bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Nature of Atmospheric Turbulence Effects on Imaging and Pseudo-Imaging Systems, and its Quantification
Authors: L. David 
Published: June 2019

AbstractOver the last two decades, an extensive body of knowledge has been developed concerning the effects of atmospheric turbulence on optical propagation. Much of this is directly relevant to astronomical imaging, and with proper interpretation, to the type of pseudo-imagery that is of concern to us at this conference. This paper will provide an overview of this matter, hopefully with sufficient insight developed that the reader will be able to quickly estimate the nature and magnitude of the turbulence effects to be expected in a pseudo-imagery process. The paper starts with a review of turbulence effects on conventional imagery, reviewing the “nondimensional” nature of the turbulence statistics, presenting the local measure of the optical strength of turbulence,, and developing the resolution scale, r0. It presents a statistical view of the nature of the wavefront distortion geometry, indicating the dominance of the random wavefront tilt component. The MTF for conventional imagery and for speckle interferometry (Labeyrie) is presented with comments concerning their relationship. Following that, the foundation of the speckle imagery concept (Knox-Thompson) is presented. Results are then set forth for the allowable spectral bandwidth in speckle techniques, as well as results defining the allowable field-of-view size (isoplanatism) and the allowable exposure time for speckle techniques. Taken all together, these results provide a basis for estimating most of the significant effects of atmospheric turbulence in speckle interferometry and speckle imagery.
The Signal to Noise Ratio in Speckle Interferometry
Authors: Dainty J.C. , Greenaway A.H. 
Published: June 2019

AbstractRecent theoretical studies of the signal to noise ratio (SNR) of photon limited speckle (image plane) interferometry are reviewed. The SNR of an estimate of the object power spectrum is evaluated for both the single and double aperture cases, for arbitrary light levels. The SNR for the auto-correlation function method of analysis is also given for the low light level case and applied to the special case of binary star observations. The SNRs for the power spectrum and autocorrelation function analyses are compared and a comparison is also made between speckle (image plane) and amplitude (pupil or aperture plane) interferometry. Limiting observable magnitudes are estimated for some relevant cases.
Diffraction-Limited Observations Of Binary Star Systems
Authors: Scaddan R.J. , Morgan B.L. , Dainty J.C. 
Published: June 2019

AbstractA speckle interferometer is described which has been used to measure the separations and position angles of binary star systems. The present instrument uses an image intensifier to enable the enlarged stellar images to be recorded on cine-film. The exposure time is typically 8 msec and the camera can be operated at up to 20 frames per second. The instrument incorporates a means of calibrating the magnitude difference of the binary star systems.A pair of achromatising lenses have been designed which will correct the radial chromatic dispersion in the speckle patterns and allow exposures to be made in “white” light. A system is under development which uses an image intensifier and a plumbicon television camera to acquire the data and a hard-wired autocorrelator to perform the analysis in real time. With this system the limiting magnitude of the technique should be significantly improved.
Speckle Interferometry and Image Reconstruction
Authors: Weigelt Gerd P. 
Published: June 2019

AbstractThe angular resolution of conventional astrophotography is limited to about 1 sec of arc due to image degradation by the atmosphere and telescope aberrations. Higher resolution can be achieved by Labeyrie's speckle interferometry, which yields the autocorrelation of astronomical objects with diffraction-limited resolution, e.g. 0.02 sec of arc with 5m telescope aperture.We have investigated modifications of speckle interferometry, which yield diffraction-limited images. We investigated (1) “speckle holography” for image reconstruction of objects near an unresolvable point source (reference star), (2) “speckle masking” for image reconstruction of binary stars (without a reference star), and (3) “phase flipping” for image reconstruction of centro-symmetric objects. Together these three image reconstruction methods represent a set of speckle evaluation procedures, which can yield high resolution images of most astronomical objects that are bright enough for speckle interferometry. Speckle holography was already applied to astronomical objects. We reconstructed real images of the binary star Zeta Cancri A-B and the triple star ADS 3358 A-B-C ( 0.07 sec of arc resolution with 1.8m telescope aperture).
Dynamical Effects in the EUV Chromospheric Network
Authors: Chiuderi-Drago F.G. , Poletto G. 
Published: June 2019

