bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ry Sgr: Can the time of the Next Deep minimum Be Predicted?
Authors: Menzies J W 
Published: July 2016

AbstractThe L magnitude of the RCB star, RY Sgr, varies with an amplitud of up to 2.0 mag on a time scale of about 1500 days. The last two deep optical minima have occurred approximately one year after a maximum in L. This behaviour may be characteristic of the star and may allow the time of onset of the next deep minimum to be predicted, in which case it will occur in the second half of 1986.
Hydrogen Deficiency in Algol Secondaries
Authors: Nagar Praveen , Abhyankar K.D. 
Published: July 2016

AbstractA study was carried out for 309 Algol systems to show that most of the secondary components of low mass-ratio systems are hydrogen deficient stars. This hydrogen deficiency is evident from their positions on a Δ log L - Δ log T plot, where Δ is the difference between the observed quantity, log L or log Te, and the value of the same quantity for a star of the same mass on the empirical Main Sequence. The secondary components are shown to occupy the region of mass losing helium dwarfs on this plot. A correlation has also been obtained between the excess of effective temperature and the mass ratio of the system.
Theory of Dust Formation in R Coronae Borealis Stars
Authors: Fadeyev Yu. A. 
Published: July 2016

AbstractApplication of the homogeneous nucleation theory to the problem of R CrB stars shows that the radial distance of the inner boundary of the carbon supersaturation region is at about 12 photospheric radii for a stellar effective temperature Te = 6000 K. Formation of an optically thick dust shell becomes possible at mass loss rates Ṁ ≳ 10−6 M⊙/yr. However, the upper limit of this mass loss rate cannot considerably exceed 10−5 M⊙/yr since, at higher Ṁ, the theoretically predicted rate of the visual brightness decline is larger than that derived from observations. Comparison of the theoretically predicted radii of dust grains with those observed in R CrB and RY Sgr shows that the mass loss rate in these stars should be in the range of 1 × 10−7 M⊙/yr to 3 × 10−6 M⊙/yr.
On the Origin of Helium Rich Stars
Authors: Tutukov A. 
Published: July 2016

Abstract:The modem theory of stellar evolution leads to several possible scenaria for the formation of many types of hydrogen deficient (usually helium rich) stars. Some of these scenaria are briefly discussed in this paper to provide possible explanations for origins of R Cr B, hot helium and Wolf-Rayet stars; hot sub dwarfs, non-DA degenerate dwarfs and helium stars in binaries like KS Per. The merger of two degenerate stars in close binaries due to the radiation of gravitational waves can lead to several types of helium and carbon rich stars as well as to supernova explosions.
Model Atmospheres and Radiative Transfer in Chemically Peculiar Stars: Interpretational Significance of Non-LTE
Authors: Hubený I. 
Published: July 2016

One of the main problems in studying chemically peculiar (CP) stars is the question of the extent to which the conceptual framework of the contemporary spectroscopic diagnostics is reliable. As the first step, it should be clarified whether the traditional assumption of local thermodynamic equilibrium (LTE) provides an adequate approximation to reality, or whether a more general non-LTE approach should be employed.The period of rapid development of computational methods and extensive calculations of NLTE model atmospheres is now past its culmination point. The importance of a relevant NLTE description is viewed as unquestionable for hot stars (B and earlier). Consequently, the hot stars attract the attention of most “NLTE theoreticians,” while considerably less attention is being devoted to later types (late B and A). Moreover, the abundance anomalies found in the CP stars are no longer expected to be a spurious result of an inadequate (LTE) analysis (Cowley 1981). It is not commonly accepted that other phenomena such as diffusion, magnetic field, inhomogeneous abundance distribution, etc., are quite essential ingredients of the general atmospheric pattern of CP stars. Therefore, a large part of the astronomers investigating the CP stars now consider the NLTE effects to be rather minor perturbations of the LTE predictions.
Influence of the Magnetic Field on the Polarization of Radiation Scattered by Electrons in Stellar Atmospheres and Envelopes
Authors: Dolginov A.Z. , Gnedin Yu.N. , Silant’ev N.A. 
Published: July 2016

