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135 heliosphere, its variation in structure, and its effect on the modulation of cosmic rays. In situ observations with the International Solar Polar Mission and the Origin of Plasmas in the Earth's Neighborhood (OPEN) mission will provide needed information on these questions and on the solar spindown due to the solar-wind transport of angular momentum. IV. DETAILED DESCRIPTION OF THE WOIR PROGRAM FOR THE 1980 'S We now give a detailed justification of the new initi- atives in our proposed WOIR program for the 1980'S . In Section A we describe and justify our major recommen- dations; in Sections B and C we discuss other categories of W OIR projects that we believe are also vitally important to the health of astronomy. A. Major Recommendations 1. The 15-Meter New Technology Telescope and Closely Related Projects The time is now ripe for a full-scale attack on the prob- lems 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. The optical and infrared (JR) regions of the spectrum are unique in their ability to provide morphological studies and spectral diagnostics of velocities, compositions, and excitation that are crucial to the interpretation of astronomical phenomena. New space observatories of all types, as well as radio facilities on the ground, will increase the demand for ground-based optical and IR observations--particularly for high-resolution spectro- photometry of faint sources. Space Telescope (ST) will permit astronomers to image galaxies and stars with spatial resolution an order of magnitude greater than that routinely achievable on the ground. This capability will result in the detection of unresolved objects up to 100 times fainter than has been
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136 possible in the past. This tremendous gain in spatial resolution, coupled with access to the ultraviolet (W) region of the spectrum, are the main reasons that moti- vated the astronomical community to unite behind ST as a major initiative for the 1980's. We expect ST to provide fundamental new insights into the scale and geometry of the Universe and into the formation and evolution of gal- axies. For example, ST will provide a glimpse of objects at the very limits of the observable cosmos. However, many of the sources to be discovered will be too faint for effective spectroscopic and spectrophotometric analy- sis by ST itself. Such analysis is essential for the proper understanding of the basic physical properties-- temperature, density, excitation, chemical composition, velocity--of the newly discovered objects. Rapid vari- ability is a common feature of matter near compact objects and makes high time resolution an important additional consideration. Hence, for many programs, we also require a very much larger ground-based telescope to complement, fully utilize, and understand the discoveries made by ST. As ST will do in the optical and W regions, the Shuttle Infrared Telescope Facility (SIRTF), 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. This telescope will greatly expand our knowledge of luminous objects in galac- tic nuclei, the early evolution of stars, and the proper- ties of star-forming regions through imaging, photoelec- tric, and moderate spectral resolution observations. SIRTF will lift the gray-body curtain of thermal radiation generated by warmer telescopes and by our own Earth's atmosphere to reveal a new thermal view of our Galaxy and Universe. However, the capabilities of SIRTF in the areas of very high spectral and spatial resolution are limited by its relatively small aperture. For obser- vations of high spectral resolution, SIRTF will generally be strongly detector-noise limited. While improvements in this area can be achieved by development and use of more sensitive detectors (both discrete and array), it is nevertheless likely that the detailed study of kinematics and chemical abundances will depend in large measure on the availability of a very large telescope capable of carrying out spectroscopic observations at a spectral resolution of about 105.
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137 The SIRTF telescope is intended to be diffraction limited beyond 5 Em. A 15-m telescope located at a good site can be diffraction limited at 20 Em during periods of excellent seeing and will provide more than 10 times the spatial resolution of SIRTF in the near- and mid-infrared regions. Thus, a large ground-based telescope can also provide an essential, high-resolution imaging capability as a complement to the SIRTF observing program. High-energy observations, especially those from the Einstein x-ray observatory, have demonstrated that the full utilization of x-ray data demands extensive optical work. Samples of quasars and galaxy clusters selected by x-ray criteria require extensive optical analysis for determinations of magnitudes, spectra, and red shifts. While this work is within the reach of ground-based telescopes of moderate size, not enough telescope time is available at present to carry it out effectively. Finally, we note that the Very Large Array (VLA)--a centerpiece of the astronomy program for the 1970's--is now in nearly full operation. It has begun to map the radio sky at spatial resolutions once thought to be the province of optical astronomy alone. Critical problems such as the origin and evolution of energetic galactic nuclei are receiving major impetus from VLA observations. Again, appropriate complementary studies at optical and IR wavelengths require spatial and spectral resolutions difficult to achieve with current ground-based tele- scopes. Already half of the requests for use of the 4-m telescope at Kitt Peak National Laboratory (KPNO) are for programs directly related to, or stimulated by, space- craft and radio observations. The reason for this is clear--observations at optical and IR wavelengths are necessary for a broad understanding of the physical mech- anisms responsible for the peculiar behavior of these unusual and newly discovered objects. a. The Scientific Impact of the New Technology Telescope A 15-m New Technology Telescope (NTT) will have capabilities unique in the long history of astronomy. It will increase by an order of magnitude the photon- gathering 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. NTT will provide the spectroscopic capability that
