bluuebunny/crossref_metadata_2025 huggingface dataset:
Star Density Distribution in Young and Old Globular Clusters of the Large Magellanic Cloud
Authors: Geyer E. H. , Hopp U. , Kiehl M. , Witzigmann S.
Published: July 2016

The star density distribution in NGC 1818, 2004, 1806 and 1846, which are representative for the “blue” and “red” globular clusters of the LMC, have been determined from star counts on B- and V- ESO Schmidt telescope plates. These have limiting magnitudes of about 21, thus stars with absolute magnitudes of about Mv ~ +2 are reached. It was found that the two cluster types can be treated as “polytropic stargas spheres” according to the Schuster law with an index n ~ 2.75.
A Search for Main-Sequence Binaries in Globular Clusters
Authors: Liller Martha H.
Published: July 2016

It is becoming increasingly clear that no (or only one or two) binaries occur among the evolved stars in globular clusters. Therefore, if binaries exist at all in these systems, they must be found on or near the main sequence. I have chosen 6 clusters to search for faint eclipsing binaries by the following criteria:

(1)

the apparent visual distance modulus (Harris 1976) (m-M)V ≤ 14.5 mag;

(2)

the Peterson and King (1975) concentration class c ≤ 1.5, so that the search can be conducted near or at the cluster center where binaries would most likely be found; and

(3)

the galactic latitude is sufficiently large to avoid problems of extreme contamination by field stars.

The clusters thus chosen are NGC3201, 5139 (Omega Cen), 6121 (M4), 6218 (M12), 6254 (M10), and 6809 (M55). The plate material obtained on three nights with the 4-m telescope at CTIO in 1979, consists of seven to nine plates of each cluster on IIIa-F emulsion with an RG610 filter; the search is being conducted with a blink microscope.
Membership and Binarity of Red Giants in Open Clusters Determined by Photoelectric Radial Velocities
Authors: Mermilliod J.-C. , Mayor M.
Published: July 2016

An observing programme was started in the summer of 1977 to measure radial velocities of red giants in open clusters with the spectrovelocimeter “Coravel” (Baranne et al. 1979) attached to the 1 m telescope of the Geneva Observatory installed at the O.H.P. (France). 750 measurements for 160 stars in 30 open clusters north of −20°, with ages ranging from those of NGC 752 to Pleidades, have been obtained. The limiting magnitude is B = 12.5.
Dynamics and Evolution of Globular Clusters
Authors: Heggie Douglas C.
Published: July 2016

This paper reviews some recent theoretical results on the evolution of cores in globular clusters, including the effects of relaxation, binaries, and a central black hole.
The Main Sequence of the Very Old Globular Cluster NGC 6397
Authors: Alcaino Gonzalo , Liller William
Published: July 2016

We present photographic photometry for 1135 stars in the globular cluster NGC 6397, which, at a distance of 2.4 kpc, is most likely the second nearest globular to the Sun. The Racine wedge with the CTIO Yale 1 m telescope (Δm=3. 60 mag), the CTIO 4 m telescope (Δm=6. 83 mag) and the ESO 3.6 m telescope (Δm=3. 87 mag) was used to extend the photoelectric calibration from V≃16.1 to V≃20.7. The main sequence turnoff at V=16.7 and B-V=0.52 with respectively Mv =4.30 and (B-V)o =0.36 yields (m-M)v=12.40 and E(B-V)=0.16. Using the models of Iben and Rood (1970) and the isochrones of Demarque and McClure (1977), we deduce the cluster's age to be 17 × 109 years. This makes this object the oldest of the nine globular clusters with age determination and gives a lower limit to the age of the universe, rendering Ho ≤ 57 km sec−1 Mpc−1 if qo ≥ 0 is assumed. The large age spread of 6 billion years between NGC 6397 and 47 Tuc (the youngest counterpart with age data) indicates both that the protogalaxy underwent a slow collapse phase and that the abundances in globular clusters are lower for the oldest. The fact that the galactocentric distances for these clusters have the narrow range of 6 <R < 13 kpc makes it highly important to secure age data for extremely metal poor globulars far out in the halo.
Spectrum Scans of Globular Clusters in M87
Authors: Hanes David A. , Brodie Jean F.
Published: July 2016

Spectrum scans at 10 A resolution have been obtained for four likely clusters in the field of the giant elliptical galaxy NGC 4486 (M87), using the IPCS at the 4-metre Anglo-Australian Telescope. A wavelength range of 3500–7000 A was covered, with the objects having brightnesses from V=19.5 to V=19.8 mag. Preliminary analysis suggests that one of these objects is comparable to the metal-richest known Galactic globular clusters, while the other three seem to be even more metal-rich. Alternative explanations, such as gross differences in the stellar mix within the M87 clusters compared to those in our own Galaxy, may account for the observed spectroscopic differences; quantitative analysis is just beginning.
White Dwarf Candidates in the Globular Cluster NGC 6752
Authors: Richer Harvey B.
Published: July 2016

