bluuebunny/crossref_metadata_2025 huggingface dataset:
Cepheid Diameters from Optical Interferometry: The NPOI Survey
Authors: Nordgren Tyler E. , Germain M. E. , Sudol J. J. , Hindsley R. B. , Armstrong J. T. , Hajian Arsen R.
Published: June 2019

We present linear radii for four Cepheid variable stars, spanning a pulsation period range from 3 to 11 d, measured with the Navy Prototype Optical Interferometer (NPOI). We compare these radii to those found using traditional indirect methods, and to various period–radius relations found in the literature.
RR Lyrae Stars in Globular Clusters
Authors: Walker Alistair R.
Published: June 2019

Of the several types of variable stars that occur in globular clusters, RR Lyrae stars have deservedly received the most attention. These stars are ideally suited for comparisons between evolution and pulsation theory, they play a prominent role in distance determinations, and are valuable tracers of the oldest stellar populations. After a brief discussion of technical aspects, we review some of the recent observational work.
Light Curves and Metal Abundances of RR Lyrae Variables in the Bar of the Large Magellanic Cloud
Authors: Clementini G. , Bragaglia A. , Fabrizio L. Di , Carretta E. , Gratton R. G.
Published: June 2019

The Large Magellanic Cloud (LMC) is widely considered a corner-stone of the astronomical distance scale. However, a difference of 0.2−0.3 mag exists in its distance as predicted by the short and long distance scales. Distances to the LMC from Population II objects are founded on the RR Lyrae variables. We have undertaken an observational campaign devoted to the definition of the average apparent luminosity, and to the study of the mass–metallicity relation for RR Lyrae stars in the bar of the LMC. These are compared with analogous quantities for cluster RR Lyrae stars. The purpose is to see whether an intrinsic difference in luminosity, possibly due to a difference in mass, might exist between field and cluster RR Lyrae stars, which could be responsible for the well-known dichotomy between short and long distance scales. Preliminary results are presented on the V and B − V light curves, the average apparent visual magnitude, and the pulsational properties of 102 RR Lyrae stars in the bar of the LMC, observed at ESO in January 1999. The photometric data are accurately tied to the Johnson photometric system. Comparison is presented with the photometry of RR Lyrae stars in the bar of the LMC obtained by the MACHO collaboration (Alcock et al. 1996). Our sample includes 9 double-mode RR Lyrae stars selected from Alcock et al. (1997) for which an estimate of the metal abundance from the ΔS method is presented.
Revised Baade–Wesselink Analysis of RR Lyrae Stars
Authors: Cacciari Carla , Clementini1 Gisella , Castelli Fiorella , Melandri Fabrizio
Published: June 2019

We have applied the Baade–Wesselink method to two field RR Lyrae stars, i.e. SW And and RR Cet, and derived their distances and physical parameters. With respect to previous B–W analyses we have applied the following improvements: i) use of all sets of available data, after proper comparison for homogeneity and compatibility; ii) use of the most recent and accurate model atmospheres, with turbulent velocity Vturb = 4 km s−1 and the no-overshooting approximation, and comparison with other treatments of convection; iii) use of the instantaneous gravity along the pulsation cycle rather than the mean value; iv) comparison with modified radial velocity curves according to various assumptions on radial velocity gradients in the atmosphere; and v) careful reanalysis of the temperature scale. The main aim of this study is to evaluate the effect of the above items on the B–W results and verify whether any (or a combination) of them can possibly account for the discrepancy of the absolute magnitude zero-point with respect to other independent determinations.
Evolutionary Period Changes in ω Centauri!?
Authors: Jurcsik Johanna
Published: June 2019

The periods of most of the RRab stars in ω Centauri have increased during the past century at the same rate as evolutionary model calculations predict. This result raises the possibility that evolutionary changes in the periods are directly observed in this cluster.
New Pulsational Constraints to the Distance of Globular Clusters and the MV(RR)–[Fe/H] Relation
Authors: Ripepi Vincenzo , Caputo Filippina , Castellani Vittorio , Marconi Marcella
Published: June 2019

We applied the pulsational method (Caputo 1997) to derive the distances to a sample of galactic globular clusters with well-observed RR Lyrae populations. To apply the method we calculated a set of pulsational theoretical boundaries of the instability strip for the range of masses and chemical compositions spanned by the analysed clusters. In this way we were able to fix simultaneously the apparent distance modulus and the absolute visual magnitude of the RR Lyrae population of each cluster in the sample. As a result we derived the following relations:
Origin of Irregularities in RR Lyrae Pulsations
Authors: Chadid Merieme
Published: June 2019

For the first time important irregularities in atmospheric pulsations of RR Lyrae itself are clearly detected. They occur from one pulsation cycle to another. Their origins cannot be directly explained by the Blazhko effect. We suggest that these irregularities are mostly provoked by strong shock waves propagating within the atmosphere.
The Variable Stars in NGC 6229
Authors: Borissova J. , Valchev T. , Catelan M. , Ferraro F. R. , Sweigart A. V.
Published: June 2019

We present results of a variability survey in the outer-halo globular cluster NGC 6229. Our main goal is to shed light on the origin of the bimodal horizontal branch (HB) of this cluster.
Nonradial Modes in the Galactic Bulge RR Lyrae Stars
Authors: Moskalik P.
Published: June 2019

