bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Slot Gap Model of Pulsars
Authors: Arons Jonathan 
Published: July 2016

A general picture of pulsar magnetospheres is outlined which suggests polar current flow should proceed within a magnetic flux tube with conducting boundaries. The dynamics of this current flow is considered, including the effect of formation of pair plasma on the potential. A slot gap surrounding the stream of pair plasma is described, and the electric fields and J·E work done in the gap are calculated. The inapplicability of curvature emission to the formation of γ-ray pulses is discussed. The dynamics of pair plasma flow is described, including electrostatic trapping of low energy positrons, polar cap bombardment and heating, and the emission of soft X-rays from the cap. The relation of this current flow and polar cap heating to the formation of fluctuations on the radio subpulse time scale is also described. The importance of the boundary layer between the pair plasma and the slot gap is illustrated by calculations of the boundary layer structure and microscopic instability, which show that this region may be the source of pulsar emission.I will describe a number of quantitative results and qualitative aspects of work in progress on the “slot gap” model for the emission regions of a pulsar, proposed by Arons and Scharlemann (1979, hereafter AS) and by Arons (1979b, hereafter I). The results and ideas concern the dynamics and emission physics of relativistic plasma and current flow along the polar field lines of an isolated, rotating magnetized neutron star with the axis of its dipole moment oblique to the rotation axis - a pulsar. The quantitative modelling is confined to the physics within a polar flux tube and is therefore “local”. Full detail will be given in papers now being written. However, development of this type of model requires the use of boundary conditions which follow from a qualitative view of the whole magnetosphere. Because this view involves some qualitative ideas not widely discussed in the literature, I describe it briefly.
18. Model Atmospheres for Hydrogen-Deficient White Dwarfs
Authors: Bues I. 
Published: July 2016

The determination of atmospheric parameters for non-DA white dwarfs is investigated with the computed helium-rich model atmospheres by Bues (1970). Only poor predictions are possible from UBV colors alone for DB and DC stars. From uvby colors a determination of effective temperature is possible within 1000 K. Profiles of lines in different parts of the spectrum are necessary for better results.A deficiency of metal abundances for the cooler non-DA stars is obtained.
19. Convection Zones and Coronae of White Dwarfs
Authors: Böhm K. H. , Cassinelli J. 
Published: July 2016

Outer convection zones of white dwarfs in the range 5800 K ≤ Teff ≤ 30000 K have been studied assuming that they have the same chemical composition as determined by Weidemann (1960) for van Maanen 2. Convection is important in all these stars. In white dwarfs Teff < 8000 K the adiabatic temperature gradient is strongly influenced by the pressure ionization of H, HeI and HeII which occurs within the convection zone. Partial degeneracy is also important.Convective velocities are very small for cool white dwarfs but they reach considerable values for hotter objects. For a white dwarf of Teff = 30000 K a velocity of 6.05 km/sec and an acoustic flux (generated by the turbulent convection) of 1.5 × 1011 erg cm−2 sec−1 is reached. The formation of white dwarf coronae is briefly discussed.
On the Motion of the Equator and the Ecliptic
Authors: Fricke Walter 
Published: July 2016

