Annual Review of Astronomy and Astrophysics - Volume 40, 2002
Volume 40, 2002
- Preface
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- Review Articles
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A Generalist Looks Back
Vol. 40 (2002), pp. 1–25More Less▪ AbstractI fled with my parents from Hitler's Austria to Australia and studied physics at Sydney University. I obtained my Ph.D. in quantum electrodynamics with Rudolf Peierls at Birmingham University and came to Cornell to work with Hans Bethe. I have stayed at Cornell ever since, and I have essentially had only a single job in my whole life, but have switched fields quite often. I worked in nuclear astrophysics and in late-stellar evolution, estimated the Initial Mass Function for star formation and the metal enrichment of the interstellar medium. I suggested black hole accretion as the energy source for quasars, worked on molecule formation on dust grain surfaces, and was involved in 21-cm studies of gas clouds and disk galaxies. I collaborated with my wife on the neurobiology of the neuromuscular junction and with one of my daughters on the epidemiology of tuberculosis.
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Ultra-Compact HII Regions and Massive Star Formation
Vol. 40 (2002), pp. 27–62More Less▪ AbstractThis review discusses three main topics: evolution to the ultra-compact (UC) state; the properties of UC HII regions and their environments; and UC HII regions as probes of Galactic structure. The evolution to UC HII regions begins in giant molecular clouds that provide the natal material for prestellar cores that evolve into hot cores, the precursors of UC HII regions. The properties of each evolutionary phase are reviewed, with particular emphasis on those of hot cores. The observed properties of UC HII regions and their environments are summarized with emphasis on the physical processes that may produce the observed properties. The final section summarizes the use of UC HII regions as probes of Galactic structure: in particular, the Galactic population and distribution of newly formed massive stars, the location of spiral arms, and the average galactocentric temperature and abundance gradients.
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Kuiper Belt Objects: Relics from the Accretion Disk of the Sun
Vol. 40 (2002), pp. 63–101More Less▪ AbstractThe Kuiper Belt consists of a large number of small, solid bodies in heliocentric orbit beyond Neptune. Discovered as recently as 1992, the Kuiper Belt objects (KBOs) are thought to hold the keys to understanding the early solar system, as well as the origin of outer solar system objects, such as the short-period comets and the Pluto-Charon binary. The KBOs are probably best viewed as aged relics of the Sun's accretion disk. Dynamical structures in the Kuiper Belt provide evidence for processes operative in the earliest days of the solar system, including a phase of planetary migration and a clearing phase, in which substantial mass was lost from the disk. Dust is produced to this day by collisions between KBOs. In its youth, the Kuiper Belt may have compared to the dust rings observed now around such stars as GG Tau and HR 4796A. This review presents the basic physical parameters of the KBOs and makes connections with the disks observed around nearby stars.
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Theory of Giant Planets
Vol. 40 (2002), pp. 103–136More Less▪ AbstractGiant planet research has moved from the study of a handful of solar system objects to that of a class of bodies with dozens of known members. Since the original 1995 discovery of the first extrasolar giant planets (EGPs), the total number of known examples has increased to ∼80 (circa November 2001). Current theoretical studies of giant planets emphasize predicted observable properties, such as luminosity, effective temperature, radius, external gravity field, atmospheric composition, and emergent spectra as a function of mass and age. This review focuses on the general theory of hydrogen-rich giant planets; smaller giant planets with the mass and composition of Uranus and Neptune are not covered. We discuss the status of the theory of the nonideal thermodynamics of hydrogen and hydrogen-helium mixtures under the conditions found in giant-planet interiors, and the experimental constraints on it. We provide an overview of observations of extrasolar giant planets and our own giant planets by which the theory can be validated.
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Theories of Gamma-Ray Bursts
Vol. 40 (2002), pp. 137–169More Less▪ AbstractThe gamma ray burst phenomenon is reviewed from a theoretical point of view, with emphasis on the fireball shock scenario of the prompt emission and the longer wavelength afterglow. Recent progress and issues are discussed, including spectral-temporal evolution, localizations, jets, spectral lines, environmental and cosmological aspects, as well as some prospects for future experiments in both electromagnetic and nonelectromagnetic channels.