Recently (Richer 1978, hereafter Paper I), the results of a search for faint blue objects in and around the globular cluster NGC 6752 were reported. The aim of the program was to isolate a sample of white dwarf candidates in this cluster which could then be studied in further detail. The statistics of this survey are as follows: (1) 68 objects found with B ≤ 22.7 and (U-B) ≤ −0.4 within 20 arcmin of the cluster center; (2) of the 68, 36 also had a measurable V magnitude; (3) of these 36, only 11 lay in the area of the color-color diagram occupied by white dwarfs, while the remaining 25 were generally well above the black body line and are probably QSOs or peculiar blue stellar objects; (4) of these 11, 7 are within 14 arcmin of the cluster center and hence have a probability of greater than 50% of being cluster members (King et al. 1968); (5) CTIO 4-m SIT vidicon spectra were obtained of 5 of these 7 candidates, 4 of which appear to be white dwarfs and 1 of which is a QSO with Z = 2. Table 1 lists the derived properties of the 4 white dwarfs assuming that they belong to NGC 6752. The star names are from Paper 1.
Introductory Review
Authors: Hewish A.
Published: July 2016

In this review my aim is to mention very briefly the present state of knowledge over a wide area in order to provide some focus for the wealth of information that this symposium will bring forth. During 13 years a great deal has been discovered, but the jigsaw puzzle of the pulsar model is still in pieces. Some of these have intriguing shapes and seem to fit together, but they do not yet indicate what the picture will be.
Electric Field Near a Rotating Neutron Star
Authors: Tsygan A. I.
Published: July 2016

An electric field near a rotating magnetized conducting sphere is found in the cases when the sphere (a) rotates in vacuum and (b) is surrounded by a magnetosphere. The accretion of the interstellar neutral hydrogen onto the cold neutron star is discussed.
Evolution and Radiation in Pulsar Polar Cap Models
Authors: Ruderman M.
Published: July 2016

Positively charged particle emission from pulsar polar caps evolves through many stages as the cap temperature cools. In “infant” pulsars, stripped Fe ions interact with secondary e± from a 1012 V discharge maintained just above the cap to give coherent radio emission at very high frequencies in a very broad beam. In “adolescent” pulsars such as the Crab and Vela, lower energy Fe ions interact with streams of protons produced in the surface by photonuclear reactions to give lower frequency highly linearly polarized radiation. There is no cap e± discharge. In mature “adult” pulsars proton and/or Fe ion streams from discharge heated patches on the polar cap interact with a relativistic e± plasma to give coherent radio subpulse beams which can drift, have strong submillisecond modulations, and orthogonal polarization mode switching. Young pulsars, and some older ones, can support additional more energetic e± discharges on some open field lines in the outer magnetosphere. These all give strong double beams of GeV γ-rays and weaker γ-ray beams above ~ 1012 eV. With Crab pulsar parameters an e± plasma associated with such a discharge also can give optical and X-ray double beams. If illuminated by the normal pulsar beam (precursor) coherent inverse Compton scattering also contributes a double beam of harder radio frequencies.
Pulsar Radio Emission and Bunching Mechanisms
Authors: Asséo E. , Pellat R. , Sol H.
Published: July 2016

Galactic pulsars have been discovered by their radio emission. The emission has the common feature of being periodic, polarized, weakly frequency dependent (in the frequency range 100 MHz 10 GHz). Their energy is large for radio emission but still negligible as compared with the observed emission in the γ-ray range. They are also characterized by a very high temperature of brightness (1027–1031 Kelvin) which implies a coherent emission mechanism (this temperature is much larger than the possible particle energy). The only radiation mechanism which may produce such emission seems to be some kind of relativistic plasma instability. Unfortunately, available plasma models for pulsar magnetospheres are up to now too preliminary to make any definite statement. Nevertheless we will adopt the most popular scenario which relates the radio emission to the field aligned currents (relativistic electrons, positrons, ions) produced in the vicinity of the neutron star. These currents may result from a spark gap mechanism with pair creation (as proposed by Ruderman and Sutherland (1975) and others) or implied by the star's neutrality (as a return current system).
Some Characteristics of Pulsars with Long Pulse Nulling
Authors: Zhen-ru Wang , Yi Chu
Published: July 2016

The phenomenon of pulse nulling was first found by Backer (1970). The fraction of time, we denote it by n(%), for a pulsar in a null state was given by Ritchings (1976) for 32 pulsars. We have found that the average value of n(%) increases with the period of pulsars. It perhaps implies that the pulsars with pulse nulling could constitute a subtype of pulsars. In this paper, the pulsars with pulse nulling are regarded as a subtype to be investigated.
Optical Observations of Pulsars
Authors: Smith F. Graham
Published: July 2016

Optical identification of radio pulsars has only been achieved for the Crab and Vela Pulsars. The luminosity limits for others could be considerably improved: better astrometry and time-resolved photometry could reach mv = 27. The limits for pulsars with unknown periods, for example in extragalactic nebulae, are usually about mv = 20. The luminosity falls rapidly with increasing period: if it follows a power law the index is minus ten at least.

