bluuebunny/crossref_metadata_2025 huggingface dataset:
Relations between the galactic evolution and the stellar evolution
Authors: Audouze Jean
Published: June 2019

The question which has been raised in many chapters of this book is about the existence of constraints on stellar evolution coming from related topics like cosmology or in the case of the present chapter the chemical evolution of the galaxies. As it will be seen in this contribution it seems wiser to consider that chemical evolution of galaxies is indeed related to the problem of stellar evolution discussed here but is not going to provide as many constraints on it as one would expect. The purpose of this presentation is therefore to outline the principal relations between these two fields and to discuss the impact of some recent works on them.
Primeval oxygen overabundance and type I-1/2 supernovae
Authors: Matteucci F. , Tornambé A.
Published: June 2019

Models of chemical evolution of the Galaxy have been computed by taking into account the different roles played by TypeI-1/2 (single stars suffering degenerate C-ignition) and Typell supernovae in the chemical enrichment. The overabundance of oxygen observed in the Halo stellar population has been well reproduced.
Evolutionary track of an intermediate mass first-generation star
Authors: Eryurt-Ezer D.
Published: June 2019

An evolutionary track for a metal-free star of intermediate mass with parameters (M/M⊙, X, Z)= (3,0.80,0.00) has been constructed. The evolutionary behaviour of the star in the theoretical H-R diagram is compared with that of a normal star with the same mass and its implication on the chemical evolution of the interstellar medium is discussed.
Reduction of the Past ILS Data in a Uniform System
Authors: Yumi S.
Published: June 2019

Analyses of the nutation terms based on the results of astronomical observations of time and latitude provide valuable information to promote studies on the constitution of the Earth's interior. Indeed, the results of analyses of the nutations agree well with those predicted by theory for a fluid core. This shows that the matter of the outer core, 3,000 km and more below the Earth's surface, is not only in a fused state but also is a “fluid” which can move in response to the external forces. Many additional studies on the nutation terms are now in progress, for example, to estimate an extreme value of viscosity of the fluid core, to discuss the possibility of the geomagnetic dynamo being driven by the precession, and so on.
Nutation Terms Derived from the z- and the τ-Term of the IPMS System
Authors: Yokoyama K.
Published: June 2019

The non-polar common terms, z and τ, of the IPMS system are analyzed for determining amplitudes of some terms of the forced nutation. The method of analysis and the results obtained are described briefly. Comparison is made with theoretical and other observational results. A fuller account of this work will be published elsewhere.
Short-Period Terms in Time and Latitude Observations Made with the Herstmonceux Photographic Zenith Tube
Authors: O'hora N. P. J. , Griffin S. F.
Published: June 2019

The effects of some short-period tidal and nutational terms in the observations of the Herstmonceux PZT have been re-examined using observations that extend over a longer period and have been re-reduced using improved catalogue positions. Analytic smoothing of these data has furnished observational residuals that reveal very clearly the effects of short period terms with relatively small amplitudes.
A Normal Mode Study of Wobble and Nutation
Authors: Smith Martin L.
Published: June 2019

The observed eigenperiod of the Chandler Wobble is about 435.2 sidereal days while the theoretical eigenperiod of a rigid body having the same composition and geometry as the Earth is about 305 days. The attempt to reconcile these two numbers has led scientists to study theoretically the free wobble and nutation of various classes of rotating bodies.
On Random Excitation and Damping of the Polar Motion
Authors: Opalski W.
Published: June 2019

The paper deals with the behavior of the Earth's pole when exclusively random excitations are at work (e.g. internal displacements of matter, treated as a process of stochastic character). The title of the paper is similar to that of a paper of N. Sekiguchi whose probabilistic final deductions are very ingenious. However they have been applied to a wrong solution of the basic differential equation system. The correct solution is more complicated and does not afford such an advantageous practical possibility of applying the probabilistic treatment with success.
Variations of Differences of Latitudes and of Mean Latitudes of Stations Located in the Vicinity of a Common Meridian
Authors: Kołaczek B. , Galas R. , Barlik M. , Dukwicz M.
Published: June 2019

Differences of latitudes and of mean latitudes of stations located along a common meridian were studied in order to find influences of local geophysical phenomena on their variations. Some correlation of variations of the mean latitude of Belgrade with the occurrence of earthquakes in the vicinity can be noticed as well as instabilities of the mean latitude of stations located near sea coasts. Some attempts at measurements of variations of the meridian component of the vertical and a discussion of spectral analysis of latitudes and of mean latitudes of considered stations are presented.
The Distribution of Molecular Clouds in Spiral Galaxies
Authors: Solomon P. M.
Published: June 2019

The use of millimeter wave CO emission as a tracer of molecular hydrogen in the Galaxy (Scoville and Solomon 1975) showed that most of the H2 unlike HI is concentrated in the inner part of the Galaxy in a “ring” between 4–8 kpc and in the inner 1 kpc. Subsequent surveys (Gordon and Burton 1976, Cohen and Thaddeus 1977, Solomon etal. 1979) confirmed this picture with more extensive data. The molecular interstellar medium was shown to be dominated by Giant Molecular Clouds with individual masses between 105 and 3·106M⊙ (Solomon etal. 1979, Solomon and Sanders 1980). The GMC's confined to a layer with a half thickness of only 60 pc are an important component of the galactic disk, and the most massive objects in the galaxy. They affect the dynamics of the disk by contributing significantly to the surface density and through their individual gravitational interactions with stars.
The CO Rotation Curve of the Milky Way : Accuracy and Implications
Authors: Blitz Leo
Published: June 2019

