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286 both to astronomy and to the missions of the Department of Energy and other agencies. These laboratories can make unique contributions to the studies of many astrophysics problems, especially by satellite observations; by the study of properties of matter at high temperatures and densities; and by large-scale numerical calculations involving hydrodynamics, nuclear reactions, and energy transport. Access by astronomers to the powerful com- puters at the DOE laboratories has been a particularly unique and valuable resource. DOE needs scientists with astrophysics backgrounds in many aspects of energy research, and these scientists are helped to retain their originality and versatility by par- ticipation in fundamental research activities. There is a strong synergism between the physics of many terrestrial energy problems and the situations encountered in astro- nomical environments, and theoretical astrophysicists are often uniquely qualified to make important contributions to energy research as a result of their broad training in gas dynamics, plasma physics, atomic processes, and radiative-transfer theory. We recommend a continuing effort to strengthen the ties between the DOE institu- tions and the astrophysics community. Involving their staff more directly in astronomical research will enhance their awareness of areas where they can make special con- tributions; similarly, an awareness by university faculty of the capabilities of the government laboratories can lead to productive research collaborations. III. LABORATORY ASTROPHYSICS We take laboratory astrophysics to be theoretical and experimental physics and chemistry that relates directly to the interpretation of astronomical observations and that enters into astronomical theories of the phenomena involved. It includes atomic, molecular, and solid-state physics, together with chemistry, nuclear physics, elemen- tary-particle physics, plasma physics, condensed-matter physics, and fluid mechanics. A. Atomic and Molecular Physics and Chemistry Because spectroscopy has been the main measurement tech- nique used by astronomers to derive the element abun- dances, temperatures, densities, and motions of astro-

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287 nomical objects, atomic physics has long been an integral part of astronomical research. With the discovery of astrophysical molecules, molecular physics has assumed a similar significance. The accuracy with which the physi- cal conditions can be inferred from the spectroscopic observations depends directly on the precision and breadth of the data base of atomic and molecular processes. Atom- ic and molecular processes are more than diagnostic probes of the physical environment. They are often critical in the determination of the evolution of the astronomical object in question. Recent advances in our capability to carry out spectro- scopic observations at high resolution in the radio, sub- millimeter, infrared, ultraviolet, x-ray, and gamma-ray regions of the electromagnetic spectrum (in addition to the optical region) offer unprecedented opportunities for the detailed study of the physical conditions of such varied environments as those of the dark interstellar clouds where star formation is in progress; the outer envelopes of stars (with associated stellar winds and mass loss); novae and supernovae; the accretion flow onto white dwarfs, neutron stars, and black holes in binary systems; and the nuclei of active galaxies and quasars. The development of astronomical spectroscopy over the extended wavelength range now used in astronomy makes new demands on atomic and molecular data, and the extraordi- nary range of physical conditions makes new demands on our quantitative understanding of atomic and molecular processes. Technological progress in experimental atomic and molecular physics and chemistry has been extremely rapid, and the potential for substantial improvements in mea- surement accuracy and for extensions to new kinds of experiments is considerable. Many, though not all, of the advances have stemmed from the development of tunable lasers, which will soon cover the range from the far infrared through to the ultraviolet regions, with an emerging possibility for the construction of lasers operating at x-ray wavelengths. Important developments have occurred in the production of controlled beams of neutral and highly ionized atomic particles and in the use of synchrotron sources of ultraviolet and x-ray photons. Of particular significance to astronomy are advances in submillimeter spectroscopy, which have opened to astronomical study the wavelength region in which most of the power emitted by interstellar clouds may appear. The ability of laser techniques to prepare and to moni-