The optical spectrum of the Crab Pulsar falls toward the infra-red and is flat in the ultra-violet. No self-absorption effect is seen in the infra-red. New observations of the minimum intensity and of the polarisation show a highly linearly polarised component continuing through the whole pulse cycle.
Pulsar Magnetic Field: Spectral Formation in Her X-1
Authors: Ventura J.
Published: July 2016

The spectrum of Hercules X-1 reveals line features at 58 keV and probably at 110 keV, which have been interpreted as first and second cyclotron harmonics originating in the radiation from the hot polar cap region of a magnetic neutron star. The inferred magnetic field strength is ~ 5.3 × 1012 Gauss (Trümper et al. 1978). Other noteworthy spectral characteristics of this source are the very ‘flat’ intensity continuum in the frequency range 2 – 20 keV followed by a rather sharp spectral break near 25 keV and an intensity minimum near 40 keV. This spectrum is certainly not reminiscent of typical black-body emission. How can one understand these diverse characteristics?
Asymmetric Supernova Explosions: The Origin of Runaway Pulsars and Binary Pulsars
Authors: De Cuyper Jean-Pierre
Published: July 2016

It is known from observations that pulsars are high velocity objects. As a sizable fraction of these collapsars originates from low velocity single stars, they must have received a “kick” velocity at their birth. Which we assume to be due to the asymmetry of the SN-explosion and to be randomly orientated. Hanson (1979) estimated this asymmetric velocity in a statistical study to be about 102 km s−1. For SNe occurring in binaries the runaway velocities depend on the initial conditions. According to hydrodynamical calculations by Fryxell and Arnett (1979) the momentum imparted by the SN shell to the companion is some 80% of the momentum incident on the geometric cross-section of the star. This is due to mass stripping, which reduces the radius of stars with extended atmospheres, and to a smooth flow of the SN shell around the spherical companion and the nearly spherically symmetric ablation of some mixed stellar material. The mass loss of the companion is negligible.
Supernovae — Birthplace of Pulsars?
Authors: Chevalier Roger A.
Published: July 2016

Recent developments in the theory of the light from supernovae indicate that while Type II supernovae probably involve the explosion of a massive star with an extended envelope, Type I supernovae may involve the total thermonuclear disruption of a white dwarf. The energy release in a Type II supernova is presumably related to the contraction of the core to a neutron star and pulsar formation is likely. The hypothesis that Type II supernovae leave pulsars while Type I supernovae do not leave compact remnants is shown to be consistent with the available information on X-ray sources containing neutron stars, young supernova remnants, and the distribution of pulsars in the galaxy. Some pulsars are probably formed in the explosion of a massive star that has lost its envelope. These events may not be accompanied by a bright supernova display.
Pulsar Activity and Supernova Remnant Morphology
Authors: Radhakrishnan V. , Srinivasan G.
Published: July 2016

We use the recently introduced concept of a “window” of magnetic field strengths in which pulsars can be active to explain the variation in morphology of supernova remnants. Neutron stars created with field strengths of a value permitting pulsar activity result in particle production and Crab-like centrally concentrated remnants. Other field values lead to strong magnetic dipole radiation and consequent shell formation, e.g., Cas A.
4. Trigonometrical Parallaxes of LB 3303 and LB 3459
Authors: Churms J. , Thackeray A. D.
Published: July 2016

Radcliffe spectra of this star in 1961 confirmed Luyten's suspicion on the basis of colour and proper motion that this object is a bright white dwarf. The profile of Hγ was found to be closely similar to that of o2 Eri B. Hill and Hill have published photometry yielding V = 11.40. The only known white dwarfs brighter than this are Sirius B, o2 Eri B, Procyon B, Feige 34 and CD −38° 10980.
9. New Spectroscopic Results on Subluminous Stars, V
Authors: Greenstein J. L.
Published: July 2016

Determination of temperature and surface gravity by colors and hydrogen-line profiles have been carried out for hot halo stars. A narrow horizontal branch is found stretching to above 40000 K; the hot O subdwarfs show a nearly vertical sequence, dropping towards the hot white dwarfs.

Spectra for 285 white dwarf stars have been obtained, and the classification scheme is reviewed. Theoretical problems of these spectra remain, largely, unsolved.

The red subluminous stars found by Eggen were studied spectroscopically; among 68 stars only one new red degenerate star was found. The others are very metal-poor, high-velocity stars with large ultraviolet excess.
12. The Nuclei of Planetary Nebulae as Progenitors of White Dwarfs
Authors: O'Dell C. R.
Published: July 2016

Stellar evolution is characterized by fast and slow phases. Usually the periods of rapid change are difficult to follow observationally; but, this does not seem to be the case when passing through the planetary nebula stage. Because of their high intrinsic luminosities and easy identification, it is possible to identify and study these objects and their central stars rather completely. It is quite relevant to discuss these objects at a symposium on white dwarfs since the central stars may be in the immediate progenitor stage before white dwarfs. The actual picture of the evolution of the nuclei has changed rather little in the past few years and is the subject of an earlier review article (O'Dell, 1968) to which the reader is referred.
14. White Dwarf Atmospheres
Authors: Weidemann V.
Published: July 2016

We first consider the general information scheme for the interpretation of observational data (Figure 1). From the relations plotted it is evident that (in going from left to right) this scheme can only be solved if distances are known and if we are able to determine the atmospheric parameters: effective temperature, Teff, surface gravity, g, and chemical composition from observations of colors and spectra – which is the genuine task of the theory of stellar atmospheres.
20. Gravitational Sorting and Overstability in White Dwarfs
Authors: Baglin A.
Published: July 2016

