bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistics of Pulsating Variables
Authors: Novikova M.F. , Fadeyev Yu.A. 
Published: July 2016

AbstractClassification of pulsating variables is based on a number of properties but the most important of them are the period and amplitude of the light variation. These quantities also play an important role in understanding the evolutionary status of the pulsating stars since the pulsation period is related to the mass and radius through the period--mean density relation while the amplitude of the light curve characterizes the efficiency of the mechanism responsible for the pulsational instability. In the present study we considered the period--frequency and light amplitude--frequency distributions for ten types of the most numerous pulsating variables from the fourth edition of the General Catalogue of Variable Stars. The following types of pulsating variables were considered: DSCT, DSCTC, DCEP, RR, RRAB, RRC, CWA, CWB, RV and M. Using these distributions we estimated the upper and lower limits of the period and light amplitude within which 95% and 99% of the pulsating stars of a given type are contained.
The Binary Cepheid S Sagittae Revisited
Authors: Slovak Mark H. , Barnes Thomas G. , Evans Nancy R. , Welch Douglas L. , Moffett Thomas J. 
Published: July 2016

AbstractA new orbit has been derived for the binary Cepheid S Sagittae = HD 188727 = BD+16°4067, using both extant data and new radial velocities derived from radial velocity spectrometer observations at McDonald Observatory and the Dominion Astrophysical Observatory. We deconvoled both the pulsational and orbital components from the observed velocities in order to fit a truncated Fourier series to the pulsation velocities and to derive orbital elements respectively. We confirm the orbital elements given in Herbig and Moore (1952) and speculate that the secular trend evident in the orbital (O-C) diagram may be interpreted as evidence for a third component. (See Evans, Slovak and Welch, this volume, for IUE observations supporting this interpretation.)
Emission Lines From Hot Astrophysical Plasmas
Authors: Raymond John C. 
Published: July 2016

AbstractThe spectral lines which dominate the X-ray emission of hot, optically thin astrophysical plasmas reflect the elemental abundances, temperature distribution, and other physical parameters of the emitting gas. The accuracy and level of detail with which these parameters can be inferred are limited by the measurement uncertainties and uncertainties in atomic rates used to compute the model spectrum. This paper discusses the relative importance and the likely uncertainties in the various atomic rates and the likely uncertainties in the overall ionization balance and spectral line emissivities predicted by the computer codes currently used to fit X-ray spectral data.
Recent Advances in Atomic Modeling
Authors: Goldstein W. H. 
Published: July 2016

AbstractPrecision spectroscopy of solar plasmas has historically been the goad for advances in calculating the atomic physics and dynamics of highly ionized atoms. Recent efforts to understand the laboratory plasmas associated with magnetic and inertial confinement fusion, and with X-ray laser research, have played a similar role. Developments spurred by laboratory plasma research are applicable to the modeling of high-resolution spectra from both solar and cosmic X-ray sources, such as the photo-ionized plasmas associated with accretion disks. Three of these developments in large scale atomic modeling are reviewed: a new method for calculating large arrays of collisional excitation rates, a sum rule based method for extending collisional-radiative models and modeling the effects of autoionizing resonances, and a detailed level accounting calculation of resonant excitation rates in FeXVII.
X-ray Lines From Mg VIII and Si X Ions and Their Diagnostic Use
Authors: Dwivedi Bhola N. 
Published: July 2016

AbstractThe solar X-ray emission lines from Mg VIII and Si X ions have been studied. The variation of theoretical line intensity ratio I(λ 75.03)/I(λ 74.86) from Mg VIII and I(λ 50.69)/I(λ 50.52) from Si X as a function of electron density is found to be good density monitors of the emitting regions of solar plasma. The computed values of line intensity from these ions based on Kopp and Orrall model have been used to derive electron density of the quiet Sun and coronal holes. The electron densities of 109 cm-3 and 4.6 × 108 cm-3 are estimated at the electron temperatures of 8 x 105 K and 1.6 x 106 K for the quiet Sun whereas the respective values of 5.4 x 108 cm-3 and 1.7 x 108 cm-3 are obtained for the coronal holes. The line intensity ratios studied here are independent of temperature variation and are therefore excellent candidates for electron density diagnostics. However, observational data with improved spectral resolution is needed for using X-ray line pairs studied for their diagnostic use.
Measurement of Carbon Ion Photoabsorption Cross Sections Using Laser Plasmas
Authors: Wargelin B. , Kahn S.M. , Craig W. , London R. 
Published: July 2016