The CO rotation curve exhibits an increase in circular velocity beyond R = 12 kpc (Blitz, Fich, and Stark 1980) which may be as much as 50 km s−1 at R = 18 kpc. Recently, Blitz and Fich (1983) have examined the uncertainties in the rotation curve at large R and have concluded that : 1) Of all the uncertainties, small changes in Ro and θo have the most serious effect on the rise at large R. However, unless ωo < 20 km s−1 kpc−1, a value smaller than that accepted by all observers, the rotation curve rises beyond R = 12 kpc. 2) Systematic errors in stellar distances and non-circular motions might have an effect on the magnitude of the rise. Both effects are thought to be small, but probably work to make the rotation curve even steeper. 3) The global value of the Oort A constant is < 12.5 km s−1 kpc−1, and the local value of 15 km s−1 kpc−1 is most likely due to a local velocity perturbation.
Molecular Clouds in Spiral Galaxies
Authors: Young Judith S.
Published: June 2019

A large observational program investigating the 2.6 mm CO line in spiral galaxies is being conducted by myself and Nick Scoville using the 14 m telescope of the Five College Radio Astronomy Observatory (HPBW = 50″). Thus far we have observed 46 galaxies of types Sa, Sb, Sc and Irr, detected 31, and mapped 16. Our major findings are:

(1)

In several late type spiral galaxies (IC 342, NGC 6946 and M51) the radial distribution of molecular gas out to 10 kpc follows the exponential blue luminosity profile of the disk within each galaxy (Young and Scoville 1982a, Scoville and Young 1983).

(2)

From a comparison of the CO and B luminosities of the central 5 kpc in a sample of Sc galaxies, we find that the blue luminosity is proportional to the first power of the CO content (Young and Scoville 1982b). We interpret this to mean that the star formation rate per H2in Sc galaxies (indicated by the B luminosity) is constant.

(3)

No molecular rings like the one in the Milky Way at radii 4 to 8 kpc were seen in the Sc galaxies.

(4)

We have found molecular rings in two Sb galaxies, NGC 7331 and NGC 2841, with peaks at radii of 4–5 kpc (Young and Scoville 1982c). The central holes in the CO distributions are possibly related to the presence of large nuclear bulges in these galaxies.
Do Spiral Galaxies have a Variable Disk Thickness?
Authors: Rohlfs Kristen
Published: June 2019

Estimating the forces in the z-direction that affect the disks of spiral galaxies in reasonable galactic mass models we find (Rohlfs and Kreitschmann 1981) that all external forces are small compared to the self-gravity of the disk so that Spitzer's (1942) self-consistent sheet model should give a good description for the z-distribution of the disk where it is well visible. But then the three parameters describing this shape are connected by the formula
Global Instabilities of a Galaxy Model
Authors: Haass Jon
Published: June 2019

A simple two-component fluid model of a galaxy is analyzed numerically. For this equilibrium configuration a large number of unstable spiral modes is found. It is of particular interest that some of these modes are well described by the asymptotic theory developed for tightly wound trailing spirals, while others are best understood in terms of the swing formalism which includes both leading and trailing waves.
On the Evolution of Perturbed Gas Disks
Authors: S⊘rensen S⊘ren-Aksel
Published: June 2019

Numerical experiments have shown that axisymmetric shearing gas disks will develop a spiral pattern when a non axi-symmetric contribution is introduced. This mechanism initially seems to be a prime candidate as the source of galactic spiral arms. The experiments have, however, failed to explain the formation of more than the most open systems and the smooth transition in the morphological sequence does not indicate any change in the physical mechanism between Sa and Sc types.
The Ballistic Particle Model
Authors: Bash Frank N.
Published: June 2019

Bash and Peters (1976) suggested that giant molecular clouds (GMC's) can be viewed as ballistic particles launched from the two-armed spiral-shock (TASS) wave with orbits influenced only by the overall galactic gravitational potential perturbed by the spiral gravitational potential in the arms. For GMC's in the Milky Way, the model predicts that the radial velocity observed from the Sun increases with age (time since launch). We showed that the terminal velocity of CO observed from l ≃ 30° to l ≃ 60° can be understood if all GMC's are born in the spiral pattern given by Yuan (1969) and live 30 × 106 yrs. Older GMC's were predicted to have radial velocities which exceed observed terminal velocities.
Possible Evidence for Lin's Three-Wave Interaction Mechanism at Corotation in the Galaxy NGC 1566
Authors: Comte G.
Published: June 2019

In a previous paper, (Comte and Duquennoy, 1982), we have reported observations of the distribution and kinematics of the ionized hydrogen in the large southern spiral NGC 1566 (SAB(r?s)bc I). We found evidence for a severe warping of the galactic disk, and discussed the spiral distribution of 477 detected HII regions. The observed spiral structure, deduced from the positions of the regions deprojected in a (ln r, θ) diagram, shows a four-armed design (Fig. 1):
Onset of Stochasticity in Barred Spirals
Authors: Teuben P. J. , Sanders R. H.
Published: June 2019

Stellar orbits in the plane of a strong bar potential demonstrate the breakdown of the second integral of motion well inside corotation (Sanders(1980) and more recently Contopoulos (1982), Athanassoula et. al. (1983), Sanders and Teuben (1982)).
The Barred Galaxy NGC 7741
Authors: Duval M. F.
Published: June 2019

