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103 evolution of the interstellar medium, the formation of galactic halos, and the formation of stars. Understanding the formation of stars is critical to understanding the origin of our Sun and solar system and, ultimately, the formation and evolution of galaxies. Advances in infrared and millimeter-wave techniques have permitted astronomers to probe the current birthplaces of stars--dark interstellar clouds. We have begun to under- stand the early evolution of stars and perhaps have ob- served circumstellar disks similar in appearance to the solar system during its formative phases. How star forma- tion is triggered, how protostellar gas clouds fragment to form protostars, how, when, and with what frequency multiple stars or solar systems form are, however, funda- mental questions as yet unanswered. The 1980's will wit- ness major efforts aimed at understanding these problems. Most stars appear to be losing significant amounts of material, either in slow leaks of gas, in more vigorous winds, or in spectacular outbursts. Infrared, ultra- violet, and optical studies have permitted astronomers to piece together a rough outline of how mass is lost by stars of various types, the range of mass loss, and the chemical composition of the ejected material. m e recent discovery of stellar coronas in almost all stellar types together with detailed studies of stellar chromospheres show that stars have far more complex atmospheres than previously suspected. Monumental work still needs to be done to understand these phenomena and their role in stellar evolution. The Sun provides the only accessible laboratory for probing into the physics of, for example, energy gen- eration, magnetic-field generation, internal convection and circulation, chromospheric and coronal heating, explosive dissipation of fields, mass loss and stellar winds, and short-term and long-term activity cycles, not to mention all the many possible planetary implications of these activities. We must exploit these opportunities for study afforded by the solar laboratory in order to make progress in understanding the activity of other stars. I I . HIGHLIGHTS OF ASTRONOMY IN THE 1970'S A. Management, Facilities, and Instrumentation During the 1970's, the Kitt Peak National Observatory (KPNO) and the Cerro Tololo Inter-American Observatory

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104 (CTIO), both National Astronomy Centers, were equipped with 4-m telescopes and became fully competitive with the best university and private observatories. The growth in optical facilities at KPNO and CTIO, the conversion of the Sacramento Peak Observatory into a National Center, the completion of the NASA 3-m infrared (JR) telescope on Mauna Kea, and the initiation of extensive guest-investi- gator programs on the Copernicus, IUE, and Einstein x-ray observatories have opened observing opportunities to many more scientists than ever before. A few private and uni- versity observatories, employing privileged staffs working with the world's largest telescopes, no longer dominate observational astronomy. National Center facilities, located at excellent sites and available to all astrono- mers, are today playing an increasingly important role in furthering our knowledge of the Universe. Despite the growth of ground-based facilities and im- provements in instrumentation, requirements for observa- tional programs to support the expanded space effort, in combination with the traditional ground-based programs, are now placing such heavy demands on the National Center facilities that the rational assignment of telescope time is almost impossible. Usually the choice lies among sev- eral programs of comparably high merit. In an effort to schedule as many programs as possible, assignment commit- tees often give too little observing time to worthy pro- posals. One clear result of the pressure for telescope time is a marked shift in the style of observational astronomy, away from the lone investigator working at the telescope night after night, and toward the team of astronomers attempting to make a single pivotal observa- tion. Both styles can yield outstanding results: the classic work that led to the concept of stellar popula- tions required the wartime blackouts of Los Angeles and many nights at the 2.5-m Mt. Wilson telescope, whereas the discovery of optical pulses from the Crab nebula pulsar needed only a few hours on a small telescope. When, under astropolitical pressure, time-assignment committees allocate too little time to a worthy project, it sometimes happens that even the assigned time is wasted if the project is not completed. We clearly need more telescopes, together with even more efficient ways to handle the increasing demand for telescope time. Very rapid growth in instrumental techniques and capabilities occurred during the 1970's. Highly sensi- tive spectrometers capable of accurate subtraction of the night-sky background were developed and put into regular