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138 will be absolutely essential to follow observations and will provide high angular resolution at IR wavelengths less than 20 Em. For spectroscopy, a 15-m telescope is superior to ST at all wavelengths acces- sible from the ground except for observations requiring high angular resolution (e.g., galactic nuclei). Spectra of faint stars are necessary for an under- standing of the chemical evolution of our Galaxy, the dynamics of the Galactic halo, and the ages of dwarf spheroidal galaxies. With a 15-m telescope, halo stars down to magnitude 25 can be found by broadband photo- graphy and studied using abundance-sensitive intermediate- band spectrophotometry. White dwarfs in the nearest glob- ular clusters can be studied, and the main sequence can be reached in nearby dwarf spheroidal galaxies. All of these problems are threshold problems in the sense that there are no nearby bright objects suitable for study. Without the light-gathering power of a 15-m NTT there will be insufficient photons to mount these decisive spectroscopic programs. Distant galaxies and dim quasars provide their own challenge to image and to study spectroscopically. When did clusters collapse? Inhomogeneities in the surface density of galaxies can be measured out to a red shift of unity. Spectrophotometry of high-red-shift galaxies will allow us to see the 2000-3000-l region in the spectra of distant galaxies and search for spectral evidence of young stars. Study of QSO absorption lines will allow us to measure directly the chemical and isotopic composition of gas at large red shifts. Present-day spectra do not achieve a high enough signal-to-noise ratio at high dis- persion to determine the strengths of faint lines needed to obtain accurate chemical composition; for example, neither H2 nor D has been detected with certainty in quasar spectra. m e combination of high spatial resolution with suf- ficient 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. and SIRTF
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139 b. Technical Considerations for a 15-Meter New Technology Telescope The New Technology Telescope will almost certainly take a form rather different from that of the traditional telescope, which has a long primary focal length and thick, monolithic primary mirror. A short-focal-length telescope based on the MMT concept, or a segmented pri- mary mirror, or perhaps even a thin monolith are examples of new approaches that can substantially reduce the weight, dome size, and, hence, cost of very large tele- scopes. There are, furthermore, compelling reasons for constructing a very large collecting aperture in the form of a single telescope, rather than simply combining data obtained by all the existing ground-based telescopes. To begin with, we anticipate that one important class of applications of such a facility will center around its power for infrared observations. The IR scientific impact of a 15-m-class ground-based telescope is based primarily on two aspects of its performance: photon-collecting power and spatial resolution capability. Photon-collecting power is particularly crucial for IR spectroscopy. At wavelengths less than 2.5 ~m, the thermal emission of the telescope itself is very small, and the performance of present-day large telescopes and of the proposed SIRTF facility is detector-noise limited at these shorter wavelengths. A 15-m telescope will provide the aperture for at least an order-of-magnitude increase in sensitivity for a wide range of spectral observations, ranging from moderate-resolution studies of continuum and emission lines from atoms and molecules to very high spectral-resolution studies of atomic and molecular emission and absorption systems. In the 3-25-pm wavelength range, thermal emission by the telescope will generally limit performance at low and moderate spectral-resolutions, but at a resolution of 105 or greater, similar order-of-magnitude gains are possible. In addition, as mentioned earlier, the spatial- resolution 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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140 1. Present IR detectors and near-future prospects for the 1-25-pm range are such that moderate- and high- resolution spectroscopy will be detector-noise limited. Thus, an efficient, convenient system for focusing photons from the entire collecting area onto a single detector element is required to take full advantage of the larger collecting area. - ~ The gain in signal-to-noise ratio (S/N) tor a collecting area focused on a single detector, compared with n separate elements/detectors of the same total collecting area, is equal to the square root of n. The most straightforward configuration for this arrangement would place the entire collecting area on a single mount. 2. m e capability for high-spatial-resolution obser- vations at the shorter IR wavelengths requires phased beam combining for interferometric purposes at wavelengths of about 1 Am or greater. _ This can be most easily achieved with a single mount. The gain in spatial resolution is approximately the maximum separation of phased elements divided by the diameter of a coherent array element, which is also equal to the square root of n if the n elements are combined into a filled phaseable aperture. 