bluuebunny/crossref_metadata_2025 huggingface dataset:
P Cygni Type Stars: Evolution and Physical Processes
Authors: Lamers Henny J. G. L. M.
Published: June 2019

The class of P Cygni Type (PCT) stars is defined and the brightest members in our galaxy, LMC, M31 and M33 are identified. They are located near the upper luminosity limit in the HRD in the range of 8500 ≤ Teff ≤ 27,000 K and −11.0 ≤ Mbol ≤ −7.8. We suggest that all PCT stars are S Dor variables, and that the reverse may also be true. The basic parameters of the PCT stars are derived and compared with those of normal supergiants: the effective gravity is a factor 3 to 10 lower, the mass loss rate is a factor 3 to 10 higher, the terminal velocity is about a factor 10 lower. This results in a wind density which is a factor 30 higher and thus produces the P Cygni lines in the visual spectrum. The history and the physical processes in the star P Cygni are discussed. The photometric variability and the shell ejections on a timescale of about a month are probably due to non-radial pulsations. The acceleration of the wind is due to radiation pressure by numerous (∼103) metal lines in the Balmer continuum. This can also explain the S Dor type of variability. The proposed mechanism will automatically lead to a P Cygni phase in the evolution of the most massive stars and to the existence of an upper limit in the HR diagram. The expected lifetime of the PCT phase is about 104 to 105 years. Some unresolved problems and recommendations for future research are discussed.
Optical and Ultraviolet Spectral Morphology of Luminous OB Stars in the Galaxy and the Magellanic Clouds
Authors: Walborn Nolan R.
Published: June 2019

Three areas of current progress relevant to the theme of this Symposium will be discussed. (1) New spectroscopic observations of the 30 Doradus central cluster, obtained independently by the author and by J. Melnick, confirm the presence of numerous very early O-type members, including several of type O3. In combination with sophisticated new direct imagery of the luminous central object R136 by A. Walker and by G. Weigelt, these results have evident implications for understanding the ionization of the supergiant H II region, as well as for the interpretation of R136 itself and of the apparently similar regions seen in more distant galaxies. In particular, no evidence remains for a supermassive object in 30 Doradus, but its central cluster is revealed as a spectacular grouping of very massive hot stars. (2) A further member of the Ofpe/WN9 category in the LMC has been identified, bringing their number to seven, with no exact spectroscopic counterparts yet known in the Galaxy. One of these objects is currently in a state of outburst and has been interpreted by O. Stahl et al. as the hottest known Hubble-Sandage variable. (3) An extensive survey of IUE high-resolution data has revealed a strong correlation between the ultraviolet stellar wind features and the optical spectral classifications for the majority of normal O stars. These results are relevant to future studies with the High Resolution Spectrograph on the Hubble Space Telescope, which may observe restricted UV wavelength ranges in faint extragalactic OB stars lacking optical data of comparable quality.
A New Survey for Hα-Emission-Line Stars in the Small Magellanic Cloud
Authors: Azzopardi Marc , Meyssonnier Nicole
Published: June 2019

A number of surveys for emission-line objects have been made in the Magellanic Clouds (see Westerlund, 1983). Hα-emission-line objects in the Small Magellanic Cloud (SMC) have been identified mainly by Henize (1956) and Lindsay (1961). Since this pioneering work took place, no other extensive survey for this kind of object - such as the one by Bohannan and Epps (1974) in the Large Cloud - has been carried out in the SMC. Consequently the detection of Hα-emission-line objects in the SMC is still rather incomplete.
Is AS 431 a Superluminous WR Star?
Authors: Stickland D. J. , Lloyd C. , Willis A. J.
Published: June 2019

The recent study by Caillault et al. (1985) has shown the emission-line star AS 431 (= WR 147) to be a strong X-ray source and moderately strong radio emitter. Combining optical, near-infrared and radio data, they deduced that its mass loss rate was ∼ 4 × 10−4 M⊙yr−1, an order of magnitude greater than is normal for WR stars. They also suggested that it would show up in the IRAS survey and that such data would help to elucidate whether its extreme reddening had a significant circumstellar component. To investigate this possibility and to study the general properties of the object, we have raided the IRAS Point Source Catalogue.
Rapid Ultraviolet Spectral Variations in HD 50896 (WN5+?)
Authors: Willis A J , Howarth I D , Conti P S , Garmany C D
Published: June 2019

