bluuebunny/crossref_metadata_2025 huggingface dataset:
CCD Observations of Forgotten Cepheids
Authors: DuPuy David L. , Todd Viar W. , Bloomer Raymond H. , Ward Bradley J.
Published: June 2019

CCD observations have been obtained of eight Cepheids which have few recent observations, or an uncertain period, or an uncertain finder chart. All CCD images were flat-fielded, with 4-min exposures (0.5-m telescope) or 6-min exposures (0.4-m telescope). The stars chosen for observation were CY Aqr, EV Aur, V395 Cas, V588 Cas, DW Per, HZ Per, MM Per, and SX Per.

Photometry shows clean, Cepheid light curves for six of these eight stars, with the results for MM Per shown as an example below. V588 Cas did not show a periodicity in our data set (only 9 points), and the results for EV Aur will be published separately. We obtained standard deviations of comparison-star differences for all useable stars in our CCD images, to aid future observers in choosing suitable comparisons.
New Ways of Revealing Cepheid Binaries
Authors: Szabados L.
Published: June 2019

Two methods involving the observed amplitudes of radial velocity and UBVR light variations for classical Cepheids have been analysed, both being implicitly known: their principle is trivial but these methods had not yet been used systematically as indicators of duplicity.

The slope method is based on the alteration of the wavelength dependence of the light variation amplitude if either a blue or a red companion is added to the light of the Cepheid. The amplitude ratio (AR) method makes use of the fact that the companion reduces the amplitude of the light variation without observable effect on the pulsational radial velocity amplitude. This means that the ratio of these two amplitudes (Arad.vel./AB) has a larger value for binary Cepheids as compared with the single pulsators.

Each method has been applied to more than 100 Cepheids, thus allowing to study how the uncontaminated parameters (amplitude ratio and slope) depend on the pulsation period. Binary Cepheids deviate from the regular pattern in these diagrams, and a number of new binaries can be discovered in this way. The effect of duplicity is revealed by both methods independently for VZ CMa, FM Cas, CR Cep, V402 Cyg, VI154 Cyg, V440 Per and DR Vel.
The Periods of RR Lyrae
Authors: Cox Arthur N.
Published: June 2019

RR Lyrae (0.566 day period) exhibits the Blasko effect that suggests another natural mode with almost the same period as the accepted fundamental radial mode. This mode might be nonradial, but no one has done an extensive evaluation of this idea. An investigation requires a model that includes the deep composition structure where g-modes of low angular (observable) degree have weight and amplitude. An RR Lyrae model including the outer half of the mass and more than 99% of the radius, based on an asymptotic giant branch model from Hollowell (private communication), see below, was used for this study. It includes composition gradient ramps between the primordial surface hydrogen and helium and the almost pure helium shell and the one between this helium shell and the convective core that is burning helium.

Nonradial mode periods almost resonant with the radial fundamental mode period seem to occur for all low ℓ values. In addition to significant pulsation amplitudes in the composition gradient regions where the Brunt Väisälä frequency is large, these low degree and low radial order modes have near-surface amplitudes very similar to the low order radial modes. These modes are evanescent in the convective core. Classical K and γ effects give enough driving in the very low mass surface layers, so that important deep radiative damping for these modes does not completely stabilize nonradial g-mode pulsations. The g4, ℓ=1 mode gives a. double-mode RR Lyrae with Blasko effect.

A nonradial mode may not always be visible, depending on how rotation presents the nonspherical pulsations to the observer. Thus the Blasko effect might come and go, as observed for maybe 20% of all RR Lyrae variables. For many, the Blasko effect may not be observable, even when a nonradial mode is there.
The m1 Index in RR Lyrae Stars
Authors: Eloy Rodríguez  , Rolland Angel , de Coca Pilar López
Published: June 2019

We have carried out simultaneous uvbyβ photometry for several RR Lyrae stars. For each of these stars, the observed m1 index variation along the pulsation cycle is compared with that expected variation from the (Δm1*,β) grids of Rodriguez et al. (1991) for the corresponding temperatures, gravities and metallicities. The m1 index variations are also calculated using the Kurucz's models. Good agreement is found
Period Variation of the Pop.II Cepheid AU Peg
Authors: Vinko J.
Published: June 2019

