bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Planetoid-Impact Hypothesis of CP F, A, and B Star Formation: Possibilities and Perspectives
Authors: Drobyshevski E.M. 
Published: July 2016

AbstractA possibility is analyzed of explaining the chemical anomalies of chemically peculiar (CP) F-A-B stars basing on the assumption of the formation of a large number of moonlike planetoids both in the course of separation of the components and in late stages of close binary evolution.Primitive igneous differentiation of such planetoids results in their crust becoming deficient in Mg, Ca, Sc and enriched in Pe, Sr, Ba, and the Rare Earths. Infall of such planetoids or crust fragments ejected in their collisions with one another onto an A star makes it Am-type. The deficiency of some elements relative to normal abundance can be accounted for if one assumes that these elements present in the matter streaming from one binary component to another condense with subsequent rain-out into a component or formation of the planetoids.The more diverse and complex anomalies (including the separation of isotopes) can be explained in the same context of the close binary evolution by invoking the ideas of magnetic cosmochemistry which considers the consequences of extremely nonequilibrium processes associated with the flow of magnetic-field generated electrical currents through a rarefied matter in space.
The Historical Contribution of Amateurs to the Study of Double Stars
Authors: Couteau P. 
Published: July 2016

Double stars are favourite objects for amateurs, who can see them with modest instruments and easily observe their eventual motion. Moreover, it is possible to calculate their orbits, and even masses, with no other equipment than a pencil, a piece of thread and two pins to draw the ellipses that these systems have been following for centuries.Binary stars are part of those classes of objects whose geometrical structure remains the same at different scales, they are internally homothetic and represent a field to which fractal geometry may be applied. All this explains the popularity of these objects with amateurs: anyone is able to see some of them, whatever the power of their instruments.
Achievements in Astronomical Video Data Collection
Authors: Maley Paul D. 
Published: July 2016

Observation by amateurs has been traditionally viewed with some suspicion by the professional astronomical community, especially in the case of transient events(1). For example, data from variable star monitoring where information from many observers can be integrated over long intervals, have a higher weight than visual observations of an asteroid occultation. Serious amateurs who choose to contribute to the science face a continuing challenge to maintain the highest standards.In an effort to upgrade the quality of information transmitted to professional institutions, we have experimented since 1984 with a baseline design of mobile video equipment which can be coupled to objective lenses ranging from 28mm to 625mm aperture (2).
Video Grazing Occultations
Authors: Dunham David W. 
Published: July 2016

Grazing occultations are always visible at the projections onto the surface of the Earth of the lines tangent to the lunar limb that are created by the motion of the Moon relative to the star being occulted.Most information about the lunar profile continues to be provided by visual observers using simple equipment. Everyone is to be encouraged to join expeditions to observe grazes, because the accuracy of the observed profile is proportional to the number of stations. The use of grazes improves knowledge of the lunar profile (needed for the analysis of solar eclipse timings), data about close binaries, and galactic rotation from stellar reference-frame determination. Contact timings made near the edges of a solar eclipse track, for example, enable the diameter of the Sun to be derived relative to the lunar diameter, the latter being determined from occultations.
Asteroid and Cometary Occultations
Authors: Dunham David W. 
Published: July 2016

Occultations of stars by minor planets and comets can be used to determine the diameter of the occulting body. With photoelectric equipment, it might also be possible to measure the diameter of the occulted star or to resolve close binary systems at the same time.On 1983 May 29, (2) Pallas occulted the 4.7-mag. star 1 Vulpeculae. A star this bright is occulted by one of the four largest asteroids only once every 60 years. Timings were sent by 130 observers in Florida, Louisiana, Texas, Arizona, Sonora, and Baja California, making it the best-observed asteroidal occultation to date. Asteroidal grazing phenomena were confirmed for the first time. The star is a spectroscopic binary. Several observers timed contacts of the 6th-mag. companion, determining the separation to ± 0.0004 arcsec. An elliptical fit to the timings projected onto the plane of the sky has been made. Unfortunately, clouds prevented timings from near the southern limit, so about 100° of Pallas’ circumference was not observed.
Video Recordings of Asteroidal Occultations
Authors: Boninsegna Roland , Lecacheux Jean 
Published: July 2016

