bluuebunny/crossref_metadata_2025_split huggingface dataset:
SOME COMMENTS ON A CATALOGUE OF ATMOSPHERIC PARAMETERS AND [Fe/H] DETERMINATIONS
Authors: de Strobel G. Cayrel 
Published: July 2016

A few examples are given showing the utility of the catalogue of iron/hydrogen determinations for astrophysical researches. These are:
(a)Histograms of dwarfs and giants analyzed in detail with spectral type between O and M.(b)Logarithmic abundances diagrams of given stars.(c)The impact on spectral classification of high-dispersion-detailed-analysis results.(d)The use of well-determined chemical and physical parameters of nearby stars for the construction of HR diagrams in the (Mbol –log Teff) plane.The spectra of F, G and K stars having the iron lines at their best visibility, special emphasis has been given to the results concerning these stars.
The Bonner Spectral Atlas and Three-Dimensional Classification at Low Dispersions
Authors: Seitter W. C. 
Published: July 2016

Work on the third part of the Bonner Spectral Atlas: Peculiar Stars has well progressed during the past year. Observations of the more than 200 stars – photographed with a dispersion of 240 Å mm−1 at Hγ on I-N plates – is nearing completion.The arrangement of the spectra will be as follows:
1.WR-stars2.O-stars Of sequence3.Peculiar B-type stars emission-line objects4.Ap-stars with various sequences: Cr-Mn-Hg-rare earths5.Asi-stars6.Am-stars7.Late-type peculiar stars Ba II, CH8.C-stars9.Late M-type stars10.S-stars11.Composite spectra12.Spectra with large rotational broadeningThe 12 groups are displayed on 40 plates, each with 6–8 objects. Stars of groups 8 to 10 will be presented with different exposures in order to facilitate the discovery of faint objects.Sample plates will be shown and discussed.
Cometary volatiles
Authors: Bockelee-Morvan D. 
Published: July 2016

Comets are believed to be the most pristine material surviving from the origin of the Solar System. The nature of their volatiles should in principle provide chemical and physical clues to their formation environment in the solar nebula. Another important aspect of the study of comets is the extent to which they may incorporate relatively unprocessed interstellar material.Our knowledge of the composition of cometary ices has been greatly improved in this last decade. The years 1995-1996 were rich in new results, with the close approach to Earth of comet C/1996 B2 Hyakutake and the discovery of the bright comet C/1995 O1 Hale-Bopp at large heliocentric distance. We will present the current knowledge of the nature and abundances of cometary volatiles and mention some of the outstanding issues related to the origin of comets and their links to interstellar material.
New Observational Data Concerning 4 Her and ζ Tau
Authors: Harmanec Petr , Koubský Pavel , Krpata Jiří , ŽĎárský František 
Published: July 2016

Rectified intensity profiles of the Hα and Hβ Balmer lines of the shell star 4 Her were studied on 86 coudé spectrograms taken during 1969–1974. The central intensities of both lines vary periodically with the period of velocity changes equal to 46.194 days, reaching two maxima and minima each cycle. Radial-velocity curves of individual Balmer lines differ systematically one from another, the amplitude of the Hα variations being largest. The V/R ratio of the Hα emission peaks varies in phase with the velocity changes. The velocity of the Hα emission is found to be almost invariable. A model is suggested to explain the observed variations in which 4 Her is considered to be an interacting binary. The full paper will appear in Bull. Astron. Inst. Czech.27, No. 1 in 1976.Radial velocities of high-dispersion spectrograms of ζ Tau, obtained mostly during the last observing season, indicate the following facts: (1) Several distinct velocity systems are present in the Balmer lines, not a continuous progression. (2) The main absorption component of the Hα line does not share the long-term velocity variations, its velocity being always rather close to the systemic velocity + 22 km s−1. (3) The pseudoperiod of the long-term velocity variations has changed and is probably decreasing.
On the Detection of Binary Be Stars
Authors: Polidan R. S. 
Published: July 2016