AU Peg, a short period BL Her-type variable, is unique among short period Cepheids. It is a member of a close binary system with an unseen companion. In t his paper the pulsational period variation is presented. It is shown that the period variation is very rapid and highly non-linear. It seems that there is no simple explanation of this phenomena by standard evolution or tidal interaction.
Long-Term Brightness Changes in Cool Pulsating Variables
Authors: Percy John R.
Published: June 2019

Several types of cool pulsating variables show unexplained long-term changes in brightness, typically on time scales of 10 to 20 times the basic (pulsational) period. The visual and photoelectric programs of the American Association of Variable Star Observers (AAVSO) are well-suited for detecting and studying these changes. Some examples are given here, including yellow hypergiants, RV Tauri stars, small- and large-amplitude red giant and super giant variables. The study of pulsating variables on long time scales provides “new perspectives” on their behavior.
Period Changes in the SX Phoenicis Star CY Aquarii
Authors: Joner Michael D. , Powell John M.
Published: June 2019

CY Aquarii is a Population II dwarf Cepheid that has been observed on a regular basis since 1930. We present evidence from unpublished times of maximum light from Brigham Young University observations secured in the mid-1970s to the present that indicate that the period of CY Aqr has changed in a discontinuous manner. Furthermore, we find that the period has changed significantly since the epoch of the last published investigation (1988). Finally, contrary to some past claims, examination of our high time resolution light curves yields no indication of multi-periodic pulsation in CY Aqr.
28 And: Simultaneous Strömgren Photometry
Authors: Rodríguez E. , A. Rolland  , López de Coca P. , Garrido R. , Mendoza E.E.
Published: June 2019

We have carried out simultaneous uvby photometry of the low amplitude δ Set star 28 And. Analysis of the data, using the Fourier Transform method, establishes 28 And as a monoperiodic pulsator. Using the classical O-C method, it is found that the pulsation of this star can be well described by means of a linear ephemeris with a period of P=0.d069304118 over the last twenty-four years. Amplitude variations are also shown to be present from season to season. The physical parameters of this star are determined and the nature of radial or nonradial pulsation is discussed on the basis on the derived phase shifts and amplitude ratios between Strömgren colours. The results indicate that 28 And pulsates in a nonradial mode with ℓ = 2.
ρ Pup: A Monoperiodic Radially Pulsating δ Set Star
Authors: Rodríguez Eloy , Rolland Angel , de Coca Pilar López
Published: June 2019

ρ Pup is a δ Scuti type pulsator with relatively low amplitude (ΔV∼0.m09). Analysis of the data from different sources, using the Fourier Transform method, establishes ρ Pup as a monoperiodic pulsator. Using the classical O-C method, it is found that the pulsation of this star can be well described by means of a linear ephemeris with a period of P=0.d140881372 over more than eighty years. The nature of radial or nonradial pulsation is discussed on the basis on the derived phase shifts and amplitude ratios between different colours. The results indicate that ρ Pup is a radial pulsator.
The Shape of the Interstellar Reddening Curve
Authors: Underhill Anne B. , Walker Gordon A. H.
Published: June 2019

When the Observed Spectral Intensity Distribution of an early-type star has been freed from the distortions caused by absorption in the Earth's atmosphere and by instrumental sensitivity factors, it is a measure of the true spectral intensity distribution of the star and of the modifications to that distribution caused by the interstellar material between the Earth and the star. Thus, if one knew the true intensity distribution from the star, one could derive the shape of the interstellar reddening curve. In practice it is customary to compare the intensity distributions of pairs of stars of apparently the same spectral type, within the errors of classification, but which suffer different amounts of reddening, and to attribute the difference to interstellar reddening. In this way one can determine the shape of the interstellar reddening curve.
A Search for the Regional Variations in the Wavelength Dependence of Interstellar Polarization
Authors: Serkowski K. , Chojnacki W. , Rucinski S.
Published: June 2019

