bluuebunny/crossref_metadata_2025 huggingface dataset:
Consistent spherical NLTE-models for BN-like objects
Authors: Höflich Peter
Published: June 2019

Spherical NLTE-model photospheres surrounded by envelopes are calculated in order to interpret BN-like objects. Both the existence and the emitted spectra of the HII-region can be understood by such models.
Polarization measurements in B5, L1 34 and Heiles Cloud 2 and evidence of newly born stars
Authors: Joshi U. C. , Kulkarni P. V. , Deshpande M. R. , Sen A. , Kulshrestha A. K.
Published: June 2019

Polarization measurement of the background stars in the region of dark globules is important to study the magnetic field geometry and grants characteristics in the globule. These parameters are important for the formation and evolution of dark globules. We made Polarimetric observations of stars in three nearby dark clouds - B5, L134 and Heiles Cloud 2. Polarization measurements of stars in the region of B5 were made with ‘MINIPOL’ (Frecker and Serkowski, 1976) on 61″ telescope of University of Arizona. Observations for the stars in the region of L134 and Heiles Cloud 2 were made using PRL Polarimeter (Deshpande et al. 1985) on 1 meter telescope of Indian Institute of Astrophysics, Bangalore. Results are presented and discussed here. Figure 1 shows the polarization vectors projected on the sky plane for the above globules.
Magnetic flux dissipation during the contraction of a magnetic protostellar gas cloud
Authors: El-Nawawy M.S. , Aiad A.Z. , El-shalaby M.A.
Published: June 2019

The role of the magnetic field and the possibility of its leakage during the contraction of an interstellar cloud need more studies both quantitatively and qualitatively.
Theoretical models of Herbig-Haro objects
Authors: Dyson J. E.
Published: June 2019

A brief overview of the observational characteristics of HH objects is given. Current models for their production by the interaction of stellar winds and jets with interstellar gas are critically discussed. Models for two specific systems of HH objects, namely, the Orion HH objects and the HH46-47 system are described with reference to the general production mechanisms.
HH 34: The bow shock of a jet
Authors: Bührke Th. , Mundt R.
Published: June 2019

Deep CCD imaging of HH 34 in H∝ shows that the HH-object has a bow shock-like structure, of which the wings can be traced over about 1 arcmin ( pc). A knotty jet is pointing towards the apex of the bow shock structure. Long-slit spectroscopy reveals that 1) the jet has approximately a constant radial velocity and electron density. 2). The spectrum of the jet is of a much lower excitation than that of HH 34. 3) HH 34 has a complex velocity and line excitation structure. The extended bow shock is interpreted by a jet of which the working surface is propagating with high velocity (≈ 200 km/s) through a partially ionized medium.
Herbig-Haro emission in two bipolar reflection nebulae
Authors: Staude H. J. , Neckel Th. , Sarcander M. , Birkle K.
Published: June 2019

CCD images show that the reflection nebula associated with PV Cep is bipolar. From spectroscopy of this object as well as of the bipolar Boomerang Nebula we find low excited Herbig-Haro emission and indications for collimated high velocity flows along the polar axes of both nebulae. The central star of the Boomerang Nebula is probably double.
IRAS results on circunstellar shells
Authors: Habing H. J.
Published: June 2019

The IRAS Point Source Catalog contains tens of thousands of stars with circumstellar shells. Most are cool stars surrounded by dust-rich envelopes, but many B and A stars are present with ionized circumstellar envelopes. IRAS and its main products are briefly discussed.
Shock waves - The trigger mechanism of SiO masers in circumstellar envelopes of cool giants and supergiants
Authors: Heske Astrid
Published: June 2019

Circumstellar envelopes of cool giants and supergiants are composed of different parts which can be observed through characteristic spectral features. One is SiO-maseremission which is typically found in Miras and some semi-regular variable supergiants. These masers are thought to originate in those parts of the upper atmosphere or lower circumstellar envelope where still no mass-loss takes place. Location and trigger mechanism was still not definitely clear.
Theory of circumstellar envelopes
Authors: Wehrse R.
Published: June 2019

After a comparison of conventional photospheres with circumstellar envelopes the radiation in spherical shells is considered. We discuss the transfer equation and a new quasi-exact solution in term of the transition matrix-Various methods used for the numerical evaluation of the specific intensities are summarized. The general properties of the radiation fields and some recent detailed model calculations are briefly reviewed.
What is the essential physics of mass loss from late-type stars?
Authors: Linsky Jeffrey L.
Published: June 2019

In this review I consider what clues the data are providing us concerning the mass loss from late-type stars. I consider in turn the major classes of mass-loss mechanisms (thermally-driven winds, radiatively-driven winds, and wave-driven winds), and consider whether the empirical mass loss rates and other data are consistent with any of these mechanisms acting alone. It is likely that several mechanisms act together to produce the large mass loss rates in the Mira and non-pulsating M supergiants. Studies of the solar atmosphere suggest that thermal bifurcation driven by molecular condensation instabilities may play a critical role in cooling the atmospheres of luminous cool stars and forming silicate dust. It is possible that several metastable modes of atmospheric structure may exist for a given set of stellar parameters.
Circumstellar envelope of the supergiant 89 Herculis
Authors: Climenhaga J.L. , Smoliński J. , Krempeć-Krygier J. , Krygier B. , Krawczyk S.
Published: June 2019

