bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Plasma Spectroscopy in Understanding Plasma Processes on the Sun
Authors: Raja Rao P. Meenakshi , Sarswathy P. , Raja Sekhar B.N. , Krishnamurty G.
Published: July 2016

Emission spectroscopic methods are very useful in determining the plasma parameters such as electron density, electron temperature, chemical abundances and energy levels of atoms and ions. A knowledge of the above mentioned parameters and collision cross sections provides an insight into various plasma processes on the Sun. As one passes from photosphere to chromosphere and corona the temperature as well as the electron density changes drastically (Te ~4500 − 2×1060K; n e ~ 108 − 1013 cm−3) (1). Hence the solar spectrum.excited by different mechanisms and different equilibrium conditions, extends from vacuum ultraviolet to visible and infrared regions. For example the spectrum in the region between 3000−1300Å is produced by the upper photosphere and lower chromosphere. In this region the temperature is in the range of 6000-10000 K. This region is characterised by several emission and absorption Lines superimposed over continuum. Below 1600Å consists of emissions from highly ionised atomic species originating from chromosphere and corona (2).A correct interpretation of the spectral features is possible only after understanding the influence of various factors on spectral line shapes and intensities. They are 1) damping by collisions with neutral atoms; 2) collisions by charged particles leading to linear and quadratic Stark effects on atomic lines of hydrogen and helium; 3)thermal Doppler broadening 4) Doppler broadening or shift due to microturbulent velocity field.
Dual Frequency Variability Study of an Active Region
Authors: Shevgaonkar R. K. , Kundu M. R.
Published: July 2016

A short-time variability study of a solar active region simultaneously at 6 and 2 cm wavelengths was carried out using the VLA. The observations show interesting uncorrelated brightness temperature variation at the two wavelengths. The observed low brightness temperatures indicate that the emission is mainly originating from the chromosphere - corona transition region.

A transition region model with constant pressure and power-law temperature variation as a function of height has been assumed to analyse the data. The uncorrelated variation of the observed brightness temperature at the two wavelengths suggest different dominant emission mechanisms (bremsstahlung at 2cm and gyro-resonance at 6cm) operative at the two wavelengths. It is shown that an independent variation of a few percent in the magnetic field (900 ±45 G) and a factor of two variation in the density (2 to 4 × 1010 cm−3) over a time scale of few hours is required to explain the uncorrelated brightness temperature variations at the two wavelengths.
Clark Lake Radio Observations of Coronal Mass Ejections
Authors: Gopalswamy N.
Published: July 2016

We review some recent studies of mass ejections from the Sun using 2-D imaging observations of the Clark Lake multifrequency radioheliograph. Radio signatures of both fast and slow coronal mass ejections (CMEs) have been observed using the Clark Lake radioheliograph. Using temporal and positional analysis of moving type IV and type II bursts, and white light CMEs we find that the type II's and CMEs need not have a direct cause and effect relationship. Instead, the type II seems to be generated by a “decoupled shock”, probably due to an associated flare. The moving type IV burst requires nonthermal particles trapped in magnetic structures associated with the CME. Since nonthermal particles can be generated independent of the speed of CMEs, moving type IV bursts need not be associated only with fast CMEs. Specific examples are presented to support these views.
Higher Harmonic Plasma Radiation in Type II Solar Radio Bursts
Authors: Fomichev V.V. , Chertok I.M. , Gorgutsa R.V. , Markeev A.K. , Kliem B. , Aurass H. , Kruger A. , Kurts J. , Urbarz H.
Published: July 2016

The large behind -limb (W 140, 0900 UT) flare on February, 16, 1984 was followed by a complex of radio bursts - type II, III, IV and V bursts.
Clusters, Associations and Galactic Structure
Authors: Lyngå Gösta
Published: July 2016

Distances to clusters are not more accurately determined today than twenty years ago. Effects of different abundances in different clusters can seriously influence distance determinations. There is, however, no immediate call for a revision of the cluster distance scale as obtained by curve fitting assuming the distance of the Hyades to be known.
Massive Stars: Evolution with Mass Loss. III. Low Metal Stars, and WR's in SMC
Authors: Chiosi C. , Bertelli G. , Nasi E.
Published: July 2016

In this paper we investigate the effect of mass loss by stellar wind on the evolution from the main sequence to the He exhaustion stage of stars in the range of mass 20 to 100 M⊙ with low metal abundance. To this purpose we compute the set of evolutionary sequences with initial mass 20, 30, 40, 60, 80, and 100 M⊙ and chemical composition parameters X=0.700, Z=0.001. The models are first computed at constant mass to provide the fundamental network to which we compare the mass losing models. This choice of the initial chemical composition is aimed to represent the case of luminous supergiants in the Small Magellanic Cloud. The rate of mass loss follows the formulation of Castor, Abbot and Klein (1975), but it incorporates the effect of different metal content in the regions of high effective temperatures in the HR diagram. The rate of mass loss for models at low effective temperature is given by the acoustic flux mechanism according to the formulation of Chiosi, Nasi and Sreenivasan (1978). The results are compared with those of Chiosi, Nasi and Sreenivasan (1978), and those of Chiosi, Nasi and Bertelli (1979) for normal metal abundance supergiant stars of the Galaxy. On the basis of the present results we suggest an interpretative scenario for the existence of single WR stars in galaxies of different chemical composition. These results allow us to interpret also the different percentages of WR's among subclasses that are observed in the Galaxy, LMC, and SMC (Conti and Vanbeveren, 1979).
Hidden Clusters in the Southern Milky Way
Authors: Lodén Lars Olof
Published: July 2016