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288 tor very-short-lived species heralds new applications of laboratory astrophysics. AS one example, resonance- ionization spectroscopy allows the detection of single atoms and introduces the possibility of studying extremely reactive transient species and of measuring the rate coef- ficients of very slow processes, which are still important on astronomical time scales. The techniques for the production of slowly moving beams will permit the measurement of cross sections for collision processes at the low temperatures occurring in molecular clouds and will provide a vital ingredient of theoretical models of molecular formation and the associated cooling processes. In planetary science, the need is urgent for spectro- scopic information about a lengthy list of molecular species. Line intensities, pressure shifts, broadening coefficients, and line shapes at pressures and tempera- tures and in gas mixtures relevant to planetary atmo- sphere environments are required. Obtaining such data is not easy and will require the provision and maintenance of highly sophisticated experimental and theoretical programs with a strong astronomical interest. In the study of stellar atmospheres, and of the solar atmosphere, there is a rapidly growing need for accurate atomic and molecular data. The sophistication of the theory of stellar atmospheres greatly exceeds the quality of the atomic and molecular data that enter into the theory. Particularly noteworthy was the provision of new oscillator strengths for iron, which led to an increase by an order of magnitude in the derived iron abundance in the Sun. The influence of solar opacities on the pre- dicted neutrino flux is an important unsettled question today. Detailed theory of redistribution for the forma- tion of hydrogen Lyman and Balmer lines is especially needed for the solar atmosphere. The past decade has seen a marked deterioration in laboratory facilities for basic spectroscopic studies, which, if not reversed, will have dismal consequences for astronomy. m e advance of astronomical spectroscopy into the vacuum ultraviolet region places unprecedented demands on our knowledge of atomic and molecular spectroscopy. Many ultraviolet lines have been observed with the Inter- national Ultraviolet Explorer that may be critical diag- nostics but remain unidentified. To realize the scien- tific potential of the ultraviolet spectroscopic capabil- ity of the Space Telescope will require a renewed effort in laboratory spectroscopy. . . . _ ~

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289 In x-ray astronomy, the interpretation of spectral data will place new demands on laboratory astrophysics. Accu- rate values of transition probabilities and collisional excitation rates of highly stripped systems are needed. More accurate collisional ionization rates are needed for the proper interpretation of x-ray emission spectra. For example, in supernova remnants the departures from ioniza- tion equilibrium are likely to have important consequences for abundance determination. Charge-transfer processes require elucidation, and the effects of the secondary emissions that they generate must be explored. Auger ionization and dielectronic recombination processes in highly ionized systems and the fluorescent responses need to be delineated. Similar data are required in the study of fusion plasmas such as those produced with Alcator and Tokomak devices, and a close coordination between x-ray diagnosis of fusion plasmas and the study of x-ray sources in astronomy would be mutually beneficial. Accelerator- based experiments have been very productive in providing data on highly stripped systems and should be continued. The infrared and submillimeter spectroscopy of the interstellar medium in our own and in external galaxies offers exciting possibilities. Shocks in dense inter- stellar clouds lead to emission in the rotation- vibrational levels of molecular hydrogen. The excitation cross sections for rotation-vibration transitions are critical parameters in the interpretation of the infrared observations. m e mechanism of collisional dissociation in astrophysical shocks is still highly uncertain. Other emissions from ionized and neutral carbon and from carbon monoxide appear in the submillimeter region, and their interpretation involves the excitation cross sections by collisions with atomic and molecular hydrogen. In interstellar clouds, schemes have been advanced for the gas-phase formation of interstellar molecules. Part of their success may be due to inadequacies and uncertain- ties in the rates of the postulated chemical processes. We hope to progress sufficiently so that the distribution in the galaxy of isotopic forms such as D and 13C could be obtained reliably from observations of interstellar molecules. Accurate molecular data would transform inter- stellar chemistry from a qualitatively attractive descrip- tion of possibilities to quantitative diagnostic procedure and would lead to a realistic description of the role of chemical processes in cloud collapse and star formation. Rapid progress in laboratory and theoretical studies is technically possible on many fronts. To achieve it