HD 50896 has become one of the most promising candidate WR+collapsar systems (Moffat 1982) exhibiting optical light, RV and polarisation variations with a 3d.763 period (cf Firmani et al. 1980) yet direct evidence for its postulated n.s. component is lacking. UV spectra of analogous OB X-ray binaries show P-Cygni profile changes as a function of binary phase which are well understood in terms of anisotropic wind ionisation caused by X-ray emission from the accreting n.s. - the Hatchett & McCray (1976) effect. Observations of such UV variability in WR+c candidates with a clear phase dependence would thus provide good evidence for any n.s. companion. To this end we have obtained IUE spectra of HD 50896 in sequential NASA/VILSPA shifts over 6 consecutive days in 1983, together with complementary IUE data secured at various epochs during 1978–82, to search for the Hatchett & McCray effect in this star.
B[e]-Stars of the Magellanic Clouds
Authors: Zickgraf F.-J. , Wolf B. , Stahl O. , Leitherer C.
Published: June 2019

We carried out a spectroscopic and photometric study of the 8 presently known B[e] -stars of the Magellanic Clouds (MC), i. e. R4 and R50 of the SMC, R66, R82, R126, Hen S12, Hen S22 and Hen S134 of the LMC. These stars are characterized by the following typical properties: a) strong Balmer emission lines, frequently with P Cygni profiles, b) permitted and forbidden emission lines predominantly of Fe II, [Fe II], [O I] etc., c) strong IR excess due to circumstellar dust. Photospheric absorption lines are usually weak or even not detectable.
The Exciting Stars of Giant Extragalactic H II Regions
Authors: Rosa Michael , D'Odorico Sandro
Published: June 2019

Recent investigations of the stellar content of giant H II regions and star formation bursts in nearby galaxies are summarized. The preliminary results of a spectroscopic survey of 78 H II regions in 15 galaxies are presented. A minimum frequency of 30 percent is found for the occurrence of luminous Wolf-Rayet stars in such bursts of star formation. Observations of the positions of historical type II supernovae revealed the presence of WC stars, indicating very high ZAMS masses for the SN progenitors. The application of population synthesis models to the analysis of the integrated stellar spectra in terms of IMF parameters is discussed. An example of such an analysis for a giant H II region in Cen A is presented.
Bright Stars in the SMC Clusters
Authors: Kontizas E. , Dapergolas A. , Kontizas M.
Published: June 2019

The bright stars for 15 SMC clusters were classified in order to derive the distribution of various spectral types. The studied clusters represent all evolutionary ages (disk, intermediate and halo) and are located at various places of the parent galaxy. The spectal classification of the stars was carried out using film copies of the 1.2 m Schmidt telescope objective prism plates. Low dispersion (2440 Å at Hγ) and medium dispersion (830 Å at Hγ) unwidewed UJ and RI spectra were examined by means of a binocular microscope. Short exposure plates were used as well for the most bright stars and particularly for the stars at the central areas where crowding is more severe. More details about the used material and the criteria used for the classification are described by Kontizas et al (1985). For each cluster a circular area was examined inside its tidal radius. (Kontizas, 1984). The stars in the innermost part of the populous clusters were not classified because of the overlapped images. Stars of fields in the vicinity of each cluster were also classified to find the contribution of field stars in the cluster area. The magnitude range of the studied stars is 14.5<V<17.50.
Luminous Content of Galaxies: Inferences from Supernovae
Authors: Wheeler J. Craig
Published: June 2019

Some luminous stars undoubtedly explode as supernovae, but it is not yet certain that fate awaits them all. The connection between luminous stars and supernovae is reviewed in terms of the statistical rates of supernovae and pulsars, the constraints of nucleosynthesis, and the various classifications of supernovae by their spectra and light curves, including a newly confirmed class of peculiar Type I supernovae.
A Search for Wolf-Rayet Stars in Giant Extragalactic Bursts of Star Formation
Authors: Campbell Alison W. , Smith Linda J.
Published: June 2019

