bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiation Bursts from a Presupernova Collapsar
Authors: Kryvdyk Volodymyr
Published: June 2019

The radiation from the magnetic presupernova star is calculated. This radiation will generate when the magnetosphere of presupernova star compresses during collapse and its magnetic field increases considerably. The variable magnetic field will accelerate the charged particle, which generate radiation when moving in the magnetic field. The particles dynamics and their non-thermal emission in the magnetospheres of presupernova collapsing star with initial dipole magnetic fields and a certain initial energy distribution of charged particles in a magnetosphere are considered. The radiation flux depend on the distance to the star, its magnetic field, and the particle spectrum in the magnetosphere. This flux can be observed by means of modern instruments in broad band (from radio waves to gamma rays). The radiation flux grows with decreasing stellar radius and frequency and can be observed in the form of radiation bursts with duration equal to the stellar collapse time.
Deep Radio Imaging with MERLIN of the Supernova Remnants in M82
Authors: Muxlow T.W.B. , Pedlar A. , Riley J.D. , McDonald A.R. , Beswick R.J. , Wills K.A.
Published: June 2019

An 8 day MERLIN deep integration at 5GHz of the central region of the starburst galaxy M82 has been used to investigate the radio structure of a number of supernova remnants in unprecedented detail revealing new shells and partial shell structures for the first time. In addition, by comparing the new deep 2002 image with an astrometrically aligned image from 36 hours of data taken in 1992, it has been possible to directly measure the expansion velocities of 4 of the most compact remnants in M82. For the two most compact remnants, 41.95+575 and 43.31+592, expansion velocities of 2800 ± 300 km s-1 and 8750 ± 400kms-1have been derived. These confirm and refine the measured expansion velocities which have been derived from VLBI multi-epoch studies. For remnants 43.18+583 and 44.01+596, expansion velocities of 10500 ± 750km s-1 and 2400 ± 250 kms-1have been measured for the first time. In addition, the peak of the radio emission for SNR 45.17+612 has moved between the two epochs implying velocities around 7500km s-1. The relatively compact remnants in M82 are thus found to be expanding over a wide range of velocities which appear unrelated to their size. The new 2002 map is the most sensitive high-resolution image yet made of M82, achieving an rms noise level of 17μJy beam-1. This establishes a first epoch for subsequent deep studies of expansion velocities for many SNR within M82.
Two New Possible Mechanisms of Supernova-Like Explosions
Authors: Tikhomirov V.V. , Yuralevich S.E.
Published: June 2019

Primordial black holes (PBHs) of microscopical size can completely absorb neutron stars (NSs) and white dwarfs (WDs) for less than the Hubble time. NS absorption is accompanied by inverse URCA process giving rise to emission of antineutrino. However considerable part of these antineutrino fails to escape NS being drawn into the growing black hole by accreting NS matter. The final stage of dense WD absorption is accompanied by 1051 erg neutrino burst able to ignite nuclear burning giving rise to supernova-like WD explosion.
Tests for Supernova Explosion Models: from Light Curves to X-ray Emission of Supernova Remnants
Authors: Sorokina Elena , Blinnikov Sergey
Published: June 2019

The successful theoretical supernova explosion models should be able to explain any features of the emission from supernovae at any evolutionary stage. We check several models from two different points of view. With the multi-frequency radiation hydro code STELLA we calculate gamma-ray, bolometric and broad-band UBVI light curves. Then we use the same models to calculate the emission from young supernova remnants. Here we present new plots for gamma-ray luminosity from several SN Ia models and recomputations of bolometric and UBVRI light curves of model 13C for SN 1993J.
Nucleosynthesis in Multi-Dimensional Simulations of SNII
Authors: Travaglio C. , Kifonidis K. , Müller E.
Published: June 2019

We investigate explosive nuclear burning in core collapse supernovae by coupling a tracer particle method to one- and two-dimensional Eulerian hydrodynamic calculations. Adopting the most recent experimental and theoretical nuclear data, we compute the nucleosynthetic yields for 15 M⊙ stars with solar metallicity, by post-processing the temperature and density history of advected tracer particles. We compare our results to 1D calculations published in the literature.
The Infrared Supernova Rate
Authors: Mannucci F. , Cresci G. , Maiolino R. , Valle M.Della
Published: June 2019

Optical searches can detect supernovae (SNe) only if they suffer of a limited amount of dust extinction. This is a severe limitation as most of the core-collapse SNe could explode inside dusty regions. We describe a few ongoing projects aimed at detecting dusty SNe at near-IR wavelengths both in ground-based and HST images and to study their properties.
The Rate and the Origin of Type Ia SNe in Radio Galaxies
Authors: Della Valle M. , Panagia N. , Cappellaro E. , Padovani P. , Turatto M.
Published: June 2019