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290 will require sophisticated and expensive instrumentation supported by extensive general laboratory facilities. Theoretical analyses should augment all measurement programs. Basic theoretical procedures for the calculation of atomic and molecular properties have advanced substan- tially in the past decade, and many critical questions of laboratory astrophysics can be answered reliably. m e necessary research will usually involve large amounts of fast computer time supported by experienced research groups with a diversity of theoretical and computational expertise. Such groups can be created and maintained only with the provision of a secure funding basis. The interplay between theory and experiment in atomic and molecular physics has long been a mutually productive one. Because of the vast range of physical conditions encountered in astronomical research it is particularly important to maintain their interaction in research in laboratory astrophysics. Recent studies have suggested that the discipline of atomic and molecular physics has been seriously under- funded over many years, so much so that the future lia- bility of atomic and molecular physics research in the United States is brought into question. If the pattern of funding persists, it could affect most severely those areas of greatest relevance to astronomy. B. Nuclear Physics Nuclear physics has been a basic aspect of astrophysics because of the importance of nuclear processes in stars The diminishing research into low-energy nuclear processes in this country is viewed with concern by the astrophysi- cal community, which wishes to incorporate low-energy laboratory data of higher quality into the construction of more accurate models of stars in all stages of evolution. There are five areas to which we wish to draw special attention, areas that we expect greatly to affect astro- physics in the coming decade: the solar neutrino ques- tion, stellar nucleosynthesis, supernova theory, cosmic- ray isotopic composition, and nuclear chronology. The solar neutrino problem remains one of the most per plexing in astrophysics, apparently striking at the very roots of our understanding of stars and stellar evolution. An important result of the last decade is the failure by . -

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291 Davis to detect solar neutrinos at a level predicted by theory. Recent laboratory results on an important cross section [the 3He(alpha, gamma)7 Be reaction] and new calculations for solar opacities have led to large dif- ferences (in opposite directions) for the predicted neu- trino flux, and it still remains on the order of three times the measured upper limit. It is of very high impor- tance to re-examine carefully all the relevant cross sec- tions and atomic-physics data that go into the nuclear reactions and stellar models. With the new high-current accelerators, sensitive detectors, improved atomic models, and appropriate computer support, this is all possible and should have the highest priority. It is important also to continue the development of techniques that show promise of measuring the flux and spectra of the neutrinos from the primary proton-proton reaction of solar energy generation. The flux and spectra of these neutrinos are model-independent, and their measurement will lead to a crucial test of the fundamental idea of hydrogen burning in main-sequence stars. Stellar nucleosynthesis research is expected to take a new and qualitatively different turn in the coming decade because of the large increases in computer capability. Instead of the idealized, parameterized models of the past, calculations can be carried out in specific astro- physical contexts, for specific stars of specific com- position. Necessary for these techniques to make sense are not only large computers but accurate reaction rates and realistic stellar-evolution models. This program should yield testable predictions for differences in nucleosynthetic products from stars of different metal- licity, a reliable framework for interpretation of astro- nomical abundance data, and information on the production of short-lived nuclei that may carry important evidence on the formation of the solar system and may produce decays that are observable from satellites such as the Gamma Ray Observatory. These calculations will provide a framework for constructing accurate chemical evolutionary models for the Galaxy, including constraints on the behav- ior of past stellar populations. Also emerging from these studies should be an understanding of the puzzling iso- topic anomalies now being found in primitive solar-system material. Predictions for the return of the products of nucleo- synthesis to the interstellar medium will be more reliable with accurate nuclear reaction data derived from labora- tory cross-section measurements over the entire range of

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292 nuclear species. Similarly, a better knowledge of nuclear physics and many-body techniques is needed to generate accurate equations of state at or near nuclear density. A proper understanding of the supernova phenomenon may require accurate two-dimensional models of collapse, in which the effects of rotation, nonlocal convection, and magnetic fields are included. Use of the best computer technology is necessary for these developments, and much work at the conceptual level remains to be done. Studies of cosmic-ray isotopic composition are expected to advance significantly in the next decade if the satel- liteborne experiments now planned are launched. Isotopic ratios carry a wealth of information about the abundances and nucleosynthetic history of the material at the source much less ambiguously than do elemental abundances. Num- bers of recent experiments have revealed isotopic ratios that differ significantly from the solar-terrestrial ones, and future work promises to be very exciting. Questions that may be answered include the old one of whether the cosmic rays are accelerated from the material of the interstellar medium or from fresh supernova ejecta. If the latter, what sort of supernova? If the former, or conceivably even if the latter, what is the metallicity and overall abundance pattern of the region from which the comic rays come? Abundances of the light elements, together with laboratory data on spallation, should permit a correct interpretation of the results for the ~ heavier species. The great hope for nuclear chronology in the coming decade may be understanding the potentially extremely powerful Re-Os chronometer, which may be understood with (1) more accurate information about the relevant neutron- capture cross section; (2) a more precise measurement of the 187Re half-life; and (3) an improved analysis of the abundances and geochemical effects for Re and Os. The u-m chronometer may also be improved through the inclusion of more sophisticated nuclear physics and better reprocess models. Laboratory investigations relevant to nuclear astro- physics are supported generally by the Nuclear Science Divisions of the National Science Foundation and of the Department of Energy. The arrangements have worked satis- factorily, and the support has been effective. There is a continuing need to encourage experimental and theoret- ical studies of the nuclear processes occurring in astro- physical environments, and it should be recognized by the