AbstractVideo recordings of two occultations were shown, the first concerning the star AGK3+29 0398 and (93) Minerva on 1982 November 22, 03:31 UT, using the 1-m telescope at Pic du Midi. The occultation was also observed in Spain and in the U.S.A. The second event involved AGK3+17 1309 and (146) Lucina on 1982 April 18, 20:23 UT, using the 1-m telescope at Meudon. A short secondary occultation (0.6 sec) was observed, not caused by the minor planet. A possible interpretation is a small satellite (5.7 km minimum diameter) near Lucina.
Scientific Goals for a Collaboration Between Amateur and Professional Astronomers in the Study of Variable Stars
Authors: Poretti Ennio 
Published: July 2016

Variable stars are a field where the contribution of amateur astronomers is of great importance. This contribution can be separated in to complementary parts:
1)collaboration with professional institutes that well-equipped amateurs can easily undertake in the field of photoelectric observation;2)visual observation of variable stars, which in many cases can be a preliminary approach to photoelectric photometry.
Professional/Amateur Cooperation in the Study of Variable Stars as Illustrated by the Fourth Edition of the GCVS
Authors: Frolov M.S. 
Published: July 2016

Let us divide variable stars into two main groups: the first “classical” group, includes objects known for a long time, such as Cepheids, RR-Lyrae stars, Miras, cataclysmic variables, eclipsing binaries, etc. The second group includes micropulsating variables of δ Scuti and β Cephei types, magnetic variables, rotating variables of BY Draconis type, etc.Historically, the contribution of amateurs in investigating the first group was very significant, and it continues to increase. On the other hand, involvement in studying the second group of stars was practically equal to zero some years ago, but today one can see the beginnings of an expansion of amateur work on this second group of variables – among brighter objects, of course. One reason is the beginning of cooperation between amateurs and professional astronomers having powerful instruments.
Comet Halley: A Media Event
Authors: Heudier Jean-Louis 
Published: July 2016

Comet P/Halley’s life as a “media event” started long ago, because the first use of communication (in the modern sense of the term) goes back to Rabelais, who published in Patagrueline Prognostication pour l’an 1532:“And whyth the comete sene laste yeare and the retrograte of Saturne a greate skoundrell shalle die, all weazynge and courd in scabbes, in the hospitall, and at his death there will be horrible warre between cattes and rattes, dogges and hares, faulcons and duckes, monkes and egges.”Since then ways of spreading ideas have progressed enormously, but comets have remained “fashionable” and each of the last six apparitions of P/Halley has been the occasion of outbursts that are far removed from the scientific view.
Observed Lithium Abundances as a Test of Stellar Internal Structure
Authors: Vauclair Sylvie 
Published: July 2016

The “lithium gap” observed in the Hyades and other galactic clusters by Ann Boesgaard and her collaborators (Boesgaard and Tripicco 1986, Boesgaard 1987, Boesgaard, Budge and Burck 1987) gives a challenge to theoreticians. Indeed a good fit between the theoretical results and the observations will give a clue for our understanding of the stellar internal structure and evolution.A theoretical explanation of the “lithium gap” by gravitational and radiative diffusion has been proposed by Michaud 1986. In G type stars, the convection zone is too deep for gravitational settling to take place: the density at the bottom of the convection zone is so large that the diffusion time scale exceeds the age of the star. Increasing the effective temperature leads to a decrease of the convection zone, and consequently to a decrease of the diffusion time scale. In F stars it becomes smaller than the stellar age, leading qualitatively to a lithium abundance decrease as observed. When the convection zone is shallow enough, the radiative acceleration on lithium becomes important as lithium is in the hydrogenic form of li III (while it is a bare nucleus, li IV, deeper in the star). This radiative acceleration may prevent lithium settling for hotter F stars. This is a very attractive explanation, which leads to a minimum of the lithium abundance nearly at the place where it is observed in effective temperature. However it suffers from some difficulties: the theory predicts an increase of the lithium abundance larger than normal in the hottest F stars, which is not observed, and the predicted minimum lithium abundance is one or two orders of magnitude higher than the minimum observed in the Hyades. The former may be overcome if mass loss occurs in these stars (Michaud 86). Let us focus on the latter.
Stellar mass loss and atmospheric Instability
Authors: de Jager Cornelis , Nieuwenhuijzen Hans 
Published: July 2016

