Astronomy and Astrophysics for the 1980's, Volume 2 Reports of the Panels (1983) / Chapter Skim
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IV. Detailed Descriptions of the UVOIR Program for the 1980's
IV. Detailed Descriptions of the UVOIR Program for the 1980's
Pages 135-177
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From page 135... ...
The 15-Meter New Technology Telescope and Closely Related Projects The time is now ripe for a full-scale attack on the problems of the formation and evolution of galaxies and clusters of galaxies, the nature of nonluminous matter in galactic halos, the character of supermassive objects in galactic cores; the evolution of molecular clouds; and the formation and evolution of galaxies, stars, and planetary systems. Ground-based observations are a key element in all of these areas of research.
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From page 136... ...
, a 0.85-m cryogenically cooled telescope in space, will vastly extend our capabilities in the IR spectral region. At wavelengths beyond 3 ~m, the low thermal background of SIRTF will permit a gain in sensitivity for low-resolution spectrophotometry between 100 and 1000 times that of the largest ground-based facilities.
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From page 137... ...
will have capabilities unique in the long history of astronomy. It will increase by an order of magnitude the photongathering power of our largest telescopes; with the use of interferometric techniques it will furthermore achieve angular resolution of 0.03 arcsec at the shorter IR wavelengths and resolution of about 0.3 arcsec near 20 Em.
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From page 138... ...
m e combination of high spatial resolution with sufficient photon-collecting power to achieve spectral resolution on the order of 105 will permit definitive IR studies of molecular clouds and imbedded objects. For studies at wavelengths less than 20 Am, the 15-m NTT will provide an important programmatic and scientific link between SIRTF and a Large Deployable Reflector in space.
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From page 139... ...
In addition, as mentioned earlier, the spatialresolution capabilities of a 15-m telescope, utilizing interferometric techniques, will permit observations at spatial resolutions of about 0.03 arcsec or less at the shorter IR wavelengths, while resolutions of about 0.3 arcsec will be possible near 20 ~m. In order to realize the scientific potential of such a New Technology Telescope, it appears necessary that the collecting area be placed on a single mount rather than distributed among individual telescopes, for the following reasons:
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From page 140... ...
2. m e capability for high-spatial-resolution observations at the shorter IR wavelengths requires phased beam combining for interferometric purposes at wavelengths of about 1 Am or greater.
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From page 141... ...
The use of the highest possible resolution at all wavelengths would be helpful in trying to understand the process of star formation and the origin of protoplanetary condensations. At a distance of 200 pa, the range of angular resolution available would cover the linear range from 0.75 AU in the visible to 30 AU at 20 Am.
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From page 142... ...
Seeing is of extreme importance in determining the limiting magnitude of a ground-based telescope. A reduction of a factor of 2 in the diameter of the seeing disk reduces the threshold brightness by a factor of 2; for sky-limited observations this is equivalent to doubling the telescope aperture.
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From page 143... ...
The New Technology Telescope: Summary Broad support exists within the astronomical community for construction of larger telescopes. Evidence for this support comes from the initiatives already taken by the Universities of California, Texas, and Arizona and
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From page 144... ...
d. Support Telescope Program for the 1980's Most of the NTT observing time will of necessity be dedicated to those frontier and threshold programs that require the enormous photon-gathering power and high spatial resolution of this magnificent instrument.
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From page 145... ...
The application of advanced spectroscopic-diagnostic techniques makes it possible to extract, from subtle features of spectral-line contours, information concerning such properties as the distribution of temperature and density in the atmosphere, the amplitude and structure of velocity and magnetic fields, the abundances of the elements, and the rotation rate of the star. The reliable inference of some of these properties from stellar spectral lines requires very-high-resolution, high-S/N data of the kind routinely obtained in solar studies but hitherto unobtainable with stellar instrumentation.
