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id New Programs The New Programs recommended by the Committee for approval and funding during the coming decade have been divided into three categories according to the scale of resources required for their com- pletion. A. Major New Programs The Committee believes that four major programs are critically important for the rapid and effective progress of astronomical research in the 1980's and is unanimous in recom- mending the following order of priority: 1. An Advanced X-Ray Astrophysics Facility (AXAF) operated as a permanent national observatory in space; 2. A Very-Long-Baseline (CAB) Array of radio telescopes designed to produce images with an angular resolution of 0.3 milliarc- second; 3. A New Technology Telescope (N=) of the 15-m class operating from the ground at wavelengths of 0.3 to 20 ~m, with rel- evant design studies to be undertaken immediately; and 4. A Large Deployable Reflector (LDR) in space, for spectroscopic and imaging observations in the far-infrared and submilli- meter regions of the spectrum that are inaccessible to study from the ground. B. Moderate New Programs In rough order of priority, these are: 133

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134 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's 1. An augmentation to the National Aeronautics and Space Administration (NASA) Explorer program, 2. A far-ultraviolet spectrograph in space, 3. A space VERB interferometry antenna in low-Earth orbit, 4. The construction of optical/infrared telescopes in the 2-5-m class, An Advanced Solar Observatory in space, 6. A series of cosmic-ray experiments in space, and 7. An astronomical Search for Extraterrestrial Intelligence (SETI). C. Small New Programs The program of highest priority is: A 10-m submillimeter-wave antenna. 5. Other programs of outstanding scientific merit, in which the order of listing carries no implication of priority, are as follows: A spatial interferometer for the mid-infrared region, A program of high-precision optical astrometry, and A temporary program to maintain scientific expertise at U.S. universities during the 1980's through a series of competitive awards to young astronomers. . ~ A. MAJOR NEW PROGRAMS 1. Advanced X-Ray Astrophysics Facility The Astronomy Survey Committee recommends the construction of an Advanced X-Ray Astrophysics Facility (AXAF) to be operated as a permanent, national observatory in space and urges the National Aeronautics and Space Administration (NASA) to begin its develop- ment in time to ensure AXAF operation by the end of the decade. In less than 20 years, x-ray astronomy has advanced from the discovery of the first extrasolar x-ray source (through a brief, ex- ploratory rocket experiment) to the detailed study of thousands of Galactic and extragalactic sources with the image-forming x-ray tele- scope on the Einstein (HEAo-2) Observatory. X-ray observations have revealed important new classes of astronomical objects and have dramatically advanced our understanding of astrophysical processes in virtually every field of astronomical research, from stellar physics to studies of quasars and the formation and evolution of galaxies. Finding x-ray observations to be of vital significance in their work, many astronomers from other fields participated in planning and interpreting the Einstein observations during its two years of oper- ation, and x-ray observations have now attained an importance in contemporary astronomy comparable with those in other wavelength

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New Programs 135 regions. An urgent scientific need therefore exists for a long-lived satellite observatory with capabilities for x-ray astronomy that com- plement those of Space Telescope (ST) in the optical/ultraviolet region and those of the Very Large Array in the radio region of the spectrum. The AXAF will fulfill that need with an instrument that utilizes the same basic principles that were tested and proved in the Einstein mission but which is capable of providing up to a hundredfold greater sensitivity for the study of faint stellar or quasistellar objects and a tenfold increase in angular resolution for the study of structure in extended objects. Major improvements will be achieved in spectro- scopic sensitivity and resolution, and a capability for sensitive po- larimetry will also be provided. The Space Shuttle will provide the means for launching AXAF, maintaining it in orbit, and retrieving it for major refurbishments. Thus, like ST, AXAF will be a national facility that can meet fundamental needs of astronomy for a decade or more. AXAF will permit the observation of sources with x-ray luminosities as small as 1 percent of the Sun's total luminosity lying in the farthest reaches of our Galaxy, as well as the study of all the individual high- luminosity x-ray sources in the hundreds of galaxies of the Virgo cluster. The composition and dynamics of extended sources such as supernova remnants, galaxy halos, and clusters of galaxies can be revealed by spectroscopic and polarimetric observations of high an- gular resolution. The great sensitivity of AXAF will permit investi- gation of x-ray galaxies and clusters of galaxies out to distances so large that the effects of evolution in the early Universe should be apparent. Because of its power and versatility, AXAF will profoundly influence and enhance the development of nearly all areas of Galactic and extragalactic astronomy. The Committee also suggests that NASA consider the establishment of special institutional arrangements similar to those embodied in the Space Telescope Science Institute, to provide scientific guidance for the development and maintenance of AXAF, to manage the sci- entific direction of the mission during orbital operations, and to facilitate the participation of the scientific community in the acqui- sition and interpretation of x-ray observations. Consideration should be given, as in the case of the Space Telescope Science Institute, to appropriate international participation. 2. A Very-Long-Baseli?~e NAB) Array of Radio Telescopes The Astronomy Survey Committee recommends the construction of a ground-based Very-Long-Baseline (VERB) Array of radio telescopes

