scholarly journals Helioseismic Investigation of Solar Internal Structure

1990 ◽  
Vol 121 ◽  
pp. 305-326
Author(s):  
Jørgen Christensen-Dalsgaard
Keyword(s):  
Internal Structure ◽  
The Sun ◽  
Solar Oscillation ◽  
Solar Oscillations ◽  
Oscillation Frequencies

AbstractThe solar oscillation frequencies provide our only means of obtaining detailed information about conditions inside the Sun. Here I give a brief overview of the relevant properties of solar models and solar oscillations, and present examples of the dependence of the oscillation frequencies on the structure of the model. Furthermore I discuss some results obtained so far from analysis of observed frequencies.

scholarly journals Introduction

1995 ◽  
Vol 10 ◽  
pp. 319-320
Author(s):  
W. Däppen
Keyword(s):  
Spherical Harmonics ◽  
Solar Rotation ◽  
Solar Neutrinos ◽  
The Sun ◽  
Solar Oscillations ◽  
Good Information ◽  
Solar Neutrino Problem ◽  
Oscillation Frequencies ◽  
Very High ◽  
Better Than

Since the early 1960s the surface of the Sun has been know to be in a regular pulsating motion with periods of about 5 minutes. While at the beginning various explanations were offered, only in the 1970s it was recognized that these so-called solar oscillations are manifestations of global motions of the Sun about its equilibrium. Helioseismology is the name of the branch of astrophysics that deals with deciphering these data, that cover the whole range of spherical harmonics from l = 0 (radial) to very high angular order (above l = 1000). Thanks to observational data of superb quality (each of the oscillation frequencies is measured accurately to better than one part in ten thousand), our knowledge of the Sun has leap-frogged in the last 20 years. For instance, we now know the run of temperature inside the Sun, or have good information about the internal solar rotation. In the solar neutrino problem the data from solar oscillations have become a compulsory testing stone for any model proposed to explain the discrepancy between observed and theoretically predicted solar neutrinos.

Helioseismic Search for Magnetic Field in the Solar Interior

2000 ◽  
Vol 179 ◽  
pp. 343-347
Author(s):  
H. M. Antia ◽  
S. M. Chitre ◽  
M. J. Thompson
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Large Scale ◽  
Solar Interior ◽  
The Sun ◽  
Solar Oscillation ◽  
Oscillation Frequencies

AbstractThe observed splittings of solar oscillation frequencies can be utilized to study possible large-scale magnetic fields present in the solar interior. Using the GONG data on frequency splittings an attempt is made to infer the strength of magnetic fields inside the Sun.

scholarly journals The Internal Structure of the Sun and Solar Type Stars

1976 ◽  
Vol 71 ◽  
pp. 453-466 ◽  
Author(s):  
IAN W. Roxburgh
Keyword(s):  
Internal Structure ◽  
Solar Neutrino ◽  
Convective Zone ◽  
The Sun ◽  
Solar Oscillations ◽  
Solar Constant ◽  
Solar Neutrino Problem ◽  
Solar Type

Our understanding of the internal structure of the Sun and solar type stars has been undermined by recent observations. In this paper we consider some of the puzzles and possible resolutions; the solar neutrino problem, lithium and beryllium abundance, rotation and calcium emission, variation of the solar constant, solar oscillations and the solar convective zone. The picture that emerges is one of confusion, and so it should be since we have no idea of what is going on inside the Sun and a fortiori of what is going on inside other stars.

scholarly journals What can we Learn from Oscillation Studies about Irradiance and Radius Changes?

1994 ◽  
Vol 143 ◽  
pp. 252-263 ◽  
Author(s):  
Douglas Gough
Keyword(s):  
Internal Structure ◽  
The Sun ◽  
Solar Oscillations ◽  
Thermal Modulation

Dynamical and thermal modulation of the internal structure of the Sun can be manifest at the surface as changes in irradiance and radius. The relative magnitudes of these changes could provide a diagnostic of at least the location of the primary modulation, if only the mechanism were known. Variations of the frequencies of solar oscillations offer additional potentially valuable diagnostics, but unfortunately at present the mechanisms causing those variations and their relation to the structural and irradiance changes are not yet understood. In this lecture I shall review some of the theoretical conjectures that have been put forward to explain the observations.

scholarly journals Delta Scuti Stars: Theory

1998 ◽  
Vol 185 ◽  
pp. 331-338
Author(s):  
J. A. Guzik
Keyword(s):  
Internal Structure ◽  
The Sun ◽  
Individual Stars ◽  
Theoretical Approaches ◽  
Stellar Interiors ◽  
Delta Scuti ◽  
Oscillation Frequencies ◽  
Scuti Stars ◽  
Δ Scuti Stars ◽  
Extremes Of Temperature

The purpose of asteroseismology is not only to derive the internal structure of individual stars from their observed oscillation frequencies, but also to test and extend our understanding of the physics of matter under the extremes of temperature, density, and pressure found in stellar interiors. In this review, I hope to point out what we can learn about the Sun by studying δ Scuti stars, as well as what we can learn about stars more massive or evolved than the Sun. I will discuss some of the difficulties in theoretical approaches to asteroseismology for δ Scuti stars, using FG Vir, δ Scuti, and CD −24° 7599 as examples.