A bright enigmatic supergiant, 89 Her (HD 163506; F2Ia, Mbol=-7m.5), exhibits the light variations (Percy et al. 1979, Fernie 1981, 1983) as well as the changes of radial velocities and structures of Balmer and sodium lines. Sargent and Osmer (1969) have given some evidences for the existence of expanding circumstellar envelope around 89 Her and have discovered 24 emission lines of neutral metals in its spectra.
Observations of stellar coronae
Authors: Vaiana G. S. , Sciortino S.
Published: June 2019

We present an overview of recent stellar X-ray observations, with some discussion of the requirements for future observations. We argue that solar observations indicate that coronal X-ray emission is strongly related to surface magnetic field activity; we show that the interpretation of X-ray stellar coronal emission from late-type stars within the framework of models analogous to those developed for the solar corona is viable, and it is supported by many experimental results. The extension of this solar analogy to the early-type stars is quite questionable and remains an unsolved problem, while the working hypothesis of an X-ray phase, related to phenomena of magnetic field-related activity, as contrasted to a wind phase during the PMS evolutionary stage is suggested by the present status of observations.
On the existence of hot coronae around cool stars
Authors: Hammer R.
Published: June 2019

A star cannot have a solar-like corona if the available mechanical energy flux in the chromosphere is either too large or decreases outward more rapidly than the pressure. This result might be relevant for hybrid stars and cool giants.
A new treatment of water vapor opacity
Authors: Alexander D.R. , Johnson H.R. , Augason G.C. , Wehrse R.
Published: June 2019

Although the bands of H2O are strong in cool stars, water vapor opacity has generally not been accurately treated due both to the inadequacy of laboratory data and the difficulty of treating the millions of lines involved. We report a new treatment based upon a statistical representation of the water vapor spectrum derived from available laboratory data. The statistical spectrum of water follows an exponential distribution of line strengths and random positions of lines to reproduce the line spacings and mean opacities observed in the laboratory. This statistical spectrum is then randomly sampled in the spirit of opacity sampling. Significant improvements are made in both the opacities and in the thermal structure and emergent fluxes of the model atmospheres.
On the puzzling line spectrum of the B[e]-supergiant R 4 of the SMC
Authors: Zickgraf F.-J. , Wolf B.
Published: June 2019

The early-type supergiants of the Magellanic Clouds (MC's) include a class of objects, the B[e] -supergiants, which are described in detail in Zickgraf et al. (1985, 1986) who suggested a two-component wind model consisting of a cool, dense and slowly expanding disk-like equatorial wind component and a hot line-driven fast polar wind. This model could explain many properties of most of the B[e] -supergiants as e. g. the occurrence of “shell” absorption lines. R 4 of the SMC, however, although well fitting to the general scheme of B[e) -supergiants exhibits several pecularities of its line spectrum, which make this particular star an exceptional case among the B[e] -supergiants of the MC's.
A preliminary model for HR 8752
Authors: Zsoldos E.
Published: June 2019

HR 8752 is a G5 hypergiant in the Cep OBI association. It is an SRd variable according to the GCVS. The V and B-V curves of the star are plotted in Figure 1. One point in the figure is the mean of all measurements made in a ten-day interval. The circles contain the observations of Arellano Ferro (1985) which show large deviation in two cases. Neglecting these circles, it is clear from Figure 1 that HR 8752 has alternating brighter and fainter maxima, the difference between them being some hundredth of magnitude, A possible explanation will be outlined for this phenomenon.
A non-eclipsing binary model of the symbiotic star AG Dra
Authors: Iijima T.
Published: June 2019

The light variation of AG Dra is considered as a result of a variation of free-free emission from a gaseous envelope around the hot component. The emission measure of the envelope at a light maximum is estimated to be about Ne2V = 6.5 × 1059 cm−3. The amplitude of the light variation in the U band should be less than 1.4 mag. which is consistent with the observed results. The emission measure of the envelope might vary according to a variation of mass transfer rate in an elliptical binary system.
Polarimetry of southern symbiotic stars
Authors: Schulte-Ladbeck Regina E. , Magalhães Antonio Mario
Published: June 2019

We present the first results of an ongoing survey of the linear polarization properties of symbiotic stars. With these multifilter optical measurements, we aim to obtain a statistically significant sample from which to study the nature and geometrical arrangement of their circumstellar matter and its relationship to the stellar components. Up to now, the observations show.
Experimental studies on simulated circumstellar grains
Authors: Nuth Joseph A. , Donn Bertram
Published: June 2019

Over the last few years a better understanding of the chemistry inherent in the refractory nucleation process has emerged from experimental studies performed in several laboratories. These studies shed light not only upon the factors which might control the onset of grain formation, but also on the spectral characteristics of freshly condensed grains.
NASA plans relevant to the study of circumstellar matter
Authors: Stencel Robert E.
Published: June 2019

