bluuebunny/crossref_metadata_2025 huggingface dataset:
Abundance analyses: methods, results and implications
Authors: Cottrell P. L.
Published: June 2019

The methods by which abundance analyses can be undertaken, especially with the growing use of high quantum efficiency digital detectors, are reviewed. The importance of the differential curve of growth technique is discussed, followed by a review of some recent results involving both late-type dwarf and giant stars. These include (1) the F and G dwarf abundance analyses of the elements sodium through nickel, which show an important differentiation between stars belonging to the young and old disk populations, (2) the possibility that departures from local thermodynamic equilibrium can effect sodium and aluminium abundances in late-type giants and supergiants and (3) that significant differences exist between the abundances of carbon, nitrogen and oxygen in old disk and young disk giant stars. Finally, the implications of these abundances in terms of stellar and galactic evolution are briefly addressed.
The DDO photon-counting spectrometer: a well-dressed Shectograph
Authors: Mochnacki S. W. , Chew S. , Kunowski W. , Hawker F. , Kamper K. , Blyth D. , Zerafa L. , Platzer A.
Published: June 2019

We have built a Shectman-type photon-counting spectrometer based on the Latham-Geary “Z-Machine” design. The system is innovative in that the entire system rides on the telescope and communicates to the outside world via standard serial lines. Microprocessor architecture, memory controllers and new interconnect and packaging technologies have been employed. The system is portable and can be easily connected to almost any computer. It is suitable for calibrated spectrophotometry on a smaller telescope as well as for conventional spectroscopy.
Summary: Opportunities for research with small telescopes
Authors: Graham J. A.
Published: June 2019

Our meeting has been unusual in that we have covered so many fields of present-day astronomy and astrophysics. The common link has been the potential of small telescopes for making substantial advances in our knowledge of the observable universe. Attention has been focussed not just on those programmes which can be done best with small telescopes but we have also highlighted many which can only be done with small telescopes.
Low-Energy Molecular Collision Processes in Space
Authors: Takayanagi Kazuo
Published: June 2019

Among the low-energy nonreactive molecular collisions, the rotational and vibrational transitions are the most important inelastic processes. the collision partner is an electron, an ion, or a neutral particle. Depending on the process and the collision system concerned, the magnitude and the energy dependence of the relevant cross sections are widely different. the present status of our knowledge is briefly summarized and some sample cross section data for H2and CO are shown. Useful relations among the rotational cross sections are indicated. the importance of the long-range intermolecular forces in determining some chemical reaction rates is also pointed out.
Photodissociation Processes of Astrophysical Molecules
Authors: van Dishoeck Ewine F.
Published: June 2019

The photodissociation processes of molecules in various astrophysical regions are discussed, and the rates for photodissociation by the unattenuated interstellar radiation field are reviewed.
Microwave Spectroscopy of Molecular Ions in the Laboratory and in Interstellar Space
Authors: Claude Woods R.
Published: June 2019

Refinements of the instrumentation and methods used for laboratory microwave spectroscopy of molecular ions in the last few years have led to successful observation of spectra of several new molecular ions of particular astrophysical interest. Notable among these enhancements have been the use of magnetic fields to increase the density of ions in discharge plasmas and the extension of upper frequency limits of the spectrometers towards and into the sub-millimeter regime. the number of ions now observed by laboratory microwave spectroscopy is more than a dozen, and about two thirds of these have also been detected, at least tentatively, by radioastronomy. Even where detections are uncertain or impossible, useful upper bounds on ion abundances can be gleaned from radioastronomical observations once exact transition frequencies and assignments are known from laboratory studies. Special attention will be given in this presentation to the status of laboratory and radioastronomical work on HOC+, H2D+, and SO+, molecular ions which have been the object of our own recent interest and effort in this area.
Hyperfine Structure in the Spectra of Diatomic Molecules with Two Nuclear Spins
Authors: Tatum J. B.
Published: June 2019

The presence of a nuclear spin in a molecule splits the rotational levels and microwave lines into hyperfine components. A second nuclear spin (such as exists, for example, in the molecule DCN) further splits these into hyperhyperfine components.
Far-Infrared and Submillimeter Observations of Interstellar Clouds
Authors: Melnick Gary
Published: June 2019

This paper reviews a number of ways in which the results of far-infrared and submillimeter (FIR/SMM) observations (50 μm ≤ λ ≤ 1 mm) have been used to address some of the important questions in astrochemistry. On scales of kiloparsecs these might include questions of abundance gradients; on scales of parsecs these might include questions about the chemical structure of molecular clouds; and on scales of tenths of parsecs or less, these might include questions about chemical processing in shocks.
Theoretical Studies of Dense Cloud Chemistry
Authors: Herbst Eric
Published: June 2019

Based on analyses by a variety of investigators, it has become understood that gas phase reactions can account for much of the chemistry observed in dense interstellar clouds. However, quantitative calculations of molecular abundances utilizing gas phase reactions are beset with difficulties. These difficulties include uncertainties in needed rate coefficients at the low temperatures of interstellar clouds, uncertainties in the dynamics of physical processes such as cloud collapse and clumping, and uncertainties in our understanding of gasgrain interactions. New work in some of these areas and its impact on modelling is emphasized.
The Ionization Rate in Dense Interstellar Clouds
Authors: Lepp S. , Dalgarno A.
Published: June 2019

