bluuebunny/crossref_metadata_2025_split huggingface dataset:
The IOTA Expedition Results from the Total-Annular Eclipse in Gabon, 1987
Authors: Maley Paul D. 
Published: July 2016

AbstractThe results of the IOTA expedition to Gabon to observe the rare total-annular eclipse of 1987 March 29 were described. Multiple stations were used to determine data from Baily’s Beads about the contact times. The techniques used and their application to future eclipses were evaluated. An additional aim was to develop a database to resolve corrections to the solar radius at specific epochs in order to determine the amplitude of time-dependent oscillations of the Sun’s surface.
The Moonwatch Program: A Model for Amateur Contributions to the ISY
Authors: Cornell James 
Published: July 2016

Largely forgotten today is the role that amateur astronomy played in the early days of space exploration. For example, 1987 is not only the 30th anniversary of the first artificial satellite but also of history’s most successful global organization of amateur astronomers: Moonwatch.As a worldwide network of volunteer visual observers, Moonwatch was a vital adjunct to Western satellite tracking efforts. In nearly two decades of operation, more than 500 individuals made some 400,000 observations of approximately 6000 objects. Although now only a footnote to space history, Moonwatch suggests that some comparable organization of dedicated and talented amateurs might contribute to the International Space Year of 1992.
GEOS – Groupe Europeen d’Observations Stellaires
Authors: Dumont Michel 
Published: July 2016

GEOS was formed in 1973 from several European groups (French, Italian, Spanish and Belgian). All the members of GEOS have the same aims: to observe variable stars and to analyse their observations themselves.Other objects are also observed by GEOS: artifical satellites and minor planets, in particular minor-planet occultations. Observations are treated statistically and the procedures allow accidental, and – if there are several observers of the same star – systematic, errors to be corrected, thus improving the accuracy of the results and the light-curves.
A Planetarium for Astronomy
Authors: Acker Agnès 
Published: July 2016

Planetariums are continuing to open in Europe and recent years have seen several organizations and meetings devoted to their use. How should a planetarium show be constructed? What are the principles to be followed and the pit-falls to be avoided? This is a problem, because people running planetariums are only rarely astronomers. One great debate centres around the question of whether to use a pre-recorded show or a “live” one.An automatic show allows a constant level of presentation, however tired or incompetent the lecturer. The Sun rises at the right moment, just as the chosen music starts and either a piece of text or a picture appears. Simultaneous effects can be incorporated, even complicated ones, which often explains a difficult point better.
Main Sequence Abundances, Mass Loss and Meridional Circulation
Authors: Michaud Georges 
Published: July 2016

AbstractConstraints that abundance anomalies observed on main sequence stars put on turbulence, meridional circulation and mass loss are reviewed. The emphasis is on recent observations of Li abundances.Upper limits to turbulence are obtained from the Be abundance in the Sun and from underabundances of Ca and Sc in FmAm stars. The Li abundance in G type stars suggests the presence of turbulence below convection zones.The abundance anomalies, both over and underabundances, observed in FmAm and λ Booti stars can be explained by diffusion in the presence of mass loss. A mass loss rate of 10−15 Mo yr−1 is required to explain the FmAm stars while a mass loss rate of 10−13 Mo yr−1 is required by the λ Booti stars.The position and width of the Li abundance gap observed in Hyades and other open clusters is explained by diffusion. A detailed reproduction of the Li(Teff) curve seems to require a mass loss rate of slightly more than 10−15 Mo yr−1, of the same order as the mass loss rate required by the FmAm stars. In the presence of such a mass loss only small overabundances of heavy elements are expected. The observed variations in the Li abundance as a function of the age of clusters suggests that the Li abundance observed in old halo stars does not represent the cosmological abundance.Detailed two dimensional calculations of diffusion in presence of meridional circulation for HgMn and FmAm stars lead to a cut-off of about 100 km s−1 for the maximum equatorial rotational velocity at which abundance anomalies are expected in these objects. This agrees with observations. A similar calculation for the F stars of the Hyades where Li underabundances are observed leads to a contradiction, unless meridional circulation patterns are modified by the presence of convection zones once they become as large as in late F stars. There remains a possibility that meridional circulation would be responsible for some of the reduction of the Li abundance as observed in the Hyades and UMa. Further observations are suggested to distinguish the effects of settling and nuclear destruction.
On the Distribution of the Lithium Abundance in Normal Late-Type Giants
Authors: Hänni Liia 
Published: July 2016