An analysis of type Ia supernova (SNIa) events in early type galaxies from the Cappellaro et al. [6] database provides strong evidence that the rate of type Ia supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate measured in radio-quiet galaxies, i.e. SNIa-rate(radio-loud) SNe per century and per 1010 (SNU) as compared to SNIa-rate(radio-quiet)= 0.11 ± 0.03 SNU. The exact value of the enhancement is still rather uncertain, but is likely to be in the range ~ 2 – 7. We discuss the possible causes of this result and we conclude that the enhancement of the SNIa explosion rate in radio-loud galaxies has the same common origin as their being strong radio sources, but that there is no causality link between the two phenomena. We argue that repeated episodes of interaction and/or mergers of early type galaxies with dwarf companions are responsible for inducing both strong radio activity in ~14% of early type galaxies, and the ~ 1 Gyr old stellar population needed to supply an adequate number SNIa progenitors.
Supernovae in Galaxy Clusters
Authors: Gal-Yam A. , Maoz D. , Sharon K. , Prada F. , Guhathakurta P. , Filippenko A.V.
Published: June 2019

We present the results of several surveys for supernovae (SNe) in galaxy clusters. SNe discovered in deep, archival HST images were used to measure the cluster SN Ia rate to z = 1. A search for SNe in nearby (0.06 ≤ z ≤ 0.2) Abell galaxy clusters yielded 15 SNe, 12 of which were spectroscopically confirmed. Of these, 7 are cluster SNe Ia, which we will use to measure the SN Ia rate in nearby clusters. This search has also discovered the first convincing examples of intergalactic SNe. We conclude with a brief description of ongoing and future cluster SN surveys.
On the Central Engine of Short Gamma-ray Bursts
Authors: Rosswog Stephan , Ramírez-Ruiz Enrico
Published: June 2019

We assess the ability of neutron star binary coalescence to produce short gamma-ray bursts (GRBs). We find that the neutrino annihilation above the merged remnant will drive bipolar, relativistic jets along the initial binary rotation axis. This outflow can be collimated by the energetic, neutrino-driven baryonic wind that is blown off the remnant. Despite the narrow neutron star mass distribution the apparent luminosities will be spread over a broad range from ~ 1049 to ~ 1052erg s−1, typical jet opening half-angles are around 5 degrees. If the central core of the merger remnant does not collapse immediately convective dynamo action will set in and the available kinetic energy can be transformed into magnetic fields in excess of 1017 G. The corresponding spin-down time scale is ~ 0.2 s, just about the duration of a short GRB.
The Expanding and Accelerating Universe
Authors: Schmidt Brian P.
Published: June 2019

Measuring distances back to a significant portion of the look back time probes the make-up of the Universe, through the effects of different types of matter on the cosmological geometry and expansion. Over the past five years two teams have used type Ia supernovae to trace the expansion of the Universe to a look back time more than 70% of the age of the Universe. These observations show an accelerating Universe which is best explained by a cosmological constant, or other form of dark energy with an equation of state near w = p/ρ = −1. There are many possible lurking systematic effects. However, while difficult to completely eliminate, none of these appears large enough to challenge current results. However, as future experiments attempt to better characterize the equation of state of the matter leading to the observed acceleration, these systematic effects will ultimately limit progress.
Observing the First Stars, One Star at a Time
Authors: Loeb Abraham
Published: June 2019

Gamma-Ray Bursts (GRBs) are believed to originate in compact remnants (black holes or neutron stars) of massive stars. Their high luminosities make them detectable out to the edge of the visible universe. We describe the many advantages of GRB afterglows relative to quasars as probes of the intergalactic medium during the epoch of reionization. The Swift satellite, planned for launch by the end of 2004, will likely open a new era in observations of the high redshift universe.
A Geometric Determination of the Distance to SN 1987A and the LMC
Authors: Panagia Nino
Published: June 2019

Using the definitive reductions of the IUE light curves by [15] and an extensive set of HST images of SN 1987A we have repeated and improved our original analysis [8, 9] to derive a better determination of the distance to the supernova. In this way we have obtained an absolute size of the ring Rabs = (6.23 ± 0.08) × 1017 cm and an angular size R″ = 808 ± 17 mas, which give a distance to the supernova d(SN1987A) = 51.4±1.2 kpc and a distance modulus (m − M)sN1987A = 18.55 ± 0.05. Allowing for a displacement of SN 1987A position relative to the LMC center, the distance to the barycenter of the Large Magellanic Cloud is also estimated to be d(LMC) = 51.7±1.3 kpc, which corresponds to a distance modulus of (m − M)LMC = 18.56 ± 0.05.
Astronomy Education: an international perspective
Authors: Percy John R.
Published: June 2019

Education is important to astronomers because it affects the recruitment and training of future astronomers, and because it affects the awareness, understanding and appreciation of astronomy by taxpayers and politicians who support us. We have an obligation to share the excitement and the significance of our work with students and the public. Education is often neglected by the scientific and professional community - not by us, of course - and by many research universities. Our task is not only to be better astronomy educators ourselves, but to convince and train our students and colleagues to do likewise.
Use of the World Wide Web in astronomy teaching
Authors: Pasachoff Jay M.
Published: June 2019

I discuss the burgeoning World Wide Web and how it can be used to aid astronomy teaching.

I supply a list of a variety of useful Web sites.

The World Wide Web was invented 5 years ago at CERN, which is now translated as the European Laboratory for Particle Physics, as a way of aiding access to information from remote sites. The invention of graphic interfaces, notably Mosaic by a group at the National Supercomputer Center in Illinois and then Netscape Navigator as a private development by many of the original Mosaic people, led to an explosion in use of the Web. Millions of people around the world are now able to access information from over 100,000 Web sites.