The Polarization of 19 Bright, Highly Polarized Stars was measured from March until July 1965, with a differential polarimeter installed at the Cassegrain focus of the 90-cm telescope of the Toruń Observatory in Poland. The stellar light was split by the calcite Wollaston prism into two beams falling upon the cathodes of the photomultipliers. The observations were made at eight position angles of the polarimeter differing by 45°, alternately with and without the quartz depolarizer. The yellow 2-mm Schott GG 14 and the blue Schott BG 12 (l-mm) + GG 13 (2-mm) filters were used. No optical elements except the depolarizer were placed between the Wollaston prism and the telescope mirrors.

Usually only the Stokes parameters having the larger absolute values were accurately measured. The resulting polarization ratios pv/pB of the Stokes parameters expressed in magnitudes, measured with yellow and blue filters, are given in the ninth column of table I.
Scanner Observations of λ4430
Authors: Joseph Wampler E.
Published: June 2019

The Interstellar Band at λ4430 has been observed in over 100 stars by using the Lick Observatory scanning spectrograph mounted on both the 120-inch telescope and on the Crossley telescope. Although in some instances the feature is badly blended with stellar lines, particularly with early B supergiants, in general the central depth of λ4430 has been determined to an accuracy exceeding 0.5 percent of the stellar continuum.

The feature has been found to have a fairly symmetrical profile, although there may be changes in the profile from star to star. The extended wings reported by other observers were not detected, and also the feature does not seem to be polarized.

The correlation between the absorption band at A.4430 and color excess is not one-to-one. Even field stars lying in the galactic plane show much intrinsic scatter in the ratio of this absorption band to color excess.
Infrared Radiation From Interstellar Grains
Authors: Stein Wayne A.
Published: June 2019

The Past Several Years there has been a growing interest in the possibility of observing infrared radiation at wavelengths greater than 10 μ, from various astronomical objects. For example, Gould in references 1 and 2 has suggested trying to observe several lines in the infrared with emphasis on the 12.8-μ line of Ne+ and the 28-μ line of molecular hydrogen. The possibility of being able to observe the emission from interstellar grains in the wavelength region between 10 μ and 100 μ was suggested in a discussion presented in references 3 and 4. The intensity expected from thermal emission by the grains has also been investigated by F. D. Kahn at Manchester.

The present paper indicates information about interstellar grains that could be gained by measuring the intensity as a function of wavelength and the polarization of radiation emitted by the grains in the far infrared.
Some Problems of Interstellar Grains
Authors: Mayo Greenberg J. , Lind A. C.
Published: June 2019

The Interactions of Grains With Radiation show up either as modifications of the radiation field (scattering, extinction) by grains or as modifications of grains by the radiation. The principal effects on grains are to control their temperature and to exert forces (radiation pressure). This paper presents some radiation pressure calculations which may be pertinent to the problem of propulsion of grains outward from very hot, bright stars or more generally OB complexes. The radiation force is equal to the rate of transfer of momentum to the grain, which is equal, in turn, to the net rate of loss of momentum in the incident beam of electromagnetic radiation.
The Application of High Angular Resolution Stellar Interferometry to the Study of Single Objects in the Visual Region of the Spectrum
Authors: Davis John
Published: June 2019

A brief review of existing angular diameter measurements of single objects is given. Potential astronomical programmes for high angular resolution stellar interferometry in the visual region of the spectrum are discussed with particular regard to the sensitivity, resolution, and accuracy required for significant astrophysical results to be obtained. This discussion is used as a basis for suggesting the minimum requirements for future high angular resolution stellar interferometers.
The Nature of Atmospheric Turbulence Effects on Imaging and Pseudo-Imaging Systems, and its Quantification
Authors: L. David
Published: June 2019

Over 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

Recent 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

A 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

The 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).
Resonance Charge Transfer Effects in Carbon Plasmas and Measured Population Inversion
Authors: Dixon R.H. , Elton R.C.
Published: June 2019