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136 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's designed to produce images with an angular resolution of 0.3 mil- liarcsecond. Because the Array utilizes proven technology, this proj- ect may be begun immediately after completion of final management and design studies. Extraordinarily high angular resolution is now possible at radio frequencies. Precision atomic clocks, more sensitive and reliable re- ceivers, high-speed tape recorders, sophisticated image-processing techniques, and modern antennas now make it feasible to build a radio array with the angular resolution of a telescope covering an entire continent. This may be done by synchronizing the operation of about ten widely spaced antennas of approximately 25-m diameter, whose outputs are recorded and later combined in a central com- puter. This VLB Array will produce high-quality radio images capable of resolving features down to 0.3 milliarcsecond (the size of a dime in New York as seen from Los Angeles). This is a hundred times better angular resolution than that of any other image-forming telescope at any wavelength and will yield detailed new radio images of a wide range of astronomical objects at the frontiers of modern astrophysical research. These include quasars and the nuclei of galaxies, features of interstellar molecular clouds, the center of our Galaxy, and a variety of energetic Galactic objects such as x-ray, binary, and flare stars. The high angular resolution of the VERB Array will permit the direct study of small-scale structure surrounding the central regions of quasars and stars in the process of formation. Through the method of statistical parallaxes, it will furthermore permit direct measure- ments of distances to many objects throughout our Galaxy and even to some in nearby galaxies. The VERB Array can also be applied to important problems in Earth science (including precision geodesy and geophysics), to the navigation of interplanetary spacecraft, and to tests of the General Theory of Relativity. Although the VERB Array is a complex and sophisticated instrument, it will make use of proven concepts and instrumentation. Construc- tion should begin immediately upon completion of management and design studies with the building of the antennas and the develop- ment of the data-reduction system and other instrumentation. Col- laboration with groups in other countries, particularly in Europe and North America, would improve the performance of the instrument by increasing the resolution even further (particularly in the north- south direction) and by improving the image quality at low decli- nations.

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New Programs 137 3. A New Technology Telescope (NTT) of the 15-Meter Class The Astronomy Survey Committee recommends the construction of a New Technology Telescope (NTT) of the 15-m class on the ground for observations in the optical and in the near- and mid-infrared regions of the spectrum (0.3- to 20-~m wavelength). The design studies needed before the NTT can be constructed are of the highest priority and should be undertaken immediately. Recent progress in optical fabrication techniques, design concepts, and electronics now make it possible to build a large optical/infrared telescope at a cost much lower than was possible a decade ago. Such a New Technology Telescope (NTT), having a diameter of approxi- mately 15 m, will increase our observing capabilities in the critical 0.3~20-~m spectral region in two important ways. First, throughout this spectral region, the vast area of the mirror-nine times larger than that of the 5-m Mt.Palomar reflector-will collect light at a rate exceeding the combined capabilities of the world's 20 largest existing optical telescopes, furnishing the image brightness needed for a new generation of spectroscopic observations. Second, at a good site, the NTT should frequently achieve 0.3-arcsec resolution at 20-~m wave- length; in the absence of special speckle or interferometric tech- niques, this angular resolution can generally be surpassed only by Space Telescope, at much shorter wavelengths. For many infrared applications, NTT'S combination of large collecting area and high angular resolution will lead to a tenfold increase in limiting sensitivity and a hundredfold increase in speed over present capabilities. NTT'S large collecting area will make it an enormously powerful tool for the spectroscopy of faint astronomical sources. For example, detailed spectra of faint, old stars on the fringes of our Galaxy will outline for us the early history of element building and nucleosyn- thesis during the birth of our Galaxy. Similar observations in nearby dwarf spheroidal galaxies, satellite systems of the Milky Way, will tell us how the formation and early evolution of these small sister galaxies differed from that of our own Galaxy. In yet a third such study, astronomers will determine the compositions and motions of the equally old swarms of globular clusters that surround many neighboring galaxies. These clusters, currently believed to be prod- ucts of the initial galactic collapse phase, hold still further clues to the mysteries of galactic birth and evolution. All of these are thresh- old problems, in the sense that there are no brighter objects nearby that are suitable for study; without the light-gathering power of NTT,

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38 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's an insufficient number of photons can be collected to mount the decisive spectroscopic programs needed to address these important issues. In addition, spectroscopic observations of the most distant galaxies and quasars will greatly advance our understanding of cosmic evo- lution. For example, NTT studies of quasar absorption lines will permit measurements of the distribution and composition of intergalactic gas as it existed very early in the history of the Universe. These measurements offer the exciting possibility of tracing back the origin of the chemical elements and the birth of clusters and superclusters of galaxies to a time much earlier than we can currently see directly; indeed, we should be able to study the large-scale properties of the Universe when it was only one quarter as old as it is now. Such studies are completely impossible with present optical telescopes because of their inadequate collecting areas; the faintness of quasars, in particular, requires the enormous light-gathering power of NTT for systematic spectroscopic study. The combination of NTT'S high spatial resolution with sufficient photon-collecting power to achieve very high spectral resolution will also permit definitive studies of molecular clouds and obscured pro- tostars in the near- and mid-infrared regions of the spectrum. The fundamental vibration-rotation transitions of molecules are found primarily in the 2-10-llm wavelength region. The study of these and of molecular rotational transitions and continuum radiation will lead to a much better understanding of the composition, abundances, excitation, and dynamics of collapsing gas clouds. NTT will provide a probe of gas dynamics in regions of star formation by permitting the examination of optical and infrared spectral lines at very high spectral resolution on an exceedingly fine spatial scale. Present ob- servations indicate that the brightest protostellar candidates are about 1 arcsec in diameter in the 2-10-~m wavelength region, whereas the diffraction limit of a filled-aperture 15-m telescope is about 0.0~0.15 arcsec over the same range; thus, the use of NTT with interferometric techniques will permit detailed study of the geometry and structure of such objects. In addition, NTT'S high spatial resolution will allow the isolation and study of individual source components. All of these studies will be complementary to those that can be carried out by the Shuttle Infrared Telescope Facility (SIRTF), which has high sen- sitivity but low angular resolution; by ST, which has high angular resolution but limited collecting area; and by the Large Deployable Reflector in space, which will be designed for far-infrared work at wavelengths longer than 20 ~m.