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293 agencies that nuclear astrophysics is a discipline that merits strong support. C. Elementary-Particle Physics Cosmology and the astrophysics of cataclysmic events such as supernovae and quasars involve matter at extremely high temperature and density. These exciting areas of modern astronomy stand to benefit by the continued sup- port of elementary-particle physics using high-energy accelerators both with stationary targets and colliding beams. There is a crucial need to know about the true nature of baryon/lepton conservation, about the masses and other properties of the vector bosons that mediate the universal weak interaction, about the possibility of neutrino exchange and the determination of neutrino masses, and about the reality and implications of quark confinement. The nature of the nucleon-nucleon interaction, deter- mined through collisions of relativistic baryons, is vital to our understanding of the origin and structure of neu- tron stars and of the formation of black holes. Astronomical observations may provide useful con- straints on elementary-particle theories. The limits on the observed cosmic deceleration place restrictions on the sum of all neutrino masses, and the observed helium abundance limits the total number of neutrino flavors permitted within the framework of big-bang cosmology. Phase transitions may have occurred in the early Universe in which the electroweak gauge symmetry and the strong interaction chiral symmetry were successively broken. A possible consequence of the phase transitions is the development of dynamical perturbations leading eventually to the density perturbations from which are formed the gravitationally bound structures now present in the Universe. Since these structures provide evidence on the form and spectra of the perturbations, there is an exciting potential link between the interactions in the very early Universe and the macroscopic structure of the Universe today. The Department of Energy holds elementary-particle and high-energy physics as a national trust. Astronomy ac- knowledges this trust in part because of its contribution to fundamental knowledge but also because of its critical applications to astrophysical circumstances involving extremes of density and temperature.

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294 D. Solid-State Physics and Chemistry The physics and chemistry of the solid state is poten- tially of great significance to astronomy, and many experiments that address critical astrophysical questions can be carried out in the laboratory. For example, inter- stellar grains play a basic role in star formation. Their surfaces are locations for the formation of molecules, and by absorbing destructive ultraviolet radiation, the grains permit molecules to survive. Photoelectric emission from grains is a substantial heat source for the interstellar gas. The grains may be the source of the diffuse inter- stellar absorption lines, and the formation and destruc- tion of grains is an important sequence in the return of material to the interstellar gas. It has become clear that the solar system contains iso- topically heterogeneous materials from different stellar sources. Some of these sources appear to have injected freshly synthesized materials formed immediately before the solar system formed. This injected material contains short-lived radioactive nuclei and stable nuclei that can be used to establish the state of the interstellar medium from which the solar nebula separated. The discovery of isotopic heterogeneities and of extinct short-lived radio- active elements in the solar system has opened new approaches to solar-system formation. mese observations also yield insight into the particular nuclear astrophysi- cal processes within supernovae, in the isotopic and chem- ical state of supernova debris and interstellar matter. Given reliable laboratory data on primitive solar-system materials (meteorites and comets), it becomes possible to explore the early stages of condensation in the solar nebula. This field should expand and become a major field of activity for the next decade, involving nuclear phys- ics, astrophysics, and cosmochemistry. Because it is now possible to analyze directly in the laboratory aggregates from the early solar nebula, interplanetary dust grains, and partially preserved pre-solar-system materials, a major shift in the experimental approaches will occur. Experimental activities should be expanded to include the study of these exotic materials, using sophisticated equipment and techniques that allow the study of grains composed of 101-lOll atoms. Extended efforts will be needed to study the morphology, chemistry, and iso- topic composition of interplanetary dust grains and cometary material. Experiments to investigate the mechanism of grain condensation and formation under