Measurements of the abundances of OH, HCO+ and DCO+ are employed to derive the ionization rate in molecular clouds.
The Role of Metallicity and H2 in Star Formation in the Galaxy
Authors: Rana N. C. , Wilkinson D.A.
Published: June 2019

A new law of star formation is proposed which suggests an explicit dependence on the abundance of metals and H2.
High-Resolution 3 μm Spectroscopy of Extreme Carbon Stars
Authors: Maillard J.-P. , Foster S.C. , Amano T. , Feldman P.A.
Published: June 2019

We have used the Cassegrain-focus Fourier Transform Spectrometer of the Canada-France-Hawaii Telescope to record high-resolution (0.03 cm−1), high signal-to-noise ratio spectra of the extreme carbon stars IRC+10°216 and CIT6 in the 2850–3100 cm−1 region. Upper limits were obtained for the column densities of silicon nitride (2-0 band of the A-X system), ethylene (ν11 fundamental band at ν0 = 2988.7 cm−1), and ethane (ν7 fundamental band at ν0 = 2985.4 cm−1).
Oxygen Abundance in Normal and Peculiar B and A Type Stars
Authors: Van Santvoort J.
Published: June 2019

The prominent OI(3s 5S°−3p 5P) triplet near 7774Å has been observed in normal and peculiar B and A type stars, and compared with synthetic non LTE profiles.
The Computation of Molecular Abundances and Opacities in the Atmospheres of Late-Type Stars
Authors: Sharp Christopher M.
Published: June 2019

The presence of molecules in cool stellar atmospheres can dominate the opacity. Some calculations have been done with a carbon-rich mixture of C/0=2, and the molecules C2, CN, HCN and C2H2 are major sources of opacity due to their large abundances. New calculations with HCN and C2H2 show they can be important.
Excitation Mechanism of Cometary Lines
Authors: Krishna Swamy K.S.
Published: June 2019

The Cometary Spectra in the visible and ultraviolet regions are dominated by the strong emission lines of various molecules. These can be explained in terms of the resonance fluorescence process in the solar radiation.
Isotopic Abundances in Comets
Authors: Vanysek V.
Published: June 2019

It is belived that the unprocessed material of the solar nebula may be preserved in comets. Thus the data concerning the chemical composition and the abundance of stable isotopes in these primitive bodies are of some importance in cosmological and cosmogonical context. Although the isotopic abundance in the small bodies of the Solar System are poorly known, owing to the forthcoming Halley fly-by missions, the discussion as whether or not the comets have preserved the cosmic isotopic ratio in their nuclei became more relevant. From this point of view expected data of the cosmologically and cosmogonically significant isotopic ratios of stable isotopes of the light elements in comets are discussed.
Basic Laboratory Studies of Grains
Authors: Greenberg J. Mayo
Published: June 2019

Laboratory investigations of grain mantles are shown to have a direct application to observations of interstellar grains. the experiments have made it possible to show how infrared spectra may be used as a probe not only of the grains as they are but also as they have evolved both chemically and physically. Growth by accretion, ultraviolet photoprocessing, gradual heating, explosions and general effects of grains on interstellar chemistry provide a consistent basis for understanding evolution of grains in terms of interactions with the gas, and ultraviolet radiation in both diffuse and dense regions of space.
Observational Evidences for the Evolution of the Quasar-Luminosity Function
Authors: Lorenz Hilmar
Published: June 2019

The results of objective-prism spectrophotometry for a sample of quasar candidates investigated in an area of approximately 100 deg2 of sky are presented. The selection effects and the collective properties of the sample are discussed in terms of the consequences for the present understanding of the cosmological evolution of the quasar luminosity function.
Search for Variable Extragalactic Objects
Authors: Pittella G. , Trevese D.
Published: June 2019

Preliminary results of a study of automatically detected variable objects are presented.

The sample is divided into stellar and diffuse objects and the corresponding integrated counts as a function of magnitude are evaluated and compared with results in the literature.
On the Hydrodynamical Conception of the Spiral Structure in Galaxies with a Velocity “Kink” on the Rotation Curve (Theory, Laboratory Experiments, Numerical Simulation, Observations)
Authors: Fridman A.M. , Morozov A.G. , Nezlin M.V. , Pasha I.I. , Polyachenko V.L. , Rylov A. Yu. , Snezhkin E.N. , Rorgashin Yu. N. , Trubnikov A.S.
Published: June 2019

The hydrodynamical conception of the spiral structure generation in the galaxies with a “kink” on the rotation curve is discussed. It treats the spirals as density waves in gas component of galactic disks. The main results of the fifteen-year study are presented. References are made to the papers of authors that prove a) the “gas” conception of the Galaxy spiral structure, b) the identity of equations for rotating shallow water and galactic gas disk, c) the method of laboratory modelling of galactic spirals induced by hydrodynamical mechanisms in shallow water experiments with the “Spiral” set up. The linear stability theory describes the mechanism of spiral arm formation and gives the parameters of the arms. Experiments agree with theory. Besides, they show banana-like vortices between the arms near the generator. Observational data on the galaxy NGC 1566 reveal a pronounced velocity kink and may be explained in terms of the spiral-vortex gas conception. The results of laboratory experiments and numerical simulations allow us to suggest certain hypothesis concerning observational evidences of the spiral-vortex structure.
Photoelectric Observations of Continuous and Emission Lines Variability in Spectra of Seyfert Galaxy NGC 1275 Nucleus
Authors: Pronik I. , Merkulova N.
Published: June 2019

