bluuebunny/crossref_metadata_2025_split huggingface dataset:
A New Evolutionary Interpretation of the IRAS Two-Colour Diagram
Authors: García-Lario P. , Manchado A. , Pottasch S.R. 
Published: June 2019

A new evolutionary interpretation of the sequence of colours observed in the IRAS two-colour diagram by AGB and post-AGB stars is given, which is capable of explaining the observational properties of both kind of objects. It is useful to define a parameter λ to define the position of a given star in this “infrared main sequence” (IRMS). Adopting

and from the analysis of the expansion velocities, mass loss rates and luminosities observed in a selected sample of non-variable OH/IR stars with no optical counterpart in the Galactic bulge as a function of λ, we conclude that the position in the IRAS two-colour diagram at which a star leaves the IRMS (λmax) only depends on the initial mass Mz of the progenitor star, so that only massive objects can reach the upper end of this sequence. The relation found is:
Expansion velocities increase with the initial mass while every point in the IRMS is found to be associated to a certain value of the mass loss rate. This model also predicts the evolution with time of the mass loss rate during the AGB as a function of the initial mass of the progenitor star, and confirms that most known planetary nebulae are the result of the evolution of considerably massive stars (between 2–3 solar masses) which means that the contribution of processed material to the interstellar medium is considerably higher than what theoretical models predict. Type I PNe are the result of the evolution of 3 — 5 M⊙ progenitors while progenitors with Mi ≤ 1.2 M⊙ probably do not give PNe. The model is also in agreement with the narrow distribution of core masses found in central stars of PNe and white dwarfs and with the usual expansion velocities found in OH/IR stars.
Sur la perte de masse et les processus de freinage de la rotation
Authors: Schatzman E. 
Published: June 2019

Deux mécanismes importants de perte de masse s'accompagnent d'une grande perte de moment angulaire:
1°une étoile en contraction et en rotation peut perdre de la matière le long de son équateur. Sa vitesse de rotation est alors telle qu'à l'équateur la gravité et la force centrifuge s'éuilibrent;2°l'étoile peut perdre de la matière par des processus éruptifs. La perte de moment angulaire est d'un ordre de grandeur très différent suivant que la matière éjectée est ou non guidée par les lignes de force d'un champ magnétique.
Boxy Isophotes and Dust Lanes in Bright Virgo Ellipticals
Authors: Möllenhoff C. , Bender R. 
Published: June 2019

The CCD camera of the Landessternwarte Heidelberg was used at the 1.2 m Calar Alto Telescope for a V, R, I - survey of ~70 dusty and non-dusty elliptical galaxies. We report here about morphological studies of ten bright elliptical galacxies in the Virgo cluster. After the usual CCD data reduction the following procedures were carried through:1. The CCD-frames were filtered and centered to an accuracy of ~ 0. 2 pixels. By division we obtained V-R, V-I, R-I color index images which allow to separate dust absorption and gaseous emission from the stellar distribution. Five of the 1 0 bright Virgo ellipticals evidently show dust/gas, two other objects have weak features. The dust lanes in NGC k26 (cf. Fig. l), NGC 4365 and NGC 4552 were detected for the first time. A dust lane must be visible in all three color index frames in order to avoid fake identifications.2. The isophotes in all three colors were fitted by least square ellipses. From these fits we obtained in dependence from the radius: color profiles, color index profiles, ellipticity profiles, isophote twists (cf. Fig. 2). The deviations of the isophotes from ideal ellipses were studied by a Fourier series analysis. The fourth coefficient is the main indicator for such deviations. Six of ten galaxies show box-shaped isophotes of an amount between 0. 3 % and 1. 5 % of the semi major axis (cf. Fig. 3) 5 two galaxies show disc components (0. 8 1.5 %), only one galaxy is a perfect elliptical up to an error of ±0.2 %. The deviations are equal in all three colors and therefore are not produced by dust.
Spectrophotometry of Shell Galaxies
Authors: Pence W.D. 
Published: June 2019