The abundance of lithium in stellar atmospheres presents an important observational constraint to the hydrodynamical models of the outer layers of stars. It can be considered as a cumulative measure of the extent of matter exchange between surface and deeper layers during the stellar evolution.From the observed large scatter of lithium abundances in evolved stars it follows that the efficiency of mixing has been highly variable from one object to another. At present, it seems to be difficult to find any satisfactory explanation to the lithium abundances of individual stars. We suppose that at this stage the statistics of lithium abundances in different types of stars can give some insight into the character of mixing processes operating in stars. In this report some observational results about the distribution of the lithium abundances in normal late-type giants are presented.
SiO Isotope Emissions from Late-Type Stars
Authors: Ukita N. , Kaifu N. 
Published: July 2016

AbstractThe J=2-1, v=0 emissions of 28SiO, 29SiO, and 30SiO from three late-type stars were simultaneously observed with the Nobeyama 45-m telescope in Jaunuary 1987. The relative intensities of [29SiO] / [30SiO] were measured to be 2.4 for χ Cyg, 1.5 for NML Tau, and 2.9 for V1111 0ph. These values are lower limits for the relative isotope abundance of [29Si] / [30Si], and are larger than the terrestrial value of 1.51. Recext theoretical studies suggest that hydrostatic nucleosysnthesis and supernova explosions result in smaller values of [29Si / [30 Si] than solar. These models cannot explain the observed excess of 29Si.
Chemical and Expansion Properties of Compact Planetary Nebulae in the Galactic Anti-Center Region
Authors: Tamura Shin’ichi 
Published: July 2016

A spectroscopic diagnosis on M1-5, M1-9, K3-66, and K3-67 is presented. Our sample were chosen from the catalogue of radial velocities (Schneider et al 1983) by the reason of not only their kinetic peculiarity, but also apparently compact images. Main purpose is to analyze the chemical properties which should give us an information about galactic chemical abundance distribution in the direction of galactic anti-center region based upon kinetic peculiarity. Another one is to study on an expansion characteristics by which we can recognize intrinsically compact planetary nebulae in young phase.Spectroscopic observations were made at the Okayama Astrophysical Observatory (Shibata and Tamura 1985), the Steward Observatory, and Lick Observatory (Tamura and Shaw 1987).
Atmospheric Diagnostics of Wolf-Rayet Stars
Authors: Doom C. 
Published: July 2016

Wolf-Rayet (WR) stars are the descendants of massive stars that have lost their hydrogen rich envelope. Recently more accurate data on WR stars have become available: mass-loss rates (van der Hucht et al. 1986), radii and luminosities (Underhill 1983, Nussbaumer et al. 1982).It may therefore be worthwhile to investigate if combinations of observed parameters shed some light on the structure of the extended stellar wind of WR stars.In many WR stars the photosphere is situated in the stellar wind. We assume that the wind is stationary and isotropic. Further we assume a velocity law v(r)=v∞(1−Rs/r)β where v∞ is the terminal velocity of the wind in km/s, Rs is the radius where the wind acceleration starts and β > 0 is a free parameter. We can then easily compute the level R in the wind where the photosphere is located (de Loore et al. 1982): R is the solution of the equation 6.27 10−9 τat R v∞/ = fβ(Rs/R) where τat is the optical depth at the photosphere (2/3 or 1), (>0) is the mass loss rate in M⊙/yr and fβ > 1 is a slowly varying function (Doom 1987).
The Galactic Distribution and Subtype Evolution of Wolf-Rayet Stars
Authors: Hidaya B. , Admiranto A. G. , Supeill K. R. , van der Hucht K. A. 
Published: July 2016