The spectral observations of NGC 1275 nucleus in the range of 3700-7000 AA being carried out since 1971 to 1978 showed the existance of hydrogen and forbidden emission lines variability with the time scale of 5–6 and 1–2 years (Pronik, 1980). Observations on 6-m telescope during 4 nights in January, 1977 permit to reveal the scale variability of these lines 2–3 days, too (Merkulova, Pronik, 1985). These results evidenced the necessary of close photoelectric series of spectral observations of the galaxy nucleus with the filling factor of several days and hours.
Multifrequency Observations of Blazars
Authors: Robson E I , Gear W K , Brown L M J
Published: June 2019

This paper reports the results of a programme of multifrequency observations of a sample of Blazars concentrating particularly on the millimetre through infrared region. Our observations have demonstrated the need for a new model to explain the spectral behaviour of a major flare in 3C273. This also provides a good description of the variability exhibited by Blazars. We have also shown that the radio through mid-IR synchrotron spectrum of 3C273 is a separate component from the optical/IR.
High Spatial Resolution Observations of the Quasar MR2251-178
Authors: Macchetto F. , Perryman M.A.C. , diSerego-Alighieri S.
Published: June 2019

The possibility that quasars are activated by interactions between galaxies has received considerable attention following the discovery of extended emission surrounding many low and moderate redshift quasars, and the distored morphological appearances of some of these extensions. We have obtained high resolution narrow-band optical images of the field of the low-redshift quasar MR2251-178 which reveal, in addition to nebulosity closely associated with the quasar, diffuse line-emitting regions separated by up to 100 kpc from the nucleus but kinematically associated with it. We attribute these regions to density perturbations of the gaseous envelope or disc now known to rotate about this quasar, caused by a tidal interaction between the quasar and a nearby active galaxy in the same cluster. Limits of between 2–4 × 108 years can be placed on the time elapsed since this interaction.
Spectra of Nucleus of NGC 6240
Authors: Andreasian N. K. , Khachikian E. Ye.
Published: June 2019

The results of spectrophotometry of two nuclei of NGC 6240 are presented. One of them has properties of Sy 2 nucleus, the other seems to be a complex of HII regions.
A Spectral Study of Markarian 297
Authors: Burenkov A. N.
Published: June 2019

The results of a spectral study of the galaxy Mr 297 with the 6-m telescope are presented. Estimations of mass and heavy element abundance for some knots in galaxy are made. Chemical composition of these knots is close to the normal one.
Fifteen years of “Sonderforschungsbereich” in Heidelberg: Research on circumstellar matter
Authors: Baschek B.
Published: June 2019

At the end of this year, the Sonderforschungsbereich (Special Collaborative Programme) no. 132 on “Theoretical and Observational Stellar Astronomy” in Heidelberg will terminate after fifteen years. Although 15 years are only 2 1/2 per cent of the age of the University of Heidelberg, which is celebrating its 600 th anniversary this year, they are nevertheless a long and important time for astronomical research in Heidelberg. On the occasion of the termination of the Sonderforschungsbereich, we are now given the opportunity to present an essential part of its research, namely that on circumstellar matter at an international conference, and we are grateful to the International Astronomical Union that this could be realized, and that we can welcome here so many participants to this Symposium. As the Speaker of our Sonderforschungsbereich I would like to briefly introduce to you the general concept of the institution of an SFB and give an overview over its structure and research activities.
Circumstellar maher of young low-mass stars: Observations versus theory
Authors: Bertout Claude
Published: June 2019

After presenting NGC 7129 as a prototypical star-forming region, I discuss what can be learned from the radio spectra of embedded infrared sources. I then review available observational evidence for disks around young stellar objects, with emphasis on accretion disks around T Tauri stars. Finally, new results on the role of magnetic fields in the circumstellar activity of T Tauri stars are presented.
Evidence for helical velocity field in molecular bipolar flows - Support for magnetodynamic model
Authors: Uchida Y. , Shibata K.
Published: June 2019

A search for the helical velocity field that had been predicted in a magnetodynamic theory of Uchida and Shibata was made in the bipolar flows L1551 by using 12CO 115 GHz line, and evidence was obtained for it in the low velocity maps as the skew inter-invasion of the root part of the blue- and red shifted lobes into different sides of the opposite lobes. Theoretical implications of this and other findings are discussed, and the advantage of models with magnetic field is stressed.
TH 28: A new bipolar Herbig-Haro jet
Authors: Krautter Joachim
Published: June 2019

A bipolar Herbig-Haro jet system associated with the emission-line object Th 28 has been discovered from direct CCD-imaging, long-slit spectroscopy, and broadband infrared observations. The observations were carried out using the facilities of the European Southern Observatory, La Silla, Chile. A direct CCD-image taken through a narrow band Hα interference filter is shown in Figure 1.
Dense cores in the HH24–26 outflow region
Authors: Menten K. M. , Walmsley C. M. , Mauersberger R.
Published: June 2019

We have made observations of the (1,1) and (2,2) inversion lines of ammonia (NH3) towards the dark cloud region containing the Herbig-Haro (HH) objects 24–27. These transitions are only excited at H2 densities >104 cm−3, and thus probe high density gas. From the observed hyperfine splitting one can calculate optical depths. The optical depth ratio can be used to determine the rotational temperature T21 which is equal to the kinetic temperature under dark cloud conditions.
A jet model of Herbig-Haro objects
Authors: Wilson M. J. , Falle S.A.E.G. , Innes D. E.
Published: June 2019