A report is given on work in progress on the available observational evidence for an excess secular change of the obliquity of the ecliptic. Some of the recent determinations suggested that the conventionally adopted value of the secular change requires a correction of the order of per century. Since an error of this size in the adopted motion of the ecliptic must be ruled out, the observed corrections may indicate either a rotation of the equatorial plane with respect to an inertial system about an axis passing through the equinox or the existence of systematic errors of the observations. In following Aoki's suggestion of a real motion of the equator, the averaged proper motions in the systems FK4 and N30 yield a rotation of the galaxy with an angular velocity of 43.6 km s−1 kpc−1 near the Sun and a positive gradient of the circular velocity in the galaxy near the Sun. If the distance of the Sun from the galactic center is 10 kpc, the circular velocity of the galaxy would be 436 km s−1. Should, however, the circular velocity be less than 300 km s−1, the distance of the Sun from the galactic center would have to be smaller than 7 kpc.For the following reasons such far reaching conclusions are not well founded:(1) Fundamental observations of the stars, the Sun and the planets carried out before about 1900 show appreciable systematic deviations from the average of the observations carried out after 1900. The excess secular change of the obliquity is suspected to be the consequence of systematic errors of older observations.(2) The determinations of individual values of Δɛ from observations of the Sun and the planets show a steep decrease of Δɛ from about 1780 to 1900; the individual values of Δɛ derived from observations after 1900 do not deviate significantly from zero and do not show a significant secular decrease. On the other hand, a small secular decrease cannot be excluded.(3) The first results of determinations of Oort's constant B from proper motions of stars with respect to galaxies do not indicate significant deviations from the results derived on the basis of proper motions measured in the fundamental system.This investigation, which is not yet completed, concentrates on an analysis of fundamental observations of stars, the Sun and planets. From the systematic errors of observations which have contributed to the formation of the FK4 it can already be stated that modern observations cannot exclude the possibility of an excess secular change of the obliquity within the limits of per century and, consequently, the possibility of a real motion of the equatorial plane within these limits. It appears, therefore, that Aoki's suggestion deserves further attention, but that its effect on galactic rotation is smaller than was originally assumed.
O and Of Stars
Authors: Conti Peter S. 
Published: July 2016

My intention here is to discuss the ‘high temperature’ portion of this symposium and call attention to those stars that are called Of. There are some similarities in spectral appearance to WR stars, e.g. emission lines. I should first like to define what I think are the essential differences among four groups of hot stars;O stars: Stars that have only absorption lines in the visible spectrum. Type O is distinguished from type B by the presence of He ii 4541 at MK dispersion. It may be that some (supergiants) O stars will have emission lines in the rocket UV region but this description will be primarily concerned with ground based observations.Of stars: These are O type stars that also have λλ 4634,40 N iii in emission above the continuum. In addition to normal O star absorption lines and N iii emission, they may also have other lines in emission. I will discuss this further below.Oe stars: These are O type stars that have emission in the hydrogen lines (or at least at Hα), but with no emission in N iii or in other lines. I personally think that this small class of objects is related to the Be stars in their evolutionary status and in their emission mechanism.WR stars: These stars are primarily characterized by emission lines. The only absorption lines seen are violet shifted (P Cyg type). Although in some cases emission lines appear which are similar to those found in some Of stars, the latter types always have some unshifted absorption lines present. Several Of stars have P Cyg profiles in some lines.
Applications of the UB1B2V1G Photometric System
Authors: Golay M. 
Published: July 2016

This photometric system which was described for the first time in 1963 by Golay has been in use at the Geneva Observatory since 1959. We are involved in a long term observational programme having as objective the study of cluster stars, peculiar stars and interstellar extinction. This research aims at the determination of physical parameters such as effective temperature, gravity, abundance, or those of spectral type, absolute magnitude, [Fe/H]. To permit such an analysis the photometric effects of rotation, of multiplicity and of interstellar extinction were given particular attention. Attempting to attain the above mentioned purposes, we have had to give great care to the precision of the measurements during their acquisition as also during their reduction. Finally, in view of allowing a valid comparison between observations and the theory of stellar atmospheres, particular care had to be given to the maintenance of the pass-bands and to the knowledge of their form.We intend here to give the main bibliographical references relative to the articles which present the general properties of the system, its applications and the catalogues.
Narrow Band Photometry of Supergiant Stars
Authors: Mendoza V. E. E. 
Published: July 2016

At the National Astronomical Observatory in San Pedro Mártir, B. C. (Mexico), we have performed photoelectric photometry for 31 stars in a narrow-band system. The system allows the measurements of total absorptions of neutral oxygen at 7774 Å through three interference filters (20–25 Å half-width), one for the OI lines and two for the continuum.The preliminary results are very encouraging: Supergiant stars, ranging in spectrum from the later subdivisions of type B to early G, can be clearly separated from other luminosity classes. The total absorptions depend strongly on the stellar luminosity and, to a lesser degree on the effective temperature (spectral type) of the star. The system may be improved by using narrower filters and detectors with a higher quantum efficiency, already in existence.
Two Dimensional Spectral Classification of Early Type Stars by Low Dispersion Spectrophotometry
Authors: Gutiérrez-Moreno A. , Moreno H. 
Published: July 2016