AbstractThe galactic distribution of Wolf-Rayet stars is redetermined. In the solar neighbourhood within d < 2. 5 kpc the WN/WC number ratio is 0.54, indicating a larger influence of mass loss and convectlve overshooting than most present evolutionary models account for. The WR density gradient In the solar neighbourhood is constant. From a comparison of WR galactocentric distances and WR cluster and association membership, we find indications that WCE stars descend from WNL stars at R > 6.5 kpc, and that WCL stars descend from WNL stars at R < 8.5 kpc.
Intermittent Transition to Irregular Pulsation with Mass Loss in Hydrodynamic Models
Authors: Aikawa Toshiki 
Published: July 2016

Hydrodynamic simulations of non-linear pulsation for less-massive cooler supergiants have been perfoemed by several authors (Tuchman, Sack and Barkat, 1979; Fadeyev and Tutukov, 1981; Fadeyev, 1982, 1984; Nakata, 1987; Buchler et al., 1987). The outburst of large amplitude pulsation at times is one of common features of these models, and renders mass-loss from the atmosphere of pulsating stars by generating strong shock waves.To find out routes of the transition from limit cycles to this type of irregular pulsation, we performed hydrodynamic simulations for a series of models the luminosity log(L/L⊙ ) = 3.505, and Te = 5300 K with a narrow range of the mass, 1.4 M⊙<M<1.5 M⊙ by using the hydrodynamic code, TGRID (Simon and Aikawa, 1986).
Classical Novae – Before and After Outburst
Authors: Livio Mario 
Published: July 2016

Classical nova (CN) and dwarf nova (DN) systems have the same binary components (a low-mass main sequence star and a white dwarf) and the same orbital periods. An important question that therefore arises is: are these systems really different ? (and if so, what is the fundamental difference ?) or, are these the same systems, metamorphosing from one class to the other ?The first thing to note in this respect is that the white dwarfs in DN systems are believed to accrete continuously (both at quiescence and during eruptions). At the same time, both analytic (e.g. Fujimoto 1982) and numerical calculations show, that when sufficient mass accumulates on the white dwarf, a thermonuclear runaway (TNR) is obtained and a nova outburst ensues (see e.g. reviews by Gallagher and Starrfield 1978, Truran 1982). It is thus only natural, to ask the question, is the fact that we have not seen a DN undergo a CN outburst (in about 50 years of almost complete coverage) consistent with observations of DN systems ? In an attempt to answer this question, we have calculated the probability for a nova outburst not to occur (in 50 years) in 86 DN systems (for which at least some of the orbital parameters are known).
The Evolution of the Progenitor of SN 1987A
Authors: de Loore C. , Doom C. 
Published: July 2016

It is now almost certain that the progenitor of SN 1987 is the B3 supergiant Sk −69°202 (e.g. Walborn et al. 1988). This provides us with valuable constraints on the SN precursor: According to West et al.(1987) the star has Mv=−6.8. Using the calibrations of Humphreys and McElroy (1984) we find that the precursor had Teff = 13000 − 16000K, −Mbol= 7.7 - 8.1 (log L/L⊙ = 5.04) and a radius of 48 - 60 R⊙.The SN precursor was not a red supergiant, but a rather blue supergiant, which also explains the peculiar form of the light curve (Woosley, 1988; Schaeffer et al. 1987). However, standard evolutionary calculations would expect such stars to explode as red supergiants.
Model Calculations and Spectroscopic Constrains for SN1987A
Authors: Höflich P. 
Published: July 2016

SummaryWe present synthetic spectra for atmospheres in order to interpret the observed spectra of the supernova 1987A during the first few months after the initial event. Spherical symmetry and density profiles are assumed which are given by the homologous expansion of the stellar structure of a B3 supergiant. For hydrogen, up to eight levels and, for helium, 16 levels are allowed to deviate from LTE. The radiation transport is calculated consistently with the rate equations both for the continua and for the lines. Radiative equilibrium is assumed. The observed spectra and colours in the optical wavelength range can be well reproduced by pure hydrogen models during the first few weeks. The behaviour of the UV flux is due to changes in the effective temperature and the photospheric radius. For later stages, the influence of elements other than hydrogen and helium must be taken into account in order to compare the calculated and observed spectra in the optical wavelength range. Reasonable agreement between calculations and observations can be obtained with the assumption of half solar abundances for all elements but for the s-process elements Sc, Ti and Ba which are overabundant. To explain the small changes in the spectra after about 3 weeks up to 4 months, we need a total hydrogen mass of about 8 to 10 M⊙.
Lα Radiation and CaII Ionization in the TYPE II Supernovae at Late Times
Authors: Chugai Nikolai N. 
Published: July 2016