OGLE-1 photometry of RR Lyrae stars has been analyzed in search of multiperiodic pulsations. A second periodicity corresponding to a nonradial mode has been found in 11 RRab and 2 RRc variables.
Theoretical UBVI Light Curves of Pulsating Stars
Authors: Feuchtinger Michael U. , Dorfi Ernst A.
Published: June 2019

By performing detailed frequency-dependent radiative transfer computations we are able to calculate light curves in particular bandpasses from stellar pulsation models calculated by the Vienna nonlinear convective pulsation code. As a sample application we discuss UBVI light curves of RR Lyrae stars. The properties of these light curves are analyzed by means of standard Fourier decomposition, and a comparison to recent observations is performed. As main results we find a good agreement with important observed RR Lyrae properties like pulsation amplitudes and Fourier parameters in B, V, and I bands. Additionally, from the synthetic color curves we derive linear transformation laws between amplitudes as well as Fourier parameters in the different bandpasses.
Oscillations of Rapidly Rotating Stars
Authors: Dintrans B. , Rieutord M.
Published: June 2019

We present numerical simulations of gravito-inertial waves propagating in radiative zones of rapidly rotating stars. A first model, using the Boussinesq approximation, allows us to study the oscillations of a quasi-incompressible stratified fluid embedded in a rapidly rotating sphere or spherical shell. In a second step, we investigate the case of a γ Doradus-type star using the anelastic approximation. Some fascinating features of rapidly rotating fluids, such as wave attractors, appear in both cases.
The Effect of Noise and Finite Sampling on the Line Profile Variations of m = 0 Modes
Authors: Montgomery M. H.
Published: June 2019

Figure 1 is of the same form as Fig. 3 in Schrijvers et al. (1997): the upper part of each panel is the amplitude of the variation across the line at the mode frequency and the lower part is the phase shift of these two components across the line (in units of Φ). The parameters {Vavg, k, Ω/ω0, W} were chosen to have values representative of the δ Scuti star 4 CVn. Each panel in this array of plots has m=0, with a value of ∓ of 0, 1, or 2, and an inclination angle θi between 10° and 80°. In order to generate the synthetic line profiles, we use sampling times taken from the last week of the 1996 δ Scuti campaign on 4 CVn, and we assume that the signal-to-noise ratio of the spectrum is 250.
Upgrading the MHD Equation of State to Include Relativistic Electrons
Authors: Gong Zhigang , Däppen Werner
Published: June 2019

So far, the effect of relativistic electrons has not been included in the Mihalas-Däppen-Hummer (Hummer & Mihalas 1988; Mihalas, Däppen, & Hummer 1988; Däppen et al. 1988; hereinafter MHD) equation of state, although degeneracy was taken into account. Following the findings about the detectability of the relativistic effect in helioseismological data of the solar center (Elliot & Kosovichev 1998; hereinafter EK98), we have upgraded the MHD equation of state to include relativistic degenerate electrons. Our numerical calculation confirms the result of EK98.
A List of Stars in the β Cephei and SPB Instability Strips
Authors: Blay P. , Fabregat J.
Published: June 2019

For the purpose of observing β Cephei and SPB stars with optical telescopes on board future space missions, we have developed an automatic photometric search of stars falling inside the β Cephei and SPB instability strips. A list has been compiled which is available upon request from the authors (blay@castor.daa.uv.es;juan@pleione.daa.uv.es).

The boundaries of the instability strips have been defined by observational β – c0 HR diagrams based on Stræmgren photometry (Sterken & Jerzykiewicz 1993 = SK93). The ZAMS has been set as the lower limit of both strips. Low and high temperature limits are set as those given by SK93 and the upper limit is fixed by the photometry β of Cep stars found in the literature. For the SPB stars we have followed the same procedure. We have found the following boundaries: β Cephei: 0.2295c0 + 2.6263 > β > 0.0394c0 + 2.5656; 0.17 > c0 > –0.1; SPB: 2.630 > β > 0.2642co + 2.6207; 0.8 > c0 > 0.17.
Preliminary New Results on β Cephei Stars in NGC 4755
Authors: Stankov Anamarija
Published: June 2019

β Cephei stars are early B-type stars which show periodic variations of luminosity, radial velocity and line profiles. They have periods between 2 and 7 hr. Their variability is now believed to be caused by the classical κ-mechanism operating in the heavy-element ionization zones. Many of the β Cephei stars are multimode pulsators, and radial as well as nonradial pulsation may occur. Advances in the last few years in both the observational and theoretical studies of multiple pulsation modes of δ Scuti stars have reached the stage that realistic comparisons of the results and examination of predictions can be carried out (Breger et al. 1998; Stankov et al. 1999). We now want to apply those asteroseismological methods to the much hotter β Cephei stars.
Periods of β Cephei and SPB Stars from Hipparcos Photometry
Authors: Molenda-Żakowicz J.
Published: June 2019

For the β Cephei variables, we compare the periods derived from ground-based observations with those given in the Hipparcos catalogue. For the SPB stars, of which most have been discovered by Hipparcos, we examine the question of multiperiodicity.
The Radial Velocity Projection Factor in the Pulsating Helium Star V652 Her
Authors: Rodriguez P. Montañés , Jeffery C. S. , Cuadrado R. Aznar , Pollacco D.
Published: June 2019