We present results of steady jet calculations in which the cooling and compression behind internal shocks leads to optical emission with an intensity pattern similar to the regular well-aligned emission knots characteristic of stellar jets.
Theory of winds from cool stars
Authors: Holzer Thomas E.
Published: June 2019

The goal of this paper is to provide a framework for thinking about the various physical processes that may play significant roles in driving the massive winds of cool, low-gravity stars. First, some general theoretical considerations involving mass, momentum, and energy balance are discussed. Next, the value of the solar wind as an analog for these late-type stellar winds and for related astrophysical flows is briefly examined. Finally, four specific mass-loss mechanisms are discussed, and the possible importance of each of these mechanisms for massive winds from cool, low-gravity stars is evaluated.
Chromospheric density distribution, opacity, ionization and windacceleration of 3 K supergiants in ζ aurigae systems
Authors: Schröder Klaus-Peter
Published: June 2019

Results from 58 chromospheric eclipse spectra of three ζ Aurigae type binary systems - with a K supergiant primary and a B star companion -taken with IUE at high resolution are presented. Curves of growth have been constructed at 20 phases using selected chromospheric absorption lines superposed upon the B star spectrum. In order to fit average density models to the chromospheres, 3 samples of column densities (for ζ Aur., 32 Cyg. (fig.1) and 31 Cyg. K giants) have been used.
Circumstellar shells of A-K luminous supergiants
Authors: Hinkle Kenneth H.
Published: June 2019

Infrared vibration-rotation bands of CO are ideal probes of the circumstellar environment of yellow supergiants. Results for a sample of stars are reviewed.
Evidence for stellar chromospheres in globular clusters
Authors: Liller William , Alcaino Gonzalo
Published: June 2019

We suggest that the conspicuous gaps frequently seen in the color-magnitude diagrams of globular clusters are caused by a sudden increase in chromospheric activity shortly after stars evolve away from the main sequence.
Evidence for extended chromospheres and transition zones in the uv spectra of FK comae stars
Authors: Bianchi L. , Grewing M.
Published: June 2019

The chromospheres and transition zones of the fast rotating giants of the FK Comae type can be studied by analysing their ultraviolet emission line spectra. From relative line intensities, electron densities of the order of 1010to 1011cm−1 are found for the region where the Si IV emission arises. The sizes of the chromospheres and transition regions can be inferred from the emission measure distribution, and a temperature-height relation can be found on the assumption that hydrostatic equilibrium holds. We find the atmospheres of these stars to be clearly more extended than those of normal giant stars, and the flux in the higher excitation chromospheric and transition zone lines (e.g. C II, C IV, Si IV) is significantly stronger than in other stars of similar spectral type. Indeed, the location of these stars in the standard rotation-activity-correlation diagrams places them close to or even above the saturation limit for main sequence stars.
Mira model photospheres
Authors: Scholz M.
Published: June 2019

The temperature stratifications and the emitted fluxes of Mira model photospheres based upon the extended density distribution of a pulsation model differ substantially from those of conventional model photospheres based upon a hydrostatic density distribution. Hence, the interpretation of Mira spectra by means of hydrostatic models is inadequate, and the spectral characteristics of Miras may deviate significantly from those of non-Miras.
Theory of winds from hot stars
Authors: Hearn A. G.
Published: June 2019

Mass loss from hot stars was first established by Morton (1967). He observed 3 OB supergiants, δ, ε and ζ Orionis, with an ultraviolet spectrograph sent up with a rocket. In the wavelength range of 1200 A to 2000 A he observed 6 resonance lines of highly ionized atoms such as C III, C IV, N V and Si IV. These resonance lines showed a P Cygni type line profile with an absorption component displaced to the blue corresponding to a velocity away from the stars of 1400 km s−1. Since the escape velocity from these stars is about 800 km s−1 these observations indicated the loss of mass from the stars. With rather simple assumptions he deduced a mass loss from the stars of 1 to 3 10−6 M⊙ yr−1. In spite of many more refined satellite observations and interpretations, the accepted value for mass loss from these stars has not changed by more than a factor of 2 or 3.
The 06.5 IIIf star BD + 60°2522 and its interaction with the surrounding interstellar medium
Authors: Chavarrîa-K. C. , Jäger C. , Leitherer C.
Published: June 2019

The luminous O-type star BD +60°2522 is embedded in the extended H II region S 162. Part of S 162 is NGC 7635, the striking spherically symmetric bubble nebula surrounding BD +60°2522. This star itself is unique in that it is the only known O star apparently associated with warm dust.
The behaviour of λ 4686 line of He II in Wolf-Rayet binaries
Authors: Shylaja B. S.
Published: June 2019

Being one of the brightest lines in emission in the optical region of Wolf-Rayet (WR) stars, the λ4686 line of He II has attracted the attention of many investigators (Sahade, 1958; Ganesh and Bappu, 1967). Here, the binaries with subgroup WN components have been chosen, with periods ranging from 1.64d to 21.63d, for understanding the effect of the companion on the formation of this line.
UV and optical spectroscopy of CH Cygni in 1980–86
Authors: Mikołajewska J. , Mikołajewski M. , Biernikowicz R. , Selvelli P.L. , Turło Z.
Published: June 2019