At visual inspection of objective-prism plates of Milky Way regions one frequently detects pairs or sometimes higher multiples of spectra which are so similar in appearance and so close together that they form a conspicuous configuration for the eye. A statistical analysis shows that the observed occurrence of this phenomenon, down to a certain limiting magnitude and up to a certain value of the angular separation of the components, considerably exceeds the expected one - if it should be considered as produced entirely by random coincidence. Therefore it is reasonable to assume a physical explanation behind this sort of agglomeration. According to the working hypothesis it is essentially a part of very loose or star-poor clusterings which do not show a sufficiently high degree of contrast against the surrounding galactic stellar background to be discovered “directly”. The phenomenon might thus be comparable to an optical multiple system, although it is produced by members of a physical cluster of some kind. In connection with a large survey of the Southern Milky Way, carried out at the Stockholm and Uppsala observatories, several thousands of such coincidences have been registered. About a hundred of them have been subjected to a special investigation, intended to give an answer to the question about their physical interpretation. Although the methods have been neither very rational, nor always point-to-point reliable, the scrutiny has shown pretty well that an overwhelming majority of the “candidate” objects do reveal stellar clusterings of various types. In fact, it has been possible to distinguish between at least four more or less well-defined types of objects in the shape of stellar clusterings. 1. Relatively ordinary clusters, a few of which are already known or even well-known. The “rediscovery” is then some sort of a confirmation of the working hypothesis. 2. Very loose clusterings. 3. Extremely small and star-poor clusters, possibly cluster remnants. 4. Multiple systems with extreme separation between the components, maybe the ultimate stage of a cluster in disintegration. The relative frequency of the four interpretations in order will approximately be: 1–20%, 2–35%, 3–20%, 4–10%. In addition, there is also a certain admixture of spurious objects without astrophysical interest.
Galactic Rotation From Young Open Star Clusters
Authors: Maitzen H. M. , Moffat A.F.J. , Schmidt-Kaler Th.
Published: July 2016

The rotation of the Galaxy can best be studied with the aid of tracers for which distance and velocity can be obtained simultaneously, accurately and unambiguously out to large distances. Clearly, the best objects are the very young clusters. The local gradient of the angular velocity is contained in Oort's constant

and, due e.g. to perturbations from spiral features, may not reflect the smoothly varying, underlying global component of rotation. Thus, it is necessary to reach out as far as possible in order to allow a smoothing of the rotation curve.
Stars With Abnormal Spectra in Open Clusters
Authors: Feinstein A.
Published: July 2016

From the literature a list of stars with abnormal spectra belonging to open clusters was compiled. This list is included in Lyngå's catalogue of open clusters. With this data it becomes possible to derive a correlation with the age, compiled by W. Buscombe and which appears also in Lyngå's catalogue.
Spectroscopic and Photometric Observations of the Southern, Intermediate-Age Clusters NGC 2477 and NGC 2660
Authors: Hesser James E. , Smith Horace A.
Published: July 2016

47 A mm−1 image-tube spectra show that the turnoff region and blue straggler stars in NGC 2477 are not, in general, rapid rotators, as postulated by Hartwick and Hesser (1974) to explain, via mixing induced by meridional circulation, the widely differing photometric metallicity estimates based upon uvbyβ photometry of the main-sequence stars and DDO photometry of the giant stars. However, the discrepant metallicity estimates are largely reconciled by recent revisions in the reddening corrections for the DDO system (Boyle 1979, Janes 1979); and by small color corrections of the type described by Muzzio (1978) and Schmidt and Taylor (1979) applied to the β-photometry. The mean radial velocity is found to be 5.6 kms−1 while the mean Vsini is 105 km s−1. Star “m” is spectroscopically confirmed to be an Am star.
Spectral Morphology in the Open Cluster NGC 2287
Authors: Levato Hugo , Malaroda Stella
Published: July 2016

As part of a long range program on spectral classification in open clusters we have obtained high quality spectrograms (39 A mm−1 and 125 A mm−1 both 1.2mm wide) of 35 stars in NGC 2287.
The Older Clusters in the Magellanic Clouds
Authors: Gascoigne S.C.B.
Published: July 2016

We begin with Fig. 1, which somewhat aged though it may be still illustrates important aspects of the subject (Gascoigne 1971)

(i)

There is a clear division of cloud clusters into a blue and red group. The division corresponds to the mass around 2.51M⊙, at which core degeneracy first develops in stars approaching the giant branch. Such stars spend about three times as long on the giant branch and travel higher up it than the slightly heavier non-degenerate stars, and so dominate the colours of the clusters in which they occur.

(ii)

The red clusters are somewhat less luminous than the globular clusters in the galaxy. Freeman and Chun (1972) have shown from dynamic arguments that the cloud clusters are also less massive, by enough to keep the M/L ratios roughly the same as those in the galaxy.