The behavior of the velocity projection factor was studied for three individual Lines, He ɪ 4438 Å, Si ɪɪɪ 4553 Å, and N ɪɪ 4442 Å, and for the complete spectrum in the radially pulsating helium rich star V652 Her. It is shown that the projection factor is itself a function of expansion velocity.
Driving g-mode Pulsations inγDoradus Variables
Authors: Guzik J. A. , Kaye A. B. , Bradley P. A. , Cox A. N. , Neuforge C.
Published: June 2019

We suggest that the modulation of radiative flux by convection at the base of a deep envelope convection zone during the pulsation cycle is responsible for driving high-order g modes with periods 0.4 to 3 d observed inγDoradus variables.
g Modes in F Stars – A Non-adiabatic Investigation of the Stability of g Modes in ϒ Doradus Stars
Authors: Löffler Wolfgang
Published: June 2019

We investigate a sequence of 1.5 M⊙ models for g-mode instabilities. For the computation of the nonradial, non-adiabatic oscillations we make use of the Riccati method introduced by Glatzel & Gautschy (1992) to integrate the pulsation equations as given by Unno et al. (1989).
Excitation Mechanism in roAp Stars
Authors: Balmforth N. J. , Cunha M. S. , Dolez N. , Gough D. O. , Vauclair S.
Published: June 2019

In the present work we develop a theoretical model for roAp stars characterized by the suppression of convection around the magnetic poles. When calculating the growth rates of acoustic oscillations in models of this type we find that most models whose positions in the HR diagram coincide with that of the observed roAp stars are unstable against high-order pulsations.
Solar-Like Oscillations of Procyon A: Stellar Models and Time Series Simulations versus Observations
Authors: Barban C. , Michel E. , Martic M. , Schmitt J. , Lebrun J. C. , Baglin A. , Bertaux J. L.
Published: June 2019

The aim of this paper (further developed in Barban et al. 1999) is to present new evidence of the possible stellar origin of the observed excess power in the power spectrum of Procyon A presented in Martic et al. (1999) by comparing these observational data with theoretical predictions and numerical simulations.
New Progress in Mode Detection and Identification in δ Scuti Stars by the Analysis of Line Profile Variations
Authors: Mantegazza L. , Poretti E. , Bossi M. , Nuñez N. S. , Sacchi A. , Zerbi F. M.
Published: June 2019

δ Sct stars are among the most promising targets to perform ground-based asteroseismology. High resolution spectroscopy offers us a powerful technique to identify radial and nonradial pulsation modes, since we can easily detect oscillations and travelling features in the line profiles.
Delta Scuti Stars in Open Clusters: w2 and w20 in NGC 2264 and h501 and h906 in α Per
Authors: Peña J. H. , Peniche R. , Cervantes F. , García R. M. , Sareyan J. P.
Published: June 2019

There are many advantages to studying variable stars in open clusters; the parameters that determine the evolution of the stars, such as chemical composition and age, can be considered to be the same for all the stars in the cluster. These data, along with the mass, effective temperature and superficial gravity, allow us to better determine the physics which explain the pulsation mechanisms. In the present paper the variable stars h501 and h906 in α Per and w2 and w20 in NGC 2264 are studied. In particular, the reasons why δ Scuti stars coexist with early type stars in NGC 2264 is examined.
The STACC 1998 Campaign on Praesepe: The Photometry
Authors: Frandsen S. , Pigulski A. ,   the STACC collaboration
Published: June 2019

This is a preliminary report on the CCD (mainly) photometry of the two δ Scuti stars, BN Cnc and BV Cnc, in the Praesepe open cluster.
A Photoelectric Study of the Am δ Scuti Variable 60 Tau
Authors: Zhiping Li , Yanying Liu , Aiying Zhou
Published: June 2019

Five nights of photoelectric photometric observations through v and y filters confirm the pulsation of the Am δ Scuti variable 60 Tau. Power spectra of the light curves show multiple periods; two modes f1 = 13.0364 d−1 and f2 = 11.8521 d−1 are definitely identified. The phase differences, ϕv − ϕy, suggest that 60 Tau pulsates in low-degree modes; the pulsation constants, Q, suggest these are low overtone modes; and the frequency ratio implies that at least one mode is nonradial.
Ten Years of STEPHI Multisite Campaigns on δ Scuti Stars
Authors: Michel E. , Chevreton M. , Belmonte J. A. , Li Z. P. , Alvarez M. ,   the STEPHI Team
Published: June 2019

STEPHI is a photometry network that aims to obtain data to reach a better understanding of the physics of stellar interiors by seismology of δ Scuti stars. For ten years now STEPHI has been harvesting multisite rapid photometry data of δ Scuti stars on the main sequence. With 12 δ Scuti stars observed during three-week, three-site campaigns, STEPHI has produced a significant amount of the data available on δ Scuti stars for seismological study of this stage of evolution. The STEPHI data have already been basis of several theoretical interpretations (see http://dasgal.obspm.fr/˜stephi). Here we focus on some aspects of our observational strategy and results.
A Survey for Pulsating Ap Stars from Naini Tal
Authors: Martinez Peter , Kurtz D. W. , Chaubey U. S. , Gupta S. K. , Joshi S. , Sagar R. , Ashoka B. N. , Seetha S.
Published: June 2019

