bluuebunny/crossref_metadata_2025_split huggingface dataset:
Voyager planetary radio astronomy: Grain and particle impacts shot noise in Saturn's ring plane
Authors: Aubier M.G. , Meyer-Vernet N. , Pedersen B.M. 
Published: July 2016

ABSTRACTRadio emissions were observed by Voyager 1 and Voyager 2 planetary radio astronomy experiments during saturnian ring plane crossings. Several mechanisms are proposed and tested. Quasi-thermal noise is negligible. Shot noise due to electrons and ions collected and/or emitted by antennas and spacecraft can explain not too intense noise. However, for the strong noise in the ring plane, observed by Voyager 2 at ~ 2.9 Rs, we must take into account shot noise due to grain impacts. A quantitative evaluation of this process gives an estimation of the dust size ~ 1.1 µm close to the G ring.
On the radial structure of planetary rings
Authors: Harris A.W. , Ward W.R. 
Published: July 2016

ABSTRACTA ring of particles in orbit about a planet experiences a viscous shear stress due to the radial gradient of orbital velocity. This stress tends to spread the ring with time. At low optical depth (τ ≲ 0.5), and again at high optical depth (τ ≳ 2), the shear stress is an increasing function of optical depth. In the intermediate range (0.5 ≲ x ≲ 2), stress may decrease with increasing τ, leading to a diffusive instability which will tend to break an Initially uniform ring into ringlets of high and low optical depths.
Dense but «collisionless» orbiting rings
Authors: Michel F.C. 
Published: July 2016

ABSTRACTThe discovery by Voyager, that the rings of Saturn are substructured into a multitude of narrow ringlets, has posed some severe theoretical difficulties. These rings have substantial optical depths, implying high collision rates and therefore rapid diffusive spreading, which would lead to the ringlet structure being eradicated.Suggestions have been forwarded that this substructure is either a) dynamically maintained by many small perturbing subsatellites or b) is not actually in the form of closed rings but is a spiral pattern of density waves. Voyager II was unable to detect such subsatellites, and many of the broader isolated ringlets (albeit not necessarily the finest features at the few kilometer scale) are clearly observed to be closed rings, rather than segments of a spiral.We propose that convective motion, a helical rolling motion of a ringlet as it orbits, provides a stabilizing influence. For ringlets of negligible mass orbiting a point mass, the ringlets can be arbitrarily dense without collisions acting to dissipate them. For the realistic case of an oblate planet and finite ring mass, a small but finite collision rate (or other compensating perturbations) are required. Convective motions then serve to vastly reduce the effective viscosity within a ringlet and thereby greatly increase its evolutionary lifetime.
Supernova Remnants and their Supernovae
Authors: Kirshner Robert P. 
Published: July 2016

AbstractObserving supernova remnants provides important clues to the nature of supernova explosions. Conversely, the late stages of stellar evolution and the mechanism of supernova explosions affect supernova remnants through circumstellar matter, stellar remnants, and nucleosynthesis. The elements of supernova classification and the connection between supernova type and remnant properties are explored. A special emphasis is placed on SN 1987a which provides a unique opportunity to learn the connection between the star that exploded (whose name we know) and the remnant that will develop in our lifetimes.
The Early Evolution of Supernova Remnants
Authors: Chevalier R.A. 
Published: July 2016

AbstractThe density distribution of the supernova ejecta and that of the surrounding medium are the most important parameters for the early evolution of supernova remnants. The distribution of the ejecta depends on the detailed hydrodynamics of the explosion, but the outer parts of a supernova can probably be represented by a steep power law density distribution with radius. Self-similar solutions are especially useful for modeling the interaction of a supernova with its surrounding. The supernova first interacts with mass loss from the progenitor star. Evidence for circumstellar interaction is present in a number of extragalactic supernovae, including SN1987a. The explosions of massive stars probably interact with circumstellar gas for a considerable time while Type Ia supernovae interact more directly with the interstellar medium. X-ray spectroscopy is a good diagnostic for the physical conditions in young supernova remnants and for the composition of the supernova gas.
Einstein Bragg Crystal Spectrometer Observations of Cas A – A Nonequilibrium Ionization Interpretation
Authors: Markert T.H. , Blizzard P.L. , Canizares C.R. , Hughes J.P. 
Published: July 2016