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105 operation. The improvement in the performance of these devices over that of older techniques is impressive. At the beginning of the past decade, the most advanced spec- trophotometer in existence was the 32-channel instrument used on the 5-m Hale telescope. Modern spectrophotometers provide an increase of nearly a hundredfold in the number of available pixels and, with the deployment of COD detec- tors and simple optical systems, they have achieved more than a tenfold increase in sensitivity per pixel over the state of the art in 1970. Our current ability to obtain accurate spectrophotometry of sources only slightly brighter than the night sky is a major achievement of instrument design and fabrication. Without this gain, it would not be possible to follow up observations at radio, ultraviolet (W), and x-ray wavelengths with the required optical work. These achievements at optical wavelengths are fully matched by improvements in IR detectors and instruments. The military interest in IR systems has led to very rapid advances in detector technology throughout the IR region, particularly the InSb detectors for use in the 1-5-pm region, which have achieved orders-of-magnitude improve- ment over devices available in the early 1970's. The requirements for a high-quality IR observing site are different from those for optical observatories in that the amount of water vapor is a crucial factor. The addition of telescopes at high-altitude locations has therefore also been important for progress in ground- based IR astronomy. Similarly, the design requirements for an optimized IR telescope differ from those of a conventional optical telescope, since the thermal back- ground must be minimized; it is only within the last decade that large, IR-optimized telescopes have become operational. Throughout the whole of the IR spectrum, atmospheric absorption is troublesome, and it is only within the 1-30-pm region that atmospheric winnows exist that permit high-quality measurements from the ground. With the development of IR observatories that operate either high in the Earth's atmosphere (e.g., balloons, the Kuiper Airborne Observatory) or above it entirely, the full benefits of IR astronomy are beginning to be realized. The IR region also gleans advantages from its inter- mediate wavelength location between the radio (where wave detectors are used) and the optical (where photon counting prevails) wavelength regions. This has allowed hybrid technologies to be developed, such as spatial interfero- -

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106 meters, Fourier-transform spectrometers, and heterodyne spectrometers. These instruments often allow spatial or spectral resolution to be obtained that exceeds that which is possible for stellar sources at other wavelengths. Moreover, two-dimensional IR detectors seem to be just over the horizon. Because the atmospheric "seeing" is better at IR than at optical wavelengths, two-dimensional pictures in the IR region with a large telescope should show more detail than comparable photographs in the optical region. Major instrumental developments in solar astronomy include the construction of high-angular-resolution vacuum solar telescopes on good sites and the construction of spectrographs with a velocity resolution of the order of 1 m/sec. Together, these instruments yield unprecedented details of the spatial distribution of velocity fields in the solar atmosphere. Observations with high-spatial- resolution magnetometers in the past decade have com- pletely revolutionized our concepts of the solar magnetic field. We now know that virtually all magnetic fields on the Sun occur in regions of high field strength (some 1500 gauss); the small general fields observed earlier may be explained in terms of the very small filling factor of these intense fields. Astrometric astronomers achieved a major breakthrough in the past decade with the use of finer-grained emulsions and sophisticated image analysis, which produced a tenfold increase in the precision with which astrometric parame- ters can be determined photographically. Since the devel- opment of the photographic plate, the magnitude of typical external parallax error has been reduced from 0.02 arcsec to 0.002 arcsec. This advance has made possible the determination of parallaxes, and hence luminosities, for many faint dwarf and degenerate stars. Reliable paral- laxes and luminosities for stars in the middle and upper main sequence have been obtained, and astrometric binaries are being detected with increased frequency. Speckle interferometry is an emerging field and has already greatly increased the precision with which the separation of close binaries can be measured. Together with the improved parallaxes it is now possible to obtain much better knowledge of stellar masses, and hence a more precise determination of the mass-luminosity law, with implications for the theory of stellar evolution. Inten- sity interferometers have given us our first reliable estimates of the diameters of nearby blue stars. Modern techniques have also permitted the establishment of