There is much astronomical information on the Web, though that information make up only a small fraction of all the information available through this medium.
On-Line Resources for Classroom Use: data and science results from NASA's Hubble Space Telescope and other missions
Authors: Christian C.A.
Published: June 2019

The data, scientific results, and expertise from NASA's Hubble Space Telescope (HST) and other NASA Missions are being integrated into programs that support innovative and experimental methods to improve content in science and math education. Partnerships with science museums, teachers, other educators, community colleges, universities and other key organizations integrate unique and cutting edge science data and the associated satellite technology into resources which have the potential to enhance science, math and technical learning. The inspiring nature of astronomical data and the technology associated with the HST and other missions can be used by teachers to engage students in many inventive activities. The resources created through collaborative teaming will be discussed, as well as the process for creating partnerships to benefit the education community. Many NASA supported programs encourage electronic access and distribution of multi-media interactive activities and curriculum support materials distributed across the Internet.
Project LINK: A Live and Interactive Network of Knowledge
Authors: Welsh Barry , Hawkins Isabel
Published: June 2019

Project LINK (A Live and Interactive Network of Knowledge), is a collaboration of Eureka Scientific, Inc., the San Francisco exploratorium Science Museum, and NASA/Ames Research Center. Project LINK has demonstrated video-conferencing capabilities from the Kuiper Airborne Observatory (KAO) to the San Francisco Exploratorium in the context of science education outreach to K-12 teachers and students. The project was intended to pilot-test strategies for facilitating the live interface between scientists and K-12 teachers aboard the KAO with their peers and students through the resources and technical expertise available at science museums and private industry. The interface was based on Internet/macintosh video conferencing capabilities which allowed teachers and students at the Exploratorium to collaborate in a live and interactive manner with teachers and scientists aboard the KAO. The teachers teams chosen for the on-board experiments represented rural and urban school districts in California. The teachers interfaced with colleagues as part of the NASA-Funded Project FOSTER (Flight Opportunities for Science Teacher Enrichment).
What to Cover and When
Authors: Sadler Philip M.
Published: June 2019

Imagine trying to teach reading to students who do not know the alphabet or driving to someone who does not know the purpose of the brake. As teachers, we have a view of what the fundamental ideas that our field are and make decisions about their coverage and order in our courses. Yet, research shows that students rarely have the foundation that we expect; they hold misconceptions about the physical world that actually inhibit the learning of many scientific concepts. Moreover, the metaphors that we employ for building student understanding: reliving the historical development of the field, journeying from the closest to farthest reaches of the universe, and observing the objects in the sky, are only based on our own beliefs in their effectiveness. Empirical evidence shows that they are of little value; there is rarely any lasting change in students’ conceptual understanding in science.
Alternative frameworks amongst University of Plymouth Astronomy Students
Authors: Broughton Mike P.V.
Published: June 2019

In recent years much research into conceptual understanding of science has been carried out. Oddly, Astronomy (one of the smallest sciences in terms of pupil numbers) is possibly one of the most widely studied subjects, with numerous papers being produced revealing the intuitive ideas of (usually) young school children. Within these papers it is generally recognised that if students cannot assimilate the fundamental concepts of a subject, then their own initial frameworks are altered accordingly, producing mis-conceptions.

Much of this research into pre/mis-conceptions, alternative frameworks etc, has been concerned with the knowledge of gravity or the shape of the Earth, the Sun and other such bodies. Another area heavily researched is that of phases/eclipses, and how the young children of today perceive these phenomena.

The research presented here takes the findings from earlier papers and extends it by assessing astronomy students at the University of Plymouth.
Robot Telescopes: a new era in access to astronomy
Authors: Baruch J.E.F.
Published: June 2019

For the teaching of astronomy there can be no alternative to the hands-on experience of using instruments on a real telescope observing on a clear dark night. Such experience is not possible for millions of students who are excited by the ideas of astronomy. It is not merely one of cost. The logistics of assembling a class of students after school hoping for clear skies destroys the possibilities of real observing for the majority of students. Robot telescopes change all that.

In educational terms a robot telescope can provide a range of experiences of observational astronomy. The development of CD-ROM and the Internet to support classroom learning have produced the concept of REAL(Dunlap 1996): a Rich Environment for Active Learning as an appropriate framework on which to develop the classroom response to these technologies. The Bradford Robot Telescope has demonstrated student centred experiences to generate a Rich Environment for Active Learning(REAL), for astronomy.
The Total Solar Eclipse of October 24 1995
Authors: Raghavan N.
Published: June 2019

The total solar eclipse of October 24, 1995, whose central line cut across the subcontinent of India, was only the second total solar eclipse visible from India in this century. The previous total eclipse visible from India occurred on February 16, 1980. At that time the print media filed widely varying reports on what the effect of seeing the eclipse would be, without much coordinated input from astronomers. With the new confused advice reinforcing old fears, almost the entire population literally hid indoors, fearing the worst. Many Indian astronomers silently resolved to themselves then, that public education must be taken up with the same level of seriousness as research programmes during the next eclipse.
How to Suceed in Convincing Municipalities to build Astronomy Centres: the experience of Campinas Region
Authors: Bretones A.L.K. , Bretones P.S.
Published: June 2019

The objective of this work is to make known the astronomical activities in the region of Campinas, the process of developing municipal cooperation and the general conclusions that reflect this process.

