bluuebunny/crossref_metadata_2025 huggingface dataset:
Where is the Equinox ?
Authors: Fricke W.
Published: July 2016

Within the work being carried out at Heidelberg on the establishment of the new fundamental reference coordinate system, the FK5, the determination of the location of celestial equator and the equinox form an important part. The plane of the celestial equator defined by the axis of rotation of the Earth and the plane of the ecliptic defined by the motion of the Earth about the Sun are both in motion due to various causes. The intersection of the equator and the ecliptic, the dynamical equinox, is therefore in motion. Great efforts have been made in the past to determine the location and motion of the dynamical equinox by means of observations of Sun, Moon and planets in such a manner that the dynamical equinox can serve as the origin of the right ascension system of a fundamental catalogue. The results have not been satisfactory, and we have some important evidence that the catalogue equinox of the FK4 is not identical with the “dynamical equinox”. Moreover, is has turned out that the difference α(DYN) - α(FK4) = E(T) depends on the epoch of observation T. Duncombe et al. (1974) have drawn attention to the possible confusion between the catalogue equinox and dynamical equinox; they mention the difference between two Earth longitude systems, one established by the SAO using star positions on the FK4 and the other one established by the JPL using planetary positions measured from the dynamical equinox. This is undoubtedly one legitimate explanation of the difference, even if other sources of errors may also have contributed.
An Improvement of the Orbital Elements of Hyperion
Authors: Hatanaka Yoshizumi
Published: July 2016

For the improvement of the orbital elements of Hyperion, a program of photographic observations of Saturnian satellites has been made since the opposition of 1966. In this paper are presented the reduction method and results derived from the observations during the oppositions of 1968 and 1977.
An ultraviolet view of stellar winds
Authors: Snow Theodore P.
Published: July 2016

Ultraviolet observations of mass-loss effects in O stars have, over the past decade, revealed a broad picture of a phenomenon whose extent was only partially evident from earlier ground-based observations. Ultraviolet resonance lines of a variety of ionization stages of several common elements provide a comprehensive probe of the low-density, extended winds. Three general types of information have been derived from ultraviolet spectroscopy of mass-loss profiles: (1) the nature of the stars which experience mass loss via radiatively-driven winds; (2) the physical conditions in the winds; and (3) variability in the outflow, which in turn may yield clues to the origins of the winds. Observations and results in each of these areas are reviewed, and some new results are included. A good correlation of mass loss rate and luminosity is indicated by the data, in agreement with theoretical predictions. Time variations in the P Cygni profiles may be quite common, with variability on times of hours or longer. Anticipated new observations, which should be possible with existing and planned instrumentation, are described.
Analysis of UV spectrophotometric observations for O-type stars.
Authors: Morossi Carlo , Stalio Roberto , Crivellari Lucio
Published: July 2016

The ESA “Ultraviolet Bright Star Spectrophotometric Catalogue” (Jamar et al. 1976) and the “Catalogue of 0.2 A Resolution Far-ultraviolet Stellar Spectra Measured with Copernicus” (Snow and Jenkins 1976) have been used to try to separate, by means of simple diagrams, O-type stars belonging to different luminosity classes and having different temperatures. The ESA catalogue gives absolute fluxes for 43 O-type stars, mostly reddened, with a spectral resolution of 35–40 A, depending on the channel, in the wavelength range 1350–2550 A. The Copernicus catalogue gives spectra between 1000 and 1450 A for 17 O-type stars, with low reddening, at 0.2 A resolution.
The effective temperatures of the O stars
Authors: Pottasch S. R. , Wesselius P. R. , van Duinen R. J.
Published: July 2016

Far ultraviolet photometric observations (in 5 bands between λ = 1550 Å and 3300 Å) are presented for ten O stars which are also the exciting stars of diffuse nebulae. Since the number of photons shortwards of the Lyman limit is known for these stars, sufficient information on the total flux is available to determine the effective temperature without making any assumptions concerning a model atmosphere. Conversely, the distribution of flux with wavelength can be used to determine the applicability of a given model. A detailed discussion of this is presented.

A comparison of these ‘normal’ O stars and stars with O type spectra which excite planetary nebulae is given. It is concluded that the atmospheres of these two types of O stars are very similar; probably they have the same effective gravity. Further, a discussion of the Zanstra He II temperature is presented.
Near infrared spectra of O stars and related objects
Authors: Vreux J.M. , Andrillat Y.
Published: July 2016

The λ 10124 He II line has been found to be a measurable emission in three stars. Our new data are compared to theoretical predictions. The λ 10830 He I line is observed in emission in 74% of the 05–08 supergiants but only seen in 29 % of the dwarfs, all of the latter exhibiting some “pecularities” i.e. classified as Oef, Oe, ON or On. An envelope with a sufficient amount of material seems to be a favorable condition to get the λ 10830 line in emission. However the mechanism leading to the observed emission is temperature dependent as well.
Infrared observations of HDE 226868/Cyg X-1 and HDE 245770/A0535+26
Authors: Persi P. , Toniolo M. Ferrari , Spada G.
Published: July 2016