3. m e potential of improved seeing or seeing correc- tions at the longer IR wavelengths, particularly at 10 and 20 Em, can lead to smaller beam sizes for photom- etry, imaging, and spectroscopy. In order to realize this, coherent beam combining over a significant field of view is required, which again leads to a single mount if not a single dish. The potential gain in S/N is again equal to the square root of n if the n elements are combined into a filled aperture. In addition, at optical wavelengths there will also be some spectroscopic applications that will be detector- noise limited, and for such problems arguments similar to those made for the IR program apply. But of perhaps greater importance is the fact that the emerging field of speckle interferometry promises outstanding capabilities for large single-mount telescopes. Speckle techniques for faint objects have so far been limited to the derivation of simple quantities such as angular size or the separation of two or three components of a multiple stellar system. For example, studies employing two telescopes have already resolved Pluto. Full image reconstruction is available and appears to have been achieved for a star both by simple crude
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141 techniques and by detailed computer processing. The limiting magnitude for speckle studies is independent of telescope size but depends strongly on seeing. The limiting angular resolution of a 15-m equivalent aperture telescope will depend on how the aperture is arranged, but it may well be about 4 milliarcsec at 5000 A. Note that at 10 Em the corresponding resolu- tion will be 0.08 arcsec, or almost as good as the performance of ST at visual wavelengths. The visual angular resolution is comparable with that which can be achieved by radio interferometry using intercontinental baselines. A study of possible goals for these new techniques reveals that they are so advanced that they will cer- tainly open up entirely new areas of research. 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 conden- sations. 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. The fundamental requirement that the NTT be optimized for both IR and optical observations places a number of constraints on its design and location: Field of View. A large field of view for NTT is desirable both to complement the relatively small field (2.7 aramin) of ST and to take advantage of instruments that can obtain simultaneously the spectra of many objects in the same field. Coherence. NTT should be diffraction limited at 20 Am. A diffraction limit of 1 arcsec at 20 Am requires that the diameter of an individual coherent element be at least 5 m; it would be preferable for the entire collect- ing area to be coherent, since coherence over larger sizes achieved in excellent seeing or by interferometric methods will allow even better spatial resolution. Geometry. If NTT is not of a single-dish design, then for spectroscopy in both the optical and IR regions the light from the program object(s) must be brought with high efficiency to a common instrument. This is required to realize fully the low-noise potential of silicon detec- tors and to provide an optical configuration that will allow detector-noise-limited performance from existing near-IA detectors and projected arrays. Emissivity. For telescope-background-limited observa- tions in the thermal IR region, a reduction of the emis-
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142 sivity by a given factor is equivalent to an increase in collecting area by the same factor. The effective emis- sivity of NTT should be as low as possible--5 percent is a difficult but realizable goal. In addition, the tele- scope emission must be steady to avoid introduction of excess noise. Image Quality. 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 equiv- alent to doubling the telescope aperture. Good seeing is also important for spectroscopy, where the efficiency of a spectrograph is controlled principally by the size of the slit that is required to pass most of the light. Since for a well-designed telescope the site sets the limit to seeing, it is absolutely critical that the 15-m-class NTT be located at a site of known excellent seeing. At some sites already in use, the optical seeing is occasionally observed to be 0.5 arcsec or better. In the IR the seeing might be even better. Experience with the Multiple-Mirror Telescope (MMT) has shown that, if care is taken to minimize the effects of local dome and mirror seeing and to make the optics of very high quality, images of this size will be achieved for a useful frac- tion of the time. The effect of mirror seeing (convec- tion from the mirror surface) can be minimized through the use of thin mirrors, which reach thermal equilibrium in 2-3 h. Site Selection. Choice of a site is critical in obtaining optimum performance from the 15-m-class NTT-- or, indeed, from any telescope. In addition to seeing factors (such as low water vapor), absence of light pol- lution, accessibility, and reasonable cost of development are important. We note that the National Science Founda- tion (NSF) has undertaken a program of identifying and protecting excellent astronomical sites. This is an important effort because the majority of sites now in use are either overcrowded and/or threatened with light pollution. We therefore strongly endorse the NSF efforts in this area and recommend that the program proceed vigorously enough to allow selection of a site for the 15-m-class NTT by the mid-1980's. Instrument Changes and Scheduling. The 15-m-class NTT will be capable of doing more in an hour than present large telescopes can do in a night, and in some cases more than can be done in an observing run of several