scholarly journals High-Frequency Solar Oscillations

1998 ◽  
Vol 185 ◽  
pp. 415-422
Author(s):  
Stuart M. Jefferies
Keyword(s):  
Power Spectrum ◽  
High Frequency ◽  
The Sun ◽  
Solar Oscillation ◽  
Solar Oscillations ◽  
Oscillation Power ◽  
Peak Structure ◽  
Source Of Information

This paper reviews the properties of the solar oscillation power spectrum at frequencies near and above the acoustic cut-off frequency for the atmosphere. This region of the spectrum contains over 50% of the total peak structure observed and is a source of information not only on the outer layers of the sun and the origin of solar oscillations, but also on the physics of the solar core and chromosphere.

scholarly journals Solar Opacities Constrained by Solar Neutrinos and Solar Oscillations

1990 ◽  
Vol 121 ◽  
pp. 61-80
Author(s):  
Arthur N. Cox
Keyword(s):  
Electric Fields ◽  
Oscillation Frequency ◽  
Convection Zone ◽  
Solar Surface ◽  
Solar Neutrinos ◽  
Photon Absorption ◽  
Solar Oscillations ◽  
Percent Reduction ◽  
Neutrino Production ◽  
Oscillation Frequencies

AbstractThis review discusses the current situation for opacities at the solar center, the solar surface, and for the few million kelvin temperatures that occur below the convection zone. The solar center conditions are important because they are crucial for the neutrino production, which continues to be predicted about 4 times that observed. The main extinction effects there are free-free photon absorption in the electric fields of the hydrogen, helium and the CNO atoms, free electron scattering of photons, and the bound-free and bound-bound absorption of photons by iron atoms with two electrons in the 1s bound level. An assumption that the iron is condensed-out below the convection zone, and the opacity in the central regions is thereby reduced, results in about a 25 percent reduction in the central opacity but only a 5 percent reduction at the base of the convection zone. Furthermore, the p-mode solar oscillations are changed with this assumption, and do not fit the observed ones as well as for standard models. A discussion of the large effective opacity reduction by weakly interacting massive particles (WIMPs or Cosmions) also results in poor agreement with observed p-mode oscillation frequencies. The much larger opacities for the solar surface layers from the Los Alamos Astrophysical Opacity Library instead of the widely used Cox and Tabor values show small improvements in oscillation frequency predictions, but the largest effect is in the discussion of p-mode stability. Solar oscillation frequencies can serve as an opacity experiment for the temperatures and densities, respectively, of a few million kelvin and between 0.1 and 10 g/cm3. Current oscillation frequency calculations indicate that possibly the Opacity Library values need an increase of typically 15 percent just at the bottom of the convection zone at 3×106K. Opacities have uncertainties at the photosphere and deeper than the convection zone ranging from 10 to 25 percent. The equation of state that supplies data for the opacity calculations fortunately has pressure uncertainties of only about 1 percent, but opacity uncertainties will always be much larger. A discussion is given about opacity experiments that the stars provide. Opacities in the envelopes of the Hyades G stars, the Cepheids, δ Scuti variables, and the β Cephei variables indicate that significantly larger opacities, possibly caused by iron lines, seem to be required.

scholarly journals Nonradial and radial oscillations observed in non-emission line OB dwarfs and giants

1986 ◽  
Vol 7 ◽  
pp. 255-263
Author(s):  
Dietrich Baade
Keyword(s):  
Mass Loss ◽  
Emission Line ◽  
Internal Structure ◽  
Fundamental Problem ◽  
Spectral Lines ◽  
Driving Mechanism ◽  
The Sun ◽  
Ob Stars ◽  
Pulsating Stars ◽  
Reconnaissance Surveys

Only a decade ago, this talk could have concerned only the β Cephei stars which however populate a much more precisely defined strip in the Hertzsprung-Russel diagram (MED). But recent reconnaissance surveys (Smith 1977; Smith and Penrod 1984; Waelkens and Rufener 1985; Baade, in preparation) show that perhaps only one, if any, sizeable region of the upper HRD is devoid of nonradially pulsating stars. The identification of the driving mechanism is still pending (cf. the parallel talk by Osaki), and apparently our knowledge about the internal structure of OB stars is incomplete. But, turning that argument around, it also is indicative of how much may be learned about OB stars from and through the solution of that fundamental problem. This seismologial potential, the ubiquity of the phenomenon, and the effect, as suggested by recent observations of some stars, of the pulsations on the mass loss of OB stars make the oscillations of OB stars one of the most important problems of current astrophysics. On the observational side, rotationally broadened spectral lines, large amplitudes, comparatively long periods, and high luminosities permit information to be gathered which otherwise is accessible only for the sun.

scholarly journals Variability in the solar output

1990 ◽  
Vol 330 (1615) ◽  
pp. 641-643 ◽  
Keyword(s):  
Solar Cycle ◽  
Solar Neutrino ◽  
Neutrino Flux ◽  
Convective Zone ◽  
Solar Oscillation ◽  
Dynamo Action ◽  
Solar Neutrino Flux ◽  
Oscillation Frequencies

Evidence for variability in the solar output is briefly discussed. If the solar neutrino flux and the solar oscillation frequencies vary over a solar cycle this could indicate that the solar cycle has its origin in the solar core rather than be due to dynamo action in the solar convective zone.

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