This research has been done by means of interviews with people related to the creation of astronomical centers in the region of the city of Campinas that is located in the state of São Paulo in Brasil (Fig. 1 and 2).

The conditions studied are related with this region but many ideas could be used in developing countries or others.
Solar Eclipses and Public Education
Authors: Pasachoff J. M.
Published: June 2019

Solar eclipses draw the attention of the general public to celestial events in the countries from which they are visible, and broad public education programs are necessary to promote safe observations. Most recently, a subcommittee of IAU Commission 46 composed of Julieta Fierro (from the National University of Mexico), the Canadian professor of optometry Ralph Chou (from the University of Waterloo) and me provided information about safe observations of the 24 October 1995 eclipse to people in Pakistan, India, Cambodia, Vietnam, and Guam. An important point is that there are advantages to seeing eclipses, including inspiration to students, and that people must always be given correct information. If scare techniques are used to warn people off eclipses, when it is later found out that the eclipse was not dangerous and, indeed, was spectacular, these students and other individuals will not trust warnings for truly hazardous activities like smoking, drugs, and behavior that puts one at risk for AIDS.
“Plaza del Cielo” Complex: its state of evolution
Authors: Camino N.
Published: June 2019

We consider that one of the most important aspects in the harmonic development of a person is his relationship with the natural environment in which he lives: in that environment he initially trains and enlarges his curiosity and the capacity for astonishment, both innate properties of human beings. It is so much so that we could locate the germ of all creative future activities, scientific or otherwise, in what happens with those characteristics during the years of childhood, that if fully developed will help children to become sensitive and critical adults. So we consider it necessary to generate the mechanisms to reinforce the sensibility, the critical observation and the interaction with natural phenomena, in a systematic way, as we propose in “Plaza del Cielo”.
Astronomy as a School Subject
Authors: Fouquet J-L.
Published: June 2019

a) From 9 to 11, a “Science and Technology” curriculum is extensively provided by primary schools :

“Pupils, through some aspects of the scientific approach, are encouraged to develop their abilities to formulate questions and logical answers through a wide scope of investigative and practical observations and other scientific activities such as collecting measures, linking data, interpreting documents“ - extract from the official syllabus which includes the following chapters :

1. Unity and Diversity of the Living World :

•

the development of living creatures,

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animal reproduction,

•

human sexuality,

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ecology,

•

nutrition.
A Program Incorporating Physics, Astronomy and Environment
Authors: Kononovich E.V. , Fadeeva A.A. , Kiselev D.F. , Zasov A.V.
Published: June 2019

A cultural role of astronomical education at all levels is well known and it is needless to repeat the corresponding arguments. Nobody denies it, but nobody can propose any universal way of introducing Astronomy on a level this branch of science deserves.

There is a good tradition to appreciate Astronomy in Russian schools. For more than a century part of the natural history science in school dedicated to the Universe has been considered as a separate part of the school curriculum in Russia. Before 1917 it was named Cosmography, and Astronomy thereafter. And up to now there is no decision or prescription to rule it out of the school program.
Magnetic Fields in Be Stars? (Review Paper)
Authors: Barker Paul K.
Published: June 2019

No mean longitudinal or toroidal magnetic fields have yet been detected on any classical Be star. Models of stellar winds and circumstellar envelopes around magnetic Be stars are not appreciably constrained by present observed upper limits on field strength. A few magnetic Be stars do exist among the helium strong stars, but these objects show spectral phenomenology which is unmistakably distinct from that shown by every other object known as a Be star.
Short Term Photometric and Spectroscopic Variability of a Sample of Be Stars
Authors: Alvarez M. , Michel R.
Published: June 2019

Previous studies of variable Be stars show that the short-term variability is a common, but not well understood phenomena. From a list of ‘candidates’ given by Alvarez (1980) and Schuster & Alvarez (1983) under a cooperative program between France and México, we choose some interesting Be objects to study their behaviour both in spectroscopy and photometry. We are reporting some preliminary results of our observations.
Is HR 9070 Really Pulsating?
Authors: J.P. Sareyan , M. Alvarez , J. Chauville , J.M. Le Contel , R. Michel , D. Ballereau
Published: June 2019

As Be stars and classical β CMa variables both have a distribution peak at B2, one can wonder if there is a connection between these two phenomena. A way to solve this problem could be to carry out a systematic survey of emission on short periodic B variables,over months and years.

Another way, chosen by our grouns in Nice, Ensenada and Meudon, is to improve time resolution in photometric and spectrographic observations on the Be stars already known to have short time scale variations. Special attention is paid to longitude cooperation, essential to detect or measure longer time constants.
Some Important Results From Two Photometric Campaigns on Short Term Variability in Be Stars
Authors: Stagg C.R.
Published: June 2019

In 1983 and 1984 a programme of UBV observations was carried out to set up a network of standard stars, identify short term variables, and analyse the variability of the 86 bright (V ≳ 6.5) southern (δ < -20°) Be stars.