Possible methods for detecting the presence of a cool companion to a Be star are discussed. Photometric observations are shown to be incapable of detecting companions in all but the most extreme cases. Spectroscopic investigation is also unlikely to yield many new discoveries. It, however, remains the most promising method for the detection of binary Be stars. The four known binary Be stars are also discussed.Infrared calcium triplet emission in Be stars is discussed in detail. The lines are shown to originate in a region of large optical thickness and low temperature (T ~ 5000 K). The possible connection between the presence of calcium triplet emission and binary nature is briefly discussed.
The Cause of the Nova Outburst
Authors: Starrfield S. , Sparks W. M. , Truran J. W. 
Published: July 2016

We have evolved a large number of models of thermonuclear runaways in the hydrogen-rich envelopes of 1.00 M⊙ carbon-oxygen white dwarfs. Models characterized by enhanced CNO abundances satisfy the observations of the common nova outburst. They eject from 1027 to 1029 g moving with velocities of 200–2400 km s−1: kinetic energies of 1044 to 1045 erg. The theoretical light curves are similar to the observed light curves of common novae during the early stages of the outburst. As a consequence of our studies, we can present an explanation for the continuous ejection of mass which is observed for long times after the initial outburst and for the relationship between maximum magnitude and the decline to minimum. We are also now able to present an explanation for the constant luminosity phase of the outburst and the oval shapes of the ejected nebulae.We have extended our earlier work to models with extreme enhancements of 12C and to models which include the infalling material in the evolution. The extreme 12C studies result in outbursts which reach near supernova proportions while the accretion models result in light curves which resemble observed light curves quite closely. Finally, the accretion studies also demonstrate the need for enhanced abundances.
Rotational Angular Momenta of Close Binary System Components
Authors: Ureche V. 
Published: July 2016

The ratio between rotational angular momentum, Jrot, and orbital angular momentum, Jorb, in close binary systems and its variation with mass ratio is studied. The tables and the graphs give this variation for detached systems, contact systems, semidetached systems and for systems containing a supernova-remnant component and a contact component. For this study some statistical relations of close binary stars were used.The ratio Jrot/Jorb is sensitive to the variation of the mass ratio q. If q differs much from unity and if the concentration of the stellar matter is moderate (polytropic index n ~ 3), the neglect of rotational angular momentum, Jrot, is not justified.
The Origin of the RS CVn Binaries
Authors: Biermann P. , Hall D. S. 
Published: July 2016

We consider six possible origins for the RS CVn binaries based on the following possibilities. RS CVn binaries might now be either pre-main-sequence or post-main-sequence. A pre-main-sequence binary might not always have been a binary but might have resulted from fission of a rapidly rotating single pre-main-sequence star. The main-sequence counterparts might be either single stars or binaries.To decide which of the six origins is possible, we consider the following observed data for the RS CVn binaries: total mass, total angular momentum, lack of observed connection with regions of star formation, large space density, kinematical age, and the visual companion of WW Dra. In addition we consider lifetimes and space densities of single stars and other types of binaries.The only origin possible is that the RS CVn binaries are in a thermal phase following fission of a main-sequence single star. In this explanation the single star had a rapidly rotating core which became unstable due to the core contraction which made it begin to evolve off the main sequence. The present Be stars might be examples of such parent single stars.
Dynamical interpretations of the galactic center region
Authors: Sanders Robert H. 
Published: July 2016

I will define the central region of the Galaxy as being the inner four kiloparsecs. The distinguishing characteristics of this region are:
1)The dominance of a central spheroidal component in the mass distribution – a bulge.2)An apparent deficiency of gas, at least between radii of 500 pc and 4000 pc.3)High non-circular gas velocities. Now let us consider these characteristics in some detail.
Identifications from the WSRT Deep Surveys
Authors: Katgert J. K. , de Ruiter H. R. , Willis A. G. 
Published: July 2016