AbstractLaser plasmas are well-suited to studies of ionic photoabsorption because they can provide highly ionized, low temperature plasmas of high column density, as well as bright, compact continuum X-ray sources which can illuminate the plasma under study. In our experiment, continuum X-rays from a gold laser plasma are partially absorbed as they traverse a carbon plasma and are then dispersed by a grazing incidence reflection grating. An X-ray imaging camera records both the absorbed and unabsorbed spectra simultaneously for later computer analysis to determine the photoabsorption cross sections for each carbon ion species.
The Effect of Magnetic Fields Upon Cosmic X-ray Spectra
Authors: Mészáros P. 
Published: July 2016

AbstractThe effect of strong magnetic fields (B ≳ 1011Gauss) upon various atomic line emission mechanisms in the X-ray range is considered, in particular for H and H-like or He-like ions, and a discussion of the detectability and significance of possible measurements is given. The cyclotron mechanism, the one- and two-photon scattering and the bremsstrahlung effects in a strong B are reviewed, as well as the role they play in determining X-ray spectra. These considerations are applied to typical models of X-ray pulsars and Gamma-ray bursters, contrasting observations of magnetic related features to the present theoretical understanding of these objects.
Effect of Vacuum Polarization in a Strong Magnetic Field and Spectral Features of X-Ray Source Emission
Authors: Gnedin Yu. N. 
Published: July 2016

AbstractIn strong magnetic fields of neutron stars electron-positron vacuum behaves as an anisotropic medium. Vacuum influences the generation and propagation of electromagnetic radiation in plasma and changes the spectrum of radiation. As a result the change of cyclotron lines shape and appearance of specific “vacuum lines” should be observed in X-ray spectra of accreting neutron stars.
High Resolution Spectroscopy and Plasma Diagnostics of Supernova Remnants
Authors: Canizares Claude R. 
Published: July 2016

AbstractThe MIT group has used data from the Focal Plane Crystal Spectrometer on the Einstein Observatory to perform plasma diagnostics of four supernova remnants (SNRs), the Cygnus Loop, Puppis A, N132D, and Cas A. The ratio of luminosities of the forbidden line to resonance line of He-like ions of oxygen and neon allow us to show that all four SNRs depart from ionization equilibrium in that they are under-ionized for their electron temperatures. Thus despite the fact that their ages range from 300 yr to 20,000 yr, all four SNRs are still ionizing and, in that sense, are still young. We derive values of ionization time and electron temperature for one or more components in each remnant. The agreement between these values and those deduced by others using entirely different means (e.g. broad-band spectroscopy or imaging) gives us confidence in the reliability of the diagnostics. Two of the SNRs, Puppis A and N132D, show evidence for an overabundance of oxygen by factors of three or more. These results, based on a handful of weak lines, show the great promise of the much more powerful future spectroscopy missions for revealing detailed information about astrophysical plasmas.
Signatures of Cooling Flows
Authors: Fabian A.C. 
Published: July 2016

AbstractThe evidence for cooling flows in clusters of galaxies is discussed. Peaked X-ray surface brightness profiles and the presence of soft X-ray spectral components are characteristic signatures of cooling flows. The best available data are consistent with gas cooling at a rate of ~ 100M⊙yr-1 and depositing cooled matter over a radius of 100 – 200 kpc. The same rate is obtained from observations of gas cooling over a range of temperatures and thus a range of cooling times covering less than 3 × 107 yr to more than 3 × 109 yr. It appears that cooling flows are both steady and long-lived. Some indirect optical evidence for distant cooling flows (0.5 < z < 1) is presented.
The X-ray Astronomy Satellite SAX
Authors: Butler R.C. 
Published: July 2016