The radiation scattering by electrons play an important role for stars with the surface temperature ≥ 2.104 °K. Many among these stars have magnetic fields of the order 1 - 100 G. We shall consider the role of the field for the radiative transfer in continuum spectra.Electrons in the field form an axisymmetric medium similar to the single axis crystal. Hence, the medium will have dichroism and birefringency. If the gyrofrequency ωB is much less than the radiation frequency ω then the dichroism can be neglected. The circular birefringency can be characterized by the angle of the Faraday rotation
Missing Levels and Lines of Astrophysical Importance
Authors: Johansson Sveneric , Cowley Charles R. 
Published: July 2016

The purpose of this paper is to make a brief survey of the knowledge of iron group elements as concerns energy levels and transition arrays in neutral and singly ionized atoms and to give rough predictions of missing levels and lines. The amount of data that have been published for these elements after the edition of the Multiplet Tables are considerable. For detailed information about sources of new data and compilations the reader is referred to the Report from Commission 14 in the Transactions of IAU. In this paper we will focus on still missing energy levels and associated missing transitions, which have to be considered in the construction of synthetic spectra.The structure of the iron group elements is complex not only because of the filling of the 3d shell but also because of the competition in binding energy between the 3d- and the 4s electron. For a given number of valence electrons, k, we have to consider three different low configurations in the complex (3d + 4s)k having about the same energy in neutral and singly ionized atoms. In neutral atoms the 3dk−2 4s2 configuration generally occupies the ground state, while the 3dk configuration appears at rather high excitation energy. In the singly ionized atoms all three configurations have about the same energy, giving the most pronounced complexity.
Space Observations of Chemically Peculiar and Related Normal Stars
Authors: Leckrone David S. 
Published: July 2016

AbstractProgress in the spectroscopic study of CP stars and related sharp-lined normal stars from the IUE is briefly reviewed as a preamble to a discussion of the potential for research with the Hubble Space Telescope. The substantial gains in spectral resolution, signal-to-noise ratio and photometric accuracy that will be realized with the High Resolution Spectrograph on the HST will dramatically increase our ability to disentangle the complex ultraviolet spectra of these stars and to carry out accurate quantitative analyses.
Hα and OI Photometry of Upper Main Sequence Stars with Anomalous Abundances
Authors: E. Eugenio , V. Mendoza 
Published: July 2016

AbstractAdditional α(16)Λ(9)-photometry of upper main sequence stars with anomalous abundances confirm our previous results, namely, Ap stars are neatly separated from normal main sequence stars. Furthermore, Ap stars are located on three different zones of the α(16)Λ(9)-plane, according to their abundance anomalies to form three photometric groups, (i) Si stars, (ii) Hg,Mn stars, and (iii) Cr,Eu,Sr stars.
Short-Periodic Radial Velocity Variations of the B9P Star ET and
Authors: Gerth E. 
Published: July 2016

AbstractSpectroscopic observations of the B9p star ET and secured at the Bulgarian National Observatory Roshen in the years 1981–1984, consisting of 97 plates, show clearly a radial velocity period of 0.198 d - with a ratio to the photometrical period of exactly 2:1. This behaviour would hint at a close binary system; but there arise difficulties in explaining it by this way because of the extreme short period, so that pulsation must be taken into account. However, besides of the confident period of 0.198 d, there is evidence for shorter periods in the region of 45 min, which may be attributed only to pulsational processes.
On the Ultraviolet Photometric Variability of the Helium-Weak B Stars (From ANS Data)
Authors: Želwanowa E.I. , Sohöneich W. 
Published: July 2016

AbstractPhotometric observations in the ultraviolet region obtained by the ANS satellite enabled us: to confirm with a slight improvement the rotational period of HD 22470 (UV lightcurves of HD 22470 compared with u and magnetic curves are shown in fig. 1); to confirm the variability with very small amplitudes for HD 74196, a member of the open cluster IC 2391 (Fig. 2)to compare the amplitude-wavelength relations of some other He-weak stars with known periods (HD 35298, HD 142884, HD 144334, HD 175362, and HD 109026). A preliminary rotational period for the star HD 109026 using the 11 ANS observations was found to be about 1.5 days.
A Spectroscqpic Study of the Bp-Star θ Aur
Authors: Kolev D. , Georgeva E. 
Published: July 2016