(iii)

For a long time it has been taken that the blue clusters are young and the red clusters old. Thus the clouds present us with a truly two-parameter family of globular-like clusters, the parameters being of course age and abundance.
Wide Binaries in the Pleiades
Authors: Brosche P. , Hoffmann M.
Published: July 2016

The number and distribution of visual binaries in the Pleiades agree with the frequencies in the solar neighbourhood, except for an apparent deficiency of systems with faint secondaries. A full account of the work is scheduled to appear in Astrophysics and Space Science.
Photometric Studies of the Extreme SMC Wing
Authors: Kunkel William E.
Published: July 2016

Among the currently interesting problems of interpreting the Magellanic Stream as an instance of tidal disruption is that of finding some demonstrable phenomenon in the makeup of the involved material that parallels the better known cases of tidal interaction, as for example NGC4038/39, where the dynamic and star-formation time scales are in agreement (Schweizer 1977). The observational problems that beset the interpretation of the Magellanic Stream are numerous (Mathewson and Schwartz 1976, Kunkel 1979, Bregman 1979), and the marked difference between the composition of the Stream (evidenced purely through HI) and the stellar systems (at least 80 percent stars) is among the outstanding dilemmas remaining. Finding some counterpart in the Magellanic scene comparable to the better recognized instances of tidal interaction may go some way towards clarifying a perplexing situation.
Globular Cluster Systems in Galaxies
Authors: Racine René
Published: July 2016

The study of globular cluster systems is very important. Because these systems are so old, their investigation is a form of archeo-astronomy whereby a slow and, at times, tedious gathering of fragmentary data laboriously uncovers the skeleton of early galactic structures. Our theories and our imagination can then try to put some flesh on these bones in attempts to visualize what these early inhabitants of the Universe might have looked like.
Accretion of Gas by Stars in Globular Clusters
Authors: Faulkner D. J.
Published: July 2016

One of the two classes of models that have been proposed for the production of X-rays in globular clusters involves accretion of gas by a more or less massive (10 M⊙–1000 M⊙) black hole at cluster centre (Cowie, Ostriker and Stark 1978 - COS). The accretion rates are not large (~1017 g s−1), and we may enquire how such rates compare with those for accretion on cluster stars in general.
Fundamental Temperatures and Surface Gravities for HB Stars in the Field and in Globular Clusters
Authors: Davis Philip A.G. , Hayes D. S.
Published: July 2016

Scans have been made of ten BHB stars in the globular clusters M92, M13 and M5 and of eight stars in 1 HLF 2 with the multi-channel spectrometer on the Hale 5 meter telescope during July 1979. Twenty-four additional stars are being scanned at CTIO and KPNO using the Harvard scanner. Four-color observations were made of most of the BHB stars on the Steward Observatory 90″ telescope and these measures indicated that there were stars, at the same (b-y) color on the horizontal branch, with quite different values of the c1 index. The scans confirm these results, showing that the shape of the intensity vs wavelength curve for λ<4210 is related to the c1 index. These features are illustrated in the two figures, where it can be seen that a c1 value formed from the scans [(u-v)-(v-b)] is greater for the star in Figure 1.
Two Simple Forms of Phase Density and Models of Star Clusters
Authors: Veltmann Ülo-Illmar K.
Published: July 2016

Two versions of the restrictions of the phase density are found and studied:

when the integral equation for the phase density is reduced to the Abel equation. r1, λ and α or p are parameters of models. r1 is the radius of the model; -X is the energy integral; - a half of the angular momentum integral squared; φ(r) is the gravitational potential. The functions ψ(ξ) or f(u) are determined as solutions of the Abel equation, the given functions being the space density, ρ(r), or the potential, φ(r), known from observational data. The observational data have been approximated by two types of models: generalized Schuster models,

or two-parametric generalized isochronous models,

ρo or φo where ro or rh are scale parameters, β or q and c are structure parameters. Details of the report will be published in Publ. Tartu Astrophys. Obs.48, 1980 and in Astron. Zh. (Moscow)58, 1981.
Pulsar Electrodynamics
Authors: Ardavan Houshang
Published: July 2016

This paper briefly discusses the salient features of quasi-steady electrodynamics; that is to say it considers certain general properties of Maxwell's equations and their solutions when these equations are subjected to the constraint

where ω is a constant angular frequency, ⊘ and t are the azimuthal angle and time, and the operators are applied only to quantities which are scalars or the cylindrical components of a vector (Mestel 1971).
Hot Relativistic Winds and the Crab Nebula
Authors: Fujimura F. S. , Kennel C. F.
Published: July 2016

We review efforts to construct a self-consistent model of pulsar magnetospheres that links the particle source near the pulsar to the outflowing relativistic wind and couples the wind to the surrounding nebula. Pair production source models (Sturrock, 1971; Ruderman and Sutherland, 1975; Arons, 1979) produce outflowing positronic plasmas which are too dense to support a plasma wave of relativistic amplitude (Kennel et al., 1973). Therefore an appropriate description seems to be a relativistic magnetohydrodynamic (MHD) wind. Radiation from a relativistic wind will be collimated forward and can only be observed along the line of sight to the wind source. This makes relativistic winds essentially unobservable and provides an almost invisible method of energy transport. Photons can be emitted in all directions and the existence of the wind inferred only after the wind has been decelerated by a confining shock (causing the flow to become subsonic and non-relativistic).
Pulsar Winds
Authors: Kundt Wolfgang
Published: July 2016