AbstractThe SAX satellite is forseen for launch at the end of 1992 to study the X-ray emission from galactic and extra-galactic sources in the energy range 0.1-200 keV. The payload consists of four concentrator/spectrometer systems (3 units 1-10keV, 1 unit 0.1-10keV), a high pressure gas scintillation proportional counter (3-120keV), a phoswich scintillation counter (15-200keV), and two wide field cameras (2-30keV). Together these instruments will perform the following:-
- Broad band spectroscopy (E/ΔE=12) in the energy range 0.1-10 keV with imaging resolution of 1 arcmin- Continuum and cyclotron line spectroscopy (E/ΔE=5-20) in the wide energy range 3-200 keV- Variability studies of bright source energy spectra on time scales from milliseconds to days and months- Systematic long term source variability studies in selected regions of the sky down to a source intensity of 1 mCrab.
Isotopic Ratios in Comets
Authors: Vanysek V. 
Published: July 2016

Abstract.The isotopic abundances depend on the universal evolution of elements and on the individual history of particular objects. Since it is believed that unprocessed material of the solar nebula is preserved in comets, the data concerning the abundance of stable isotopes in these primitive bodies are of some importance in the cosmological context. The present status of this problem is reviewed. The reliability of results for nuclear species with cosmological and cosmogonical implications, such as D/H, C 12/13, N 14/15, O 16/18, and Mg 24/25/26, is discussed. Significant variation is found for the isotopic abundance of carbon, depending upon which carbon reservoir is sampled. Deuterium is probably enhanced relative to the interstellar ratio. For other isotopes, the ratios are close to those of the terrestrial data. The tendency of the D/H ratio to be at higher values indicates a low temperature in the environment of the comet’s formation, and, together with similar effects in the outer planets, suggests that there were two different primordial reservoirs of deuterium in the solar system. The 12C/13C ratio inferred from in situ mass spectrometry of the dust, as well as from the ground-based optical spectra of the Swan band, tends to be approximately equal to the average terrestrial ratio (89) or larger. Recent results obtained from the CN band provide a significantly lower value (about 65), which corresponds to the carbon isotopic ratio in the diffuse interstellar clouds. The enhancement of deuterium and the possible differences of the carbon isotopic ratio in different species and refractory material are indicative of chemical fractionation processes in the protosolar nebula.
The Hydrogen Clouds of Comets
Authors: Shimizu Mikio 
Published: July 2016

Abstract.In a cometary coma, various hydrogen compounds, especially water, that are photodissociated by solar ultraviolet radiation form a gigantic hydrogen cloud with a radius of several million kilometers around the cometary nucleus. These cometary hydrogen clouds have been observed by a number of spacecraft outside the terrestrial atmosphere and in interplanetary space. For instance, the hydrogen cloud of Comet Halley was a good target for the ultraviolet photometers and spectrometers on board the International Ultraviolet Explorer (IUE), Suisei, Pioneer Venus, DE-1, and sounding rockets. Hydrogen cloud activity could be used as a good measure of cometary activity, but some problems remain to be explored in the future.
The Forest and the Trees
Authors: Whipple Fred L. 
Published: July 2016

AbstractSome 24 points are made concerning the author’s understanding of the cometary nucleus as developed in this colloquium. Comparisons with an earlier report are noted, and most of the earlier advances in concept are substantiated. The mean density of the Halley nucleus may have been underestimated. The dust/gas ratio apparently needs to be increased by as much as two times, perhaps to unity or higher. The nature of the rotation remains puzzling. CHON grains now appear to be more important sources of gas than thought earlier. A very low temperature at, and subsequent to, the formation of the nucleus continues to receive support, as does a solar-system composition. The 12C/i:3C ratio may, however, be lower than expected.
Source-noise in radio synthesis images
Authors: Anantharamaiah K.R. , Deshpande A.A. , Radhakrishnan V. , Ekers R.D. , Cornwell T.J. , Goss W.M. 
Published: July 2016

