bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistics Of Multiple Stars
Authors: Tokovinin A. 
Published: June 2019

AbstractThe statistics of stellar systems of multiplicity three and higher is reviewed. They are frequent, 0.15−0.25 of all stellar systems. Some 700 multiples are expected among the 3383 stars of spectral type F, G, and K within 50 pc, while only 76 of them are actually known. Many (if not all) close binaries have distant tertiary components, indicating that angular momentum exchange within multiple systems was probably critical in forming short-period binaries. The ratio of outer to inner periods in the best-studied nearby multiples and in low-mass pre-main sequence multiples does not exceed 104 at the formation epoch; larger ratios are produced by subsequent orbital evolution. All multiples with well-defined orbits are dynamically stable, the eccentricities of outer orbits obey the empirical stability limit Pout(1 – eout)3/Pin > 5 that is more strict than current theoretical limits. Relative orientation of orbits in triple stars shows some degree of alignment, especially in weakly-hierarchical systems. The statistics support the idea that most multiple stars originated from dynamical interactions in small clusters.
The Spectroscopic orbit of ϕ Cygni, A System with two Late-Type Giants
Authors: Fekel Francis C. 
Published: June 2019

AbstractImproved orbital elements for ϕ Cygni have been determined from 47 new high-dispersion spectroscopic observations. The period and eccentricity are 434.14 days and 0.559, respectively. Minimum masses plus the inclination of the visual orbit result in masses of 2.16 and 2.06 M⊙ for the two giants. The small magnitude difference of 0.25 mag and a mass ratio of 1.044 indicate that both giants are most likely in the helium-burning phase of their evolution.
Photometry of Eclipsing Binary Stars in the Large and Small Magellanic Clouds
Authors: Bayne G.P. , Tobin W. , Pritchard J.D. , Bond I. , Pollard K.R. , Besier S.C. , Noda S. , Sumi T. , Yanagisawa T. , Sekiguchi M. , Honda M. , Muraki Y. , Takeuti M. , Hearnshaw J.B. , Kilmartin P.M. , Dodd R.J. , Sullivan D.J. , Yock P.C.M. 
Published: June 2019

AbstractThe light curves for three eclipsing binaries in the Magellanic Clouds have been obtained using CCD uVJIC photometry. One target in the LMC, MACHO*05:36:48.7−69:17:00, is an eccentric system, e = 0.20, with a period of 3.853534 ± 0.000005 d. Initial solutions indicate a primary component in the range Teff,1 = 20,000−35,000K and the secondary Teff,2 1000−2000K cooler than the primary, with inclinations ranging i = 84.2° − 86.0°. Two targets in the SMC, MOA J005018.4-723855 and MOA J005623.5−722123, have periods of 1.8399±0.0004 and 2.3199 ± 0.0003 days respectively. Both have circular orbits with the former being a semi-detached system.
Accretion of Protobinary and Evolution of the Mass Ratio
Authors: Hanawa Tomoyuki , Ochi Yasuhiro , Sugimoto Kanako 
Published: June 2019

AbstractWe have reexamined accretion in a protobinary system with two dimensional numerical simulations. We consider protostars which rotate around the center of the mass with circular orbits. The accreting gas is assumed to flow in the orbital plane. It is injected from a circle whose radius is 5 times larger than the orbital separation of the binary. The injected gas has constant surface density, in fall velocity, and specific angular momentum. The accretion depends on the specific angular momentum of the injected gas, jinf. When jinf is small, the binary accretes the gas mainly through two channels: one through the Lagrangian point L2 and the other through L3. When jinf is large, the binary accretes the gas only through the L2 point. The primary accretes more than the secondary in both cases, although the L2 point is closer to the secondary. After flowing through the L2 point, the gas flows half around the secondary and through the L1 point to the primary. Only a small amount of gas flows back to the secondary and the rest forms a circumstellar ring around the primary. The accretion decreases the mass ratio, q = M2/M1, where M1 and M2 denote the masses of the primary and secondary, respectively. The accretion rate increases with time. When jinf is large, it is negligibly small in the first few rotation periods.
IR Geminorum: Complex Disk Behavior During Quiescence
Authors: Li Zongyun , Leung Kam-Ching , Martin Gaskell C. 
Published: June 2019