It is argued that pulsar windzones are pulsed γ-ray emitters, and X-ray emitters. The wind consists of a strong subluminal wave, in approximate equipartition with a relativistic electron-positron plasma; it also contains a weak frozen-in magnetic flux. Trailing filaments may be responsible for large-angle particle scattering, giving rise to one-sided X-ray appearance.
Time Asymmetries in Pulsar Signals
Authors: Stinebring Dan R. , Cordes James M.
Published: July 2016

The average shape of micropulses in two pulsars is highly symmetric, unlike the subpulse emission which is skewed in the same sense as the average profiles. These conclusions stem from a third-order correlation analysis of the emission from PSR 0950+08 and PSR 2016+28. The symmetric micropulses may be produced either by temporal modulation or angular beaming of the radiation. If due to temporal modulation, this average symmetry implies a distribution of time-scales in the emission process: the difference between the rise time-scale (τr) and the decay time-scale (τd) must be small compared to δτr and/or δτd. Subpulses in PSR 0950+08 are narrower than and have the same sense of asymmetry as the average profile. In PSR 2016+28 the two subpulses typically present in a pulse are both tapered toward the outside edge of the pulse. In both pulsars, the skewness of the subpulses contributes significantly to the skewness of the average profile; a symmetrical distribution of these subpulses within the pulse window could then give rise to an asymmetrical profile.
Pulsar Astrometry
Authors: Backer D. C. , Sramek R. A.
Published: July 2016

The 35-km interferometer at NRAO was used at 2.7 GHz during 1974–1979 to determine pulsar proper motions. Observations from each epoch were reduced to pseudo-position vector offsets which include both unknown, and constant, absolute position errors for the pulsars and their reference sources, as well as the time-varying proper motion of the pulsars. The coordinate system for which the errors in the offset components are independent is chosen. Proper motions resulting from a linear fit to the offsets for five pulsars are given in Table 1.
The Radio Interpulse from PSR 0950+08
Authors: Hankins T. H. , Cordes J. M.
Published: July 2016

Two hypotheses exist to explain the radio interpulse of PSR 0950+08 within the context of polar cap emission models:

1)

The emission originates at a single magnetic pole as for other two-component pulsars, except that the component spacing is much wider.

2)

The interpulse emission originates at the opposite magnetic pole. We discuss here some new observations and their implications for the single and double pole hypotheses.
Mode-Changing, Drifting Subpulses, and Interpulse Emission in PSR 1822-09
Authors: Fowler L. A. , Wright G.A.E. , Morris D.
Published: July 2016

PSR 1822–09 is a nearby galactic disk pulsar with a typical .769 s period. Its large period derivative indicates a young timing age of 250,000 yrs and a strong estimated surface magnetic field of 6.4 × 1012 G. We have observed this pulsar at frequencies around 1700 MHz and 2650 MHz. The mean pulse profile at these frequencies consists of a double peaked main pulse with two dissimilar components and a weak interpulse 185° of pulse longitude after the main pulse second component. The interpulse is detected in both frequency ranges, and the main pulse - interpulse separation does not change between these frequencies and the low frequencies around 327 MHz where the interpulse was discovered by Cady and Ritchings (1977).
Radio Timing Observations
Authors: Manchester R. N.
Published: July 2016

The most recent review of pulsar timing observations (and pulsar astronomy generally) is contained in the monographs by Manchester and Taylor (1977) and Smith (1977). This paper reviews developments in radio timing observations since the time of writing these monographs (~ 1976). In Section 2 results based on the secular variation of pulsar period are reviewed and timing irregularities are discussed in Section 3. Results for binary pulsars, three of which are now known, are reviewed by Taylor (1981).
Pulsar Glitches: Superfluid Unpinning
Authors: Anderson P. W. , Alpar M. A. , Pines D. , Shaham J.
Published: July 2016

In the neutron star crust, the neutron superfluid coexists with a lattice of nuclei. There are two different local densities of superfluid neutrons, inside and outside the nuclei, with a corresponding difference in the values of the superfluid gap and condensation energy.
Neutron Star Models
Authors: Canuto V. , Bowers Richard L.
Published: July 2016

The current state of neutron star structure calculations is reviewed. Uncertainties in the equation of state for matter at and above nuclear density remain. The role of the delta resonance, pion condensates, and quark matter is reviewed. Despite uncertainties, we find that recent models yield stable neutron star masses which are consistent with observational estimates.
Binary Pulsars
Authors: Taylor Joseph H.
Published: July 2016

There are now three radio frequency pulsars known to be in binary systems: PSRs 1913+16, 0820+02, and 0655+64. The first of these, discovered in 1974, moves in a tight, highly eccentric orbit with a period of approximately 7h 45m. Its companion has not yet been identified with certainty, but must be a compact object of mass comparable to that of the pulsar. PSRs 0820+02 and 0655+64, recognized as binaries during the past fifteen months, have nearly circular orbits with periods of over three years and about one day, respectively. All three objects are of great interest for the opportunity they provide to measure the masses of neutron stars. In addition, the first has proven to be a useful probe of gravitational theories, and the study of all of them should yield important information concerning the evolution of binary systems and the formation of neutron stars.
New Observations of HI Absorption for Pulsars
Authors: Manchester R. N. , Wellington K. J. , McCulloch P.M.
Published: July 2016

