bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the SN 1993J Radio Shell Structure
Authors: Marcaide J.M. , Martí-Vidal I. , Ros E. , Alberdi A. , Guirado J.C. , Lara L. , Pérez-Torres M.A. , Weiler K.W. 
Published: June 2019

SummaryAn accurate measurement of the expansion deceleration of SN 1993J depends on how well the shell size and its emission structure are known. With the goal of determining the emission structure of the shell, we have developed a new approach, which we call “Green Function Deconvolution” (GFD), based on iterative use of Green functions on the sky plane to reconstruct the radial emission profiles of spherically symmetric sources. This approach works reasonably well in the case of optically thin emitting sources, which is not the case for SN 1993J since, as we find, the emission from the central part of SN 1993J further away from us is strongly or totally absorbed. We describe the GFD method and present our findings about the emission structure of the shell. We also present the expansion of SN 1993J based on a method complementary to GFD, which will be described elsewhere.
SN 1994W: Evidence of Explosive Mass Ejection a Few Years Before Explosion
Authors: Chugai Nikolai N. , Cumming Robert J. , Blinnikov Sergei I. , Lundqvist Peter , Filippenko Alexei V. , Barth Aaron J. , Bragaglia Angela , Leonard Douglas C. , Matheson Thomas , Sollerman Jesper 
Published: June 2019

SummaryWe present and analyze spectra of the Type IIn supernova 1994W obtained between 18 and 202 days after explosion. During the first 100 days the line profiles are composed of three major components: (i) narrow P Cygni lines with absorption minima at −700 km s−1; (ii) broad emission lines with blue velocity at zero intensity ~ 4000 km s−1; (iii) broad, smooth, extended wings most apparent in Hα. These components are identified with the expanding circumstellar (CS) envelope [5], shocked cool gas in the forward postshock region, and multiple Thomson scattering in the CS envelope, respectively. The absence of broad P Cygni lines from the supernova (SN) is the result of the formation of an optically thick, cool, dense shell at the interface of the ejecta and the CS envelope. Models of the SN deceleration and Thomson scattering wings are used to recover the Thomson optical depth of the CS envelope, τT ≥ 2.5 during first month, its density (n ~ 109 cm-3) and radial extent, ~ (4 — 5) × 1015 cm. The plateau-like SN light curve, which we reproduce by a hydrodynamical model, is powered by a combination of internal energy leakage after the explosion of an extended presupernova (~ 1015 cm) and subsequent luminosity from circumstellar interaction. We recover the pre-explosion kinematics of the CS envelope and find it to be close to homologous expansion with outmost velocity ≈ 1100 km s-1 and a kinematic age of ~ 1.5 yr. The high mass (≈ 0.4 M⊙) and kinetic energy (≈ 2 × 1048 erg) of the CS envelope combined with small age strongly suggest that the CS envelope was explosively ejected only a few years before the SN explosion.
Radio Monitoring of Supernova 2001ig: The First Year
Authors: Ryder Stuart D. , Sadler Elaine , Subrahmanyan Ravi , Weiler Kurt W. , Panagia Nino , Stockdale Christopher 
Published: June 2019

SummarySupernova 2001ig in NGC 7424 has been observed with the Australia Telescope Compact Array at ~2 week intervals since its discovery, making this the best-studied Type IIb radio supernova since SN 1993J. We present radio light curves for frequencies from 1.4 to 20 GHz, and preliminary attempts to model the observed behavior. Since peaking in radio luminosity at 8.6 and 4.8 GHz some 1-2 months after the explosion, SN 2001ig has on at least two occasions deviated significantly from a smooth decline, indicative of interaction with a dense circumstellar medium and possibly of periodic progenitor mass-loss.
Models of Supernova Explosions: Where Do We Stand?
Authors: Hillebrandt Wolfgang 
Published: June 2019

SummaryThe present status of our understanding of core-collapse and of thermonuclear supernovae is reviewed. It will be argued that the failure of numerical simulations of the collapse of massive stars to produce explosions is probably caused by our incomplete knowledge of the (micro-) physics involved. In contrast, for thermonuclear (type Ia) supernovae the basic physics seems to be well under control and, therefore, it is not surprising that model predictions and observations are in good agreement.
Neutrino Gas in Equilibrium with Self-Interaction
Authors: Sirera M. , Perez A. 
Published: June 2019