The timing of the observations was designed specifically to reveal short term variability. Each group of Be and comparison stars was observed at least four times. Where possible, the first two sets of observations were made on one night and the next two sets on the next night (and sometimes a fifth set of observations was also made). Eleven Be stars were identified as possible short or intermediate term variables (Stagg, in preparation). These included the Be star 28 ω CMa, whose V and B-V (but not U-B) variations were consistent with the spectroscopic period of 1.37 days found by Baade (1982).
Rotating Stellar Atmospheres (Review Paper)
Authors: Cassinelli Joseph P.
Published: June 2019

The effects of rapid rotation on the emergent energy distribution, line profiles, atmospheric motions and polarization are discussed. A simplified explanation of some of the effects is presented. Results of detailed radiation transfer calculations are briefly reviewed. The rotation can lead to circulation and turbulent motions in the photospheric layers which could affect the outflow from the Be stars. The rotation rates actually observed in the Be stars are sufficiently below the critical rate that many of the effects predicted by the plane parallel atmosphere calculations should be small. Nevertheless, the models are useful and necessary for estimating rotation speeds from lines that are widely separated in wavelength. The rapidly rotating photospheric models predict far too small an infrared excess, as well as too small an intrinsic polarization. The explanation of these observations requires that geometrically extended envelopes be considered. Theoretical models for the intrinsic polarization are critically discussed. It is stressed that polarization is a powerful diagnostic for determining the asymmetrical structure of the outer atmospheres of the Be stars.
Double Periodicity in Be Stars
Authors: Clarke D. , McGale P.A.
Published: June 2019

Photometric periodicities with two unequal maxima and minima reported for Be stars are shown to result from a fundamental and overtone associated with rotation of an atmospheric bulge. It is the form of the scattering function of the free electron that produces the double periodicity; the stellar geometry — co-latitude of the bulge and inclination of the stellar rotational pole — controls the amplitudes of the two components. The form of the light curves is consistent with the oblique rotator model.
Long-Term Polarization Changes of 88 Her
Authors: Arsenijević J. , Jankov S. , Djurašević G.
Published: June 2019

Linear optical polarization of 88 Her has been measured in V spectral region during the period 1974–1985. The mean annual values of the intrinsic polarization parameters are presented. The polarization percentage changes from 0.15%(1976) to 0.56%(1979). Small values of the polarization percentage correspond to the period when the envelope effect is negligible. The maximum of polarization percentage has been found during the early period of strong shell phase. The polarization position angle varies between 53 and 83 degrees.
Near Infrared Spectra of Southern Be Stars
Authors: Pastori L.
Published: June 2019

Spectra of northern Be stars in the near infrared region have been already described by some authors (see Slettebak, 1979 for a brief review). This paper presents general results for southern Be stars obtained from more than 100 spectrograms in the region λλ7750-9000 Å the spectra were taken in four nights of February 1985 at the 1.5m ESO telescope with the reticon instrumentation; the dispersion is 58 Åmm-1. All the available southern Be stars (right ascension between 4h and 17h) listed in the Bright Star Catalogue (Hoffleit and Jaschek, 1982) were observed. Table 1 lists the number of stars vs. spectral type (columns 1 and 2) and the number of stars which display emission at the Paschen series, 0I λ8446 Å and Call triplet (columns 3 to 5).
Profiles of Emission Lines From Rotating Disks
Authors: Brown D.A.
Published: June 2019

Profiles of emission lines contain key information on the dynamics, the physical condition, and the geometry of the cool envelopes of Be stars. Despite much observational evidence, doubts persist about the rotating, equatorial ring model first proposed by Struve (1931) to explain the gross features of the profiles and later developed by Huang (1972) in the two-dimensional, transparent limit. The basic rotating model is now reconsidered and profile formation studied from a physical point of view.

The excitation structure of a disk rotating around a B star in circular, Keplerian orbits is computed by means of a new, iterative approach. The approach takes full account of both stellar and diffuse radiation at line and continuum frequencies and makes no assumptions about the optical properties of the disk. It is applied to an isothermal model with parameters based on observations of the shell star 48 Librae.
A Rotating, Magnetic, Radiation-Driven Wind Model Applied to Be Stars
Authors: Poe C. H. , Friend D. B.
Published: June 2019

With their rotating, magnetic, radiation-driven wind model, Friend & MacGregor (1984) found that rapid rotation and an open magnetic field could enhance the mass loss rate (ṁ) and terminal velocity (V∞) in an 0 star wind. The purpose of this paper is to see if this model could help explain the winds from Be stars. The following features of Be star winds need to be explained: 1) Be stars exhibit linear polarization (Coyne & McLean 1982), indicating an enhanced equatorial density. 2) There appears to be enhanced mass loss (at low velocity) in the equatorial plane, from IRAS observations of Waters (1986). 3) The width of the broad Balmer emission lines remains unexplained.
HE I Lines in the BE + K Binary KX and
Authors: Štefl S.
Published: June 2019

KX And (HD 218:193) is a peculiar interacting binary with the period of about 38.9 days. This study is a first attempt to model the system as a double-line binary. The main results of the He I - line analysis are summarized.