We know from Copernicus ultraviolet observations that all O-type stars are losing mass by stellar wind. The ionized expanding circumstellar envelope formed by the stellar wind is emitting through free-free and bound-free radiation processes. This radiation is detectable at the infrared wavelengths where the stellar continuum is negligible. The measurement of the IR excess (defined as the difference between the total flux and the stellar continuum at a given wavelength) and the knowledge of the terminal velocity of the envelope, allow us to derive for OB stars the mass loss rate. From the analysis of our IR observations of two O stars, HDE 226868 and HDE 245770, identified as optical counterpart of X-ray sources, we give an estimate of their mass loss rate. The IR observations were carried out with the Jungfraujoch 76 cm telescope using a GE bolometer with a focal plane chopping system and with the Merate 132 cm telescope using an InSb detector.
Radio observations of stellar mass loss
Authors: Kwok Sun , Purton C. R.
Published: July 2016

A program to search for steady-state thermal emissions from stars has been in progress for several years in Canada (Purton 1976). In this program we have specifically excluded flaring objects (such as β Lyr or HR1099) where non-thermal emission is probably responsible. Out of the 30 or so detections, about 1/4 of them show a ~+1 spectral index, suggesting a 1/r2 density profile in the emitting region. This implies the existence of a non-static circumstellar envelope which is mostly likely the result of continuous mass outflow.
Radio emission from hot stars at two centimeters
Authors: Morton Donald C. , Wright Alan E.
Published: July 2016

Radio fluxes of 7.2 ± 1.1 and 69 ± 5 mJy at 14.7 GHz have been detected from the stars ζ Pup (O4If) and γ Vel (WC8+O9I) respectively with the 64-m telescope at Parkes, and upper limits have been determined for 9 more hot stars. The interpretation of these fluxes as free-free emission from a shell of ionized gas resulting from a stellar wind gives mass-loss rates = (6.5 ± 1.4) x 10−6 M⊙ yr−1 for ζ Pup and (3.9 ± 0.7) x 10−5 M⊙ yr−1 for γ Vel if H/He = 10 by number and the He is fully ionized. If the gas around γ Vel originates mainly from the WC8 star, the helium predominates and = (5.2 ± 0.9) x 10−5 or (17 ± 3) x 10−5 M⊙ yr−1 depending on whether the helium is doubly or singly ionized.
Radiatively-driven winds: Model improvements, ionization balance and the infrared spectrum
Authors: Castor John I.
Published: July 2016

Recent improvements to theoretical stellar wind models and the results of empirical modelling of the ionization balance and the infrared continuum are discussed. The model of a wind driven by radiation pressure in spectral lines is improved by accounting for overlap of the driving lines, dependence of ionization balance on density, and stellar rotation. These effects produce a softer velocity law than that given by Castor, Abbott and Klein (1975). The ionization balance in ζ Puppis is shown to agree with that estimated for an optically thick wind at a gas temperature of 60,000 K. The ionization model is not unique. The infrared continuum of ζ Pup measured by Barlow and Cohen is fitted to a cool model with a linear rise of velocity with radius; this fit is also not unique. It is concluded we should try to find a model that fits several kinds of evidence simultaneously.
The corona plus cool wind model for of stars and OB supergiants
Authors: Cassinelli Joseph P.
Published: July 2016

The anomalously strong OVI and NV lines in O stars and the CIV and Si IV lines in B supergiants may be due to Auger ionization by x-rays from a thin coronal zone at the base of their cool stellar winds. This paper summarizes the results of several studies to determine constraints on the size and temperature of coronal zones from calculations of the effects of coronae on continuum and line spectra. The model that has resulted can be tested by observations from HEAO-B of the predicted 2 kev emergent fluxes. The model explains very well the persistence of the OVI and NV in the ultraviolet spectra of supergiants to class B0.5 and B2 respectively, and it predicts that CIV should be observable in the ultraviolet spectra at and beyond B5I.
Wind models for ζ Orionis
Authors: Olson Gordon L.
Published: July 2016

Several models for the winds of O stars have been proposed to explain the unexpected presence of high ionization potential ions such as N+4 and O+5. Lamers and Snow (1978) proposed that the winds of stars showing N V and O VI lines have elevated temperatures near 4±2 × 105K while cooler stars with anomalous Si IV lines have Te ≈ 7±3 × 104K. Alternately, Cassinelli and Olson (1978, CO) and Olson (1978) have explained the presence of these ions by showing that a thin corona at the base of a cool wind (Te ≲ Teff) can produce these ions by the Auger photoionization process where a single x-ray photon causes the ejection of two electrons. A third possibility is that the winds are at only slightly elevated temperatures (40 000 to 60 000K) and photoionization in an optically thick wind produces the unexpected ions. The problem of determining the local radiation field in such a wind is discussed by Klein and Castor (1978). The purpose of the present analysis is to test the ability of these three wind models to fit the observations of ζ Orionis A 09.7 Ib.
The O-type spectroscopic binary system HD 149404
Authors: Massey Philip , Conti Peter S.
Published: July 2016

HD 149404 (HR 6164) was noted to have double lines by Conti, Leep and Lorre (1977). The spectrum has been previously classified as 09Ia, and shows strong Si IV λ4089, 4116 absorption, He I stronger than He II, N III λ4634, 41 weakly in emission, He II λ4686 “filled in,” and all the Balmer lines through H13 in absorption except Hα, which is strongly in emission.
Hydrogen deficiency and mass loss
Authors: Bidelman William P.
Published: July 2016