The type of this galaxy (SB(s)cd) is intermediate between symmetrical early type galaxies and asymmetric late-type barred spirals. Three different components are clearly seen: a bar (B), a central disk (c) and an extended disk (d).
Models of Ellipticals and Bulges
Authors: Binney James
Published: June 2019

During the last seven years we have become much more aware of the importance of velocity anisotropy in spheroidal components. There were never any sound arguments for assuming that the velocity ellipsoids in spheroidal components would be spherical, but the mathematical convenience of this assumption is such that velocity anisotropy was either absent from or unimportant in the models that seemed so promising at the last Besancon meeting in 1974. With the advent of accurate velocity information from absorption-line studies of early-type systems, it became apparent that the real world is a good deal more complex than it might have been, and the theoretical situation is now less satisfactory than it seemed in 1974. All I can do here is to report on our somewhat painful efforts to pick ourselves up from the floor to which the observers knocked us in 1975–7.
X-ray Spectra of Young Supernova Remnants
Authors: Holt S. S.
Published: June 2019

The early identification of the strong X-ray source in Taurus with the Crab nebula (Bowyer et al. 1964) was the first milestone in the association of X-ray emission with supernova remnants. Unfortunately, it proved to be “red herring” which clouded the interpretation of X-ray emission from supernova remnants for a decade. Because the Crab was one of the brightest X-ray sources in the sky at a few keV, the interrogation energy of the early surveys, and because it was the first (and for several years the only) X-ray source conclusively identified, the potential association of a supernova origin with the large body of unidentified X-ray sources was not an unreasonable hypothesis.
The Evolution of Young Supernova Remnants
Authors: Fabian A. C. , Brinkmann W. , Stewart G. C.
Published: June 2019

Einstein X-ray observations of the young supernova remnants Cassiopeia A (Murray et al. 1980) and Tycho (Seward, Gorenstein and Tucker 1982) indicate that the swept-up mass does not much exceed that of the observed ejecta. The initial density distribution of the ejecta and surrounding material is then important in determining the X-ray structure and evolution. Some aspects of this behaviour have been dealt with in previous numerical (e.g. Gull 1973; Itoh 1977; Jones, Smith and Straka 1981) and analytical (e.g. Chevalier 1982a,b) studies. We present here results obtained from numerical models covering a wider range of initial conditions. In particular, we consider the effect of a constant stellar wind from the progenitor star on the expansion of the remnant. We have previously suggested that variable mass loss from SN1006 may explain its warm filled interior (Fabian, Stewart and Brinkmann 1982).
A Dynamical Study of the Young Oxygen-Rich Supernova Remnant in the Small Magellanic Cloud
Authors: Tuohy Ian R. , Dopita Michael A.
Published: June 2019

We present a velocity map of the young oxygen-rich supernova remnant (1E0102.2–7219) in the Small Magellanic Cloud, obtained with the Anglo-Australian Telescope. The velocity structure is complex, and implies a high degree of asymmetry during the Type II supernova explosion. Our data can be modelled geometrically in terms of a severely distorted ring of oxygen-rich ejecta. This result, together with the evidence for expanding rings in similar remnants, suggests non-spherical ejection to be an intrinsic characteristic of Type II supernovae. We have also obtained two-dimensional spectroscopy of the diffuse halo of emission which partially surrounds 1E0102.2–7219. The halo exhibits the high excitation line of HeII λ4686, and is either a fossil HII region created by a UV flash accompanying the supernova, or alternately, is being excited by intense UV radiation from the remnant itself. It is the first clear association of a high excitation region with a supernova remnant.
High Resolution X-ray Spectra of Supernova Remnants
Authors: Canizares C. R. , Winkler P. F. , Markert T. H. , Berg C.
Published: June 2019

We review results obtained with the Focal Plane Crystal Spectrometer (FPCS) on the Einstein Observatory. Clear evidence is found for departures from ionization equilibrium in the interior of Puppis A. This comes from the observed weakness of the forbidden lines relative to the resonance lines for the He - like triplets of O VII and Ne IX. However, it is shown that this departure from equilibrium does not alter our conclusion, based on previous FPCS results, that O and Ne are overabundant relative to Fe. The spectrum of N132D shows strong O VIII emission and very weak Fe emission, suggesting an even greater O/Fe abundance enhancement than in Puppis A. In the Cygnus Loop, the O to Ne abundance ratio is approximately solar; we have no information about Fe. The O VII triplet shows clear evidence for departures from ionization equilibrium in the Cygnus Loop. The spectrum of Tycho's SNR contains lines from ionization stages of Fe XVII through Fe XXIII and XXIV, indicating that a wide range of ionization conditions are present. Cas A and Kepler's SNR show relatively less emission from the higher ionization stages. For Tycho, we measured the strength of the strong Si XIII lines, and we find that a many-fold overabundance of Si relative to Fe is required regardless of the equilibrium state of the emitting plasma (confirming the Solid State Spectrometer results). On a separate topic, the completed analysis of X-ray Doppler shifts in Cas A suggests that the emitting material is concentrated in a ring that is inclined to the line of sight and is expanding at ~5000 km s−1.
Non-Equilibrium Modelling of the Structure and Spectra of Shock Waves
Authors: Dopita Michael A. , Binette Luc
Published: June 2019