AbstractThe ionization of CaII by the Lα quanta in the envelope of the type II supernova 1970g on 270th day is considered. The ratio CaII/CaIII is found to be very low (<0.1). This results in the low theoretical intensities of the CaII emission lines; they are at least an order of magnitude weaker than the observed ones. The implications are discussed.
Nucleosynthesis in exploding massive Wolf-Rayet stars
Authors: Eid M.F. El , Langer N. 
Published: July 2016

Recent observations of the young supernova remnant Cas A (Fesen et al., 1987) suggest an exploding Wolf-Rayet (WR) star of WNL type as a progenitor of this object. The majority of the WR stars seems to originate from massive O-stars of M > 40 M⊙. According to current investigations (Schild and Maeder, 1984; Langer, 1987; cf. also: Langer, this volume) WNL stars rank among the most massive WR stars. Hence, it is possible to assume that the stellar progenitor of Cas A was indeed a very massive star.As shown by Langer and El Eid (1986), (see also Woosley, 1986) a population I star of initially 100 M⊙ may loose enough mass during its evolution up to core He exhaustion to become a WN star of ∼ 45 M⊙, which then mainly consists of oxygen (more than 80%) synthesized during He burning.
The iron curtain of the WC 9 star HD l64270
Authors: van der Hucht Karel A. , Conti Peter S. 
Published: July 2016

AbstractThe emission lines in the optical and UV spectrum of the WC 9 star HD 164270 indicate a terminal velocity of its wind of v∞ ≈ 1400 km s-1. In the UV spectrum Fe III absorption lines appear from transitions with metastable lower levels. Because they are displayed over only 830 km s-1, it is suggested that they are formed in the decelerating part of the wind. A radius of 1.8 x 104 R⊙, is found for the circumstellar Fe III shell. This value is within the range of radii calculated by Cohen et al. (1975) for the dust shells of WC 9 stars.
Mass loss rates for twenty one Wolf-Rayet stars
Authors: Barlow M.J. , Smith L.J. , Willis A.J. 
Published: July 2016

AbstractMass loss rates have been derived for twenty one WR stars encompassing most subtypes in the WN and WC sequences, from measurements of their infrared free-free fluxes. The resultant mass loss rates show a range of only a factor of four. WC stars generally have larger mass loss rates than WN stars, the mean rates being Ṁ(WC) = 4.1x10-5 M⊙y-1 and Ṁ(WN) = 2.7x10-5 M⊙y-1. Optical and ultraviolet data have been used to estimate bolometric luminosities for a range of WR spectral types, and it is shown that the derived mass loss rates are too large to be powered by radiation pressure. The total kinetic energy ejected into the interstellar medium through mass loss during the WR phase of a massive star is estimated to be 7x1050 ergs, comparable to that of a supernova event.
Mass outflow in AG Carinae and a comparison with P Cygni
Authors: Bensammar S. , Gaudenzi S. , Rossi C. , Johnson H.M. , Thé P.S. , Zuiderwijk E.J. , Viotti R. 
Published: July 2016

AbstractAG Car is a variable supergiant surrounded by a small ring nebula. Its ultraviolet and optical spectrum, and UV to IR energy distribution are similar to those of P Cyg with v∞ = -290 km s-1. Also the strength of the 2200 A band is the same and suggests E(B-V) = 0.55 for both stars. The possible variability of the infrared flux is discussed.
The fraction of O-type supergiants in our galaxy in the LMC and in the SMC: an evidence of the correlation between mass loss rate and chemical abundance
Authors: Bisiacchi G.F. , Firmani C. 
Published: July 2016