SummaryWe study a neutrino gas in equilibrium both at T = 0 and at finite temperature. The neutrinos are assumed to be massive Dirac particles with two generations interacting with each other via neutral currents and with a background of matter. We analyze the main properties of the neutrino eigenmodes in the medium, such as effective masses and mixing angle.
Computer as a tool in astronomy teaching
Authors: Berthomieu Francis 
Published: June 2019

As yet, astronomy, the most ancient of all sciences, surprisingly is not included in French secondary science classes. Recent trends in favour of a more attractive and motivating scientific education have taken it up.Astronomy has, at all times, been arising curiosity, and now provides a privileged field to scientific approach :•Observation of the vault of heaven and its peculiarities•Description of its general appearance and of the specific movement of stars and planets•Measurement of distances, coordinates and angles.•This will make it possible to define successive models, which will be ever closer to the observed reality.
The presence of multimedia in astronomy teaching
Authors: Fogh Olsen H. J. 
Published: June 2019

Sometimes I find my self in a society in the middle of The Global Village and sometimes in a society in a little state with a large number of computers not speaking the language I usually talk. When a prevailing part of the population are working in one area the society is named after that area, allthough a lot of other things can characterize the society. The latest societies are:•Agricultural society•Industrial society•Information societyThe agricultural and industrial societies have come to an end. When a society comes to an end, it is usually because the efficiency of production reaches a level higher than necessary, to keep all the workers busy. Many of the workers are attracted to other kinds of work, which gives rise to the next culture.
The Current Role of Planetariums in Astronomy Education
Authors: Gutsch William A. , Manning James. G. 
Published: June 2019

For decades, planetariums have been created to serve the cause of astronomical enlightenment - to offer people knowledge and understanding and a sense of place in a universe far bigger than themselves. It is an important role and one that we in planetariums continue to play - changing, we hope, as times, technology, educational philosophies, and our view of the universe change.The first projection planetarium was demonstrated by the Zeiss Optical Company at the Deutsches Museum in Munich, Germany in 1923. By 1970, the height of the Apollo moon program, there were an estimated 700 to 800 planetariums in the world, half of them less than six years old. Today, 26 years later, that number has more than doubled to a little over 2,000.
Teaching Astronomy at Secondary School Level in Europe
Authors: Ros R. M. 
Published: June 2019

The status of teaching Astronomy in European countries is variable. Sometimes Astronomy appears as a compulsory subject or as an optional subject, but on many occasions Astronomy appears within another subject, depending on the country. It is even possible for Astronomy not to appear anywhere in the curriculum. But of course the position here is better than in other less developed places. In Europe there are various topics which can be organized into two main groups: aspects related to relative motions and aspects related to properties of light. Some examples of teaching activities and materials in various countries will be described.It is also necessary to emphasize several initiatives such as the review of Astronomy curricula, the publication of general books on Astronomy for secondary schools and the organisation of new journals to promote Astronomy in schools.
Observations of Rapid Variability in Be Stars (Review Paper)
Authors: Percy John R. 
Published: June 2019

AbstractPhotometric and/or spectroscopic variability on time scales of approximately 0.2 to 2 days has been observed in over 40 Be stars, and is suspected in many more. This paper reviews the observational aspects of this phenomenon: both surveys and studies of individual objects. This phenomenon is not easy to study and interpret: (i) the time scale is inconvenient (ii) there have been very few simultaneous photometric and spectroscopic studies of individual objects (iii) the photometric variability is small, often irregular and superimposed on longer-term variability and (iv) the spectroscopic variability is usually observed as absorption line profile variability, which requires special instrumentation. For these and other reasons, there is not yet a universal agreement about the nature of this phenomenon. Nevertheless, it deserves further intensive study, not only because it is common, but also because in one or two stars, there is evidence that the rapid variability may be related (causally perhaps?) to the longer-term variability in these stars - variability whose ultimate cause is still not known.
The Magnetic Be Star Sigma Orionis E
Authors: Bolton C. T. , Fullerton A. W. , Bohlender D. , Landstreet J. D. , Gies D. R. 
Published: June 2019