Pulsation is ubiquitous among chemically normal A-type stars, but comparatively rare among chemically peculiar Am and Ap stars of the same temperature range. The conventional explanation for this is that diffusion produces the surface abundance anomalies in the Am and Ap stars, and also drains He from the He-II ionisation zone, thus quenching the κ-mechanism that drives δ Scuti pulsation. The pulsating Am and Ap stars exhibit dichotomous pulsation characteristics. The Am stars (and related stars) exhibit low-overtone δ Scuti pulsation, with amplitudes ranging from a few mmag to 0.1 mag. The pulsating Ap stars exhibit high-overtone pulsation with periods in the range 6-16 min and Johnson B semi-amplitudes typically ≤ 5 mmag. These stars are referred to as rapidly oscillating Ap stars, or ‘roAp’ stars (the see review by Martinez & Kurtz 1995).
Radial Pulsation of the roAp Star HD 122970?
Authors: Handler G. , Paunzen E. , Garrido R. , Guzik J. A. , Beach T. E. , Medupe R. , Chagnon F. , Shobbrook R. R. , Matthews J. M. , Ryabchikova T. A. , Hatzes A. P.
Published: June 2019

We acquired multisite observations of the newly discovered rapidly oscillating Ap star HD 122970. A frequency analysis shows the presence of two independent modes, one singlet and one equally spaced triplet. By applying the oblique pulsator model and asymptotic theory we infer that the triplet originates from a distorted dipole mode and that the singlet most probably corresponds to a radial mode.
Oscillation Patterns of SX Phœnicis Variables in Globular Clusters
Authors: Petersen J. O. , Quaade M. , Andersen M. I. , Freyhammer L. M.
Published: June 2019

Based on new analyses of light curves of SX Phœnicis variables in globular clusters and on results taken from the literature, an overview of oscillation patterns in this subgroup of δ Scuti variables is given. Belonging to the Blue Straggler stars, they are expected to have a more complicated life history than “normal” δ Scuti stars in the field or in open clusters. The overall picture is that the patterns found in this SX Phe group seem to be similar to the patterns that are well established for standard field δ Set stars.
Excitation of Gravity-Mode Pulsations in DA & DB White Dwarfs
Authors: Wu Yanqin
Published: June 2019

Oscillations in white dwarfs of hydrogen or helium envelopes are believed to be excited close to the surface, where convective energy transport dominates the stellar luminosity. The convective motion in these stars is fast and can respond instantaneously to the pulsation state. In this limit, we find the convective envelope to be the seat of mode excitation because it acts as an insulating blanket with respect to the perturbed flux that enters it from below. This retaining of the flux leads to driving. Driving exceeds radiative damping providedωτc≥ 1, whereωis the radian frequency of the mode andτc≈ 4τthwith τthbeing the thermal time constant evaluated at the base of the convective envelope. We follow Brickhill (1991) in naming this mechanism as ‘convective driving’. We also studied the dynamical interaction between turbulent convection and pulsation. In the limit of fast convection, turbulent damping inside the convective region is negligible, while that coming from the overshoot region is more significant. I discuss the application of ‘convective driving’ in other types of pulsating stars.
A Model Survey of DAV White Dwarfs
Authors: Kleinman S. J. , Kawaler S. D. , Bischoff A.
Published: June 2019

We have created a grid of DAV (ZZ Ceti) pulsation models to test whether ensemble observations of DAV pulsation periods can be used to determine the nature of the DAV interiors.
Observational constraints on the composition and nature of comet D/Shoemaker-Levy 9
Authors: Crovisier Jacques
Published: June 2019

What did the break-up of comet Shoemaker-Levy 9 (SL9) and its subsequent impact on Jupiter teach us about the nature and constitution of this comet? The break-up of the comet apparently triggered activity of the fragments. Although a dust coma was continuously present around the fragments that orbited Jupiter, spectroscopic observations did not reveal any sign of gas. The impact itself was so energetic that most molecules of the impactor were dissociated and that any chemical memory was lost. Ultraviolet and visible spectroscopy of the impact sites revealed emission lines from several atoms, giving potential information on elemental abundances. However, the fact that both neutral and ionized atoms are emitting, and that both fundamental and inter-system lines are present, suggest that the medium is out-of-equilibrium and that emitting mechanisms other than simple resonance fluorescence are at work. Ultraviolet, infrared, and radio spectroscopy revealed lines of several molecular species, in emission and/or absorption, that are not normally present in Jupiter's upper atmosphere. In the visible, dark spots due to aerosols developed at the impact sites. It is not clear at the present time which part of this material is coming from preserved impactor material, from the recombination of the dissociated impactor material, from reactions between the impactor's and Jupiter's material, or from material coming from the lower layers of Jupiter's atmosphere. Realistic modelling of the impacts and of the following chemical reactions will be necessary to address all these issues. In this chapter, we will review the observational clues to the composition and structure of SL9 in the context of our knowledge of the composition and structure of comets and asteroids.
Dynamics and chemistry of SL9 plumes
Authors: Zahnle Kevin
Published: June 2019