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Cosmic Microwave Background Anisotropies
Wayne Hu, and Scott DodelsonVol. 40 (2002), pp. 171–216More Less▪ AbstractCosmic microwave background (CMB) temperature anisotropies have and will continue to revolutionize our understanding of cosmology. The recent discovery of the previously predicted acoustic peaks in the power spectrum has established a working cosmological model: a critical density universe consisting of mainly dark matter and dark energy, which formed its structure through gravitational instability from quantum fluctuations during an inflationary epoch. Future observations should test this model and measure its key cosmological parameters with unprecedented precision. The phenomenology and cosmological implications of the acoustic peaks are developed in detail. Beyond the peaks, the yet to be detected secondary anisotropies and polarization present opportunities to study the physics of inflation and the dark energy. The analysis techniques devised to extract cosmological information from voluminous CMB data sets are outlined, given their increasing importance in experimental cosmology as a whole.
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Stellar Radio Astronomy: Probing Stellar Atmospheres from Protostars to Giants
Vol. 40 (2002), pp. 217–261More Less▪ AbstractRadio astronomy has provided evidence for the presence of ionized atmospheres around almost all classes of nondegenerate stars. Magnetically confined coronae dominate in the cool half of the Hertzsprung-Russell diagram. Their radio emission is predominantly of nonthermal origin and has been identified as gyrosynchrotron radiation from mildly relativistic electrons, apart from some coherent emission mechanisms. Ionized winds are found in hot stars and in red giants. They are detected through their thermal, optically thick radiation, but synchrotron emission has been found in many systems as well. The latter is emitted presumably by shock-accelerated electrons in weak magnetic fields in the outer wind regions. Radio emission is also frequently detected in pre–main sequence stars and protostars and has recently been discovered in brown dwarfs. This review summarizes the radio view of the atmospheres of nondegenerate stars, focusing on energy release physics in cool coronal stars, wind phenomenology in hot stars and cool giants, and emission observed from young and forming stars.
Eines habe ich in einem langen Leben gelernt, nämlich, dass unsere ganze Wissenschaft, an den Dingen gemessen, von kindlicher Primitivität ist—und doch ist es das Köstlichste, was wir haben.
One thing I have learned in a long life: that all our science, measured against reality, is primitive and childlike—and yet it is the most precious thing we have.
A. Einstein 1951, in a letter to H. Mühsam, Einstein Archive 36-610
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Modified Newtonian Dynamics as an Alternative to Dark Matter
Vol. 40 (2002), pp. 263–317More Less▪ AbstractModified Newtonian dynamics (MOND) is an empirically motivated modification of Newtonian gravity or inertia suggested by Milgrom as an alternative to cosmic dark matter. The basic idea is that at accelerations below ao ≈ 10−8 cm/s2 ≈ cHo/6 the effective gravitational attraction approaches
, where gn is the usual Newtonian acceleration. This simple algorithm yields flat rotation curves for spiral galaxies and a mass-rotation velocity relation of the form M ∝ V4 that forms the basis for the observed luminosity–rotation velocity relation—the Tully-Fisher law. We review the phenomenological success of MOND on scales ranging from dwarf spheroidal galaxies to superclusters and demonstrate that the evidence for dark matter can be equally well interpreted as evidence for MOND. We discuss the possible physical basis for an acceleration-based modification of Newtonian dynamics as well as the extention of MOND to cosmology and structure formation.
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Cluster Magnetic Fields
Vol. 40 (2002), pp. 319–348More Less▪ AbstractMagnetic fields in the intercluster medium have been measured using a variety of techniques, including studies of synchrotron relic and halo radio sources within clusters, studies of inverse Compton X-ray emission from clusters, surveys of Faraday rotation measures of polarized radio sources both within and behind clusters, and studies of cluster cold fronts in X-ray images. These measurements imply that most cluster atmospheres are substantially magnetized, with typical field strengths of order 1 μGauss with high areal filling factors out to Mpc radii. There is likely to be considerable variation in field strengths and topologies both within and between clusters, especially when comparing dynamically relaxed clusters to those that have recently undergone a merger. In some locations, such as the cores of cooling flow clusters, the magnetic fields reach levels of 10–40 μG and may be dynamically important. In all clusters the magnetic fields have a significant effect on energy transport in the intracluster medium. We also review current theories on the origin of cluster magnetic fields.
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The Origin of Binary Stars
Vol. 40 (2002), pp. 349–385More Less▪ AbstractAlthough we have a general understanding of the manner in which individual stars form, our understanding of how binary stars form is far from complete. This is in large part due to the fact that the star formation process happens very quickly and in regions of the Galaxy that are difficult to study observationally. We review the theoretical models that have been developed in an effort to explain how binaries form. Several proposed mechanisms appear to be quite promising, but none is completely satisfactory.