Over the past two years, we have obtained high resolution high signal/noise (S/N) spectra of the magnetic Be star σ Ori E at the Canada-France-Hawaii Telescope and McDonald Observatory. These spectra, which cover the spectral regions 399-417.5 and 440-458.5 nm and the Hα line and have typical S/N>200 and spectral resolution ≃0.02 nm, were obtained at a variety of rotational phases in order to study the magnetic field structure, the distribution of elements in the photosphere, and the effects of the magnetic field on the emission envelope. Our analysis of these spectra confirms, refines and extends the results obtained by Landstreet & Borra (1978), Groote & Hunger (1982 and references therein), and Nakajima (1985).The Hα emission is usually double-peaked, but it undergoes remarkable variations with the 1.19081 d rotational period of the star, which show that the emitting gas is localized into two regions which co-rotate with the star.
IUE Spectra of the Be Star HD 174237
Authors: Tarafdar S. P. 
Published: June 2019

AbstractHigh-resolution spectra of the Be star HD 174237 taken on September 9, 1980 will be presented. They show stellar absorption lines and superionized NV lines shifted redward equivalent to a velocity of 20 km s-1. This velocity when compared to the earlier measured velocity of - 20 km s-1 (cf. Hoffleit) suggests that the Be star HD 174237 is really a binary and the IUE and previous observations are in different phases of binary motion. The spectra also show strong A1III and SilV absorption lines together with strong NV lines but surprisingly the CIV lines are very weak. It appears that the A1III doublet is associated with a narrow blue-shifted component suggesting an outflow of cool gas from the star.
Be Stars as Nonradial Pulsators (Review Paper)
Authors: Baade Dietrich 
Published: June 2019

AbstractThe observational status of the ubiquitous rapid variability of Be stars is summarized. The most comprehensive interpretation is obtained with a traveling velocity field and associated temperature variations. But neither the available observations nor theoretical predictions presently allow an unambiguous mode determination of these nonradial pulsations. In addition to rapid rotation, an NRP mode of low azimuthal order, m ≈ 2, seems another prerequisite for a B star becoming a Be star. The amplitudes of these modes are variable and have been observed to decrease with some delay after an outburst. For low-order sectorial modes, NRP's therefore have the potential of explaining the three oldest unsolved problems of Be stars: the difference between Be and Bn stars (the latter do not usually have a low-order mode), the episodic component of the mass loss from Be stars, and the equatorial density maximum of their winds. Mechanisms for the transfer of energy to the atmosphere and its transformation into the kinetic energy of an outburst are discussed.
Ultraviolet Observations of CX Draconis
Authors: Koubský P. , Horn J. , Harmanec P. , Peters G. J. , Polidan R. S. , Barker P. K. 
Published: June 2019

CX Draconis /HD 174237, B2.5Ve, v.sin i = 160 km.s-1/ is a typical Be star displaying most of the well known spectroscopic and photometric characteristics of these stars.Koubský /1978/ disclosed that CX Dra is a SB1 /P=6.69603d, K = 35 km.s-1, e = 0/. Penrod /1985/ confirmed that the secondary is a F star. Peters and Polidan /1984/ reported strong, variable lines of NV, CIV and SilV from high-resolution spectra secured with IUE satellite. These features were interpreted to arise from gas stream and accretion close to the photosphere of the B-component of the system.
Observations and Evolutionary Scenario For Be/X-Ray Binaries
Authors: Habets G.M.H.J. 
Published: June 2019

Rappaport & Van den Heuvel (1982) suggested the following formation scenario for B emission (Be)/X-ray binaries: the progenitor of the neutron star is the initial primary star with mass M1 = 10-20 M⊙, which during hydrogen-shell burning transfers mass to the companion (with M2 < M1). The secondary is spun up due to disk-accretion (e.g. Packet 1981) and has become a rapidly rotating Be star (M ≃ 10-20 M⊙).With this scenario the observed orbital periods (Porb > 15 d) of the Be/X-ray binaries can be explained. This was shown by van den Heuvel (1983) by adopting an idealized period distribution for unevolved O- and B-type close binaries with Porb, < 30 d (see Fig. 1) and assuming conservative evolution, i.e. that mass and angular momentum are conserved during mass transfer.
Period-Luminosity-Metal Abundance Relations for Population II Variable Stars
Authors: Nemec James M. , Lutz Thomas E. 
Published: June 2019