The Astrophysics program of the National Aeronautics and Space Administration of the United States emphasizes use of vehicles to obtain above-the-atmosphere observational advantages, including expanded electromagnetic frequency access, enhanced sensitivity resulting from reduced or eliminated atmospheric absorption of light and image smearing. Space technology provides a superior means for astrophysical inquiry, particularly in the case of circumstellar material. Much of the flight program is undergoing intensive review following the Space Shuttle disaster of January 1986.
The Kinematics of Pulsars
Authors: Lyne A.G.
Published: June 2019

Pulsars have a galactic radial distribution similar to that of many galactic populations such as HII regions, massive stars and supernova remnants. However they are generally much further from the plane of the Galaxy than these objects. Proper motion measurements sho that this is because they are typically moving with high velocities. The measurements also indicate that most pulsars were formed a few million years ago close to the plane, within the normal Population I regions. Some pulsars will escape from the Galaxy, although the majority will end up in a halo population. The origin of the high velocities is not clear at present but may be due either to some asymme try in the formation event or to the disruption of a close binary system.
The Effects of Inverse Compton Scattering on the Pulsars' Radiation
Authors: Xia X.-Y. , Deng Z.-G. , Qiao G.-J. , Wu X.-J. , Chen H.
Published: June 2019

Our calculations show that the cross section of the inverse Compton scattering in strong magnetic fields may be larger than that of Thompson scattering by sevaral orders of magnitude in the case of polar cap surface of pulsars. We can also see that when the energy of e± exceeds a certain value, their energy loss caused by the inverse Compton scattering may be larger than the energy gain from electric field in the inner gap, which implies that the e± could not be accelerated to γ = 106. Meanwhile, the electrostatic forces acting on the electrons will be balanced by the radiative pressure if temperature T > 108 K.

It is beleived that the surface temperarure for most of pulsars is less than 106 K, in that case the ions of iron can not be emitted from the surface of pulsars. However, the temperarure at the polar cap can be increased to 3×106 through the bombardment of electrons to the polar cap according to R-S model. This quasi-equilibrium state by self-regulating must make the coherent radio emission unstable on the contrary.
Pair Production in Intense Electromagnetic Fields of Pulsars
Authors: Shi T.Y.
Published: June 2019

The possible existence of strong electromagnetic fields in pulsars has motivated extensive interest in investigation of various quantum electrodynamics processes. In particular, the process of converting high energy photons into electron-positron pairs is of great significance in pulsar theory.
High-Resolution Radio Observations of the Crablike Supernova Remnant 3C 58
Authors: Reynolds Stephen P. , Aller H. D.
Published: June 2019

We report Very Large Array1 observations of 3C 58, the Crab Nebula's closest relative at radio wavelengths. We combined A, B, C, and D configurations (baselines ranging from 0.08 to 35 km) at frequencies of 1446 MHz and 4886 MHz, achieving resolutions of 1″.9 and 2″.5, respectively, and a sensitivity at both frequencies of about 70 μJy per beam. We deconvolved the point-source response from the images using a maximum-entropy technique. The 1446 MHz total-intensity image shows that filamentation not only dominates the spatial distribution of flux in the bright inner regions, but appears to continue into the faint outer envelope as well. This envelope fades smoothly into the noise over about half the circumference of the remnant; the lowest contours of our map show maximum extents in RA and δ of 10′.3 and 6′.3 respectively. However, in some places the edge is relatively well-defined, suggesting confinement of some kind. A remarkably jet-like extension can be seen protruding from the south central part of the remnant, with a position angle of about 150° with respect to the radio peak. Unlike the Crab's jet, this is wedge-shaped and somewhat resembles the brighter extension to the north. The X-ray point source (Becker, Helfand, and Szymkowiak 1982, Ap. J. 255, 557) lies about 30″ east of the peak in the radio map. No obvious radio feature coincides with it. We have made spectral-index maps of the remnant, and find only small variations, with little apparent correlation of spectral index with structure. The rms deviation from the remnant mean spectral index is 0.18, but profiles of filaments show less than 0.1 difference in spectral index between peaks and adjacent valleys. Thus the bright filaments are neither flatter nor steeper in spectrum than the remnant mean, ruling out a picture in which bright filaments are locations where shock acceleration produces a steeper particle energy spectrum. Filaments have brightness contrasts of factors of 1.5 to 2, steep edges (<10″, sometimes unresolved) and widths of 10″–30″; if they have similar thicknesses along the line of sight, their emissivity ranges up to 40–50 times the remnant mean.
Supernova Remnants with Radio Jets
Authors: Kesteven M.J. , Caswell J.L. , Roger R.S. , Milne D.K. , Haynes R.F. , Wellington K.J.
Published: June 2019

Two examples are given of probable radio jet/supernova remnant association, G332.4+0.1 and G315.8-0.0. In both cases the jet length is larger than the radius of the remnant's shell; the jet diameter is barely resolved, and is substantially less than the observed shell thickness. The jet luminosity is 5–10% that of the shell. The G332.4+0.1 jet termi nates in an extended plume whose luminosity is ∼50% that of the shell.
A Hard X-ray Observation of CYG X-1 in 1985
Authors: Ma Y.Q. , Li G.H. , Zhang C.M. , Xiao Q.Y. , Qian Y.M. , Li Z.G. , Wu M. , Dai CJ. , Gu Y.D. , Zhang X.Y. , Li T.P.
Published: June 2019