Spectrophotometric data of early type stars (spectral intensity distributions from 3100 to 6000 Å and equivalent widths of Hβ, Hγ and Hδ) have been analysed, looking for the best parameters for a two dimensional spectral classification. It was found that the best correlation with MK classification is given by the equivalent width of Hβ and the Balmer discontinuity.The classification scheme is well defined for stars from B0 to A1 of luminosity classes V to III. No stars of luminosity class II were observed. Luminosity class I is clearly separated from the less luminous stars, but the number of supergiants observed is too small to give a clear separation of spectral types.
Discussion of Observations of the Flow of Matter Within Binary Systems
Authors: Batten Alan H. 
Published: July 2016

Observational determinations of density, dimensions, temperatures, and velocities of circumstellar features are surveyed and discussed, with a view to establishing limiting values that could be useful in any theoretical treatment of circumstellar structure. Densities of the order of 1013 particles cm-3 are found for streams and disks, although there is evidence for regions of much lower density in many systems, and some systems may have much denser circumstellar matter.Dimensions of disks seem to be remarkably constant (fractional radius ∼ 0.3) in a wide variety of systems. The total mass of circumstellar matter is always a small fraction of the mass of the system. Temperatures are usually similar to the temperatures of the stars in the system, although hot spots certainly exist in some systems, and ‘flare’ activity is evidence of localized very high temperatures. On the other hand, some systems may contain solid circumstellar matter. Observed velocities are usually several hundred km s-1. The empirical relation between the velocity of rotation of disks and the orbital period is described. Finally, the stability of these features is briefly discussed.
Evolutionary Aspects of Circumstellar Matter in Binary Systems
Authors: Plavec Miroslav 
Published: July 2016

Several groups of close binary stars are considered in an attempt to explain their present state as a consequence of a large-scale mass transfer or mass loss in the past: Algol-like semidetached binaries, some shell stars (AX Mon), some binary X-ray sources (Cen X-3, Her X-1), the recurrent nova T CrB, helium-rich binaries v Sgr and KS Per, and the symbiotic variables.Algol-like binaries like U Sge cannot be products of a conservative case A of mass transfer; rather, mass loss from system and/or a temporary contact stage must be invoked. Nova T CrB as well as the symbiotic variables probably contain a mass-losing giant and a helium star, which again may be a product of a previous mass transfer of type B. Similarly, some of the X-ray sources may actually be binaries undergoing a second process of mass transfer. The systems v Sgr and KS Per may contain helium stars expanding to the right of the helium main sequence, while the other component may be a rather inactive main-sequence star. Some shell stars may be products of mass transfer. Mass loss from convective envelopes is also discussed.Loss of mass and of angular momentum from many binary systems must be anticipated. Behavior of the mass-accreting stars may often be decisive for the appearance and evolution of the system.
Simultaneous X-Ray, Optical and Radio Observations of Galactic X-Ray Sources
Authors: Hiltner W. A. 
Published: July 2016

Simultaneous observations of the X-ray source Sco X-1 are reviewed and discussed. Several conclusions can be drawn from the observations. (a) There is no correlation of the radio intensities with either the optical or X-ray intensities. (b) The X-ray intensity is high and variable only when the blue optical magnitude is brighter than 12.6–12.7. (c) There is often correlation of X-ray and optical flares, but the relationship is not one to one.Attention is called to the paucity of simultaneous observations of other identified X-ray sources.
Structure and motions in the interstellar medium (Introductory Report)
Authors: van Woerden Hugo 
Published: July 2016