CH Cyg is a binary (P∼5750 days) consisting of a normal M6-7 giant and an unseen companion. During active phase its spectrum is similar to that of a symbiotic star - the strong B-A continuum and numerous low-excitation emission lines dominate the visual and UV spectrum. The last outburst, started in 1977, is conspicuous by the highest brightness level observed since monitoring begun in 1935. In mid 1984, a drop in brightness was accompanied by large continuum and emission line changes and correlated with a radio outburst and two expanding jets appearance (Taylor et al. 1985).
Evidence of a circumstellar dust cloudlet orbiting around the central star of NGC 2346
Authors: Costero R. , Tapia M. , Echevarría J. , Quintero A. , Barrai J.F. , Roth M.
Published: June 2019

The photometric behaviour of AGK3-0°965, the central star of the bipolar planetary nebula NGC 2346, has been monitored photometrically for several months at the Observatorio Astronómico Nacional at Tonantzintla and San Pedro Mértir, Mexico. A model is proposed in which the eclipses were caused by the passage of an elongated cool dust cloudlet of size ~ 2–5 × 1012 cm and total mass ~ 10−12 M⊙. This model can explain most of the observations. The velocity of the cloud in the direction of the major axis of the projected central binary orbit is vp = 0.14 km s−1. Another warmer (T ≲ 1000 K) circumstellar cloud is responsible for the infrared excess at wavelengths from 3 to 12 μm. Its emission, as seen from the Earth, has not changed significantly at λ > 3 μm during the past twelve years, as shown by new infrared observations also reported. Its most relevant physical properties are still to be determined. The present results provide the first evidence of a dense circumstellar cloudlet of mass similar to that of a minor planet which is probably the result of the fragmentation of a disk or toroid around the central star of NGC 2346. Although the presence of many other similar cloudlets in its vicinity is expected, the probability of similar events occurring in the next few hundred years is very small.

The details of the present work will be published in the Revista Mexicana de Astronomía y Astrofísica.
The dust envelope of IRC +10216
Authors: Ridgway Stephen T. , Peak Kitt , Keady John J. , Alamos Los
Published: June 2019

Infrared speckle measurements and photometry are used to assess the shape and thickness of the dust shell of the carbon rich Mira variable IRC + 10216. A spherically symmetric radiative transfer model has been developed to approximate the physical parameters.
Pulsar Polarization Limiting Radii and the Evolution of Pulsar Beams
Authors: Barnard John J.
Published: June 2019

We estimate the polarization limiting radius, rp1, as a function of rotation period P, magnetic field strength B, and radio frequency v, in radio pulsars assuming plasma parameters that are typical of polar-cap pair-creation models of pulsars. We find that rpl ⋍ 9 × 108(P/1s)0.4 cm, for a surface magnetic field strength of 1012 G, and radio frequency of 109 Hz. For short rotation periods, rpl approaches the light cylinder radius, rlc. Here the magnetic field becomes more azimuthal, and the excursion in position angle over a pulse is less, on average, than when rpl ≪ rlc. With the assumption of a vacuum magnetic field we calculate the polarization position angle as a function of pulse longitude, and the angles i (the angle between the magnetic moment and the rotation axis) and α (the angle between the line of sight and the rotation axis). We calculate the average change in polarization angle as a function of pulsar period, assuming a circular beam, and find consistency with the polarization data summarized by Narayan and Vivekand (1983). We conclude that the evidence is consistent with beams that are roughly constant in shape, providing an alternative to the evolving elliptical beam model of Narayan and Vivekand (1983). This interpretation is further supported by the frequency dependence of the polarization angle in the Crab Pulsar, the frequency of pulsars with double and multiple pulse components, the frequency of pulsars with interpulses, and the absence of pulsars in plerions. See Barnard (1986) for further details.
Observations of X-ray Burst Sources
Authors: Tanaka Y.
Published: June 2019

Recent observational results on X-ray bursts and burst sources are reviewed. Two distinct types of bursts, Type I and Type II bursts, are discussed in relation to the mass and radius of neutron stars and to the problems of unusual mass accretion in some burst sources.
X-ray Bursting Neutron Stars
Authors: Inoue H.
Published: June 2019

The maximum peak luminosity of the X-ray bursts from a burster is most likely interpreted as the Eddington luminosity of a helium-rich envelope surrounding a neutron star. If this interpretation is true, we can obtain a relation between the mass and the radius of the neutron star in terms of the maximum effective temperature of bursts. On the other hand, the most naive understanding of the origin of the 4.1 keV absorption line often detected in X-ray burst spectra gives us another relation of the neutron star mass with its radius. By solving two simultaneous equations, we can determine the values of the mass and the radius of the neutron star, respectively. However, the result is critical to every neutron star model currently considered.

The persistent emissions from X-ray bursters are also discussed.
An Inverse Compton Scattering Model for the Spectra of X-ray Pulsars
Authors: Qiao G.J. , Wu X.J. , Chen H. , Xia X.Y.
Published: June 2019

Many observations have been reported in the field of X-ray pulsars, but the mechanism for X-ray emission is not well understood. The X-ray spectra can not be simply described in terms of blackbody or thermal bremsstralung. The high-energy cutoff could be due to cyclotron absorption in high (≧1012 Gauss) magnetic fields. For the lower energy it can be fitted by a power law with energy index α.
X-ray Spectra and Atmospheric Structures of Bursting Neutron Stars
Authors: Ebisuzaki Toshikazu
Published: June 2019