AbstractThe atmosphere parameters, spectral variability and the magnetic field geometry of the Bp-star θ Aur are evaluated from 30 coude-spectrograms. We adopt Te = 10 800K and lgg = 3.40 (with lower reliability of lg g ) . The equivalent widths of the metalic lines show a relatively great scattering which troubles the period search. The best fit to our data gives the period P = 3.620d, but the variability is clearly seen only for Sill lines. The uncertainties in the star parameters obtained bring to a great uncertainty in the magnetic dipole geometry: i = 86° + 39° and β = 18° + 80°. We adopt the most plausible star parameters to be: R = 3.8R⊙ M = 3.5R⊙, i = 80°, β = 20°, Bp = 1 KGs.
Absorption Lines of Call and H in the Near IR Region of the Magnetic Star HD 152107
Authors: Kuznetsova T.N. 
Published: July 2016

AbstractA behaviour of H lines P12 - P13 and CaII triplet of the star HD 152107 is studied in the range λλ 8400 - 8800 Å. An analysis of the obtained data enabled us to suspect the presence of a relationship between the variation of equivalent widths of the lines of the Paschen series of Hydrogen CaII lines and that of the star’s magnetic field.
Diffusion Processes and Chemical Peculiarities in Magnetic Stars
Authors: Alerian G. 
Published: July 2016

AbstractThis review tries to expose some essential aspects of our current understanding of diffusion processes in magnetic CP stars. Many problems remain to be explained due to the fact that the presence of strong magnetic fields increases the number of free parameters in “diffusion models”. More observational constraints are needed before one can attempt modelling every aspects of magnetic CP stars.
Particle Transport in Non-Magnetic Stars
Authors: Michaud G. 
Published: July 2016

AbstractThe observations of AmFm, λ Booti, HgMn and He rich stars that are explained without any arbitrary parameter by diffusion are briefly reviewed, followed by those observations that are not explained by this simple model. Mass loss is then shown to explain a large fraction of the observations that are not explained in the parameter free model. It seems to play a role in the λ Booti, AmFm, He rich and the hot horizontal branch stars. It is only of about 10−15 to 10−13 Mo/yr. Abundance anomalies then help to determine stellar hydrodynamics. It is finally suggested that recent observations of Li underabundances in F stars of the Hyades represent an extension of the AmFm star phenomenon.
The Map of the Heavens at the Chateau de Saint-Jean-de-Chepy
Authors: Barbier Joël 
Published: July 2016

AbstractIn the Dauphiné, near Tullins, there is a fortified manor-house known as the Chateau de Saint-Jean-de-Chépy, built in the 13th century, that has in one of its towers an Italian Renaissance map of the heavens painted on the ceiling. The south tower could have been designed for astronomy, with the octagonal-roofed, second floor with its seven windows being used for observation. The first and ground floors have hemispherical vaults, and painted on the ceiling of the first floor there is a map of the heavens that is unique in France. It is painted on the ceiling, with the southern constellations extending down onto the cylindrical wall. It is similar to Italian Renaissance maps, like those in the Old Sacristy at San Lorenzo in Florence (painted by Brunelleschi in 1429), in the Villa Farnesine at Rome (Peruzzi, 1511), and in the Villa Farnese at Caprarola (artist unknown, 1575).An owner of Saint-Jean-de-Chépy was Maurice Bressieu (1546–1617), a distinguished mathematician, holding the mathematical chair at the Collège de France between 1575 and 1586. He wrote Metrices Astronomicae, which was “highly regarded by mathematicians” and became Speaker for the Kings of France at the Vatican. Pope Sixtus-Quintus made him steward of the Vatican Library. It therefore seems very likely that the map could have been painted for him.
Amateur Astronomers’ Contribution to the HIPPARCHOS Programme
Authors: Bacchus P. 
Published: July 2016

The HIPPARCHOS satellite (High Precision Parallax Collecting Satellite) is designed to determine position, proper motion and parallax for a large number of stars. The precision expected (0.002 arcsec), and the absence of systematic errors with position in the sky arise from the following characteristics of the system:
–Measurements of angular distances between stars a long way apart (58°), are by comparison with a very stable angular reference. This reference is formed by an optical block consisting of two plane mirrors, rigidly mounted, forming an angle of 29° between them, and sending two separate stellar fields into the same telescope;–the absence of flexure (thanks to weightlessness) and of thermal deformation (non-expansion material and thermal control) ensure that the angular reference is very stable;–operation outside the atmosphere allows the theoretical resolution to be reached; refraction, dispersion and atmospheric scintillation are avoided; diurnal and seasonal effects that interfere with ground-based measurements are non-existent.
The S.A.F. Double Star Section’s Contribution to the INCA-HIPPARCHOS Programme
Authors: Durand P. 
Published: July 2016