AbstractWe use Einstein FPCS observations of lines of highly ionized neon, silicon and sulfur to constrain the parameters of the supernova remnant Cas A.
Line Emission Processes in Atomic and Molecular Shocks
Authors: Shull J. Michael 
Published: July 2016

AbstractThis review discusses the observations and theoretical models of interstellar shock waves in diffuse and molecular clouds. After summarizing the relevant gas dynamics, atomic, molecular and grain processes, and physics of radiative and magnetic precursors, I describe observational diagnostics of shocks. I conclude with a discussion of two new topics: unstable or non-steady shocks and thermal conduction in metal-rich shocks.
Radio Studies of Supernova Remnants: Patterns and Statistics
Authors: Caswell J.L. 
Published: July 2016

AbstractMost supernova remnants (SNRs) in our galaxy have been discovered from their radio emission and for the majority this remains the only means of studying them. In this review the impact of new radio observations is discussed.The increased detail of recent radio maps reveals some common patterns among SNRs, despite their generally diverse appearance. The patterns can give us clues to both the intrinsic properties of the supernova and the influence of the interstellar medium. With a fuller understanding of individual remnants, there are better prospects for meaningful interpretation of statistical studies.
An Infrared Survey of Galactic Supernova Remnants
Authors: Arendt Richard G. 
Published: July 2016

AbstractPresented here are preliminary results from a survey of supernova remnants (SNRs) in the data base collected by the Infrared Astronomical Satellite (IRAS). About one-third of the known galactic SNRs are visible in the IRAS data. Confusion with other sources in the galactic plane prohibits the detection of many remnants. The objects that are detected have similar spectral characteristics and temperatures, except that the three youngest remnants known, Tycho, Kepler, and Cassiopeia A, are distinctly warmer.
Analysis of Multiwavelength Observations of IC443
Authors: McColloug M.L. , Mufson S.L. 
Published: July 2016

AbstractHigh resolution observations at radio, infrared, optical and X-ray wavelengths have been made (Mufson et al. 1986). The infrared spectrum determined from the IRAS observations has been fitted with models which include shock heated dust, infrared line emission, and radiatively heated dust emission. Numerical simulations of a supernova expanding into a uniform medium, which describe the X-ray and large scale radio emission, are presented.
The Radio Properties of Symbiotic Stars
Authors: Seaquist E.R. 
Published: July 2016

AbstractRadio thermal bremsstrahlung emission has now been detected at centimeter wavelengths from about thirty symbiotic stars. These data combined with optical and IR data show that the radio emission in most systems may be understood in terms of the ionization of part of the wind of a red giant by a hot companion. The radio properties of symbiotic stars are reviewed and the agreement with and the limitations of this picture are examined.
Accretion from Stellar Winds
Authors: Livio Mario 
Published: July 2016

AbstractRecent calculations have demonstrated that accretion from a stellar wind is very probably unsteady. The average rate of accretion of angular momentum is lower by about a factor 5 than the rate at which angular momentum is deposited into the Bondi-Hoyle accretion cylinder. This makes disk formation from wind accretion very difficult, in particular in the case of massive x-ray binaries. A combination of x-ray, uv and optical observations of symbiotic and related systems, as well as spin-up information on x-ray binaries, can be used to determine whether an accretion disk does form. Such observations can provide us with valuable information on the process of accretion from an inhomogeneous medium.
Spectral Variations of AG Dra Between 1981 and 1985
Authors: Huang C.C. , Chen Y.F. , Chen L. 
Published: July 2016

After a long quiet phase AG Dra underwent an outstandingly active phase with two outbursts in 1980 Nov. and 1981 Nov.(Viotti et al, 1984). Since then a new quiet phase has followed. In this work we analyse two spectra of AG Dra, of which, one was taken in 1981 by C.C. Huang at the Haute-Provence Observatory using the Marly spectrograph with a dispersion of 80 A/mm at the 1.2 m telescope, the other was obtained by Dr Y.Andrillat in 1985 with the same instrument.Figure 1 shows the spectral variations of AG Dra between 1981 and 1985. The main features of the emission line spectrum are not much different between the two spectra, except that in 1985 there was a new wide weak emission line at 3488 A possibly due to FeII. There were a lot of strong emission lines due to H, HeI, HeII and 0III in both spectra. The spectrum of the late-type component was much more obvious in 1985 than in 1981. In 1985 the lines of CaII K, CaIλ4227 and the G-band of CH were quite strong. In addition we measured a lot of absorption lines due to FeI, SrII and TiII on the 1985 plate. The Balmer continuum emission and the blue contiuum were enhanced in 1981. On the 1981 plate the stellar spectrum in ultraviolet can be traced beyond 3200 A and the blue continuum heavily veiled the spectrum of the cool component. In 1985 they were much weaker.
Future Objective-Prism Spectral classification at MK Dispersion
Authors: Houk Nancy 
Published: July 2016