AbstractWe discuss the distribution of source- and receiver- noise in radio synthesis images and show that the source-noise is maximum at the position of the source but also appears in the off-source region because of the sidelobes. Analytical expressions are derived for the rms noise at any location of both “total-power” and “correlation” images. We show that under certain conditions, deconvolution can remove the source noise from the off-source region in snap-shot images. Some of the results are verified experimentally.
The design of high frequency antennas
Authors: Delannoy J. 
Published: July 2016

AbstractThe conceptual guidelines in designing mm radio-telescope antennas are enlightened by some recent progress in their mechanical construction, and opto-radio-geometrical adjustment. This paper reviews concepts, illustrated in many existing solutions, including the new “phaseretrieval” holography for single dish adjustment (D.Morris, IRAM, 1982): 2 amplitude only maps at focus and out of focus, with enough dynamic range and signal to noise ratio, give surface errors within hours.
Direct Imaging Digital Lens for Transient Radio Source Survey
Authors: Daishido Tsuneaki , Asuma Kuniyuki , Nishibori Kazuhiko , Nakajima Junichi , Yano Motoko , Otobe Eiichiro , Watanabe Naoki , Tsuchiya Akira , Iwase Seiichiro 
Published: July 2016

AbstractFFT based 2D Dygital Lens is discussed comparing with Fourier synthesis. The sensitivity of constructing Large Array will be 50mJy. Precise manipuration of the radiation field is possible in it.
Phase Control in the Digital Lens
Authors: Asuma Kuniyuki , Iwase Seiichiro , Nisibori Kazuhiko , Nakajima Junichi , Otobe Eiichiro , Tuchiya Akira , Watanabe Naoki , Daisido Tsuneaki 
Published: July 2016

AbstractPhase and amplitude is controlled by manipulating the digitized radiation field. Application to the phase switching, and the calibration of phase and amplitude is discussed.
A Portable Holographic Antenna Measurement System
Authors: Shaffer David B. , Gipson John M. 
Published: July 2016

AbstractInterferometrics has developed a portable holographic antenna measurement system. The system is comprised of a small interferometer which uses satellite signals to measure the complex beam pattern of the antenna under test. A PC controls all aspects of data collection and analysis. The system produces maps of surface profile errors and the illumination power in reflector antennas.
The use of beam-sets in the Analysis of wide-field maps from the CLFST
Authors: Waldram Em 
Published: July 2016

AbstractThe Cambridge Low Frequency Synthesis Telescope (CLFST) has baselines which are offset from the E-W direction by about 3°. The wide-field mapping problem has been overcome by the use of beam-sets, or artificial maps consisting of grids of synthesized beams, which incorporate the effects of both the geometric and chromatic aberration. By appropriate interpolation we can find a good approximation to the beam-shape at any point on a map.
State-of-the-art VLBI imaging: 3C345
Authors: Wehrle Ann E. , Unwin Stephen C. 
Published: July 2016

AbstractMost VLBI images have low dynamic range because they are limited by instrumental effects such as calibration errors and poor u, v-coverage. We outline the method used to make a new image of the bright quasar 3C345 which has very high dynamic range (peak-to-noise of 5000:1) and which is limited by the thermal noise, not instrumental errors. Both the Caltech VLBI package and the NRAO AIPS package were required to manipulate the data.
VHF Radio Interferometry of Lightning
Authors: Krehbiel P.R. , Shao X.M. , Thomas R.J. , Rhodes C.T. , Hayenga C.O. 
Published: July 2016

AbstractLightning discharges radiate strongly at radio frequencies, and studies of the radiation provide valuable information on lightning breakdown processes. Interferometric techniques can be used to locate the numerous radiation events as a function of time during a discharge and to generate images of the developing lightning channels inside a storm, where they are obscured from view at optical wavelengths.
A Dynamical Systems Approach to Nonlinear Stellar Pulsations
Authors: Buchler J. R. 
Published: July 2016