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295 conditions simulating the solar nebula and stellar atmo- spheres should be encouraged in order to develop our understanding of the different types of stellar debris in the dust and gas phases of the interstellar medium and their chemical interactions during aggregation. Labora- tory investigations should provide sufficient clues to permit the development of realistic models of the forma- tion of the solar system and star formation generally. Data are also needed on the optical properties of solids, especially at infrared and ultraviolet wave- lengths. They are required to aid in understanding the reflectance characteristics of the surfaces of the Gali- lean satellites and the asteroids in order to infer their mineralogical types, as well as for the study of the rings around Saturn and Uranus. The structure of planetary interiors and the behavior of volatiles depend on equa- tions of state, phase changes, solubility, vapor pres- sures, condensation, and nucleation properties of a wide range of materials over a wide range of pressures and temperatures. An important step in the next decade will be the growth of a multidisciplinary scientific community actively work- ing to understand the detailed state of the interstellar medium and the mechanism of accumulation of matter to form stars and planetary systems. E. The Physics of Condensed Matter The behavior of matter under extreme conditions of den- sity, temperature, magnetic, and gravitational fields is one of the frontier problems in physics. It is not only a challenging problem in itself, but it is also central to our understanding of pulsars, compact x-ray sources (accreting neutron stars, black holes, and white dwarfs), a gravitational collapse, and the early Universe. During the past decade, extended temporal and broadband spectro- scopic studies carried out by x-ray astronomical satel- lites have led to the identification of specific compact x-ray sources as accreting neutron stars, black holes, or white dwarfs in close binary systems. Such sources pro- vide a unique opportunity to study matter under extreme conditions not accessible in the terrestrial laboratory. Quantitative theoretical models of neutron stars have been developed that demonstrate that detailed studies of pulsars and pulsating x-ray sources will lead to a greatly increased understanding of dense and superdense hadron

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296 matter, hadron superfluidity, high-temperature plasma in superstrong magnetic fields, and the possible existence of pion condensates, neutron solids, or quark liquids in their cores. We may expect significant progress in the coming decade in our understanding of the equation of state of cold neutron matter at densities greater than that of nuclear matter, which determines the mass-radius rela- tion, crustal extent, and maximum mass of neutron stars. We need a better understanding of neutron and proton superfluidity and its relation to the glitch behavior in pulsars and of new phases of matter at very high den- sities, including a condensed Bose pion fluid and/or a phase transition to a quark liquid. An understanding of the equation of state of hot (about 10 meV) high-density matter, which determines the behavior of collapsing cores, is probably crucial for the proper description of the supernova phenomenon and the production of supernova rem- nants. The behavior of condensed matter in superstrong magnetic fields may well determine the behavior of the pulsar phenomenon through its influence on the conduc- tivity and effective work function of the neutron star surface. High-energy observational astronomy will continue to provide an arena for the interaction of the physics of condensed matter and astrophysics to the benefit of both. F. Plasma Physics The discipline of plasma physics had its origin in astron- omy, and it continues to play a fundamental role in the interpretation of almost all astronomical phenomena. Among the many critical areas of direct relevance to astrophysics are magnetic-field reconnection, the inter- action of magnetic fields with turbulence, the nonlinear growth of plasma instabilities, the nature of collision- less shocks, the interaction of magnetic fields with plasma motions, and particle-transport processes. Laboratory investigations of plasma processes can make substantial contributions to research into astrophysical plamas. The extraordinary complexity of the phenomena has obscured the connections and communication between those active in laboratory research and those in astro- physical research. We believe it is most valuable in the next decade to create closer relationships by which the intrinsic synergism between laboratory and astrophysical