Some conclusions concerning the luminous hydrogen-deficient stars are presented, as is also a list of 45 such objects.
Evolution of a 30 M⊙ star with mass loss
Authors: Falk H. J. , Mitalas R.
Published: July 2016

Evolutionary tracks for a 30 M⊙ star with mass loss rates (0.0, 1.0, 2.5, 5.0, 10.0)x10−7 M⊙/yr have been calculated. The effect of the different rates on the main sequence lifetime and on the effective temperature of the core He burning is discussed.
HD 50896: an other WR binary star
Authors: Firmani C. , Koenigsberger G. , Bisiacchi G. F. , Ruíz E. , Solar A.
Published: July 2016

The current ideas concerning the evolution of close binary systems (van den Heuvel, 1976), accepting the hypothesis that the system is not disrupted by the first supernova (SN) explosion, predict that the Wolf-Rayet phase can occur twice. The first time the companion of the WR star is a normal OB star and the second time it is a collapsed object. In this context, the importance of searching for binary systems with collapsed companions among the “single” WR stars is evident. Due to its large distance from the galactic plane, z = 280 pc (Smith, 1968a), when compared with the average height (z = 60 pc, Cruz-González et al., 1974) of extreme Population I stars, HD 50896 was considered to be a likely candidate to this type of system.
The chemical nature and evolutionary status of the Wolf-Rayet stars
Authors: Willis A. J. , Wilson R.
Published: July 2016

Much interest has been shown in recent years concerning the possible link in stellar evolutionary terms between the O-type (particularly Of) and the WR stars, arising from both observational studies of O stars (Conti 1976, Bohannon and Conti 1977) and theoretical studies of the evolution of massive hot stars with high mass loss (Chiosi and Nasi 1974, de Loore et al. 1977, 1978). These investigations and ideas coincided with a renewed attack on the abundance problem in the WR stars based on the acquisition of new ultraviolet observations and the application of recently developed techniques for treating line transfer in rapidly expanding atmospheres (Willis and Wilson 1978a). The aim of this paper is to summarize some of the salient aspects of this latter reference and to examine the evolutionary status of the WR stars in the light of these new results.
Large-scale structure of spiral galaxies: problems old and new
Authors: Roberts Morton S.
Published: July 2016

Introductory remarks for IAU Symposium No. 84 are made. These include a brief history of previous symposia dealing with galactic structure, basic research problems in this area, and parallels regarding our galaxy which can be drawn from extragalactic research.
The galactic distribution of OH/IR stars
Authors: Baud B. , Habing H. J. , Oort J. H.
Published: July 2016

Through systematic surveys (Johansson et al., Caswell and Haynes, Bowers, Baud, Caswell et al.) some 200 OH masers have been detected that are presumably associated with long period variables of very late spectral type (>M5). Tentatively these stars will be called “OH/IR stars”. They are characterized by their strong emission in the 1612 MHz line which shows a double peak due to the expansion of the shell surrounding these stars. The velocity difference ΔV between the peaks is generally between 10 and 50 km s−1.
Radio observations of the galactic plane CH distribution
Authors: Johansson L.E.B. , Hjalmarson å. , Rydbeck O.E.H.
Published: July 2016

The CH distribution in the galactic plane has been determined through observations of the ground state main line transition 2π1/2, J=1/2, F=1-1 at 3335 MHz. The longitude ranges 10°≤ℓ≤60° and 60°<ℓ≤230 have been covered with the spacings 2°.5 and 5°, respectively. The derived radial distribution is similar to that of CO, although differencies may exist. From observations at ℓ=30° and 43°.26 the CH layer halfwidth is estimated to be 50 pc, in close agreement with that of CO. A CH displacement below the standard plane is observed in these directions.
HI in the galactic disk
Authors: Kerr F. J.
Published: July 2016

This review of 21-cm studies of the galactic disk will be rather short, because several aspects of such studies are being covered by other speakers. These include the galactic rotation curve, the warp, the outer limits of the hydrogen layer, high-velocity clouds, large supernova remnants and comparisons between observations and theory with respect to density waves.
Faint optical spiral tracers
Authors: Muzzio Juan C.
Published: July 2016

The use of modern photographic emulsions and techniques allows for the discovery of optical spiral tracers much fainter than was possible in the past. Our searches for such faint objects deal with the Puppis, Vela, Crux, Circinus, Norma and Ara regions of the Milky Way using Kodak plates (baked in dry nitrogen) obtained with the Curtis Schmidt-telescope at Cerro Tololo Inter-American Observatory. We have discovered OB stars as faint as 15 mag on IIIa-J plates obtained with the thin prism, and Hα emission-line objects (many of which are Be stars) as faint as 16 mag on 127-04 plates obtained with the 4° prism.
Lifetime of density waves and classification of spirals
Authors: Feitzinger J. V. , Schmidt-Kaler Th.
Published: July 2016

Checking the density-wave theory against observations of our own Galaxy has proven very difficult, as witnessed also at this Symposium. Less ambiguous results, however, are obtained for other galaxies. These results involve a) calculating convincing models for a sample of 25 fairly well observed spirals (Roberts et al. 1975) and b) locating the compression zones on the inner edges of the spiral arms.
Compression of interstellar clouds in spiral density-wave shocks
Authors: Woodward Paul R.
Published: July 2016

A mechanism of triggering star formation by galactic shocks is discussed.
The galactic distance scale
Authors: Graham J. A.
Published: July 2016