Extreme ultraviolet observations of the chromospheric network obtained by the Harvard College Observatory experiment aboard Skylab on May 31st, 1973, are analyzed.The data, which have a spatial resolution of 5“ x 5“, cover an area of 5‘ x 5‘ near the center of the sun, where a large coronal hole was present, and are recorded in several lines formed in a range of temperatures from 104 to 106 °K.By studying the EUV spatial intensity distribution, the average intensity in cell and network, the contrast, and the emission measures have been derived.The network distribution, highly asymmetrical and skewed to higher intensity, suggests an inhomogeneous network structure, probably associated with the presence of spicules, not resolved by the instrument.A dynamical model of the transition zone is therefore developed, and the resulting EUV emission in spicules is computed and compared with available observations, and with previous network models.
Phase Differences Between Intensity and Doppler Shift and Between Two EUV Emission Lines of Sill For 300 Second and 95 Second Chromospheric Oscillations
Authors: White O.R. , Athay R.G. 
Published: June 2019

Phase differences between intensity and doppler shift in each of the two bright emission lines of Sill at λ1816.93, λ1817.45 are determined for chromospheric oscillations with periods near 300 seconds and 95 seconds. Phase differences between the oscillations in the two lines are determined also.For the 300 second oscillation, maximum intensity most often leads maximum blue shift by about 40 seconds and the oscillation in the fainter line at λ 1817.45 most often leads the oscillation in the stronger line at λ 1816.93 by about 35 seconds. For the 95 second oscillation, maximum intensity most often lags maximum blue shift by about 20 seconds and the oscillations in the fainter line most often lags the oscillations in the stronger line by about 12 seconds.
Studies of the Solar Atmosphere Using Density-Sensitive Line Ratios
Authors: Jordan C. 
Published: June 2019

The density sensitivity of lines in the Be I-like ion sequence has been discussed by several authors. The observed behaviour of the 977Å and 1175 Å lines of C III was studied using the Harvard instrument on Skylab, and limits were placed on the density variations across the quiet solar network and in active regions. Some limb data were also analyzed.More recently, further observations of the intensities of the 1175 Å, 1909 Å and 1247 Å lines of C III at the solar limb have been published,. Similar observations have been made for the 1371 Å and 1218 Å lines of o v ,.The present paper will discuss the interpretation of the above data in terms of Ne and other parameters in the solar atmosphere.
The Computation of Energy Levels and Oscillator Strengths of Fe X to Fe XIII Involving the Adjustment of Parameters to Achieve Consistency with Observations
Authors: Fawcett B.C. , Bromage G.E. , Cowan R.D. 
Published: June 2019

Energy levels and oscillator strengths are calculated for the 3s23pn–3s23pn–13d transition arrays of Fe X, Fe XI, Fe XII and Fe XIII. The Slater radial integrals for these computations are adjusted so as to become consistent with established energy levels. Pertinent configuration interactions are included and the interaction integrals are reduced by up to 35% from values calculated ab initio, to achieve consistency.Initial theroretical calculations are made using the ab initio Hartree-X, Slater-Condon programme of Cowan (1967, 1968), the second of which now includes configuration interaction. The first programme computes values for the average energy of the configuration Eav, the electrostatic direct integrals Fk and exchange integrals Gk , the spin-orbit parameters ζ, and the configuration interaction integrals Rk. From these the second programme computes energy levels, wavelengths and oscillator strengths for the transition arrays concerned.
High Dielectronic Satellite Lines in Solar Flare Iron Spectra
Authors: Bely-Dubau F. , Gabriel A.H. , Volontè S. 
Published: June 2019

New calculations have been carried out in intermediate coupling of the wavelengths and intensities of the Fe XXIV transitions ls2nℓ-ls2pnℓ with n ≥ 3.It is shown that some of these lines are situated on the short wave-length side of the helium-like Fe XXV resonance transition. For the intensities new calculations of the rates of autoionization and radiative decay have been made for the levels involved. Only dielectronic capture has been considered because the contribution of direct inner-shell excitation of the doubly excited states with n ≥ 3 is expected to be small in low density astrophysical plasmas.For this reason both wavelengths and intensities are compared with the only available solar flare Iron spectra of Grineva et al. (1973). Some features not yet identified in these spectra can be explained with the results of the present calculations. These lead to an important new diagnostic capability for solar flare soft X-ray spectra.
Definition of the Physical Problems Connected with Extended Atmospheres
Authors: Thomas R. N. 
Published: June 2019