The WSRT yields samples of radio sources which are well suited for systematic identification work for the following reasons:
a)The surface density is high: at 1415 MHz an average of 10 to 30 sources can be detected within 0°.55 from the field centre; at 610 MHz the numbers are 40 to 100 within 1°.0. In any given field, most sources will fall within the boundaries of plates for the present generation of optical telescopes.b)The positional accuracy is, on the whole, rather high. One can thus propose identifications based on positional agreement only, avoiding selection effects present when selecting “on type”.
Evolution of Stars with M8 M⊙
Authors: Massevitch A. G. , Tutukov A. V. 
Published: July 2016

A review of research in the field of evolution of massive stars during the last three years is presented. The analysis of computed stellar models in the helium-burning stage provides evidence for the existence of neutrino emission predicted by the theory of universal Fermi-interaction. The criterion for convective stability in the zone of variable molecular weight still remains uncertain despite several possibilities for a unique choice of the stability criterion that were recently suggested.Evolutionary computations of massive star models in the carbon, oxygen, neon and silicon-burning stages provide opportunities to obtain models of presupernovae of different types and to investigate the cause of instability responsible for the implosion as a function of the initial mass of the star.If the neutrino emission is included in computations the core of a star with M≳90 M⊙ loses stability due to the positron-electron pair formation in the oxygen-burning stage. A star with 16 M⊙ ≲ M ≲ 90 M⊙ collapses because of photodissociation of the iron nuclei but a core of a star with 9 M⊙ ≲ M ≲ 16 M⊙ collapses due to neutronization of silicon or iron nuclei.Attention is paid to the possibility of circulation mixing of matter within the boundary of a carbon-oxygen core, due to the fast rotation of the core in advanced stages of evolution, if the angular momentum is conserved in the course of evolution. As the molecular weight barrier is low in late stages of chemical evolution, it can not prevent the penetration of circulation flows outside the convective core.Difficulties of the present theory of convection in stars are stressed and the necessity of a two-dimensional approach to the solution of the stellar constitution equations is emphasized.
20. The ablation of solid meteoroids
Authors: Kaiser T. R. , Jones J. 
Published: July 2016

Ablation profiles for compact meteoroids have been obtained which take account of the effects of thermal radiation, conduction, meteoroid heat capacity and deceleration, while retaining the simplifying assumption that the onset of massive ablation occurs at a well-defined temperature.The dependence of the air density, ρa, at the onset of ablation on the initial meteoroid radius, R0, is in agreement with the results of Ceplecha and Padevět (1961). For a meteoroid of given composition, velocity and zenith angle there are four critical values for the radius, R1, R2, R3 and R4. R1 is the micrometeorite limit such that if R<R1, the ablation temperature is not reached. For R1<R<R2 the onset of ablation is delayed due to thermal radiation and occurs at air density ρa1, which is substantially independent of radius. If R2<R<R3 the delay in onset of ablation is due to the finite heat capacity of the meteoroid; it occurs at an air density ρa2, which is proportional to R0, i.e. to m01/3, where m0 is the initial mass. If R > R3 the meteoroid develops a marked thermal gradient and, if it is brittle, will fragment before ablation commences. The smallest fragments will ablate at the air density ρa1, which is shown to be close to the experimental result of Jacchia et al. (1967) for photographic meteors. If such a particle survives fragmentation, the molten droplet will fragment due to distortion if R > R4 (Lebedinec and Portnjagin, 1966); it is shown that R4 is not substantially different in magnitude from R3. Meteoroids in the size range R2<R<R3 produce underdense meteor trains and experimental measurements of echo decay as a function of echo amplitude are in agreement with the expectation that ρa2 ∝ m0n where n ~ 1/3 (Poole and Kaiser, 1967). This would support the view that the bulk of radio meteors are produced by compact particles and that the fragmentation observed with photographic meteors may be a result of thermal shock.The ablation profiles have been computed for initial meteoroid velocities between 20 and 70 km sec−1 and radii between R1 and R3; the deceleration and residual size (at the end of ablation) have also been calculated. Even quite close to the micrometeorite limit, the residual particle is small compared with the initial size. Hence, meteoroids with R > R1 will make negligible contribution to the micrometeorites reaching the Earth's surface, except, perhaps, where a significant proportion of the mass of larger meteoroids fragments into particles with radius less than R1. By neglecting deceleration, it is possible to arrive at an analytic expression for the ablation profile; this is found to be in good agreement with the computed profiles except for particles near to the micrometeorite limit.
41. On the width of the Geminid shower at faint radio magnitude
Authors: Forti G. 
Published: July 2016