Our understanding of the structure of radiative shocks of modest (vs ≲ 200 km s−1) velocity has improved greatly since the pioneering work of Cox (1972). This advance has been accomplished primarily by a more complete development of the physics of the shock front, its ionisation precursor and of the cool recombination zone. (Dopita 1976, 1977; Raymond 1979; Shull and McKee 1979; Shull, Seab and McKee, this conference; D'Odorico and Dopita, this conference). However, all models used for spectrum synthesis have so far involved one dimensional steadyflow hydrodynamics and most have covered only a very limited range in parameter space. This has meant that whilst they can be used to estimate shock velocities and metallicities of the (assumed) fully radiative shocks found in nearby SNRs, they are of limited applicability in more exotic types of objects.
New High Resolution Radio Observations of 3C10, 3C58 and Part of the Cygnus Loop
Authors: Green D. A. , Gull S. F.
Published: June 2019

We present new high resolution observations of 3C10 (Tycho's SN) and 3C58, made at 2.7 GHz with the Cambridge 5 km telescope. These observations have a resolution of ∼ 4 arcsec, considerably better than previous observations, giving a detailed view of the radio morphology of these two remnants. These maps have also been processed by the Maximum Entropy Method (MEM).
Large Scale Features of the Hot Component of the Interstellar Medium
Authors: Garmire Gordon P.
Published: June 2019

The interstellar medium contains identifiable hot plasma clouds occupying up to about 35% of the volume of the local galactic disc. The temperature of these clouds is not uniform but ranges from 105 up to 4 × 106°K. Besides the high temperature which places the emission spectrum in the soft x-ray band, the implied pressure of the hot plasma compared to the cooler gas reveals the importance of this component in determining the motions and evolution of the cooler gas in the disc, as well as providing a source of hot gas which may extend above the galactic disc to form a corona. The following report presents data from the A-2 soft x-ray experiment on the HEAO–1 spacecraft concerning the large scale features of this gas. These features will be interpreted in terms of the late phases of supernovae expansion, multiple supernovae and the possible creation of a hot halo surrounding the region of the galactic nucleus.
Possible Contributions of Supernova Remnants to the Soft X-ray Diffuse Background (0.1 - 1 keV)
Authors: Sanders W. T. , Burrows D. N. , McCammon D. , Kraushaar W. L.
Published: June 2019

Almost all of the B band (0.10–0.19 keV) and C band (0.15–0.28 keV) X-rays probably originate in a hot region surrounding the Sun, which Cox and Anderson have modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5–1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra-galactic power law flux and any large-scale-height stellar (or galactic halo) emission.
Are Filaments Cylindrical or Sheet-Like?
Authors: Smith M. D. , Dickel J. R.
Published: June 2019

Rapid cooling and collapse in a thermally unstable medium can lead to filamentary structures that are comparable to those observed in old supernova remnants. Here, simple formulae are derived for the shape of a filament forming in this manner. The cross-sectional shape of a filament will flatten and the ratio of major to minor axes (aspect ratio) increases in proportion to the density as it becomes sheet-like. Thus the aspect ratio of observed filaments is expected to be of the same order as the temperature change during the collapse, T1/T0. In very old remnants the filaments may appear to be tubes or sheets depending on perspective with aspect ratios less than 10. This model predicts a correlation between optical morphology and the temperature of the shock-heated gas. For T1 between 105K and 106K, the thin sheet that forms is likely to split up through asymmetric warping disturbances, leading to several parallel striations, consistent with observations in the Cygnus Loop. Above 106K, the instability may cause the sheet to degenerate before it has cooled to 104K. Hence, an absence of well-defined filaments is expected near X-ray emitting regions.
Strong Waves from Pulsars and Morphologies in SNRs
Authors: Benford Gregory , Ferrari Attilio , Massaglia Silvano
Published: June 2019

Canonical models for pulsars predict the emission of low–frequency waves of large amplitudes, produced by the rotation of a neutron star possessing a strong surface magnetic field. Pacini (1968) proposed this as the basic drain which yields to the pulsar slowing–down rate. The main relevance of the large amplitude wave (LAW) is the energetic link it provides between the pulsar and the surrounding medium. This role has been differently emphasized (Rees and Gunn, 1974; Ferrari, 1974), referring to absorption effects by relativistic particle acceleration and thermal heating, either close to the pulsar magnetosphere or in the nebula. It has been analyzed in the special case of the Crab Nebula, where observations are especially rich (Rees, 1971). As the Crab Nebula displays a cavity around the pulsar of dimension ∼1017cm, the function of the wave in sweeping dense gas away from the circumpulsar region is widely accepted. Absorption probably occurs at the inner edges of the nebula; i.e., where the wave pressure and the nebular pressure come into balance. Ferrari (1974) interpreted the wisps of the Crab Nebula as the region where plasma absorption occurs, damping the large amplitude wave and driving “parametric” plasma turbulence, thus trasferring energy to optical radiation powering the nebula. The mechanism has been extended to interpret the specific features of the “wisps” emission (Benford et al., 1978). Possibly the wave fills the nebula completely, permeating the space outside filaments with electromagnetic energy, continuously accelerating electrons for the extended radio and optical emission (Rees, 1971).
The X-ray Properties of Supernova Remnants in the Large Magellanic Cloud
Authors: Long Knox S.
Published: June 2019