On September 22, 1985, a hard X-ray observation of Cyg X-1 was performed by using a balloon-borne CsI-NaI phoswich telescope HAPI-2 at Xianghe Balloon Facility in China. The main detector is CsI(T1) with a thickness of 0.4cm and an area of 140cm2. The energy range is 20–200KeV. The telescope reached a float altitude of about 38Km(4g/cm2). The photon's arrival time and energy loss spectrum were measured for both background and active tracking on-source observations.
Polar Cap Accretion onto Magnetized Neutron Stars: An Analytic Solution
Authors: Arons Jonathan , Klein Richard I.
Published: June 2019

This abstract should be read in conjunction with the papers by Arons and by Klein and Arons in these proceedings. In the context of the accretion models described there, one can find an analytic solution for the flow down the polar field lines if a number of simplifying assumptions are made. These are (1) steady flow in the co–rotating frame; (2) radiation pressure large compared to gas pressure; (3) pure scattering for the Rosseland opacity, with the magnetic corrections set equal to constants instead of using the actual functions of temperature; (4) diffusion flux of radiative energy proportional to the gradient of the energy density alone, instead of the correct sum of terms proportional to the photon energy density and the number density gradients; and (5) below a radiative shock, subsonic flow in approximate hydrostatic equilibrium. We assumed dipole geometry, and also assume the mass flux is independent of distance from the magnetic axis. The essential trick is to use (1), (2) and (5) to write the advective contribution to the radiation transfer equation as Mg/area = rate at which gravity does work on a fluid element, and use (3) and (4) to write the nonlinear diffusion flux as the ratio of gradients in the energy density. Then the multidimensional diffusion equation can be cast in a separable, linear form by using the logarithmic radial gradient of the energy density as the basic variable (see also Kirk, J., 1985, Astron. and Astrophys., 142, 430). The result is exponential stratification of the energy density, velocity and mass density along B with scale height R*[L(EDeff)/4Lco-p]; the effective Eddington luminosity is discussed by Arons, these proceedings. This result can be understood as the result of almost exact balance between upward diffusion and downward advection of photons in the optically thick medium. The same fluid quantities are stratified in a Gaussian manner across B, with angular half width at half maximum Δθ = [L(EDeff)/Lcap](r/R*)3/2. These distributions agree well with more sophisticated computational results, during times when the flow is steady. When used as a basis for calculations of the radiative entropy, the calculated emergent spectra are not dissimilar to the spectra of high luminosity, accretion powered pulsars.
Radiation Gas Dynamics of Polar Cap Accretion onto Magnetized Neutron Stars
Authors: Klein Richard I. , Arons Jonathan
Published: June 2019

We present results of the first self-consistent, time-dependent, 2-D calculations of the accretion of plasma onto polar caps of high luminosity (L*>1036erg-s−1) magnetized neutron stars. We follow the temporal and spatial evolution of three fluids, electrons, ions and photons in a superstrong (B=3×1012 Gauss) dipole magnetic field where radiation pressure dominates plasma pressure by solving coupled 2-D equations of radiation hydrodynamics. We have included several physical processes in the radiation-plasma coupling in superstrong magnetic fields (Klein, et al., 1984, Santa Cruz Workshop on High Energy Transients, and Arons, this conference). We solve the resulting system of coupled 2-D PDEs on a Cray XMP-48 by applying implicit finite-difference techniques with iterative operator splitting methods. We present results for two models of 5×1037 erg-s and 1.5×1038 erg-s−1 super-Eddington luminosity on one polar cap, each having initial mass flux independent of co-latitude of a field lines footprint. We find (a) Radiation develops a broad transverse fan beam that emerges from an annulus 0.2–0.5km above the polar cap. (b) The beam profile is determined by advective trapping of radiation in optically thick (τ11,τ⊥ ≈103) flow. Here the time for diffusion of radiation up through the accretion column is ≫ the time for downward advection. (c) There is a three fluid nonequilibrium with Ti≫Tγ≥Te. (d) Maximum photon temperature of ≈ 10–20 keV in the fan beam is in the observed range. (e) Cyclotron emission ≫ bremsstrahlung as a source of photons. (f) At early times (≪lms) radiation pressure strongly decelerates flow to 10−3 of freefall in central regions of accretion column resulting in a density mound, but plasma freefalls down the sides of the column. (g) Analytical models have reasonable agreement with numerical calculations; velocity and energy density roughly Gaussian transversally and exponential vertically, until the onset of “photon bubbles” after several dynamical times (∼lms). (h) Multiple “photon bubbles” rising subsonically in the accretion column form in the high luminosity model. We believe the photon bubbles to be a possible consequence of overstable convection in super-Eddington flows. These photon bubbles could be observable as 10–100μs fluctuations in the emergent flux and, thus, be an important diagnostic for inhomogeneous structure of the column.
Numerical Experiments and Neutron Star Formation
Authors: Arnett W. David
Published: June 2019

Theory and numerical experiments on neutron star formation are critically reviewed. Several new numerical experiments are summarized, and the importance of advection is discussed.
The Beat Frequency Model for QPOs
Authors: Shaham Jacob
Published: June 2019