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297 plasma research can be reinforced. Theoretical and experimental studies of the interplanetary medium should be especially productive in joining the interests of the two communities of plama physicists . The Department of Energy supports research on fusion plamas and on magnetohydrodynamic plasmas. In astronomi- cal environments, energy generation appears often to be a result of as yet poorly understood plama processes whose study may be particularly rewarding in the exploration of new energy sources. G. Fluid Mechanics An understanding of fluid mechanics is vital to astro- physics. Progress in astrophysics will continue to demand use of the concepts and techniques of modern fluid dynamics. In modern fluid dynamics the computer provides a vitally important laboratory. The use of carefully posed numerical experiments has been a powerful tool for under- standing the subtle phenomena prevalent in this field. In astrophysics these techniques have been used to model astronomical situations, but the level of usage has often fallen short of that required to understand properly the processes involved. Increased availability of computing power will lead to substantial expansion in nonlinear modeling and in numer- ical experimentation. An effective strategy for astro- physical fluid dynamics and magnetohydrodynamics is the development of numerical techniques that are to be tested by comparison with critical laboratory experiments and analytic solutions and then used to extrapolate to other- wise inaccessible astrophysical conditions. Particularly amenable to such techniques are problems related to turbulence, for which classical mixing-length approaches are not adequate. The energy flux carried by convection, convective overshoot, hydromagnetic dynamos, and turbulence in radiation-pressure dominated fluids are all areas in which considerable progress is expected. Related areas in which considerable emphasis is being placed in fluid dynamics are studies of intermittence and of nonlinear waves, both of which have immediate applica- bility to astrophysics, through the physics of accretion disks, jets, chromospheres and coronas, and the origin of spiral structure. Progress should occur in the descrip- tion of two-phase flows (such as stars and gas in gal-

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298 axles, dust and gas for protostars, radiation and gas in hot stars and the young Universe, and neutrinos and had- rons in gravitational collapse). The study of the dynam- ics of "chemical" waves in astrophysics, for example in the interstellar medium and in oscillating nuclear reac- tions in convective stars, is just beginning. Several basic gaps in our understanding of the evolution of stars are related to hydrodynamic flow in otherwise static objects, specifically, the effects of rotation, mixing, and mass loss. The fluid dynamics of jets is ripe for experimental and numerical study, which may elucidate processes fun- damental to the understanding of jets in Galactic binar- ies, radio galaxies, and quasars. Continued experimental studies of the properties of rotating superfluids are important to an understanding of neutron-star interiors. Other aspects of fluid dynamics are the coupling of con- vection and pulsation for application to variable stars, the interaction of fluid dynamics and spectral radiation for application to theory of spectral lines, the theory of drops and bubbles for application to the formation of dust through the liquid drop phase, and the dynamics of fluids with large molecular weights to allow simulations of small scale heights in the laboratory. The experimen- tal studies of convection will be particularly valuable. The problems of astrophysics demand an increasing knowledge of detailed aspects of fluid-dynamical processes and their relation to the other physical processes that are occurring. In order to make progress in understand- ing these complex phenomena, state-of-the-art techniques and resources should be made available to astrophysicists. Thus, there is a general need for increased support of experimental and theoretical research into astrophysical fluid mechanics. H. Recommendations for Laboratory Astrophysics RECOMMENDATION III. 1: The National Aeronautics and Space Administration should establish, as part of its mission planning, the support for research in the basic physics and chemistry that is needed for the interpretation of astronomical observations from space and for the develop- ment of quantitative theories of astrophysical phenomena. We have already pointed out the reasons why NASA should support research in theoretical astrophysics. Equally compelling are the arguments for support of