AbstractOver the last decade we have seen the application of novel techniques to the old problem of nonlinear stellar pulsations. Together with numerical hydrodynamics this approach provides a more fundamental understanding of the systematics of the pulsational behavior. For weakly nonadiabatic pulsations, whether regular or multi-periodic, dimensional reduction techniques lead to amplitude equations and to a description in terms of modal interactions and resonances. In particular they shed new light on the bump progression in the classical Cepheids. In more dissipative stars numerical hydrodynamical modelling has uncovered the existence of irregular variability, both in radiative and in convective models. An application of modern dynamical systems techniques has shown that this behavior occurs according to well understood routes from regular to chaotic behavior. The mechanism is very robust and represents the first nonad hoctheoretical explanation of irregular stellar variability. Finally, we discuss how a comparison with observations of irregular variability shows the need for more suitable observations, on the one hand, and of better techniques of signal processing, on the other.
Nonlinear Expansion Triggered by Magnetic Stress in Accretion Flow onto a Black Hole
Authors: Yokosawa M. 
Published: July 2016

AbstractThe paper is an investigation of the magnetohydrodynamics (MHD) of the quasi-radial accretion onto a rotating black hole. It is demonstrated that the nonlinear effects in the accretion flow accelerate the rate of expansion of the Alfven mode. The accretion flow becomes unstable at the weak strength of magnetic field which is about one-thirtieth of the expected value by the linear theory.
Spatial Pattern Formation of Interstellar Medium
Authors: Tainaka K. , Fukazawa S. , Nishimori H. , Yokosawa M. , Mineshige S. 
Published: July 2016

AbstractPopulation dynamics of multi-phased interstellar medium (ISM) is investigated by using the lattice model in position-fixed reaction. Interactions between three distinct phases of gas, cold clouds, warm gas, and hot gas give rise to cyclic phase changes in ISM. Such local phase changes are propagated in space, and stochastic steady-state spatial pattern is finally achieved. We obtain the following two characteristic patterns:
(1)When the sweeping rate of a warm gas into a cold component is relatively high, cold clouds associated with warm gas form small-scale clumps and are dispersively distributed, whereas hot gas covers large fraction of space.(2)When the sweeping rate is relatively low, in contrast, warm gas and cold clouds are diffusively and equally distributed, while hot gas component is substantially localized.
Low Amplitude New Type Variable Stars in Globular Clusters
Authors: Bao-An Yao , Chung-Sheng Zhang , Dao Qin , Jian-Hua Tong 
Published: July 2016

Rapid progress in the stellar pulsation research has presented many new challenges to traditional pulsation theory. The following progress made by us should belong to one of the new challenges:
1)There are many variable stars located at the Horizontal Branch (HB) but outside the instability strip with amplitude larger than 0.02 mag.Maybe some astronomers have already doubted of the 1950’s conclusion-the RR Lyrae stars are confined to the narrow instability strip in the C-M diagram, the boundaries of the gap are extremely sharp and definite, beyond the edges no light variations occur with ranges greater than 0.02 mag. We are changing the conclusion by observations. Here we do not mean the microvariability. We still raise the question from the classical viewpoint. We want to show that there are variable stars outside the strip with peak to peak amplitudes larger than 0.02 mag.
Stellar Pulsation: (I) Analysis of Stability of Envelope
Authors: Zhi-Yao Yu 
Published: July 2016

AbstractThe life-time of the star on AGB is approximately 6 × 104 yr. We divide it into front half and back half of AGB (including to optical Mira variable and OH/IR star) according to their evolution character. The observations show that the star has non-pulsation, but constant mass loss rate (~ 5 × 10−7M⊙ yr−1) on front half of AGB. Its circumstellar envelope is formed. When the star has pulsation on back half of AGB, its mass loss rate is relative with time, and increases gradually. In this time the star is on the stage of optical Mira variable. When the mass loss rate reaches the value of ~ 3 × 10−6M⊙ yr−1, the star evoluted from the stage of optical variable into the stage of radio bright OH/IR star. On the end of AGB the mass loss rate reaches ~10−4M⊙ yr−1. (Band and Habing 1983, Hermen and Habing 1985).