Astronomy and Astrophysics for the 1980's, Volume 2 Reports of the Panels (1983) / Chapter Skim
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II. Highlights of Astronomy in the 1970's
II. Highlights of Astronomy in the 1970's
Pages 103-118
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From page 103... ...
Most stars appear to be losing significant amounts of material, either in slow leaks of gas, in more vigorous winds, or in spectacular outbursts. Infrared, ultraviolet, and optical studies have permitted astronomers to piece together a rough outline of how mass is lost by stars of various types, the range of mass loss, and the chemical composition of the ejected material.
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From page 104... ...
In an effort to schedule as many programs as possible, assignment committees often give too little observing time to worthy proposals. One clear result of the pressure for telescope time is a marked shift in the style of observational astronomy, away from the lone investigator working at the telescope night after night, and toward the team of astronomers attempting to make a single pivotal observation.
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From page 105... ...
At the beginning of the past decade, the most advanced spectrophotometer in existence was the 32-channel instrument used on the 5-m Hale telescope. Modern spectrophotometers provide an increase of nearly a hundredfold in the number of available pixels and, with the deployment of COD detectors and simple optical systems, they have achieved more than a tenfold increase in sensitivity per pixel over the state of the art in 1970.
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From page 106... ...
; the small general fields observed earlier may be explained in terms of the very small filling factor of these intense fields. Astrometric astronomers achieved a major breakthrough in the past decade with the use of finer-grained emulsions and sophisticated image analysis, which produced a tenfold increase in the precision with which astrometric parameters can be determined photographically.
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From page 107... ...
The 1970's saw an impressive series of scientific successes, ranging from the interpretation of the thermonuclear evolution of stars to the discovery of theoretically predicted neutron stars and even objects that are good candidates for black holes. Galactic astronomy has benefited from the normal progress of a vigorous research area and, like the rest of astronomy, has received a major push from the opening of previously inaccessible electromagnetic spectral regions to routine astronomical observa
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From page 108... ...
OAO-2 and Copernicus observations of interstellar dust extinction investigated the absorbing properties of the dust in the W region and its variation in different regions of space. Far- W photometry and imagery of dust reflection nebulae and the diffuse Galactic background radiation revealed that interstellar dust is highly efficient at scattering W starlight.
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From page 109... ...
In conjunction with new global models of the interstellar medium, this result suggests that interstellar clouds are a complex of cold, quiescent regions and expanding, evaporating surfaces, impinged upon from all directions by shock waves, sometimes with quite high velocities. Direct observations have been made of the stellar, ionized-gas, dust, and probably the nonthermal components of the Galactic center region.
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From page 110... ...
The discovery of vibrational emission from hydrogen molecules at a temperature greater than 1000 K, near the core of the Orion Molecular Cloud, provides evidence that energetic dynamical phenomena are associated with young stars. Subsequent high spectral resolution IR observations of CO, H2, and ionized gas leave little doubt that a shock front is moving out from a central source with a velocity of 30 to 50 km/see and is at a radius of about 1017 cm.
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From page 111... ...
Instead, heating by dynamo-generated or remnant turbulent magnetic fields, either through magnetohydrodynamic wave processes or field annihilation, is now felt to be likely. A major theoretical effort to understand these heating processes is now under way, guided by in-depth studies of the spatially resolved solar corona.
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From page 112... ...
Globular clusters are of essential value to the study of Galactic astronomy because of the relative simplicity of their structure and dynamics, the extreme character of their stellar population, and the information they provide about the dynamical and chemical evolution of the Galaxy. It now appears that there are significant variations of age and chemical composition among the globular clusters.
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From page 113... ...
Great advances have been made in the past decade in the observation and theoretical understanding of late stages of stellar evolution and in the detailed understanding of collapsed objects. The study of counterparts of x-ray sources with ground-based optical spectroscopy and the IUE satellite has revealed many close binary systems, which often include compact objects, high magnetic fields, accretion disks, gas streams, and beamed emission.
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From page 114... ...
Galaxies and Clusters of Galaxies The completion of several 4-m telescopes, coupled with major advances in detector technology during the past decade, have led to a virtual revolution in our analysis of the large-scale mass distribution in the Universe, which has strengthened evidence in favor of a dominant, nonluminous component of cosmic matter. Observations suggest that the total mass distributions of ordinary spiral galaxies extend far beyond the optically visible disks.
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From page 115... ...
Limits put on distant quasars by the x-ray background suggest that this apparent decline in numbers is real and that the increase in quasar numbers does not continue beyond z = 3. Very recent studies have suggested that the mysterious quasar absorption lines have multiple origins.
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From page 116... ...
Despite the enormous energies involved in some of the outbursts observed in quasars and active galaxies, there is no strong theoretical reason to doubt the cosmological nature of the observed red shifts or to believe that "new physics" is required to understand these objects. Still, the mystery posed by their energetics is one of the most challenging in contemporary astronomy.
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From page 117... ...
The magnitude of the Hubble constant Ho, which measures the present rate of expansion of the Universe, remains a source of controversy, and the currently accepted value is probably uncertain by a factor of 2. The value assigned to Hb affects the assumed luminosities, sizes, and densities of virtually all extragalactic objects; it also sets an upper limit to the age of the Universe and clustering time scales for galaxies.
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From page 118... ...
b. Coronal Holes and the Solar Wind l One of the outstanding discoveries in solar physics during the past decade was the recognition that the socalled solar M regions responsible for the geomagnetic storms do not coincide with regions of solar activity but, quite to the contrary, with extremely inactive regions on the Sun.
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