AbstractThe necessity of carefully defining the phenomenological basis for classification of atmospheres as being “extended” is emphasized, and four alternative bases for such classification are suggested (1) the necessity to include curvature terms; (2) the presence of an ejected shell surrounding a central star; (3) an observational discrepancy between predicted and observed density gradient; (4) an anomaly between predicted and observed phenomena in stars with “dynamic” atmospheres such as cepheids. A number of physical problems connected with the presence of an extended stellar atmosphere are then categorized according to these alternative bases.
Comparison of Discrete Space and Differential Equation Methods in Non-LTE Line Transfer Problems
Authors: Grant I. P. , Hunt G. E. 
Published: June 2019

AbstractNumerical methods are essential to the treatment of line formation in inhomogeneous non-LTE atmospheres. The new methods due to Hummer and Rybicki and to Feautrier now make it possible to make such calculations, although these are often quite timeconsuming.We shall describe an alternative approach using discrete space techniques depending on concpets of invariance. The solution algorithm is closely related to the method of Hummer and Rybicki, whose equations are obtained as a limiting case. The stability and errors of our algorithm are susceptible to mathematical analysis, and make it possible to identify the critical parameters in the calculation with precision. The results for a two-level problem will be compared with those from an implementation of the Rybicki-Hummer equations and a comparison will be made of the performance of the two procedures in respect of speed of computation and storage requirements.
The Crust Cooling Curve of the Neutron Star in MXB 1659-29
Authors: Wijnands Rudy 
Published: June 2019

AbstractWe have monitored the quasi-persistent neutron-star X-ray transient MXB 1659-29 in quiescence using Chandra. The purpose of our observations was to monitor the quiescent behavior of the source after its last prolonged outburst episode and to study the cooling curve of the neutron star in this system. We discuss the results obtained and how they constrain the properties of the neutron star in MXB 1659-29.
SS433: The Microquasar Link with ULXS?
Authors: Charles P. A. , Barnes A. D. , Casares J. , Clark J. S. , Clarkson W. I. , Harlaftis E. T. , Hynes R. I. , Marsh T. R. , Steeghs D. 
Published: June 2019

AbstractSS433 is the prototype microquasar in the Galaxy and may even be analogous to the ULX sources if the jets kinetic energy is taken into account. However, in spite of 20 years of study, our constraints on the natur of the binary system are extremely limited as a result of the difficulty of locating spectral features that can reveal the nature and motion of the mass donor. Newly acquired, high resolution blue spectra taken when the (precessing) disc is edge-on suggest that the binary is close to a common-envelope phase, and hence providing kinematic constraints is extremely difficult. Nevertheless, we do find evidence for a massive donor, as expected for the inferred very high mass transfer rate, and we compare SS433's properties with those of Cyg X-3.
Super-Eddington Accretion in Black Hole X-Ray Binaries
Authors: Truss M. R. 
Published: June 2019

AbstractI present, very high resolution hydrodynamical simulations of accretion discs in black hole X-ray binaries accreting near the Eddington limit, including the effects of disc irradiation and mass loss. I show that the extreme variability displayed by sources such as GRS 1915+105 can be explained within the framework of an outburst in a partially irradiated, turbulent, disc.
Far-Ultraviolet Surveys of Globular Clusters: Searching for the Products of Stellar Collisions and Near Misses
Authors: Knigge C. , Zurek D. R. , Shara M. M. , Long K. S. , Gilliland R. L. , Charles P. A. 
Published: June 2019

AbstractFar-ultraviolet (FUV) observations with the Hubble Space Telescope are an excellent way to find and study the hot, blue stellar populations in the cores of globular clusters. These populations include dynamically formed blue stragglers and interacting binaries (such as cataclysmic variables, i.e. the products of stellar collisions and near misses. Using the cluster 47 Tuc as an example, we show how the combination of FUV imaging and slitless spectroscopy can be used to uncover and study these populations.
Are the Precursors of Type Ia Supernovae Double Degenerate Mergers?
Authors: Ferrario Lilia 
Published: June 2019