We have to date reports of Quasi-Periodic-Oscillation (QPO) observations in some twelve X-ray source, of which at least seven are low mass X-ray binaries (van der Klis 1987). They constitute a formidable zoo of phenomenae with so much variety that they, at times, do not at all even seem amenable to a single model. Some of the other QPO talks in these proceedings will try and present observations in the context of various models. My task is to talk about the Beat Frequency Model which, it seems to me, is by far the prime model for at least some of the QPOs.
Quasi-Periodic Oscillations: The Rapid Burster (MXB 1730-335): Models vs. Observations - A Brief Review
Authors: Lewin Walter H. G.
Published: June 2019

The salient features of quasi-periodic oscillations (QPO) observed in type 2 bursts and in the persistent emission from the Rapid Burster are discussed. In addition, a brief review is given of the models that have recently been proposed to explain high-frequency QPO observed in several bright low-mass X-ray binaries. We do not yet know the mechanism(s) of the QPO, not even whether they are magnetospheric in origin. However, some of the proposed ideas could well be relevant to the various rather complex aspects of the QPO. It is likely that more than one mechanism is at work.
Monte Carlo Simulations of Radio Pulsars and Their Progenitors
Authors: Dewey Rachel J. , Cordes James M.
Published: June 2019

The formation of neutron stars in binary systems is often used to explain the nature of specific radio pulsars and characteristics of the pulsar population as a whole. We have investigated the extent to which such scenarios provide a self-consistent description of the pulsar population. Using a computer simulation, we modeled the evolution of the main sequence stellar population and compared the predicted neutron star population to the observed radio pulsar population, focusing our attention on the pulsar velocity distribution and the incidence of binary pulsars. These characteristics relate very directly to the binary nature of pulsar progenitors, and are not strongly dependent on models of pulsar magentic field and luminosity evolution.

The need to reproduce both the high velocities typical of pulsars and the low incidence of binary pulsars strongly constrains the formation of pulsars in binary systems. Unless one assumes that virtually all pulsars originate in close binary systems, the observed velocity distribution cannot result from the disruption of binary systems by symmetric supernova explosions; some additional acceleration process (e.g. asymmetric supernova mass ejection or asymmetries in pulsar radiation) must act during or soon after a pulsar's formation. It is possible to reproduce the velocity distribution by assuming that all pulsars are born in binary systems with initial orbital periods less than about 30 years. However, the predicted incidence of binaries is then too large by more than an order of magnitude, unless one also assumes that the process of mass transfer from the primary to the secondary is almost always non-conservative, or that the minimum mass necessary for a stripped helium core to explode as a supernova is larger (over 4 M⊙) than currently believed. Further analyses of the radio pulsar population, the X-ray binary population and the abundances of elements ejected in supernovae should help determine which of these alternatives is most reasonble. Additional studies of the main sequence stellar population, accounting more accurately for evolutionary and observational selection effects, will reduce the uncertainties in modeling the formation of the neutron star population.

It has also been suggested that the observed correlation between pulsar velocities and magnetic moments (see Cordes, these Proceedings) is induced by the differing evolutionary paths by which stars in binary systems form radio pulsars. Our simulation does not reproduce this correlation, and we do not find any paths likely to produce low velocity, low magnetic field neutron stars not in binary systems.

We are submitting a full description of our model and results to The Astrophysical Journal.
Constraints to Possible Progenitor Systems of PSR 1831-00
Authors: Pylyser E.H.P.
Published: June 2019

Numerical computations were carried out to simulate the evolution of the recently discovered radio pulsar binary PSR 1831-00 with a very low mass function (Porb = 1.81 days, Dewey et al. 1986). These show that the minimum value of the initial mass of the progenitor of the mass-losing secondary is about 1 M⊙. All computed systems with a final period equal to the observed one, and an initial progenitor mass of 1 M⊙ have an age of the order of the Hubble time (∼ 1.3 × 1010years). For a 1.5 M⊙ progenitor of the mass-losing secondary we find that the final (= presently observed) orbital period sets strong constraints to the possible initial system configuration: the binary period should have been such that the 1.5 M⊙ star was just at the onset of the over-all contraction phase (Porb = 0.74 days, XC = 0.05) when it began to fill its Roche-lobe, and the initial mass or the compact mass-accreting star must have been < 0.85 M⊙. (This star was then presumably a white dwarf, which later collapsed due to the accretion). For example, the final period and remnant secondary mass for a system with an initial configuration of 1.5 + 0.8 M⊙ are 1.83 days and 0.20 M⊙, respectively.

If one would start out from a more evolved initial state of the 1.5 M⊙ secondary than the end of the overall-contraction phase, the maximum initial mass of the compact object will become drastically smaller and the final remnant mass of the secondary becomes larger than 0.20 M⊙ in all cases.

Calculations for a 2.0 M⊙ progenitor of the secondary suggest that if such a progenitor can produce the present system, the initial mass of the accreting primary was at maximum 1.30 M⊙.