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From page 146... ...
to years (stellar activity cycles) , the stellar instrumentation should be operated in a mode permitting both highly efficient use of observing time ("automated")
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From page 147... ...
Scientific Impact The large collecting areas, high angular resolution, and total freedom from atmospheric interference will give LDR unique capabilities to carry out classes of observations not otherwise possible. While it is already pos
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From page 148... ...
h. Galactic Nucle hi and Galactic Structure The angular resolution of LDR in the far-IR spectral region is some 3 arcsec or less.
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From page 149... ...
mese two possibilities have differing implications concerning the source of the luminosity and the triggering of the high-luminosity phase. If the mapping at higher angular resolution uncovers regions that appear to be sites of enhanced star formation, high-angular-resolution spectroscopy of the associated atomic and molecular gas would yield crucial diagnostic information about velocities, composition, and excitation conditions.
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From page 150... ...
m e preceding remarks about star formation reflect the current state of our knowledge in that they pertain chiefly to massive, luminous stars forming in nearby regions of the Galaxy. It is important to remember, however, that LDR in space will permit us to extend our studies of star formation to regions that are currently inaccessible because of limitations on sensitivity and/or angular resolution.
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From page 151... ...
. A number of active military programs are pursuing technologies relevant to a large space telescope.
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From page 152... ...
It is now clear that studies of galactic-halo gas must include the O VI lines before astronomers can reliably measure temperatures, pressures, and halo extent. Atomic and molecular lines not available in the ST spectral region include the only strong lines of D I, H2, and HO.
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From page 153... ...
The 17thmagnitude unreddened BO star limit is probably within the reach of a 1-m telescope and spectrograph of modern design with a minimum number of optical elements, high reflectivity, and two-dimensional photon counters. The proposed far- W spectrograph can be designed to accommodate other spectral regions as well.
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From page 154... ...
, now an approved NASA program for Space Shuttle flights in the late 1980's, will revolutionize the study of stellar atmospheric structure and dynamics as the result of its tenfold increase in angular resolution compared with previous observations in the wavelength range 0.1-10 Am. SOT is designed to provide better than 0.1-arcsec resolution observations of physical parameters at all layers in the solar atmosphere up to the low corona; the corresponding spatial scale on the Sun (70 km)
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From page 155... ...
Introduction For many applications the information-gathering capability of astronomical telescopes and instruments can be improved as much by increased detector capabilities as by a costly increase in telescope aperture. Although there have been major advances in detector technology in recent years, resulting in increased capability of existing ground-based and space telescopes, there is still much room for improvement.
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From page 156... ...
Prototype optical detectors currently being tested (but not yet widely available to astronomers) include solid-state array detectors -- charge-coupled devices (CCD)
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From page 157... ...
Heterodyne techniques offer potentially very powerful spectroscopic capability, par ticularly for wavelengths beyond 100 ~m. Improvements in detectors and associated circuitry are required over this entire wavelength range, in addition to the incorporation of IR photoconductive materials into array detectors.
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From page 158... ...
Application of opaque III-V photocathodes, having high near-IA quantum efficiency, to ICCD's and other photon-counting detectors and to electrographic detectors, should be actively pursued. New Technology At present CCD's offer the greatest advance in detector technology.
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From page 159... ...
As CCD's become more generally used, astronomers will want to measure the entire spectrum, from the vacuum W to 1.1 Am, with near-unity quantum efficiency. For ground-based observations, unmodified devices will be used; in the vacuum W it may be necessary to coat the CCD with high-efficiency phosphors.
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From page 160... ...
d. Ultraviolet Spectral Region Detectors.
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From page 161... ...
The programs listed below continue to receive a very strong endorsement from the W OIR Panel. We have separated them from our major recommendations only because they are approved or continuing programs.
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From page 162... ...
A two-dimensional detector would also permit spatial resolution in one coordinate in addition to spectral resolution; higher quantum yield for the detectors may also be possible. Development of suitable detectors should have high priority.