High quality spectra of Japanese X-ray satellite TENMA permit us detailed studies of X-ray burst on color temperature vs. luminosity diagram. Using this diagram, Sugimoto Ebisuzaki and Hanawa (1984) divided bursts from MXB1636-536 into two classes: bright class and faint class. In the decay phase of bright class bursts, surface of neutron star should be covered with pure helium matter processed on the surface of neutron star because hydrogen-rich matter is completely lost due to mass loss. On the other hand, surface of neutron star should be covered by hydrogen-rich matter in the case of faint class bursts because any mass loss is not driven in the faint class bursts. I constructed color temperature vs. luminosity diagrams of X-ray burst sources MXB1636-536 and MXB1608-522 using data of Japanese X-ray satellite TENMA and found systematic deviations between evolutional paths of the bright class and faint class bursts on these diagrams. The deviations are successfully accounted for by the difference in chemical composition between bright class and faint class bursts: evolutional paths of bright class and faint class are respectively in good agreement with theoretical curves for pure helium and hydrogen-rich matter. This is a direct evidence of ejection of hydrogen-rich envelope in the bright class bursts.
On the Evolution of Magnetic Inclination with Age
Authors: Li L.S.
Published: June 2019

In this paper, the author studied the evolution of magnetic inclination with age for several pulsars. According to the results obtained by the author (1981), the formula for this evolution is given below

The evolutionary curves of magnetic inclination, calculated from this formula, for three pulsars — PSR 0525+21, PSR 0329+54 and PSR 1133+16 — are presented in Fig. 1.
Tortion Influence on the Magnetic Field of Rotating Neutron Stars
Authors: Zhang C.N. , Shi J.G. , Chen F.P.
Published: June 2019

Using the axisymmetric tortion tensor given by J. Nitsh in U4 gravitational gauge theory. Applying G. S. Yang and L. F. Luo's magnetic field model of neutron stars, i.e. magnetic field is originated from long-arranged neutron spin. Precession of spin coupled with tortion has been studied, indicating an influence on the magnetic field. The results show that the initial magnetic filed B made of long-arranged spin magnetic moment is at an angle of α with rotating axis, if radians, B makes a so small angle to the rotating axis at time 108 sec. that no pulses could be radiated from the neutron stars. Only when radians, the pulse radiation could be done. Based on the assumption that the orientation of the initial magnetic fields is isotropic, we can get then that only about ten percent of the rotating neutron stars radiate pulses.
Neutron Stars Formed from Supernova Explosion and Quark Matter
Authors: Li Y. C. , Kong X.J. , Wei C.W. , Ge Y.Z.
Published: June 2019

We study the possibility of the existence of quark matter during the early stage of hot neutron stars. According to Walecka (1978) and Shuryak (1980), we calculate the EOS of neutron matter and quark matter at different temperatures, T, in which we take the coupling constant αs to be 0.5 (Rafelski, 1982) and the bag constant B 1/4 to be 145, 170 and 190 Mev (Chin, 1978) due to a slight influence of αs and a great influence of B on our results. Supposing that neutron matter-quark matter phase transition is the first order phase transition (Baym and Chin, 1976), we obtain the phase transition pressures and densities at T = 3×1010 and 1012 K, respectively, from the relation between the pressure and the chemical potential. Then we try to determine the existence of quark matter thru the comparison of these densities with those of stable hot neutron stars.
Neutron Star Cooling and the Vela Pulsar
Authors: Nomoto Ken'ichi , Tsuruta Sachiko
Published: June 2019

We have calculated cooling models of young neutron stars.3 The theoretical cooling curves for several models are compared with the Einstein X-ray observations of young supernova remnants (Figure 1).
A High Resolution Far-UV Spectral Atlas of CSPNs and Hot White Dwarfs
Authors: Tweedy R.W.
Published: June 2019

A high-resolution IUE spectral atlas of central stars of planetary nebulae and hot white dwarfs has been produced (part of Tweedy, 1991, PhD thesis from the University of Leicester, UK), and examples from it are shown here. It has been sorted into an approximate evolutionary sequence, based on published spectroscopic analyses, from the cool 28,000K young central star He 2–138, through the hot objects like NGC 7293 and NGC 246 at 90,000K and 130,000K respectively, down to 40,000K DA white dwarfs like GD 2, which is the chosen cutoff for this selection. Copies of a revised version of this atlas, which will include more recent spectroscopic information and also white dwarfs down to 35,000K – to include the Si III object GD 394 – will be sent to anyone who requests one.
Energy Distribution of Planetary Nebulae (UV to Radio)
Authors: Zhang C.Y.
Published: June 2019

The past decade has seen significant progress in our understanding of spectral energy distribution of planetary nebulae over the entire wavelength range from UV to radio. In this review we show the detailed breakdown of the energy budget for a planetary nebula as a system of the three components, i.e., the central star, the gaseous nebula and the dust shell. This picture of the energy distribution is further discussed in the context of planetary nebula evolution.
Mean Electron Densities, Distances and Filling Factors for Galactic Planetary Nebulae
Authors: Kingsburgh Robin L. , Barlow M.J.
Published: June 2019

Mean electron densities are presented for over 100 planetary nebulae (PN). Distances to the majority of these PN are then derived, based on calibrations from observations of Magellanic Cloud PN. Absolute radii and filling factors have also been determined. A trend is seen in that for larger radii, smaller filling factors are found, however we show that such a trend results from uncertainties in the observed angular diameters.
Observations of the Bowen Fluorescence Mechanism and Charge Transfer in Planetary Nebulae I
Authors: Liu Xiao-Wei , Danziger John
Published: June 2019