All the calculations were performed with the inclusion of magnetic braking in so far as the extent of the convective envelope allowed this (see Pylyser & Savonije 1986, in preparation). The effects of the explosion effects due to the accretion induced collapse of the white dwarf were not taken into account.
Geodetic Precession in Binary Pulsars
Authors: Bailes M.
Published: June 2019

We have calculated the probability of observing geodetic precession in the binary pulsar PSR1913+16 for several different progenitor systems. Such an observation would support the asymmetric kick hypothesis for the origin of pular velocities. The results are shown to be dependent on the assumed progenitor but not to a strong degree. It is concluded that the probability of an observation to date is less than 20 percent in contrast to past predictions. In 15 years we expect this figure to be near 60 percent. We conclude that the null result to date cannot be taken as evidence against the asymmetric kick hypothesis for the origin of pulsar velocities. We develop our model and apply it to binary pulsars in general. We conclude that the likelihood of observing geodetic precession in the near future is low.

A complete version of this paper is soon to be submitted to a scientific journal.
Neutron Star Cooling: Criticical Test of Dense Matter Physics
Authors: Itoh Naoki
Published: June 2019

Recent developments in the standard theory of neutron star cooling is critically reviewed. Emphasis is placed on the recent developments in the calculations of thermal conductivity and neutrino energy loss rates.
The Nutations of Neutron Stars and Core-Crust Coupling
Authors: Gwinn C. R.
Published: June 2019

Neutron stars, like the earth, are rotating fluid-filled ellipsoids. Poincaré (Bull. Astron. 27, 321, 1910), Hough (Phil. Trans. R. Soc. A186, 469, 1895) and others have discussed the nutations of such objects through a simple model, which treats the crust as rigid and the core as an ideal fluid of uniform density and vorticity. The core and crust are coupled by inertial coupling: the forces which constrain the fluid to its cavity within the crust can produce a net torque, since the cavity is ellipsoidal. Additional torques, and the effects of the elasticity in the crust and density stratification in the core, may be accomodated in such models as well (Sasao et al., Proc. IAU Symposium 78, p. 165, 1980, and references therein).
Einstein Observatory Limits on Neutron Star Surface Temperatures
Authors: Harnden F.R.
Published: June 2019

For years the theoretical models of neutron star formation and evolution had remained largely unconstrained by observation. Following the Einstein X-ray Observatory surveys of supernova remnants and pulsars, however, strict temperature limits were placed on many putative neutron stars. The Einstein search for additional objects in the class of supernova remnants with embedded pulsars has increased the number of such objects by two. For the four objects in this class, the surface temperature limits (see Table 1) provide meaningful logically sound constraints on the neutron star models. For the future, however, still better X-ray observations are needed, both to increase the number of objects available for study and to refine the spatial and spectral capabilities of the X-ray measurements.
Model Atmospheres for Cooling Neutron Stars
Authors: Romani Roger W. , Blandford Roger D. , Hernquist Lars
Published: June 2019

The failure of Einstein X-ray observations to detect central neutron stars in most young supernova remnants (Helfand and Becker 1984) has provided interesting constraints on cooling theories (cf. review by Tsuruta 1985). The comparison of the measured fluxes with the predicted effective temperatures is sensitive to the nature of the emitted spectrum, commonly assumed to be blackbody. The presence of a substantial absorbing atmosphere can, however, produce significant departures. We have calculated model atmospheres for unmagnetized neutron stars with effective temperatures 105K ≦ Teff ≦ 106.5K using Los Alamos opacities and equations of state (Romani 1986). We consider a range of surface compositions, since the accretion of ∼10−19M⊙ will cover the surface to the X-ray photosphere and subsequent settling in the strong gravitational field can severely deplete the heavy species. In a low Z atmosphere (eg. He) the measured X-ray flux will substantially exceed the blackbody value–the Einstein limits on Teff are correspondingly lowered (eg. by ∼1.6 for SN1006 with a helium surface). For high Z atmospheres, the flux is close to the black body value, but prominent absorption edges are present. Recent calculations of the electron heat transport in magnetized neutron star envelopes (Hernquist 1984, 1985) have shown that, contrary to earlier estimates, magnetic fields will have a small effect on the heat flux (≳ 3 for parallel field geometries and ∼1 for tangled fields). Extension of the atmosphere computations to the magnetic case is important for comparison with X-ray observations of known pulsars.
The Nonlinear Dispersion Relation and the Relationship of the Forming Soliton Area to the Evolution of Pulsars
Authors: Xinjie Mao , Yi Tong
Published: June 2019

Based on Zakharov's equations, Karpman et al. claimed that there were solitons in the magnetosphere. According to the model proposed by Goldreich and Julin, there is a strong induced electric field in the magnetosphere. It seems that we should include the nonlinear effects of the electric field on the polarization of hydrogen atoms if there really are some hydrogen atoms spreading in the magnetosphere of the pulsar. Assuming the magnetosphere is symetric, therefore the electric polarization of hydrogen atoms is of the form P=χ(1)E +χχE3. We treat χ(1) and χ(2) as scalars because most hydrogen atoms in the universe are in the ground state and χ(3) is much smaller than χ(1).
Theory of Gamma Ray Bursters
Authors: Bisnovatyi-Kogan G.S.
Published: June 2019