It is well known that some giant extragalactic star-forming regions contain WR stars. D'Odorico, Massey, Rosa and coworkers found many examples in nearby galaxies of giant HII regions whose spectra show that they contain WN, and occasionally, WC stars. The dwarf emission-line galaxies He 2–10 (Allen et al. 1976) and Tol 3 (Kunth & Sargent 1981) have a strong broad emission feature near HeII 4686Å; in the latter object ∼150 WN stars are required to explain the observed equivalent width.
Dark Matter in the Galactic Disk
Authors: Bahcall John N.
Published: June 2019

The Poisson and Vlasov equations are solved self-consistently for realistic Galaxy models which include multiple disk components, a Population II spheroid, and an unseen massive halo. The total amount of matter in the vicinity of the Sun is determined by comparing the observed distributions of tracer stars, samples of F dwarfs and of K giants, with the predictions of the Galaxy models. Results are obtained for a number of different assumed distributions of the unseen disk mass. The major uncertainties, observational and theoretical, are estimated. For all the observed samples, typical models imply that about half of the mass in the solar vicinity must be in the form of unobserved matter. The volume density of unobserved material near the Sun is about 0.1M⊙pc−3; the corresponding column density is about 30M⊙pc−2. This so far unseen material must be in a disk with an exponential scale height of less than 0.7 kpc. If the unseen material is in the form of stars with masses less than 0.1M⊙, then the nearest such object is about 1 pc away and has a proper motion of more than 1 arcsecond per year.
Constraints on the Dark Matter from Optical Rotation Curves
Authors: Rubin Vera C.
Published: June 2019

From the observed rotation curves of Sa, Sb, and Sc spiral galaxies, it is possible to deduce a dozen constraints on the nonluminous matter in spirals. Within the optical image, the dark matter is less concentrated than the luminous, and contributes about 1/2 of the mass, for spirals of all Hubble types and luminosities.
Mass/Luminosity Ratios from Rotation of HI in so Galaxies
Authors: van Driel Wim , van Woerden Hugo
Published: June 2019

At Westerbork, we have mapped the distribution and motions of HI in about twenty gas-rich SO and SO/a galaxies, with resolutions of order 30 arcsec. Gas-rich SO's often have most of their HI in an outer ring, with diameters between 0.9 and 2.5 times the optical (D0). Assuming circular shape and motions for this ring, radius R, and a spherical distribution of matter, we derive the inclination and rotation speed of the ring, the amount of mass MT(R) interior to it and the corresponding ratio MT/LB0 to blue luminosity.
Simulations of Compact Groups of Galaxies with Halos
Authors: Ishizawa T.
Published: June 2019

Self-consistent simulations of seven groups are performed from the maximum expansion to the present using Aarseth's N-body code. An initial galaxy consists of 100 stars. Its mass, half-mass radius, and central velocity dispersion are 1, 0.41, and 0.96. Units of mass, length, velocity, and time are 1.4×101 2M⊙, 100 kpc, 245 kms−1 and 4.0×108y. Table 1 gives the elapsed time from the Big Bang to the formation of a multiple merger tm+Tc*/2. For H0=80 kms−1Mpc−1, the Hubble time H0−1=30.6 in our units. Dense groups except B form multiple mergers in a Hubble time.
Halos around Ellipticals and the Environment Dependence of Hubble Type
Authors: Zurek W. H. , Quinn P. J. , Salmon J. K.
Published: June 2019

Shells are often observed around elliptical galaxies (Malin & Carter 1983). Stars in the shells can be regarded as test particles. Therefore for a simple shell morphology (Hernquist & Quinn 1985) the distances between shells allow one to trace the shape of the potential of the host galaxy (Quinn 1984). One can also deduce the distribution of gravitating material. Following this method one concludes that the distribution of luminous matter alone cannot account for the observed shell structure. Depending on the age of the outermost shell one can conclude that either the massive halo terminates at a radius ≃ 5 re≃ 15 kpc., or that the core of the halo γ≃2.5 kpc, where the halo density is given by ρ≃ {r2+ γ2}−1. In either case, the central density of the halo is no less than an order of magnitude in excess of that expected for a spiral galaxy of comparable luminosity (Figure 1.).
Hierarchical Clustering: Angular Momentum Density Anti-Correlation
Authors: Hoffman Yehuda
Published: June 2019