Resonance line CV and CVI plasma spectra in the 40 Å region indicate a reduced (Nn /wn) population density inversion of ∽4X between n=4 and n=3 excited levels. Inversion between n=5 and n=3 is also observed. The ions are created from a graphite target by a 5 J, 16 ns Nd glass laser pulse focused to a 0.5 mm spot, i.e., 2 x 1011 W/cm2 . These ions expand into a gaseous atmosphere (H, He, Ne, Ar, …) . The greatest degree of inversion is observed at ∽15 mm from the target surface at a pressure of 1-2 Torr in helium or hydrogen. At this distance both ions and neutrals are detected by space - and time-resolved spectroscopy, and an electron density of 5 x 1016 cm– is measured from Stark broadening.
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.
Non-Equilibrium Excitation and Ionization of Be-Sequence Ions
Authors: Raymond J .C . , Dupree A.K.
Published: June 2019

Intensities of resonance and subordinate lines in C III and O V are calculated for several non-equilibrium states expected to occur in the solar atmosphere. In particular, cooling (recombination) phases of solar flares, and regions of mass flow such as coronal holes and the network offer conditions where non-equilibrium phenomena can be significant. In such situations, the ionization state may not be in equilibrium with the electron temperature. Detailed comparison is made with the ultraviolet observations from the Harvard College Observatory experiment on Skylab which show temporal variations as well as clear non-equilibrium enhancement of the ratio of the 2s2p 3P - 2p23P transition 2 1 1 to the resonance line 2s21S - 2s2p 1P in both C III and O V.
Density Sensitive Lines in the EUV Region
Authors: Vernazza J. E. , Mason H.E.
Published: June 2019

A search for density sensitive line ratios was made in the 1400 Å to 300 Å region of the solar spectra. The emergent intensity of resonance and subordinate lines from ions of the beryllium and boron isoelectrcnic sequence were calculated for typical solar plasmas. For individual ions, line, ratios which are sensitive to electron densities changes between 107 to 1013cm –3were selected. These line ratios were then compared to observations made by the Harvard College Observatory spectrometer aboard SKYLAB. From all the potential candidates only few are adequately observed to estimate electron densities. In particular the Mg VIII lines at 430 and 436 Å are good indicators of the coronal densities. Comparisons of the densities of coronal holes, flares, and active regions are made.
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.
Complex Atomic Spectra Made Easy — A Multichannel Quantum Defect Treatment and Proposal for Experiment
Authors: Lu K. T.
Published: June 2019

Non-polarized one photon excitation in atoms from a lower state with non-zero total angular momentum J will always reach opposite parity final states with three different total angular momentum, J' = J, J ± 1. In the case of heavy elements, e.g. Rare Earth or Actinides atoms, there are more than two electrons in the un-occupied open valence shells and in turn, many series are generated for one J' alone. All these make the population of levels close to ionization potential to be extremely dense, besides, accidental degeneracy will further defy the resolution and identification of the levels. An experiment is proposed to select final states with one J only and therefore simplifies the spectra by a factor of 3. The J-selection spectroscopy incorporated with Multichannel Quantum Defect Theory can thus make the complex spectral analysis easy. Uranium spectra is investigated as an example.
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.
Calculation of the Temperature Structure of an Optically Thin Plasma From its Emission Line Spectrum
Authors: Evans K.D. , Pye J.P. , Hutcheon R.J.
Published: June 2019

Knowledge of the (differential) emission measure function (with temperature), Y(Te), is likely to be of fundamental significance in attempts to understand the behaviour of any optically thin plasma - and this is certainly true of present studies of the solar atmosphere. In this latter case the gross temperature structure of material below 106K has been deduced from uv line measurements since the early 1960's and, since 1968, similar analyses of the material above 106K have been made using emission lines at x-ray wavelengths. In this latter case the validity, and even desirability, of published results has recently been quite strongly challenged. Comment is made upon those criticisms of early results and upon their relevance to present day analyses. In this paper the crucial value of fine temperature resolution in the determination of the emission measure function of this coronal material is argued.
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.
The Tools to determine Orbital Parameters
Authors: Heintz W. D.
Published: June 2019