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New Programs 139 Because most of the known objects in the Universe either emit visible or infrared radiation or are associated with objects that do, optical and infrared spectroscopy provide powerful and versatile techniques for investigations of the Universe. As the worldJs most capable instrument for such spectroscopic observations, NIT will be an extraordinarily productive facility. The Survey Committee finds the scientific importance of NIT to be equal to that of any other facility considered and regards it as one of the cornerstones of the recommended research program for the 1980's. 4. A Large Deployable Reflector in Space The Astronomy Survey Committee recommends the construction of a Large Deployable Reflector (LDR) of the 10-m class in space to carry out observations in the far-infrared and submillimeter regions of the spectrum that are inaccessible from the ground. Design studies for such a facility should begin at once. Much of the matter in the Universe is relatively cool, from cool stars at a few thousand degrees to dense interstellar clouds at tens of degrees. Radiation from these objects lies in the infrared and submillimeter regions of the spectrum, at wavelengths from a few to a few hundred micrometers. Instruments in space are essential for observations at wavelengths between the atmospheric windows and at wavelengths beyond 20 ~m, for which the elimination of atmospheric absorption and background thermal noise is critical. STRTF will offer a thousandfold improvement in our ability to detect infrared sources, bringing many millions of them into view. How- ever, the requirements of cryogenic cooling put a practical limit on the aperture of the STRTF telescope; as a result, it cannot collect enough photons for high-resolution spectroscopy, and its angular resolution is high only at shorter infrared wavelengths. A LDR in space of approximately 10-m diameter, for observations at the longer infrared and submillimeter wavelengths inaccessible from the ground, is needed to collect enough photons for high- resolution spectroscopy and to provide high angular resolution at these long wavelengths. Such a telescope could carry out detailed morphological and spectroscopic studies of all the far-infrared sources discovered in the forthcoming Infrared Astronomy Satellite (IRAS) all- sky survey and of the brighter objects discovered by SIRTF. Because mirror-figure and pointing requirements are a hundred times more

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140 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's relaxed than for ST, a 10-m-class LDR capable of arcsecond resolution at 20-~m wavelength should be less expensive. A number of important scientific problems are uniquely accessible to such a LDR in space. For distances less than 500 parsecs, the projected beam diameter will be less than 1000 astronomical units. Direct measurements of the sizes of nearby clouds collapsing to become stars will thus be possible at far-infrared wavelengths, which can penetrate the surrounding clouds of dust that invariably obscure small-scale features at optical wavelengths. In addition, the wave- length regions accessible to a LDR contain spectral lines of atoms, ions, and molecules that reflect a wide range of astrophysical con- ditions. Studies of these features will yield otherwise unobtainable information about the structure and dynamics of planetary atmo- spheres; the heating, cooling, and chemical composition of the in- terstellar medium; and because of the penetrating power of long- wavelength radiation- chemical abundances in the highly luminous but optically obscured nuclei of active galaxies. The sensitivity and high angular resolution of a LDR will also make it possible to study newly forming stars in optically obscured regions of nearby external galaxies, enhancing our understanding of galactic evolution and of the dynamical processes that stimulate star for- mation. Such an instrument can also probe the structure of the early Universe and the mechanisms of galaxy formation through studies of small-scale spatial fluctuations in the cosmic microwave back- ground radiation. The capabilities of a LDR in space will complement those of ST, which is optimized for observations in the ultraviolet, optical, and near-infrared spectral regions, and those of the NIT, which will offer large collecting area and high angular resolution but will be restricted to the atmospheric windows between 0.3- and 20-~m wavelength. The Committee believes that design studies for a LDR should begin at once. B. MODERATE NEW PROGRAMS 1. Explorer Program Augmentation The Astronomy Survey Committee recommends an immediate and substantial augmentation to the NASA Explorer satellite program, with the aim of restoring it to at least the healthy real level of effort of 1970. NASA is now proceeding with four Explorer missions in the areas