Zones with μ gradient in stars have been discussed extensively in recent years in relation with the so-called ‘semi-convective zone’ which forms in massive stars when the convective core shrinks.
Revised Values (1941–1961) of the Coordinates of the Pole Referred to the CIO
Authors: Vicente Raimundo O. , Yumi Shigeru
Published: July 2016

Coordinates of the pole from the past ILS for the period 1900.0–1962.0 were reduced to the Conventional International Origin and published by us in 1969. Among them, data for 1941.0–1962.0 were revised owing to the revisions in their original values which were made and published recently by Nicolini and Cecchini.
Separating the Secular Motion of the Pole from Continental Drift Where and What to Observe?
Authors: Mueller Ivan I. , Schwarz C. R.
Published: July 2016

The paper estimates the expected rates of changes in the coordinates of various observatory networks (IPMS, BIH, VLBI, etc.) due to the secular motion of the pole and/or continental drift according to the Le Pichon Model. Based on these estimates, suggestions are made as to what to observe and over what time span to separate the effect of continental drift and secular polar motion.
Secular and Nonpolar Variation of Washington Latitude
Authors: Mccarthy Dennis D.
Published: July 2016

Observations of astronomical latitude made at Washington are analyzed for a secular trend. Comparison with the variation of latitude based on the path of the rotational pole of the International Polar Motion Service shows linear trends in good agreement. No evidence is found for a 24 yr libration of the pole. Systematic differences between observed and derived latitudes indicate that there are nonpolar variations in Washington latitude. Evidence is presented for the correlation of seismic activity with abrupt changes in the nonpolar variation, and the consequences of a changing geopotential surface are discussed with regard to observations of the rotational pole of the Earth.
Seasonal Effects Observed in Time Determinations at Santiago
Authors: Noël F.
Published: July 2016

A comparison of the Universal Time and local latitude deduced from the Astrolabe observations since 1966 to 1970, with respect to similar results obtained from BIH datas, show significative annual differences, specially in time, of a stable pattern. The consistence of the latitude differences (Astrolabe – BIH) and latitude group corrections, computed by the chain method, prove that these differences could be explained by the influence of a systematic error in the FK4 of Δδα type. On the other hand the inconsistence of the strong annual differences in time with the time group corrections, show that these differences can not be explained by catalogue systematic errors. The group corrections in time are compared with an investigation of the FK4 Δαα error based in the observations made with a transit instrument at Santiago.
Estimation of Random Changes in the Earth's Rotation
Authors: Tapley B. D. , Schutz B. E.
Published: July 2016

The usual procedures for estimating the motion of the Earth's pole use a least squares data reduction procedure to estimate the coefficients in a time series solution for the coordinates of the pole. Whether optical data or radar tracking data from near Earth satellites is used, the presence of random accelerations in the equations which describe the motion of the Earth's pole will lead to errors if the data is reduced in the classical least squares manner. This investigation presents a technique for estimating the polar motion in the presence of unmodeled accelerations. The unmodeled acceleration is represented by a first order stationary Gauss-Markoff process which can be separated into a timewise correlated component and a purely random component. Using this model, a sequential estimation procedure is developed for estimating the orientation of the pole, the components of Earth's angular velocity and the magnitude of the components of the unmodeled acceleration. The application of the method using both optical and radar tracking data from near Earth satellites is discussed.
Possible Changes in the Core-Mantle and Inner-Outer Core Boundaries
Authors: Jacobs J. A.
Published: July 2016

This paper investigates the possibility that the boundaries between the Earth's mantle and core and between the inner and outer core might show temporal changes. The evolution of the Earth's core is not discussed, but the question is raised as to whether these boundaries might not undergo small changes both in size and shape over comparatively short time intervals.
An Explanation of the Polar Motion by a Rigid Core-Mantle Model
Authors: Kubo Yoshio
Published: July 2016

The Earth with a rigid core and a rigid mantle is considered and a recovering force is assumed between the constituents.

The equations of motion in canonical form are derived in terms of the Andoyer's variables. Applying the perturbation theory, the phenomenon of the polar motion is investigated.

The polar motion obtained with this model is a circular motion of the rotational axis on the mantle's surface with its radius gradually changing.
Kimura's Z-Term and the Liquid Core Theory
Authors: Wako Yasujiro
Published: July 2016

Kimura (1902) pointed out that there might be an unknown cause other than polar motion which would produce an apparent latitude variation, and introduced the Z-term as, Δϕ = Xcos λ + + Ysin λ + Z.

The theoretical results by Jeffreys-Vicente (1957) and Molodensky (1961) have shown that the effect of a liquid core of the Earth may increase the coefficients of the semi-annual solar nutation term (2 ⊙) which is involved in the diurnal nutation (the so-called Oppolzer term) by 0″.02. It is reasonable to accept this correction which will appear in the Z-term with an argument of (2 ⊙ −α).

From comparison of the observed amplitudes and the phase angles of the annual Z-terms derived from the ILS data, it is concluded that the argument of the principal annual term in Z is (2 ⊙ −α) and not ⊙. The following results were obtained for the annual Z-term for 1955-1966 from the analysis of data by two independent methods (Wako, 1970): 0″.0137 sin (2 ⊙ −α + 2°.2), 0″.0203 sin (2 ⊙ −α + 4°.3).