AbstractA brief review and summary of results from Volumes 1 (-90° to -53°) and 2 (-53° to -40°) of the University of Michigan Catalogue of Two-Dimensional Spectral Types for the HP Stars is given. Plans for the classification of the remaining southern HD stars are outlined. Future plans for observation and classification of northern stars are discussed, including the problem of whether to limit such classification to the HD stars. More general remarks about spectral classification in the future, especially for fainter stars, conclude the paper.
A Study of Main Sequence Early Type Stars
Authors: Sinnerstad Ulf 
Published: July 2016

AbstractA spectroscopic and photometric study of 75 normal main sequence B2-B6 stars has been carried out. From the spectra (12 Å/mm, 3700-4800 Å) are determined: equivalent widths of all measurable lines, line profiles of hydrogen lines and v sin i. The photometric work includes besides uvby and β photometry, also photoelectrically determined line strengths of Hα and He I 4471 Å. Some preliminary results concerning the relation between the MK types and the atmospheric fundamental parameters (Teff, log g) of the stars are briefly discussed.
Comparisons of Temperature Classes Obtained by Spectroscopic and Photometric Techniques: M-Type Dwarfs, Giants, and Supergiants
Authors: Wing R. F. , Yorka S. B. 
Published: July 2016

AbstractTemperature classes based on photometric measurements of the 7100 Å band of TiO are compared with published spectroscopic classifications by various investigators. Dwarfs, giants, and supergiants are treated separately. The photometric types are in excellent agreement with types given by P. C. Boeshaar for M dwarfs and by P. C. Keenan and Y. Yamashita for M giants. In all other cases the scatter is larger. The usefulness of the types given by various authors for dwarfs and giants is tested by examining their correlation with color temperature determined by narrow-band photometry.
The International Ultraviolet Explorer
Authors: Heck A. 
Published: July 2016

AbstractAs the IUE satellite is the subject for a series of detailed papers to be published in a forthcoming issue of Nature. we will give only a brief description here. The interested reader should refer to Nature.The telescope is a Ritchey-Chretien type with a clear aperture of 45 cm. The effective focal ratio is f/15. Two spectrographs can be operated, one, in the low dispersion mode (about 6 A) and another in the high dispersion mode (about 0.1 A). The detectors are SEC Vidicon television cameras. Each spectrograph has two apertures: a 3 arc sec circle and a 10 X 20 arc sec ellipse. The limiting magnitudes for objects observed are V = 8 for hot stars at high dispersion, V = 14 for galaxies at low dispersion. The output is available as plots, magnetic tapes and photowrites. The observatories are located at Goddard Space Flight Center, Greenbelt, Md. for U.S. observers and Villafranca Satellite Tracking Station, Madrid, Spain for U.K. and E.S.A. observers.
The Nature of RW Sextantis
Authors: Bolick U. , Beuermann K. , Bruch A. , Lenzen R. 
Published: July 2016

AbstractPhotometry and first results of extensive CCD-spectroscopy of the UX UMa system RW Sex are presented. The period is found to be P = 0.24486 days and the semi-amplitude of the radial velocity is K1 = 101 km s−1. The mass of a Roche-lobe filling secondary is M2 = (0.54±0.09) Mo and, for M1 ≧ M2, the mass ratio is M1/M2 = 1.5±0.5. The accretion rate is about (2–3) 1017 g/s. The model for RW Sex by Greenstein and Oke is discussed and rejected.
Periodic Modulations in the Optical Light Curves of EX Hydrae
Authors: Seetha S. , Sharma D.P. , Padmini V.N. , Marar T.M.K. , Kasturirangan K. , Rao U.R. , Bhattacharyya J.C. 
Published: July 2016