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New Programs of astronomy and astrophysics. The Infrared Astronomy Satellite MORASS is at present under development; the Cosmic Background Ex- plorer (COBE), Extreme Ultraviolet Explorer (EUVE), and X-Ray Timing Explorer (XTE) are in various stages of final planning in preparation for development. Unless the present Explorer funding level is in- creased, however, these are likely to be the only Explorer satellites dedicated to astronomical observations that can be flown in the 1980's. The Astronomy Survey Committee believes that such a limitation would present a serious obstacle to the progress of space astronomy during the coming decade. Today's Explorer budget, as currently charged for mission costs, provides only about half the support in real terms that was available to the Explorer program a decade ago. As a consequence, the flight of new Explorer missions has in recent years fallen much below the rate needed for healthy advance. The rate will decline even more drastically during the early 1980's if present budget levels are not increased. The Astronomy Survey Committee thus recommends an immediate and substantial augmentation to the Explorer program to restore it to at least the real level of effort of 1970. As emphasized in Chapter 4, the Explorer program has been a vital component of the NASA space-science program for over 15 years, and it promises to continue to provide the best means for pursuing a wide range of scientific problems in the years ahead. Determination of priorities among the most promising individual Explorer mission possibilities in astronomy and astrophysics for the 1980's remains the responsibility of other advisory groups, particularly the Space Science Board's Committee on Space Astronomy and Astrophysics (CSAA). However, among the scientific areas that at present appear to offer special promise for additional Explorer-class missions are the following, in which the order of listing carries no implication of priority: 141 A spectroscopic study of physical conditions and element abun- dances in a wide variety of x-ray sources. Such a study could address one or more of the regimes of spectroscopy that may not or will not be addressed by AXAF, e.g., observations of spectral lines (such as Fe lines) with exceptionally high spectral resolution or with the spa- tial resolution permitted by large apertures, the study of spectral lines emitted by newly synthesized matter and of cyclotron-reso- nance features at energies above 10 keV, and wide-field spectroscopic studies of the interstellar medium. These investigations would yield important new information on the structure and composition of young

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142 ASTRONOMY AND ASTROPHYSICS FOR THE 1980 s supernova remnants and the interstellar medium; the structure and dynamical behavior of the coronas of nearby stars; the nature of the plasmas associated with compact x-ray sources in Galactic x-ray bi- naries and in quasars; and the distribution, composition, and origin of the hot intergalactic gas pervading clusters of galaxies. A study of the isotopic and elemental composition of low-energy Galactic cosmic rays and solar energetic particles in the interplanetary medium. A primary aim of such an investigation is an accurate determination of the isotopic composition of the elements through nickel in a direct sample of contemporary solar and Galactic inter- stellar matter. In addition, it should be possible to analyze the com- position of solar energetic particles through uranium and to study the processes that accelerate particles on the Sun and in the inter- stellar medium. These measurements hold the key to understanding the processes that synthesized and accelerated both solar and Galactic matter. A study in soft x rays (preferably with moderate-resolution spec- troscopic capability) of those objects now known to radiate predom- inantly in the 100-2000-eV energy range, including cataclysmic var- iable stars, AM Herculis-type systems, RS CVn binary stars, stellar coronas, isolated white dwarfs, central stars in planetary nebulae, hot neutron-star remnants of recent supernovae, and x-ray pulsars. Such an investigation should include extended searches for, and studies of, regular and quasi-regular pulsations as well as aperiodic variability, studies of binary orbital light curves, measurements of spectral-line ratios (to determine temperatures and densities in the hot, emitting plasmas), and observations correlated with measure- ments at other wavelengths. The results of these studies would have an important bearing on our understanding of the evolution of com- pact binary systems, the composition and cooling of isolated very hot stars, and stellar activity and variability cycles. A study of high-energy transient phenomena, particularly ob- servations of cosmic and solar gamma-ray bursts up to 10 MeV with high resolution and sensitivity, in conjunction with a program of wide-field x-ray imaging with fine angular resolution. Such a com- bination will provide both accurate timing and location of the burst sources from the same spacecraft and very probably lead to their identification. The cosmic gamma-ray observations will also provide probes of nuclear and electromagnetic processes in compact objects and measure spectral features that have been reported in burst mea- surements, including cyclotron-resonance features, red-shifted 511- keV photons, and nuclear lines. Continuous observations of solar

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New Programs gamma-ray lines may also be possible from the same spacecraft; such observations, carried out over a several-year period bracketing a solar maximum and with the highest energy resolution obtainable, would greatly advance our understanding of solar flares. A study of the physical processes that deposit both energy and momentum into the solar corona and the solar wind, through mea- surements of the structure, expansion velocity, electron-density dis- tribution, transition-region plasma density, and magnetic properties of the corona. Such investigations will furnish essential new infor- mation on the detailed relation of coronal structure to x-ray bright points and coronal holes through studies of the fate of newly emerg- ing magnetic-flux tubes; the interaction of coronal plasma with the solar magnetic field in general; and mechanisms for the acceleration of the solar wind, which are best studied in conjunction with si- multaneous observations of the evolution of coronal holes, bright points, transients, active regions, and magnetic structures on all scales. A study of the interior dynamics of the Sun, as one important component of a more general program to understand the funda- mental mechanisms responsible for the solar cycle. The goals of such an interior-dynamics study include measurements of photospheric velocities, as a probe of the solar convection zone and the variation of rotation rate with depth; of radiation from the large-scale convec- tive pattern in the photosphere, to permit correlations with magnetic measurements and inferences concerning the influence of magnetic fields on solar radiative output; of radiation from the entire disk of the Sun over periods ranging from days to the length of a solar cycle, to determine the degree of variations in the so-called "solar con- stant"; and of magnetic activity in the upper solar atmosphere, to determine the effects of such activity on the atmospheres of both the Sun and the Earth. These results are also expected to play a role in the more general effort to understand the nature of stellar convection and of energy and magnetic-field maintenance. 143 Two further possibilities merit detailed study by NASA and by other advisory groups for inclusion in the Explorer program. The first is an Explorer satellite to map the Milky Way at moderate angular resolution, both in the lines of selected submillimeter-wavelength transitions thought to be important for the heating and cooling of interstellar gas clouds and in wavelength bands relevant to deter- minations of temperature and density distributions in cold clouds. The second is the Explorer flight of optical and infrared interferom