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107 fundamental positions with respect to extragalactic objects and the subsequent correction of the optical coordinate system to the very precise radio system. Astronomy from space came of age in the 1970's. The operation of stable, sophisticated satellites sensitive to radiation across the electromagnetic spectrum provided the entire astronomical community, through extensive guest investigator programs, with the ability to obtain observa- tions over a large range of wavelengths. Copernicus, IUE, and the Orbiting Solar Observatory (OSO) series have opened wavelength windows that once were seen only in brief glimpses from sounding rockets. Together with x-ray satellites, these instruments have profoundly changed our views of the interstellar medium, the physics of collapsed objects, the interaction of plasmas with magnetic fields, and the interrelationship of galaxies with the intergalac- tic medium. mese new facilities have placed heavy de- mands on ground-based telescopes used to follow up and extend the space observations; the space facilities pro- jected for the 1980's will only increase the demand for ground-based optical and IR spectroscopy and imaging, extended monitoring, and synoptic observation. B. Scientific Programs 1. Galactic Astronomy The Milky Way galaxy is a highly complex system whose structure has resulted from the cumulative effects of physical processes occurring in interrelated subcompo- nents, e.g., stars, interstellar clouds, globular clus- ters, and supernovae. Because of this diversity and complexity, our Galaxy continues to be the primary source of information concerning fundamental galactic properties in general, such as the stellar luminosity function or the conditions that cause interstellar clouds to form stars. The 1970's saw an impressive series of scientific successes, ranging from the interpretation of the thermo- nuclear evolution of stars to the discovery of theoreti- cally predicted neutron stars and even objects that are good candidates for black holes. Galactic astronomy has benefited from the normal progress of a vigorous research area and, like the rest of astronomy, has received a major push from the opening of previously inaccessible electro- magnetic spectral regions to routine astronomical observa-

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108 Lions. This has been a primary factor in the establish- ment of W and much of IR astronomy as major branches of the Galactic research effort. Simultaneously, the devel- opment of x-ray, gamma-ray, and more sophisticated radio- observational techniques, plus improvements in instrumen- tation in the traditional optical region, have revitalized areas of classical Galactic studies. Finally, major impacts on the observational effort have come as a result of new theoretical insights. Because of the great breadth of what we consider Galactic astronomy, it is not feasible to provide a comprehensive review of the field. Instead we include a representative sample of research programs. a. Interstellar Medium Sounding-rocket detections of interstellar H2 and CO were followed up by far more detailed measurements with the Copernicus satellite, which also made the first observations of many other interstellar absorption lines, such as those of D, HO, and O VI. Further analysis of Orbiting Astronomical Observatory-2 (OAO-2) observations, and of new observations by OAO-3, showed that the distri- bution of atomic hydrogen in the local region of the Galaxy is highly inhomogeneous, with regions of very low density in the solar neighborhood extending to large distances in certain directions. This was also substan- tiated by an experiment carried on the 1975 Apollo-Soyuz mission, which made the first detection of hot stars in the extreme ultraviolet (below 912 A) wavelength range. OAO-2 and Copernicus observations of interstellar dust extinction investigated the absorbing properties of the dust in the W region and its variation in different regions of space. Far- W photometry and imagery of dust reflection nebulae and the diffuse Galactic background radiation revealed that interstellar dust is highly efficient at scattering W starlight. The detection of O VI as a ubiquitous component of interstellar space started a theoretical revolution: old models gave way to new. We now believe that most of interstellar space is filled with million-degree gas instead of cool gas at a temperature less than 104 K. Stellar winds and supernovae are now thought to provide a major source of energy affecting virtually all gas, not just that in the vicinity of these objects. The study of dominant ionization stages of the first 30 elements confirmed the notion that some heavy elements are, on average, depleted in space, probably by being bound in dust grains. The range of depletions is, how-