There are at least 25 supernova remnants (SNR) in the Large Magellanic Cloud (LMC) with X-ray luminosities exceeding 2 × 1035 erg s−1. As many as 25 other SNR may be contained in the X-ray survey conducted with the Einstein Observatory of the LMC. The X-ray spectra of the 6 SNR observed with the Solid State Spectrometer (SSS) resemble their galactic counterparts; two SNR, N157B and 0540–69.3, may emit X-rays primarily by synchrotron radiation. The density of the medium in which SNR are expanding inferred from the X-ray data appears to decrease with SNR diameter; the density of the ISM inferred from the Balmer lines of 4 new SNR in the LMC is much lower than that inferred from X-ray observations. The apparent thermal energy content of LMC SNR evolves with diameter, peaking at ∼5 × 1050 ergs. The ratio of the densities of the X-ray and [SII] emitting plasmas is consistent with their being in pressure equilibrium. The SN rate in the LMC is ∼1 per 100–200 years. This is the number of SN expected from other considerations. The number diameter relation of LMC SNR is consistent with free expansion. The X-ray data are difficult to understand in terms of traditional Sedov models on SNR evolution; probably ejecta and multiphase ISM are required to explain the X-ray properties of LMC SNR.
The Quasar Redshift Limit
Authors: Osmer Patrick S.
Published: June 2019

The concept of a redshift limit for quasars was first mentioned a decade ago by Schmidt (1970, 1972) and Sandage (1972) who independently realized that faint, high redshift quasars were not being found in the numbers expected from the redshift and magnitude distribution of bright quasars. Subsequently the limit moved out in redshift to z ∼ 3.5 from z ∼ 2.5 after the discovery of OQ172 (z = 3.53, Wampler et al. 1973) and numerous other quasars with z > 3. It should be said at the outset that the limit concept is in need of definition. While it would be most interesting if an absolute limit existed, i.e., no quasars beyond a certain redshift, in reality the limit value is more likely to be the redshift at which the quasar space density turns down significantly.
Quasar Galaxies: Two-Dimensional Image Deconvolutions
Authors: Wehinger P. A. , Wyckoff S. , Gehren T. , Spinrad H.
Published: June 2019

Studies of quasar images which have adequate spatial resolution and reach sufficiently faint surface brightness levels indicate that virtually all low redshift (z ≲ 0.6) quasars are surrounded by faint nebulosities extending ∼ 3–20 arcsec from the quasar nucleus (at 26 R mag arcsec−2) (Wyckoff et al. 1980, 1981, Hutchings et al. 1981, Wehinger et al. 1983). Furthermore, the average integrated absolute magnitude and average metric diameter of the quasar nebulosities (quasar nucleus removed) are roughly those expected for galaxies at the corresponding (cosmological) quasar distances. Moreover, statistical support for the cosmological interpretation of the redshifts as well as the galaxy interpretation of the fuzz was found in correlations between the angular isophotal diameters of the quasar nebulosities and the redshifts, and between the integrated apparent magnitudes and the angular isophotal diameters (Wyckoff et al. 1981). Spectroscopic observations of quasar fuzz now convincingly support the galaxy interpretation for the quasar nebulosities (Boroson and Oke 1982, Oke et al. 1983).
The Evolution of the Radio Galaxy Population as Determined from Deep Radio-Optical Surveys
Authors: van der Laan Harry , Katgert Peter , Windhorst Rogier , Oort Marc
Published: June 2019

A first step in the study of the evolution of the radio galaxy population is the determination of the radio luminosity function (RLF), i.e. ρ(log P, z), which results from (and must finally be interpreted in terms of) ‘light curves’ of individual objects (i.e. P(t)) and the ‘birth rate’ function ṅ (log P, t).
A 6-CM Deep Sky Survey
Authors: Fomalont E. B. , Kellermann K. I. , Wall J. V.
Published: June 2019

In order to extend radio source counts to lower flux density, we have used the VLA to survey a small region of sky at 4.885 GHz (6 cm) to a limiting flux density of 50 μJy. Details of this deep survey are given in the paper by Kellermann et al. (these proceedings). In addition, we have observed 10 other nearby fields to a limiting flux density of 350 μJy in order to provide better statistics on sources of intermediate flux density.
On Population III Star Formation
Authors: Kashlinsky A. , Rees M. J.
Published: June 2019

If primordial fluctuations were isothermal their amplitude at recombination would be non-linear on scales Mo ≃ 106÷9 M⊙. Since the Jeans mass after recombination is MJo ≃ 8 × 105 Ω−1/2 M⊙ the clouds of mass Mo would be able to form the first generation of compact objects, the so-called Population III. These clouds would acquire angular momentum via tidal interactions with their neighbours. The importance of rotation can be conveniently characterised by the spin parameter λ = Vrotation/Vfree-fall and tidal interactions lead to a spin λo = 0.07 ± 0.03. As the cloud collapses λ increases as r−1/2. Any fragment forming in a rotating cloud would have the same spin λ as the whole cloud. It could therefore collapse only by ≃ λo2 in radius before centrifugal forces intervened, thus leaving a large geometrical cross-section for coalescence to be important. At radii r ≲ λo8/5 (Mo/MJo)2/15 ro the coalescence time is shorter than the free-fall time and no fragmentation is possible below this radius. In the primordial clouds two major factors prevent fragmentation at larger radii. First, the background radiation is still ‘hot’ and the trapping of it would prevent fragmentation until the whole cloud has collapsed to a radius 10−2 x−2/3 ro. Here x = 10−2(M/107 M⊙)1/3 is the ionization fraction given by the balance between gravitational contraction and recombination cooling. Furthermore, any small density fluctuation would lead to fragmentation only after the paternal cloud had collapsed by a factor (δ/5)2/3 in radius. For these reasons fragmentation is unlikely until centrifugal forces halt the collapse and a disk forms. The disk will be initially at T ≃ 104K but after a small fraction of H2 forms it will cool to T3 ≃ T/103K ≃ 1 and the final fragments mass could be as low as ≃ 0.2(λo/0.07)4 T32(MJo/Mo)1/3 M⊙.
Comments and Summary on the Cosmic Background Radiation
Authors: Smoot George F.
Published: June 2019