Recent work on the distance scale of the Galaxy has largely been in the direction of refining previously established methods. The RR Lyrae variable stars appear to be better distance indicators than was once thought and they have been used in determining Ro, the distance to the Galactic center. Ro is probably somewhat less than 10 kpc but greater than 7 kpc. Most methods point to a value near 8.5 kpc.
Quantitative classification of the galaxy from new data on the photometric properties of its spheroidal and disk components
Authors: de Vaucouleurs G.
Published: July 2016

After a brief review of previous attempts at identifying the morphological type of our Galaxy by optical or radio methods, a new approach from surface photometry is described. A two-component model consisting of an R1/4 spheroid and an exponential disk is fit to the local galactic disk brightness inferred from star counts and to new observations of the brightness distribution in the bulge along the galactic prime meridian. All parameters are in close quantitative agreement with corresponding quantities for Sbc II galaxies and confirm the AB(rs) morphology first proposed in 1963 (IAU Symposium No. 20). An average of NGC 1073, 4303, 5921 and 6744 described in 1969 (IAU Symposium No. 38) closely approximates the photometric properties of our Galaxy.
A theory of galactic evolution
Authors: Clube S. V. M.
Published: July 2016

…“there exist many galaxies where most of the light originates in an apparently flat rotating disk, and where the random stellar motions appear to be small compared to the systematic circular motion i.e. they are apparently “cold.” Our own Galaxy is such a system, and it does not seem to suffer any large scale, large amplitude, short-time-scale instability”… Ostriker and Peebles, Ap. J. 186, 467, 1973.
CO observations of spiral structure and the lifetime of giant molecular clouds
Authors: Scoville N. Z. , Solomon P. M. , Sanders D. B.
Published: July 2016

Observations of CO emission at ℓ=0 to 70°, |b| ≤ 1° are analyzed to give a map of the molecular cloud distribution in the galaxy as viewed from the galactic pole. From the fact that this distribution shows no obvious spiral pattern we conclude that the giant molecular clouds sampled in the CO line are situated in both arm and interarm regions and they must last more than 108 years. A similar age estimate is deduced from the large mass fraction of H2 in the interstellar medium in the interior of the galaxy. An implication of this longevity is that the great masses of these clouds may be accumulated through cloud-cloud collisions of originally smaller clouds.
The HI structure of the nuclear disk
Authors: Cohen R. J.
Published: July 2016

It is nearly twenty years since Rougoor & Oort (1960) reported the discovery of neutral hydrogen (HI) emission from the galactic nucleus, and I would like to summarize some of the progress that has been made since then in observing and interpreting this emission. One of the most surprising properties to be found is the tilt of the HI distribution relative to the galactic equator. This was noted originally by Kerr (1967), and recent measurements indicate that the tilt is present from within 200 pc of the centre out to a distance of some 2 kpc. (Cohen & Davies 1976, 1978). Because of the tilted distribution the properties of the nuclear emission cannot always be deduced from observations at zero galactic latitude. For example, Rougoor & Oort (1960) deduced a sharp cut-off in the negative-velocity “nuclear disk” emission at ℓ ≃ −4°, from their measurements near zero latitude, whereas the more extensive observations by Kerr (1967) show that the cut-off is only an apparent effect. In reality the emission continues to more negative longitudes, but at higher galactic latitude because of the tilt.
HII regions and star formation in the galactic center
Authors: Mezger P. G. , Pauls T.
Published: July 2016

The centimeter wavelength continuum radiation seen toward the Galactic center (Figure 1) is a mixture of thermal (free-free) and nonthermal (synchrotron) radiation which originates in the nucleus and along the line-of-sight. In this review we discuss only the thermal emission (also see Mezger 1974 and Oort 1977). High-frequency radio continuum and recombination line observations show that the thermal radiation comes from extend, low-density (ELD) HII, and a number of giant “radio HII regions” (see Mezger 1978 for definitions). The approximate half-power contour of the ELD HII (labelled EI in Fig. 1), probably represents a superposition of evolved and expanded HII regions. Thermal radiation outside EI comes predominantly from along the line-of-sight (see Pauls and Mezger 1975).
A study of the galactic centre region using Mira variables
Authors: Feast M. W.
Published: July 2016

Mira variables are attractive for galactic centre studies because (1) they are numerous there; (2) they have high luminosities (MK ∼ −7.5) in the infrared where they can be seen through heavy absorption; (3) good radial velocities can be obtained from emission lines even for very faint objects; (4) at least in the solar neighbourhood and in globular clusters the period seems a good indicator of age and/or chemical composition.
The basic state of the velocity field in the gas close to the galactic centre
Authors: Rohlfs K. , Schmidt-Kaler Th.
Published: July 2016

To explain the features in the range 340° ≤ 1 ≤ 22° which show expansion velocities, elliptical stream-lines have been proposed that happen to expose expansion components towards the sun. Three general observations, however, make this interpretation doubtful:
Is there a massive black hole at the galactic center?
Authors: Ozernoy L. M.
Published: July 2016