AbstractA review is given of rate of mass-loss values in the upper part of the Hertzsprung-Russell diagram. Near the luminosity limit of stellar existance = −10−4 M⊙ yr−1. Episodical mass loss in bright variable super- and hypergiants does not significantly increase this value. For Wolf-Rayet stars the rate of mass loss is larger by a factor 140 than for non-evolved stars with the same Teff and L; for C stars this factor is ten. This can be explained qualitatively. Rotation appears hardly to influence the rate of mass loss except for vrot-values close to the break-up velocity. This is in accordance with theory. We suggest the existence of a Red Supergiant Branch; along that branch mass loss is virtually independent of luminosity. Stellar winds along the upper limit of stellar existence are mainly due: to radiation pressure for hot supergiants (≳ 10 000 K); to turbulent pressure for cool supergiants (3000-10 000 K), and to dust-driven and pulsation-driven winds for cooler stars. The turbulent pressure may originate in largescale stochastic motions as observed in Alpha Cyg. Episodical mass loss, as observed in P Cyg, HR 8752 and other Very Luminous Variables may be due to occasional violent stochastic motions, resulting in a shock-driven episodical mass-loss component.
A New Driving Mechanism of the Episodic Mass-Loss in Be Stars
Authors: Ando Hiroyasu 
Published: July 2016

Be stars are well known to be rapid rotator and to show intermittent emission-line activity. Such an activity is now interpreted as an abrupt mass-ejection and formation of a cool disk in the equatorial region and then its gradual disappearance mass-loss is called as episodic mass-loss.Rapid rotation and mass-loss connection in Be stars was suggested for the first time by struve(1931), which necessarily leads to the requirement of break-up velocity in Be stars. However, Vsin i statistics suggests almost all Be stars are well below the break-up velocity. The additional forces have been searched for so far; i.e., stellar wind, magnetic field, mass accretion, and so on. At the moment, none of them can succeed in explaining the episodic mass-loss in Be stars.
Molecular Spectroscopy as Diagnostics of Outer Atmosphere of Cool Luminous Stars: Quasi-Static Turbulent Molecular Formation Zone and Stellar Mass-Loss
Authors: Tsuji Takashi 
Published: July 2016

AbstractThe origin of mass-loss in cool luminous stars is still obscure; several known mechanisms such as thermally driven wind, radiation-driven wind(via dust), wave-driven wind etc all have serious difficulties, if examined in the light of recent observations. At the same time, recent observations in the infrared and radio spectral domains revealed that outer envelope of red (super)giant stars has highly complicated spatial and velocity structures, while inner envelope may have new component that had not been recognized before. For example, recent high resolution infrared spectroscopy revealed a possible presence of a quasi-static turbulent molecular dissociation zone somewhere in the outer atmosphere. This new component may represent a transition zone between the warm chromosphere and the huge expanding molecular envelope, and may be a cool component of chromospheric inhomogeneity or a moleclar condensation in a cool corona extended by turbulent pressure. Such a result can be regarded as observational evidence in support of a recent theory of autocatalytic molecular formation by thermal instability due to molecular cooling. Thus, observation and theory consistently show the presence of a new component - quasi-static turbulent molecular formation zone - in outer atmosphere of cool luminous stars, and a possibility of a unified understanding of outer atmospheric structure and mass-loss, in which turbulence may play important role, can be proposed.
Mass and Energy Transfer in Semi-Detached Binary Systems
Authors: Unno Wasaburo , Kiguchi Masayoshi , Kitamura Masatoshi 
Published: July 2016

Recently, Kitamura and Nakamura have found that the anomalous gravity darkening occurs in semi-detached binary systems. The exponent of gravity darkening for the secondary components, which is defined by where F is the radiative flux and g is the gravitational accerelation, is significantly greater than the unity as shown in Table 1. We interpret this in terms of the energy transport by the mass outflow from the secondary component filling the Roche-lobe.Table 1.Empirical αc-values and physical quantities of five semi-detached binary systems.From the analysis based on this interpretation, we show that 1) the mass out-flow carries energy if ∇ < ∇ad and 2) the anomalous gravity darkening requires that the flow must originate from deep interior. The mass loss rate can be estimated from the anomalous gravity darkening. Thus, the anomalous gravity darkening can be used not only to estimate the mass transfer rate but also to probe the interior structure and the evolution of the secondary star of the semi-detached binary. This model links Morton’s instability[2] of the secondary with the accretion disk of the primary.
Numerical Modelling of the Classical Nova Outburst
Authors: Kutter G. Siegfried , Sparks Warren M. 
Published: July 2016