Melchior (1970) proposed another effect of the Earth's liquid core for the annual nutation in obliquity, thus a term such as a sin (⊙ +α + A) would appear in the Z-term and it might cause a part of semi-annual Z-term. For the determination of these corrections, analysis of Kimura's Z-term is the most effective method.
Classification and Distribution of WR Stars and an Interpretation of the WN Sequence
Authors: Smith Lindsey F.
Published: July 2016

In the three years since the Boulder Wolf-Rayet Conference, a great deal of observational material has been collected and processed. That conference was, of course, the stimulus for a great deal of the work, since it made clear where some of the large gaps in our observational knowledge lay. As a result the greatest progress has been in directions which were previously underexplored, and some subjects which were actively pursued before the last conference have been left almost untouched since. Thus, much of what was said in 1968 need not be reviewed again; I can confine my attention to topics which have been significantly changed by new observations. The new observations comprise, in particular, the systematic observation of spectra of many stars at moderately high dispersion, observation of far ultraviolet spectra, and discovery of some WR stars in M33 - the first outside of our own Galaxy and the Magellanic Clouds.
Effective Temperatures of Wolf-Rayet Stars
Authors: Morton Donald C.
Published: July 2016

We have learned from Lindsey Smith's talk how useful it would be for our understanding of Wolf-Rayet stars to have reliable effective temperatures and bolometric corrections. The ring nebulae surrounding a few WN stars provide one method for estimating the stellar temperatures. I have assumed each nebula is a normal H ii region excited primarily by the Lyman continuum radiation of the central star. Then, if the nebula is optically thick shortward of 912 Å, each stellar photon with more energy than 13.6 eV is absorbed by the nebula and re-radiated in a predictable way as hydrogen lines and free-free radio emission. Consequently, nebular radio measures such as those recently obtained by Hugh Johnson (1971) provide a direct indication of the number of Lymancontinuum photons emitted by the central star. The exact equations have been described in the Astrophysical Journal (Morton, 1969; Morton, 1970).
Some Relations Between Wolf-Rayet and P Cygni-Type Stars
Authors: De Groot Mart
Published: July 2016

In taking up the subject of the relation between different types of early type stars one inevitably comes on ground set foot upon before by C. S. Beals. Already in 1940 he published an extensive paper entitled ‘On the Physical Characteristics of the Wolf-Rayet Stars and Their Relation to Other Objects of Early Type’ (Beals, 1940). The purpose of the present contribution is mainly to make the discussion more complete by including observations of later years.
Theory of Wolf-Rayet Spectra
Authors: Van Blerkom David
Published: July 2016

From the time of their discovery in 1867, Wolf-Rayet stars have been objects of great interest for theoretical astrophysicists. Their spectra, dominated by extremely wide emission lines, set them apart from the run-of-the-mill stars. Moreover, the classic assumptions that have enabled accurate model atmospheres to be constructed for hot main sequence stars: hydrostatic equilibrium, radiative equilibrium, local thermodynamic equilibrium, and negligible curvature effects, are probably all violated in Wolf-Rayet stars. As early as 1894, Scheiner proposed that
Photometric Investigation of IC 2944
Authors: Ardeberg A. , Maurice E. , Rickard J.
Published: July 2016

An investigation has been made of the central region of the cluster IC 2944. For about 70 stars UBV photometry has been made. For the brighter of those stars also Hβ has been measured. Slit spectra of intermediate dispersion (73 Å mm-1) have been made for the 40 brightest stars. Coudé spectra (12 Å mm-1) have been obtained for 8 stars. Fabry-Pérot measurements have been made in 5 points within the nebulosity. The number of blue stars is shown to be extremely high. Down to visual magnitude 11.5 the cluster seems to contain only O and B stars, the majority of spectral class earlier than B3. The Fabry-Pérot measurements give evidence of high internal gas motion. Evidently the gas is thin, visible only because of the great number of hot stars.

Details will be published elsewhere.
Early Results from the Michigan Southern-Hemisphere Spectral Survey
Authors: Bidelman W. P. , MacConnell D. J. , Frye R. L.
Published: July 2016

This paper discusses the present status of a preliminary inspection of the plates obtained in the Michigan objective-prism survey of the entire southern sky. A very large number of peculiar stars, and of normal supergiants as well, have been noted and lists of these are being prepared for publication.
Photometric Classification of Stars in the Vilnius Observatory
Authors: Straižys V.
Published: July 2016

The programs of three-dimensional classification of stars using eight-color intermediate band photometric system are described. They include (1) investigation of interstellar reddening and absorption in the direction of objects significant from point of view of stellar evolution, (2) investigation of spatial distribution of stars of different spectral classes, luminosities and chemical composition, (3) the detection of unique objects.
Photoelectric Measures of Hα, Hβ and Hγ in Early-Type Stars
Authors: Feinstein A.
Published: July 2016

The results of over 200 stars measured with interference filters in Hα, Hβ and Hγ are given here. 113 Be stars from the northern and southern hemispheres were included. The comparison of 60 of them, in common with the observations made by Mendoza about 15 years ago, shows that nearly half of them have differences larger than 0.m030 in Hβ (Crawford system). On the other hand the comparison with the observations made recently by Crawford indicate variations in a short time for some active Be stars.
Photometric Classification of Blue Horizontal-Branch Stars
Authors: Philip A. G. Davis
Published: July 2016