During the past 10 years an hypothesis about the presence of a massive black hole at the center of our Galaxy (Lynden-Bell, 1969) has been an object of many exciting speculations. This hypothesis is based, firstly, on attempts to explain the nature of the “point radio source” at the galactic center (as well as a presumed much more powerful activity of the galactic nucleus in the remote past), and, secondly, on the opinion that the conditions in the course of dynamical evolution of galactic nuclei are favorable for the formation of massive black holes. However, both these approaches did not succeed in predicting with any confidence the black hole mass at the center of the Galaxy. The estimates available are based on indirect arguments and range from 107-1011 M⊙ (Novikov and Thorne, 1973) to 104 M⊙ (Shklovskii, 1976). A recent dynamical approach using NeII infrared observations of the galactic center (Wollman et al., 1977) has indicated that the black hole mass does not exceed 5×106 M⊙ (Oort, 1977), although this value may well be due to a very dense star cluster whose brightest members only are seen in the infrared.
The galactic nucleus compared to those of other galaxies
Authors: Weedman Daniel W.
Published: July 2016

Observations at various wavelengths are considered for extragalactic nuclei and are compared to how our galaxy would appear at comparable distances. The starlight from our nucleus is similar to that from the spirals in the Virgo Cluster. Our nucleus would show no sign of activity to a distant observer, neither unusual color, nor emission lines, nor excess infrared radiation. For example, the luminosity in Hβ emission is about 1038 ergs s−1, which is 100 times fainter than that in the faintest Seyfert galaxy or emission line galaxy. It is also emphasized that there is no evidence from X-ray data for a massive, condensed object in the Galactic nucleus.
HI and continuum structure of external galaxies compared to the situation in the galaxy
Authors: Rots Arnold H.
Published: July 2016

Continuum observations of NGC 6946 strongly suggest the presence of an exponential non-thermal disk component. When applied to galactic 408 MHz observations, the scale length is found to be between 5 and 6 kpc. Continuing the parallel with NGC 6946, a total luminosity of 2 × 1010L⊙is derived. Observations of the edge-on galaxies NGC 891 and 4631 show the existence of flattened halos with a steep spectrum around these galaxies. This is consistent with the constraints that are known for the galactic radio halo. On the basis of the radial distribution of HI in the Galaxy and in M81 three regimes can be defined: a central one which is hyperdeficient in hydrogen; a middle one which is deficient in HI, but not necessarily in total hydrogen; and an outer one which is neither deficient in HI, nor in H. Density wave theory, combined with gas flow dynamics appear a powerful tool in interpreting the kinematical data. No rotation curve is yet known to become Keplerian in the outer parts. Many external galaxies are warped, like our own; one of them, NGC 5907, does not have a visible companion.
Radial distributions of some constituents in M31, the galaxy and M33
Authors: Berkhuijsen Elly M.
Published: July 2016

The Figure shows the distributions perpendicular to the planes of the galaxies of: (a) the surface density of HI, σHI(R), (b) the surface density of HII regions, σHII(R), and (c) the radio brightness temperature, σTB(R). Details may be found in Berkhuijsen (A.A. 57, 9, 1977; Proc. IAU Symp. 77, 1978); here σHI(R) of the Galaxy was taken from Gordon and Burton (Ap. J. 208, 346, 1976) and σTB(R) of M31 has been revised. Distances to the centre are scaled with the Holmberg radius RH (21, 15 and 7.8 kpc for M31, Galaxy, M33).
Cosmic-ray evidence for a halo
Authors: Ginzburg V. L.
Published: July 2016

Cosmic rays were discovered in 1912, but it was only about forty years later that they were found to play an important role in astronomy. Firstly, cosmic rays (including the electron component) are an important source of astronomical information, namely the cosmic synchrotron radiation. Secondly, cosmic rays are essential as energetic and dynamical factors in the galaxy and also as a source of heating and transformation of the interstellar gas composition. Suffice it to remember, for example, that near the solar system the cosmic ray energy density is about the same as the thermal energy of the interstellar gas, and the cosmic ray pressure is likewise about the same as the interstellar gas pressure. Thus, there is every reason to believe that galaxies do not consist of stars and gas only, but of cosmic rays as well.
Observational description of the warp in our galaxy
Authors: Henderson A. P.
Published: July 2016

In 1975 F. J. Kerr and P. F. Bowers of the University of Maryland made a full coverage survey of the neutral hydrogen in the southern hemisphere between ±10° latitude from 240° to 350° in longitude. This survey taken with the CSIRO 18 meter telescope is still in the reduction stage but when completed it will provide an ideal complement to the full ±10° coverage of the northern sky by H. Weaver and D. R. W. Williams (1973). The possibility of a unified analysis of the outer region of the Galaxy has inspired this present study. The plan here is to use the ±10° Weaver-Williams survey in the region 10° < ℓ < 130°; the ±30° extension to this survey (H. Weaver and D. R. W. Williams, 1974) in the region 115° < ℓ < 245° and finally the Kerr-Bowers survey, 240° < ℓ < 350°. Since the latter survey is incompletely reduced at this time we have only used profiles at 5° intervals in longitude and thereby have produced a preliminary determination of the plane in the southern hemisphere. The northern hemisphere determination is complete.
The persistence of warps
Authors: Tubbs Allan D. , Sanders Robert H.
Published: July 2016