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109 ever, very large (up to 103) from region to region and from cloud to cloud. The theory of grain destruction in shock waves plausibly explains this result, but detailed abundance studies have still not isolated a unique grain- formation mechanism. m e major component of the grains, which is probably C, N. or O. has not been empirically identified. Theories of molecule formation were sorted out with the detection of H2 and HD. At least for diffuse clouds, charge-exchange reactions between ions and mole- cules can explain most observations, as opposed to for- mation on dust grains. Formation of H2 itself was con- firmed to occur on grains, the general theory agreeing with observations of the ratio of H2 to total hydrogen over a factor of 107 Studies of light elements (Li, B. and Be) and isotopes (for example, D) helped to confirm older ideas on the origin of these elements, which are destroyed as gas is processed through stars. The unexpectedly large amount of D suggests that it is primeval in origin and that the density of the explosion in which D was created was quite low, suggesting an open Universe if the standard ages and simple theories of the Universe are correct. Data on interstellar B. Be, and Li are consistent with their for- mation in situ by reactions between C, N. and O atoms and . . cosmic rays. Near the end of the decade verY-hinh-resolution obser- vations using Michelson techniques allowed detection of hyperfine structure in Na I. m is long-searched-for result implies that internal motions in a few clouds are much more nearly thermal than had been previously thought. In conjunction with new global models of the interstellar medium, this result suggests that interstellar clouds are a complex of cold, quiescent regions and expanding, evapo- rating surfaces, impinged upon from all directions by shock waves, sometimes with quite high velocities. Direct observations have been made of the stellar, ionized-gas, dust, and probably the nonthermal components of the Galactic center region. Within a complex structure with scale sizes down to less than 1 parsec, there exist intricate rotational and random motions as large as 300 km/sec. These data have been interpreted as providing indications of continuing star formation and perhaps even for the presence of a massive black hole. The dense interstellar clouds within which star for- mation occurs shroud the stellar-birth process in the optical spectral region but not in the IR. Large molecu-

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110 lar clouds are detected as luminous, low-temperature ther- mal sources, but the energy-production process remains uncertain. At later stages, protostars are found to emit copious amounts of IR radiation, but detailed knowledge of the structure and evolution of the protostar is still missing. The discovery of vibrational emission from hydrogen molecules at a temperature greater than 1000 K, near the core of the Orion Molecular Cloud, provides evidence that energetic dynamical phenomena are associated with young stars. Subsequent high spectral resolution IR observa- tions of CO, H2, and ionized gas leave little doubt that a shock front is moving out from a central source with a velocity of 30 to 50 km/see and is at a radius of about 1017 cm. Millimeter observations of broad CO emission also indicate an outflow; the total energy involved has been estimated at more than 1047 ergs. Thus an evolutionary process on a time scale of about 1000-3000 years is taking place inside the molecular cloud. The observation of dynamical events associated with young stars is an exciting research area in which rapid advances are now possible. Future observations taking full advantage of new techniques may yield obser- vations of protostellar collapse, which in spite of much effort has not yet been observed. - This is also an imPor- tant area of research, particularly necessary for compari- son with theories of star formation, which require more observational guidance. More and better data are now being acquired for the distribution of elements in H II regions that show that the Milky Way, like other spiral galaxies, is likely to have a radial gradient in the abundances of common ele- ments such as C, N. O. and S. Observations of planetary nebulae are suggestive of a similar trend, indicating that the degree to which matter has been processed within the Galaxy has varied systematically with position throughout much of the Galaxy's history. The origin of the abundance gradient is not fully understood, but it could result from the more frequent processing of matter by spiral-arm- induced star formation at smaller radii. ~ _ _ _ ~ b. Stellar Astronomy The Copernicus and IUE spacecraft have for the first time opened the W spectral region to the powerful tech- niques of high-resolution spectroscopy. As a result of extensive surveys by these spacecraft, we now realize that stellar winds are a ubiquitous phenomenon among