How can an apparently cut-and-dried textbook matter such as orbits become the topic for an international conference? The answer is found in statements from the reports of presidents of Commission 26 which criticize the existing state of affairs and is further elaborated upon by van den Bos (1962) in his well-known query “Is this orbit really necessary?” The objections refer to useless repetitions or multiple solutions and results that are distinctly inferior to observational accuracy. Unanimous agreement on what constitutes a useful orbit, or revision, is unlikely to be achieved, but considerable published work which is based more on computer experience than on double-star knowledge is clearly of inferior quality. To some extent, errors of observation (including poor distribution of data, etc.) are unavoidable, but published material contains errors due to the method of analysis which could have been avoided.
Definition of the Physical Problems Connected with Extended Atmospheres
Authors: Thomas R. N.
Published: June 2019

The 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

Numerical 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

We 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

SS433 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.
Populations of Massive X-Ray Binaries
Authors: Negueruela Ignacio
Published: June 2019

The population of massive X-ray binaries in a galaxy can provide important constraints on its recent history of star formation. However, further knowledge of the Galactic population and formation mechanisms is needed before deeper inferences can be made for other galaxies.
Super-Eddington Accretion in Black Hole X-Ray Binaries
Authors: Truss M. R.
Published: June 2019

I 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

Far-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.
Population Synthesis Studies of White Dwarf Binaries
Authors: Kolb U. , Willems B.
Published: June 2019

We present population synthesis studies of white dwarf - main-sequence star binaries, of cataclysmic variables that are driven by circumbinary discs, and of eclipsing binaries in the exoplanet transit search SuperWASP.
Are the Precursors of Type Ia Supernovae Double Degenerate Mergers?
Authors: Ferrario Lilia
Published: June 2019

I 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.
Non-Linear Resonances in Accretion Disks and QPOs
Authors: Kluźniak Włodek
Published: June 2019

Non-linear oscillations in the accretion disk are favored as an explanation of high-frequency QPOs observed in the light curves of low-mass X-ray binaries containing neutron stars, black holes, or white dwarfs.
SPH Simulations of Early and Late Superhumps
Authors: Kunze S.
Published: June 2019

Smoothed 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

We 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

In 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

I 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

The 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

We 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

In 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 Nature of the Compact Object in the Hard X-Ray Source 4U2206+54
Authors: Torrejón J. M. , Kreykenbohni I. , Orr A. , Titarchuk L. , Negueruela I.
Published: June 2019

We present an analysis of archival RXTE and BeppoSAX data of the X-ray source 4U2206+54. For the first time, high energy data (≥ 30 keV) is analyzed. The data is well described by comptonization models in which seed photons with temperatures between 1.1 keV arid 1.5 keV are comptonized by a hot plasma at 50 keV thereby producing a hard tail which extends up to 100 keV. From luminosity arguments it is shown that the area of the soft photons source must be small (r ≈ 1 km) and that the presence of an accretion disk in this system is unlikely. Here we report on the possible existence of a cyclotron line around 30 keV . The presence of a neutron star in the system is strongly favored by the available data.
Integral Observations of the Transient Source IGR J19140+098
Authors: Cabanac C. , Rodriguez J. , Petrucci P. O. , Henri G. , Hannikainen D. C. , Durouchoux P.
Published: June 2019

IGR J19140+098 was (re-)discovered during the early INTEGRAL observations of GRS1915+105 in March 2003. The following observations by INTEGRAL and RXTE show significant variability on various time scales from 100s to 1ks, but no pulsations. The ISGRI spectra show strong spectral variability in the 20-80keV range. Combined JEMX 2-ISGRI spectra are well fitted by a “multi-coulour” disk model with a rather high inner disk temperature (≃1.8 keV). RXTE data also reveal an apparently broad ionised iron line not detected in earlier INTEGRAL observations. These results are compatible with a galactic X-ray binary source.
Rapidly Evolving Light Curves of Low Mass X-Ray Binaries
Authors: Muhli P. , Hakala P. J. , Hjalmarsdotter L. , Hannikainen D. C. , Schultz J.
Published: June 2019