The second Molongo pulsar survey (Manchester et al., 1978) provides a large sample of pulsars in the southern sky. It is of interest to obtain non-dispersion-dependent distances for as many of these pulsars as possible. Since most of these pulsars are relatively weak, a system of high sensitivity is required. In this paper we report on preliminary observations made at Parkes during June 1980 with such a system.
1. The White Dwarfs: Discovery and Observation
Authors: Luyten W. J.
Published: July 2016

White dwarfs have been known for slightly more than fifty years; with their planetlike diameters, and stellar-like masses their densities are enormously much higher than those of ‘normal’ stars. They thus appear to represent a state of matter totally unknown and possibly unattainable on earth.
11. Effective Temperatures of White Dwarfs
Authors: Oke J. B. , Shipman H. L.
Published: July 2016

White dwarf stars are among the most challenging and interesting objects which can be studied. Because they represent the interiors of highly-evolved stars, the chemical composition can be enormously variable from object to object. Furthermore, because of the very large gravities, the composition of the atmosphere may be very different from that in the interior. The theory of the degenerate interior provides a relation among mass, radius and chemical composition. Since temperatures, effective gravities, and redshifts can, for certain stars, provide further relations between mass and radius, one can hope to make checks on the theory which are not possible with ordinary stars.
General Considerations about the Revision of All the Calculations of the International Latitude Service
Authors: Melchior P. , Dejaiffe R. , Verbeiren R.
Published: July 2016

A general revision of the calculations of the ILS is necessary, for several reasons. The first fundamental step has been performed with the Melchior-Dejaiffe catalogue. From it, improved values of the screw pitches and their adjustments, new investigations upon closing errors in all the ILS stations with introduction of the tidal deflection of the vertical, new deduction of the Kimura z-term and definitive calculations of x, y, z are obtainable.
Old and New Methods of Observing Polar Motion
Authors: Vicente R. O.
Published: July 2016

The motion of the pole has been observed by means of visual telescopes, employed by the ILS, photographic zenith tubes and astrolabes. It is pointed out the difficulties of combining the results of different types of instruments employing several observation techniques.

The new astronomical methods of Doppler observations on satellites and laser pulses sent to the Moon give another possibility of determining polar motion with greater precision. It is forecast that the results will not agree with the older ones and, in order to compare the methods, it is suggested that stations should be equipped with both techniques of detecting polar motion.
Some Results from the Automatic PZT at Richmond, Florida
Authors: Monger Don R.
Published: July 2016

Automatic operation of the PZT located at the U.S. Naval Observatory Time Service Substation, Richmond, Florida was initiated February 1, 1970. A comparison of one year's automatic operation with the previous year's operation has shown a significant increase in the number of time and latitude sights obtained.

Based on an improved ventilating system within the PZT, the probable error of a single night's observation has been reduced.
Historic Variations in the Rotation of the Earth
Authors: Newton R. R.
Published: July 2016

The purpose of this work is to investigate changes in the rotation of the Earth in the past few thousand years. Since most available observations involve the Moon, study of the Earth's rotation is inseparable from study of the Moon's motion. Since it is doubtful that present theories of tidal friction account for the present acceleration (Spencer Jones, 1939; Van Flandern, 1970; Pariisky et al., 1972) of the Moon, we cannot safely assume that consequence of the theories which says that tidal friction has been almost constant.
Motion of the Core, and Its Influence on the Earth's Axis
Authors: Mateo Jose
Published: July 2016

After the advent of artificial Earth satellites, an accurate knowledge of the harmonic coefficients of the Earth's potential has enabled us to determine the size and shape of the Earth with extraordinary accuracy.

The gravitational force between the core and the rest of the Earth, which makes both centers of mass tend to coincide, is so enormous that there is a strong possibility of a very slow motion of the core forcing its way into the mantle. It includes secular variations in both latitude and the time of rotation of the Earth.
Nearly Diurnal Nutation Derived from the Observations of Time and Latitude
Authors: Débarbat Suzanne
Published: July 2016

The results, given below, of investigations are based on 14 yr of observations carried out with the Danjon astrolabe at the Paris Observatory; such observations allow the measurement of time and latitude.

Previous analysis, based on 6,5 yr showed some periodic terms and, in particular, it had been possible to determine values of the nearly diurnal nutation (results presented at the 6th Symposium on Earth Tides, 1969).
On the Comparison of Diurnal Nutation Derived from Separate Series of Latitude and Time Observations
Authors: Yatskiv Ya. S.
Published: July 2016

Several authors tried to derive the period, amplitude and initial phase of the free diurnal nutation using separate series of latitude and time observations. The results obtained by them are compaired and discussed in the present paper.
The Spectra of Wolf-Rayet Stars at High Dispersion
Authors: Bappu M. K. V.
Published: July 2016