AbstractWe have carried out nearly continuous V-band photometry from Yunnan Observatory (China) and Behlen Observatory (Nebraska, USA) of IR Gem for over six days starting three days after a normal outburst in January 2002. Our observations show that the behavior of this SU UMa star is unexpectedly complicated, and that for IR Gem, quiescence is potentially more interesting than outbursts. We find a photometric modulation with a period of 98.5 min, exactly equal to the spectroscopically determined orbital period. We tentatively attribute this to heating of the secondary. During the first three days a modulation appeared with a period 5% longer than the orbital period. We suggest that this might be a signature of apsidal precession of an eccentric disk. During the middle of our period of observations a modulation with a period 3% shorter than the orbital period appeared. We invoke nodal precession to explain this. A slower modulation we found with a period of about 1.7 d is roughly consistent with the expected period of nodal precession. There is a puzzling 4.3 d period modulation that we suspect may be the result of beating between apsidal and nodal precession frequencies. We also find inexplicable quasi-periodic cycles on timescales drifting from ~ 0.2 to ~ 0.4 days.
X-ray Observations of SN 1993J
Authors: Zimmermann H.-U. 
Published: June 2019

SummaryIn April 2001 SN1993J was observed with both the PN and MOS cameras of the XMM-Newton observatory. A 2-component thermal emission model assuming ionization equilibrium provides a good fit to the spectrum in the 0.3 to 11 keV energy band, but fits to shock models show also acceptable results. The development of the X-ray temperatures over the first 8 years after the explosion is discussed in the light of the standard SN model. The long term X-ray lightcurve shows a general decline of the luminosity with Lx ∝ t−0.30.
High-Resolution Radio Imaging of Young Supernovae: SN 1979C, SN 1986J, and SN 2001gd
Authors: Pérez-Torres M.A. , Marcaide J.M. , Alberdi A. , Ros E. , Guirado J.C. , Lara L. , Mantovani F. , Stockdale C.J. , Weiler K.W. , Diamond P.J. , Van Dyk S.D. , Lundqvist P. , Panagia N. , Shapiro I.I. , Sramek R. 
Published: June 2019

SummaryThe high resolution obtained through the use of VLBI gives an unique opportunity to directly observe the interaction of an expanding radio supernova with its surrounding medium. We present here results from our VLBI observations of the young supernovae SN 1979C, SN 1986J, and SN 2001gd.
Thermonuclear Supernova Explosions and Their Remnants: The Case of Tycho
Authors: Badenes Carles , Bravo Eduardo , Borkowski Kazimierz J. 
Published: June 2019

SummaryWe propose to use the thermal X-ray emission from young supernova remnants (SNRs) originated in Type Ia supernovae (SNe) to extract relevant information concerning the explosion mechanism. We focus on the differences between numerical 1D and 3D explosion calculations, and the impact that these differences could have on the modeling of young SNRs. We use the remnant of the Tycho supernova (SN 1572) as a test case to compare with our predictions, discussing the observational features that allow to accept or discard a given model.
Weak Interaction Processes in Core-Collapse Supernovae
Authors: Martínez-Pinedo G. , Langanke K. , Sampaio J.M. , Dean D.J. , Hix W.R. , Messer O.E.B. , Mezzacappa A. , Liebendorfer M. , Janka H.-Th. , Rampp M. 
Published: June 2019

SummarySupernova simulations to date have assumed that during core collapse electron captures (EC) occur dominantly on free protons, while captures on heavy nuclei are Pauli-blocked and are ignored. Using microscopic calculations we show that the EC rates on heavy nuclei are large enough that, in contrast to previous assumptions, electron capture on nuclei dominates over capture on free protons. This leads to significant changes in core collapse simulations.
The Surroundings of Gamma-Ray Bursts: Constraints on Progenitors
Authors: Chevalier Roger A. 
Published: June 2019

SummaryThe association of a supernova with a gamma-ray burst (GRB 030329) implies a massive star progenitor, which is expected to have an environment formed by pre-burst stellar winds. Although some sources are consistent with the expected wind environment, many are not, being better fit by a uniform density environment. One possibility is that this is a shocked wind, close to the burst because of a high interstellar pressure and a low mass loss density. Alternatively, there is more than one kind of burst progenitor, some of which interact directly with the interstellar medium. Another proposed environment is a pulsar wind bubble that has expanded inside a supernova, which requires that the supernova precede the burst.
International Schools for Young Astronomers, Astronomically Developing Countries, and Lonely Astronomers
Authors: Wentzel Donat G. 
Published: June 2019