The Strömgren four-color system has been used to classify blue horizontal-branch stars in globular clusters and in the general field. A relation between δ log g (log gmain sequence–log gstar) and δc1 (c1observed–c1main sequence) has been determined which gives log g to within ±0.2 for stars with log g's between 4.4 and 2.0. Newell (1970) has determined a relation between (B–V)0 and θe. Thus the gravities and effective temperatures of blue horizontal-branch stars can be determined from photometric measures alone. Five globular clusters have been studied at the present time. The BHB stars in the globular cluster M3 and M13 have lower surface gravities than BHB stars in the other clusters studied. Iben and Rood (1970) have recently suggested that the BHB stars of M3 may have lost more mass than BHB stars in more metal poor clusters.
Hypercollapsed Nuclear Matter
Authors: Ne'eman Y.
Published: July 2016

We evoke the possible existence of hypercollapsed tightly bound nuclear isomers, due to the existence of an attractive ‘heart’ deep inside the repulsive core.
Matter in Superstrong Magnetic Fields
Authors: Ruderman M.
Published: July 2016

We consider the structure of atoms and atomic chains in the presence of ultra-strong magnetic fields as might be found in pulsars or neutron stars. Some consequences of these models for neutron star surfaces are mentioned.
Matter-Antimatter Separation and the Antimatter Problem in Cosmology
Authors: Omnès R.
Published: July 2016

I shall report on some work done in France in the last few years concerning the possible existence of antimatter in the Universe. It will be shown that, by taking due account of several physical effects which have been theoretically predicted, one can propose a coherent theory for the origin of matter and galaxies that appears to be quantitatively satisfactory. In this model there should exist as many antigalaxies as galaxies. During the course of this paper, I shall try to make it clear what the basic physical processes are and the present state of their investigation. This discussion will therefore be restricted to the two aforementioned problems, viz., the origin of matter and protogalaxies, leaving aside other astrophysical applications.
Quasar Counts and the Lagging Core Model (‘White Holes’)
Authors: Ne'eman Y.
Published: July 2016

The lagging core model for quasars (i.e., ‘white holes’) is shown to impose a negative exponential for the number of quasars at any given time as measured from the start of the cosmological expansion. Models in which quasars and other dense cores result from collapse yield a different behavior. A recent observational count appears to fit a negative exponential.
X-Radiation from Supernova Remnants
Authors: Pounds K. A.
Published: July 2016

Available X-ray observations of supernova remnants are reviewed. The number of SNR seen above 2 keV remains small after inclusion of the UHURU results and for only the Crab Nebula is the data adequate to clearly indicate the radiation mechanism. The increasing importance of low energy X-ray studies (below 1 keV) of older and relatively nearby remnants is noted. Brief discussion is given of the relation of the X-ray data to current ideas of the evolution of SNR.
Models for Compact Pulsing X-Ray Sources
Authors: Ostriker Jeremiah P. , Davidson Kris
Published: July 2016

Cen X-3 is probably a neutron star, releasing the infall energy of accreted matter. Sufficient material for accretion will be provided by a conventional stellar wind from its more massive companion star. That star is not likely to rotate synchronously; therefore a ‘Roche lobe’ analysis of the eclipses is not valid. A ‘tidal lobe’ analysis allows the neutron star to have a mass of the order of one solar mass. Overflow of the ‘Roche lobe’ is neither necessary as a source of mass nor probable in view of the observed stellar line widths of the two identified X-ray companions.

The mass flow onto the condensed star is very small in all cases. It is limited, for an object of m solar masses by the Eddington Limiting Luminosity to Ṁac < 10–7.4m(M⊙ yr−1), which limit applies even if the accreting object contacts or traverses its companion star.

The observed 4.84 s rotation period of the Cen X-3 neutron star is very simply explained as the critical value where a centrifugal barrier regulates the rate of infall to the surface. The X-ray spectrum is understood as blackbody radiation coming from a well-defined area near each magnetic pole of the neutron star.
The Properties of Extragalactic X-Ray Sources from Visible Light Observations
Authors: Sargent Wallace L. W.
Published: July 2016

We describe the optical properties of the radio galaxy NGC 5128, the Seyfert galaxy NGC 4151 and the QSO 3C 273 all of which appear to be point sources of X-rays. We emphasize how the X-ray observations, particularly the low energy absorption cutoff, may help us to understand the detailed structure and source of energy in these diverse objects.

The clusters of galaxies in Virgo, Perseus, Coma and Centaurus, all associated with extended X-ray sources are described. They have diverse shapes, central concentrations and galactic populations, but all contain a radio galaxy and, in several cases, a low frequency radio halo around it. It is concluded that the X-ray emission is likely to be non-thermal in origin.
Radio observations of interstellar molecules
Authors: Robinson B. J.
Published: July 2016

Investigations of the 18-cm lines of the16O1H radical are still in an exploratory phase. The detection of the strongest line of the18O1H radical has just been reported. Searches for the microwave lines of CH and SiH are in progress.

OH absorption has been observed for a few of the stronger radio sources, for a dozen galactic H 11 regions and for the source complex at the galactic centre. The ratio τOH/τHvaries by three orders of magnitude between these sources. In most cases the intensity ratios for the four OH lines are anomalous, which indicates that the populations of the energy levels are perturbed.