AbstractNew period-luminosity-metallicity (P-L-[Fe/H]) relationships for Pop. II Cepheids, RR Lyrae stars, anomalous Cepheids and SX Phe (variable-blue straggler) stars are presented. These were computed by fitting regression lines to observed pulsation periods and mean B, V, K magnitudes for over 1200 stars in ∼40 stellar systems. The stars were assumed to be pulsating in either the fundamental (F) or first-overtone (H) modes (excluding double-mode and other multi-periodic variables). Eight P-L-[Fe/H] relationships (one for each of the two pulsation modes for the four kinds of stars) were simultaneously fitted for each filter. After accounting for the metal abundance differences, the slopes of the P-L relations were tested for departures from equality. The results are consistent with the assumption that, for each kind of star, the relations for the F and H stars are vertically offset, with a family of lines corresponding to the different metallicities. In the case of the globular cluster Cepheids, the available B, V data support Arp's 1955 contention that the Cepheids are oscillating in the F and H modes; moreover, the majority of the short-period Cepheids (BL Her stars) appear to be first-overtone pulsators, while most of the Cepheids with periods between 10 and 30 days (W Vir stars) appear to be fundamental-mode pulsators. For the RR Lyrae stars, the slopes of the P-L-[Fe/H] relations in B, V and K show a clear trend with filter type, namely, the absolute values of the slopes increase from B to K. Finally, for the SX Phe stars the differences between the P-L-[Fe/H] relations in B and V for the F and H stars are found to be consistent with the known period-ratio for the double-mode star SX Phe.
Calibration of the Cepheid Distance Scale
Authors: Gieren Wolfgang P. , Fouqué Pascal 
Published: June 2019

AbstractThe absolute calibration of the Cepheid period-luminosity (PL) relation with galactic Cepheids is discussed. Various methods, most importantly the cluster ZAMS-fitting scale and the Baade-Wesselink scale are found to yield PL zero points which agree within ∼ ± 0.1 mag. The present Cepheid calibration sets the Large Magellanic Cloud at μ0 (LMC) = 18.6 ± 0.1 mag, in good agreement with the distance derived from SN 1987A and other methods except RR Lyrae stars which seem to give a shorter distance scale.
Magnetic fields of rapidly oscillating Ap stars
Authors: Mathys G. 
Published: June 2019

Magnetic field appears to play a major role in the pulsations of rapidly oscillating Ap (roAp) stars. Understanding of the behaviour of these objects thus requires knowledge of their magnetic field. Such knowledge is in particular essential to interpret the modulation of the amplitude of the photometric variations (with a frequency very close to the rotation frequency of the star) and to understand the driving mechanism of the pulsation. Therefore, a systematic programme of study of the magnetic field of roAp stars has been started, of which preliminary (and still very partial) results are presented here.Magnetic fields of Ap stars can be diagnosed from the Zeeman effect that they induced in spectral lines either from the observation of line-splitting in high-resolution unpolarized spectra (which only occurs in favourable circumstances) or from the observation of circular polarization of the lines in medium- to high-resolution spectra.
Pulsation and Mass Loss in LPVs
Authors: Bowen George H. 
Published: June 2019