The intensity tracings of sixty blue-violet spectra were used. All the spectra were obtained in the coudé focus of the Ondřejov 2m telescope in the period 1972 – 1981. The original dispersion was 8 or 16 A mm -l. The phases of the observations were computed according to the ephemeris derived from the radial velocities of optical shell lines (Štefl et al. in preparation). Phase zero corresponds to the velocity maximum.
On the Percentage of Be Stars in Galactic Open Clusters
Authors: Reitermann A. , Krautter J. , Wolf B. , Bashek B.
Published: June 2019

Knowing that especially young clusters can contain a considerable high fraction of Be stars (Mermilliod 1982, Feast 1972) we made a spectroscopic study of Hα on the ratio of B/Be stars. The aim was to select normal B stars for chemical abundance analyses.

It is well known that a promising way to investigate the evolutionary status of Be stars is to study their frequency and positions in the H-R diagram of open clusters. However, these studies have not yet provided satisfactory results (cf. e.g. Slettebak 1985); observations concerning the B/Be star ratio are badly needed. Therefore we present our observations although they are only a by-product from a different program.
Evolutionary Models For Be X-Ray Binaries
Authors: de Loore C. , Sybesma C. H. B.
Published: June 2019

Be X-ray binaries have the following general characteristics of interest for evolutionary scenarios: the spectral type of the non-compact star is B2 - 09 (e), the orbital periods are large, ranging from 16 to 581 days, the orbital eccentricities can be large, which could be related to the fact that the X-ray stages are transient; the masses of the optical components range from 10 to 20 M⊙ and their radii are relatively small (5 - 10 R⊙). The optical luminosity is lower than 3 x 10 4L⊙.
Spectral Variability of Beta Pictoris and the Search for Nearby Proto-Planetary Systems
Authors: Bruhweiler F.C. , Kondo Y.
Published: June 2019

Continued UV monitoring at high spectral resolution utilizing the International Ultraviolet Explorer (IUE) of the IRAS candidate proto-planetary system, Beta Pictoris (Also see Kondo and Bruhweiler 1985; and references cited therein.), has revealed two components to the circumstellar absorption. The first is a stable absorption component at or near the stellar photospheric velocity, possibly arising from gas orbiting in a gaseous disk, while the second component represents strong variable excess absorption sometimes extending up to +200 km s-1. The variability of this second component accounts for most of the spectral variability observed in Beta Pic. Variable circumstellar absorption observed in the resonance lines and UV62 and 63 multiplets of Fe II reveal an episode of mass inflow which lasted over a period of 12 to 13 months (see Fig. 1).
The Infrared Period - 2.2/µm Magnitude Relation for RR Lyrae Stars
Authors: Longmore A.J.
Published: June 2019

The observational and theoretical basis for the log P vs. K-mag relation is reviewed. The observed gradient in all well observed globular clusters agrees well with the theoretical prediction. An indistinguishable result is found for field RR Lyrae stars whose absolute magnitudes have been determined from infrared Baade-Wesselink analyses. A full reference list is given for the source of these magnitudes. Application of the results to find the distance to globular clusters and the Galactic Centre is discussed.
Cepheids in IC 4182, Calibration of SNIa 1937C and the Hubble constant
Authors: Saha A. , Sandage A. , Panagia N. , Tammann G. A. , Labhardt L. , Schwengeler H. , Macchetto F. D.
Published: June 2019

Observations with the Wide Field Camera on HST were examined, and 27 Cepheids were discovered. Photometry and period analysis have produced unambiguous light curves free of alias. The observed P-L relation has a slope consistent with seminal calibration studies of Galactic and LMC Cepheids. An apparent distance modulus (in V) of 28.47 ± 0.10 to IC 4182 is derived. This implies that Mv(max) for SNIa 1937C is -19.92 ± 0.2 mag, independent of everything except differential absorption between the Cepheids and the supernova. Using this to calibrate Hubble diagrams for SNIa by several authors, and allowing for a 1-σ uncertainty in the absolute magnitude from the calibration of only one SNIa, we obtain H0 = 45 ± 14kms-1Mpc-1.
Implication of a P-L Relation of Mira Variables
Authors: Shibahashi Hiromoto
Published: June 2019

Feast et al. (1989) obtained observationally a period-luminosity (P-L) relation of Mira variables in LMC. Basically, fundamental periods of stellar pulsation should be determined by two quantities —a mass and a radius of the star. The existence of a P-L relation implies a special condition that reduces a function of two variables into a function of only a single variable. Though the AGB appears as a thin line in the HR diagram like the Cepheid instability strip, it is an “asymptotically” merged line of evolutionary tracks of stars in a range of about 0.5-3 solar masses. This fact means that the masses of stars on a point of the AGB are not unique though the radii and the effective temperatures are unique, respectively. Therefore we cannot expect, in the case of AGB stars, that a period is reduced to a function of a single variable.
The Internal Structure of White Dwarf Stars Using the Whole Earth Telescope
Authors: Bradley P.A.
Published: June 2019

White dwarfs are the final end state for the majority of stars, and hold clues to help solve many current pressing astrophysical problems. We can perform asteroseismology on the pulsating white dwarfs to better understand their internal structure and input physics, paving the way to a better understanding of astrophysics, stellar evolution, and the history of our Galaxy. I describe briefly the potential of asteroseismology by using it to infer the internal structure of PG1159-035.
Chaos in Pulsating Variable Stars: Preliminary Analysis of Photometric Photometry and Observational Constraints of Detection
Authors: Kreidl T.J.
Published: June 2019