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143 nights. To take the best advantage of the varying conditions that arise at ground-based observatories-- changes in seeing, in cloud cover and photometric con- ditions, and in sky brightness from moon and twilight-- provision for rapid interchange of key instruments should be an integral part of the telescope design. (For example, sky-limited imaging or spectroscopy should be carried out in the best seeing. Again, it would be advan- tageous to change instruments at moonrise or moonset and again at dawn and dusk.) It follows that NTT should be queue-scheduled for at least a large fraction of its operation, with several programs interleaved. The pattern of use will probably be rather different from what is now customary; one can anticipate scheduled programs that require as little as an hour of integration, given the enormous power of the telescope, and in many cases the observer will not need to come to the telescope. Construction. The experience gained from the building of this decade's 4-m-class telescopes allows the design and construction of much larger telescopes that will be substantially less expensive than the extrapolated costs of the traditionally designed facilities constructed in the past. Indeed, there is now general agreement that, through the use of thin mirrors (10 cm) and altazimuth mounts, the weight and dome size of 10- to 15-m telescopes can be kept comparable with those of 4-m telescopes built in the last decade. A number of groups are already considering the prob- lems associated with the construction of 7- to 15-m-class instruments. The concepts that now appear most viable are a multiple-mirror telescope with 5- to 6-m monolithic elements or a single-mirror telescope of short focal ratio, probably synthesized from separately constructed off-axis segments. During the early 1980's, support should be provided for a coordinated program of technology development leading to the selection of a specific tele- scope design. With these studies in hand, it should be possible to select an appropriate design for a 15-m NTT in the mid-1980's and to begin construction with a goal of First light" by the end of the decade. The New Technology Telescope: Summary Broad support exists within the astronomical com- munity 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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144 by KPNO to carry out design studies and tests of various concepts for building very large telescopes. Indeed, it is precisely because of these initiatives that we have a clearer picture of the performance standards for a 15-m NTT and confidence that these standards can be met. If the steps outlined in this recommendation are taken, we will enter the 1990's with the first dramatic increase in telescope aperture since the completion of the 5-m Hale telescope 35 years ago. 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 spa- tial resolution of this magnificent instrument. However, each of these scientific programs encompasses a continuum of sources; for each quasar, star, and galaxy of the 20th magnitude, there are objects in the magnitude range 17-19 that are just accessible to the largest telescopes cur- rently available. Observations of these still-faint objects will teach us the astrophysics of quasars at a variety of lookback times. Other observations will determine the shapes of color-magnitude relations of stars in external galaxies and hence delineate the his- tory and evolution of stellar populations external to our own. Still other observations of halo stars in our own Galaxy in the magnitude range 17-20 will yield insights into the early history of galactic formation. It is reasonable to expect NTT to work only at the limits of these populations. The combination of the 15-m threshold observations with those from the ~smaller" telescopes will be crucial in solving many of the frontier problems of the 1980's. These "smaller" telescopes might range in sizes from about 2.5 m to larger than 7 m, but they must be state-of- the-art facilities with the capability of producing results competitive with the largest telescopes in use today. For the National Astronomy Centers, dedicated telescopes of the 4- to 5-m class seem more appropriate than a versatile, fully instrumented telescope. Such new telescopes should be dedicated to one or two primary programs. This will result in decreased construction, instrumentation, and operating costs. Scientific results obtained with the 2.5-m telescope at Las Campanas offer convincing evidence that a well- constructed, imaginatively instrumented telescope of this size at a superb site can attack and solve problems at
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145 the forefront of astronomy. Telescopes of this class are attractive to university groups and offer the opportunity for a wholesome diversity of styles and approaches to observational astronomy. They could accommodate the needs of specialized programs and would also encourage technical innovation. One telescope might concentrate on long-term, large-scale programs or on astrometry or on observations coordinated with those from space vehicles. Still another might arrange its scheduling to emphasize speed of response to sudden events such as the appear- ances of comets or supernovae or maximum coverage of periodic phenomena in predictable systems. Instrumental innovations such as the development of the pulse-counting Reticon system often grow out of such environments, where technically adventurous projects can be attempted. As emphasized at the beginning of the section on scientific opportunities for the 1980's, the problem of access to telescopes with sufficient aperture to attack the important problems perceived by the astronomical community as scientifically exciting and fruitful has reached a critical state. The need is so severe that university groups have begun on their own to search for nonfederal funding for large telescopes to serve their needs. The federal government can play an important role here by providing matching funds and encouragement through the National Centers. Other large instruments should be part of our national facilities. The selection of new telescopes for construction during the 1980's will depend on a variety of considerations, including the impact on major scientific objectives, state of the relevant technology, cost, and timeliness. Particularly important initiatives are as follows: A 2-Meter-Class Telescope Dedicated to High-Resolution Spectroscopy for Solar-Stellar Studies. 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. The spectroscopic resolution should be high enough (greater than 2 X 105) to over-