Gamma ray bursters are interpreted as nuclear explosions under the surface of neutron stars. The explosions occur after transportation of the matter with nonequilibrium composition during starquakes in outer layers where the matter becomes unstable and explodes as a result of a developing chain reaction. In the nonequilibrium matter nuclear charge Z decreases with increasing density, contrary to the equilibrium composition. Formation of a shock wave and total energy output are calculated. Parameters of the mighty burst of 5 March 1979 are estimated. Formation of observed lines in different partions of the range and a possible nature of accompanying optical bursts are discussed with the proposed model as a basis.
A New Aspect of Galactic Ridge X-ray Emission: — SNRS in a Tenuous Medium? —
Authors: Koyama Katsuji
Published: June 2019

Thin thermal natures of a plasma temperature of several keV are observed in the diffuse X-ray spectra from the galactic ridge region by the Tenma satellite. Within the constraints imposed by the observational results, possible origins of the ridge X-ray emission are discussed. We show that unidentified young supernova remnants in a tenuous medium could be a significant contributor to the ridge emission.
Inverse Compton Model of Gamma Ray Burst Spectra
Authors: Howard W. M. , Liang E. P.
Published: June 2019

We study gamma ray spectra produced by the inverse Compton upscattering of soft photons by relativistic electrons with a one dimensional momentum distribution, which is relevant to gamma ray burst if the source magnetic field is strong enough so that the synchrotron cooling time of transverse energy becomes much shorter than isotropization time via couloub or Compton collisions. We find that for high electron longitudinal temperatures the output power is strongly beamed in the momentum direction and the spectrum softens rapidly with increasing view angle from the momentum direction.
What Type of Binary System is Cygnus X-3?
Authors: Bonnet-Bidaud J.M.
Published: June 2019

Results of the final analysis of COS-B X-ray observations of Cygnus X-3 (more than 220 days of observations from 1975 to 1982) are presented. Variations of the 4.8h period have been investigated and a new ephemeris including previous and later (Exosat) results, is established. Both long and short-term changes in the period are apparent. The long term variation is found to be consistent with orbital changes expected from mass transfer and mass loss in a standard low-mass binary system with an accreting neutron star. Short term period fluctuations (of the order of 4 10−3 d.) are definitively present and not fully explained. A critical discussion of the recent claimed high energy gamma (E > 1012eV) detections of the source is also presented. It is argued that, if confirmed, these results are inconsistent with the typical X-ray picture of Cygnus X-3. In particular, the eclipse duration required in the Vestrand and Eichler (1982) imply a totally unphysical companion for a 4.8h orbit.
High Energy Cosmic Rays from Young Neutron Stars
Authors: Miyaji Shigeki
Published: June 2019

Cosmic ray spectrum has an intensity enhancement at energy range 1014–16 eV/nuc. Recently Takahasi et al. (1986) called an attention to chemical composition there. Although the data still contain large uncertainties, they argued an overabundance of calcium at high energies (Ca/Fe ≥ 2 above 1014 eV/nucleus) and some enhancements of medium heavy nuclei (C ∼ Ar) instead of no anomalous p, He, and Fe abundances.
Four New Evolved Planetary Nebulae
Authors: Tamura S. , Weinberger R.
Published: June 2019

While examining Palomar Observatory Sky Survey prints for various purposes, we came upon a number of hitherto uncatalogued nebulous objects, all of them of low surface brightness. Four of them are considered by us as new planetary nebula candidates due to their morphology. For the brightest one of them, spectroscopic observations were carried out with the Cassegrain spectrograph attached to the 74-inch telescope of the Okayama Astrophysical Observatory: this object (1 = 65.49°, b = +3.18°) is clearly confirmed as a planetary nebula and obviously is in an advanced stage in its evolution; in Fig. 1, a spectrum of it is shown.
Three Possible Planetary Nebulae from Near-IR Observations
Authors: Persi P. , Marenzi A. , Preite-Martinez A. , Ferrari-Toniolo M.
Published: June 2019

A catalogue of 388 new possible planetary nebulae was selected by Preite-Martinez (1988) from the IRAS Point Source Catalogue. These unidentified sources have IRAS colours in the range F(12)/F(25) ≤ 0.35 and F(25)/F(60) ≥ 0.35, and are located in the proximity of the galactic equator (|b| ≤ 15°). In order to identify these IRAS sources we have undertaken a programme of near-IR observations using an InSb photometer and a near-IR camera. We report here on results relative to four of these sources.
Interstellar Reddening Towards S188, Hw4 and We1–6
Authors: Saurer W.
Published: June 2019

Photoelectric UBV photometry of stars was carried out in the angular vicinity (radius = 15′) of 3 planetary nebulae. An extinction distance relation was constructed for the line of sight towards each planetary nebula. This relation was verified by published data on nearby stars and star clusters. The distances derived are 850 ± 300 pc for PK 128 −04 1 (S 188, Simeis 22), 400 ± 200 pc for PK 149 −09 1 (HW 4), and (less reliable) 800 pc ± 400 pc for PK 224 +01 1 (We 1–6). For the central star of PK 224 +01 1 our observations gave V = 15.76 ± 0.03 mag, (B–V) = −0.08 ± 0.03 mag and (U–B) = −0.87 ± 0.03 mag.
CCD Photometry of NGC 2453
Authors: Mallik D.C.V. , Sager Ram , Pati A.K.
Published: June 2019