A few Galactic Low Mass X-Ray Binaries (LMXBs) have shown drastically evolving X-ray and/or optical orbital light curves. In two short-period LMXBs, MS 1603+2600 (= UW CrB, Porb = 111 min) and 4U 1916-053 (see e.g. Homer et al. 2001), the variations in the light curve morphology seem to be repeating in a periodic manner. We present first results of a photometric monitoring campaign of MS 1603+2600, showing evidence of a 5-day superorbital period in this yet unclassified source. The observations also unraveled optical flares, reminiscent of type I bursts, suggesting a neutron star primary.
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.
Dust Obscuration Events of the Symbiotic Nova RR Tel in the Near IR
Authors: Kotnik-Karuza D. , Friedjung M. , Whitelock P. A.
Published: June 2019

By use of ground based IR photometry, we have studied the dust obscuration events of the symbiotic nova RR Tel which is a binary composed of a cool mira and a hot white dwarf. The JHKL light curves were corrected for Mira pulsations and correlated to the AAVSO visual light curve. We compare the behaviour of the three obscurations in different wavelength bands and propose interpretations of the results.
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.
V1493 AQL an Extremely Distant Nova?
Authors: Dobrotka A. , Retter A. , Hric L. , Novak R. , Shemmer O. , Lipkin Y.
Published: June 2019

Analysis of CCD photometry performed during 12 nights and the estimate of the distance based on the light curve is presented. The photometric data is modulated with a period of 3.7 h, which we interpret as the orbital period above the period gap distribution of cataclysmic variables. The VSNET light curve combined with data from IAU Circulars suggests a distance of 4.5±0.4 kpc based on t2/t3 time estimates. Two spectra 11 days after the maximum were taken. The expansion velocity of the envelope was derived to be 1658±62 km s–1.
Time-Resolved Spectroscopy of Q CYG
Authors: Kafka S. , Tappert C. , Honeycutt R. K. , Bianchini A.
Published: June 2019

A time-resolved optical spectroscopic study of the long-period (P=10.08h) old nova Q Cyg has revealed persistent yet erratic absorption features indicating the presence of a wind, while the system was rising to one of its stunded outbursts. Data taken with the WIYN 3.5m telescope show P Cygni profiles in the He I triplet lines at 5876Å and 7065Å, which are absent in the He I singlet emission line at 6678Å, despite the fact that the relevant energy levels of those three lines are at very similar excitation levels. The Hα line often has a red ward emission tail, characteristic of a receding outflow, and it possess a blueward absorption profile during only one wind event. Kafka et al. (2003) argued that this behavior is due to the strongly metastable 2 3S effective ground state of the He I triplets, which becomes over-populated in conditions of low density and a dilute radiation field, over-populating in turn the 23P common lower level of He I 5876Å and 7065Å, leading to absorption from a low density wind. Therefore, the triplet/singlet lines trace two different parts of the system: the wind and the disk respectively.
Analysis of Long-Term Variability of Cataclysmic Variables
Authors: Kafka S. , Honeycutt R. K.
Published: June 2019

Photometric variability in cataclysmic variables (CVs) on time scales longer than a few days can be most effectively addressed by automated long-term monitoring programs such as that of RoboScope (Honeycutt & Turner 1992): more than 100 CVs have been monitored for about 13 years, obtaining 75 to 150 measurements per year for each system. Among the techniques being explored for analysing this data set is the use of the structure function (SF), an autocorrelation tool employed extensively for the study of the light curves of AGNs (e.g. Hufnagel & Bregman 1992). A first order SF measures the scatter in a time series of magnitudes, m, as as a function of the time lag, τ (Hughes, Aller & Aller 1992).
HST/FOS Spectral Mapping of IP Pegasi in Outburst
Authors: Saito R. K. , Baptista R. , Horne K.
Published: June 2019

We report the results of a time-resolved eclipse mapping of the dwarf nova IP Pegasi during the decline of its May 1993 outburst from HST/FOS fast spectroscopy covering 3 eclipses in the spectral range 1100 – 2500 Å.