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167 Universe and the objects in it. We give here a brief dis- cussion and endorsement without implication of priority of some of the other programs and initiatives that we believe are vital to the health of astronomy in the 1980's. 1. Solar-Physics Program In addition to launching the SOT and ASO, it is necessary to initiate two other programs that address important problems that ASO and SOT cannot study. a. Solar Coronal Explorer Satellite The basic physics of solar-wind acceleration and the time-evolution of solar coronal structures in response to changing magnetic-field configurations are two fundamental problems that can be addressed by a solar coronal mission of the Explorer class. Measurements provided by this mis- sion will provide unique insight into the more general astrophysical problems of mass loss from stars and the energy and momentum balance of stellar coronas, topics that are becoming increasingly important as a result of recent Einstein x-ray observatory and IUE discoveries. The Solar Coronal Explorer (SCE) should contain at least five complementary instruments: 1. A resonance-line coronagraph operating at Lyman- alpha and the O VI resonance line at 1032 ~ is a new type of instrument recently flown successfully on a rocket but not yet orbited. This instrument provides a new capabil- ity for directly measuring expansion velocities low in the corona. It also yields information on hydrogen column densities and measures coronal kinetic temperatures from line widths. 2. A white-light coronagraph on SCE will provide elec- tron column densities. 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. 4. A coronagraph operating at the He+ 304-A resonance line will, in combination with the hydrogen Lyman-alpha coronagraph, give the observations necessary to determine the probably variable He/H abundance ratio in the solar corona and inner solar wind. The mechanisms leading to
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168 the fractionization of atomic species in the solar wind should be elucidated by these coronal observations. 5. Finally, a magnetograph aboard SCE will measure the input of magnetic flux to the corona. Together, these five instruments will measure a com- plete set of coronal plasma parameters (temperatures, densities, magnetic fields, abundance differentiation, and expansion velocities) as a function of radial dis- tance from 1 to 5 solar radii with which to test in detail our present theory of the solar wind. While the SCE is a unique facility in its own right, which ideally should fly during the next solar minimum (1986) when the wind structures are relatively simple, it takes on added importance if flown simultaneously with solar polar passages of the spacecraft of the Inter- national Solar Polar Mission (ISPM) and the operation of the Interplanetary Plasma Laboratory (IPL) spacecraft at the Sun-Earth libration point. Simultaneous observations by the coronagraphs and x-ray telescopes on SCE and ISPM would give stereo views of the solar corona, which is absolutely fundamental for understanding the three- dim!ensional structure and evolution of coronal structures and transients. b. Solar Interior Dynamics Program The discovery of an unexpectedly low neutrino flux from the Sun has stimulated a broad re-evaluation of our ideas about the structure and dynamics of the solar inte- rior. Such questions as whether the Sun has a rapidly rotating core or whether the interior undergoes episodes of mixing have an important bearing on our understanding of solar and stellar activity cycles. Solar seismology, the measurement of the frequencies and amplitudes of various solar modes of oscillation, is an important new tool for the study of the structure and dynamics of the solar interior. The Solar Interior Dynamics Program has the following four major goals: 1. m e determination of the interior dynamics and structure of the Sun (e.g., rotation versus depth, large-scale flows, pulsations, properties of the radiative core); 2. The combination of the resulting models with dynamo theories to illucidate the global magnetic behavior of the Sun and specifically to explain the
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169 observations of the solar activity cycle; 3. The development of a more physically self-con- sistent theory of convection; and 4. The application of these results to other stars on which activity cycles, surface activity, and rotation have been observed as the result of high-resolution spectroscopy and x-ray observations by satellites. Components of the Solar Interior Dynamics Program are as follows: 1. Theoretic modeling, including computer simulations of solar interior dynamics with dynamo processes. 2. High-precision observation of solar surface behav- ior, specifically solar-surface motions by means of Doppler shifts with accuracies of about 1 m/sec. The development of a tachometer capable of 1 m/see precision on an absolute scale is crucial. We also require mea- surements of large-scale magnetic patterns, of large- scale brightness patterns related to interior circula- tions with relative accuracies of about 0.01 percent, and of solar-diameter measurements with accuracies of 1 milli- arcsec. The accurate measurement and identification of the frequencies of oscillation necessary for the solar internal temperature stratification will require continu- ous observing sequences of a week or more. Such obser- vations can best be obtained from experiments in Sun- synchronous orbits. The program should begin with long-duration observations from the South Pole, followed by a two-week Shuttle experiment, followed later by a longer-duration experiment (6 months or more) flown on a free-flyer (Solar Interior Dynamics Mission) or in conjunction with the ASO. 3. An understanding of other causes of spectral line shifts, which, if misinterpreted, may lead to systematic errors in the surface-motion observations. SOT will make major contribution toward this understanding and will, in addition, provide important information on the relation- ship 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. 2. Sky Surveys Needed to Support Major Missions ST, SIRTF, and the 15-m ground-based telescope are all expensive facilities that require the support of surveys