The Wolf-Rayet stars have perhaps the most spectacular spectra among the various celestial species that have been examined with the aid of the spectrograph. The wide emission lines that provide a striking display continue to be the enigma they have been for decades. Progress, however, in evaluating the contributions to the spectrum by different ions has been fairly complete, thanks to the splendid efforts in the laboratory by Edlen and his collaborators. Many lists of wavelengths of individual features exist from the studies of Plaskett, Beals, Cecilia Payne and Swings. Efforts at identification have been such as to provide a list of likely contributors, that by wavelength position and plausible intensity could be present in the emission band at a specified wavelength. The large width of the lines form the principal limitation. For, one can have a wide limit of coincidence in wavelength with resultant emission features that are complexes covering well over a hundred Ångstrőms. The wide nature of these complexes have perhaps encouraged in the past the use of low spectral resolution only, for the many studies that have been carried out. Seldom has one used the resolutions and dispersions that have been usefully employed for the study of the more common relatively narrow absorption lined objects. This situation pertaining to the Wolf-Rayet stars is happily undergoing a change in recent years when coudé spectra with the larger telescopes are becoming increasingly available. The southern hemisphere has been particularly rich in these objects both in variety of behaviour and in having many bright ones, and one can, therefore, justifiably hope that our information on these objects will progress henceforth with remarkable rapidity.
An Interpretation of the WC Stars
Authors: Smith Lindsey F.
Published: July 2016

I wish to draw your attention to a (quite unexpected) property of the WC binaries. I believe that it gives us a clue to one of the parameters that controls the subclasses of the WR stars.
Étude des étoiles supergéantes du Grand Nuage de Magellan, leurs magnitudes absolues et couleurs
Authors: Fehrenbach Ch.
Published: July 2016

Nous indiquons une liste de 29 étoiles membres du Grand Nuage de Magellan que nous proposons comme standards de type spectral des Supergéantes. La situation de ces étoiles dans les diagrammes RH et couleur-couleur est indiquée. Nous proposons des valeurs de (U − B)0 et (B − V)0 pour ces étoiles.
Quantitative Spectral Classification in the BCD System for LMC Supergiants
Authors: Divan L.
Published: July 2016

In December 1970 and January 1971, spectra of 13 LMC supergiants have been obtained with the Chalonge spectrograph attached to the Cassegrain focus of the 152 cm ESO reflector at La Silla. The spectrophotometric parameters λ1, D, φb and φuv were measured and the first results deal with (a) spectral classification and (b) the distance modulus of the LMC.
Advantages and Limitations of Quantitative Spectral Classification
Authors: Spite F.
Published: July 2016

The measurements of spectral lines of moderate dispersion slit spectrograms for F, G and K type stars give a large quantity of information. The measurements are time-consuming in comparison with visual classification, but the use of digitized microphotometers reduces the task, and the method is now promising. The interpretation of the measurements raises some problems, which are briefly discussed.
The Identification of T Tauri-Like Stars by Multicolour Photometry
Authors: Nandy K.
Published: July 2016

A method of distinguishing between T Tauri-like stars and reddened early type field stars by the application of UBVRI photometry is described, and the results for T Tauri-like variables in NGC 2264 are presented. The plates have been measured using the new measuring machine GALAXY. (V–R) colours, which are less affected by spectral peculiarities, are used to determine infrared and ultraviolet excesses. The range of variability in UBVRI colours of these varables has also been studied.
Classification of Population II Stars in the RGU System
Authors: Steinlin U. W.
Published: July 2016

The theoretical treatment of the blanketing effect and the first photometric results had shown that the separation of stars of different metal content should be better in the RGU system than in the UBV system. A three color photometry of the globular cluster M5 is undertaken to show the position of these stars in the RGU two-color diagram, to derive the conversion formulae between the two photometric systems for these stars and to use the results for the classification of population II field stars in statistical investigations of the galactic halo.
Remark in Regard to Bidelman's Data-Bank Project
Authors: Bidelman W. P.
Published: July 2016

The concept of a general stellar data bank is not a new idea, but the desirability of this project at the present time has been emphasized by a number of astronomers (Bidelman, Jaschek, Cayrel, Hauck and others) and work is proceeding both in the United States and elsewhere. The status of my own activities in this direction is as follows:

The general stellar data file now at the Warner and Swasey Observatory is continually being updated and much more of the astronomical literature is being systematically searched and the resulting data and references entered into the file. However this project is still largely unfunded and progress is far slower than desirable. In particular the file is still not available in machine-readable form, though several of the newer large data catalogues, such as the Warner and Swasey southern OB-star survey of Stephenson and Sanduleak, will be entered into the file in IBM card-form rather the entire file will be converted to punched cards.
The Southern Objective Prism Survey
Authors: Stock J. , Wroblewski H.
Published: July 2016

Five thousand sq deg of the Southern sky of intermediate to high galactic latitude have been surveyed with deep objective prism plates, taken with a UV-transparent prism. The plates reach on the average the 13th photographic magnitude and have been searched for the following types of objects: (1) high luminosity stars, (2) planetary nebulae, (3) metal weak late-type giants, (4) Me stars, (5) carbon stars, (6) early-type subdwarfs, (7) peculiar objects. Catalogues containing a total of over 3200 objects of these types have been compiled and will soon be published in Publ. Dpto. Astron. Univ. de Chile.