A search for major streams has been performed among the orbits of meteors observed with the six station meteor radar of the Harvard-Smithsonian Radio Meteor Project at a limiting radio magnitude of about + 10 on the visual scale.The analysis of the Geminid shower from observations made in December 1961, 1962, 1963 and 1964, shows some evidence that meteors belonging to this stream are detected at an earlier date than the bright photographic meteors. From observations made on December 28–31 of the same years during the hours in which the Geminid radiant is within the collecting area of the six station system, 15 orbits were identified as possible members of the shower.It is suggested that the stream might be active for a period longer than the previous observations indicated.
Planetary Nebulae as a Part of the Galaxy
Authors: Perek L. 
Published: July 2016

Planetary nebulae form one of the most important subsystems of the Galaxy. If we knew more about this subsystem, an important gap in our ideas about the galactic structure would be filled. Very briefly, we are facing the following situation:Population I, which contributes to the total mass of the Galaxy by hardly more than 7 %, can be tracked almost over the entire Galaxy thanks to the radio observations of neutral hydrogen at 21 cm wavelength. Other data, for a wide solar neighbourhood, follow from observations of Cepheids and early-type stars.
The Atmospheres and Spectra of Central Stars
Authors: Böhm K.H. 
Published: July 2016

After a brief discussion of the determination of the effective temperature, the surface gravity and the chemical composition of the central stars, we describe the typical problems arising in the computation of static and dynamical models of the very hot atmospheres of these objects. Special attention is paid (1) to the strong non-greyness of the atmosphere, (2) the electron-scattering contribution to the source function, (3) the contribution of the higher ions of C, N, O and Ne to the absorption coefficient, (4) the importance of radiation-pressure effects. The application of the computed energy distribution to the determination of the ionization stratification of the nebula and to the calculation of the bolometric correction is discussed.A formation of emission edges due to the Schuster effect does not seem to occur in any of the static non-grey model atmospheres which have been computed so far. The reason is that the steep temperature gradient in the uppermost layers of these models strongly favors the formation of absorption edges. Using very simple dynamical models by Schmid-Burgk (1967) we discuss the possibility of a considerable flattening of this temperature gradient by a hydrodynamic outflow driven by radiative acceleration. We argue that the Schuster effect may be much more important, if these atmospheres are not in hydrostatic equilibrium.The position of central stars of different spectral type in the Teff-g plane is discussed.
A Method of Determination of the Temperature of Nuclei of the Planetary Nebulae
Authors: Khromov G.S. 
Published: July 2016

I would like to make a few comments on the problem of the determination of the temperatures of nuclei of planetary nebulae.It can be shown that in a high-excitation planetary nebula two independent Strömgren zones of heavy elements can be found. The first is a He III zone; the second corresponds to a zone of the luminescence of Ne V forbidden lines and originates due to combined absorption by the heavy ions Ne IV, O V and N V. If so, a relatively independent method of the determination of the color temperature of nuclei can be suggested.
Long-Period Variables and Planetary Nebulae
Authors: Menzel Donald H. 
Published: July 2016