This review summarizes information obtained from studies of dark matter, of optical interstellar absorption lines, and of the 21-cm line observed in absorption and in emission.Great improvements in the velocity resolution of interstellar lines (Section 4) are making possible a detailed analysis of their component structure, and determination of the internal motions in the clouds. The 21-cm absorption spectra of strong radio sources (Section 5) have yielded statistics of the optical depths and the internal velocity dispersions of absorbing clouds. Studies of the 21-cm line in emission (Section 6) supply a wealth of data on internal motions in the clouds. Comparisons of Gaussian component parameters at neighbouring positions allow delineation of cloud boundaries on the sky, but estimates of size and mass depend on (usually unknown) distance. The Green Bank telescope has revealed the existence of ‘cloudlets’ containing a few solar masses within a volume of about 5 pc diameter.Structural details in the interstellar medium show a wide variety of size, density and mass. Recent studies tend to emphasize the smaller and thinner structures. The external cloud motions are best approximated by an exponential velocity distribution, with a root-mean-square velocity of 7 km/sec in one coordinate. Internal motions within the clouds probably have Gaussian distributions, with velocity dispersions ranging from o·6 to possibly 7 km/sec; part of these may be due to non-thermal mass motions.
On Petschek's mechanism for dissipating interstellar magnetic fields
Authors: Wentzel Donat G. 
Published: July 2016

Petschek's solution for the hydromagnetic flow at a magnetic neutral plane is applied to the interior of interstellar clouds. The stationary flow between the opposed magnetic fields involves a streaming speed of about 3 km/s and a gas density of roughly 102atoms/cm3. At most one-tenth of all the gas resides in these streams, but their low temperatures should make them observable in absorption at 21 cm; they may even dominate the interstellar absorption lines of Ca+and of Na, since the abundance of these absorbing ions, proportional to the recombination rate of the dominant ions with electrons, depends on the square of the gas density. Optical and 21-cm lines may, therefore, represent somewhat different samples of the interstellar velocity and density distributions.In analogy to the geomagnetic field, which is separated from the interplanetary field, interstellar clouds may be separated from the general galactic magnetic field. Such magnetic bubbles can move through the galactic field without twisting it, but they can maintain their identity only if they contain a twisted magnetic field. This field leads to the operation of Petschek's Mechanism and makes these clouds prominent in the optical absorption lines. A full evaluation of Petschek's Mechanism must involve some plasma instability to reconnect the lines of force.Details of this work have appeared elsewhere (Wentzel 1966).
Interstellar gas in the central region of the Galaxy
Authors: Kerr F. J. 
Published: July 2016

A review is given of information on the galactic-centre region obtained from recent observations of the 21-cm line from neutral hydrogen, the 18-cm group of OH lines, a hydrogen recombination line at 6 cm wavelength, and the continuum emission from ionized hydrogen.Both inward and outward motions are important in this region, in addition to rotation. Several types of observation indicate the presence of material in features inclined to the galactic plane. The relationship between the H and OH concentrations is not yet clear, but a rough picture of the central region can be proposed.
Radio-frequency emission from supernova ejecta
Authors: Colgate S. A. 
Published: July 2016

A new mechanism is proposed for non-thermal radio emission, which depends upon the scattering of photons within an unstable counter-streaming plasma. This mechanism may play a dominant role in several phenomena:(i)the short-wave emission from quasi-stellar sources;(ii)the emission from symmetric supernova nebulae in the early stages of the nebular expansion;(iii)maintenance or modification of the 3 °K black-body background radiation of the Universe.
The latitude variation of water vapor on Mars
Authors: Tull Robert G. 
Published: July 2016