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Radio Emission from Supernovae and Gamma-Ray Bursters
Vol. 40 (2002), pp. 387–438More Less▪ AbstractStudy of radio supernovae over the past 20 years includes two dozen detected objects and more than 100 upper limits. From this work it is possible to identify classes of radio properties, demonstrate conformance to and deviations from existing models, estimate the density and structure of the circumstellar material and, by inference, the evolution of the presupernova stellar wind, and reveal the last stages of stellar evolution before explosion. It is also possible to detect ionized hydrogen along the line of sight, to demonstrate binary properties of the stellar system, and to show clumpiness of the circumstellar material. More speculatively, it may be possible to provide distance estimates to radio supernovae.
Over the past four years the afterglow of gamma-ray bursters has occasionally been detected in the radio, as well in other wavelengths bands. In particular, the interesting and unusual gamma-ray burst GRB980425, thought to be related to SN1998bw, is a possible link between supernovae and gamma-ray bursters. Analyzing the extensive radio emission data avaliable for SN1998bw, one can describe its time evolution within the well-established framework available for the analysis of radio emission from supernovae. This allows relatively detailed description of a number of physical properties of the object. The radio emission can best be explained as the interaction of a mildly relativistic (Γ ∼ 1.6) shock with a dense preexplosion stellar wind–established circumstellar medium that is highly structured both azimuthally, in clumps or filaments, and radially, with observed density enhancements. Because of its unusual characteristics for a Type Ib/c supernova, the relation of SN1998bw to GRB980425 is strengthened and suggests that at least some classes of GRBs originate in massive star explosions. Thus, employing the formalism for describing the radio emission from supernovae and following the link through SN1998bw/GRB980425, it is possible to model the gross properties of the radio and optical/infrared emission from the half-dozen GRBs with extensive radio observations. From this we conclude that at least some members of the “slow-soft” class of GRBs can be attributed to the explosion of a massive star in a dense, highly structured circumstellar medium that was presumably established by the preexplosion stellar system.
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Shapes and Shaping of Planetary Nebulae
Bruce Balick, and Adam FrankVol. 40 (2002), pp. 439–486More Less▪ AbstractWe review the state of observational and theoretical studies of the shaping of planetary nebulae (PNe) and protoplanetary nebulae (pPNe). In the past decade, high-resolution studies of PNe have revealed a bewildering array of morphologies with elaborate symmetries. Recent imaging studies of pPNe exhibit an even richer array of shapes. The variety of shapes, sometimes multiaxial symmetries, carefully arranged systems of low-ionization knots and jets, and the often Hubble-flow kinematics of PNe and pPNe indicate that there remains much to understand about the last stages of stellar evolution. In many cases, the basic symmetries and shapes of these objects develop on extremely short timescales, seemingly at the end of AGB evolution when the mode of mass loss abruptly and radically changes. No single explanation fits all of the observations. The shaping process may be related to external torques of a close or merging binary companion or the emergence of magnetic fields embedded in dense outflowing stellar winds. We suspect that a number of shaping processes may operate with different strengths and at different stages of the evolution of any individual object.
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The New Galaxy: Signatures of Its Formation
Vol. 40 (2002), pp. 487–537More Less▪ AbstractThe formation and evolution of galaxies is one of the great outstanding problems of astrophysics. Within the broad context of hierachical structure formation, we have only a crude picture of how galaxies like our own came into existence. A detailed physical picture where individual stellar populations can be associated with (tagged to) elements of the protocloud is far beyond our current understanding. Important clues have begun to emerge from both the Galaxy (near-field cosmology) and the high redshift universe (far-field cosmology). Here we focus on the fossil evidence provided by the Galaxy. Detailed studies of the Galaxy lie at the core of understanding the complex processes involved in baryon dissipation. This is a necessary first step toward achieving a successful theory of galaxy formation.
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The Evolution of X-Ray Clusters of Galaxies
Vol. 40 (2002), pp. 539–577More Less▪ AbstractConsiderable progress has been made over the past decade in the study of the evolutionary trends of the population of galaxy clusters in the Universe. In this review we focus on observations in the X-ray band. X-ray surveys with the ROSAT satellite, supplemented by follow-up studies with ASCA and Beppo-SAX, have allowed an assessment of the evolution of the space density of clusters out to z ≈ 1 and the evolution of the physical properties of the intracluster medium out to z ≈ 0.5. With the advent of Chandra and Newton-XMM and their unprecedented sensitivity and angular resolution, these studies have been extended beyond redshift unity and have revealed the complexity of the thermodynamical structure of clusters. The properties of the intracluster gas are significantly affected by nongravitational processes including star formation and Active Galactic Nuclei (AGN) activity. Convincing evidence has emerged for modest evolution of both the bulk of the X-ray cluster population and their thermodynamical properties since redshift unity. Such an observational scenario is consistent with hierarchical models of structure formation in a flat low-density universe with Ωm ≃ 0.3 and σ8 ≃ 0.7–0.8 for the normalization of the power spectrum. Basic methodologies for construction of X-ray–selected cluster samples are reviewed, and implications of cluster evolution for cosmological models are discussed.