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170 directed to discovering important rare objects that will be studied in greater detail by these more powerful instruments. A number of important survey programs have been proposed. The W OIR Panel notes and endorses the following. a. Infrared Surveys from Space Deep, all-sky surveys covering the IR from 5 to 130 Am at various spatial resolutions are essential as a foundation for the orderly progress of IR astronomy in the 1980's. 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. By virtue of their unbiased sky cover- age and high sensitivity, these surveys will vastly increase our knowledge of the IR sky and will identify significant classes of IR emitters in the Universe, some of which may represent the discovery of new types of objects. It is of the utmost importance that deep-IA surveys from space be successfully completed. b. Moderate and Wide-Field Imaging in the 1200-10,000-' Wavelength Region The ST Wide-Field/Planetary Camera and Faint Object Camera will provide a capability for imagery in the visible and W wavelength ranges with 10 times better than ground-based resolution and with correspondingly improved point-source detection sensitivity. However, the Wide-Field Camera (WFC) has a maximum field of view of 2.7 arcmin square, and there is a demonstrated need for imagery over larger fields in the 1200-10,000-[ range from space-based telescopes, supplemental to the imagery to be provided by ST. This imagery would tenta- tively have two characteristic combinations of field and resolution: (1) high-resolution, moderate-field (nominal 0.5° field of view, 0.3 arcsec resolution) and (2) wide- field, moderate-resolution (roughly 5° field of view, 1 to 2 arcsec resolution). In the following discussion, we present the scientific rationale and justification for these two types of supplemental imagery. High-Resolution, Moderate-Field Imagery. There are a number of important astrophysical problems requiring photometric-quality imagery at considerably better than ground-based resolution but with a much wider field of view than provided by ST. Additional advantages of such imagery, in comparison with ground-based imagery, include
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171 accessibility to the W and the darker sky background. The particular advantages of a wide field of view (0.5°, or 10 times that of the ST WFC) are for programs requir- ing the observation of objects of large angular extent (e.g., star clusters, nearby external galaxies, cluster of galaxies); programs requiring large statistical sam- ptes; study of positional dependencies; and searches for rare objects. Such programs would require inordinately large amounts of observing time with the ST cameras and also would represent inefficient and perhaps inappro- priate use of such observing time in comparison with the programs likely to be of highest priority for ST. The use of a "grism" with the imaging camera on the wide-field telescope would allow spectrographic surveys over large fields. This capability permits more accurate determinations of spectral type and effective tempera- ture, correction for interstellar extinction, and easier identification of QSO's and other peculiar objects than would be possible with imaging photometry alone. Inclu- ~ _ g . . · · . . Sian of the W (1200-3000 A) is especially important for grism surveys. Wide-Field, Moderate-Resolution Imagery. The scien- tific problems addressed by a space-based telescope with a wide field (5°) and ground-based resolution (1-2 arcsec) are primarily (1) deep surveys in the ground-inaccessible W region and (2) studies of extended, low-surface- brightness objects at all optical wavelengths, for which a fast focal ratio (f/3 or faster) and observations above the terrestrial airglow are especially important. Deep- W surveys provide a much more sensitive means for mapping the spatial distributions of high-temperature objects than is possible in ground-based surveys. Also, for specific problems, far- W observations can provide quantitative photometric data that are much more useful than those obtained from the ground. This is particu- larly true in the cases of hot, subluminous objects near the end points of their evolutionary cycles, in the central bulges or disks of external galaxies, and in crowded regions of the Milky Way, where the far more numerous late-type stars dominate ground-based measure- ments. In addition, a wide-field telescope would be appli- cable 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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172 Ground-Based Survey. There is a need to improve the Palomar Sky Survey by repeating it on fine-grained emul- sions. There have been several proposals to construct a large Schmidt telescope to undertake such a survey. The W OIR Panel suggests, however, that the Palomar Schmidt, finished in 1948, be upgraded and used instead. To permit the use of the fine-grained emulsions, the Palomar Schmidt should be upgraded with an achromatic corrector that will reduce the image size at all optical wavelengths to less than 20 ~m; a IIIaJ sky survey should be then carried out. Such a survey would be invaluable for ST pointing and for astrometric purposes. Also, an objective prism can be mounted without creating balance and weight- distribution problems. This would permit low-resolution spectroscopy over a wide field, a valuable capability in the search for distant, high-red-shift quasars. 