The growth of angular momentum in a general clustering scenario is analyzed and its dependence on the primordial density perturbation, δo, is calculated. High density peaks are found to evolve into low angular momentum and low spin parameter (η = J E½ G−1 M−5/2) systems. The basic mechanism behind this anti-correlation is that anisotropic structure, which leads to the growth of angular momentum, is statistically uncorrelated with δo. The collapse time, on the other hand, depends on δo and it is this time scale which determines the angular momentum of bound objects. Three cases are studied: (1) Lagrangian sphere (quasi-linear evolution): J (1σ)/J(3σ) = 3.3 and η (1σ)/η (3σ) = 1.9 where δ is given in σ(= <δ2>1/2)units.
The Formation of Galactic Halos in Universes Dominated by Cold Dark Matter
Authors: Ryden Barbara S. , Gunn James E.
Published: June 2019

If the universe is dominated by cold dark matter (CDM), had an inflationary phase, and has Ω = 1, then the spectrum of primordial density perturbations can be calculated. Using the spectrum calculated by J. Bardeen, we have found the structure of halos which form around peaks in the density. If the initial density is given by , where ) is a Gaussian process, then the mean run of density around a peak is proportional to the correlation function of . If the mass about a peak comes to equilibrium in near-circular orbits, the exact equilibrium configuration can be calculated. The resulting rotation curve for a 1.5σ perturbation is shown as the curve HB in the figure below. As the baryon mass cools and condenses, it drags the CDM in with it, conserving the adiabatic invariants. Putting a 5×1010 M⊙ exponential disk and a 2×1010 M⊙ bulge at the center of the system, the rotation curve of the resulting compressed dark halo is given by the curve HA. D and B show the disk and bulge contributions, and T gives the net velocity. There are many arguments for wanting large galaxies to form from perturbations rarer than 1.5σ. Our spectrum was normalized by assuming that mass clusters as galaxies do on large scales; if Ω = 1, however, galaxies cannot trace the mass and the amplitude must decrease. The flatness of the rotation curve from the baryon-dominated to the CDM-dominated region comes about, in this case, from the imposition of the phenomenological baryon distribution, but the following argument indicates that the result is general. The ratio of baryonic to dark matter is ∼1/15; the rotation parameter Λ, the ratio of rotation velocity to halo dispersion, is also ∼1/15. When baryons fall though the CDM to the point at which they are rotationally supported, their density increases by (15)3. The CDM density increases by (15)2. Hence, baryon and CDM densities are comparable at the mean baryon radius.
Faint Photometry of Edge-on Spiral Galaxies: A Search for Massive Halos
Authors: Skrutskie Michael F. , Shure Mark A. , Beckwith Steven
Published: June 2019

Upper limits have been set to the luminosity from the massive halos of three late-type edge-on spiral galaxies: NGC 2683 (Sb), NGC 4244 (Scd), and NGC 5907 (Sc). The limits resulted from simultaneous photometry in the visual (V) and 2.2μm (K) photometric bands which is sensitive to both luminosity and color changes along the minor axes of the three galaxies. The 3σ lower limits to the mass-to-light ratios for the halo of NGC 5907 are the largest ever recorded: M/Lv > 2000 and M/Lk > 64 in solar units. Since K band M/L for M-dwarf stars lying just above the hydrogen-burning limit is about 35, the results virtually eliminate the possibility that hydrogen-burning stars comprise more than a fraction of the halo masses. If the halos contain a more realistic spectrum of stellar masses, for example Population II, the visual band measurements imply that these stars account for less than one percent of the halo mass. Similar limits were obtained for NGC 4244 and NGC 2683. Variations of the V-K colors along and perpendicular to the disks show no sign of population changes toward redder objects at large galactocentric radii.
An Infrared Search for Substellar Objects
Authors: Low F. J.
Published: June 2019

Preliminary results from a systematic search for nearby substellar objects in the IRAS data bases has revealed only a single candidate among the 12 μm sources in the region of the polar caps. This object appears to be a distant carbon star. All 5700 sources were positionally associated with stars or galaxies.
The research potential of small telescopes
Authors: Warner Brian
Published: June 2019