The Double Star Section of the Société Astronomique de France has been in existence since 1980. It has set up observing groups covering various areas: close binaries, photographic measurements, re-observation of neglected pairs, and astrolabe measurements. All this has been thanks to our sceintific advisors, professionals specializing in double stars: Muller, Couteau, Soulié, Bacchus, and Dommanget. The Section meets twice a year, and it was at Lille in 1984 that J. Dommanget suggested that we should collaborate in the programme of identifying doubtful doubles for the input catalogue for the future satellite Hipparcos.The first observations were made after the meeting in November 1984, from Paris and with amateur equipment, thanks to an initial list prepared by Prof. Bacchus. After several months we could tell that our equipment was insufficient, and that photocopies of the Palomar Sky Survey were not accurate enough. We needed more powerful instruments and a different organisation to resolve the ambiguity in identification that can arise by two close stars being confused and given the same coordinates, by the presence of a cluster, or by the existence of a faint star that is not given in the catalogues. In all these cases, identifying the star means being able to give it a designation, allowing it to be found on an atlas, and obtaining better coordinates so that the ambiguity is removed. It is a question of astrometry.
A Spectrograph for the T.60 at Pic du Midi
Authors: Bardin Daniel , Buty Didier 
Published: July 2016

For several years now the 60-cm telescope at Pic du Midi has been made available to amateur astronomers. We felt that this telescope, which fulfils its role of gatherering light very well, could be fitted with equipment to analyze light. To this end the members of the Teachers and Astronomers Liaison Committee (which includes one of the authors of this communication) collaborated in producing and perfecting a spectrograph suitable for the T.60.Of basic construction, this equipment enables spectra to be recorded on photographic cassettes. It should be transported to the summit at the end of 1987, and will then be available for any amateur projects that may want to use it.
Amateur Polarimetric Research
Authors: Böhme Dietmar 
Published: July 2016

AbstractThe construction of both single- and twin-channel polarimeters was described. Refractors are suitable for this form of work, and Cassegrains may be used, but Newtonians are not recommended, because of the polarization it introduces. A summary of objects and their degree of polarization was given. Examples of variation in the amount of polarization and its correlation with visual observations of μ Cephei were given.
Astrometric Measurements of Rarely-Observed Minor Planets
Authors: Chanal Roger 
Published: July 2016

AbstractThe 1986 Minor Planet Ephemerides call observers’ attention to the need for astrometric observations of 120 objects on the “critical list”. Their magnitudes are generally between 15 and 18 at opposition. The author’s programme of observation with simple means was described. The equipment used was a Newtonian 41-cm, f/4.8 reflector, a standard camera back, and Kodak TP2415 film, hypersensitized in forming gas. Out of 25 observations attempted, 20 photographs were obtained, 8 of which were of sufficient quality for the positions to be measured and to be published in Minor Planet Circulars. On two photographs, the minor planet (1982 KM) was detected, but there were no suitable reference stars within the field. (The lack of reference stars brighter than mag. 10 in certain regions should be noted.) The return of measured positions versus photographs obtained (40%) appears very acceptable.
The Contribution of Amateur Astronomers to Cometary Observation
Authors: Heck André 
Published: July 2016

Most professional astronomers do not conduct specific comet-discovery programmes and a new comet is, in general, an intrusion into an observational programme, although one that does, of course, receive all the attention it deserves. Comet discoveries are by-products of professional work. This may also be the case with some amateurs (G.E. Alcock discovered his fifth comet while looking for novae). Most amateur discoveries are the result of active and systematic work. Over the period 1951–70, on average 9 comets per year were discovered by amateurs.The time spent scanning the sky before discovering a comet is typically hundreds of hours. The times of W. Bradfield between his first comets were 260, 306, 145 and 106 hours. Astronomers at Skalnaté Pleso discovered eight comets in six years, averaging one comet for 206 hours of searching. R.D. Austin and R. Meier spent 151 and 105 hours, respectively, between discoveries. These figures are only indicators, because many other factors (including luck) play a part. Alcock’s two comets in six days is quite exceptional.
Amateur/Professional Cooperation in 2 Solar Studies
Authors: Roudier T. , Muller R. , Hulot J.C. , Vaissière F. 
Published: July 2016