Of particular interest are the metal-weak late-type giants, which are believed to be members of the galactic halo population. Slit spectra were obtained for a number of these stars and radial velocities derived. In each case the object was found to be a high velocity star. In view of the large number of such objects found in the survey, a method of determining relative radial velocities from pairs of objective prism plates was developed. The method, which is described in detail in the following paper, was tested successfully on several plate pairs, confirming the high velocities for the metal weak stars and showing that the method could be used for an exhaustive search for high velocity stars.
Observations of Stellar Spectra Related to Extended Atmospheres
Authors: Wright K. O.
Published: July 2016

Although the Struve Symposium was planned to discuss conditions in binary stellar systems, it is necessary to consider the observations of extended atmospheres in single stars in order to compare them with those of binary systems. The Sun, being the closest star, has the first chromosphere that was observed, and we can assume that the many features observed on the Sun will be much enhanced in giant stars with more extended atmospheres. Among the early-type stars, the hydrogen emission lines in the spectra of Be stars are known to vary and this suggests the atmospheres are unstable. Similar, even more pronounced effects, are seen in the spectra of shell stars such as 48 Librae. The supergiant stars have also been shown to have spectral lines that change, often quite rapidly, with time. Smolinski has observed in the spectra of some F and G-type supergiants much-broadened absorption lines that also vary with time. Wilson's systematic studies of the H and K emission lines in late-type stars have greatly extended our knowledge of stellar chromospheres, and the ionized magnesium lines at 2800 Å should give additional information as more extra-terrestrial observations are obtained. Numerous observations of the ζ Aur stars have been obtained near eclipse; ζ Aur and 31 Cyg seem to be similar systems and show similar phenomena – a rise in temperature outward from the photosphere and an extensive, variable calcium chromosphere, but a viable theory for these chromospheres has not yet been given. VV Cep and 32 Cyg probably are larger and more complex systems. The emission lines in the ultraviolet spectra of the M-type stars may be indicators of coronae in these cooler atmospheres. Most variable stars seem to have extended atmospheres and, when detailed studies are made, show changes in both light and spectrum. Shock-wave phenomena are undoubtedly important in the analysis of many of these stars, as also are fluorescent, selective-excitation processes. Flare stars, though generally dwarfs, are of great interest in studies of stellar atmospheres.

Extended atmospheres can be detected from observed gross deviations from local thermodynamic equilibrium, as in the study of emission lines, large velocity fields, and dilution effects. It is probable that the presence of a companion affects the atmosphere of the primary star in close double stars, but in stars like ζ Aur and 31 Cyg, the atmospheric effects produced near eclipse may be among the best clues for the interpretation of extended stellar atmospheres.
Properties and Synthesis of Heavy Nuclei and Properties of Neutron Star Matter
Authors: Buchler J. Robert
Published: July 2016

The nuclear Thomas-Fermi model which is based on nuclear matter calculations has been successfully applied to the study of the bulk properties of nuclei. It is ideally suited for extrapolation into the region of very neutron-rich and of superheavy nuclei. It is therefore a valuable approach for r-process calculations as well as for the study of neutron star matter at subnuclear densities.
Observations of Cosmic X-Ray Sources by the MIT Instrument on the OSO-7
Authors: Clark G. W.
Published: July 2016

The Seventh Orbiting Solar Observatory, OSO-7, carries on board a 1–60 keV X-ray detector for the purpose of measuring the positions, spectra and time variations of X-ray sources. The instrument is described herein, and several topics under investigation and results in publication are mentioned.
Binary Systems as X-Ray Sources: A Review
Authors: Kraft Robert P.
Published: July 2016

The observational properties of Sco X-1, Cyg X-2, and Cen X-3 are reviewed in connection with the hypothesis that X-ray power is derived from gravitational energy released when matter is accreted onto the surface of one component in a mass transfer binary star. Evolutionary mechanisms for producing suitable types of binaries are considered. The following boundary conditions on possible evolutionary models are also treated briefly: (1) a quite significant fraction of hard X-ray sources are associated with the nuclear bulge of the galaxy; (2) mass-transfer binaries such as U Gem stars are not hard X-ray sources; (3) counts of binary stars lead to a considerably larger number of X-ray source candidates than are actually observed.
Radio Counterparts of X-Ray Sources and X-Ray Counterparts of Radio Stars
Authors: Hjellming R. M.
Published: July 2016

Some of the implications of the data on radio counterparts of X-ray sources are discussed. Data on the radio counterpart of Cyg X-3 is compared with the data on the radio star β Persei (Algol), to show that similar radio emission mechanisms are involved. The data for such radio stars not yet known as X-ray sources imply that such objects should be transient X-ray sources.
Black Holes in Binary Systems: Observational Appearances
Authors: Shakura N. I. , Sunyaev R. A.
Published: July 2016

The outward transfer of angular momentum of accreting matter can lead to the formation of a disk around the black hole. The structure and radiation spectrum of the disk depends, in the main, on the rate of matter inflow Ṁ into the disk at its external boundary. Dependence on the efficiency of mechanisms of angular momentum transport (connected with the magnetic field and turbulence) is weaker. If Ṁ = 10−9–3 × 10−8 M⊙/yr, the disk around the black hole is a powerful source of X-radiation with hv ∼ 1–10 keV and luminosity L ∼ 1037–1038 erg s−1. If the flux of the accreting matter decreases, the effective temperature of radiation and the luminosity will drop. At the same time when Ṁ > 10−9M⊙ yr−1, the optical luminosity of the disk exceeds the solar one. The main contribution to the optical luminosity of the black hole is due to the re-radiation of that part of the X-ray and ultraviolet energy which is initially produced in the central high temperature regions of the disk and which is then absorbed by the low temperature outer regions. The optical radiation spectrum of such objects must be saturated by the broad emission recombination and resonance lines. Variability is connected with the character of the motion of the black hole and the gas flow in binary systems and possibly with eclipses. For well defined conditions, the hard radiation can evaporate the gas. This can counteract the matter inflow into the disk and lead to autoregulation of the accretion.