No thermal emission from OH has been found, even where τ ≈ 1. It thus becomes exceedingly difficult to estimate excitation temperatures and to derive surface densities.

Strong non-thermal emission is seen from about a third of the H 11 regions observed. The line profiles are composed of many narrow spikes, quite different for each of the four lines. The intensity ratios of the emission peaks are highly anomalous. The OH emission comes from exceedingly small areas (< 0·1 pc) on theedgeof the ionized regions, with brightness temperatures higher than 106°K.

It has been suggested that the populations are inverted. Maser amplification of the background continuum then occurs. Power gains of 104to 105are required. To produce such a gain in a very small region would require high OH densities and a considerable degree of population inversion.

In at least eight sources the emission is highly polarized. Complete circular polarization is common, and the sense varies rapidly between adjacent spikes in the profile. The observed polarization is incompatible with Zeeman multiplets.
Supernovae and interstellar gas dynamics
Authors: Kahn F. D. , Woltjer L.
Published: July 2016

The efficiency of the transfer of energy from supernovae into interstellar cloud motions is investigated. A lower limit of about 0·002 is obtained, but values near 0·01 are more likely. Taking all uncertainties in the theory and observations into account, the energy per supernova, in the form of relativistic particles or high-velocity matter, needed to maintain the random motions in the interstellar gas is estimated as 1051·4±1ergs.
Theories of spiral structure*
Authors: Prendergast K. H.
Published: July 2016

This will be rather an unusual introductory talk: I have no slides, almost no equations, and I will not be talking about my own work. I am supposed to speak about the theories of spiral structure, and I will have to begin by redoing some quite ancient considerations.

Obviously the first thing that has to be decided is: what is a spiral arm? I am not going to attempt to answer this, but I would like to point out that one can split opinions to a certain extent between those people who would like to think of spiral arms as largescale coherent structures, extending almost from the nucleus to the edge of the Galaxy, and those who would like to think of spiral structure as a combination of many detached features (Figure 1), where the structures that one can really follow do not extend over a considerable fraction of the radius of the Galaxy. For the most part I shall be speaking about people who attempt to explain something by the first picture.
On the development of non-circular motions in the Galaxy
Authors: Helfer H. L.
Published: July 2016

An approximate analytic solution of the non-linear equations governing the large-scale galactic dynamics of the interstellar medium is discussed. Non-circular orbital motion results in the rapid development of spiral-like loci upon which the fluid velocity and density tend to become multi-valued. For some simple cases, properties of these loci and of the fluid in their vicinity are given.
Physical halo and radio halo
Authors: Ginzburg V. L.
Published: July 2016

A distinction is necessary between two concepts: the physical halo, forming a transition between the gas in the galactic disk and that in intergalactic space, and the radio halo, a spherical component (withR~ 15 kpc) in the distribution of non-thermal radio emission.
Theoretical ideas concerning X-ray sources
Authors: Burbidge Geoffrey R.
Published: July 2016

Several possible mechanisms for the emission of galactic X-ray sources are briefly reviewed. Synchrotron radiation is probably responsible for the X-ray emission from the Crab Nebula and from Cas A. The source Sco X-1 probably radiates by thermal bremsstrahlung in a cloud at 50 × 106°K, associated with an old nova. The energy source of the hot gas in such a model, and the conditions for formation of the line spectrum are considered.
Remarks on the galactic magnetic field
Authors: Woltjer L.
Published: July 2016

According to the program I am to speak on the theory of the galactic magnetic field and to summarize. About the theory of the magnetic field I can be very short because no coherent theory exists. In our present state of knowledge one is not even sure what should be expected of the theory. To summarize summarizing papers is probably not too fruitful; I therefore will restrict myself to making a number of somewhat loosely connected remarks on the galactic magnetic field and on some of the observations that might be useful in elucidating the situation.
Extinction curves for graphite-silicate grain mixtures
Authors: Wickramasinghe N.C.
Published: July 2016

Mixtures of graphite particles ejected from carbon stars and silicates from oxygen-rich giants are capable of producing excellent fits to the observed interstellar extinction curve. The fits extend over the entire wavelength range of the observations, and include a hump at ~ 2200 Å in the ultraviolet due to the graphite components of the mixtures. The agreement with the observed extinction curve remains good if the small silicate particles acquire mantles of either ice or solid H2. If no mantles are present around the silicate grains comparable mass densities of graphite and silicates are indicated; if mantles of either ice or solid H2 are present the mass density of silicates may be an order of magnitude below that of graphite in the interstellar medium.
Rocket spectroscopy of ζ Puppis below 1100 Å
Authors: Smith Andrew M.
Published: July 2016