The use of small telescopes for the production of significant research is examined from the points of view of cost-effectiveness, notable successes already achieved, the advantages over large telescopes in the areas of efficiency, availability, flexibility and serendipitous and speculative observation. It is concluded that small telescopes have an increasingly important role to play in modern astronomy.
Reproducing the UBV and cousins (RI) photometric systems with a Hamamatsu Ga-As photomultiplier
Authors: Menzies J. W.
Published: June 2019

The Hamamatsu R943-02 photomultiplier appears to be suitable for UBV(RI)c photometry. This paper discusses the tube's characteristics on the basis of one year's experience in the use of such a device on the 0.5m telescope at Sutherland.
University of Toronto Southern Observatory
Authors: Garrison R. F.
Published: June 2019

Why are Canadian astronomers so keen on going to Chile to study the stars with a small telescope? First and foremost, the southern half of the celestial sphere contains scientifically exciting and unique objects which have long been neglected. Secondly the rapid growth of Canadian cities and the cloudy Canadian climate renders nearby telescopes less effective than they used to be for some (though not all) types of research.
An automated photometer for a one meter telescope
Authors: Young Andrew T. , Beale Frank L. , Angione Ronald J.
Published: June 2019

A new photometer is described which has some unique optical features. Emphasis is given to those features that improve the measurement precision and efficiency of use.
Monitoring of variable stars on a long time-baseline
Authors: Sterken C.
Published: June 2019

The functioning of a project for systematic observations of variable stars on a long time scale is described.
Scanner observations of some close binary systems
Authors: Sullivan D. J. , Walkington M. , Budding E.
Published: June 2019

Using our intermediate bandwidth photometric scanner, we have obtained light curve data at a range of spectral intervals for a number of close eclipsing binary systems. This paper reports briefly on the instrumentation system, the data obtained for two of the variables AE Phe and ε CrA, and a preliminary modelling of the light curves.
Photographic monitoring
Authors: Belserene Emilia Pisani
Published: June 2019

The usefulness of photography in long term studies of variable stars is demonstrated by recent results on pulsation periods. Photography has been in use long enough for evolutionary changes to be detected, at least during stages that are relatively rapid, such as after core He exhaustion.
The structure of globular clusters
Authors: Djorgovski S. , King I. R. , Vuosalo C. , Oren A. , Penner H.
Published: June 2019

We report the preliminary results of a CCD surface photometry survey of a large fraction of all known Galactic globular clusters. About 1/5 of all surveyed clusters show a characteristic post-core-collapse (PCC) morphology. The PCC clusters are on average closer to the Galactic center than the King-model-like clusters.
Phase-night diagram for periodic variable stars
Authors: Kvíz Z.
Published: June 2019

A program has been developed for the Hewlett-Packard Computer 9845 to represent in a graphical form the period of observability, for individual nights, of periodic phenomena of stars with respect to the phase. One version of the program (Fig. 1) gives the observability with respect to the phase for the whole year. The other version (Fig. 2) gives the beginning and end of the suitable observing interval for several observatories around the world thus facilitating preparation of a program for 24-hour continuous observation.
Photometry of apsidal motion stars - a progress report
Authors: Scarfe C. D.
Published: June 2019

Times of minima of apsidal motion binaries have been obtained at this observatory and at Siding Spring and Cerro Tololo Observatories. This paper discusses the results for CW Cephei, DR Vulpeculae, V477 Cygni and the seldom-observed southern system YY Sagittarii.
Low dispersion spectral classification with small telescopes
Authors: Levato Hugo
Published: June 2019

We review the spectral classification work with low dispersion. It is mainly concentrated on the MK-System. First we summarize the original properties of this system, its evolution and its present properties. We describe the MK Process and emphasize its importance as a tool for future research on spectral classification. In the third section we comment briefly about the instrumentation and the techniques used in spectral classification work and finally we mention a list of research programs that can be undertaken with a 1m-telescope and a good spectrograph.
Stellar spectrophotometry with a microcomputer based, intensified, silicon vidicon
Authors: Jeffers S. , Stiff T.
Published: June 2019