If M ≫ 3 × 10−8 (M/M⊙) M⊙ yr−1, the luminosity of the disk around the black hole is stabilized at the critical level of Lcr = 1038 (M/M⊙) erg s−1. A small fraction of the accreting matter falls under the gravitational radius whereas the major part of it flows out with high velocities from the central regions of the disk. The outflowing matter is opaque to the disk radiation and completely transforms its spectrum. As a consequence, a black hole in a supercritical regime of accretion can appear as a bright star with a strong outflow of matter.
UHURU Results on Extragalactic X-Ray Sources
Authors: Kellogg Edwin M.
Published: July 2016

Data from the UHURU satellite have provided a list of more than forty high latitude sources (|b| > 20°). X-rays have been detected from among the nearest normal galaxies, giant radio galaxies, Seyferts, QSOs and clusters of galaxies. The cluster sources appear to be extended by several hundred kiloparsecs as well as being very luminous. These cluster sources have systematic differences in their X-ray spectra from individual galaxies.

About twenty sources are not reliably identified so far. A few of these are located near undistinguished 3C or MSH radio sources. The rest are either located near distant clusters or undistinguished bright galaxies, or are too far south, so that we have not sufficient optical data to allow a thorough search for possible association with clusters or unusual individual galaxies.

The luminosity function for weak, high latitude X-ray sources is determined, and the contribution of sources just below the UHURU threshold of detectability to observed fluctuations in the diffuse X-ray background is evaluated. The total contribution of all observed types of extragalactic sources to the X-ray background is estimated.
Absorption and Production of Soft X-Rays in the Galaxy
Authors: Hayakawa S.
Published: July 2016

The column densities of interstellar hydrogen to X-ray sources derived from their spectra are compared with those obtained from 21 cm radio observations. Referring to several observed results on Cyg X-2, Cygnus Loop etc., the interpretation of the low energy cut-off of the spectrum in terms of the interstellar absorption is subject to ambiguities due to a modification of the emission spectrum by Compton scattering in the sources and the contribution of emission lines.

The result of soft X-ray sky surveys indicates that the diffuse component of soft X-rays consists of the extragalactic and the galactic components. The former has a hard component with a power law spectrum and a soft component which may be represented by an exponential spectrum. The galactic component is so soft that its spectrum may also be explained by thermal bremsstrahlung of temperature of about 0.1 keV. Its generation rate may account for the heating and ionization of interstellar matter. It is suggested that galactic diffuse soft X-rays are produced by active stars of a rather high number density.
Coincident calcium and hydrogen interstellar lines
Authors: Goldstein Samuel J.
Published: July 2016

Observation of the 21-cm line in the directions of 34 high-latitude stars shows narrow emission features in most cases; in 18, the velocities of calcium- and hydrogen-line components agree within 2·5 km/sec. From the frequency of such coincidences as a function of the distance of the stars, a layer thickness of 350 pc for the gas is derived.
Ionized-hydrogen clouds associated with young stellar clusters
Authors: Tovmasjan H. M.
Published: July 2016

Observations of the 20-cm continuum with the 210-foot (64-m) Parkes telescope have furnished, for fifteen O-type clusters, the electron density and mass of associated ionized-hydrogen clouds.
Observations of the spatial structure of interstellar hydrogen
Authors: Heiles Carl
Published: July 2016

High-resolution 21-cm line observations in a region aroundlII= 120°,b11= +15°, have revealed four types of structure in the interstellar hydrogen: a smooth background, large sheets of density 2 atoms cm-3, clouds occurring mostly in groups, and ‘Cloudlets’ of a few solar masses and a few parsecs in size; the velocity dispersion in the Cloudlets is only 1 km/sec. Strong temperature variations in the gas are in evidence.
Anomalous OH absorption in the direction of Cassiopeia A
Authors: Rogers A. E. E. , Barrett A. H.
Published: July 2016

At radial velocities around zero, the optical depths in the 1665- and 1667-MHz OH absorption lines in the spectrum of Cas A are in the expected ratio, 5 : 9. In both lines, the zero-velocity component is split into two clearly-resolved features. However, neither the 1612- nor the 1720-MHz lines shows any splitting. Absorption in the 1612-MHz line is stronger than expected, while the 1720-MHz line shows evidence of emission.
The radial velocity of the Orion Nebula from radio observations
Authors: Menon T. K.
Published: July 2016

Recent radio measurements in the 109 α line, together with earlier optical data, indicate that the Orion Nebula moves away from the Orion Nebula Cluster, towards the observer, at 8 km/sec. The paper discusses briefly the associated problems of the time scale, the origin, and the energy source of the nebula.