Low dispersion spectra of two shell galaxies, NGC 3923 and NGC 3051, have been obtained covering the 5300Å to 10000Å spectral range. These long-slit spectra go through the nucleus of each galaxy and also through 12 shells in NGC 3923 and through 3 shells in NGC 3051. the main results are:1) In NGC 3051 the surface brightness of the 2 inner shells is nearly constant with radius. These plateaus of luminosity have very abrupt outer cutoffs but have no detectable inner limits.
Far Infrared emission from post-T-Tauri stars
Authors: Tsikoudi Vassiliki 
Published: June 2019

We have investigated a large sample of faint Post-T-Tauri stars located far from dark cloud complexes, for far-infrared emission and infrared excess, using the IRAS data-base. ~12% of the stars studied here were detected by IRAS at 12 μm. Their 12 μm luminosities L12 are in the range of 4×1030 − 6×1033 erg/sec and correlate well with the stars, bolometric luminosities (Lbol).IRAS has detected emission from the photospheres of the stars studied here and for a few of them it may have observed far-IR excess.
Interferometric observations of OH and H2O masers in protoplanetary nebulae imaged with HST - A unique diagnostic of their spatial-kinematic structure
Authors: Sahai Raghvendra , Claussen Mark J. , Morris Mark 
Published: June 2019

One of the most exciting challenge facing theories of post-main sequence evolution today is to understand how Asymptotic Giant Branch (AGB) stars transform themselves into aspherical planetary nebulae (PNe). Recently, high-resolution imaging surveys of young planetary nebulae and protoplanetary nebulae (PPNe: objects in transition between the AGB and PN phases) have revealed that the majority of these objects are characterised by multipolar bubbles distributed roughly point-symmetrically around the central star. These data strongly suggest that the current model for the shaping of PNe is no longer adequate. High angular-resolution kinematic information is sorely needed to complement the imaging data in order to test new hypotheses, such as our proposal that episodic high-speed jet-like outflows, operating during the protoplanetary or very late-AGB phase, are the primary agent.We have therefore begun a program of using interferometric mapping of OH (and H2O, when feasible) maser emission in order to trace the kinematics of the structures discovered in protoplanetary nebulae with HST. These masers provide a unique and crucial probe of the kinematics of the circumstellar material in PPNe, because of the lack of other emission-line diagnostics. Although our work is still in its infancy (only two objects have been studied in detail), we find that the OH masers indicate the presence of multiple low-latitude outflows and an increase of outflow velocity with latitude. This paper summarises our progress so far, the state of current studies, and future prospects.
Fringe Interferometry in Space: The Fine Structure of R136A with the Astrometer Fine Guidance Sensor Aboard HST
Authors: Lattanzi M.G. , Burg R. , Hershey J.L. , Taff L.G. , Holfeltz S.T. , Bucciarelli B. 
Published: June 2019

We report on the highest angular resolution observation to date of the bright core, R136a, of the massive star cluster R136 within the 30 Doradus complex in the LMC. This visual observation was obtained with the interferometric fringe mode of operation of Fine Guidance Sensor No. 3 (FGS3) on board HST. Crowding and strong diffuse background from nebular emission make this a challenging observation.The giant HII region 30 Dor has provided some of the best candidates for the most massive stars, like R136al. We provide evidence for a new component, R136a1B, within the previously known R136a1-a2 system with a separation of 80 mas (or ≈ 4000 au from a1 at the distance of the LMC), and δV = 1.1 mag fainter than the brightest component a1. Estimates from current evolutionary models of massive stars based on the new FGS photometry predict, after subtraction of a1B, that the present mass of R136a1 is 30 M⊙with a main sequence progenitor of 60 M⊙. To date, this is thelowestdirect estimate of the mass of R136a1.The success of this difficult observation adds a new, unique feature to FGS3 and gives a much expanded, astrophysically very rewarding, role to the interferometer.
High Accuracy Astrometry Benefits for Celestial Mechanics
Authors: Seidelmann P. K. 
Published: June 2019