Hunter and Toomre (1969) have demonstrated that a simple warp of a stellar disk will damp out within one or two galactic rotation periods due to rapid differential recession of stellar orbits. If, however, the galactic gravitational field is more nearly spherically symmetric, the rate of differential recession is decreased and the warp may persist for a longer time. We therefore propose that the observed gaseous warps exist in regions outside of the massive stellar disk; that is, in regions where the gravitational field is essentially spherically symmetric. A necessary condition of this hypothesis is that long-lived warps are present only in a low mass, low random velocity component of the galaxy – presumably the gas.
Theoretical considerations of the warp and thickening
Authors: Saar E.
Published: July 2016

As a theoretical subject, the study of the bending of the gaseous planes of galaxies has not been extremely popular. It seems that this is due to an excellent and thorough paper on the subject, published by Hunter and Toomre in 1969. At that time there existed three (or four) rival theoretical mechanisms:

(1)

vertical oscillations of the galactic disk, considered first by Lynden-Bell (1965);

(2)

asymmetrical pressure on the disk due to intergalactic wind (Kahn and Woltjer 1959);

(3)

tidal influence of the Magellanic Clouds, from

(a)

the case of Stationary Clouds, and

(b)

the case of Clouds orbiting around the Galaxy (Elwert and Hablick 1965, Avner and King 1967).
The anticenter high-velocity-cloud streams as a galactic phenomenon
Authors: Moore R. L. , Burton W. B.
Published: July 2016

The galactic anticenter region contains several streams of high-velocity clouds of HI. The principal stream is associated with a localized HI feature at forbidden negative velocities near ℓ, b = 197°, 2° (Weaver 1970, 1974). Here we show that the forbidden-velocity feature, in addition to being the culmination of three streams of high-velocity clouds, is correlated with a disturbance in the permitted-velocity gas. Evidence suggests that this disturbance is located within the Galaxy, implying by association that the anticenter high-velocity clouds and the culmination feature are at distances interior to the Galaxy.
Intergalactic HI and tidal debris within groups of galaxies
Authors: Haynes M. P.
Published: July 2016

A population of isolated intergalactic HI clouds has yet to be recognized in the intergalactic medium. On-going high sensitivity studies of loose groups of galaxies, however, show that tidal debris in the form of HI streams is commonly found in such aggregates.
Vibrations of Non-Uniform Spherical Systems
Authors: Severne G. , Kuszell A.
Published: July 2016

Dispersion relations have been obtained and analyzed for a non-uniform, non-rotating spherical gravitational system. A restriction to short wavelengths makes it possible to consider a linearized form of the collisionless Boltzmann equation, differing from that for homogeneous systems by the appearance of a term expressing the effect of the mean self-gravitational field upon the motion. The mean field affects the radially directed wave perturbations, with a breaking of symmetry.

Inwardly and outwardly directed modes have quite different propagation characteristics, inward modes being preferentially propagated. Locally, the stability of the system is enhanced due to the effect of the mean field.
Tidal Effects on Spherical Stellar Systems
Authors: Keenan D. W. , Innanen K. A.
Published: July 2016

Many self-gravitating stellar systems are satellites of larger galaxies and must therefore be subjected to the tidal field of the parent system. Examples are the globular clusters and dwarf elliptical galaxies, which are satellites of our Galaxy. Most previous studies of tidal effects have been highly simplified, e.g. clusters in circular planar galactic orbits (Bok, 1934), or have assumed that the tidal field acts to limit the size of a star cluster without any effects on its internal structure or stability (Spitzer and Shapiro, 1972; Spitzer and Thuan, 1972).
Binary Evolution in Stellar Systems
Authors: Miller R. H.
Published: July 2016

Aarseth has shown by means of n-body calculations that, in star systems with a range of particle masses, the most massive stars quickly form a binary which soon takes up a large fraction of the total binding energy of the cluster. Similar effects appear in other kinds of physical systems as well; mesic atoms behave in much the same way. The phase volumes of two otherwise equivalent stellar systems, each dominated by a tightly bound binary, favor exchange to incorporate the more massive star in the binary by a factor equal to the cube of the ratio of masses.
Formation of Double Galaxies by Tidal Capture
Authors: Alladin S. M. , Potdar A. , Sastry K. S.
Published: July 2016

The conditions under which double galaxies may be formed by tidal capture are considered. Estimates for the increase in the internal energy of colliding galaxies due to tidal effects are used to determine the magnitudes Vcap and Vdis of the maximum relative velocities at infinite separation required for tidal capture and tidal disruption respectively. A double galaxy will be formed by tidal capture without tidal disruption of a component if Vcap > Vi and Vcap > Vdis where Vi is the initial relative speed of the two galaxies at infinite separation. If the two galaxies are of the same dimension, formation of double galaxies by tidal capture is possible in a close collision either if the two galaxies do not differ much in mass and density distribution or if the more massive galaxy is less centrally concentrated than the other. If we assume, as statistics suggest, that the mass of a galaxy is proportional to the square of its radius, it follows that the probability of the formation of double galaxies by tidal capture increases with the increase in mass of the galaxies and tidal disruption does not occur in a single collision for any distance of closest approach of the two galaxies.
Ellipsoidal Stellar Systems
Authors: Hunter C.
Published: July 2016

This paper gives a unified account of exact solutions for ellipsoids of uniform density. An approximate solution for a slightly spheroidal system of non-uniform density is given in the final section.
A Method for Solving Poisson's Equation for Systems with Axial Symmetry
Authors: Van Albada T. S.
Published: July 2016