Deep, medium resolution, long-slit spectrophotometric data have been taken for a number of high-excitation planetary nebulae, covering a wavelength range from 3100 Å to 7200 Å with some selected regions observed at higher resolution. For about half the objects, the whole optical region has been observed, from 3100 Å to 11600 Å. Accurate flux calibration is achieved over this whole wavelength range. These data allow a detailed quantitative study of the Bowen fluorescence mechanism and the charge transfer reaction in planetary nebulae, the primary goal of this program. In this paper measurements of O2+ Bowen fluorescence and charge transfer lines are presented. We show that LS coupling fails for the O2+ permitted transitions studied in this program and intermediate coupling may be a better assumption. Efficiencies of the Bowen fluorescence mechanism are derived for 15 objects, and a wide range of possible values is apparent. There is a remarkable linear positive correlation between the Bowen efficiency and the fractional abundance of oxygen in the ionization stage of O2+ and the fractional abundance of helium in the form of He+. Evidence that the Bowen efficiency is anticorrelated with the electron temperature, as first noted by Likkel and Aller, is established. The Bowen efficiency drops substantially when the nebular expansion velocity 2Vexp(O2+) > 55 km/sec. For lower expansion velocities there is no detectable correlation between these two quantities. There are no observable differences in Bowen efficiency among objects of different morphological type nor between objects excited by stars of different spectral types as suggested by Likkel and Aller.
Bowen Resonance Fluorescence Lines of OIII in Planetary Nebulae
Authors: O'Dell C. R. , Miller C. O.
Published: June 2019

New and published line intensities are used to test the role of the pumping of the Bowen Lines of O III by absorption of the O1 and O3 lines and population by Charge Exchange. Although general agreement is obtained, noticeable deviations from theory exist.
High Dispersion Spectra of Bright Planetary Nebulae
Authors: Hyung Siek , Aller Lawrence H.
Published: June 2019

The Hamilton Echelle Spectrograph at the coudé focus of the Shane 3 m telescope at Lick Observatory permits us to obtain high resolution spectra of bright planetary nebulae over the spectral range from 3500á to 10300á. Not only is it possible to separate pairs such as λ 5198, 5200 [NI], 4860 HeII and 4861 HI, but one may secure the profiles of Doppler broadened lines. It appears to be possible to separate the HI and HeI contributions of the 3889 line in Hu 1–2. The nebulae most suitable for observation are those of high surface brightness. NGC 7027 was the first nebula intensively studied with this equipment (Keyes et al. 1990); subsequently we have observed NGC 2440, 6537, 6543, 6567, 6572, 6741, 7009, 7662, IC 351, 418, 2149, 2165, 4634, 4997, 5217, Hb 12, and Hu 1–2. In NGC 7009 we measured line fluxes at the ends of major and minor axes. Small compact objects were centered on the slit; other were observed in the bright ring. These planetary nebulae cover a range in excitation level, chemical composition, and evolutionary status.
Extended Structures in the Planetary Nebulae He2-111 and He2-119
Authors: López J.A. , Tapia M. , Roth M.
Published: June 2019

He 2-119 is a bright, elliptical, planetary nebula of relatively large size (117 arcsec along the major axis and 74 arcsec along the minor one). Digital, unsharp masking CCD imaging of this object is presented, revealing a filamentary, nearly bipolar inner structure. In addition, the discovery of an extended, faint halo in this object is reported. The halo has a diameter of 208 arcsec and has a nearly circular form. He 2-119 thus becomes a new member of the group of planetary nebulae with halos. Its general characteristics are discussed.
CO Interferometric Maps of CIT 6 and CRL 618
Authors: Meixner M. , Welch W.J.
Published: June 2019

We present CO (1−0) interferometer maps of carbon star, CIT 6, and carbon rich proto-planetary nebula, CRL618. Both objects were mapped with the Berekeley-Illinois-Maryland millimeter array (BIMA). The resulting resolution is ∼ 4″ and structure larger than ∼1′ is completely filtered out. Two velocity resolutions were employed; 0.4 km s−1 and 0.8 km s−1 permitting a velocity coverage of 52 and 104 km s−1. We find evidence for non-spherical expanding envelopes in both objects. The interferometer detected all the single dish CO flux in CRL618 (840 Jy km s−1), and 70% of the CO flux in CIT 6 (or 1030 Jy km s−1). For CIT 6, we obtained single dish maps at the NRAO 12m to measure the zero spacing flux distribution. We measure an envelope diameter of 90″ (2.6 × 1017 at 190 pc) for CIT 6 and 15″ (4.5 × 1017 at 2 kpc) for CRL 618 and expansion velocities of 17 km s−1 for both. The small scale structure seen by the interferometer in CIT 6 has a core and an elongation to the SW. We interpret this elongation as the beginning of an equatorial density enhancement and predict that that CIT 6 will evolve into a bipolar planetary nebula. In CRL 618, the elongated structure seen in CO is perpendicular to the optical reflection nebula, which has an east-west orientation. Hence the Asymptotic Giant Branch (AGB) wind appears as an expanding waist band around this bipolar nebula giving credence to the idea that equatorial density enhancements in AGB winds produce bipolar planetary nebulae (Balick 1987).
Polarized Line Profiles in Planetary Nebulae
Authors: Walsh J.R. , Clegg R.E.S.
Published: June 2019