AbstractI argue that the observational evidence for white dwarf-white dwarf mergers supports the view that they give rise to ultra-massive white dwarfs or neutron stars through accretion induced collapse. The implications for the progenitors of Type Ia SNe are discussed.
SPH Simulations of Early and Late Superhumps
Authors: Kunze S. 
Published: June 2019

AbstractSmoothed particle hydrodynamics is a Lagrangian method for the solution of the hydrodynamic equations. Here this method is used to simulate the accretion disk in dwarf novae with very low mass ratio, q < 0.25, typical for SU UMa-type systems where the accretion disk can become eccentric and precessing during a superoutburst, leading to periodic brightness variations, so-called superhumps. Two phenomena are examined. First the late superhumps, i.e., the occasional persistence of superhumps well after the return to quiescence, seen e.g. in OY Car and IY UMa. This is due to a varying brightness of the hot spot region, as the eccentric disk continues to precess in quisecence. Second, the occurence of early superhumps in the superoutburst of WZ Sge. Tidal forces compress the rim of the disk, the tidal dissipation leads to a double-peaked strucure in the orbital light curve during the early stage of the superoutburst.
Modeling of Oxygen-Neon Dominated Accretion Disks in Ultracompact X-Ray Binaries: 4U 1626-67
Authors: Werner K. , Nagel T. , Dreizler S. , Rauch T. 
Published: June 2019

AbstractWe report on first results of computing synthetic spectra from H/He-poor accretion disks in ultracompact LMXBs. We aim at the determination of the chemical composition of the very low-mass donor star, which is the core of a former C/O white dwarf. The abundance analysis allows to draw conclusions on gravitational settling in WDs which is an important process affecting cooling times and pulsational g-mode periods.
Some Updates on the Role of Magnetic Fields in Cataclysmic Variables
Authors: Hellier Coel 
Published: June 2019

AbstractIn this review talk I cover some recent developments in understanding the role that magnetic fields play in cataclysmic variables. I discuss the recent DNO QPO unification models; the disk-magnetosphere boundary; some issues concerning the soft blackbody component and the nature of the X-ray spectra in MCVs; whether the SW Sex stars are magnetic, and finally I mention the weird behavior of FS Aur and HS 2331+3905.
Observational Studies of Cataclysmic Variable Evolution: Of Samples, Biases and Surprises
Authors: Gänsicke B.T. 
Published: June 2019

AbstractI present, brief status reports on three large observational projects that are designed to test our current understanding of the evolution of cataclysmic variables (CVs): The spectroscopic selection of new CVs in the Hamburg Quasar Survey, the search for pre-CVs based on Sloan colours and UK Schmidt/6dF multiobject spectroscopy, and the identification of CVs that descended from supersoft X-ray binaries using a HST/STIS far-ultraviolet spectroscopic survey.
Modeling the Diverse FUV Spectra of Disk-Dominated Cataclysmic Variables
Authors: Long Knox S. , Knigge Christian 
Published: June 2019

AbstractThe FUSE and HST spectra of dwarf novae in outburst, and of nova-like variables exhibit a wide range of characteristics. In a few systems, there are obvious signatures of a fast wind in the form of P-Cygni-like profiles of OVI and other relatively high ionization state ions. But this is rare. More common are systems with FUV spectra, showing a complex mixture of high and low ionization state lines. Here we describe attempts to reproduce the spectra using a Monte Carlo radiative transfer code developed to model bi-conical winds in disk systems.
FS Aur as a Permanent Superhump System
Authors: Tovmassian Gaghik H. , Zharikov Sergei V. 
Published: June 2019

AbstractWe discovered that the short period cataclysmic variable FS Aur at some epochs shows a photometric period close to the orbital. It exceeds the orbital period by ∽2%, which is a sign of the presence of a permanent superhump in the system. Superhumps tend to appear near short, low amplitude outbursts. We assume that FS Aur possesses a large thermally stable accretion disc and that the outburst may be due to the variable mass transfer rate. This, however, does not alter our previous explanation of yet another, 2.4 times longer than orbital, photometric period of FS Aur, found earlier, and persistently observed in its light curves.
Recovery of Old Novae
Authors: Schmidtobreick L. , Tappert C. , Mennickent R. E. , Bianchini A. 
Published: June 2019