Achieving angular accuracies at milli- and microarcsecond levels for objects within the solar system presents real challenges concerning the meaning of the observations due to the effects of phase and due to the sizes of the objects being observed. The use of retroreflectors or transmitters located on solar system objects may be the most promising technique.However, if these accurate observations can be achieved, this provides the opportunity for significant improvements in the orbits of the planets, satellites, and minor planets, and will provide, or require, improvements in the models for the tidal interactions, secular accelerations, and masses. The observations will provide a test, or improvement, of the ties between radar, optical, and radio observations. This should provide an opportunity for improving the reductions of pulsar timing observations and improve our determination of the solar system reference system. This will also test the accuracy of the equivalence between Atomic Time and Dynamical Time. These accuracy levels should permit the discovery of other solar systems and the resulting increase in our knowledge, based on more than a single solar system.Improvements in the accuracy level of observations provide increases in our knowledge and raises new challenges to explain the signatures detected by the observations.
Gravitational Radiation Detector Magnetic Tapes from Rochester and Maryland
Authors: Lee M. , Weber J. 
Published: June 2019

The Maryland Univac 1108 computer has analyzed magnetic tapes, one set having outputs of a 1661 Hz gravitational radiation detector at the University of Maryland and another set having outputs of a 710 Hz gravitational radiation detector at the University of Rochester. For a seven day period beginning August 23, 1973, 391 coincidences were found. Time delay experiments performed by the computer observed 338 accidental coincides. The zero delay excess is therefore 53 coincidences.These data have not been verified by the Rochester group and any errors in this report are solely the responsibility of the Maryland authors.
On the Evaluation of the Munich-Frascati Weber-Type Experiment
Authors: Kafka Peter 
Published: June 2019

Both the theory of optimal evaluation, developed in Munich, and tests with artificial pulses suggest that the Munich-Frascati experiment was more sensitive to short gravitational pulses than the Maryland-Argonne experiment. This was the case even in April 1973, before the Munich sensitivity was increased by another factor of 5. Nevertheless, the coincidences between Munich and Frascati did not show any surplus number for zero time delay.It is concluded that Weber's events very likely were not due to gravitational radiation. However, a tape with four days of data from Maryland and Argonne (June 1973), which Weber kindly sent to us, does show a peak at approximately zero time delay, about 0.3 s wide and centered at 0.1 s time delay. The significance is not quite 2 standard deviations for the zero delay bin, but higher when the bins are chosen 0.3 s wide. No explanation can be offered at the moment.
Properties of Black Holes Relevant to their Observation
Authors: Bardeen James M. 
Published: June 2019

Black holes are very small objects by astronomical standards, so in many circumstances they interact with their surroundings like a Newtonian mass point. However, if black holes are present in X-ray binary systems, the X-rays emitted in the inner part of the accretion disk probe the highly curved spacetime geometry near the horizon, particularly if the black hole is rapidly rotating. Some of the properties of circular orbits near the black hole are quite sensitive to the amount of angular momentum. The relativistic corrections remove a Newtonian degeneracy between several of the characteristic frequencies associated with perturbations of the circular orbits.Hot spots in the inner part of the disk can produce dramatic fluctuations in intensity, since the frequency shifts of photons emitted by a given point on the disk are strongly time-dependent. The bending of the photon trajectories by the strong gravitational field can drastically affect the energy balance of the disk; much of the radiation emitted by the inner part of the disk is reabsorbed. The dragging of inertial frames by the angular momentum of the black hole can have striking consequences for the structure of the disk at quite large radii if the angular momentum of the accreting matter is not in the same direction as the angular momentum of the black hole.Dynamic perturbations of black holes are now being intensively studied to see if there are any surprising physical effects associated with the rotation of the black hole. Unfortunately, though quite interesting methods of extracting energy from the black hole exist in principle most of them are unlikely to be realized to an important extent in the real astrophysical world.
The Setting
Authors: Jennings Jesse D. 
Published: June 2019

The pages which follow are a report of the findings from a series of archeological excavations in western Utah. The archeological sites were Danger (42To13), Juke Box (42To20), and Raven (24EK2) caves. Of these three Danger Cave was the most informative and lends its name to the report. Juke Box and Raven provided interesting problems in excavation, but their evidence as to cultural events was meager.The human story inferred in this report was set in one of the most remarkable of North American environments—the desert West. The natural subsistence resources of this land are today quite sparse; the balance between success and failure in survival has always been delicate. The fact that human groups survived in this environment deserves serious ecological note. Although no intensive study of this aspect of the problem is being undertaken here, the cultural data cannot be appreciated or evaluated without a modicum of information regarding the terrain and the biotic resources of the region.
Fe II Fluorescence in Symbiotic Stars
Authors: Eriksson M. , Veenhuizen H. , Wahlgren G.M. , Johansson S. 
Published: June 2019