The occasional appearance of a red giant or long-period variable in planetary nebulae poses a problem for theoretical astrophysics. Such a cool nuclear star would not ordinarily provide a source of ultraviolet radiation necessary for the excitation of the spectrum of a gaseous nebula.One possible solution of this problem postulates the existence of intense magnetic fields in the star. Second, the star itself has a structure resembling that of a miniature, highly compressed planetary, with a high-temperature nuclear star at the centre and a distended atmospheric shell enveloping chiefly the stellar equator.The magnetic field induces a sort of pumping action that creates the tire-shaped envelope from matter ejected near the poles. As this shell grows denser, it radiates like a stellar photosphere at low temperature. Eventually the shell becomes unstable and disperses outward to form and maintain the nebula. A quasi-periodic situation occurs, which explains the variation of light. Ultraviolet light absorbed during the minima, when the shell has vanished, adequately accounts for the nebular excitation. A wide variety of such symbiotic stars occurs, including repeating novae as well as the long-period variables.
Evolution of Ca plages of the CSSAR active regions
Authors: Godoli G. , Monsignori Fossi B. C. 
Published: July 2016

For each plage of the CSSAR period the daily projected areas have been determined and plotted versus time. Also the correction for foreshortening has been taken into account.Daily fluctuations, of the plage corrected areas, certainly greater than the errors, have been found. Also area fluctuations of shorter periods have been observed.
A model of solar flares
Authors: Sturrock P. A. 
Published: July 2016

A model of solar flares is proposed in which the preflare state comprises a bipolar magnetic-field structure associated with a bipolar photospheric magnetic region. At low heights, the magnetic-field lines are closed but, at sufficiently great heights, the lines are drawn out into an open structure comprising a bipolar flux tube containing a ‘neutral sheet’ or ‘sheet pinch’. Such a sheet pinch is probably related to a coronal streamer. The energy stored in the closed-field region is derived from photospheric motion whereas energy stored in the open-field region is derived from the non-thermal energy flux which heats the corona and drives the solar wind.The flare itself is identified with reconnection of magnetic field by the tearing-mode resistive instability. If the thickness of the sheet pinch is determined by resistive diffusion and a growth time of the bipolar region of order 1 day, the transverse dimension will be about 104 cm. The rise time of the tearing-mode instability is then a few seconds, compatible with the characteristic time of Type-III radio bursts. One can understand that the time-scale of the reconnection process is of order 102–103 sec if reconnection proceeds by the Petscheck mechanism, with the modification that resistive diffusion is replaced by the more rapid Bohm diffusion.The evolution of a flare, according to this model, appears to fit a number of the observational characteristics of flares.
Homology of solar radio events
Authors: Fokker A. D. 
Published: July 2016

Successive flares within the same centre of activity sometimes produce radio events that are remarkably similar. The occurrence of such homologous radio events is commonly restricted to periods of less than 48 hours.Typical for certain centres of activity is their tendency to give rise to impulsive microwave bursts. Such bursts may occur repeatedly during a period of more than a week. The distributions of the lengths of periods during which series of homologous bursts and of impulsive microwave bursts occur are compared.
Sunspot Magnetic Fields and High Energy Electrons in Flares
Authors: Takakura Tatsuo 
Published: July 2016

A balloon observation of an impulsive hard X-ray burst on September 27, 1969 showed the size of the source to be one arc minute or less. It was remarkably smaller than the associated Hα flare with a size of 3 arc min.The efficient acceleration of electrons and the trigger of the flares are suggested to be attributed to a large scale electric potential field caused by a gas motion near the photosphere. The primary cause of the onset of flares would be the acceleration of electrons. The electrons excite plasma waves which make the conductivity lower by several orders, so that the electromagnetic energy I2L stored before the onset of the flare would be suddenly converted into the heat due to the ohmic loss.
An Attempt to Associate Observed Photospheric Motions with the Magnetic Field Structure and Flare Occurrence in an Active Region
Authors: Martres M. J. , Soru-Escaut I. , Rayrole J. 
Published: July 2016

We have tried to find empirical evidence for the role of photospheric motions in the building up of the flare productive magnetic patterns in Active Regions.The bright Hα faculae are associated with V∥ structures different from a classical Evershed flow and particularly ‘anomalous’ in the regions and periods of high flare occurrence. The flares observed occurred at ‘crossings’ of the lines V∥ = 0(V ≠ 0) and H∥ = 0 and at places where V∥ = 0 showed abrupt changes of direction. It is suggested that these anomalous V∥ structures are evidence of vortex motions.