The SL9 impacts are known by their plumes. Several of these were imaged by HST towering 3000 km above Jupiter's limb. The heat released when they fell produced the famous infrared main events. The reentry shocks must have been significantly hotter than the observed color temperature would imply, which indicates that the shocks were radiatively cooled, and that most of the energy released on reentry was radiated. This allows us to use the infrared luminosities of the main event to estimate the energy of the impacts; we find that the R impact released some 0.3 — 1 x 1027 ergs. Shock chemistry generates a suite of molecules not usually seen on Jupiter. The chemistry reflects a wide range of different shock temperatures, pressures, and gas compositions. The primary product, apart from H2, is CO, the yield of which depends only weakly on the comet's composition, and so can be used to weigh the comet. Abundant water and S2 are consistent with a somewhat oxidized gas (presumably the comet itself), but the absence of SO2 and CO2 shows that conditions were neither too oxidizing nor the shocks too hot. Meanwhile, production of CS, CS2, and HCN appears to require a source in dry jovian air; i.e., the airbursts occurred above the jovian water table. Tidal disruption calculations and models of the infrared light curves agree on an average fragment diameter of about half a kilometer. Chemical products and atmospheric disruption models agree on placing the terminal explosions around the 1 to 4 bar levels. The plumes were spectacular because the explosions were shallow, not because the explosions were large.
Chemistry induced by the impacts: Observations
Authors: Lellouch Emmanuel
Published: June 2019

This paper reviews spectroscopic measurements relevant to the chemical modifications of Jupiter's atmosphere induced by the Shoemaker-Levy 9 impacts. Such observations have been successful at all wavelength ranges from the UV to the centimeter. At the date this paper is written, newly detected or enhanced molecular species resulting from the impacts include H2O, CO, S2, CS2, CS, OCS, NH3, HCN and C2H4. There is also a tentative detection of enhanced PH3 and a controversial detection of H2S. All new and enhanced species were detected in Jupiter's stratosphere. With the exception of NH3 (and perhaps H2S and PH3), apparently present down to the 10-50 mbar level, the minor species are seen at pressures lower than 1 mbar or less, consistent with a formation during the plume splashback at 1-100 microbar. NH3 may result from upwelling associated with vertical mixing generated by the impacts. The main oxygen species is apparently CO, with a total mass of a few 1014 g for the largest impacts, consistent with that available in 400-700 m radius fragments. The observed O/S ratio is reasonably consistent with cometary abundances, but the O/N ratio (inferred from CO/HCN) is much larger, suggesting that another N species was formed but remained undetected, presumably N2. The time evolution of NH3, S2, CS2 shows evidence for photochemical activity taking place during and after the impact week.
Jupiter's post-impact atmospheric thermal response
Authors: Conrath Barney J.
Published: June 2019

Measurements of thermal emission in spectral regions, ranging from the near-infrared to mm wavelengths provide information on the atmospheric thermal structure over impact sites fromμbar levels in the upper stratosphere down to the upper troposphere. Systematic time series of observations relevant to this entire height range over individual spots do not exist. However, by piecing together information at different times from various spots, it is possible to obtain a provisional, semi-quantitative picture of the behavior of the thermal structure over a typical impact site. Immediately after fall-back of the ejecta plume, the upper stratosphere is heated to ∼ 600-1300 K above ambient temperature. The amplitude of the temperature perturbation diminishes with increasing depth in the atmosphere, but even in the upper troposphere a temperature increase of a few kelvins is observed. Initially, the upper stratosphere cools very rapidly with time scales of tens of minutes, presumably the result of strong radiative cooling associated with the high temperatures. After the initial cooling, all levels continue to cool at slower rates with time scales of a few days; however, this is still very rapid compared to radiative cooling of the ambient atmosphere. Enhancements in infrared opacity necessary to produce the cooling radiatively do not appear to be viable, suggesting that dynamical effects may play a dominant role. Possible mechanisms include horizontal mixing with the ambient atmosphere and adiabatic cooling produced by upward motion associated with an anticyclonic vortex. Many questions remain concerning the thermal structure above the impact sites; these are being addressed through ongoing data analysis and modeling efforts.
The Potential for Astronomy in the Infrared
Authors: Storey John W. V.
Published: June 2019

Infrared Interferometry promises to be a useful astrometric technique. Preliminary measurements of the star α Orionis made with a heterodyne interferometer exhibit phase coherence over a period of at least 1000 seconds. The measurements were equivalent to a positional determination of 60 second accuracy every 5 seconds of integration.
Observations of High-Density Corrections to VUV Line-Wing Shapes in a Plasma with a Few Particles Per Debye Sphere
Authors: Baker E.A.M. , Burgess D.D.
Published: June 2019

Observations of high density effects on spectral line shapes are reported for neutral, singly- and doubly-ionized emitters in a dense plasma with a small number of particles per Debye sphere. The source used in these experiments was a well-diagnosed linear pinch,run in argon, producing a plasma with electron density between 0.5 x 1018 and 3 x 1018 cm–3, and temperature between 22,000 K and 27,000 K.