A spectrum of ζ Pup extending from 920 Å to 1360 Å with approximately 0.8 Å resolution has been recorded at rocket altitudes. Tentative identification of 38 multiplets below 1100 Å has been made from which it is concluded that all the lines appearing in a model atmosphere (Hickok and Morton, 1968) with Te = 37450K have been detected with the exception of those masked by telluric N2 or strong P Cygni-like profiles. Additional absorption lines indicate a wide range of ionization and excitation entirely consistent with observations in the visible spectral region of similar type stars; they also appear to affect sensibly the energy distribution within the spectrum. From newly detected blue-shifted absorption features produced by the ions Svi (933.4 Å, 944.5 Å), Niv (955.3 Å), Niii (991.0 Å), and Ovi (1033.8 Å) mean radial velocities of 1200, 530, 1800 and 1900 km sec−1 respectively have been derived. It is pointed out that the transition in Niv (955.3 Å) does not originate in the ground state configuration as do the other P Cygni profile transitions, but from an excited level which can decay radiatively to the ground state. It seems likely, therefore, that the profile is generated close to the photosphere, and this, together with previously reported results, constitutes evidence for a positive velocity gradient in the detected portion of the circumstellar envelope. On the basis of available data, ions in the ground state of Nv, Niv (by inference) and Niii are all present in the circumstellar envelope, the abundance of the latter remaining large enough to produce a strong P Cygni profile.
Radiative acceleration and ultraviolet resonance line profiles in OB supergiants
Authors: Hutchings J. B.
Published: July 2016

The rocket spectra taken by Morton et al. (1967) were used as a basis for the investigation. These are in the far ultraviolet region of the Orion supergiants δ, ∊, ζ Orionis. Because of the similarity in spectral type and luminosity of these stars and the great strength of the shifted resonance lines it was possible to derive a mean P Cygni profile (standard error 5 % of the continuum) representing a typical single ultraviolet resonance line for a star of spectral type ~B0, Mv ~ −6.2. This is the ‘observed’ mean profile in Figures 2 and 3.
On the contribution of solar activity to the ultraviolet spectrum of the Sun
Authors: Bruns A. V. , Prokofiev V. K. , Severny A. B.
Published: July 2016

As measured from space, the contribution of one moderate flare to the emission spectrum of the Sun in the far-ultraviolet (304 Å, Lyman continuum, etc.) is comparable with the emission of the whole undisturbed solar disc.
Intensity distribution in the Lyman-α line at the solar limb
Authors: Vial J. C.
Published: July 2016

The distribution of the solar intensity in the Lyman α line has been measured close to the visible limb. It is compared to a computation including LTE departures (as evaluated by Y. Cuny). As far as the profile of the line and the intensity (integrated over the line) are concerned, the interspicular model of Coates is the only one which seems to agree with the observations.
Observations of interstellar Lyman-α absorption
Authors: Jenkins Edward B.
Published: July 2016

Absorption at the Lyman-α transition from interstellar neutral hydrogen has been observed in the ultraviolet spectra of 18 nearby O and B stars. Radiation damping is the dominant cause of line broadening, which makes the derived line-of-sight column densities proportional to the square of the observed equivalent widths. An average hydrogen density on the order of 0.1 atom cm−3 has been found for most of the stars observed so far. This is in contrast to the findings from surveys of 21-cm radio emission, which suggest 0.7 atom cm−3 exists in the local region of the Galaxy. Several effects which might introduce uncertainties into the Lyman-α measurements are considered, but none seems to be able to produce enough error to explain the disagreement with the 21-cm data. The possibility that small-scale irregularities in the interstellar gas could give significantly lower values at Lyman-α is explored. However, a quantitative treatment of the factor of ten discrepancy in Orion indicates the only reasonable explanation requires the 21-cm flux to come primarily from small, dense, hot clouds which are well separated from each other. The existence of such clouds, however, poses serious theoretical difficulties.
The ultraviolet background (intergalactic gas, the Galaxy, and subcosmic rays)
Authors: Kurt V. G. , Sunyaev R. A.
Published: July 2016

(1)

Observations. – A survey is made of observations of the background radiation at UV wavelengths from above the atmosphere. Sources of the background radiation and ways of determining the extragalactic component of the background are discussed. Future observations are also discussed.

(2)

Cosmology. – Limits to the properties of the intergalactic gas follow from observations of the UV background. The problem of detecting galaxies at early stages in their evolution is considered.

(3)

The Galaxy. – Observations and theoretical estimates are given for the integrated brightness of the Galaxy at UV wavelengths beyond the Lyman-α line. Also discussed are the nature of the Lyman-α emission from the Milky Way and the principal ways of constructing the luminosity function of stars in the Galaxy from observations of the integrated UV spectrum.

(4)

Subcosmic Rays in the Interstellar Medium. – Fast neutral excited hydrogen atoms can be formed from charge-exchange interactions between subcosmic-ray protons and neutral interstellar gas. Upper limits are given to the energy density of subcosmic rays having E ~ 100 keV.

(5)

Limits on the Background Radiation in the range <912 Å. – The distribution of neutral hydrogen in the peripheries of galaxies allows limits to be obtained for the flux of metagalactic ionising radiation. The heating and ionisation of the interstellar medium by X-rays is considered.
Models of the Venus ionosphere
Authors: Herman J. R. , Hartle R. E. , Bauer S. J.
Published: July 2016

Theoretical modeling of the daytime Venus ionosphere can be used to augment the measurements of Mariner V made during the 1967 fly-by mission of Venus. The models discussed here are obtained by solving the equations of heat conduction for the electron, ion, and neutral gases along with the momentum and chemical equations for the charged particle densities [1, 2, 3]. When the model is brought into conformity with as much of the data as is possible, constraints can be placed on some of the unknown parameters such as the electron and ion temperatures, and the strength of the magnetic field in the topside Venus ionosphere.