We have developed several detector systems for use in observational astronomy. These include a rapid scanning spectrometer (Jeffers and Weller, 1973), a rapid chopping spectrophotometer (Stiff and Jeffers, 1978) and an intensified, silicon vidicon detector for use either for spectrophotometry (Jeffers, Stiff and Weller, 1983) or direct imaging (Jeffers, 1982). These detector systems have been used for rapid variability studies of emission line strengths and profiles in Wolf-Rayet and Of stars (Weller and Jeffers, 1979; Jeffers, Stiff and Weller, 1985) and for low dispersion spectrophotometry of these stars (Jeffers and Weller, 1985). Here we report on the spectrophotometric performance of the intensified, silicon vidicon detector (RCA 4804H) when used with a low dispersion spectrograph.
State-Diagnosed Ion-Neutral Collisions leading to Charge Transfer
Authors: Mathur D. , Badrinathan C. , Rajgara F. A. , Raheja U. T.
Published: June 2019

A significant reservoir of potential energy in hot astrophysical plasmas exists in multiply charged positive ions. Inelastic collisional processes involving such ions govern the ionization and energy balance in such plasmas. Although inelastic processes such as, charge transfer, have been widely investigated, there remains a paucity of knowledge about charge changing processes where both reactions and products are state-diagnosed. We have applied high-resolution translational energy gain/loss spectroscopy to investigate state-diagnosed collisions between Kr2+ and H2 leading to single electron capture into specific electronic states of Kr+ at collision energies in the range 1–6 keV.
Infrared Observations of Interstellar Molecular Hydrogen
Authors: Gatley Ian , Kaifu Norio
Published: June 2019

Emission from vibrationally excited molecular hydrogen has been detected from a wide range of astronomical targets during the last decade (e.g. Shull and Beckwith 1982). in all cases the H2has been shock excited, and we have grown accustomed to the idea that H2is a useful tracer of interstellar shocks.
Observations of Unidentified Lines
Authors: Turner B. E.
Published: June 2019

The three existing spectral surveys in the 3 mm window are compared. the NRAO and BTL surveys of SgrB2 are quite consistent, the NRAO and Onsala surveys of Ori(KL) less so. Lists of U-lines are assembled from the three surveys, and total 86 in Ori(KL), 66 in SgrB2, of which only 12 are common. Difficulties in selecting reliable lists of U lines are emphasized. Methods of identifying such lines include “direct,” “hybrid,” and “Shotgun” approaches; the probability of misidentification is analyzed for each. the “Shotgun” method is least reliable, although a few candidates should be followed up.
New Interstellar Molecular Detections: Implications for “Shock Chemistry”
Authors: Ziurys L. M. , Turner B. E.
Published: June 2019

Several new interstellar species have recently been detected in the molecular gas, including rotationally-excited CH, vibrationally-excited HCN, and a new molecular ion, HCNH+. These detections have raised some interesting questions concerning the relative importance of “shock” or “high temperature” chemistry vs. ion-molecule reactions in the synthesis of interstellar molecules in dense clouds.
Effects of Nonthermal Internal Energy on Postshock Oxygen Chemistry
Authors: Graff M. M. , Dalgarno A. , Wagner A. F.
Published: June 2019

The internal energy distributions of reactants in shocked interstellar clouds are discussed. Rate coefficients appropriate for the oxygen chemistry of shocks differ significantly from those deduced by simple extrapolation of thermal measurements. A one-fluid MHD shock model examines nonthermal effects for a 10 km s−1 shock propagating through clouds of initial densities of 10 and 105 cm−3, using oxygen-hydrogen reaction rates that are specific to the vibrational, rotational, and fine structure temperatures of the reactants.
Chemical Properties of Interstellar Polycyclic Aromatic Molecules
Authors: Omont Alain
Published: June 2019

There is substantial evidence of the presence of polycyclic aromatic molecules, mainly hydrocarbons (PAH's) in the interstellar medium (Léger and Puget, 1984, Allamandola et al. 1985, Léger and d'Hendecourt in these proceedings). They should contain typically NC = 20–100 carbon atoms, and they can contain perhaps 1–10% of the total interstellar carbon. I have recently discussed in detail their physical and chemical properties (Omont, 1986), which should be intermediate between that of conventional interstellar molecules and grains.
Ionization and Kinematics of the Narrow Line Region in Seyfert Galaxies
Authors: Wilson A. S.
Published: June 2019