Satellite-like features observed in the wings of H I Lyman α are attributed to the influence of unbound quasimolecular states. A number of the satellites are apparently due to states of H–Ar+ (similar to two such Lyman α satellites observed by Preston 1977). However, it seems likely that at least one of the satellite features observed should be attributed to the influence of Ar++ perturbers. Such quasimolecular features might be expected to become increasingly important at higher densities, and for more highly-ionized perturbing ions.
Recent High Spectral and Spatial Resolution Spectroscopy of Laser-Produced Plasmas and Electron-Ion Beam Plasmas
Authors: Doschek G.A. , Feldman U. , Johnson D.J. , Nagel D.J.
Published: June 2019

Spectra of plasmas produced by a CO2 laser have recently been obtained using a normal incidence slitless spectrograph and a high spectral resolution (0.028 mÅ) grazing incidence spectrograph. The slitless spectrograph forms images of the plasmas in spectral lines and is similar to the instrument flown by NRL on Skylab. The total wavelength coverage is from about 100 Å to about 600 Å. The shapes of the images depend markedly on the type of atomic transition. Time-averaged electron densities in the expanding plumes are calculated, and the expansion velocity is estimated from the profiles of lines recorded by the grazing incidence spectrograph. In addition, spectra of electron-ion beam plasmas between ∼200 Å and 2000 Å were obtained using a stigmatic normal incidence slit spectrograph. The distribution of plasma emisston between the anode and cathode, and the mass motions in the plasmas are discussed.
Bandwidth Requirements in Spectral Line Transfer Calculations
Authors: Athay R. Grant
Published: June 2019

Accurate evaluation of a line source function, S, requires that the frequency bandwidth be sufficiently large to include properly transfer effects in the line wings. The bandwidth required to achieve a given level of accuracy in the evaluation of S can be specified, in units of the Doppler width, in terms of three parameters: the ratio of continuum to line opacity, ro, the probability for collisional deexcitation, ε, and the Voigt wing parameter . Bandwidths required to give S to an accuracy of 2 percent are given for values of ε and ro from 10-2 to 10-8 and for values of from 10-2 to 10-5.
What Do We Know Through Spectral Information on Stellar Chromospheres and Coronas?
Authors: Praderie Françoise
Published: June 2019

Four problems in interpreting spectra to infer chromospheres-coronas are summarized. (1) The a priori difficulties in interpreting spectra lie in uncertainty on the range of possible models, coming from uncertainty as to which conservation equations may be applied, and from lack of an exhaustive list of spectral indicators that may be used for uniqueness tests. (2) As spectral indicators we consider: emission lines, self-reversed emission cores, the presence of He I lines in stars not of early type, coronal-type high ionization, excess continuum emission in the rocket UV and the far infrared. (3) To determine what we can infer from observations, we summarize information: inferred by comparison of models to data, on velocity fields, and on spectral variability which might suggest chromospheric activity. (4) We summarize the evidence for chromospheres in A stars, as being those where convection-induced acoustic heating is marginal.
Ionization in Nova Atmospheres
Authors: Wellmann P.
Published: June 2019

Calculations on the expansion of novae shells are presented, from which the degree of ionization is obtained using a simplified form of a non-LTE ionization equation. From this, estimates of the time of vanishing of the Balmer absorption spectrum can be made.
An X-Ray View of Interacting Binaries Outside The Galaxy
Authors: Prestwich Andrea H.
Published: June 2019

Chandra and XMM-Newton are revolutionizing our understanding of compact binaries in external galaxies, allowing us to study sources in detail in Local Group Galaxies and study populations in more distant systems. In M31 the X-ray luminosity function depends on the local stellar population in the sense that areas with active star formation have more high luminosity sources, and a higher overall source density (Kong. Di Stefano. Garcia, & Greiner 2003). This result is also true in galaxies outside the Local Group; starburst galaxies have flatter X-ray luminosity functions than do spiral galaxies which are in turn flatter than elliptical galaxies. These observational results suggest that the high end of the luminosity function in star forming regions is dominated by short-lived high mass X-ray binaries.

In Chandra Cycle 2 we started a Large Project to survey a sample of 11 nearby (< 10Mpc) face-on spiral galaxies. We find that sources can be approximately classified on the basis of their X-ray color into low mass X-ray binaries, high mass X-ray binaries and supersoft sources. There is an especially interesting class of source that has X-ray colors softer (“redder”) than a typical low mass X-ray binary source, but not so extreme as supersoft sources. Most of these are probably X-ray bright supernova remnants, but some may be a new type of black hole accretor. Finally, when we construct a luminosity function of sources selecting only sources with low mass X-ray binary colors (removing soft sources) we find that there is a dip or break probably associated with the Eddington luminosity for a neutron star.
Bowen Fluorescence from Companion Stars in X-Ray Binaries
Authors: Casares J. , Steeghs D. , Hynes R. I. , Charles P. A. , Cornelisse R. , O'Brien K.
Published: June 2019

This paper will review a new technique of detecting companion stars in LMXBs and X-ray transients in outburst using the Bowen fluorescence NIII lines at 4634-4640. These lines are very efficiently reprocessed in the atmospheres of the companion stars and, thereby, provide estimates of the K2 velocities and mass functions. The method has been applied to Sco X-1, X1822-371 and GX339-4 which, in the latter case, provides dynamical evidence for the presence of an accreting black hole. Preliminary results from a VLT campaign on V801 Ara, V926 Sco and XTE J1814-338 are also presented.
A ULX in NGC 4559: A “Mini-Cartwheel” Scenario?
Authors: Soria R. , Cropper M. S. , Pakull M. W.
Published: June 2019