Chaos theory has been applied to a variety of variable stars, but few convincing candidates for chaos have been identified. Here, well-established analysis methods have been applied to some very extensive data sets of rapidly oscillating Ap (roAp) stars and one white dwarf. It it shown that in spite of the amount of data, the signal-to-noise ratio makes positive detection of chaos extremely difficult, especially due to scintillation noise. A new form of dimension computation is presented and discussed. Simple models were constructed to show what noise levels can be tolerated before the detection of chaos is no longer possible and comparisons are drawn with data that could be obtained in the future from space. The lack of phase and amplitude stability in HD 134214 and mode switching in HD217522 and HD 137949 are pointed out as the possible results of chaos, making frequent monitoring of roAp stars desirable.
Pulsation of Rotating Magnetic Stars
Authors: Shibahashi H. , Takata M.
Published: June 2019

Recently, one of the rapidly oscillating Ap stars, HR 3831, has been found to have an equally split frequency septuplet, though its oscillation seems to be essentially an axisymmetric dipole mode with respect to the magnetic axis which is oblique to the rotation axis (Kurtz et al. 1992; Kurtz 1992). In order to explain this fine structure, we investigate oscillations of obliquely rotating magnetic stars by taking account of the perturbations due to the magnetic fields and the rotation. We suppose that the star is rigidly rotating and that the magnetic field is a dipole field and its axis is oblique to the rotation axis. We treat the effects of the rotation and of the magnetic field as perturbations. In doing so, we suppose that the rotation of the star is slow enough so that the effect of the rotation on oscillations is smaller than that of the magnetic field.
The Pulsation Characteristics of HD 93044
Authors: Zong-li Liu , Zhi-ping Li
Published: June 2019

The amplitude and period of the first frequency increased, but the amplitude and period of the second frequency decreased. Two new frequencies (10.5011 and 2.0484 c/d) were found. The frequency (2.0484 c/d) might be an interaction term from which resonances can occur and then lead amplitude and period variations.
Line Profile Variations of Rotating Pulsating Stars
Authors: Aerts C. , De Pauw M.
Published: June 2019

Line-profile variations (LPVs) are often seen in early-type stars. They were first detected in the β Cephei stars, where they are due to radial as well as to nonradial pulsations (NRP). It is still a matter of debate whether NRP is also the cause of LPVs in broad-lined B- and Be stars.

The study of LPVs of nonradially pulsating stars is often considered to be especially interesting in the case of rapid rotators, because in such stars the line profiles may offer a Doppler image of the stellar surface. Almost all investigators conclude that only sectorial modes with high -values can properly account for the observations of LPVs in broad-lined stars; on the other hand, high-degree modes are almost never seen in slowly rotating stars.

We point out here that the expression for the velocity field which is usually adopted, is not valid for rapid rotators.
β Cephei Pulsation Anomalies: Potential New Windows into the Instabilities and Evolution of Early B Stars
Authors: Goldberg B.A. , Polidan R.S. , Crowe R.A. , Aikman G.C.L. , Bambery R.J. , Gathright J.T. , Odgers G.J.
Published: June 2019

We have obtained Voyager Ultraviolet Spectrometer (UVS) measurements of well-known β Cephei stars, which now total more than 1500 hours (> 300 pulsation cycles!) and which constitute the most comprehensive coherent data set that can address fundamental pulsation properties of a significant cross-section of the group. The extended measurement sequences for individual stars, which cover many successive pulsation cycles at wavelengths where pulsation amplitudes reach a maximum, can provide more comprehensive tests of pulsation stability than any ground-based data. During 1990-91, we acquired more than 100 hours of ground-based high-resolution spectroscopic observations and UBV photometric observations, simultaneous and near-simultaneous with the UVS data set. Analysis has been initiated at NASA's Goddard Spaceflight Center (NASA/GSFC), the University of Hawaii at Hilo (UH Hilo), and the Dominion Astrophysical Observatory (DAO).
Variable UV Line Emission in S Carinae: Miras Do Not Fear Change
Authors: Brugel E.W. , Davis R. , Bookbinder J.
Published: June 2019

The object S Carinae is a bright, relatively hot, short (149d) period mira. As expected, the Mg II h and k lines dominate the ultraviolet line spectra during a large fraction of the pulsation cycle. There are also numerous emission lines of Fe I and Fe II produced by either fluorescense or possibly collisional excitation. The unifying “theme” for all the ultraviolet line emission is variability - during a pulsation cycle one observes changes in the intensity, the central wavelength and (for the stronger lines) the line profile.
Pulsations and declines of RCB stars
Authors: Cottrell P.L. , Lawson W.A.
Published: June 2019

We have continued to observe many of the R Coronae Borealis (RCB) stars and other related hydrogen-deficient carbon stars. We wish to more fully investigate the photometric and spectroscopic properties of these peculiar stars.

The UBVRI photometric data (acquired at Mount John University Observatory, MJUO) are being used to investigate whether the periods determined by Lawson et al. (1990), based on time intervals of up to 1100 d, are still evident in the larger datasets which now cover time intervals of up to 2200 d.