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111 stars and that mass-loss rates range up to 109 times that of the Sun. It now appears that high mass-loss rates are common among highly evolved stars as well as among very luminous young ones. The recent discovery of large mass-loss rates, as inferred from W resonance lines with P Cygni-type emission profiles, has major implica- tions for the evolution of these stars, for the dynamics of their interstellar environment, and for the dispersal throughout the Galaxy of chemical elements produced in stars. The quest to understand the acceleration mechan- isms and consequences of these strong stellar winds has become one of the most active and exciting areas of astro- physics. Circumstellar shells, strong IR emitters in the 2-20-pm region, have been discovered in both young and old stellar types. The detailed spatial and spectroscopic studies of these envelopes yield much additional informa- tion on the evolution of stars and on their interaction with the interstellar medium. Ultraviolet spectra from Copernicus and IUE, x-ray observations from the High-Energy Astronomical Observa- tory (HEAD) satellites, and ground-based optical studies have shown that phenomena previously studied mainly on the Sun, such as chromospheres, coronas, and flares, occur also in a very wide range of stars. Chromospheres, for example, are found in essentially all stars cooler than type early F. but the chromospheric heating rates vary by several orders of magnitude for stars of the same type. Observations from the Einstein and IUE satellite observatories have shown that essentially all stars, with the probable exception of cool giants and supergiants, have hot coronas. The roughly 3-orders-of-magnitude spread in the x-ray surface fluxes at each spectral type and the existence of coronas in OB stars clearly elimi- nates the long-held idea that coronas are heated by connectively generated acoustic waves. Instead, heating by dynamo-generated or remnant turbulent magnetic fields, either through magnetohydrodynamic wave processes or field annihilation, is now felt to be likely. A major theoreti- cal effort to understand these heating processes is now under way, guided by in-depth studies of the spatially resolved solar corona. Also, flares with energies up to 5 orders of magnitude higher than those of large solar flares are now being studied in both dMe and RS CVn-type close binary systems. These phenomena reveal the all- pervasive role that magnetic fields play in the outer atmospheres of stars, as was previously known for the Sun. They also point out the critical need to measure

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112 magnetic fields directly in many stars, which is now feasible, and to measure accurately stellar rotation rates on which dynamo processes depend. me major role of dust grains in the outer atmospheres of stars is now recognized, and conditions favoring dust formation are being deduced from the thermal-emission properties of dust shells. Dust is an integral part of a wide range of circumstellar environments, which include, for example, cool giants and supergiants, novae, and Wolf-Rayet stars. In most instances the dust seems to have formed in a mass outflow, and the infrared charac- teristics can therefore provide information on stellar mass loss. The chemical composition of dust in circus stellar shells has in part been revealed through the discovery of the IR silicate emission feature. Further- more, there are suggestions that the dust in some stars, such as novae, may be present mainly in the form of graphite. Curiously, the silicate-emission properties of dust embedded in comets have proved to be similar to those of dust formed in the winds of dying stars. High-dispersion spectroscopy of fainter stars has resulted from the implementation of better detectors on existing coude spectrographs and the construction of echelles for use at the Cassegrain focus. A variety of metal-poor stars has been subject to detailed abundance studies. m is has uncovered patterns in abundance ratios as a function of overall metallicity, which can be related to the origins of heavy elements in the early Galaxy through the theory of stellar nucleosynthesis. Globular clusters are of essential value to the study of Galactic astronomy because of the relative simplicity of their structure and dynamics, the extreme character of their stellar population, and the information they provide about the dynamical and chemical evolution of the Galaxy. It now appears that there are significant variations of age and chemical composition among the globular clusters. These results will play an important role in future efforts to reconstruct the evolution of the Galaxy. They already suffice to show that the postulate of an initial rapid collapse of the halo represents an oversimplifica- tion of the processes that must have occurred during the formation of the Galaxy. The discovery during the 1970's of x-ray sources in globular clusters is especially excit- ing because of the possibility that their presence signals the existence of massive objects (such as black holes) in the cores of clusters. At the least, these x-ray sources