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299 laboratory astrophysics: without the understanding of the nature of the physical processes underlying the astronomi- cal phenomena observed in space missions and without the base of data on those physical processes, the interpreta- tion of the observations is surely tentative and may be misleading in the design of future missions. In many cases, a relatively modest expenditure for laboratory studies is the most effective way for NASA to ensure that a given space mission will yield a better understanding of the cosmos. NASA should recognize its larger responsi- bilities to the sciences that its missions help to illumi- nate and create a program of research in better balance with its essential objectives. RECOMMENDATION III.2: Because laboratory astrophysical processes are common to a wide range of energy-related researches, the Department of Energy should continue to recognize laboratory astrophysics as an appropriate area for funding support. The Department of Energy is concerned with the dis- covery, development, and efficient utilization of energy resources. No other science offers insight into such a range of potential energy sources as does astronomy. No other science is concerned with such a range of physical environments as is astronomy. Laboratory astrophysics, responding to the demands of astronomy, embraces a broad extent of research that encompasses many of the perceived needs of energy-related research but also enlarges the potential for innovative discoveries. m e Department of Energy appears in practice to have recognized this close relationship, which is mutually beneficial. RECOMMENDATION III.3: The National Science Foundation's (NSF) Astronomy Division should seek to augment existing research programs in basic physics to ensure that labora- tory astrophysics is included as a strong component of these activities. In addition, the NSF Physics Division should continue support of its programs in laboratory astrophysics. There are many programs of research in basic physics that are supported by various agencies for diverse pur- poses. There already exist experimental apparatus and techniques, together with theoretical and computational skills, that could effectively address problems of astro- physical interest if these research programs could be moved in that direction. Selective augmentation of such

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300 funding, so that astrophysical demands could be met as part of these research programs, is to be encouraged. Relatively modest expenditures could lead to a substan- tial return in the provision of the basic data of labora- tory astrophysics and in encouraging a continuing inter- est by researchers whose motivation is largely stimulated by other areas of scientific activity. RECOMMENDATION III.4: Subject to periodic review, long- term support should be provided to strengthen existing centers to ensure that laboratory astrophysics is a major influential part of the research. Laboratory astrophysical research is necessarily con- ducted on a long time scale. In periods of restricted funding, it is particularly important that existing cen- ters with a record of distinguished contributions be main- tained and strengthened. Support over a longer term must be secured; otherwise the research will inevitably respond to the demands of mission-oriented agencies with immediate problems, and a pattern develops that inhibits the approach to deep and difficult questions that can be answered only by careful and lengthy examination. In laboratory astrophysics we draw attention in particular to the critical role of the National Bureau of Standards (NBS) in supporting laboratory spectroscopy. This pro- gram, which has a long record of productivity, is rele- vant to a broad range of national research needs includ- ing astrophysics. We also urge continued support by NBS for the compilation of atomic energy levels. We urge renewed and vigorous support by NBS of laboratory astro- physics. Astronomers demand and contribute to the devel- opment of a broad base of knowledge of fundamental atomic and molecular processes that is the proper concern of this agency. We more generally urge a new examination by fed- eral agencies of their responsibilities for the long-term health of the national research enterprise. RECOMMENDATION III.5: Funding agencies should encourage the convening of workshops attended by astronomers and by laboratory astrophysicists to ensure that astronomical needs are recognized . The effective implementation of our other recommenda- tions requires mechanisms for improved communication among astronomers, physicists, and chemists. Therefore, we encourage workshops in which these scientists may meet in close interaction. Workshops provide an economical means of information exchange where new opportunities can be

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301 identified and different disciplines can associate in th development of innovative approaches to common problems. RECOMMENDATION III.6: A number of visiting fellowships e should be created to encourage astronomers and laboratory astrophysicists to visit institutions where research relevant to astronomy can be pursued. As a supplement to Recommendation 5, we encourage the creation of visiting fellowships, established on a regu- lar basis, so that laboratory astrophysicists and astrono- mers may join institutions that maintain facilities for the support of research activities of interest to astron- omy. The program at the Joint Institute for Laboratory Astrophysics has been a notable success. It should be strengthened and adopted as a model for a number of other institutions where laboratory astrophysics and astronomy can be pursued jointly. RECOMMENDATION III.7: Support should be maintained for data centers to provide critical compilations and assessments of the basic physical data required in quantitative applications. Easy access to data is ultimately as important as its acquisition. Data centers can play an important role by providing access to data and also by providing an expert assessment of the accuracy of the data. By emphasizing quality, data centers can set new standards of measure- ment and of calculation. As in other areas in which physics and chemistry is applied to the understanding of physical phenomena, data centers are important to astronomy.