In computer experiments on the dynamics of stellar systems special methods are often required for the computation of the forces to keep the problem manageable. For collisionless systems a method based on solving Poisson's equation with Fourier-series expansions has been used with success (Miller et al., 1970; Hohl, 1973). The systems in these studies consist of a large number of particles moving on a rectangular grid.
Is There a Third Integral of Motion?
Authors: Pişmiş P.
Published: July 2016

It is argued that in a galaxy like ours a third integral of motion, a third independent argument in the distribution function, should exist if the potential function has to satisfy a third condition imposed on it, namely symmetry with respect to a plane. Orbit computations of single stars in a symmetric potential of the kind (Martinet and Hayli, 1971) indicate that a third integral seems to exist for Population I stars while it ceases to exist for Population II objects. This situation is explained by the author as follows. We state that a third integral should exist for all populations alike if the Boltzmann equation is interpreted within the statistical context for which it is valid. When applied to a complex system like the galaxy the third integral of the Boltzmann equation, which holds for an elementary volume in phase space, will also hold for a single particle if the latter is representative of the behavior of the element of volume as in Population I (coherent motion) whereas it will not necessarily hold for a single star of Population II; in the latter population the elementary volume, containing the same number of stars, does not represent the behavior of the element of volume during the motion of this in phase space.
The Collapse and Formation of Galaxies
Authors: Larson R. B.
Published: July 2016

The ultimate aim of studies of the dynamics of stellar systems is to gain an understanding of why they have the structures that are observed, how they might have formed, and how they might evolve with time. In the case of galaxies, unlike smaller astronomical systems such as stars and star clusters, the problem of understanding their present structure is inseparable from the problem of understanding their formation since, as has long been clear, the two-body relaxation time in galaxies is much longer than the age of the universe, so that properties such as the radial density distribution and the flattening of elliptical galaxies cannot have changed significantly since they were formed. Other features of galaxies, such as the presence of spiral patterns or nuclear activity, may be of a more transitory nature and not closely related to the formation process, but such phenomena probably involve mainly the gas component of galaxies and may be regarded as perturbations on the underlying stellar system, whose basic structure must still be understood in terms of the formation process.
Numerical Study of a Gravitating System of Colliding Particles; Formation and Dynamics of Discs
Authors: Brahic A.
Published: July 2016

The study of gravitating systems of colliding particles has many potential astrophysical applications, for instance the dynamics of Saturn's ring, the formation of the solar system, the flattening of protogalaxies and the evolution of galactic nuclei. We consider numerically a three-dimensional system of particles moving in the gravitational field of a central mass point and interacting through inelastic collisions. After a very fast flattening, the system forms a disc of finite thickness: this disc spreads slowly, and collisions still occur. A central condensation is formed and there is an outward flux of angular momentum. The energy which is continually lost in the inelastic collisions is obtained at the expense of the bodies which fall inwards.
Theoretical Limits on the Properties of Low-Velocity M-Dwarfs
Authors: Biermann P.
Published: July 2016

Using a version of the Toomre-criterion (Toomre, 1964) for a mixture of stellar populations, limits are derived for the kinematical properties of the newly discovered population of low-velocity M-dwarfs (Weistrop, 1972; Murray and Sanduleak, 1972); these stars are claimed to be a large mass-fraction (≳ 0.5) of all stars in the solar neighbourhood and to have only 10 km s−1 velocity dispersion. They could make up for the locally missing mass (Oort, 1965; Schmidt, 1974). It is found that a configuration of stellar populations with the M-dwarfs included (having such properties) is not stable in the sense of the Toomre-criterion. The limiting stability properties are given.
Dynamics of Early Type Galaxies
Authors: Bertola F. , Capaccioli M.
Published: July 2016

An attempt has been made to compute the angular momenta of the early type galaxies NGC 4697 and NGC 4762. Comparison with spiral galaxies indicates that there is a correlation between angular momentum per unit mass and morphological class.
Symmetric Ejection of Massive Objects from Galactic Nuclei
Authors: Valtonen M. J.
Published: July 2016

It is shown that massive objects can be ejected symmetrically in two opposite directions from the nucleus of a giant elliptical galaxy only under special initial conditions. A way of obtaining these conditions is outlined, and the resulting picture of evolution of galactic nuclei, including a quasar or a Seyfert galaxy phase, is shown to be compatible with observations.
Expériences numeriques sur l'éjection de masses depuis le centre d'un disque d'étoiles
Authors: Clairemidi S. , Hayli A.
Published: July 2016

Numerical experiments on simple or symmetric ejections of massive bodies from the nucleus of a disk of stars are presented. The ejected masses range from 0.04 to 0.1 of the total mass. Either spiral features or a barred structure appear but do not last for a long time. Material arms start leading and become trailing.
The Bologna Survey of Radio Sources at 408 MHz
Authors: Fanti Carla , Lari Carlo
Published: July 2016

The Bologna survey (Colla et al. 1970, 1972, 1973) does not represent a particularly new achievement since the first records refer to 1968. We will summarize here the main properties for a statistical use of the survey, the differential counts and the isotropy characteristic of this flux level, the latter being completely new.
The Molonglo Radio Source Surveys at 408 MHz
Authors: Mills B. Y.
Published: July 2016