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146 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's mits a more complete study of dynamical processes presumed to be operating at various distances from the central energy sources in these objects. Second, a space VERB! antenna greatly facilitates the study of radio sources at low declination. Any ground-based VERB Array must rely on the rotation of the Earth to vary the position and length of the baseline employed; for low-declination sources, the resulting base- lines lie largely or solely in the east-west direction, thus diminishing greatly the north-south resolution and degrading the quality of the radio map. A space antenna can provide north-south resolution of such sources, allowing full two-dimensional mapping of radio sources at all declinations. Third, an Earth-orbiting space antenna will permit the study of time variation on much shorter time scales than is possible with a purely ground-based array, which requires up to 24 h to fill in all the baselines necessary to complete a radio map. An antenna in low- Earth orbit would allow mapping of sources in a time that is half of the period of revolution of the satellite (about 1 h) and, thus, the study of source variations on this much shorter time scale. Such a capability would be immediately useful, for example, in studying dramatic relativistic-jet phenomena in SS 433. Many other time-vary- ing sources will also be accessible. Finally, a space antenna will in concert with the VERB Array's southernmost stations, southern hemisphere NASA stations, and an- tennas in other countries permit the VUB! mapping of the rich south- ern hemisphere of the sky. The Committee notes that even the first space VERB! antenna in low- Earth orbit will additionally provide angular resolution that is nearly an order of magnitude greater in solid angle than that of the ground- based SIB Array alone. Moreover, a space VUB! antenna in low-Earth orbit will provide the first step toward the achievement of baselines far longer than can ever be achieved on the Earth itself. This requires the placement of antennas in highly elliptical Earth orbits; in Chapter 7, the Committee recommends the study and development of a more extensive space VERB} system as part of a program of advanced spatial interferometry in the radio, optical, and infrared regions of the spec- trum. 4. Construction of Opticalllnfrared Telescopes in the 2-5-Meter Class The Astronomy Survey Committee recommends the construction of optical/infrared telescopes in the 2-5-m class during the coming de

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New Programs 147 cede as the ground-based facilities of choice for an extensive range of important observations. The Committee particularly encourages federal assistance for those projects that will also receive significant nonfederal funding for construction and operation. Optical/infrared telescopes in the 2-5-m class have made critically important contributions to most of our recently acquired knowledge in a number of key areas, including the following: Evidence of galaxy evolution from studies of distant galaxies; The crucial quasar observations that established the existence of the first known gravitational lens; A mass estimate for the dense component of an x-ray binary star, establishing it as the leading black-hole candidate; The discovery of quasars in clusters of galaxies, demonstrating that at least some quasars are at the great cosmological distances implied by their large red shifts; Dynamical studies of hundreds of galaxies in clusters, showing that the bulk of the matter in the Universe is nonluminous at optical wavelengths and has therefore escaped direct detection; Observations providing strong evidence that interstellar shock waves play a role in star formation; Demonstration that the old stars in our Galaxy are anomalously rich in oxygen, supporting the hypothesis that the protogalactic gas was enriched by an early generation of massive, short-lived stars; Detection of activity cycles in solar-type stars and observations of the modulation of chromospheric features by stellar rotation; Discovery of a binary-star system (SS 433) emitting huge streams of matter at about one fourth of the speed of light; and Optical confirmation of the existence of pulsars. In addition, telescopes in the 2-5-m class have furnished essential follow-on observations and identifications of a multitude of objects discovered in other wavelength regions by spacecraft or comple- mentary ground-based facilities. Such telescopes are essential for timely observations of transient phenomena, long-term survey and surveillance programs, general support of space astronomy, and the development of astronomical instrumentation under realistic observ- ing conditions. All of these scientific tasks and opportunities will assume even greater importance during the coming decade. Recent breakthroughs in telescope technology have radically reduced the cost of construc- tion of optical/infrared telescopes in the 2-5-m class, enabling a wider