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113 must be representative of late stages of stellar evolu- tion. New classes of stars are now recognized on the basis of their IR properties; some of these are new aspects of well-known types of objects. For many transient stars, such as Eta Carinae, the optical flux does not necessar- ily indicate the true luminosity, since a large fraction is often converted into IR radiation by circumstellar dust. Other examples of unusual objects include the disk IR emitters, such as CRL 2688, and the classes of stars that are completely obscured in the optical range, prob- ably the result of an optically thick dust shell. Great advances have been made in the past decade in the observation and theoretical understanding of late stages of stellar evolution and in the detailed under- standing of collapsed objects. The study of counterparts of x-ray sources with ground-based optical spectroscopy and the IUE satellite has revealed many close binary sys- tems, which often include compact objects, high magnetic fields, accretion disks, gas streams, and beamed emission. Significant improvements in our theoretical understanding have been achieved in the related problems of the equa- tion of state at very high densities, the theory of black holes, the causes of nova outbursts, the elucidation of helium-burning phases of stellar evolution, and the theory of stellar pulsation. m e proof of the existence of neutron stars is one of the major astrophysical breakthroughs of the 1970's. These objects have masses comparable with the Sun's but with mean densities more than 1014 times that of normal matter. Hard x-ray spectral observations imply that mag- netic fields associated with neutron stars may be as high as 1012 gauss. The first neutron stars were discovered as radio pulsars, one of which has been shown to be in a binary system. Four, including the Crab and Vela pulsars, were subsequently detected at gamma-ray energies. A second group of neutron stars was discovered as pulsating x-ray sources. All of these appear to be members of close binary systems, in which the x-ray emission seems to be a to a magnetic neutron star. It is apparent from all these remarkable properties that neutron stars offer a unique testing ground for our under- standing of the fundamental physical laws of nature. There has also been substantial Progress in understand- consequence of mass transfer ~ _ ing cataclysmic variables and similar systems during the past few years, and many questions involving these systems now appear to be on the threshold of resolution. There

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114 is mounting evidence that nova outbursts are thermonuclear explosions, while dwarf-nova outbursts appear to result from nuclear reactions caused by accretion events. Fur- ther theoretical studies combined with W photometry and elemental abundance measurements could firmly establish these models within the next few years. 2. Extragalactic Astronomy a. Galaxies and Clusters of Galaxies The completion of several 4-m telescopes, coupled with major advances in detector technology during the past dec- ade, have led to a virtual revolution in our analysis of the large-scale mass distribution in the Universe, which has strengthened evidence in favor of a dominant, nonlumi- nous component of cosmic matter. Observations suggest that the total mass distributions of ordinary spiral gal- axies extend far beyond the optically visible disks. At least some fraction of the nonluminous matter in the Uni- verse resides in the outer regions of individual galaxies themselves. Optical searches for this matter have been inconclusive, confirming only that its luminosity per unit mass is much lower than that of conventional stellar matter. A remarkable development is the recent discovery that the rotation curve of virtually all spiral galaxies remains flat to the limit of detectable emission. No galaxies exhibit diminishing stellar velocities at large nuclear distances, as would be expected for centrally condensed objects. This result implies that significant mass is located at large nuclear distances, so that the total size and mass of spiral galaxies are much larger than previously thought. Because most of the material in the outer region is unseen, the physical properties of the material are largely unknown. The possibility that the unobserved mass is gas can be ruled out, but there is still no evidence for large numbers of faint M dwarfs in the halo. Challenging dynamical problems must be overcome before the disturbed nature of the outer parts of the Galactic disk are understood. Many external galaxies show the same nonplanar outer structure. Although the dynamics of galactic encounters can explain some warps, they are also observed in isolated galaxies with no obvious companion. Problems of maintaining the warp against dispersive effects are particularly puzzling to theorists.