We have undertaken a detailed photometric study of the open cluster NGC 2453 in Puppis with a view to determining accurately its distance modulus and to investigate its possible association with the PN NGC 2452. We have observed the core region of the cluster in V and I photometric bands using a Thomson-CSF TH 7882 CCD chip with the format 384×576 pixels, at the f/13 cassegrain focus of the 102-cm telescope at Vainu Bappu Observatory, Kavalur, India. Each image frame covers a field of 2′.3 × 3′.4 of the sky. Bias frames and flat field exposures on the twilight sky were obtained as per standard practice.
Dielectronic Recombination in the Gaseous Nebulae as a Cooling Process
Authors: Kholtygin A.F.
Published: June 2019

The dielectronic recombination (DR) is of importance at ‘low’ (nebular) temperature. This process leads to cooling the electron gas in nebulae. The cooling rate by recombination of ion X+n is
Kinematics of the Planetary Nebula Hb 5. a Progress Report
Authors: Pişmiş P. , Manteiga M. , Mampaso A. , Cruz-Gonzalez G.
Published: June 2019

The planetary nebula Hubble 5 shows a very striking bi-symmetry; a 180° rotation around its center would bring the object into fair coincidence. Similar to this nebula is NGC 6537 and, to a lesser degree, NGC 6302. Jet outflows are reported from this “post-main sequence” nebula over a range of 260 km s−1 (Phillips and Mampaso, 1988). Otherwise not much has appeared on this object in the literature.
Imaging of Magellanic Cloud Planetary Nebulae by the Hubble Space Telescope
Authors: Dopita M. A. , Meatheringham S. J. , Wood P. R. , Ford H. C. , Bohlin R. C. , Stecher T. P. , Maran S. , Harrington J. P.
Published: June 2019

We have obtained Hubble Space Telescope (HST) Planetary Camera (PC) images of a number of Magellanic Cloud planetary nebulae. The objects, except for SMP 83 were observed as part of the Cycle I GO program. The observations were made in the [O III] λ5007Å line. The object SMP 83, was observed as part of the GTO program, and in this case observations were also made in the Hα line using the F650N filter. In order to characterise the point spread function, a star was placed at the same point on the chip as the PN. This allowed us to determine the diameters of barely resolved PN in an accurate manner, by convolving the PSF with a function until it matched the appearance of the PN image. The results are given in Table 1.
A PC-Based Quicklook-Program for PN Images
Authors: Bässgen M. , Bremer M.
Published: June 2019

We developed a computer program, running on a PC which allows a quicklook of monochromatic PN-images. Until now the data base consists of about 300 images obtained by B. Balick, M. Grewing, L. Bianchi and ourselves. This data base can easily be enhanced. Four monochromatic images (Ha, NII, OIII and Hell, if available) are shown simultaneously. It is also possible to show up to six objects in one emission line simultaneously to compare special features. Different look-up-tables are possible. The program does not compete with reduction packages, its only intention is to do some ‘quick morphological studies’ in a comfortable and easy way. In the present version the program needs a PC equipped with a mouse, a TSENG based VGA graphics card, 640 K (EMS rec.) and about 15 MB free disk space (for the images).
An Iterative Method for the Reconstruction of Two-Dimensional Density Distributions
Authors: Bremer M. , Grewing M.
Published: June 2019

As hydrodynamic models of planetary nebulae advance from 1D to 2D calculations, it becomes desirable to make the same step for reconstruction techniques, which aim at deriving from the 2D intensity distributions of PNe images their 3D structure. A basic step is the determination of a symmetry axis and its orientation in space which can be described by two angles, one measured in the plane of the sky, and one measured with respect to the tangential plane. While the first one can be determined from the images, e.g. by applying the criterion of maximum normalized correlation between the object halves, which we found to yield the best results, the second angle is treated as a free parameter (see below). The steps of the iterative reconstruction algorithm are the following (with image(x, y) = input image):

1.

Fill a 3D kartesian density grid(xyz) (random or continuous), observing the constraint ∫ grid(xyz)dz = image(x, y), where z is along the line of sight.

2.

Transform to cylindrical symmetry system (r, z', ϕ) and read out density (r, z') averaging over ϕ.

3.

Return density(r, z') into grid(xyz) and normalize the ∫ grid(xyz)dz to match the input image.

4.

Return to (2.) as long as two subsequent density(r, z') estimations differ by more than a specified limit.
1.6–1.75 and 3.1–3.75 μM Spectrum of Hb5
Authors: Magazzù A. , Strazzulla G.
Published: June 2019

We have recently obtained high resolution IR spectra (λ/δλ ≈ 1000) of the planetary nebula Hb 5, over the range 1.6–1.75 μm and 3.1–3.75 μm (Magazzù & Strazzulla 1992) at the European Southern Observatory (ESO). Emission bands have been detected the most prominent being at 3.3, usually attributed to PAH molecules, and 3.4 μm. For the predicted (de Muizon et al. 1986) first armonic (at 1.67 μm) of the 3.3 μm band we get an upper limit at least 45 times weaker than the 3.4 μm feature. This, together with the high ratio of fluxes F3.4/F3.3, challenges the hypothesis that the 3.4 μm band is the first hot band. We suggest that the first hot band may be identified with a small feature at 3.46 μm. In this case the first armonic would fall at 1.686 μm where we detect a small feature.