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148 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's group of institutions to consider their acquisition than ever before. Such telescopes, equipped with modern instrumentation and detec- tors will constitute powerful research tools for the 1980's. The Com mittee believes that federal funds for such facilities should be awarded on the basis of peer review of scientific merit. Federal agencies should be receptive to proposals from all parties that could make effective use of these telescopes, including private, state, and national insti- tutions. The Committee particularly encourages the award of federal funds for such telescopes to be located at private and state observatories that can contribute significant nonfederal funding for construction and operation. It applauds the initiative of astronomy groups that are currently seeking private and state funds for this purpose and welcomes private and state agency support of astronomical research. Some portion of the observing time at these facilities should be allocated to outside users, the fraction to depend in general on the level of federal funding. Visitor access is especially important for the larger telescopes constructed in this class. 5. Advanced Solar Observatory in Space The Astronomy Survey Committee recommends the establishment in space of an Advanced Solar Observatory (ASO) to be assembled near the end of the coming decade from facility-class instruments developed earlier through the Spacelab program-for simultaneous observations of a number of important solar properties at optical, extreme ultraviolet, x-ray, and gamma-ray wavelengths. The Solar Shuttle Facility endorsed earlier (Chapter 4, Section D) can achieve a number of the major scientific objectives of space solar physics. However, other important problems-such as the structure of the convection zone, large-scale circulation patterns, transient high- energy phenomena, and long-term evolution of the corona require observations with-a comprehensive set of high-resolution instru- ments over much longer periods of time than can be obtained in Shuttle flights. The Committee therefore recommends that the Solar Shuttle Facility evolve into a major free-flying observatory, the ASO. The ASO iS currently planned to consist of five major components: (1) the Solar Optical Telescope (SOT) truss containing the SOT itself; (2) a Solar Soft X-Ray Telescope Facility (SSXTF), an EUV Telescope Facility (EUVTF), and white-light and resonance-line coronagraphs to be mounted within the SOT truss; (3) a Grazing Incidence Solar Tele- scope (GRIST) currently under consideration for development by the

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J New Programs 149 European Space Agency; (4) a Pinhole/Occulter Facility for hard x-ray observations and high-resolution studies of the corona; and (5) a Solar Gamma Ray Telescope. It is hoped that an ASO nucleus (consisting for example of the SOT/SSXTF/EUVTF assembly and GRIST) can become operational in the late 1980's, perhaps assembled upon a space platform. The full ASO, including the Pinhole/Occulter Facility and the Gamma Ray Telescope, will be necessary for the study of transient phenomena during the next solar maximum in the early 1990's. ASO will be the first solar facility with the design goal of achieving an angular resolution much less than 1 arcsec from the infrared through the x-ray region (0.1 arcsec or better at many wavelengths), together with the spectral resolution needed to detect motions of solar material over the entire span of wavelengths required for study of such material at a wide range of temperatures. The ASO will be able to address nearly all of the problems of contemporary solar physics, including the structure of the solar core; the mechanisms responsible for the solar magnetic and activity cycles; the energy and mass-transport mechanisms operating over the full range of tem- peratures present in the atmosphere; the basic plasma processes responsible for metastable energy storage, magnetic reconnection, and particle acceleration in solar flares and related nonthermal phe- nomena; and the processes involved in the heating and acceleration of the solar wind. 6. Cosmic-Ray Experiments The Astronomy Survey Committee recommends a series of cosmic- ray experiments in space, to promote the study of solar and stellar activity, the interstellar medium, the origin of the elements, and violent solar and stellar processes. Cosmic rays high-energy particles from space that include the nuclei of all elements of the periodic table, as well as electrons and antiparticles are a sample of contemporary matter from regions far beyond the solar system that we can study in detail. For example, it has now been established that both neon and magnesium in cosmic rays are enriched in their heavier isotopes by comparison with stan- dard solar-system abundances. In their composition and energy spec- tra, cosmic rays carry unique information about the origin of the elements in stars, the nature of cosmic particle accelerators, and the interstellar gas. Cosmic-ray research has now reached the stage of maturity that permits substantial advances in all of these areas.

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150 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's At lower energies, and for the lighter elements, some of the re- quired studies could be carried out through the Explorer satellite program, as noted earlier (Section B.1~. However, determinations of abundances of the rarer isotopes (such as those of elements heavier than nickel), of the chemical composition of the ultra-heavy nuclei, and of the elemental composition and spectra of lighter elements at high energies, all require large collecting areas and the longest fea- sible exposure times. Dramatic progress in detector technology dur- ing the past decade, together with the ability of the Space Shuttle to place heavy payloads in orbit, now makes it feasible to carry out such measurements with high accuracy over a broad range of ener g~es. The Committee therefore recommends that NASA begin a system- atic program that would pursue the development and construction of the large instruments required to perform these significant cosmic- ray measurements and that would ultimately provide long-duration (approximately 6 months or more) exposures of these instruments in the most appropriate way, possibly through use of a space plat- form. The development of these large instruments for long-duration exposure will in many cases best be carried out through balloon and Spacelab flights of short duration and through use of ground-based facilities such as the Bevalac accelerator. 7. Astronomical Search for Extraterrestrial Intelligence The Astronomy Survey Committee recommends an astronomical Search for Extraterrestrial Intelligence (SETI), supported at a modest level, undertaken as a long-term effort rather than as a short-term project, and open to the participation of the general scientific com- munity. It is hard to imagine a more exciting astronomical discovery or one that would have greater impact on human perceptions than the detection of extraterrestrial intelligence. After reviewing the argu- ments for and against SETI, the Committee has concluded that the time is ripe for initiating a modest program that might include a survey in the microwave region of the electromagnetic spectrum while maintaining an openness to support of other innovative studies as they are proposed. Since the chance for a successful detection in the next decade is quite uncertain and may be small, it should be understood that the SET! effort is to be undertaken on a long-term, evolutionary basis. In the coming decade it has been proposed to use a million-channel