Direct imaging of Seyfert galaxies in emission lines and high resolution radio mapping often show their narrow line regions and linear (double or jet-like) radio sources to be aligned on the hundreds of parsecs scale. This relationship is unlikely to reflect ionization of the thermal gas by the expanding radio components or by their relativistic electrons. The most likely explanation, which is also favored by optical polarization measurements, is that ionizing photons escape preferentially along the rotation axis of the same inner (≲ pc scale) disk as collimates the radio jet. Such a bipolar form may be the most common morphology of the narrow line region. Differences of radio properties between Seyfert type 1's and 2's may be at least partially related to aspect effects. The north east radio lobe of NGC 1068 shows a limb-brightened, conical structure with the magnetic field running parallel to the edge of the cone. This source is modelled in terms of a radiative bow shock wave being driven into the interstellar medium of the galaxy by the radio ejecta. If the pre-shock density is as high as 400 cm−3, as suggested by CO measurements, the shock velocity is found to be ≃ 75 km s−1 and the jet velocity ≃ 4000 km s−1, the latter being close to the emission line widths. The narrow line region in this galaxy is morphologically and kinematically associated with the jet.
Activity in Near-Normal Galaxies
Authors: Rubin Vera C.
Published: June 2019

Modern detectors permit astronomers to examine galaxies at very low light levels, at very high velocity resolution, and for nearby objects, at very high spatial resolution. Such observations will lead to phenomenon not previously detected, and offer new insights into the phenomena we presently lump under the heading of “activity.”
STarburst Models for AGNs
Authors: Terlevich Roberto , Melnick Jorge , Moles Mariano
Published: June 2019

A significant fraction of all spiral galaxies exhibit some type of “activity” in their nuclear regions as evidenced by the presence of emission lines in their optical spectrum (Keel, 1982; Cetty-Veron and Veron, 1985). It has become standard to classify emission-line galaxies into two main groups: “active” having Seyfert or Liner nuclei and “inactive”, having Starburst or HII-region like nuclei. Two main classification criteria are used, one based in the widths (Khachikian and Weedman 1974) the other in the intensity ratios of the nuclear emission lines (Baldwin, Phillips and Terlevich, 1981).
Activity in Blue Compact Galaxies
Authors: Alloin Danielle
Published: June 2019

This paper is aimed at providing a review of recent observational facts regarding blue compact galaxies. Tightening together flux measurements from the UV to the radio range now allow us to draw a somewhat improved, more self-consistent picture of these objects. Many questions are still open however, about their nature and evolution.
Dust distribution near young stars of bipolar flows deduced from CCD polarimetry at 1 μm
Authors: Lenzen R.
Published: June 2019

Deep direct 1 μm images and polarization maps have been taken for several objects of bipolar molecular outflow, using a CCD camera at the prime-focus of the 3.5 m telescope on Calar Alto/Spain. Compact reflection nebulae are found near GL2591, GL2884 = S140/IRS1, GL2789 = V645 Cyg, L1551/IRS5 and within the red reflection nebula in Serp. The position angles of polarization vectors coincide in all cases with that of the 2.2 μm polarization of the central source itself, and it is perpendicular to the direction of mass outflow (if it is well defined). The visual extinction in front of the central source, is at least 20 mag higher than that which is affecting the scattered light. This is consistent with a model of bipolar outflow, where the active source is surrounded by a dust torus or ring.
Circular polarization in T Tauri stars
Authors: Bastien P. , Nadeau R.
Published: June 2019

We report the detection of circular polarization in three T Tauri stars with known intrinsic linear polarization. A circumstellar origin is required.
A model for maser line profiles of late-type stars
Authors: Lépine J.R.D.
Published: June 2019

The profiles of maser lines from spherically symmetric expanding shells are computed with the help of a simple model. It is shown that a beaming effect must be taken into account in order to correctly account for the OH profiles of type II OH stars.
Studies of variability of circumstellar H2O masers
Authors: Rudnitskij G. M.
Published: June 2019