One of the basic programs undertaken with the 1 mile Cross-type radio telescope at the Molonglo Radio Observatory has been a systematic survey of the sky south of +18° declination. Commencing in late 1967, the survey has been continuing at a low priority until it is now complete to a declination of −85°, except for some small areas affected by interference or instrumental problems which are being re-observed. A program of ‘deep surveys’ is also being undertaken; this involves multiple observations within narrow strips at selected declinations. The signal-to-noise ratio is some three to five times better than in normal surveying and the confusion limit is approached.
The Statistical Analysis of Anisotropies
Authors: Webster Adrian
Published: July 2016

One of the many uses to which a radio survey may be put is an analysis of the distribution of the radio sources on the celestial sphere to find out whether they are bunched into clusters or lie in preferred regions of space. There are many methods of testing for clustering in point processes and since they are not all equally good this contribution is presented as a brief guide to what seem to be the best of them. The radio sources certainly do not show very strong clustering and may well be entirely unclustered so if a statistical method is to be useful it must be both powerful and flexible. A statistic is powerful in this context if it can efficiently distinguish a weakly clustered distribution of sources from an unclustered one, and it is flexible if it can be applied in a way which avoids mistaking defects in the survey for true peculiarities in the distribution of sources.
Spectral Index Studies of Extragalactic Radio Sources
Authors: Katgert P. , Padrielli L. , Katgert J. K. , Willis A. G.
Published: July 2016

Spectral index distributions can be indicated conveniently by gSv1(αv1,v2), i.e. the distribution of the two-point spectral index between frequencies v1 and v2 for a sample of radio sources complete to flux density S at the selection frequency v1 (flux densities will be expressed in Jy and frequencies in GHz). Such a detailed specification is necessary because g(α) has been found to depend on all three parameters. The effect of varying v1 is well-known: the fraction of flat-spectrum sources increases with selection frequency. Variations of g(α) with S have also been found: both the fraction of flat-spectrum sources and the mean spectral index of the steep-spectrum sources depend on S, at least at high frequencies. The magnitude of this dependence on S as well as g(α) itself appear to depend on the choice of v2, or rather on the relation between v2 and v1. This complex behaviour of g(α) is not unexpected if one considers that the redshift and luminosity distributions of a source sample vary with selection frequency and flux density limit. Intrinsic or induced correlations between spectral index and redshift or luminosity, or different redshift distributions of flat-and steep-spectrum sources may cause variations of g(α) with v and S. An understanding of the behaviour of g(α) requires observations over large ranges of frequency and flux density. Even then, it will be difficult to interpret these data without information about the composition of the various samples, which can be obtained only through optical work. Here we describe recent spectral index information for weak sources selected at 1.4 GHz, as well as work on spectral index/optical identification correlations in 5 GHz samples.
The Angular Diameter-Redshift Relation for Scintillating Radio Sources
Authors: Hewish A. , Readhead A. C. S. , Duffett-Smith P. J.
Published: July 2016

Observational evidence on the angular diameter-redshift relation using radio sources has, until recently, been confined to studies of the overall angular size. In this paper a different approach is described in which the very compact hot spots in radio sources are used as standard measuring rods. Such hot spots appear to be especially suitable for cosmological studies for the following reasons.

(a)

Hot spots which contain one half or more of the total flux density are generally found only in the most powerful sources (P178 ≳ 1027 W Hz−1 sr−1).

(b)

Hot spots appear to show a smaller dispersion in physical size than the overall source dimensions.
QSO Identifications from a Molonglo Radio Survey
Authors: Hazard C.
Published: July 2016

For the past few years a co–operative programme involving astronomers at the Universities of Cambridge, Sydney and Groningen and Lick and Steward observatories has been in progress aimed in part at obtaining a complete sample of QSO's in a selected region down to given limits of optical and radio flux. The radio sample from the 408 MHz Mills Cross at Molonglo covers two declination strips each 2° wide and centred at declinations ∼11°N and ∼17°N respectively. Part of the survey has been published as the MC2 and MC3 catalogues (Sutton et al. 1974) covering the 11° strips in the R.A. interval 11h28m–01h23m and the 17° strip in the interval 13h30m–04h13m and this section is complete to a flux limit (S) of 0.45 Jy. The rest of the survey consists of an extension of the 11° strip around the rest of the sky and to a lower flux limit of about 0.15 Jy.
Physical Conditions in Radio Galaxies and Quasars
Authors: Osterbrock Donald E.
Published: July 2016

It is well known from the pioneering work of Baade and Minkowski that radio galaxies very often have strong emission lines in the spectra of their nuclei, indicating the presence of relatively large amounts of ionized gas. For instance, in the early survey of radio galaxies by Schmidt (1965), of the 35 galaxies observed, 32 had at least [0 II] λ3727 in their spectra and well over half had relatively strong [0 II] and other observable emission lines as well. In the recent review of optical identifications and spectroscopy of the revised 3C catalogue of radio sources by Smith et al. (1976), 137 radio galaxies are listed. Of these descriptive spectral information is given for 98, of which 49 show strong–emission line spectra, 19 intermediate–strength emission, 12 weak emission, and 18 a pure absorption–line spectrum without detectable emission lines. The fraction of objects with emission line–spectra is much higher than for normal galaxies. It is thus apparent that though the presence of emission lines is neither a necessary nor a sufficient condition that a galaxy be an observable radio source, nevertheless a large fraction of radio galaxies do contain ionized gas in their nuclei.