This session on the cosmic background radiation is remarkable for the quality of the interesting new results presented and the controversy over substantive issues. This paper reviews the status of measurements of the spectrum and anisotropy of the cosmic background and summarizes what is known of the properties of the cosmic background radiation: its spectrum, anisotropy, polarization, and statistics.
Morphology of the Local Supercluster
Authors: Tully R. Brent
Published: June 2019

The intent of this brief note is to summarize some of the fundamental properties of the region, rich in galaxies, in which we live. A more complete account can be found in The Astrophysical Journal, 257, p. 389, 1982.
Neutrino Mass and Galaxy Formation
Authors: Szalay Alexander S. , Bond J. Richard
Published: June 2019

The adiabatic theory of galaxy formation in neutrino-dominated universes is reviewed. Collisionless damping leads to a density fluctuation spectrum with a cutoff, the nonlinear evolution of which naturally results in the formation of pancakes, strings and voids.
Multimass Models for Clusters of Galaxies
Authors: Mazure A. , des Forêts G. , Gerbal D. , Mathez G. , Salvador-Solé E.
Published: June 2019

It is now a widely spread opinion that a ratio of 10:1 between dark and luminous matter exists. Supported by the existence of flat rotation curves at large radii for spirals, this fact reinforces cosmological scenarios with, for instance, massive neutrinos. This content of dark matter is often estimated from the dynamical analysis of clusters of galaxies based essentially on the application of the Virial theorem or the monomassive Emden sphere or deduced from numerical simulations. However, a careful examination shows crucial failures in such approaches1, at least the lack of a mass spectrum and/or of a dynamically influent Intra Cluster Medium. This has been included in simple models1 together with other realistic features such as temperature gradient, isovelocity and/or isothermicity of the gravitational plasma. Our aim is thus to account simultaneously for all the available data concerning both galaxies and ICM; namely, the Nonisothermal Multimass Models1 allow us to fit jointly the numerical density profiles of galaxies, the luminosity function, the velocity dispersion profiles versus magnitude or radius, the luminosity segregation2, the X-ray temperature, luminosity and surface brightness profiles.
X-Ray Observations of Active Galactic Nuclei
Authors: Urry C. Megan , Mushotzky Richard F. , Tennant Allyn F. , Boldt Elihu A. , Holt Stephen S.
Published: June 2019

HEAO 1 A2 and Einstein SSS spectral observations of Seyfert galaxies and BL Lac objects suggest that in both cases, the X-ray emission is due to relativistic particles. The five BL Lac objects have very soft spectra and at higher energies (above 10 keV) may have hard tails. Combining our X-ray data with radio, infrared, optical, and ultraviolet observations, we can fit the BL Lac spectra with the familiar synchrotron self-Compton model if we allow for relativistic beaming (Urry and Mushotzky 1982, Urry et al. 1982). We show that Doppler beaming of an underlying (Seyfert-like) source population flattens the observed luminosity function, and we emphasize that the relative numbers of BL Lacs and quasars in given spectral intervals are strong functions of selection effects, the degree of Doppler beaming, and the form of the intrinsic luminosity function.
QSO Absorption Lines
Authors: Peterson Bruce A.
Published: June 2019

The evidence for the evolution of the intergalactic clouds that produce the Lyman-alpha absorption lines in the spectra of QSOs is reviewed. The recent detection of OVI in clouds that produce both Lyman-alpha and Lyman-beta absorption lines is discussed. The identification of molecular hydrogen in the spectrum of 1442+101 (OQ172) is not confirmed by high resolution spectra.
Absorption-Line Spectroscopy of Close Pairs of QSOs
Authors: Shaver P. A. , Robertson J. G.
Published: June 2019

Close pairs of QSOs (separations ≲ 1–5 arcmin) provide a powerful approach to the study of narrow absorption lines in QSO spectra. By looking for absorption in the spectrum of the higher-redshift QSO at the redshift of the other (“associated absorption”), or absorption in both spectra at the same redshift (“common absorption”), one may address several issues: the cosmological nature of QSO redshifts, the origin of the narrow absorption lines of high redshift and excitation (intrinsic or intervening), the clustering of absorbing systems (with each other, and with QSOs), the sizes of the absorbing regions (for metal absorption lines and for Lyα lines; absorption cross-sections of individual galaxies and of clusters of galaxies), and the presence and nature of gaseous halos around QSOs.
SIT-VIDICON Surface Photometry of Globular Clusters in the Magellanic Clouds
Authors: Geyer Edward H. , Hänel Andreas
Published: June 2019