3. Planetary Observations a. Dedicated Orbital Telescope for Solar-System Studies The power of remote sensing from Earth-orbiting telescopes is now receiving wide recognition in planetary science as a result of the successful application of OAO-2, Copernicus, and IUE to a selection of planetary and cometary problems. Consequently, there is great anticipation for solar-system studies with ST and SIRTF. However, in spite of the capability of these facilities to attack many solar-system problems, there are also many drawbacks and mismatches. Many solar-system observations require telescopes to be pointed in the close vicinity of the Sun or the Earth or require special orientations of a spectrograph slit or require complex attitude maneuvers. 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. In addition, there is clearly a problem with the restricted time available. Many solar-system obser- vations have either special timing requirements or need extended periods of observations, particularly if the observations are associated with an interplanetary mission in progress. Our assessment is that special consideration should be given in the future to the concept of a dedicated orbital telescope for solar-system studies. However, we believe
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173 that it is essential that this concept be developed by NASA in the context of the overall priorities for an integrated program of solar-system exploration. b. Extrasolar Planetary Detection The detection and accumulation of statistics on other planetary systems would be an important development for planetary astronomy; given the likelihood of reaching the required accuracy by means of astrometric techniques, we support the start of a cautious program in this field. 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. The statistics of planetary formation will reflect directly on the physical status and the relative peculiarity of our own solar system. They are also involved in the estimation of the prob- ability of other life in the Galaxy. While attempts have been made in the past to detect planetary systems by astrometric means, these efforts have not attained the required accuracy. A precision of 10 4 to 10 5 arcsec--one to two orders of magnitude better than what is possible now--is required, and this precision must be maintained over a time scale of 10 years. Recent studies in NASA-sponsored workshops have indi- cated that such precision may now be technically possible through use of a dedicated astrometric facility. Other methods include the detection of small periodicities in radial velocity, spacecraft interferometry, and direct detection by means of specially apodized telescopes of larger aperture. At present, it appears that the two most likely candidate instruments are a dedicated astro- metric telescope or a high-spatial-resolution IR tele- scope that might detect fragmentation in collapsing proto- stars. While it is not now possible to identify a specif- ic instrument concept, it is likely that there will be a convergence of opinion on instrumentation for this prob- lem in the next two or three years. 4. Observatory Support Optical astronomy is in a transitional period. The optical facilities approved and proposed for spaceflight in the 1980's will provide a capability in the decade
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174 that far exceeds the capabilities of the 1970's. mere is good reason for this evolution--astronomy from space is free from the deleterious effects of the Earth's atmo- sphere. Nevertheless, ground-based astronomy will con- tinue to play a pivotal role in the 1980's. On an abso- lute scale, space astronomy will continue to be very expensive; there are many astronomical problems that can be solved using ground-based techniques, and many space programs will require ground-based support observations. For a telescope to be useful, it must be properly instrumented and used. Ground-based astronomy is now suffering from a lack of adequate support funds. Both at the National Astronomy Centers and in the universities, the corrosive effects of inflation have seriously reduced the capabilities of observatory staffs to maintain instru- mentation at a high level of efficiency. Observatories that derive a major portion of the core support from pri- vate endowments or state funds are particularly hard hit, as is the Cerro Tololo Inter-American Observatory, which has suffered from the effects of isolation from the United States, Chilean inflation, and changes in the U.S. tax laws. Observatory groups are responding to the finan- cial pressures by carefully examining their budgets and operations to find areas of cost savings. Nevertheless, it is clear that the current support of observatories is not adequate. Therefore, the W OIR Panel urges NSF and NASA to increase substantially their support of observa- tory operations. We recognize that, traditionally, NASA has been required to link this support to a space mission, but we see no difficulty in doing so, particularly since SIRTF, ST, and x-ray observations will require even more ground-based backup observations. The KAO has been extremely productive scientifically and provides a unique and flexible access to the IR region beyond 30 Em. Until the space IR telescopes are fully operational, the KAO provides one of the major facilities for observation in the 30-300 Am wavelength band. It also provides a means of rapidly testing new instruments. Flight durations have recently been cur- tailed owing to lack of funds for jet fuel. This has severely restricted the amount of observing time avail- able on this important national facility. Augmentation of the KAO flight program would increase its productivity and should be undertaken.