AbstractThe large-amplitude pulsation of long-period variables, together with a number of other interacting processes and phenomena, causes a rich variety of effects on the structure and behavior of the stars. Outflowing winds result, causing extensive mass loss, with profound consequences for stellar evolution. The present status of modeling calculations for LPVs will be discussed first, with various examples. Emphasis will be given to the great importance of complex, nonlinear, time-dependent interactions between things such as the waves and atmospheric shocks that result from pulsation; non-LTE radiative transfer; non-equilibrium chemistry; the growth, changing optical properties, and dynamics of grains; and radiation pressure on both grains and molecules. I will then survey the developing implications and insights from new results and from work now in progress. Some of these concern the structure and the behavior of individual stars (e.g. determination of the pulsation mode and limiting amplitude; properties of more massive stars); some relate to the evolution of individual stars (e.g. evolution of the wind and the mass loss rate; the wind and circumstellar region during helium shell flashes; effects of the star's metallicity); and some relate to the evolution of populations of stars (e.g. the white dwarf mass distribution). All of these, and many more, offer new perspectives and new understanding concerning the character of LPVs and their role in stellar evolution.
Element Diffusion in Pulsating Variables
Authors: Guzik Joyce Ann 
Published: June 2019

AbstractCan pulsation studies yield information on the operation of element diffusion in stars? Can diffusion explain unusual properties of pulsating variables? Element diffusion theory and recent research relevant to these questions will be reviewed, with emphasis on the Sun and δ Scuti stars. High-degree solar p-modes that are sensitive to helium ionization support a reduced convection zone helium abundance consistent with that expected from diffusion. Intermediate-degree p-modes can be used to probe the structure of the convection zone base and constrain possible diffusion-produced composition gradients. δ Scuti variables have shallow convection zones and relatively short diffusion timescales. Helium diffusion may explain unusual period ratios, influence period changes, and affect the amplitudes and light curve shapes of δ Scuti stars.
Higher Vibrational Modes In RR Lyrae Stars
Authors: Glasner S. A. , Buchler J. R. 
Published: June 2019

AbstractA simple method for computing the full spectrum of the linear (nonadiabatic) radial modes is implemented and tested on RR Lyrae models. The growthrates of the vibrational modes display unexpected, but physically correct undulations as a function of period, with the 8th through 10th overtones almost unstable. Caution must be exercised when only a small number of meshpoints is used, or when the meshpoints are not well distributed, as some of these overtones may become unstable, clearly an artifact of the differencing. The role that such unstable high overtones can play in hydrodynamic calculations is demonstrated.
A Survey of BL Herculis-Type Models
Authors: Robert Buchler J. , Moskalik Pawel 
Published: June 2019

AbstractWe have studied the nonlinear behavior of several sequences of BL Herculis-type models. The question arose whether the 2:1 resonance between the fundamental mode and the second overtone would cause the same systematic variation of Fourier parameters of the pulsation cycle with period ratio P2/P0 as was seen in the classical Cepheids. We find that for the BL Her stars, the behaviour of the light-curve Fourier phases is markedly different from the Cepheid case. In particular, ϕ21 exhibits essentially a featureless, monotone increase throughout the range of P2/P0, which is in qualitative agreement with the observed trend (Petersen & Diethelm 1986). In the velocity curves, on the other hand, the 2:1 resonance is a dominant feature and the progression of the Fourier phases and the amplitude ratios is similar to those witnessed in the Cepheids. However, here the sensitivity to the stellar masses and luminosities is significantly stronger. Our results show that radial velocity observations of the BL Her stars would pinpoint the resonance and put important new constraints on the models.
X Sources in δ Scuti Stars: an Ultraviolet Study of 71 Tau
Authors: Pasinetti Fracassini L.E. , Pastori L. , De Nile F. , Poretti E. , Antonello E. 
Published: June 2019

IUE observations of δ Scuti variables were planned to study the correlations between chromospheric activity and dynamics of pulsations, convection, rotation and to search for evidence of mass loss. So far we observed the following stars: ρ Pup, β Cas, o1 Eri, K2 Boo, τ Peg, 69 Tau, 71 Tau and τ Cyg. Results and discussions on our survey may be found in Pasinetti Fracassini et al. (1990) and Fracassini et al. (1991).Ultraviolet spectroscopic data (6 LWP and 3 SWP spectra) of 71 Tau were obtained with IUE in the year 1990, spanning an interval of 5h35rn and covering about 1.5 cycles of the pulsation period. The period, derived from new photometric observations, is 4h32m with an cimplitude of 0m.028. This variable is the most intense X-ray source in the Hyades cluster according to the results of Einstein Observatory.