The globular clusters in the Large Magellanic Cloud offer an unique possibility for the study of their spatial structures. Their ages show a very wide range from 6·107 to >5·109 years which is unknown for their galactic counterparts. The latter ones are all very old and therefore dynamically relaxed systems, whereas the young globular clusters of the Magellanic Clouds (age <108 years) have still preserved the dynamical state with which they were formed (Geyer et al. 1979). Furthermore, these young globulars show in their Hertzsprung-Russell diagram morphology the massive and luminous stars still on the main sequence with only a few evolved red supergiants. As in general the luminosity of the individual stars depends on their evolutionary state, the total mass to total luminosity ratio of a stellar cluster represents also its evolutionary state.
Disentangling Individual Star and Cluster Contributions in IUE Spectra of Magellanic Cloud Globular Clusters
Authors: Cacciari Carla
Published: June 2019

The globular clusters NGC 1786 in LMC and NGC 121 and 330 in SMC have been observed in UV with IUE, both in the long and short wavelength range, in the low dispersion mode. The spectra show stellar component(s) superimposed on the cluster contributions.
Global Evolutionary Effects in the Magellanic Clouds
Authors: Lequeux James
Published: June 2019

Following Larson and Tinsley the integrated colours of the MCs from the UV to the red can be used to obtain the ratio of the present rate of star formation to the total amount of stars formed. Other tracers of recent star formation (number of bright stars, of supernova remnants, Hα emission, etc…) will be used to determine the present rate of star formation and to obtain some information on the initial mass function. The recent (t < a few 107 years) history of star formation in the MCs will then be discussed. Finally, it is found that the ratio present rate/total amount of stars ever formed is of the order of 0.1 Gyr−1 for both Clouds, implying a rather uniform average rate of star formation if the Cloud ages are the order of 1010 years. The results will be confronted with the metallicity-age relation and the age distribution of stars and clusters.
Field Studies, Luminosity Functions, and Star Formation History in the Magellanic Clouds
Authors: Stryker L. L.
Published: June 2019

One of the most fundamental questions we might ask about galaxies is, Do all galaxies have the same age? A less general question, and one which we can surely succeed in answering is, Are the Magellanic Clouds (MCs) the same age as the Galaxy? We must also make clear what is meant by the same age if, in fact, star forming activities in these systems have proceeded along different timescales. The age of a system can be masked if the strongest star-forming epoch was not coincident with the initial epoch. Deep colour-magnitude diagrams (CMDs) and luminosity functions (LFs) have had to wait until the advent of large southern telescopes, sensitive emulsions and detectors, and accurate methods of measuring crowded images.
Detection and Photometry of Red Giants in the Magellanic Clouds
Authors: Aaronson Marc
Published: June 2019

This review will focus on photometric observations of evolved stars in the Magellanic Clouds. Emphasis is placed on red and near-infrared measurements, as these allow reasonable estimates to be made of bolometric magnitude and temperature for reliable placement in the physical HR diagram. The review is divided into three parts: field stars, cluster stars, and red variables; a summary of the surveys for objects in each of these areas is also given. Particular attention is drawn to the intermediate-age stellar population, as this component appears to be the primary tracer of the star formation rate and chemical enrichment history of the Clouds.
Spectral Types, Color Indices, and Abundances for Cepheids in the Magellanic Clouds and the Galaxy
Authors: Laney C. D. , McNamara D.H.
Published: June 2019

Accurate MK temperature and luminosity classes have been obtained for 58 Cepheids in the Galaxy and in the Magellanic Clouds from 121 spectrograms. Classification criteria for the spectral region 3700X–6000X in the spectra of F-K supergiants are described. The spectra of galactic and LMC Cepheids are found to be similar, and Cepheids in both systems appear to obey the same relation between (B-V)o and spectral type. The low E(B-V) values of Parsons (1970) and certain other recent authors are confirmed. The spectra of SMC Cepheids show slightly weaker metal lines relative to galactic Cepheid spectra, and SMC Cepheids average about 1.3 subclasses earlier in spectral type than LMC and galactic Cepheids at the same value of (B-V)o. Reddenings for both Clouds are found to be less than 0.05. Among supergiants (Mv = −4 to −8), stars of the same spectral type have the same (B-V)o regardless of luminosity class. Spectral types at minimum light are found to be later than those reported by Feast (1974) when luminosity effects are allowed for. Spectroscopic surface gravities near minimum light appear to be lower than those near maximum and slightly fainter Mv values are found at each luminosity class than those usually cited. SMC Cepheids appear to have lower surface gravities than LMC Cepheids at the same absolute magnitude, as one would expect from the lower metal abundances.
Period Changes in Magellanic Cloud Cepheids
Authors: Deasy H. , Wayman P. A.
Published: June 2019

It has been found possible to obtain information on period change in data on 115 cepheid variable stars in the Magellanic Clouds (84 LMC cepheids and 31 SMC cepheids). Harvard Observatory data of the period 1910 to 1950 (collated by Payne-Gaposchkin and Gaposchkin) are combined with Dunsink Observatory observations carried out by C.J. Butler in 1966/67 and with South African Astronomical Observatory observations covering the years 1975–1977 by Martin, Thomas, Carter and Davies to derive mean periods for the intervals between the various data sets. Using these new periods in conjunction with the very accurate Harvard periods, seperate estimates of the time averaged fractional change of period per day, d/dt (ln P), with corresponding estimated errors, could be evaluated for two epochs, one around 1950 and the other around 1971. It was found that 70 stars give rates of change of period that are not significantly different from zero, that 20 stars have two values of rate of change of period that are in agreement at the two epochs (indicative of secular period change), while 22 stars give two disparate values of rate of change of period (indicative of irregular period changes).
On the Nature of R 136, the Central Object of 30 Dor. A Comparison by the Galactic Cluster NGC 3603
Authors: Rosa Michael , Melnick Jorge , Grosbol Preben
Published: June 2019