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175 5. 2.5-5-Meter Telescope Program There is a demonstrated need for a number of small special-purpose instruments. Perhaps most of these would be operated by university groups that are likely to be successful in attracting state and private funding, particularly if some federal matching funds could be obtained. We have noted and particularly endorse the following: (a) A dedicated 4-m-class IR telescope in the southern hemisphere. The cost of such a telescope need not be large if advanced construction techniques are used. This telescope should be viewed in the perspective that Amer- ica, and indeed the world, has no large IR telescope in the southern hemisphere, the hemisphere that is often said to be the more important hemisphere for modern astrophysics. (b) A 2-m-class astrometric telescope in the southern hemisphere. There has long been felt a need for a tele- scope optimized for astrometry in the southern hemisphere. In fact, such an instrument was recommended in the 1972 report of the Greenstein Committee. This instrument would complement the U.S. Naval Observatory instrument at Flagstaff, Arizona, and rectify a major imbalance in positional astronomy in the southern hemisphere. This program is particularly important in view of the need for accurate astrometric data to support space missions that view both hemispheres. (c) Interferometric telescopes. For some specialized applications, substantial increases in our ground-based capability can be obtained with relatively modest invest- ments. Spatial interferometry in the IR region using speckle, Michelson, and heterodyne techniques has produced highly interesting results. 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. (d) University telescopes. A number of universities are seeking funds for the contraction of general-purpose, intermediate-sized (2-m-class) telescopes at good sites to support faculty research and graduate-student instruc- tion. It has been shown that such instruments can be
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176 constructed economically with today's technology. m e scientific utility of such instruments is high because they have sufficient aperture to attack frontier problems in astronomical research. Among other uses, they will permit university groups to carry out observing programs in support of space observations by staff scientists. Since major support funds for these instruments will flow from private or state sources, they are, from the federal point of view, a very cost-effective way of advancing astronomical research. (e) Balloon facilities. At present, IR experiments account for a substantial portion of the astronomical use of the National Scientific Balloon Facility. Balloon altitudes offer excellent sensitivity and atmospheric transparency at the longer wavelengths. Balloon tech- niques are especially suited to specialized experiments, the testing of new ideas, and new-technology development. Balloonborne IR astronomy warrants continued and expanded support. 6. Moderate Cost Space Missions a. Astronomy Payloads on Space Shuttle Spacelab II is intended to demonstrate the effective- ness of the Space Shuttle for carrying a variety of astro- nomical instruments on short missions. Instruments on Spacelab II include a small cryogenically cooled IR tele- scope, a W telescope, solar telescopes, and others. 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 free- flying 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. These programmatic constraints have affected Shuttle flight opportunities for a wide range of programs. However, they have had a particularly serious impact on prospects for a coherent program of W astronomy during the 1980's, which should be based to a significant extent on small, special-purpose instruments designed for Shuttle flights to obtain data in areas not well covered by IUE, ST, or the far- W spectrograph in space recommended in this report.
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177 We therefore urge an augmentation of the Shuttle small- payload program at NASA as a minimum requirement to allow currently foreseen, high-quality investigations to be carried out through reasonably frequent flight opportu- nities during the 1980's. In addition, we urge NASA to give high priority to implementation of methods for in- creasing the flight duration of individual missions, so that the observing time available can be increased without a proportionate increase in launch costs. Such methods could include extension of the orbital-stay times of Shut- tle missions or transfer of the instruments to long- duration space platforms or free-flyers that could be revisited by the Shuttle at intervals of 3 to 6 months. b. Explorer Program The NASA Explorer program provides for a class of exploratory science missions involving small, free-flying satellites, generally not recoverable, dedicated to spe- cific new types of investigations (e.g., IUE, IRAS). 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. The only currently approved Explorer mission in the area of W astronomy is the Extreme Ultraviolet Explorer. This mission is intended to survey the sky for sources of radiation in the loo-9oo-A (E W) wavelength range and provide relatively broadband photometric measurements of the sources detected. It is expected that all Explorer-class satellites (after the IRAS launch) will use the Shuttle as a launch vehicle, along with an Inertial Upper Stage (IUS) if even higher orbits are required. Although we can foresee sev- eral areas in which Explorer-class satellites would be extremely valuable to WOIR astronomy, many of these will be more expensive than the historical cost of Explorer missions. We therefore urge that both the total Explorer funding level and the cost limit for individual Explorer missions be substantially increased. Also, we urge that NASA look into means for providing the high-capability pointing systems required for astronomical observations with tele- scopes in the 1-m-aperture class and strive to minimize the cost of such pointing systems. Despite attempts at economy, it is clear that inflation and the increased sophistication required of exploratory science missions are seriously compromising the effectiveness of a highly
Representative terms from entire chapter: