bluuebunny/crossref_metadata_2025 huggingface dataset:
The first eight years of radial velocity studies at Fick Observatory
Authors: Beavers W. I. , Eitter J. J.
Published: June 2019

The stellar radial velocity (RV) observations collected during the first eight years (1976–1984) of operation of the Fick Observatory photoelectric RV spectrometer have been tabulated for publication (Beavers and Eitter, 1986). Included are 16,000 observations of over 2,000 late-type stars. For these observations at the coudé focus of the 61 cm telescope the velocity zero-point is virtually the same as that for the early Lick radial velocity survey (Campbell and Moore, 1928), i.e. Lick-Fick = −0.08±0.08 km/sec. The zero-point comparison for DAO spectrometer measurements is DAO-Fick = −0.54±0.05 km/sec. During the last four years of this study the error of the “high quality dip” observations is ±0.8 km/sec. Thirty-three of these stars have been selected for use as future bright (m < 7.0) velocity standards at Fick Observatory.
Radial velocity spectrometers on the Dominion Astrophysical Observatory 1.2m and 0.4m telescopes
Authors: Fletcher J. M. , McClure Robert D.
Published: June 2019

A photoelectric radial velocity spectrometer has been in operation for several years at the coudé focus of the 1.2m telescope of the Dominion Astrophysical Observatory (DAO). The design of this instrument has been described by Fletcher et. al. (1982) and by McClure et al. (1984). These papers discuss the similarities and differences between this spectrometer and others of its type such as that constructed by Griffin and Gunn (1974) at Palomar. The spectrum mask in the present instrument consists of more than 700 transparent slots on an opaque background, representing the spectrum of a K giant star, plus a few slots to coincide with the argon lines in a cadmium-argon discharge tube for use in obtaining comparison arc velocities. By progressively tilting the slots an appropriate amount along the mask and scanning by moving the mask relative to the stellar spectrum at 45° to the dispersion it is possible to retain a spectral match at non-zero velocities. The masks are produced using a standard measuring engine modified with stepping motors controlled by a computer to position and tilt the slots. Since guiding errors are our major source of error we hope to make a significant improvement in this area in the following manner. By inserting an image rotating prism behind the slit a 180° rotation of the slit will occur when the prism is rotated. Although this has not yet been tested, it is hoped that by making this rotation every few scans the effects of guiding errors due to uneven illumination of the slit and collimator will be vastly reduced.
An Experimental Study of the Products of Dissociative Recombination of Molecular Ions with Electrons
Authors: Vallée F. , Gomet J.C. , Rowe B.R. , Quéffelec J.L. , Morlais M.
Published: June 2019

A new experimental method has been developed which allows determination of the products nature in dissociative recombination (D.R.) of molecular ions. Results are presented on H2O+ D.R. which show that there is a large yield of oxygen atoms in this reaction. the measurements give a total yield for the two channel O + H + H and O + H2 of 0.45 and therefore a yield of 0.55 for OH + H. H2O+ ions are formed by charge exchange from N+ ions and are probably vibrationally excited in this experiment.
Collision-Induced Rotational Excitations of Interstellar Molecules due to He and H2
Authors: Kurtadikar M. L. , Mehrotra S. C.
Published: June 2019

An Effective Straight-line Trajectory (EST) approach by introducing a parameter RX has been proposed for computations of collision-induced rotational line widths (HWHM) and excitation rates in case of atom-molecule systems under the frame work of Smith, Giraud and Cooper (1976) and molecule-molecule systems under the frame work of normalized semi-classical perturbative approach. An optimised parameter RX, which is a measure of significance of the curved trajectories of the colliding molecules, can be determined from the temperature dependence of collision-induced line widths. the EST approach has been tested for HCl-Ar system and further applied to X-He and X-H2systems of interstellar interest, where X represents interstellar molecules CO, OCS and HCN. The results are given in Table I and II.
Laboratory and Astronomical Spectroscopy of Reactive Hydrocarbons
Authors: Vrtilek J. M. , Thaddeus P. , Gottlieb C. A.
Published: June 2019

The rotational spectra of C3H2, C3H, and C2D, molecules not previously studied, were investigated in a continuing program of mm-wave spectroscopy in space and in the laboratory of hydrocarbons of astrophysical interest. Laboratory measurements producing reactive species in a DC glow discharge through organic gases have been essential to the identification of these species.
Intercombination Transitions between Levels X1Σg+ and A 3Πu in C2
Authors: Le Bourlot J. , Roueff E.
Published: June 2019

We present a new calculation of intercombination transition probabilities between levels X1Σg+ and a 3Πu of the C2 molecule. Starting from experimental energy levels, we calculate RKR potential curves using Leroy's Near Dissociation Expansion (NDE) method; these curves give us wave functions for all levels of interest. We then compute the energy matrix for the four lowest states of C2, taking into account Spin-Orbit coupling between a 3Πu and A 1Πu on the one hand and X 1Σ+g and b 3Σg− on the other. First order wave functions are then derived by diagonalization. Einstein emission transition probabilities of the Intercombination lines are finally obtained.
On the Mechanism of H2 Formation in the Interstellar Medium
Authors: Pirronello Valerio
Published: June 2019

The problem of the formation of molecular hydrogen in interstellar clouds is revisited. the role played by cosmic ray bombardment under certain circumstances is considered mainly in the light of the low formation rate of H2 on grains due to the reduced mobility of adsorbed H atoms on their amorphous surfaces at interstellar temperatures.
New Constraints on Diffuse Interstellar Cloud Models. The Model of the ζ Ophiuchi Cloud Revisited
Authors: Viala Y. P. , Abgrall H. , Roueff E.
Published: June 2019

Using most recent observational data as well as new experimental and theoretical determinations of various reaction rate coefficients, we present a model of the ζ θphiuchus cloud. the radiative transfer equation is solved in a plane parallel geometry taking into account absorptions by both the gas and by dust. A part certain atypical molecules (CH+, CN) and neutral iron, we are able to reproduce the observed column densities of neutral atoms, and molecular species, including the rotational populations of molecular Hydrogen with a two shell model. the concentrations of other simple molecules are predicted.
Probability for the Formation of Complex Ring Molecules in Interstellar Medium and their Detection Proposal
Authors: Ghosh K. K.
Published: June 2019

the pathways for the formation and destruction processes of ring molecules in interstellar medium have been proposed and their abundances have been calculated under steady state conditions and calculated abundances are of the order of 10−12 n(H), where n(H) is the abundance of hydrogen. Also their detection proposal has been presented.
Hydrostatic Models of Molecular Clouds: Comparison of Equilibrium and Time dependent Chemistry
Authors: Boland Wilfried
Published: June 2019

The chemical evolution of gas and dust flowing in a molecular cloud from the outer layers to the centre according to a circulation model is studied by calculating the chemical rate equations and the heavy element depletion time-dependently. the cloud structure and the circulation velocity are discussed in paper I (Boland and De Jong, 1984, Astron. Astrophys. 134, 87). We assumed that the circulating matter is in pressure equilibrium with the surrounding gas at all depths into the cloud. In the outer parts of the cloud (AV 2) the gas is almost in chemical equilibrium because the chemical timescales are short compared to the circulation timescale. In the dense cloud cores the time required to convert C, N and O into molecular form becomes larger than the circulation time and the depletion time so that appreciable deviations from chemical equilibrium occur. Particularly the abundances of C, HC3N, H2CO, CH4 and C2H2 are significantly enhanced and those of CO, O2 and N2 are reduced compared with their equilibrium concentrations at the same depth. Comparison of the present results with those for chemical equilibrium circumstances presented in Paper I shows that the departures of chemical equilibrium affect the predicted column densities of H/T, H2CO and HC3N significantly. It appears that the time-dependent model can account for the HC3N column densities observed in L183 and TMC-1.
The Effects of Chromospheric Radiation on the Circumstellar Chemistry of Evolved Stars
Authors: Glassgold A. E.
Published: June 2019

The physical and chemical properties of the circumstellar envelopes of evolved stars are strongly affected by the interstellar radiation field. Other sources of UV radiation should be similarly effective, and some examples are nearby stars (including companions), chromospheres, and the central stars of planetary nebulae. We consider the particular case of Alpha Ori, which has a chromosphere and an extended CSE with a small dust to gas ratio. Its properties are dominated by the chromospheric and interstellar radiation fields. The most common species are neutral atoms and first ions, and the electron fraction is high throughout the entire CSE, i.e. at least 10−4. The abundances of neutrals peak in the outer CSE close to where the chromospheric and interstellar radiation fields are equal. An important application is KI, whose density has been measured by scattering. The theory predicts that the slope of the KI density should change from about −1.5 to −3.5 in the outer envelope, the exact values being determined by the temperature distribution. The mass loss rate implied by the KI density is of the order of 4×10−6 M⊙ yr−1.
Excitation Processes in Cometary Comae
Authors: Singh P. D.
Published: June 2019

Excitations of cometary NH and S2 molecules are discussed. Photodissociation and dissociative electron recombination processes may be sources of meta-stable nitrogen (2Po, 2Do) atoms in comets.
The Planetary and Interstellar Components of Meteorites: A Review
Authors: Marvin Ursula B.
Published: June 2019

Recent analyses show that, although most meteorites are collisional debris of asteroids, three meteorites collected on the Antarctic ice sheet were projected to Earth from the highlands of the Moon, and eight meteorites have chemical and isotopic compositions suggestive of derivation from Mars. Although meteorites are primarily of interest to planetary scientists for the abundance of clues they hold to the materials and processes that formed the Solar system, they have begun to engage the attention of astrochemists because of isotopic and mineralogical indications that they contain interstellar components. Although each individual observation to this effect is inconclusive, the body of evidence is becoming ever more persuasive. This paper reviews the main classes of meteorites and their probable sources, with special emphasis on components that appear to be exotic to the Solar system.
Effects of s-Process Branchings on Stellar and Meteoritic Abundances
Authors: Norman E. B. , Lesko K. T. , Crane S. G. , Larimer R. M. , Champagne A. E.
Published: June 2019

The level scheme and electromagnetic properties of 148Pm have been studied using 149Sm(d, 3He) and 148Nd(p, nγ) reactions. Combining these measurements with estimates for E2/M1 decay branching ratios leads to the tentative conclusion that 148Pmg,m are in thermal equilibrium during the s-process. The branch at 148Pm then leads to an inferred s-process neutron density of 3 × 108 cm−3.
Desorption Mechanism of Gases from Interstellar Grains and PAH Molecules
Authors: Léger A.
Published: June 2019

Many gases, including CO, should be condensed at the temperature of interstellar grains in the absence of efficient desorption mechanisms. We consider such mechanisms and find that impulsive heating by X rays and heavy cosmic rays (iron group) are the most efficient ones.

For CO rich mantles, we conclude that species as CO, N2, O2 and probably H2CO, NH3, H2O should be desorbed in most cases including dense and obscure regions. for mantles composed mainly of refractory ices (H2CO, NH3, H2O) we expect very little desorption.

The case of PAH molecules that may offer a larger surface for condensation than grains is also discussed.
Condensation and Molecular Abundances in Stellar Atmospheres
Authors: Tarafdar S. P.
Published: June 2019

Equilibrium calculation containing 211 species of 22 elements has been used to study the effect of condensation on molecular abundances as a function of temperature (T) and pressure (P). The condensation of 162 species are tested and 65 species in solar composition and 64 in a C-rich composition have been found to condense. The calculations show the expected result that the abundances of molecules containing condensable elements like Si, Al, Mg, Fe, Zr and Ti in solar composition and C together with above elements in carbon rich composition reduce significantly with condensation. Surprisingly, the abundances of molecules containing S, F and Cl in solar composition and O, S, F and Cl in carbon rich composition are enhanced with condensation but abundances of molecules containing CO like H2CO, HCO in carbon rich composition hardly varies.
Chemical Composition of Cometary Ice and Grain, and Origin of Comets
Authors: Yamamoto Tetsuo
Published: June 2019

The chemical composition of the ice and grains in a cometary nucleus is discussed by applying the condensation theory. The equilibrium condensation theory of a gas having the elemental abundances in the solar system is briefly reviewed. The composition of solids predicted by the equilibrium condensation theory is compared with that of the ice and grains in the nucleus; the latter is inferred from the observations of cometary molecules and grains. On the basis of the results of this comparison, a scenario for the formation history of comets is proposed, and discussion is given on the temperature and region of the primordial solar nebula where comets formed.
A Deep Spectral Survey on the 6-Meter Telescope
Authors: Afanas'ev V.L. , Dodonov S.N. , Lorenz H. , Terebizh V. Yu.
Published: June 2019

The observational program “Deep spectral survey of the selected sky areas” on the 6-meter telescope is described. Preliminary results for the central part of field SA57 are discussed. The spectrum of a QS0 with probable redshift z=3.87 is presented. The number of quasars per sq. degree is estimated to be 470–675 to B < 23 mag., which gives the same slope in the increasing number of QSOs with magnitude as in brighter samples.
An Emission-Line Galaxy Survey with the UK Schmidt Telescope
Authors: Kalafi M. , Savage A. , Good A.R. , Cannon R.D. , Yates M.G.
Published: June 2019

The use of objective prisms in conjunction with the large area coverage afforded by Schmidt telescopes provides a very powerful means of detecting large numbers of emission-line galaxies, and allows one to study their large scale distribution. An important question that has yet to be fully addressed is the relationship between the number-magnitude distributions of the normal field galaxy and emission-line galaxy populations. A comparison such as this would effectively probe the evolution with time of these active objects. For example, study of the distant (z = 0.458) cluster of galaxies associated with 3C 295 (Dressler & Gunn 1983) indicates that emission-line objects may have been far more numerous in the past than at present. As a preliminary investigation in advance of a larger project, we report here on a search for emission-line galaxies in four United Kingdom 1.2m Schmidt Telescope (UKST) objective prism fields.
Morphology of Isolated and Grouped Galaxies
Authors: Einasto Maret , Einasto Jaan
Published: June 2019

Most galaxies with UV-continuum avoid clusters of galaxies (Lipovetsky 1986). Until recently, however, it was difficult to compare spatial distribution of galaxies with UV-continuum with galaxies of other morphological types, since the number of galaxies with known distances was too small. Rapid accumulation of complete redshift samples in large areas of sky (Huchra 1985) makes such study now possible.
Seyfert Galaxies: Classification, Morphology, Observations at Optical Wavelengths, Environmental Factors
Authors: Osterbrock Donald E.
Published: June 2019

Recent optical work on Seyfert galaxies is summarized, particularly on their spectral classification, morphology, companions, and presence in clusters of galaxies. Their general continuity with QSOs and with Liners is emphasized. Methods of finding additional Seyfert galaxies and of assembling a complete sample for investigating the luminosity function of AGNs are also discussed.
The Structure of Galaxies and their Nuclear Activity
Authors: Afanas'ev V.L.
Published: June 2019

The structure of active galaxies is related to the activity of their nuclei. The activity of galaxies is known to be caused by the processes occurring in their central regions with sizes of less than 10 pc, luminosities of 1044 erg/s (exceeding by 3–4 orders of magnitude the typical values for normal galaxies), and masses not exceeding 1% of the total galactic mass.
Variable Objects in a Complete Sample of Faint Radio Sources
Authors: Altschuler D.R. , Forkert T.
Published: June 2019

Measurements of the 5 GHz flux densities of faint radio sources (S ~ 80 mJy) in a complete sample have been made at three epochs spanning a 15-year timebase. These measurements provide data for a statistical investigation of activity in faint radio sources. Here we report the results for some outstanding objects.
Radio Emission from Active Galactic Nuclei
Authors: Kellermann K. I.
Published: June 2019

Active Galactic Nuclei and quasars are characterized at radio wavelengths by a high surface brightness, a flat spectrum, variations in intensity on time scales of a few days to a few years, and by large internal motions which probably reflect Doppler beaming from a synchrotron source which is moving with relativistic velocity away from the central energy source and toward the observer. The observations do not support interpretations based on simple ballistic models where the observed motion and core strength depends only on the geometric orientation of a relativistic beam, but appear to require significant dispersion in intrinsic properties as well as complex dynamics.
Studies of the 3C 345 Quasar Structure at dm-Wavelengths
Authors: Matveyenko L.I. , Pauliny-Toth I.I.K. , Sherwood B. , Bååth L. , Kus A.
Published: June 2019

The structure of the quasar 3C 345 has been studied at 18 and 49 cm wavelengths by VLBI method. The structure has a nucleus and a jet, which changes direction with distance from the nucleus. The continuum emission of the nucleus and the jet regions correspond to a source with a large optical depth, the cut frequence goes down with increasing distance from nucleus.
Active Galactic Nuclei from the Extended Einstein Medium Survey
Authors: Gioia I.M. , Maccacaro T. , Schild R.E. , Wolter A. , Stocke J.T. , Morris S.L. , Danziger I.J.
Published: June 2019

This paper presents a progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS). The results obtained from the survey are briefly summarized, particular emphasis is given to the Active Galactic Nuclei (AGN) and BL Lac objects of the MSS. The basic properties of these classes of extragalactic objects are presented and discussed.
Bipolar flows and jets from stars of different spectral types: Observations
Authors: Cohen Martin
Published: June 2019

The fact that bipolar flows are widespread among stars of very different spectral types is emphasized. First, the stars associated with the phenomenon are divided into broad types: protostars and pre-main-sequence stars; red giants; symbiotic objects; protoplanetaries; planetaries; novae and cataclysmic variables; and peculiar hot stars. Second, the evidence for circumstellar “disks” or toroids is considered among these different categories of star. Finally, the possible role of binarity is discussed.
CO observations of gas surrounding B335 (IR) and L1551-IRS5
Authors: Walmsley C. M. , Menten K. M.
Published: June 2019

Recent submillimeter observations of infrared sources embedded in dark clouds have uncovered the existence of a few highly compact objects. Two examples of this phenomenon are the infrared sources observed towards B335 and L1551 (Keene et al. (1983), Davidson and Jaffe (1984)). One can estimate for these regions gas masses of approximately one solar mass, densities of at least 106 cm−3, and diameters less than 1017 cm. Both infrared sources are associated with bipolar outflows observed in CO with mass loss rates of order 10−6 solar masses per year. It is reasonable in both cases to suspect the existence of matter in some form of disc around the infrared source.

One might also expect to observe molecular counterparts to the submillimeter compact objects. In an effort to do this, we have mapped the C18O J = 1 → 0 transition in a small area surrounding the infrared sources in B335 and L1551 using the IRAM 30-m telescope. The beamwidth was 22 arc sec. which corresponds to 5 1016 cm at the distance of L1551 and 9 1016 cm at the distance of B335. In each case, we do find a compact structure which we believe to be the molecular counterparts of the compact submillimeter sources. We estimate the abundance ratio CO/H2 to be of order 10−4 in L1551 and at least 10−5 in B335. Further details of this work are contained in an article submitted to Astronomy and Astrophysics.
A model of molecular emission in bipolar flows
Authors: Cabrit Sylvie , Bertout Claude
Published: June 2019

We present a model of CO J=1→0 line formation in accelerated bipolar outflows. We find that the integrated intensity maps can be divided into four categories, depending on the view angle and the flow opening angle. We then show that no accurate values of the flow parameters can be derived from the CO observations without careful modelling of the outflow properties.
The naked T Tauri stars: The low mass pre-main sequence unveiled
Authors: Walter Frederick M.
Published: June 2019

I discuss a survey of X-ray sources in regions of star formation. The survey has revealed at least 30 low mass PMS, naked T Tauri stars (NTTS) in Tau-Aur, and a comparable number in Oph. I summarize the properties of these stars, and argue that the spectra of the classical T Tauri stars are due to the interaction of an underlying NTTS with a dominant circumstellar environment. I discuss the impact the NTTS are likely to have on our understanding of the PMS evolution of low mass stars.
Serpens-SVS 20: A new infrared double source
Authors: Eiroa C. , Lenzen R. , Leinert K. , Hodapp K.
Published: June 2019

0.9 μm CCD images and 2.2 μm slit scan observations reveal the double character of the infrared source Serpens - SVS20; the separation, position angle and brightness ratio are 1.″6, 10°, and Δm ≍ 1.6 mag respectively. The southern source is the brightest at both spectral ranges. At 0.9 μm the observed polarization of each component is p = 9.0 %, ⊙ = 155° and p = 10.4 %, ⊙ = 135° for SVS20-South and SVS20-North respectively. These results combined with 2.2 μm polarimetry and JHKLM photometry suggest that both SVS20 sources are in fact low mass, probably PMS, stars.
Observational tests of the bow shock theory of Herbig-Haro objects
Authors: Böhm K.-H. , Raga A. C. , Solf J.
Published: June 2019

We discuss four different tests of the bow-shock theory of Herbig-Haro objects, emphasizing especially tests based on position-velocity diagrams and on the appearance of “double layer” structures in the spatial maxima of the high- and low-velocity components of the emission lines. Though this latter effect is surprising, it is a fundamental consequence of the bow shock theory.
Detection of collimated bipolar mass flow in HH24
Authors: Solf J.
Published: June 2019

High-resolution long-slit spectroscopy of HH24 has revealed the presence of collimated bipolar mass flow originating from the “central” infrared source SSV63. The bipolar system consists of the well known jet-like HH24C (mean VLSR −190 km s−1 and a newly detected weak component, HH24E (~ + 170 km s−1).
Is there a signature of ice in the IRAS LRS spectra of some Mira variables?
Authors: Vardya M. S.
Published: June 2019

Some M Miras show the 9.7 and 20μm silicate emission. Recently, Vardya, de Jong & Willems (1986; hereafter VDJW) discovered using IRAS LRS spectra a weak broad emission feature ~12μm; this new feature may be silicate (VDJW). Here we investigate whether this can be due to H2O ice.
OH masers in envelopes of late type stars
Authors: Le Squeren A.M. , Sivagnanam P. , Minh F. Tran , Dennefeld M. , Foy F.
Published: June 2019

Two studies of OH maser emission in envelopes of late type stars -miras (3) and OH/IR objects- have been performed with the Nancay radio-telescope. Mainly, the OH miras are found with thicker dust envelopes than the non OH ones. A sample of unidentified IRAS point sources selected on their colors has been observed. We have detected 46 new OH sources. The OH detection rate is a function of the galactic longitude and of the IRAS spectral classification.
Circumstellar CaII lines in R Leo
Authors: Barbier M. , Mennessier M. O.
Published: June 2019

Qualitative results on the H and K CaII lines in R Leo are presented from spectra throughout all the cycle of this mira star. A scenario of explaining the observations by an outward Shockwave is proposed.
An extended nebulosity surrounding the S Dor variable R 127
Authors: Appenzeller I. , Wolf B. , Stahl O.
Published: June 2019

Using the CASPEC echelle spectrograph of the European Southern Observatory, La Silla, Chile, we obtained new high resolution spectrograms of the LMC S Dor variable R 127 in the blue and red spectral range.

The red spectrogram, which contains the [N II] 6548 and 6533 and the [S II] 6717 and 6731 lines shows the presence of a well resolved extended gaseous nebula around R 127 (see Figures 1 and 2). The nebula (which is also detected at the Balmer lines) shows blueshifted and redshifted emission (projected) on the position of the stellar continuum, and no wavelength-shift at the maximum (East-West) distance from the star. Hence, the nebulosity appears to be an expanding shell, reminiscent of the nebula around the galactic extreme supergiant AG Car. The angular diameter (or East-West extension) of the nebula around R 127 is of the order 4“, corresponding to ≈1 pc at the distance of the LMC. The expansion velocity of the R 127 nebula is found to be 28 km s−1 from our spectrograms. Hence, assuming a constant expansion velocity we derive a kinematic age of the R 127 nebula of ≈2 · 104 years. This corresponds closely to the expected lifetime of the S Dor evolutionary phase.

A more detailed description of our results will be published in the proceedings of the Workshop on “Instabilities in Luminous Early Type Stars” (C. de Loore, H. Lamers, eds.) Lunteren 1986.
The detection of a circumstellar shell around P Cygni by direct CCD imaging
Authors: Leitherer Claus , Zickgraf Franz-Josef
Published: June 2019

The star P Cygni (=HD 193237) is the proto-type of a class of stars with peculiar spectra, the so-called P-Cygni-stars (or Luminous Blue Variables). They are characterized by extreme mass-loss characteristics and wind densities surpassed only by the winds of Wolf-Rayet stars.
Dust formation in, and the structure of wolf-rayet stellar winds
Authors: van der Hucht K.A. , Williams P. M. , Thé P.S.
Published: June 2019

An infrared photometric survey of all 40 known galactic WC7-10 stars shows that around most of them hot amorphous carbon is condensing continuously at distances of about 8500 R⊙, well within the ionized stellar winds around these stars. Typical dust production rates are of the order of 10−7 M⊙/yr.
Upper limits for the effective temperature of Wolf-Rayet stars from the presence of He I
Authors: Schmutz W. , Hamann W.-R. , Wessolowski U.
Published: June 2019

A recently developed non-LTE code for realistic semi-empirical models of Wolf-Rayet atmospheres is used to calculate synthetic helium lines. From the resulting line strenghts it can be concluded that if He I lines are present, the effective temperatures of these stars have to be less than an upper limit. This limit depends on the stellar radius and is approximately 40kK for R* = 20 R⊙ to 60kK for R* = 5 R⊙.
Spectroscopy and polarimetry of the R Aquarii system
Authors: Schwarz Hugo E. , Aspin Colin
Published: June 2019

Optical spectroscopy is used to derive the electron temperature and density of the jet of R Aqr. We present polarimetric data which shows that the degree of polarization in R Aqr can vary by up to two orders of magnitude and that this variation is correlated with the phase of the Mira. The polarization angle also varies with the phase of observation.
Investigation of circumstellar shells by mid-infrared heterodyne spectroscopy
Authors: Schrey U. , Drapatz S. , Käufl H.U. , Rothermel H. , Ghosh S. K.
Published: June 2019

Heterodyne spectroscopy at 11 μm combines high spectral resolution (λ/Δ λ ~106), high spatial resolution (< 1 arcsec at 3 m telescopes) and high penetration depth. Therefore, it seems promising to use it also for the investigation of bright circumstellar atmospheres.
Temperature distributions in circumstellar dust shells
Authors: Henning Th. , Gürtler J.
Published: June 2019

The knowledge of the temperature distribution in circumstellar dust shells (CDS) is needed for both the calculation of the emergent IR spectrum and the modelling of physical processes, e.g. dust formation.
The Relation Between Radio Luminosity and Magnetic Field in Rotation-Powered Pulsars
Authors: Pineault Serge
Published: June 2019

The relationship between radio luminosity L and magnetic field B is re-investigated under the assumption that the new spindown mechanism proposed by Huang et al. (1982) becomes dominant at large periods (P ∝ P2). Magnetic dipole braking is still assumed to provide the main torque at short periods (P ∝ P−1). Both spindown torques depend on B2 (assuming proportionality between internal and external fields) so that the resultant magnetic field in this hybrid model is given by (note the difference with the standard expression):

A value of 3.6 is used for γ (Pineault 1986). For the radio luminosity we use the values tabulated by Manchester and Taylor (1981).
A Massive Glitch in PSR 0355+54
Authors: Lyne A.G.
Published: June 2019

Pulse timing observations at Jodrell Bank have shown that the relatively old pulsar PSR 0355+54 has suffered two glitches in the last 18 months, the second glitch being larger than any previously observed in any pulsar.
Crab-Like Supernova Remnants
Authors: Becker R.H.
Published: June 2019

Crab-like SNR are markers for recently formed pulsars. The current catalog of 15 objects allows a direct measure of the space distribution of pulsars, the beaming factor of pulsars, and the energetics at young pulsars. The 15 Crab-like SNR are equally divided between those with surroundings shells and those without. No other properties appear to correlate with the presence or lack of a shell. The ratio of 10 to 1 between all remnants and Crab-like remnants has important implications for the formation of pulsars.
Distribution of Two Types of Pulsars in Comparison with that of SNRs
Authors: Sun H. , Li Z.W.
Published: June 2019

Recently, pulsars are classified into two types. On the basis of these data, it is possible to discuss the relation between these two types of pulsars and supernova remnants, respectively. In this paper, the statistical K-S test is used to judge whether the two samples of distributions may come from one original distribution or not.
Results of the Timing Analyses of X-ray Pulsars Observed by Hakucho and Tenma
Authors: Nagase F.
Published: June 2019

A dozen of X-ray pulsars have been observed with the Japanese X-ray astronomy satellites Hakucho and Tenma between 1979 and 1984. The obsetvations revealed remarkable pulse period changes both in disk-fed and wind-fed pulsars. From the histories of the pulse period changes so far measured, we are able to classify the X-ray pulsars into three categories:

(1)

Pulsars which exhibit a steady spin-up with a constant rate of period change (e.g., 4U 1626-67 and GX 1+4).

(2)

Disk-fed pulsars in which considerable period changes are superposed on the secular trend of spin-up (e.g., Her X-1 and Cen X-3).

(3)

Wind-fed pulsars whose pulse periods fluctuate randomly about the average pulse period on time scales from days to years (e.g., Vela X-1 and GX 301-2).

Among the dozen X-ray pulsars observed by Hakucho and Tenma, Vela X-1 was most extensively studied. Timing studies of Vela X-1 revealed an episode of secular spin-down of the pulsar between 1979 and 1982, and large rates of short-term period fluctuations superimposed on the secular trend. Recent studies of the wind-fed pulsar suggest that the angular momentum transfer expected from the wind accretion is too small to account for the observed rates. Spectroscopic studies of Vela X-1 by Tenma observations provided a variety of phenomena related to the binary system and detailed properties of matter surrounding the system, especially using an iron emission line fluoresced thereby as a probe.

Formation of a disk in the wind-fed pulsar is proposed to accommodate a variety of phenomena observed from Vela X-1. A disk is expected to be formed through the interaction of the spherically accreting matter with the rotating magnetosphere, under the assumption that the closed magnetosphere extends to the corotation radius. Application of this model to Vela X-1 requires a large magnetic moment of μ ≈ 1032 gauss cm3 (1013 ≲ B ≲ 1014 gauss, depending on the stellar parameters), but once the large value is accepted, this model fits well with the large rates of period change and phenomena which would otherwise be regarded as strange. If this model works for Vela X-1, it will be also applied to some of other wind-fed pulsars.
Neutron Star Formation in Theoretical Supernovae — Low Mass Stars and White Dwarfs —
Authors: Nomoto Ken'ichi
Published: June 2019

The presupernova evolution of stars that form semi-degenerate or strongly degenerate O+Ne+Mg cores is discussed. For the 10–13 M⊙ stars, behavior of off-center neon flashes is crucial. The 8–10 M⊙ stars do not ignite neon and eventually collapse due to electron captures. Properties of supernova explosions and neutron stars expected from these low mass progenitors are compared with the Crab nebula. We also examine the conditions for which neutron stars form from accretion-induced collapse of white dwarfs in close binary systems.
Ancient Guest Stars as Harbingers of Neutron Star Formation
Authors: Wang Zhen-Ru
Published: June 2019

It was just after the discovery of neutrons in 1932, Landau suggested the possibility of compact stars composed of neutrons. In 1934 Baade and Zwicky proposed the idea of neutron stars independently and suggested that neutron stars would be formed in supernova explosions.
Millisecond Pulsar Formation and Evolution
Authors: van den Heuvel E.P.J.
Published: June 2019

The evolutionary history of binary radio pulsars, including the two millisecond binary pulsars, is reviewed. There are two groups of binary pulsars, the PSR 1913+16-group, which descended from massive X-ray binaries, and the PSR 1953+29-group, which descended from fairly wide low-mass X-ray binaries. The neutron stars in the second group probably formed by the accretion-induced collapse of a massive white dwarf. The companion stars in both groups of systems are expected to be dead stars, i.e. white dwarfs or neutron stars.

The large total number of millisecond binary pulsars in the galaxy (∼ 104), indicates that magnetic fields of neutron stars do not decay below a value of order 109 G. Possible explanations for this phenomenon are discussed.

Coalescence with a close degenerate companion provides a viable model for the formation of the single millisecond pulsar.
Modes of Energy Loss from Isolated Magnetized Neutron Star
Authors: Shibata S.
Published: June 2019

Pulsar may be regarded as a discharge tube by electron-positron pair creation. On this viewpoint we carry out two numerical calculations. The obtained magnetic field is consistent with the flow. We find that pulsars emit their rotational energy through three modes simultaneously. The three modes are (1)relativistic acceleration and following gamma-ray emission in the closed current circuit in the magnetosphere, (2)wind of the electron-positron pair plasma, and (3)dipole radiation.
Effects of Magnetization on Structure Parameters of Neutron Stars
Authors: Wang Q.M. , Gao S.H.
Published: June 2019

We took the magnetic susceptibility χ as a criterion in this study and supposed that the system of neutron matter has a ferromagnetic transition as 1/χ 0. The magnetic susceptibility of pure neutron matter at zero temperature was calculated by means of Owen's lowest order constraint variation method. The following results were obtained: if the interaction between neutron and neutron was the Reid soft-core potential, then no transition to ferromagnetic state was found to occur; if the interaction was HJ, IY potentials, the neutron matter would undergo a transition. These results indicate that the existence of ferromagnetic state depends on the form of potentials. If the interaction between particles is attractive, it will not profit the existence of ferromagnetic state, while the interaction between neutrons has a repulsive core, it will profit the existence of ferromagnetic state. We also calculated the equation of state and structure parameters of neutron stars. It showed that the energy of ferromagnetic state is lower than that of nonferromagnetic one and the ferromagnetic state is more stable. In other words, the ferromagnetic state may exist in neutron stars. We can readily find that ferromagnetic state has some influence on structure parameters of neutron stars, the magnitude of this effect depends on the form of potentials and the values of these structure parameters with ferromagnetism are within the allowed range. In this paper, the possibility existing the ferromagnetic state has been dsicussed. By a rough estimate, the magnetic field strength coming from the complete ferromagnetic state is about 1015 Gauss at ρ ∼ 1015 g/cm3. We assume that this is a possible origin of the strong magnetic fields in neutron stars. If there exists a ferromagnetic state in neutron stars, it will have a substantial influence on the gravitaional collapse theory, neutron superfluid and proton superconductivity.
A Review of Gamma-Ray Burst Observations
Authors: Evans W. Doyle , Laros John G.
Published: June 2019

Gamma-ray bursts are generally believed to originate in the vicinity of neutron stars, but the phenomenology is still not understood. In this paper we review the known characteristics of gamma bursts and give new observational results on temporal and spectral properties. We suggest that a class of repeating bursters exists that are spectrally harder than x-ray bursters but significantly softer than “classical” gamma bursts. The March 5, 1979, burst may be the prototype of this class of bursters.
The Origin of the Enhanced Dissipation “α” in Accretion Discs and its Relation to Gamma Bursts
Authors: Colgate Stirling A.
Published: June 2019

The source of the enhanced dissipation or “α” viscosity of Keplerian accretion discs is central in all putative mechanisms for large energy release by matter accreting onto condensed objects and for the basic mechanism of star formation. The circumstances of gamma burst formation on neutron stars suggest convective buoyancy as a necessary condition for the large α. This is because the total mass ≅ 1019 g necessary to supply the energy of a gamma burst derived from infall is a natural limit for the mass stored in a disc without α viscosity. This suggests that buoyancy driven convective turbulence is the source of the enhanced transport in disc evolution models (Shakura and Sunyaev 1973). In support of this conjecture we find that the maximum possible energy released by ideal friction operating on the velocity shear of a disc is twice that required to destabilize the angular momentum distribution of such a disc. The heat energy available from an α viscosity is twice that necessary to create α in the first place. Hence, a nonlinear instability–nonlinear to create convective turbulence and nonlinear to create shear viscosity heating–is sufficient to drive α. One characteristic that would prevent the formation of such an instability is degeneracy of the disc matter as it accumulates near a neutron star (Paczynski and Jaroszynski 1978). Degeneracy inhibits strong convection because a given energy release within degenerate matter results in a large temperature, and hence large energy transport without convection. Convection occurs in an accretion disc whenever the energy which is dissipated in the disc requires a superadiabatic temperature gradient for its radiative or conductive transport to the surface. Some gamma burst mechanisms require exactly such a mechanism as a degenerate disc close to the neutron star in the correct mass (≅ 1019 g), at the correct radius several times the neutron star radius, to supply gravitational energy for a gamma burst. The degenerate disc accumulates mass stably until the density is great enough that degenerate fluid viscosity evolves the disc into contact with the neutron star. The large energy released by velocity shear at contact heats the disc causing rapid evolution and a gamma burst.
Cosmic Ray Particle Acceleration in Pulsar Magnetospheres
Authors: Thielheim K.O.
Published: June 2019

A plausible approach to the theory of pulsars as cosmic ray particle accelerators is to integrate numerically the Lorentz-Dirac-equation, using the vacuum field of a rotating orthogonal magnetic dipole as a model field configuration. Typical parameter values are: angular velocity ω = 20 π/sec and magnetic dipole moment μ = 1030G cm3 (K.O. Thielheim, Proc. ESO-CERN Conf. 1986).
Where Neutron Stars Come From, How Neutron Stars Evolve, and Neutron Stars Go
Authors: Woltjer L.
Published: June 2019

At the end of this symposium, I shall briefly review our current knowledge on neutron stars.
New and Misclassified Planetary Nebulae
Authors: Kohoutek L.
Published: June 2019

This fourth supplementary list to the CGPN (Perek, Kohoutek, 1967) contains 81 new objects (Table 1) which were published mainly between 1987 and 1990. We did not include as new PN those objects, which are in a transition phase between AGB and PN (no emission lines), and possible post-PN namely objects having central stars on the evolutionary way to WD and without nebulae. The possible pre–PN are summarized in a separate incomplete list as an Appendix to Table 1.
Luminosities of Central Stars of PN in the Galactic Bulge
Authors: Méndez R. H.
Published: June 2019

A calibration of the nebular intensity of [O III] 5007 (relative to Hβ) in terms of stellar bolometric corrections is presented. This calibration (restricted to low- and medium-excitation PN) is based exclusively on the results of non-LTE model atmosphere analyses of absorption-line profiles in the spectra of bright central stars of PN (Méndez et al. 1988, A&A 190, 113 and subsequent papers). Knowing the bolometric corrections, the distance to the Galactic center, the amount of interstellar extinction and the visual apparent magnitudes (Tylenda et al. 1989, A&AS 77, 39) of central stars of PN in the direction of the Galactic center, luminosities for 20 of these central stars are obtained without any assumptions about nebular properties. The luminosities obtained with this method are substantially higher than those obtained for the same objects by Pottasch and Acker (1989, A&A 221, 123) and Tylenda et al. (1991, A&A 246, 221). The most probable explanation for this discrepancy is that luminosity estimates based on assumptions about nebular properties are too low, because many PN are not completely optically thick in the H Lyman continuum and/or because many ionizing photons in these PN are being absorbed by nebular dust. Which of the two effects is more important cannot be decided without solving the problem of the discrepancy between extinction determinations based on the Balmer decrement versus extinction determinations based on radio and Hβ fluxes (the radio-Hβ extinctions are too low).
Infrared Emission-Lines and the Stellar Temperature
Authors: Viegas Sueli M. , Gruenwald Ruth
Published: June 2019

Observations of near infrared emission-lines are becoming available and can be a powerful tool to improve our knowledge on planetary nebulae properties. For wavelengths in the range 1 to 5 μm, the emission-lines correspond to atomic transitions of high ionized species of heavy elements. In particular, the [Si VI] 1.96μm and [Si VII] 2.48μm lines have already been detected (Ashley and Hyland, 1988).
Stark Broadening Parameters of C IV Lines for Stellar Plasma Research
Authors: Dimitrijevic M.S. , Sahal-Brechot S.
Published: June 2019

In order to complete available C IV broadening data needed for stellar plasma research, we have calculated Stark broadening parameters for 69 C IV multiplets of large principal quantum number. The results along with a discussion of the Stark broadening parameter regularities within spectral series will be published elsewhere (Dimitrijevic and Sahal–Brechot, 1992). As an example in Figs 1 and 2 the case of C IV np2P0 − 9s2S transitions, is presented. We can see that particularly for shifts the changes of Stark broadening parameters are relatively small, permitting the interpolation of new data or critical evaluation of mutual consistency of existing data.
MBPT Results for Δn=0 Electric Dipole Transitions
Authors: Gaigalas G. , Kisielius R. , Merkelis G. , Rudzikas Z. , Vilkas M.
Published: June 2019

To identify spectra of Planetary Nebulae which usually have many atomic lines one needs very accurate theoretical atomic data.
Ring Nebulae Around PN Nuclei and Massive Stars
Authors: Chu You-Hua
Published: June 2019

Planetary nebulae (PNe) and ring nebulae around massive stars are not just superficially similar in morphologies. For massive stars that evolve through red supergiant phase, the final fast wind would sweep up the slow red supergiant wind and form a bubble of stellar material, reminiscing the two-wind formation of a PN. Sometimes it can be really difficult to determine whether the central star of a ring nebula is a PN nucleus or a Pop I massive star. Parallel studies of PNe and ring nebulae around massive stars can greatly benefit each other.
Photodissociation Regions and Planetary Nebulae
Authors: Tielens A.G.G.M.
Published: June 2019

FUV photons (<13.6eV) from the central star create a region of warm (≈1000K) atomic and molecular gas around Planetary Nebulae (PN). This paper reviews theoretical and observational characteristics of such regions, commonly called photodissociation regions or PDRs. PDRs around PN differ in some aspects from those in other galactic objects and this is briefly discussed with an emphasis on time dependent effects. It is concluded that, in evolved PN (texp>103 yr), molecules will only survive inside dense clumps (>106 cm−3). H2 emission from such dense gas will show a thermal spectrum in the low v states. Finally, the physical conditions in the PDR associated with NGC 7027 are compared to those in other galactic and extragalactic PDRs