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New Programs analyzer in the microwave region of the spectrum; such a program seems appropriate for an initial assay. While exploration of this re- gion of the electromagnetic spectrum appears to make best use of our current technology, other approaches such as searches using radiation of shorter wavelengths-can also provide interesting op- portunities, and the SET! program should allow for the possible sup- port of the ingenious new ideas and proposals that are likely to appear. Modest support of such programs by U.S. funding agencies is a legitimate scientific activity, and choice of programs within each agency should be made through the normal process of peer review. As a number of other nations have initiated steps toward SET! pro- grams, the opportunities for international collaboration are substan- tial. 151 C. SMALL NEW PROGRAMS A 10-Meter Submillimeter-Wave Antenna The Astronomy Survey Committee recommends the construction of a submillimeter-wave telescope of about 10-m aperture at a high, dry site. Recent advances in the design and fabrication of ultraprecise an- tennas and low-noise receivers make possible an instrument that can observe a substantial portion of the almost completely unexplored submillimeter-wavelength band. Such an instrument will allow de- tailed study of this rich region of the spectrum with an angular resolution as fine as 8.5 arcsec, which is a factor of 2 better than that of any existing single-element millimeter-wave antenna. The portion of the electromagnetic spectrum accessible to this antenna contains the fine-structure transition of atomic carbon and many rotational lines of important molecules. The facility will be particularly useful for observing higher molecular rotational transitions, such as those of the well-studied interstellar molecules CO and HCN, which are important for cooling processes. Information from a range of molec- ular levels will make possible a detailed examination of the physical structure of molecular clouds-especially the hot, dynamically active clouds where stars are formed. Since the 10-m telescope will achieve high angular resolution, the transitions of abundant species like car- bon and carbon monoxide can be used for studies of objects of small angular extent, such as external galaxies and the envelopes of evolved stars displaying mass loss. The study of the distribution of molecular

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152 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's clouds in external galaxies should, when combined with optical/ infrared results, greatly improve our knowledge of star formation in nearby galaxies. If both the 25-Meter Millimeter-Wave Radio Tele- scope and the 10-m submillimeter-wave antenna are placed at the same site, they may be used together as an interferometer within the short-wavelength range of the former and the long-wavelength range of the latter. The fascinating problems of star formation, stellar mass loss, and galactic structure stand at the center of many of the controversial issues of astrophysics today. The important information that this instrument can provide on these topics through observations of the more energetic molecular rotational transitions elevates it to an im- portance much greater than would be suggested by its modest cost. A Spatial Interferometer for the Mid-Infrared Region The Astronomy Survey Committee recommends the construction during the early 1980's of a dedicated two-element spatial interfer- ometer for the mid-infrared spectral region with design parameters optimized for operation at a wavelength of 10 ~m. The spectacular success of radio interferometry since World War II has illustrated forcefully the benefits of interferometry to astron- omy. Experiments during the last decade have demonstrated the feasibility of spatial interferometry in the infrared region at wave- lengths from 2 to 20 Am and have shown that there are a number of important applications for such techniques. Atmospheric propa- gation characteristics have been shown to be excellent for the 10-~m region in particular, and heterodyne detection techniques have been developed that permit sensitive, coherent detection in this wave- length region. The Committee supports the construction of a 10-~m heterodyne interferometer for the exciting scientific promise it offers in the near term and as a significant step toward the goal of extending interfer- ometric technology to a wide range of wavelengths. With the later possible addition of an infrared delay line, the interferometer could be made suitable for use with incoherent detectors, when the highest sensitivities to continuum radiation are required. A dedicated infrared interferometer will have many important as- tronomical applications. It will permit detailed mapping of infrared sources, many of which are invisible optically because of obscuration by intervening interstellar dust. Of special interest is the circumstellar distribution of dust and molecules shed during episodes of mass loss