AbstractWe present here new results on the periodic modulations in the optical light curves of EX Hydrae observed during 1982–84. The period analysis has been done using synchronous summation and discrete Fourier transform methods. We report new periodicities at 34.7 min and 26.7 min apart from confirming the detection of 46.3 min modulation recently reported. We also include our data to derive the rate of decrease of the 67 min period.
Accretion Disk Structure in SS Cygni
Authors: Hessman F.V. 
Published: July 2016

AbstractHigh-resolution Coude observations of non-axisymmetric line emission -from the dwarf nova SS Cygni are presented. By subtracting the constant line component, the asymmetric line emission responsible for the observed phase shift between the absorption and emission line radial velocity curves can be isolated. The extra emission is a large fraction of the total line emission and extends to large velocities (~1500 km sec−1). The phase stability of the emission demands a large-scale structure which is fixed in the frame of the binary. A magnetic origin of the excitation cannot De ruled out but is implausible. A simple explanation is that the accretion stream from the companion star is able to spill over the sags of the disk, introducing emission at non-circular velocities and most likely disturbing the upper layers of the accretion disk.
The Spectrum of Nova Vulpeculae 1984 N°2 at Nebular Phase
Authors: Andrillat Y. , Houziaux L. 
Published: July 2016

AbstractNova Vul 1984 n°2 has been again observed at Observatoire de Haute-Provence in the autumn of 1985, i.e. 270–295 days after maximum. It was then in the nebular phase. The spectra cover the blue-violet and the near infrared regions. Over 50 lines and blends have been identified and are given in Table 2. No clear pattern is observed in the emission bands of a width of about 1450 km/sec. The most conspicuous features observed are the forbidden NeIII and NeV lines. The infrared region is dominated by a very strong He I 1083nm emission.
Electron Scattering in Cyclotron Emission Regions in AM Herculis-Type Systems
Authors: Wickramasinghe D.T. , Meggitt S.M.A. , Wehrse R. 
Published: July 2016

AbstractThe intensity and polarisation properties of magnetic accretion columns are discussed in the regime where electron scattering is important. It is shown that the circular polarisation standstills observed in some AM Herculis type systems are inconsistent with cyclotron emission from scattering dominated regions.
Spectral Models of AM Her Stars
Authors: Langer S.H. 
Published: July 2016

AbstractMost of the optical light from AM Her systems is cyclotron radiation. Simple models for the spectrum and polarization are successful for some systems, but in others the spectrum rolls over more gently at high frequencies and is polarized over a wider range of frequencies than the models predict. This paper considers the emission from both the sides and top of the accretion column and the effects of oscillations in the shock height. These features lead to a slower roll over at high frequencies than is found in the simple models, but it is still not as flat as in some of the AM Her systems.
Mass Loss and Shell Masses of Close Binary Stars
Authors: Karetnikov V.G. 
Published: July 2016

AbstractFrom the values of period changes for 6 close binary stars the mass transfer rate was calculated. Comparing these values Mt with the values of shell masses Msh, the expressionwas derived. The analysis of this expression points out the initial character of the outflow of matter, and one may determine the time interval of the substitution of the shell matter. So one may conclude that for a certain mass transfer rate, a certain amount of matter accumulates in the nearby regions of the system.
Hot Wind in the Double Degenerate System AM CVn
Authors: Solheim J.-E. , Kjeldseth-Moe O. 
Published: July 2016

AbstractThe close binary system Am CVn consists of two helium white dwarf stars in close orbit. Strong flickering in the optical light curve and the observed spin-up in the rotation period indicate that mass transfer takes place (Solheim et al., 1984). The optical spectrum shows broad helium absorption lines (Robinson and Faulkner, 1975) sometimes partly filled in by emission (Voikhanskaya, 1982). The optical spectrum shows no sign of hydrogen, and the line profiles are interpreted as due to an accretion disk of intermediate angle of inclination with a temperature of the order of 20.000 K (Robinson and Faulkner, 1975). Another possibility is direct accretion onto a magnetized BD white dwarf (Voikhanskaya, 1982). In the latter case a magnetic field B ≃ 106to 109gauss is needed. Voikhanskaya also reports significant changes in the absorption line profiles from 1978 to 1980.
A Study of Some Astronomical Data in Muslim Calendar
Authors: Meidong Chen 
Published: July 2016