We have studied the peculiar environment around a ULX in NGC 4559 (with Lx ≈ 2 x 1040 erg s–1 and MBH ≳ 50M⊙). The X-ray source is located near the rim of a young (age < 30 Myr), large (diameter ≈ 700 pc) ring-like star forming complex possibly triggered by the impact of a dwarf satellite galaxy through the gas-rich outer disk of NGC 4559. We speculate that galaxy interactions (including the infall of high-velocity clouds and satellites on a galactic disk) and low-metallicity environments offer favourable conditions for the formation of compact remnants more massive than “standard” X-ray binaries, and accreting from a massive Roche-lobe filling companion.
Simultaneous Integral/RXTE Observations of GRS 1915+105
Authors: Rodriguez J. , Hannikainen D. , Vilhu O. , Fuchs Y. , Shaw S. E.
Published: June 2019

We present the first results of simultaneous INTEGRAL and RXTE observations of the microquasar GRS 1915+105. We focus on the analysis of the unique highly variable observation and show that we might have observed a new class of variability. We then study the energetic depenelence of a low frequency QPO from our steady observations.
Using X-Rays to Probe the Compact Binary Content of Globular Clusters
Authors: Webb N. A. , Gendre B. , Barret D.
Published: June 2019

Globular clusters (GCs) harbour a large number of close binaries which are hard to identify optically due to high stellar densities. Observing these GCs in X-rays, in which the compact binaries are bright, diminishes the over-crowding problem. Using the new generation of X-ray observatories, it is possible to identify populations of neutron star low mass X-ray binaries, cataclysmic variables and millisecond pulsars as well as other types of binaries. We present the spectra of a variety of binaries that we have identified in four GCs observed by XMM-Newton. We show that through population studies we can begin to understand the formation of individual classes of binaries in GCs and hence start to unfold the complex evolutionary paths of these systems.
On the Nature of the Binary Components of RX J0806.3+1527
Authors: Reinsch K. , Burwitz V. , Schwarz R.
Published: June 2019

We present imaging circular polarimetry and near-infrared photometry of the suspected ultra-short period while-dwarf binary RX J0806.3+1527 obtained with the ESO VLT and discuss the implications for a possible magnetic nature of the white dwarf accretor and the constraints derived for the nature of the donor star. Our V-filter data, show marginally significant circular polarization with a modulation amplitude of ≈ 0.5% typical for cyclotron emission from an accretion column in a magnetic field of order 10MG and not compatible with a direct-impact accretor model. The optical to near-infrared flux distribution is well described by a single blackbody with temperature kTbb = 35000 K and excludes a main-sequence stellar donor unless the binary is located several scale heights above the galactic disk population.
The Implications of Disc Instabilities on Cataclysmic Variable Structure and Evolution
Authors: Lasota J.-P.
Published: June 2019

Applications of the thermal-viscous disc instability model to various classes of cataclysmic variable very often require the accretion disc to be truncated. I argue that in most cases this inner truncation must be due to the white dwarf's magnetic field.
Mass-Capture Rate by the Neutron Star in Be/X-Ray Binaries
Authors: Okazaki A. T. , Hayasaki K.
Published: June 2019

We study the interaction between the Be-star disk and the neutron star in Be/X-ray binaries by three dimensional SPH simulations. We find that, the resonant, truncation of the Be disk works except for systems with extremely high orbital eccentricity or large misalignment angles between the Be disk and the orbital plane. Owing to the truncation, the mass-capture rate by the neutron star is sensitive both to the orbital eccentricity and to the angle of misalignment. It is single-peaked in coplanar systems and in systems with small misalignment angles, whereas it, becomes double-peaked in systems with large misalignment angles.
Physical Interpretation of Dwarf Nova Primary Effective Temperatures
Authors: Townsley Dean M. , Bildsten Lars
Published: June 2019

We have undertaken a theoretical study of the impact of the accumulating envelopes on the thermal state of the underlying white dwarf (WD). This has allowed us to find the equilibrium WD core temperatures, the classical nova ignition masses and the thermal luminosities for WDs accreting at rates of 10–11 – 10–8M⊙ yr–1. These accretion rates are most, appropriate to WDs in cataclysmic variables (CVs) of (Porb ≲ 7 hr), many of which accrete sporadically as Dwarf Novae. Over twenty Dwarf Novae have been observed in quiescence, when the accretion rate is low and the WD photosphere is detected and Teff measured. Comparing our theoretical work to these observations allows us to constrain the WD mass and the time averaged accretion rate, ⟨Ṁ⟩. If ⟨Ṁ⟩ is that given by gravitational radiation losses alone, then the WD masses are > 0.8 M⊙. An alternative conclusion is that the masses are closer to 0.6M⊙ and ⟨Ṁ⟩ is 3-4 times larger than that expected from gravitational radiation losses.
Chemical Abundances of the Secondary Stars in the Black Hole Binary A0620-00 and the Neutron Star Binary Cen X-4
Authors: González-Hernández J. I. , Rebolo R. , Israelian G. , Casares J.
Published: June 2019

We have determined abundances in the secondary stars of the black hole X-ray binary A0620-00 and the neutron star Binary Cen X-4. These are K type stars veiled by the emission produced by the respective accretion discs. We searched for evidence of nucleosynthetic products from the progenitor of the compact object that could have contaminated the secondary stars (as in Israelian et al., 1999).