AbstractIn the course of a long-term project investigating classical novae with large outburst amplitudes, we have performed multi-wavelength photometry and optical spectroscopy of several old nova candidates. We here introduce the aim of the project, the search for low mass-transfer novae with short orbital periods, and explain the method to recover these old novae via their colour characteristics. Finally we concentrate on first results for selected objects in our sample.
Short-Term Radio-X-Ray Correlations of Cygnus X-1
Authors: Gleissner T. , Wihns J. , Pooley G. G. , Nowak M. A. , Pottschmidt K. , Markoff S. , Klein-Wolt M. , Fender R. P. , Staubert R. 
Published: June 2019

We analyze simultaneous radio-X-ray data of Cygnus X-l from the Ryle telescope (RT) and RXTE over more than 4 a. We show that apparent correlations on short time scales in the lightcurves of Cyg X-l are probably the coincidental outcome of white noise statistics.As a measure of correlation between radio and X-ray emission, we calculate the maximum cross-correlation coefficient, ccf, of simultaneous radio and X-ray lightcurves, which are rebinned to a resolution of 32 s and smoothed. Every single X-ray lightcurve segment is cross-correlated with the corresponding radio lightcurve, up to a maximum shift Δt = ±10 h.
The New X-Ray Pulsar J1802.7-2017 Observed by BeppoSAX
Authors: Iaria R. , Augello G. , Robba N. R. , Di Salvo T. , Burderi L. , Lavagetto L. 
Published: June 2019

We report on the serendipitous discovery of a new X-ray source, SAX J1802.7-2017, ~ 22' away from the bright X-ray source GX 9+l, during a BeppoSAX observation of the latter source on 2001 September 16-20.The source was outside the FOV of the BeppoSAX/ LECS. We have verified its presence in both the MECS2 and MECS3 images, which probably excludes that this was a ghost image of a source outside the MECS FOV. Moreover, we can be sure that the source was within the PDS FOV. because the source X-ray pulsations were detected also in the PDS data (see below). We searched for known X-ray sources in a circular region of 30' centered at GX 9+1 in the SIMBAD data base. We found no known sources with a position compatible with that of the faint source; we therefore designate this serendipitous source as SAX J1802.7 2017.
SPH and Radiative Cooling
Authors: Manson K. J. 
Published: June 2019

I have investigated the effects of including a more realistic cooling law in SPH simulations of accretion discs. In order to improve the efficiency of the simulations, I have used Strang operator splitting, and I have developed a method of timestep control which guarantees the accuracy and stability of the simulations.Strang splitting (Strang, 1968) is used to numerically solve a differential equation where the differential operator is split into two or more parts. This scheme is appropriate for any such equation, but is applied most effectively in cases where one part of the equation has a different timescale to the rest, or is somehow more difficult to solve or less stable.
A Fuse Survey of Disk-Accreting Cataclysmic Variables
Authors: Froning C. S. , Long K. S. , Szkody P. , Gänsicke B. T. 
Published: June 2019

We present initial results of a survey of the FUV spectra of disk-accreting cataclysmic variables obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE).FUSE covers the 905 - 1188 Å range at spectral resolutions ≃0.1 Å. To date, FUSE has observed more than 65 cataclysmic variables (CVs). Publicly-available data include observations of 11 dwarf novae (DN), 15 non-magnetic novalikes (NLs), 7 intermediate polars and DQ Her stars, at least 15 polars, and 4 super-soft X-ray binaries.
Spectroscopy of Old Nova Candidates
Authors: Schmidtobreick L. , Tappert C. , Bianchini A. , Mennickent R. E. 
Published: June 2019

We present optical spectroscopy for several old nova candidates that hitherto lacked such observations. V842 Cen, V630 Sgr, XX Tau, CQ Vel, and V840 Oph show typical CV spectra, but V529 Ori is probably misclassified.V630 Sgr is an eclipsing system with an orbital period of 2.83 h. In spite of the high inclination, the emission lines are not, double-peaked at the resolution of 1 mm.