Astronomy and Astrophysics for the 1980's, Volume 2 Reports of the Panels (1983) / Chapter Skim
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VIII. High-Energy Solar Astronomy
VIII. High-Energy Solar Astronomy
Pages 69-83
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From page 69... ...
The Sun is the only star close enough to permit observation and measurement of its surface activity at all wavelengths with spatial, temporal, and spectral resolutions that could, in principle, reveal the finest significant details. Moreover, the properties of matter ejected from the corona as solar wind and energetic particles can be determined directly by measurements in interplanetary space.
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From page 70... ...
Nonuniform rotation and convective motions of the highly conductive material within the Sun generate magnetic flux, which is continually carried to the surface by turbulent diffusion and magnetic buoyancy. From there the field emerges into the solar atmosphere with a strength that ranges from a few gauss in quiet regions to 100 gauss in active regions.
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From page 71... ...
The origin, transport, and conversion of internal solar energy into coronal heat and kinetic energy of the solar wind are central problems of solar astronomy. With the recent discovery that hot coronas are present in stars of all spectral types and nearly every luminosity class the problem of coronal heating has become a general problem of stellar astrophysics, and the results of detailed studies of the solar corona have acquired a broad significance for all of astronomy.
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From page 72... ...
General Features of the Solar Atmosphere Among the most important developments in understanding the Sun's atmosphere during the decade of the 1970's was the discovery that it is divided into regions of two distinct kinds that are either magnetically "open" or magnetically "closed." In closed regions the field lines have the form of loops with both ends anchored in the dense plasma of the photosphere; in open regions the field lines are anchored at one end in the photosphere and stream outward into interplanetary space. Closed regions occupy typically 80 to 90 percent of the solar surface.
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From page 73... ...
In x-ray images they appear as dark regions called coronal holes. Spewing forth from these magnetically open regions, which occupy only 10 to 20 percent of the solar surface, coronal plasma spreads as it leaves the Sun and within a few solar radii is moving radially away over the entire solid angle to form the bulk of the solar wind.
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From page 74... ...
The second central problem of the corona is how it gives rise to the solar wind. Here, again, the conventional view of the wind as a free expansion of plasma heated by thermal conduction was shattered by the discovery that the solar wind originates primarily in the coronal holes.
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From page 75... ...
These particles, confined to motion along magnetic field lines, deposit a portion of their energy in Coulomb collisions and thereby heat the plasma. In rarified regions the energetic electrons emit synchrotron radiation, and some particles may escape along open field lines into interplanetary space as solar cosmic rays.
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From page 76... ...
mese and other unexpected results from the study of the nuclear radiation from solar flares, though not yet understood, illustrate how the study of elemental and isotopic abundances in solar cosmic rays yields unique information about the conditions in the solar atmosphere and about the mechanisms of particle acceleration. It is expected that correlation of the observations of particles and gamma rays by the SMM will greatly clarify our understanding of the high-energy aspects of solar flares.
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From page 77... ...
2. In solar flares and other transient solar phenomena, what are the mechanisms of energy storage and release, particle acceleration, and local heating?
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From page 78... ...
These studies will be almost entirely dependent on observations from space vehicles, though new information about particle acceleration in solar flares and the effects of solar plasma on the flux of cosmic rays over long times and at very high energies can be derived from groundbased monitors that detect the secondary neutrons produced by high-energy charged particles in the atmosphere.
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From page 79... ...
Among these advances are improvements in x-ray telescopes that make it possible to record spectrally resolved soft x-ray images with angular resolutions finer than 1 arcsec; coded aperture detectors for hard x-ray image detection with resolutions of the order of arcseconds; high spectral and spatial resolution x-ray and E W spectrometers; highly sensitive scintillation spectrometers and high-resolution nuclear gamma-ray solidstate spectrometers; and cosmic-ray detectors capable of resolving the isotopes of all the elements up to nickel and the element distribution for Z up through 26. These
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From page 80... ...
~Pinhole" Telescope/Occulter: A coded-aperature telescope employing a remote mask mounted on an extended boom will be used in conjunction with a position-sensitive detector to record images of hard x-ray events associated with flares and other impulsive solar phenomena. The pinhole telescope will achieve subarcsec angular resolution over the energy range from about 1 to 100 keV, with moderate spectral resolution.
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From page 81... ...
This instrument will complement the SOT by extending ultra-high-resolution observations to the spectral region of radiation characteristic of temperatures as high as 2 X 106 K It is intended to achieve an order-ofmagnitude improvement in angular resolution and spectral resolution compared with any currently approved instrument capable of observing material on the solar surface hotter than 2 X 105 K
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From page 82... ...
The proposed IPL Satellite in the Origin of Plasma in the Earth's Neighborhood (OPEN) series of satellite missions will carry advanced instrumentation for solar plasma measurements, magnetic fields, and instrumentation to measure the isotopes, especially the rare isotopes, of elements ejected from solar flares.
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From page 83... ...
The latter measurements must be made as close to the Sun as possible to enhance the low-energy neutron flux, which is greatly depleted by decay. These combined measurements, which are highly desirable at the next solar maximum, can establish the spectral shape of both the energetic particles accelerated at the Sun and the products of their nuclear interactions with solar matter (e.g., gamma rays and neutrons)
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