AbstractFe II fluorescence by PAR has been investigated in eight symbiotic stars having a wide range in temperature of the hot component and orbital period. The data used are spectra obtained from the IUE archive. All pumping lines investigated in this work are in the short wavelength region of IUE (1200-2000 Å), except for He ɪɪ λ1084.942 and O VI λ1032.041. The resulting Fe ɪɪ fluorescence lines are mainly in the long wavelength region (2000-3300 Å), but a few fall in the same region as the pumping lines. The aim is to understand the optimal conditions for formation of Fe ɪɪ fluorescence lines caused by PAR. Three of the selected systems, RR Tel, AG Peg and V1016 Cyg, have 10-30 active Fe ɪɪ channels. Two conditions connect those systems to each other: The hot component is a white dwarf of extreme temperature (80·103-150·103 K) and all three systems are so called symbiotic novae and have had outbursts during the last 150 years. Three systems, AG Dra, RW Hya and R Aqr, have only 2-3 active Fe ɪɪ channels. In the two remaining systems, CI Cyg and T CrB, Fe ɪɪ fluorescence lines were totally absent. These two systems have two features in common: The emission strength of highly ionized elements is less than in most symbiotic systems, and the hot component is suspected to be an accreting main sequence star rather than a white dwarf.
The Primordial Binary Population in OB Associations
Authors: Kouwenhoven M.B.N. , Brown A.G.A. , Gualandris A. , Kaper L. , Portegies Zwart S.F. , Zinnecker H. 
Published: June 2019

AbstractWe present the first results of our adaptive optics survey of 200 (mainly) A-type stars in the nearby OB association Sco OB2, which we will use, together with literature data and detailed simulations of young star clusters, to determine the primordial binary population.
Three-Body Problem and Multiple Stellar Systems
Authors: Valtonen M. 
Published: June 2019

AbstractThree-body processes go on in star clusters where binary stars meet single stars and frequently form temporary triple systems. The triples are typically unstable and break up into a new binary and a single star. Also a simple scattering of a single star from a binary may take place. Both processes can be handled by the statistical theories of three-body break-up and scattering. Here we apply the theory to binary stars, assuming that binaries have been involved in the three-body process. The distributions of binary periods, eccentricities and mass ratios are discussed from this point of view and compared with observational samples.
X-ray Spectra of Young Supernovae
Authors: Pooley David 
Published: June 2019

SummaryX-ray spectra of young supernovae (SNe) can provide information on the progenitor star and the interaction of the supernova ejecta and the circumstellar material. I will discuss some examples, with particular emphasis on SN 1998S, whose X-ray spectrum revealed for the first time in a young supernova a wealth of heavy element emission features (Ne, Al, Si, S, Ar, and Fe). By comparison with detailed calculations of supernova explosion elemental yields, these data can be used to constrain the progenitor mass. With increasingly sophisticated models and additional high quality data, application of this technique could result in many more reliable progenitor mass determinations. In addition, high resolution X-ray spectra allow us to measure the temperature evolution of a supernova and can give us a detailed picture of the progenitor’s pre-supernova evolution. As we build up additional examples from the great diversity of core collapse supernovae, we hope to come to a better understanding of the last stages of massive star evolution.
56Ni Mass in Type IIP SNe: Light Curves and Hα Luminosity Diagnostics
Authors: Elmhamdi A. , Chugai N.N. , Danziger I.J. 
Published: June 2019

SummaryWe analyze late-time observations, available photometry and spectra, of a sample of type II plateau supernovae (SNe IIP). The possibility of using Hα luminosity at the nebular epoch as a tracer of 56Ni mass in this class of objects is investigated, yielding a consistency with the photometry-based estimates within 20%. Interesting correlations are found and their impacts on our present understanding of the physics of core collapse SNe are discussed.
Teaching Astronomy at the University of South Africa
Authors: Wargau W.F. , Cunow B. , Schutte C.J.H. 
Published: June 2019