Early in this century, many cities and universities could support telescopes large enough to do serious research. There were significant observatories even in the less accesable parts of the world. Astronomy was very much an international science, and the IAU was founded to aid this international outlook.In the middle of this century, astronomy changed in two ways. First, the frontier research turned to new topics. It needed telescopes too expensive for most small and many large countries. Second, physics became a more prominent part of astronomy. That left many of the existing small observatories scientifically isolated, especially in developing countries. The scientifically lonely astronomers there needed new alliances to survive.Simultaneously, the new prominence of physics led to astronomers appearing in physics departments of developing countries. These new astronomers were also isolated and they also needed to build alliances to survive.
A multi-resource system for remote teaching in Astronomy : its aims, its design, the point of view of the learners
Authors: Gerbaldi Michele , Xerri Annie 
Published: June 2019

A distance teaching course in Astronomy was developed three years ago by the CNED (Centre National d'Enseignement Distance) in collaboration with professional astronomers from the University of Paris Sud XI.We wish to present our course with :•the conceivers and designers’ point of view•the learners’ point of view.
The STAR CENTRE at Sheffield Hallam University
Authors: Parkinson John H , Ashton D. , Atkin K. , Harrison B. 
Published: June 2019

The Star Centre is a national astronomy and space science base whichfacilitates public access to news and informationpromotes public awareness, interest, enjoyment and understanding.The Star Centre meets these twin aims by providing an information service which can be accessed in a variety of ways and by offering a menu of public observing events.The concept of a national astronomy base developed as part of the Centre for Science Educations growing portfolio of initiatives in both the formal education sector and the wider umbrella of the Public Understanding of Science. In December 1996 the Star Centre was launched with the aid of a Royal Society COPUS development grant and matching funding from Sheffield Hallam University.
Public Information Project of the Total Solar Eclipse of November 3, 1994 in Paraná State, Brazil
Authors: Trevisan R.H. 
Published: June 2019

This project had two principal objectives: to communicate safe methods to observe the Sun, so as to prevent ophthalmological accidents to people during the total solar eclipse of 3rd November 1994, and to collaborate with the primary school teachers in the science classroom, illustrating the classes, motivating the students to observe sky phenomena.In January 1993, a commission called “ECLIPSE 94“Executive Commission, of the Brazilian Astronomical Society was created to coordinate assistance with arrangements for observing the total solar eclipse of 3rd November 1994, that in Brazil was total in the western part of Paraná State, in Santa Catarina State and in a Rio Grande do Sul zone. Professional astronomers from Brazil and from several parts of the world were mobilized to observe this eclipse.
The Flux Distributions of Be Stars in the Far-UV
Authors: Stalio Roberto , Polidan Ronald S. , Peters Geraldine J. 
Published: June 2019

AbstractThe initial results of a program to investigate the far-UV (500-1700 A) spectra of Be stars using the Voyager ultraviolet spectrometers axe presented. Observations of eleven Be stars, with spectral types from B0 through B7, obtained between March 1979 and July 1984 are discussed. The Voyager resolution (∼15 A) allows only limited spectroscopic studies; shortward of 1150 A C III λ977 and LyJβ λ1025 are the most prominent spectral features. Two stars, γ Cas and 59 Cyg, showed enhanced C III λ977 absorption. The flux distributions of the Be stars were intercompared with those of reference stars with low projected rotational velocities and, in a parallel study, to predictions from rotating star models. The model calculations suggest that the observable effects of a high rotational velocity (V≳ 0.9 of critical velocity) on the flux distribution are small except in the FUV (λ < 1150A). The Voyager flux distributions were found to be indistinguishable from those of the low v sin i reference stars. No evidence was found for critical rotation in Be stars. All observations were consistent with Be stars rotating at less than 0.85 of critical velocity.
X-Ray Observations of B-Emission Stars (Review Paper)
Authors: van den Heuvel E.P.J. , Rappaport S. 
Published: June 2019

