxy. The ESO large programme TOPoS has been tailored to analyse a new set of metal-poor turn-off stars, whereas most of the previously known extremely metal-poor stars are giant stars. Aims. Sixty five turn-off stars (preselected from SDSS spectra) have been observed with the X-shooter spectrograph at the ESO VLT Unit Telescope 2, to derive accurate and detailed abundances of magnesium, silicon, calcium, iron, strontium and barium. Methods. We analysed medium-resolution spectra (R ≃ 10 000) obtained with the ESO X-shooter spectrograph and computed the abundances of several α and neutron-capture elements using standard one-dimensional local thermodynamic equilibrium (1D LTE) model atmospheres. Results. Our results confirms the super-solar [Mg/Fe] and [Ca/Fe] ratios in metal-poor turn-off stars as observed in metal-poor giant stars. We found a significant spread of the [α/Fe] ratios with several stars showing subsolar [Ca/Fe] ratios. We could measure the abundance of strontium in 12 stars of the sample, leading to abundance ratios [Sr/Fe] around the Solar value. We detected barium in two stars of the sample. One of the stars (SDSS J114424−004658) shows both very high [Ba/Fe] and [Sr/Fe] abundance ratios (>1 dex).

scholarly journals The circumstellar discs of Be stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 325-336 ◽  
Author(s):  
Alex C. Carciofi
Keyword(s):  
Angular Resolution ◽  
Central Star ◽  
High Angular Resolution ◽  
Be Stars ◽  
Keplerian Orbit ◽  
Physical Processes ◽  
Simple Description ◽  
Model Predictions ◽  
Mass Ejection ◽  
Very High

AbstractCircumstellar discs of Be stars are thought to be formed from material ejected from a fast-spinning central star. This material possesses large amounts of angular momentum and settles in a quasi-Keplerian orbit around the star. This simple description outlines the basic issues that a successful disc theory must address: 1) What is the mechanism responsible for the mass ejection? 2) What is the final configuration of the material? 3) How the disc grows? With the very high angular resolution that can be achieved with modern interferometers operating in the optical and infrared we can now resolve the photosphere and immediate vicinity of nearby Be stars. Those observations are able to provide very stringent tests for our ideas about the physical processes operating in those objects. This paper discusses the basic hydrodynamics of viscous decretion discs around Be stars. The model predictions are quantitatively compared to observations, demonstrating that the viscous decretion scenario is currently the most viable theory to explain the discs around Be stars.

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