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New Programs 153 by many stars during certain stages of their evolution. High-reso- lution maps of regions of star formation are essential to our under- standing of the birth of stars and planetary systems. The angular diameters of large numbers of stars can be measured. Such an in- terferometer is also well suited to search for an accretion disk around a black hole in the Galactic center a possibility suggested by recent observations- and to probe the intense infrared sources in the nuclei of active galaxies. A 10-~m heterodyne interferometer furthermore shows great promise as an astrometric instrument. It will measure precisely the location of infrared sources, aid in the determination of an accurate celestial coordinate system over the entire sky, allow proper motions of stars and other infrared objects to be determined with high precision, and test the General Theory of Relativity to a new order of accuracy by measuring the bending of 10-~m radiation from sources seen near the limb of the Sun. A Program of High-Precision Optical Astrometry The Astronomy Survey Committee recommends support for the de- sign and construction of innovative devices that offer the promise of greatly improved astrometric precision, particularly those that may help permit the detection of planets around other stars. Since the 1960's, the typical accuracy of observed stellar parallaxes has im- proved from +16 milliarcseconds to +3 milliarcseconds; the Com- mittee recommends support for the design and construction of in- novative devices that offer the potential for obtaining relative positions with an accuracy of +0.1 milliarcsecond. If the Earth's atmosphere allows the achievement of such accuracy but existing telescopes prove to be inadequate, serious consideration should be given to the con- struction of a specialized astrometric telescope. The major advances in astrometry during the past decade have been due to the introduction of new instrumentation and the up- grading of existing instruments. These, together with the advent of new detector technologies and data-analysis techniques, have pro- vided the astronomical community with the tools for decisive ad- vances in the accuracy that can be obtained through ground-based astrometric measurements. For example, one may now look forward to a tenfold improvement in our knowledge of relative stellar posi- tions. Such an advance would permit distance determinations of stars out to 1 kiloparsec, leading to improved luminosities, radii, and masses of stars of virtually all types and ages, including objects such

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154 ASTRONOMY AND ASTROPHYSICS FOR THE 1980's as RR Lyrae stars and members of star clusters that are crucial for calibration of the distance scale to extragalactic objects. Moreover, a substantial improvement in the accuracy of stellar-velocity measure- ments also seems possible, with important consequences for studies of stellar dynamics. Such advances can be exploited to search for evidence of extrasolar planetary systems. The detection of such systems would have a significant intellectual impact, removing immediately the apparent uniqueness of our own solar system; systematic observations would enable us to begin the accumulation of data for eventual statistical studies of planetary-formation rates, planetary multiplicity, correla- tions of physical properties with those of the parent star, and the effects of planetary formation on stellar evolution. An important goal for ground-based astrometry during the coming decade is the de- tection of Jupiter-like planets around nearby stars, if indeed they exist. The detection of Earth-like planets around other stars appears to require astrometric measurements from space, and the Committee encourages design studies of focal-plane detectors and astrometric telescopes that will yield a positional accuracy sufficient for such measurements. A The Committee also calls attention to the potential for astrometry of a very large space telescope and the advanced interferometers for the radio, infrared, and optical regions of the spectrum recommended for study and development in Chapter 7 of this report. A Temporary Program to Maintain Scientific Expertise at U S. Universities The sharp decline in the anticipated number of university under- graduates in the 1980's, coupled with the unusually small number of faculty retirements anticipated over the same period, will cause a temporary but serious reduction in the number of junior astronomy faculty members that will be appointed by U.S. universities. The intellectual energy that such faculty members bring to astronomy is crucial to progress; moreover, as explained in Chapter 4, basic re- search at U.S. universities is a critically important component of the national effort in astronomical research. The Astronomy Survey Com- mittee therefore recommends that urgent steps be taken to maintain scientific expertise at U.S. universities by ensuring that excellent younger researchers continue to flow into them during the critical decade ahead. In particular, the Committee recommends that the Astronomy Di- vision of the National Science Foundation initiate a temporary pro

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New Programs 155 gram of "Astronomy Excellence Awards." Ten to twenty 5-year po- sitions would be awarded to individuals each year on the basis of an open national competition. Each award would be for one half of the salary of a position at the assistant-professor level and would be contingent on commitment of matching funds in the form of the other half of the salary for the same period by a recognized univer- sity. It is anticipated that the status and qualifications of successful candidates would be similar to those of regular faculty members at the host institutions and would include the improvements described below. The anticipated cost of this program, which we recommend as a new initiative, would be $0.5 million to $1.0 million per year. It would generate an equal amount of matching funds from univer- sities on a short-term basis and also, the Committee believes, lead to the establishment of new, long-term positions in astronomy. In- asmuch as the problem of declining enrollments and reduced retire- ments is anticipated to abate starting in about 1990, this program should be terminated at that time. The Committee furthermore urges the universities themselves to take the following steps to respond to the declining student enroll- ments and reduced faculty retirements anticipated during the 1980's: implementing procedures that encourage the early retirement of fac- ulty, the establishment of "parallel track" positions of high prestige, and the permitting of non-tenure-track scientists with appropriate qualifications to serve as Principal Investigators on contracts and grants. Some universities have also experimented with so-called "rolling tenure," by which a scientist is granted tenure for the duration of supporting funding from a contract or grant, with tenure extended in step with funding renewal. Since this scheme raises broad issues of university policy, its consideration by a more broadly based com- mittee than the present one would be helpful. A much more detailed discussion of the issues underlying the present recommendation may be found in the report of the Panel on Organization, Education, and Personnel, to be published in Vol- ume 2 of this survey.

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Speckle interferometry permits resolution of a stellar disk. The top frame represents a short-exposure stellar image of ~ Ceti; at the lower right is the speckle image of an unresolved star, ~ Ceti; and at the lower lefties the resolved image of the surface of a red giant star, Mira, or 0 Ceti. (Photo courtesy of R. Stachnik and P. Nisenson, Harvard-Smithsonian Center for Astrophysics)