The distribution of the spectral types of the WR stars in our galaxy is different at different distances from the galactic center. This distribution is also different in all three galaxies, in our, in the LMC and in the SMC. These results have been interpreted as due to the dependence of the mass loss rate from the original chemical abundace which is known to be different in these objects.On the other hand it has been proposed by Chiosi et al. (1974) and confirmed by Bisiacchi et al. (1978) that most of the 0 supergiants should be stars in the hydrogen burning phase. These authors also find evidence that the large relative number of supergiants among th 0 and early B type stars must be related to the longer time spent by the evolutionary tracks with mass loss at the low gravity region. Recently, a new empirical formula has been proposed by Chiosi (1980) for the mass loss rate as function of the luminosity and temperature of the stars.
Mass loss from metal-poor stars
Authors: Chiosi C. , Bertelli G. , Nasi E. , Greggio L. 
Published: July 2016

1. IntroductionIt is essential to consider the effect of mass loss to understand the distribution of supergiant stars in the HR diagram. This research concerns the evolution of massive stars with X=0.700 and Z=0.001 during the phases up to central Heexhaustion with the inclusion of mass loss. Such low value of Z has been chosen in order to allow a comparison with the supergiant stars of SMC. The rate of mass loss is formulated as in Chiosi, Nasi and Sreenivasan (1978). More specifically, in the range of high effective temperatures, we adopt the mass-loss rate relationship for radiation pressure driven wind of Castor, Abbott and Klein (1975), whereas in the range of low effective temperatures we assume the mass loss rate to be driven by the acoustic flux mechanism of Fusi Pecci and Renzini (1975).
Mass loss from interacting close binary systems
Authors: Plavec Mirek J. 
Published: July 2016

AbstractMass outflow from interacting close binary systems, accompanied by loss of orbital angular momentum, appears to be a very important process affecting the evolution of binary stars. Together with accretion on the mass-gaining component, it is the least understood aspect of the general complex process we call “evolution with mass transfer and/or mass loss”, or, more briefly, “interaction”. It is therefore very imperative to assemble and examine all available facts or hints about mass loss.
The Measurement of Long-Period Oscillations at Sacramento Peak Observatory and South Pole
Authors: Stebbins Robin , Wilson Christopher 
Published: July 2016

AbstractA program to measure long-period brightness oscillations at the solar limb has been pursued at Sacramento Peak Observatory for several years. Past improvements in observing technique and data analysis are reviewed. The encouraging results aid in the verification of the reality and the origin of oscillatory signals. However, the main stumbling block to this and other observational programs is the length of observing sequences imposed by the day/night cycle. The South Pole has received considerable attention as a site where extended observations might be possible. Currently, the Sacramento Peak program is developing a South Pole telescope designed for the observing technique and data analysis proven in Sunspot. A review of pertinent South Pole site parameters is given here for other workers who may be considering South Pole observations. Observing sequences longer than 150 hr are possible, though rare. Data sets of this duration are very attractive for solar oscillation studies.
Solar Diameter(s)
Authors: Rösch J. , Yerle R. 
Published: July 2016

AbstractBecause of the renewed attention now paid to the solar diameter, its variations from equator to pole, or its secular or long-period changes, the question: what is a solar diameter? is not meaningless. Two kinds of definitions may be given: either astrophysical, each one relating to a specific physical parameter, or observational, relating to a given quantity to be measured. Only the second kind is directly accessible, and astrophysical definitions should be linked to these quantities, once they are determined with the highest possible accuracy. In practice, all the programs under way refer to the point of the limb where the brightness gradient is maximum, or to a higher order approximation of the shape of the profile. Two of them are compared: the Pic-du-Midi experiment, using fast scans of the limb to define the inflection point after a correction for the blurring effect of the atmosphere, and the SCLERA experiment, using the algorithm called FFTD to eliminate this correction. The advantage of a fast scan is emphasized, and the remark is formulated that, once the signal is digitized and stored, FFTD or any processing of it can be performed. In collecting day-long one-limb scans to calibrate the blurring correction, the authors have found fluctuations of the maximum brightness gradient which provide a new entry to the field of solar oscillations.