Most evidence on X-ray emission from the vicinity of Be stars concerns the Be/X-ray binaries. Presently some 20 of these systems are known, making them the most numerous class of massive X-ray binaries. Evidence for the binary nature of these systems comes from (i) Doppler modulation of X-ray pulse periods, (ii) periodic X-ray flaring behavior, and (iii) correlated optical and X-ray variability. The correlation between X-ray pulse period and orbital period found by Corbet (1984) can potentially provide important information on the densities and velocities in the circumstellar disks of Be stars.Evolutionary models indicate that the Be/X-ray binaries represent a later stage in the evolution of normal close binaries with initial primary masses predominantly in the the range 8 to 15 M⊙ . These models indicate that also a class of slightly less massive Be star binaries should exist in which the compact companions are white dwarfs. Be-type blue stragglers in galactic clusters may be such systems.
Interacting Binaries as Be Stars
Authors: Plavec Mirek J. 
Published: June 2019

AbstractSemidetached close binary stars of the Algol type often have primary components of spectral type A0 or earlier and display emission at Hα (sometimes also at higher Balmer lines). They are therefore Be stars. Many binaries of this type are not eclipsing and must look like “ordinary” Be stars. We have discovered high-ionization emission lines of N V, C IV, Si IV, Fe III, etc. in the ultraviolet spectra of totally eclipsing Algols. They probably originate in circumstellar turbulent regions at fairly high electron temperatures, of the order of 100 000 K. They are not detectable in most non-eclipsing systems, but may be there and may play an important role in the dynamics of accretion and mass outflow from the systems.
Omicron Andromedae Photometry, Polarimetry, and a Tentative Model of the Light Variability
Authors: Oláh K. , Božić H. , Hadrava P. , Horn J. , Koubský P. , Kříž S. , Minikunov N.H. , Muminović M. , Percy J.R. , Skcherbakov A.G. , Stupar M. , Tarasov A.E. 
Published: June 2019

Basic information about the star o and (HR 8762, HD 217675-6) is a bright (V=3.55m, B-V=-0.11m U-B=-0.50m) B6 III-Ve star. Its emission-line and shell spectrum is known to come and go on a time scale of years. In fact, the presence of a strong shell spectrum misled the authors of the HD catalogue to assign the star two HD numbers.o and is a prototype of Be rapid light variables in the sense that it has the longest record of photoelectric monitoring which goes back to 1915! The long history of attempts to understand the variations of this star has recently been summarized by Harmanec (1983). Collecting and analyzing all historical photoelectric observations, Harmanec (1984) concluded that the light variations of o And can be understood as a superposition of a long-term cyclic (8.5y) variation with an amplitude over 0.1m (the star being faintest at the recorded shell maxima) and a rapid periodic variation with a period of 1.571272 days.
NonRadial Pulsations and the Be Phenomenon
Authors: Penrod G. D. 
Published: June 2019

AbstractOver the last three years I have obtained about 2000 spectra of a sample of 25 rapidly rotating Bn and Be stars. All but two of the program stars show obvious line-profile variations due to non-radial oscillations. The non-emission stars are each pulsating in one or two short-period high-degree (l = 4 to 10) modes, while the Be stars are in all cases pulsating in a long-period % = 2 mode, and often in a short-period high-Z mode as well. The amplitude of the pulsations in several stars (λ Eri, o And, ζ 0ph, and 2 Vul) is correlated with the occurrence of Be outbursts. The amplitude of the pulsations is largest before the outbursts, declines slowly during the emission phases to a fraction of its previous amplitude, and then slowly recovers to its previous amplitude, a few months before the onset of the next outburst. The correspondence between the presence of a long-period % = 2 mode and Ha emission in rapidly rotating B stars strongly suggests that non-radial pulsation and rapid rotation are the essential components which enable single early B stars to become Be stars. The time scale between Be outbursts probably reflects the relaxation oscillation cycle of the I = 2 mode excitation and damping.
Synthetic uvby-β Photometry of HD 12856 and HD 13890
Authors: Torres A. V. , Garmany C. D. 
Published: June 2019

AbstractStromgren and Hβ colors have been measured from spectrophotometric observations of two Be stars without published photometry in Per OB1: HD 12856 (BO pe) and HD 13890 (B1 III:pe). Stellar parameters and improved spectral types are then derived from the color indices and the calibrations of Jakobsen (1986a,b,c). These are compared with the parameters of normal B stars and they are used to estimate the evolutionary status of the stars.
Galactic Cepheid Kinematics as a Probe of Large Scale Non-Axisymmetry of the Galaxy
Authors: Caldwell J. A. R. , Koen C. , Avruch I. M. , Metzger M. R. , Schechter P. L. , Keane M. J. 
Published: June 2019