The Muslim Calendar spread into China in 1385 where it was immediately translated into Chinese by the astronomer Yuan Tong and came into use. In 1477, it was further translated by the astronomer Bei Lin and compiled into the “Qi Zheng Tui Bu”, a work more or less the same in substance with the Muslim Calendar recorded in the “Ming Shi Li Zhi”, both being works of the same source. They left for us the valuable data of the results of research of ancient Arabian astronomers.On different occasions in the Muslim Calendar, values different with one another are used for the same kind of data. In that case, which of them are used for them are accurate values surveyed and calculated by people who originally worked out the Muslim Calendar? And how are these values calculated from data now available?
Trigonometry in Two Sixteenth Century Works; The de Revolutionibus Orbium Coelestium and the Sidra Al-Muntahā
Authors: Tekeli Sevim 
Published: July 2016

In Greece, Autolycos (4th cent. B.C.), Aristarchos of Samos (3rd cent.B.C.), Hipparchos (2nd cent.B.C.), Menelaos (1st cent. A.D.), and Ptolemaos (2nd cent. A.D.) are the forerunners of trigonometry. The Greeks used chords and prepared a table of chords.Later, the Hindus produced Siddhāntas (4th cent.A.D.). The most important feature of these works is the use of jyā instead of chords, and utkramajyā (versed sine).In Islam, al-Battānī al-Ṣābī (858-929) used the sine, cosine, tangent, and cotangent with clear consciousness of their individual characteristics.As is known, trigonometry developed as a branch of astronomy. Although in the thirteenth century Naṣīr al-Dīn al-Ṭūsī (in the Islamic world) and in the fifteenth century Regiomontanus (in the West) established trigonometry as a science independent of astronomy, the essential situation did not change, and the subject went on developing as before.
Image Detection System for Schmidt Plates
Authors: Maehara Hideo , Yamagata Tomohiko 
Published: July 2016

A 14-inch Schmidt plate contains 109 photographic grains and 105 to 106 images of stars and galaxies on it. Such a quantity of data is too large to be handled in a conventional way even for a big computer.There is, in general, an alternative method to solve this problem; one is to store the data of all pixels on intermediate medium (e.g., magnetic tape), and reduce them into image parameters afterwards. The other method is to do all the processing simultaneously with the measurement. The latter is very useful for the automated detection of celestial images on large Schmidt plates.
A Study of Ultraviolet-Excess Galaxies Based on the Kiso Survey
Authors: Takase Bunshiro , Noguchi Takeshi , Maehara Hideo 
Published: July 2016

AbstractA number of ultraviolet-excess galaxies have been detected during the course of our surveys using the Kiso Schmidt telescope. In this report, a classification scheme is proposed for 142 selected objects on the basis of their morphological features, and the relation between the morphological type and the degree of ultraviolet-excess is presented. In general irregular galaxies with conspicuous H II regions and pair galaxies tend to show higher degree of ultraviolet-excess, while the degree in spiral galaxies appears to range widely.
Absorption Spectroscopy of Kα Lines in Dense Laser Plasmas
Authors: Chenais-Popovics C. , Fievet C. , Geindre J.P. , Gauthier J.C. , Wyart J.F. , Luc-Koenig E. 
Published: July 2016

AbstractAbsorption of Kαlines in F-like to Be-like chlorine ions is observed in a laser irradiated layered target (Bi on C2H2C12). Substructures are evidenced in the absorption peaks corresponding to the different chlorine ions. A radiatlvely heated shallow temperature gradient aroud 110 eV in the dense part of the target is consistent with the experimental observations.
Time Variations of the Calcium Elemental Abundance in Flares from NOAA Active Regions 2562 and 2779
Authors: Sylwester J. , Zolcinski-Couet M.-C. , Bentley R.D. , Lemen J.R. 
Published: July 2016

AbstractAnalysis of flare spectra obtained with the Bent Crystal Spectrometer aboard the Solar Maximum Mission (SMM) satellite enables the determination of the fluxes in the resonance (w) line of Ca XIX and the near-by continuum. The line-to-continuum intensity ratio is a sensitive measure of the calcium elemental abundance (Aca) relative to hydrogen in the emitting plasma. In previous investigations we found the calcium abundance varies from flare to flare. In the present investigation we analyse the variations ofAcafor flares which occurred in two active regions well observed bySMM. We conclude that it is not possible to correlate the abundance variations with the time of the flare occurrence as suggested in an earlier paper for flares produced from a single active region. Further, we find no convincing correlation of abundance variation with any other flare characteristics. This negative result will stimulate future work on the physical interpretation of the calcium abundance variation.