Spectra of Mars, centered on the 8200 Å band of H2O, have been obtained using the coudé spectrograph of the 107-inch telescope at McDonald Observatory with reciprocal dispersion of 1.9 Å/mm. The plate scale (4.4 arc sec/mm) and angular resolution (3″–6″) were sufficient to measure the strength of the Doppler-shifted H2O lines at 5 points across the disk.The spectra were obtained in March and April 1969, when the apparent diameter of Mars was 10″ to 16″ during mid-summer of the northern hemisphere; the Doppler shift at 8200 Å varied from –0.42 Å to –0.28 Å. On the first plate, obtained on March 27, 1969 the abundance reached a maximum of about 48 μ precipitable H2O at 30° to 40° north latitude and decreased to about 20 μ at 30° south latitude. The second plate, taken on April 28, 1969 showed the same north-south decrease in abundance but the total amounts were about two-thirds of the March abundances.
The Use of Silicium Solid-State Detector in Solar X-Ray Measurements
Authors: Valniček B. 
Published: July 2016

The silicium solid-state detector has been used as control-detector in the X-ray photometer system on board of the satellite Interkosmos 1.The effectiveness of the use of such detector as control-unit for radiation-belts has been confirmed also as independent indicator of high energy X-ray quants during high levels emission of solar active regions.
Attempts to Observe the Absolute Intensity and the Centre-to-Limb Variations of the Sun in the Vacuum Ultraviolet Region
Authors: Nishi K. , Suemoto Z. 
Published: July 2016

Calibration for two rocket-borne spectrometers to observe the absolute intensity and the centre-to-limb variations of the Sun between 1500 Å and 2000 Å is described. The procedure of the calibration is divided into two parts, (a) the measurements of the transmission of the spectrometers, and (b) the absolute detector calibration.The double dispersive spectrometer has been planned to be launched in September 1970, but it was postponed until the coming winter, and the single dispersive spectrometer will be launched in January 1971.
Recent developments in stellar dynamics
Authors: Contopoulos G. 
Published: July 2016

In the Introduction, the main trends of present-day stellar dynamics are described, namely the application of numerical experiments and the renewed interest in then-body problem, that brings stellar dynamics close to celestial mechanics.Then a number of new results concerning applications of the third integral are described: (a) The “tube” and “shell” orbits are explained as due to near commensurabilities in the unperturbed frequencies along the directionsxandy.(b) In non-smooth potentials, in the form of waves or hills superimposed over a smooth potential, the transition from isolating to quasi-isolating and ergodic integrals is described. (c) The non-ergodic character of the non-linear system described by Fermi-Pasta-Ulam is explained.
Lunar Occultations: From Past to Future Achievements
Authors: Richichi A. 
Published: July 2016

For several decades, lunar occultations have represented a powerful and productive technique for high angular resolution investigations of a broad class of astronomical sources: from stellar angular diameters to close binaries, from circumstellar shells to the Galactic Centre.The resolution and sensitivity offered by lunar occultations still compare favorably with the capabilities of other more modern methods in the optical and near-infrared. A remarkable fact, when one considers that during the past 20 years practically nothing or very little has changed in the way we observe lunar occultations: a sharp contrast with the impressive technological and scientific advancements of other techniques.The novel possibility of using small areas of fast-readout, low-noise array detectors to record lunar occultations, however, is about to bring radical improvements. We discuss the impact of such detectors on the efficiency of observation and the gain for what concerns the resolution and sensitivity of lunar occultations measurements. New applications such as wavelength-resolved observations and investigations of low-contrast extended sources appear particularly interesting.
Molecular Cloud Structure in the Magellanic Clouds: CO-to-H2 Conversion Factor
Authors: Pak Soojong , Jaffe D. T. 
Published: July 2016

In the Milky Way, the 12CO J = 1 → 0 line traces the molecular gas content. The conversion factor, XGAL, between the H2 column density, N(H2), and the velocity integrated intensity of CO, I(CO), has been measured via the virial theorem or via γ-ray emission (Solomon et al. 1987; Bloemen et al. 1986; Digel et al. 1997; and references therein).How can we apply XGAL to other galaxies where the metallicities are different from that of our Galaxy? The metallicity dependence of the conversion factor has been an issue. Cohen et al. (1988), Wilson (1995), and Arimoto, Sofue, & Tsujimoto (1996) argued that the value of X increases as the metallicity of the individual galaxy decreases. In contrast, Taylor, Kobulnicky, & Skillman (1996) showed that some low abundance galaxies have lower X.