AbstractWe describe a mechanism that promises to explain how classical nova outbursts take place on white dwarfs of 1 M⊙ or less and for accretion rates of 4 × 10−10 M⊙ yr−1 or greater.
SN 1987A: Ultraviolet Observations and Mass Loss
Authors: Kirshner Robert P. 
Published: July 2016

AbstractMass loss from the B3 Ia progenitor star for SN 1987A is revealed by the recent emergence of narrow ultraviolet emission lines. The emitting gas is nitrogen-rich, has low velocity, and may be located a light-year from the supernova. This gives every sign of having been ejected from the SK −69 202 progenitor when it was a red supergiant, prior to its brief and ultimately violent life as a blue supergiant. Changes in the hydrogen line profiles during the early evolution provide a way to estimate the density distribution in the supernova atmosphere, and the mass of hydrogen it contains. A preliminary estimate is that the power-law index of density in the envelope goes as V−11 and the mass that lies above a velocity of 6, 000 km s−1 is between 1 and 6 solar masses.
Enrichment of s-Process Elements in the Progenitor of SN 1987A
Authors: Williams R.E. 
Published: July 2016

AbstractExisting calculations of s-process nucleosynthesis in massive stars such as Sk −69° 202 show enhancements in the He-burning shells which, when mixed to the surface, lead to Sc, Sr, and Ba enrichments of factors of 2 to 15. Abundances derived from the supernova absorption lines using a simple scattering model yield enhancements of this magnitude. Thus, the observed and predicted s-process abundances are roughly in accord, although the Ba/Sr ratio derived for the supernova may be higher than the s-process can account for.
On the Origin of Supernovae of Type Ib
Authors: Branch David 
Published: July 2016

The issue I want to discuss is this: supernovae observed during their photospheric phases display three distinct kinds of spectra - but there are four distinct chemical compositions that should be considered for the outer layers of exploding stars. What is the correspondence between the observed supernova type and the chemical composition?The three kinds of observed spectra are Type II, which by definition shows optical hydrogen lines, Type Ia, which has neither hydrogen nor helium lines, and Type Ib, which has helium but not hydrogen.The compositions to be considered are hydrogen-rich, or, speaking loosely, “solar”; helium-rich, or, loosely, “Wolf-Rayet”; deflagration - initially a mixture of heavy elements from carbon to radioactive nickel, which decays through cobalt to iron; and detonation - initially a mixture of just helium and radioactive nickel.
Spectroscopic Diagnosis of SN1987A and Lesser Lights
Authors: Wheeler J. Craig , Harkness Robert P. , Barkat Zalman 
Published: July 2016

AbstractSN 1987A gives a unique chance to study both the precursor star and the subsequent dynamical evolution of the explosion. Comparison of the light curves shows that either H0 ∼ 100 km/s/Mpc, or SN 1987A ejected significantly less 56Ni than ordinary Type II supernovae. Investigation of the stellar structure pertinent to SK -69 202 reveals multiple solutions. For given luminosity, effective temperature, core mass and core radius, there are two families of envelope mass, one with large envelope mass and one with small envelope mass. The small envelope mass solutions can be ruled out by considerations of kinematics and the light curve. Envelopes of moderate mass may avoid each of these problems, but must be helium rich to be structurally self-consistent.The spectrum in both the optical and the ultraviolet at about two days is fairly well represented by a hydrogen envelope with a power law density profile (ρ∝r-11 ) of one-quarter solar metallicity in LTE. Theoretical spectra at this early epoch tend to favor luminosities on the high side of observational estimates in order to ionize Ca II and prevent excessively strong lines at H and K and the infrared triplet, with some ramifications for distance estimates.The spectra of SN1987A present an interesting contrast to other SN II events. A McDonald Observatory spectrum of SN 1985H in NGC 3359 of uncertain epoch shows a very close resemblance to that of SN 1987A at about two month’s age, including the strong line at 607 nm attributed by Williams to Barium. SN 1985H may have been of the same class of event as SN 1987A.
X-rays and γ-rays from Supernova 1987a
Authors: Sutherland P. , Xu Y. , McCray R. , Ross R. 
Published: July 2016