The long time baseline of photometric observations that we have been able to acquire has enabled us to accumulate an extensive database of decline photometry. These are used to investigate links with the pulsations at maximum light in order to get a better understanding of this remarkable phenomenon.
Pulsations of Proto-Giant-Planets
Authors: Wuchterl G.
Published: June 2019

Nonlinear oscillations of proto-giant-planets have been found in recent numerical calculations relevant to planetary formation. Pulsations are excited in two phases of the protoplanetary evolution, (a) In an ‘instability strip’ at core masses of typically 0.2M⊙ (M⊕ is the earth mass). Perturbations grow into the nonlinear domain and saturate into perodic variations with relative luminosity-amplitudes of 0.2m (b) At the so called critical mass (typically at Mcore ≈ 15M⊕). There the pulsations drive a strong mass loss. A large portion of the envelope is ejected. Then the mass loss fades and the envelope settles into a new quasi-equilibrium. This remnant — a post nucleated instability protoplanet — has a compact envelope and is in core and envelope mass similar to Uranus and Neptune.
Time Dependent Convection and the Pulsations of Polaris
Authors: Morgan Siobahn M. , Cox Arthur N.
Published: June 2019

The low amplitude radially pulsating classical Cepheid Polaris (α UMi) has well observed decreasing radial velocity and light amplitudes and an increasing period. Recent work indicates that Polaris may stop pulsating by 1995 (Dinshaw et al, 1989), which would make it an excellent indicator for the red edge of the Cepheid instability strip in the Hertzsprung-Russell diagram.

We have calculated Population I envelope models with 200 mass shells of a 5.5 M⊙ star near Teff = 5700 K and log(L/L⊙) = 3.11 which match Polaris’ characteristics (Arellano Ferro, 1984). Models were calculated using the Linear Non Adiabatic pulsation analysis code of Castor (1971). The effects of convection on the pulsational stability were calculated with the time dependent convection theory of Cox, Brownlee and Eilers (1966) as discussed by Cox and Guili (1968). The characteristics of the models were altered until the appropriate period, temperature and luminosity were obtained.
Amplitude of RR Lyrae Star Light Curves: Comparison between Observations and One—Zone Model Predictions
Authors: Antonello E. , Cermiti S.
Published: June 2019

Stellingwerf's one–zone model is a simple and useful tool for reproducing the main observed pulsational characteristics of RR Lyrae and high amplitude δScuti stars, in particular their light and color curves (Stellingwerf et al., 1987, Ap.J.313, L75; Antonello, 1990, Astr. Ap.230, 127). In the present poster we show in better detail a comparison of the observed amplitudes of the light curve at various wavelengths with those predicted by the one–zone model; a preliminary result on this subject was reported in the short note by Grieco and Antonello (1990, in Confrontation between Stellar Pulsation and Evolution p. 101). As in the previous applications, here we use the published grids of atmospheric models (Kurucz, 1979, Ap.J.Suppl. 40, 1) and we do not consider possible shock effects.
Pulsation Variables in the AF stars of the Case Low-Dispersion Survey
Authors: Kinman T.D.
Published: June 2019

The AF stars are those of spectral types A and F that have been discovered on objective-prism plates taken with the Burrell Schmidt in the Case Low-Dispersion Northern Sky Survey (Pesch and Sanduleak, 1983). In SA 57, this survey is complete to V = 16.5. In this field and also in the Lick Astrograph RR Lyrae survey field RR 7 (in the anticenter) the AF stars comprise (a) blue horizontal branch stars and RR Lyrae stars of the halo and (b) stars which have the higher surface gravities of main sequence stars. The two groups can be separated primarily by their differing Balmer jumps and Balmer line-widths. The latter group (which may well include blue stragglers of both Pop I and Pop II) extends some 10 kpc above the galactic plane and shows a wide range of metallicity. Photoelectric photometry of this AF star sample has allowed the detection field RR Lyrae stars of lower-amplitudes than could have been found by conventional blinking techniques; this has led to a significant increase in the number of RR Lyrae stars that are known in SA 57 and RR 7. The cooler main sequence and/or blue straggler AF stars lie in the zone of pulsational instability and one higher-amplitude δ-Scuti star was detected in field RR 7. It is suggested that these AF stars provide a good sample for studying the incidence of pulsation in the population of older stars that extends beyond the thin disk.
Fundamental Mode and First Overtone Mode Cepheids in the Small Magellanic Cloud
Authors: Smith H.A. , Silbermann N.A. , Baird S.R. , Graham J.A.
Published: June 2019

We report results of a new photographic survey of variable stars in a 1 x 1.3 degree region near the Northeast Arm of the Small Magellanic Cloud. We have discovered 133 new variable stars in this field and have determined periods and B lightcurves for 78 new and 72 previously known variables. At periods shorter than about 3 days, the Cepheid period-luminosity relation splits into two sequences. The brighter sequence is believed to be populated by stars pulsating in the first overtone radial mode, wherecis the fainter sequence is populated by fundamental mode pulsators. The peak in the Cepheid period-frequency distribution occurs near a period of 1.8 days. The surface density of RR Lyrae stars in this field is comparable to that in an outlying SMC field near NGC 121.