There is much direct and indirect evidence for the presence of dust in Planetary Nebulae (PN): variations in extinction across the face of the nebulae; IR emission with strong 25 and 60μm fluxes; broad near-IR emission lines of Silicate, SiC and PAH grains; optically thick lines, such as [C IV]1550Å, have lower strength on account of the increased path length due to dust scattering; a centro-symmetric pattern of polarization vectors in a few PN (Leroy et al., A&A, 160, 171, 1986). An observational programme has begun to study the polarization profiles of bright emission lines in PN arising from dust scattering within the nebulae. The first results are discussed.
Proto-Planetary Nebulae
Authors: Kwok Sun
Published: June 2019

The progress in the search for proto-planetary nebulae (PPN) in the last 5 years is reviewed. An observational definition of PPN is developed and a list of current PPN candidates is given. The optical, infrared, and radio properties of PPN are summarized and compared with theoretical models.
Basic Problems of Planetary Nebula Gas Dynamics
Authors: Dyson J.E.
Published: June 2019

Planetary Nebulae result from the interaction of fast winds and radiation fields with slow ejecta produced in the late stages of evolution of moderately low mass stars. We review the basic principles of the interaction and describe some of the modifications needed to produce realistic models for comparison with observational data. The present status of numerical modelling is discussed and some important problems outlined.
10μM Images of AGB Stars & Supergiants
Authors: Skinner C. J. , Hawkins G. , Meixner M. M. , Jernigan J. G. , Arens J. F.
Published: June 2019

We present mid-IR and far-IR images of a variety of AGB stars and red supergiants. The mid-IR images were all taken with the Berkeley/Livermore mid-IR array camera, which employs a 10 × 64 pixel Hughes photoconductor. All the images reported here were taken using a 10% bandpass CVF, at various wavelengths in the 10μm atmospheric window. These were supplemented by IRAS images, some constructed from survey scans, others made as Additional Observations during the pointed phase of the IRAS mission. We have so far observed 11 such sources with our mid-IR camera, and report here that only two of them (R Aql and V Hya) appear to be unresolved.
Planetary and Proto-Planetary Nebulae in the IRAS Two-Colour Diagram
Authors: García-Lario P. , Manchado A. , Pottasch S.R.
Published: June 2019

We present a study of the distribution of post-AGB stars and planetary nebulae (PNe) in the IRAS two-colour diagram. From the analysis of the distribution of spectral types of post-AGB stars in this diagram we conclude that the position at which a star leaves the infrared sequence of colours observed in AGB stars depends only on the initial mass of the progenitor star. The evolution after the end of the AGB phase takes place, in a first approximation, at a constant value of [25] – [60].
Dust Driven Mass Loss from Pulsating AGB-Stars
Authors: Dorfi E.A. , Feuchtinger M.U. , Höfner S.
Published: June 2019

A new numerical method allows an acurate calculation of the radiation hydrodynamics of time dependent stellar winds including also the radiation pressure on newly formed dust grains. The numerical procedure is based on an adaptive grid which distributes the grid points at locations of large gradients. All equations are written in conservation form and a monotonic 2. order transport scheme is used to advect the physical variables through the cell boundaries. We are able to resolve the shock waves running through the stellar atmospheres. These waves are generated by a pulsating star which is simulated by a moving piston. The following plots show the radial velocity and temperature structure of an extended atmosphere and several shock waves are clearly seen. Note that the innermost shock waves is a so-called supercritical shock where the radiative cooling zone behind the wave is clearly visible. The outer waves are almost isothermal because the material is optically thin in this region. The stellar parameters of this example are given by M = 1.2 M⊙, L = 5315L⊙ and R = 270R⊙ and the period of the moving piston is fixed at 350 days yielding a massive and slow wind with a mass loss rate of · = 1.24 10−6M⊙ yr−1 and a final velocity of v = 7.7 km s−1.
Echelle Measurements of the Expansion Velocities of the Faint Giant Haloes of Planetary Nebulae
Authors: Bryce M. , Meaburn J. , Walsh J.R.
Published: June 2019

The faint, giant haloes observed in many Planetary Nebulae (PNe) are believed to be the remnants of the superwinds ejected by the progenitor asymptotic giant branch stars. Spatially resolved, high spectral resolution observations of [OIII]5007Å line profiles from the haloes of NGC 6543 and NGC 6826 have been obtained with the Manchester echelle spectrometer at the Isaac Newton Telescope. The widths of the observed profiles from NGC 6826 decrease towards the outer edge of the halo which implies a definite radial expansion of this halo. The expansion velocities vexp of the two haloes are derived using both thick and thin shell models.
The Abell 35-Type Planetary Nuclei
Authors: Bond Howard E. , Ciardullo Robin , Meakes Michael G.
Published: June 2019

The nuclei of the low-surface-brightness PNe A 35, LoTr 1, and LoTr 5 are binaries containing rapidly rotating late-type subgiants or giants and extremely hot (Teff ≳ 100,000 K) companions detected by the IUE satellite. All three objects show low-amplitude, periodic photometric variations in the optical band (with periods of 0.76 or 3.3, 6.6, and 5.9 days, respectively).
The Environs of Supernova Precursors
Authors: Tsiopa O.A.
Published: June 2019

A high activity of a precursor during the last years of its existence can be connected with a close binary system orbit changing.
A Search for Optical-UV Fading of Central Stars
Authors: Altner B. , Heap S.R.
Published: June 2019

We derive estimates of the masses of planetary nebulae central stars (CSPN), based on their rate of optical-UV fading.