SummaryThe observation of X-rays and γ-rays from SN 1987a can provide important constraints on parameters for models of this unique event. We present the results of detailed Monte Carlo calculations of the fluxes to be expected in several X-ray bands and for the strong line at 847 keV associated with the decay of 56Co. Our calculations use Model 10H of Woosley, Pinto, and Ensman(1988), with 0.075M⊙ of radioactive material. If it is assumed that there is no mixing of this material with the layers above, then the X-ray fluxes do not become detectable as early as the observations made by the Ginga team in August, 1987. If these observations correspond to X-rays arising from γ-rays Compton scattered down in energy in the supernova ejecta, rather than the interaction of the ejecta with circumstellar matter, then they can only be explained by mixing outward of radioactive material or an envelope with some combination of less mass or greater kinetic energy per unit mass.
X-Ray Observation of SN1987A from Ginga
Authors: Tanaka Y. 
Published: July 2016

AbstractAn unusual hard X-ray source was discovered in an error box of 0.2° × 0.3° including SN1987A from the X-ray astronomy satellite Ginga. The energy spectrum is quite unusual for any known classes of X-ray source, and apparently consists of two separate components, a soft component and a very hard component. This source is considered to be identified with SN1987A. The X-ray emergence occurred in July, 1987, or possibly even earlier. The soft component is significantly time-variable and also showed a flare-like increase in January, 1988, while the intensity of the hard component has remained relatively unchanged for more than 200 days.
The Evolution of the Precursor of SN 1987 A
Authors: Maeder André 
Published: July 2016

SummaryIdeally, the evolutionary models for the precursor of SN 1987 A should account for both the SN properties and the observational constraints for massive stars with relevant mass and composition.Mass loss is an essential property of massive star evolution. Recent parametrisations of mass loss rates for galactic stars cover the whole HR diagram. There are indications that for given L and Teff values, is lower at lower metallicity and therefore is lower in the LMC than in the Galaxy, thus we take with f < 1. Various models of an intitial 20 M⊙ star with f=0.2, 0.4, 0.6 and 1.0 are constructed (cf. Fig. 1) with a metallicity Z=0.006 and a moderate overshooting dover=0.3 Hp. From these models, we suggest an initial mass on the zero age sequence of 17 to 18 M⊙. The pre-SN location in the HR diagram very much depends on the remaining stellar mass, or more precisely on the mass of the remaining H-rich envelope. A final location at log Teff ≃ 4.2 is obtained for a final mass of about 9.0 M⊙ (cf. Fig.1). Scaled to an initial value of 17 M⊙, this corresponds to a final mass of about 8 M⊙ and a remaining H-rich envelope of a few tenths of a solar mass at most. The stellar surface exhibits CNO equilibrium values with C/N ≃ 0.01 and O/N ≃ 0.1 in mass fraction, and an hydrogen content X (surf) = 0.39. The blue progenitor is obtained for f=0.4, i.e. for -values in the LMC equal to 40% of the galactic values.
Evolution of the Precursor of SN1987A
Authors: Wood P.R. , Faulkner D.J. 
Published: July 2016

The evolution of a 17.5 M⊙ star, chosen to be similar to the precursor of SN1987A, has been studied using the input physics described in Wood and Faulkner (1987). The calculations: use opacities from the Astrophysical Opacity Library of Huebner et al (1977) with H, He, C, N, O and other metals in LMC ratios; treat semi-convection in the manner of Lamb, Iben and Howard (1976); and assume the mass loss rate to be the minimum of (a) α times the rate give in Waldron (1985) (this rate applied in the blue part of the HR diagram), and (b) L/(cv) (this rate applied in the red), where v is the stellar wind expansion velocity which was taken to be 12 km s−1.Typical evolutionary tracks resulting from these calculations are shown in Figure 1. The track shown as a continuous line is the one shown in Wood and Faulkner (1987) and corresponds to α = 2.5, while the track shown as a dotted line results from a slightly different treatment of semi-convection on the main-sequence and to α = 1.