AbstractWe investigate whether the currently available Galactic Cepheid kinematic data can put interesting constraints on large scale low amplitude non-axisymmetry of the Galactic plane rotation pattern. In this connection we address the experimental design problem of where in the Galactic plane additional Cepheids would prove the most useful for the axisymmetric and the non-axisymmetric modeling of the kinematics.
Mode Determination by Fourier Analysis of Line-Profile Variations: Application to τ Peg
Authors: Kennelly E.J. , Walker G.A.H. , Merryfield W.J. , Matthews J.M. 
Published: June 2019

AbstractThe identification of modes of oscillation is an important first step towards the seismology of stars. Low- and high-degree nonradial modes of oscillation may appear as variations in the line profiles of rapidly rotating δ Scuti stars. We present a technique whereby complex patterns in the line profiles are decomposed into Fourier components in both time and “Doppler space”. The technique is applied to the 7.3-hour time series of high-resolution data obtained from CFHT for the δ Scuti star τ Peg. In addition to the low-degree mode which has been identified in photometric studies (Breger 1991), we find evidence for at least three high-degree modes near 11 and 15. Correcting for the rotation of the star, most of these modes appear to oscillate with frequencies near 17 cycles day-1. Our results are found to be in good agreement with the theoretical limits imposed on the frequencies of oscillation by the models of Dziembowski (1990).
Slowly Pulsating B Stars
Authors: Waelkens C. 
Published: June 2019

AbstractWe discuss two new slowly pulsating B stars for which it can be convincingly shown that they are multiperiodic variables. The group now contains ten confirmed and likely multiperiodic mid-B stars with periods between 0.7 and 4.4 days. The multiperiodicity and the length of the periods point to g-mode pulsations. The very high order of the modes implies that the modes are excited in the core or in the very outer layers of the star. A recently proposed mechanism, in which both the inner and outer layers intervene, is discussed.
β Cep: a Magnetic Be Star?
Authors: Henrichs H.F. , Bauer F. , Hill G.M. , Kaper L. , Nichols-Bohlin J.S. , Veen P.M. 
Published: June 2019

AbstractBesides the well-known pulsation period of 4h34m, the B1 IV star β Cep has a very significant period of 6 or possibly 12 days in the equivalent width of the ultraviolet resonance lines. This was discovered by Fishel and Sparks (1972) with the OAO-2 satellite, and later confirmed with IUE data. Until now, no explanation has been put forward for this period.We propose that the UV periodicity arises from a 12 day rotational period of the star and that the stellar wind is modulated by an oblique dipolar magnetic field at the surface.Support for this hypothesis is given by the striking similarity between the UV-line behavior of β Cep and of known rotating magnetic B stars, for example the B2 V helium-strong star HD 184927 (Barker et al. 1982), and by the measured magnetic field strength of B ± σ = (810 ± 170) G for β Cep itself by Rudy and Kemp (1978). A rotational period of 12 days corresponds well with an adopted radius between 6 and 10 R⊙, given the reported values of 20 - 43 km/s for vsini.To verify our hypothesis we carried out new magnetic field measurements simultaneously with UV spectroscopy. We confirm the 12 day UV period in the equivalent width of the stellar wind lines of CIV, Si III, Si IV and N V (see Figs. 1 and 2), but find a lower and likely variable field strength (Fig. 3), which is consistent with a 12 day period, but not conclusive.It remains puzzling why our new magnetic field measurements show a lower field than in 1978. It is interesting to recall the recent discovery (Mathias et al. 1991) that β Cep has entered a new Be phase (July 1990), when Hα turned into emission (see Fig. 4). This opens the suggestion that the lower magnetic field is related to the emission phase. Because the UV period is still the same, the field must still be strong enough to modulate the wind. A possibly higher equivalent width of the 1991 UV data with respect to the 1979 data might also be related to this transition, but this needs to be confirmed.The star β Cep appears to be the only star in its class which shows this wind variability and in this respect β Cep is an exceptional β Cep star.