The massive H II region NGC 3603 is the closest galactic counterpart to the giant LMC nebula 30 Dor. Walborn (1973) first compared the ionizing OB/WR clusters of the two H II regions and suggested that R 136, the unresolved luminous WR + 0 type central object of 30 Dor, might be a multiple system like the core region of NGC 3603. Suggestions that the dominant component of R 136, i.e. R 136A, might be either a single or a very few supermassive and superluminous stars (Schmidt-Kaler and Feitzinger 1982, Savage et al. 1983) have recently been disputed by Moffat and Seggewiss (1983) and Melnick (1983), who have presented spectroscopic and photometric evidence to support the hypothesis of an unresolved cluster of stars. We have extended Walborn's original comparison of the apparent morphology of the two clusters by digital treatment of the images to simulate how the galactic cluster would look like if it were located in the LMC
The Magellanic Cloud Supernova Remnants
Authors: Dopita Michael A.
Published: June 2019

It was some twenty years ago, at the previous IAU symposium devoted to the Magellanic Clouds, that Mathewson and Healey (1964) announced the discovery of the first supernova remnant (SNR) in the LMC. The method used was to identify a non-thermal radio source with a filamentary optical emission object and this confirmed N49 in the catalogue of Henize (1956) as an SNR and suggested N63 and N132 D as likely candidates.
Age Determination of HII Regions of the LMC and SMC
Authors: Copetti M. V. , Dottori H. A. , Bica E. L. , Pastoriza M. G.
Published: June 2019

HII region models were constructed which take into account: ) A burst for the formation of the ionizing association; ) Different Salpeter's initial mass function () and upper stellar mass limit Models of stellar evolution with and without mass loss (Maeder, 1980, Hellings et al. 1981).
CO in the Large Magellanic Cloud
Authors: Cohen R. , Montani J. , Rubio M.
Published: June 2019

In our galaxy molecular clouds account for about half the total interstellar gas and are probably the sites of all star formation. The high gas content and widespread star formation in the Large Magellanic Cloud would therefore suggest a high molecular content. Very little however is actually known about molecules in the LMC. The most extensive previous survey (see Israel in this volume) found CO in half of the 22 points observed but covered less than 10−4 of the LMC area.
Average Variations of Photospheric FeI and FeII Line Parameters as Function of the Magnetic Filling Factor
Authors: Brandt P.N. , Steinegger M.
Published: June 2019

A series of 17 Fourier transform spectra taken at the McMath telescope near disk center in regions of different magnetic field strengths were analyzed. Applying a multi-variate regression analysis magnetic filling factors 0 < α ≥ 0.11 were determined. With α increasing from 0 to 0.11, line bisectors averaged over groups of lines of similar depth are found to show a blue shift decreasing from 0.35 km s–1 to nearly 0.1 km s–1, when referred to the MgI line λ5172.7å. The bisectors of FeII lines exhibit smaller blue shifts than FeI lines. The increase of bisector red shift near the continuum with increasing α, found earlier by Brandt and Solanki (1987), was confirmed and is tentatively interpreted as a manifestation of downdrafts in the vicinity of flux tubes (Deinzer et al., 1984).

A significant increase of line width (typically between 3 and 8%, depending on line strength) and a decrease of line depth is found with increasing filling factor. For strong lines the equivalent width W shows no variation or a slight increase, while for the weaker lines a reduction of W between a few % and > 10% is found.
Properties of the Solar Granulation
Authors: Karpinsky V.N.
Published: June 2019

Until recently the theory of the photospheric structure has had a modest role. This situation has qualitatively changed with the appearance of the numerical simulations of Nordlund [1], Uus [2], Gadun [3], and others.
Properties of Photospheric Fluxtubes Derived from Magnetograph Observations
Authors: Lozitskij V.G. , Tsap T.T.
Published: June 2019

Data from magnetograph observations, obtained in six Fe I and Mg I lines with the Crimean magnetograph with a spatial resolution of 1 × 1 and 1 × 2 arcsec have been interpreted using the line-ratio method and a two-component model with spatially unresolved fluxtubes and a background field. Magnetograph data obtained by other authors have also been taken into account. The magnetic field strength, its variation with distance from the fluxtube axis, the characteristics of the spectral line profiles, as well as other properties of the fluxtubes have been determined.
Small Scale Magnetic Structures in Active Centers
Authors: Dollfus A.
Published: June 2019

Active sunspot group n° 4567 was observed with high angular magnification on Sept. 2, 1984, using the instrument FPSS at Meudon Observatory. Within the sunspots umbrae, the longitudinal magnetic field shows a collection of small elements down to the limit of resolution of around 600 km. Between the trailing and leading spots, there were very sharp gradients, both in magnetization (450 gauss over 1000 km) and in Doppler velocity (350 m s-1 over 1 000 km). The line defined by these gradients was the location of a flare. Evershed driving forces may be responsible for building up these gradients and flare.