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115 The molecules CO and HCN were discovered for the first time in external galaxies during the 1970's. In the Milky Way, CO studies have played a major role in determining sites of active star formation. High-resolution CO maps of galaxies of a wide variety of Hubble types could pro- vide a cogent test of star-formation theories in other types of galaxies. Decades from now, the 1970's will be remembered as a period when the full complexity of galaxy evolution was glimpsed for the first time. that galaxies, even after formation, are not the isolated island universes that Hubble envisioned. On the contrary, galaxies interact with each other and with their environ- ments in a complex way. Some bizarre galaxy forms are now understood as two galaxies in collision, or galaxies tidally distorting one another. Within clusters, central massive galaxies can grow by mergers or at the expense of the halo stars in less massive neighbors. The sizes of the great clusters and the extent of the holes between clusters are larger than many would have imagined in 1970. There is now a realization b. Quasars The long-standing puzzle over the nature of the red shifts of the quasi-stellar objects is now close to solu- tion. Groups of galaxies have been found surrounding a number of low-red-shift quasars; these QSO's have the same red shift as the surrounding galaxies. Furthermore, some objects thought to be closely related to quasars appear to be nuclei of galaxies, again with the same red shift as the galaxy. These discoveries support the hypothesis that the red shifts of at least some quasars are cosmo- logical. It seems likely that quasars are really very distant, with enormously high luminosities. Brightness variations on short time scales indicate that the central energy source is extremely small--comparable in size with our own solar system. Studies of both optically selected and radio quasars show that quasars were much more numerous and possibly more luminous in the past. However, a decline in detected quasars sets in at a red shift of 3.5. Limits put on distant quasars by the x-ray background suggest that this apparent decline in numbers is real and that the increase in quasar numbers does not continue beyond z = 3. Very recent studies have suggested that the mysterious quasar absorption lines have multiple origins. Some evi- dently arise in the quasar, some in a surrounding galaxy,

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116 some in intervening galaxies, and some perhaps in inter- galactic clouds. m ese clouds therefore provide a unique probe of gas densities and abundances under a wide variety of conditions at very large red shifts. It is possible to study from the ground the spectra of high-red-shift quasars to below the Lyman limit at 912 L. During the 1970's it became possible to make similar studies of the much nearer ordinary and peculiar Galaxies and low-red-shift quasars. First by means of OAO-B, and later in more detail using IUE, it has been found that between 1200 and 2000 ~ the spectrum of ordinary gal- axies is dominated by spectra of hot stars. These stars give clues to the evolutionary history of the galaxies. Rocket and IUE observations of Seyfert galaxies have show that the emission lines in the W region have far differ- ent intensities than predicted by simple theories. The IUE observations support the idea that, in some of these objects, interstellar dust plays an important role. In other Seyferts, just as in quasars, there is little or no evidence for dust even though the line intensities are peculiar. IUE observations of the low-red-shift quasar 3C273 show that absorption lines are absent, supporting the view that most of the absorption lines seen in large- red-shift quasars are produced by intervening galaxies and gas clouds. Among the many possible models for quasars and active galactic nuclei, accretion of material onto black holes with masses between 106 and 101 solar masses now appears to be the most likely. Regardless of whether this spe- cific model eventually proves to be correct, however, a more important conclusion has emerged. Despite the enor- mous energies involved in some of the outbursts observed in quasars and active galaxies, there is no strong theo- retical reason to doubt the cosmological nature of the observed red shifts or to believe that "new physics" is required to understand these objects. Still, the mystery posed by their energetics is one of the most challenging in contemporary astronomy. c. Cosmology Recent research in cosmology has been dominated by the impact of the discovery of the cosmic microwave back- ground radiation in 1965. Most astronomers accept this 3 K radiation as a relic of the primeval fireball created in the big bang. During the 1970's, the blackbody nature of the microwave radiation was generally verified, al-