The University of South Africa celebrates its 50th anniversary this year. Over this period it grew, becoming one of the largest tertiary distance education institutions and the largest university on the African continent.South Africa always had a mixed racial population with each group having its own culture. This difference between people is further aggravated by differences in the level of “westernisation”. Furthermore, South Africa also suffers from an extreme urbanisation problem where on the one hand we find modern cities and on the other tribal groups. All these factors led to a differentiation of the population into a first world and third world component.
Current Trends in European Astronomy Education
Authors: West Richard M. 
Published: June 2019

Astronomy knows no geographical borders - the sky is the same over all countries. However, while professional astronomers have long established bi- and multilateral collaborations, many of which take place under the auspices of the IAU, few similar schemes exist within astronomy education.Now, following the establishment in 1995 of the European Association for Astronomy Education (EAAE), this situation is about to change on that continent. This new association offers an efficient platform for astronomy educators at various levels - in particular at the approx. 7000 secondary schools in this geographical area - to interact in all related matters, e.g. curricula, all kinds of teaching materials, student exchanges and other events. Together with the European Commission and some of the professional institutes, EAAE is now planning a major, international event in November 1996.
The Training of Teachers
Authors: Gouguenheim L. , Gerbaldi M. 
Published: June 2019

Informal and formal astronomy education is present through many channels: newspapers and TV; amateur associations; clubs and science associations; at school at any level. The teachers are not only the main agents of the educational process at school, but they are also very active in extra-curricular activities: they run clubs, educational projects etc.These activities are present everywhere in the world, as can be seen from the reading of the National Reports published every 3 years by Commission 46 “Astronomy Teaching” of the International Astronomical Union and published in its Newsletter.
The Use of Terms and Definitions in the Study of Be Stars (Review Paper)
Authors: Collins George W. 
Published: June 2019

AbstractIn this paper I shall examine the use and misuse of some astronomical terminology as it is commonly found in the literature. The incorrect usage of common terms, and sometimes the terms themselves, can lead to confusion by the reader and may well indicate misconceptions by the authors. A basic definition of the Be phenomena is suggested and other stellar characteristics whose interpretation may change when used for non-spherical stars, is discussed. Special attention is paid to a number of terms whose semantic nature is misleading when applied to the phenomena they are intended to represent. The use of model-dependent terms is discussed and some comments are offered which are intended to improve the clarity of communication within the subject.
Rotating Stellar Interiors (Review Paper)
Authors: Smith Robert Connon 
Published: June 2019

AbstractRotation has two main qualitative effects on the structure of a star: it distorts the shape and it reduces the total luminosity. The luminosity depends only on the total angular momentum but the shape, and so the observable properties, depends on the internal distribution of angular momentum. The expected distribution, even for main-sequence stars, is an unsolved problem. Redistribution of angular momentum can occur as a result of large-scale circulation currents, instabilities and magnetic stresses and there may be no steady state. If shear instabilities are dominant, then stars may rotate nearly uniformly. Studies of non-radial oscillations might perhaps eventually lead to a direct probing of the internal angular momentum distribution by the methods now being used to study the internal rotation of the Sun. Differential rotation near the surface would probably give rise to turbulent motions, which could generate the mechanical energy flux which seems to be a necessary input to the winds in hot stars.
Narrow Absorption Components in The UV Spectra of HD110432 (B1 IIIe)
Authors: Prinja Raman K. , Henrichs Huib F. 
Published: June 2019

We present high resolution IUE ultraviolet observations of multiple narrow absorption components seen in the SiIII, NV, SiIV, and CIV profiles of the B1 IIIe star, HD110432. Spectra taken during March 1986, spanning ∼ 11 days, are modelled using line profile fits. Central velocities and column densities of the discrete features are derived.The 11 observations obtained during March 1986 (SWP24923–28031) exhibit only minimal line profile variability, but are substantially different from the only other available IUE spectrum of HD110432, taken in April 1981 (fig. 1). This previous image reveals just a single extremely narrow (FWHM ∼ 50 km/s) feature at ∼ 1360 km/s.