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Lyman-Break Galaxies
Vol. 40 (2002), pp. 579–641More Less▪ AbstractIn this paper we review the properties of Lyman-break galaxies, namely starburst galaxies at high redshifts, approximately in the range 2.5 < z < 5, identified by the colors of their far ultraviolet spectral energy distribution around the 912 Å Lyman continuum discontinuity. The properties of forming galaxies in the young universe are very important to constrain the history of galaxy evolution and the formation of the Hubble sequence, and until recently, they have remained largely unexplored. The Lyman-break technique has broken an impasse in the exploration of galaxies at high redshift that lasted for about two decades, and within a few years has yielded large and well-controlled samples of star-forming, but otherwise normal, galaxies at z > 2.5, including ∼1000 spectroscopic redshifts and another few thousands of robust candidates. This dataset has allowed us an unprecedented look at fundamental properties of galaxies at 20% of the Hubble time or less. In this paper, we discuss the nature of the Lyman-break galaxies and their properties, including star-formation rate, stellar and total mass, chemical abundance, morphology, and interstellar medium (ISM) kinematics, and outline their contribution to the stellar content of the universe and their connection to the galaxies observed in the present-day universe. We also discuss what the properties of these galaxies, in particular their spatial clustering, imply about the mechanisms of galaxy formation and about the relationship between the underlying distribution of dark matter and the activity of star formation.
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Cosmology with the Sunyaev-Zel’dovich Effect
Vol. 40 (2002), pp. 643–680More Less▪ AbstractThe Sunyaev-Zel'dovich effect (SZE) provides a unique way to map the large-scale structure of the universe as traced by massive clusters of galaxies. As a spectral distortion of the cosmic microwave background, the SZE is insensitive to the redshift of the galaxy cluster, making it well-suited for studies of clusters at all redshifts, and especially at reasonably high redshifts (z > 1) where the abundance of clusters is critically dependent on the underlying cosmology. Recent high signal-to-noise detections of the SZE have enabled interesting constraints on the Hubble constant and on the matter density of the universe using small samples of galaxy clusters. Upcoming SZE surveys are expected to find hundreds to thousands of new galaxy clusters, with a mass selection function that is remarkably uniform with redshift. In this review we provide an overview of the SZE and its use for cosmological studies, with emphasis on the cosmology that can, in principle, be extracted from SZE survey yields. We discuss the observational and theoretical challenges that must be met before precise cosmological constraints can be extracted from the survey yields.
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Previous Volumes
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Volume 62 (2024)
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Volume 61 (2023)
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Volume 60 (2022)
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Volume 59 (2021)
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Volume 58 (2020)
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Volume 57 (2019)
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Volume 56 (2018)
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Volume 55 (2017)
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Volume 54 (2016)
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Volume 53 (2015)
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Volume 52 (2014)
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Volume 51 (2013)
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Volume 50 (2012)
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Volume 49 (2011)
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Volume 48 (2010)
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Volume 47 (2009)
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Volume 46 (2008)
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Volume 45 (2007)
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Volume 44 (2006)
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Volume 43 (2005)
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Volume 42 (2004)
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Volume 41 (2003)
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Volume 40 (2002)
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Volume 39 (2001)
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Volume 38 (2000)
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Volume 37 (1999)
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Volume 36 (1998)
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Volume 35 (1997)
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Volume 34 (1996)
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Volume 33 (1995)
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Volume 32 (1994)
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Volume 31 (1993)
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Volume 30 (1992)
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Volume 29 (1991)
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Volume 28 (1990)
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Volume 27 (1989)
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Volume 26 (1988)
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Volume 25 (1987)
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Volume 24 (1986)
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Volume 23 (1985)
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Volume 22 (1984)
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Volume 21 (1983)
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Volume 20 (1982)
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Volume 19 (1981)
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Volume 18 (1980)
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Volume 17 (1979)
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Volume 16 (1978)
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Volume 15 (1977)
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Volume 14 (1976)
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Volume 13 (1975)
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Volume 12 (1974)
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Volume 11 (1973)
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Volume 10 (1972)
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Volume 9 (1971)
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Volume 8 (1970)
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Volume 7 (1969)
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Volume 6 (1968)
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Volume 5 (1967)
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Volume 4 (1966)
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Volume 3 (1965)
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Volume 2 (1964)
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Volume 1 (1963)
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Volume 0 (1932)