Using high resolution spectra obtained with VLT/UVES, we have derived in a consistent way stellar parameters and the veiling caused by the accretion disc.
Numerical Simulation of the Surface Flow of a Companion Star in a Semi-Detached Binary System and its Application to Galactic Supersoft X-Ray Sources
Authors: Oka K. , Matsuda T. , Hachisu I. , Boffin H. M. J.
Published: June 2019

We numerically simulate the surface flow of a gas-supplying companion star in a semi-detached binary system and construct the Doppler map. Our numerical results indicate an eddy configuration composed of a Heddy, a L1-eddy, and a L2-eddy associated with high/low pressures on the surface of the companion star. We find that the formation of these eddies can be explained in terms of the astrostrophic wind. We apply our calculations to the Galactic supersoft X-ray source RX J0019.8+2156. This object is very attractive for the present study since the observed Doppler map might reflect the surface flow on the companion star. We have constructed the Doppler map of RX J0019.8+2156 and compare it with observations.
The effect of the compositional quality of milk on new product development
Authors: Tow G. J.
Published: June 2019

In recent years, the average consumer has become much more aware of the composition of food. Medical opinion, that diets high in fibre and low in fat are likely to result in longer and healthier lives, has provided the food industry with new market sectors and, hence, the need for new product development.

The dairy industry in the United Kingdom has, in the main, been slow to react to this challenge and has left the remainder of the food industry to manipulate the composition of the final product. At one time, the inclusion of 100 g butter per kg margarine was deemed to be a sales advantage but today the consumer believes it is a disadvantage. The cholesterol and saturated fats discussion has obviously been put forward with great fervour by members of the food industry who have sought to gain advantage. The reaction of the dairy industry has been to take a defensive stand rather than to conduct research and promote the nutritional advantage of milk and milk products. This attitude is changing, fortunately, and new dairy products are being developed and marketed aggressively. The belief of the dairy industry, that only new products containing milk ingredients alone would be manufactured, is no longer true and a whole range of new dairy-based products, incorporating varying amounts of other food ingredients, is appearing.

The latest developments in dairy technology are resulting in some new raw materials derived from milk, specially designed for specific uses in the food industry. This paper reviews some of these developments against the background of milk composition, industrial production and market consumption.
Economic implications of compositional quality and production systems
Authors: Morgan H. E. G.
Published: June 2019

Proposed changes in milk pricing to be introduced on 1 April 1984 will make milk fat payments 53% of total milk returns. Current breed averages indicate that Jersey returns will show the greatest improvement at £40 per cow but will still be £100 lower than Friesian returns. Additionally, the higher calf and barren cow values enhance the Friesian, although this can be offset if Jerseys achieve a 50% increase in longevity compared with Friesians.

The proposed seasonal differentials give a milk price variation around the mean of 29%, compared with the present 13%. However, in 1969/70, the variation was 36%. Milk values by month of calving on the new proposals vary by a maximum of £87 at a yield of 5000 1. August to October calving gives the highest and February to May the lowest milk income after seasonal adjustment.

Farm examples show that block-calving herds have seasonal quality trends that will be highlighted by contemporary payment. In the past, arithmetic averages have put block-calving herds into higher-quality classes than was warranted. Contemporary payment penalizes lapses in quality immediately. Conversely, improvements will be immediately rewarded. Summer-milk producers will have a dramatic decrease in their traditional cash flow in May and June. Comparison of weekly sample results and monthly averages with the same period last year, and with the England and Wales monthly average, enables economic corrective management steps to be taken.

The cost of computerized out-of-parlour feeders depends on herd size. Justification of their cost can be based on changes in milk sales by volume and/or compositional quality.
Health Concerns and Milk Fat Production
Authors: Fallows S. J. , Wheelock J. V.
Published: June 2019

Concerns by the consumer over the relationships between diet and health are growing and there is increased recognition that the diseases of contemporary society can only be combatted by preventive measures. Dietary change is advocated in programmes designed to reduce the incidence of obesity, coronary heart disease and cancer. Recommendations relating to fat are particularly pertinent, with suggestions to reduce total fat consumption from approximately 40% of the energy to nearer 30% and to concentrate efforts on sources high in saturated fatty acids. This means less fat from animal sources, including milk. An immediate adoption of these recommendations is unlikely but increased media coverage is stimulating interest. Evidence from overseas indicates trends away from full-fat towards skimmed and semi-skimmed milks. In Britain, such products are not universally available and demand for milk is declining. However, dairies are increasing production of fat-reduced milks, particularly for supermarkets, and many consumers select these products in the interest of better health. The consequences for the milk producer may be predicted. An increased demand for fat-reduced rather than full-fat milk, coincident with a reduced demand for butter, will result in an accelerating reduction in the demand for milk fat. Under the new payments scheme, the prices paid for fat, protein and lactose must be influenced by market forces. Therefore, there is a strong possibility that, within the foreseeable future, the value of fat, relative to that of protein, is likely to fall. This would have profound implications for milk production and relevant research and development.
6.19 Preventing Piglet Anaemia without using Injections of Iron Dextran
Authors: Sansom B. F. , Gleed P. T.
Published: June 2019

Piglets rapidly become anaemic after birth because the sow's milk provides only about 10% of their iron (Fe) requirements. Under free-range conditions, they can obtain extra Fe from soil but in modern intensive systems no soil is available and to prevent them becoming anaemic the piglets are injected with 200 mg Fe as iron dextran when 2-4 days of age. These injections are effective but they are costly in time and money and can have undesirable side effects such as the formation of abscesses, staining of the injected ham or even death from Fe toxicosis. We have considered the theoretical and practical possibilities of supplying the piglets with Fe by using their dams' faeces as a substitute for soil.