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From page 163... ...
On the other hand, because the sensitivity of low spectral resolution observations is limited by fluctuations in the thermal background radiation from the telescope and atmosphere, an enormous gain in sensitivity for these observations can be made with cryogenically cooled telescopes in space. For wavelengths between 30 and 300 ~m, observations must be made from the stratosphere or above because of absorption by water vapor in the atmosphere.
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From page 164... ...
3. Solar Optical Telescope Many astrophysical phenomena, from stellar activity to quasars, exhibit evidence of dramatic interaction between magnetic fields and hot plasmas.
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From page 165... ...
b. Plasma/Magnetic-Field Interaction in Subarcsecond Structures The relation of magnetic fields to mass flow, wave motion, and mechanical-energy transfer in the solar atmosphere is one of the major problems in astrophysics.
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From page 166... ...
Because of the strong magnetic fields present in sunspots, the energy- and mass-transport processes are very different from those in the quiet, nonmagnetic regions of the solar atmosphere. While recent observations support the idea that convection is strongly suppressed in sunspots, they also show that the kineticenergy density in small-scale motions in sunspots equals that present in the quiet sun.
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From page 167... ...
3. A soft x-ray telescope will delineate the basic coronal structures -- coronal holes in which the magnetic fields are open, loops in which the fields are closed, and x-ray bright points where new fields are emerging -- and the temperatures and emission measured in these structures.
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From page 168... ...
Together, these five instruments will measure a complete set of coronal plasma parameters (temperatures, densities, magnetic fields, abundance differentiation, and expansion velocities) as a function of radial distance from 1 to 5 solar radii with which to test in detail our present theory of the solar wind.
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From page 169... ...
SOT will make major contribution toward this understanding and will, in addition, provide important information on the relationship between plasma motions and magnetic fields at small spatial scales and the variation of surface convection across the solar surface in both space and time.
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From page 170... ...
Present survey experiments include the Infrared Astronomy Satellite (IRAS) to be launched in 1982, the Spacelab Small Infrared Telescope to follow in 1984, and military programs.
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From page 171... ...
In addition, a wide-field telescope would be applicable to many of the problems discussed in connection with the high-resolution, moderate-field telescope; although the lower resolution would make it less useful in crowded fields, the wider field of view would allow collection of a larger statistical sample of a given type of object in the observing time.
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From page 172... ...
There are solar-system observations that need to be made in spectral regions (such as shortward of 912 A) , or with combinations of spectral and spatial resolutions, that are not necessarily appropriate for astrophysical problems.
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From page 173... ...
The development that we envisage should include at least two independent research programs in order to ensure adequate cross-checking of apparently positive results. At present, it is generally assumed that the formation of planetary systems is common during star formation, but, in fact, no proof exists.
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From page 174... ...
Flight durations have recently been curtailed owing to lack of funds for jet fuel. This has severely restricted the amount of observing time available on this important national facility.
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From page 175... ...
A specialized facility for this purpose, capable of resolving structure in the 0.1-0.01-arcsec range over a wide range of wavelengths, would be extremely exciting for the detailed study of the structure of late-type stars, circumstellar shells, and embedded objects. Atmospheric windows exist from 300 Em to 1 mm, which can be effectively exploited with innovative far-IR and submillimeter telescopes.
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From page 176... ...
The Shuttle promises to be an important means for orbiting small experiments with far longer observing times than rockets provide and at a cost less than that of freeflying satellites. Unfortunately, despite the outstanding promise of the Space Shuttle for astronomical research, funding for Spacelab experiments has still not reached substantial levels; moreover, funding for a number of experiments that had already been approved was recently reduced, and the selection of additional experiments in the Principal Investigator class has been deferred.
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From page 177... ...
. Such satellites are most suitable for missions requiring very long observing times with relatively simple and routine measurement techniques and not requiring instrument changes or film recovery.
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