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117 though tantalizingly small departures from a blackbody curve may have been detected at both long and short wave- lengths. These departures are important because they trace the detailed early thermal history of the Universe. An anisotropy in the background due to the Earth's motion was apparently detected, and the amount was sur- prisingly large, near 600 km/sec. This implies that the presence of the Virgo supercluster is sufficient to slow the expansion in the vicinity of the Galaxy. With respect to the background radiation, the Galaxy and the Local Group have a velocity of about 400 km/see toward the cen- ter of the Virgo supercluster. The small-scale anisotropy of the background radiation is less than 10 4 on an angular scale of 10 arcmin. The magnitude of the Hubble constant Ho, which mea- sures the present rate of expansion of the Universe, remains a source of controversy, and the currently accepted value is probably uncertain by a factor of 2. The value assigned to Hb affects the assumed luminos- ities, sizes, and densities of virtually all extragal- actic objects; it also sets an upper limit to the age of the Universe and clustering time scales for galaxies. Classical procedures and novel techniques now being used to evaluate Ho from cosmological observations will we hope lead to a single value of high accuracy. Classical cosmological tests have been pushed to greater look-back time; the red-shift-magnitude relation for galaxies now extends out to red shifts of unity. However, our increasing understanding of galaxy evolution makes it clear that such tests are more sensitive to the evolution of galaxies than they are to the large-scale structure of the Universe. Near the end of the decade it was found that there is a strong correlation between the continuum intensity of QSO spectra and the strength of the C IV line. This promises to provide a technique for calibrating the intrinsic luminosity of quasars. Com- bining ground-based observations of high-red-shift quasars with space observations of low-red-shift quasars could, in principle, yield a firm value for the deceleration parameter go. However, because the underlying cause of the correlation is not understood, it is possible that evolutionary effects could result in a major distortion of the Hubble diagram and skew the derived value of go. Thus, we cannot yet state whether the Universe is open or closed.

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118 3. Solar Astronomy Solar Magnetic Fields Hale's early investigations of solar magnetic fields distinguished between strong, sunspot-related magnetic fields and a weak, general magnetic field of the order of 1 gauss in strength. During the last decade, high- resolution magnetographs and sophisticated observing techniques have revolutionized our concept of the solar magnetic-field structure. We now believe that virtually all solar magnetic fields occur in regions of very high field strength (1500 gauss). The 1-gauss general magnetic field observed by Hale was the result of the small filling factor of the high-field magnetic elements. The true size of these magnetic elements is unknown, since they are too small for even the best ground-based magnetographs to resolve. Theoretical attempts to explain the origin and stabilities of these magnetic-flux tubes are under way. The study of solar vector magnetic fields, spatially resolved and with unprecedented sensitivity, will be a prime objective of the SOT on the Space Shuttle, which is designed to achieve 0.1 arcsec spatial resolution. b. Coronal Holes and the Solar Wind l One of the outstanding discoveries in solar physics during the past decade was the recognition that the so- called solar M regions responsible for the geomagnetic storms do not coincide with regions of solar activity but, quite to the contrary, with extremely inactive regions on the Sun. Whereas the magnetic fields in the solar active regions of high magnetic flux are "closed," the fields in the low-magnetic-flux solar-polar regions and in some other nonactive regions on the Sun are "open, extending outward away from the Sun toward the Earth and the other planets. For reasons not yet fully understood, the high-speed component of the solar wind (expanding at about 1000 km/see) originates in these open magnetic-field regions in the solar corona, resulting in lower-density coronal plasma and easy visibility of these so-called "coronal holes" as dark regions in solar x-ray images. Since coronal holes do not share the differential rota- tion with solar latitude seen in the solar photosphere, but rather appear to rotate solidly, they are thought to be anchored in the solar interior. The energy balance in coronal holes differs fundamentally from that in active regions, as coronal-wind expansion is the dominant cooling mechanism in holes, whereas radiative losses and thermal conduction dominate for active regions. The all-pervasive