AbstractThe modification of properties of granules around magnetic flux tubes has been studied for the first time from photographs (at λ = 4803Å and 5770Å) taken with the 50-cm refractor at Pic du Midi. Statistically, these granules are more numerous, smaller, and more elongated than other granules. During their first two minutes of life they show very pronounced radial orientation to the magnetic flux tube.Angular measurements on the same granules have a precision of ± 10°, which is sufficient as theoretical studies show that they rotate by 360° in the course of their life. Initial results appeared to show that only explosive granules had intrinsic rotation, but further examination showed that it is a general trend. It seems that the granules do rotate significantly, but that there is a more important “push-pull” effect, in agreement with A. Title’s theory drawn from SOUP images.
The Contribution of Amateur Astronomers to the Study of Variable Stars
Authors: Proust Dominique , Schweitzer Emile 
Published: July 2016

The observation of variable stars is one of the most important and the most fruitful areas of stellar astronomy. The contribution of large numbers of visual observations is a determining factor in drawing up light-curves, the latter being the key to the interpretation of the process of variability within these stars.It is not easy for a professional astronomer to obtain access to modern telescopes, especially to those of large aperture, and it may even be difficult, given the large number of projects put forward. In any case, these large instruments are often unsuitable for the observation of variable stars. Amateurs, on the other hand, have instruments that have a lower degree of precision, but their greater number and the good organization that exists for the reduction of data obtained, represent trump cards in preparing light-curves.
The Role of the Amateur in Modern Astronomy
Authors: Howse H. Derek , Moore Patrick 
Published: July 2016

AbstractThis contribution dealt with the need for international coordination between amateur astronomers and the failure of the IUAA (International Union of Amateur Astronomers) to meet this need. [The substance of this contribution was given in Sky & Telescope,73, 482 (1987 November).The text was not received. – Eds.]
Nucleosynthesis and Mixing in Low- and Intermediate-Mass AGB Stars
Authors: Hollowell David , Iben Icko 
Published: July 2016

AbstractThe existence of carbon stars brighter than Mbol=-4 can be understood in terms of dredge up in thermally pulsing asymptotic giant branch (AGB) stars. As a low- or intermediate-mass star evolves on the AGB, the large fluxes engendered in a helium shell flash cause the base of the convective envelope to extend into the radiative, carbon-rich region, and transport nucleosynthesis products to the stellar surface. Numerical models indicate that AGB stars with sufficiently massive stellar envelopes can become carbon stars via this standard dredge-up mechanism. AGB stars with less massive stellar envelopes can become carbon stars when carbon recombines in the cool, carbon-rich region below the convective envelope.Neutron capture occurs on iron-seed nuclei during a shell flash, and the products of this nucleosynthesis are also carried to the stellar surface. The conversion of 22Ne into 25Mg can initiate neutron capture nucleosynthesis in largecore mass AGB stars, but only if these stars can survive their large mass loss rates. The current estimates of nuclear reaction rates do not allow for appreciable neutron capture nucleosynthesis via the 22Ne source in lower mass AGB stars. The carbon recombination that induces dredge up in AGB stars of small envelope mass, however, also induces mixing of 1H and 12C in such a way that ultimately a 13C neutron source is activated in these stars. The 13C source can provide an abundant supply of neutrons for the nucleosynthesis of both light and heavy elements. While the existence of neutron-nucleosynthesis products in AGB stellar atmospheres can be understood qualitatively in terms of an active neutron source, the combination of nuclear reaction theory and evolutionary models has yet to provide quantitative agreement with stellar observations.
Turbulence-Driven Atmospheric Instability and Large-Scale Motions in Super- and Hypergiants
Authors: Boer B. , Carpay J. , de Koter A. , de Jager C. , Nieuwenhuijzen H. , Piters A. , Spaan F. 
Published: July 2016

AbstractSpectral studies of super- and hypergiants show that the (outward directed) turbulent acceleration approaches the value of the gravitational acceleration for the most luminous stars, which makes their atmospheres unstable.