From March 1980 to December 1983, the author took part in regular observations of variability of maser radio emission in the H2O line at 22 GHz. The observations were carried out at the 22-meter radio telescope of the P. Lebedev Physical Institute (USSR Academy of Sciences) in Pushchino (Moscow Region). The interval between consecutive observational sessions was usually 1.5–2 months. The observational program included 21 late-type variable stars (Miras and SRs): R Aql, RR Aql, RT Aql, SY Aql, U Aur, NV Aur, RX Boo, VY CMa, S CrB, KY Cyg, NML Cyg, U Her, W Hya, X Hya, R Leo, U Lyn, U Ori, UU Peg, VX Sgr, RS Vir, RT Vir. The results for eight stars ending June 1982 were published by Berulis et alt (1983). A comparison was made between the time dependences of the H2O line radio flux F and the curves of visual and near-infrared brightness of the stars. Miras (R Aql, R Leo, U Ori, U Aur), as a rule, have a rise in F connected with the visual maximum (phase 0), the maximum F occurring at phases 0.1–0.2 (see figure for an example). Not all visual maxima (only one out of each two or three) are accompanied by H2O flares. This Miras! behaviour was also noted earlier in the H2O line by Berulis et al. (1984), Gómez Balboa and Lépine (1986), as well as in the SiO maser line v=1, J=2−1 by Nyman and Olofsson (1986).
Δ Andromedae (K3 III): A hybrid giant in an extended dust shell
Authors: Jordan C. , Judge P. G. , Rowan-Robinson M.
Published: June 2019

Observations made with the Infrared Astronomical Satellite (IRAS) showed the existence of a set of K stars with excess emission at 60 μ. The brightest star in the group is δ And (K3 III). Spectra of δ And have been obtained with the International Ultraviolet Explorer (IUE) in both the long and short wavelength regions. These spectra show several features unusual in a K giant as cool as δ And, in particular, emission from CIV, MgII h and k lines with blue wings stronger than the red and MgII absorption blue shifted to up to 300 km s−1. Overall δ And is similar to the known hybrid bright giant α TrA (K4 II). We have discovered the first ‘hybrid’ giant star. The IRAS observations are interpreted in terms of a cool (∼100 K) dust cloud surrounding δ And - a spectroscopic binary system- and a third component at 1200 A.U.
A compact nebulosity surrounding the peculiar blue emission-line supergiant HD 37836 of the LMC
Authors: Stahl O. , Wolf B.
Published: June 2019

HD 37836 (= R 123; Feast et al., 1960) is one of the brightest slightly variable (V ≃ 10.5–10.7; Stahl et al., 1984) emission-line stars of the LMC. Since it is also likely to be a hot star (see below) it is also bolometrically very bright (Mbol ≤ −11).
Dynamical effects of stellar winds and associated HII regions on the interstellar medium
Authors: Breitschwerdt Dieter
Published: June 2019

A dynamical model has been developed, describing the joint evolution of a stellar wind and an associated HII region during the main sequence life time of an OB-star. It is proposed that in case of spherical symmetry all dynamical features are obtained by dividing the flow into spatially homogenous regions separated by discontinuities (shock fronts, contact discontinuity and ionization front). Different phases in the dynamical evolution can be distinguished. The results show that the extension and structure of the HII region depends sensitively on the initial density of the ambient medium, the Lyman continuum photon rate and the mechanical wind power of the central star. This will be important for future high resolution observations.
Variation of linear polarization in R Aquarii system
Authors: Deshpande M. R. , Joshi U. C. , Kulshrestha A. K.
Published: June 2019

R Aquarii is a very interesting symbiotic system. There is an emission nebulosity close to the star which extends in North-South direction and a “jet” feature of about 6″ with a position angle of 29° has also been observed (Sopka et al. 1982; Mauron et al. 1985; Kafatos et al. 1983). Polarization measurements are important to understand the peculiar geometry of the circumstellar material around the central objects. Wavelength and time dependence of polarization can be used to put constraints on the geometry of the object and to identify the mechanism(s) responsible for polarization. In view of this linear polarization measurements of R Aquarii were carried out by us in UBVRI bands. Observations were made during November-December 1984 on 1 meter telescope of Indian Institute of Astrophysics, Bangalore, with a dual channel photo polarimeter discussed elsewhere (Deshpande et al. 1985). Measured values of percent polarization and position angle at different phases alongwith the earlier observations of Serkowski (1974) and Ladbeck (1985) are plotted in Figure 1.
The circumstellar matter in the Be + K binary KX and seen in the uv spectra
Authors: Štefl S.
Published: June 2019

KX And (HD 218393) belongs to well-known and often observed Be stars. The periodicity of spectroscopic characteristics as well as other observations led to the conclusion that the star is a peculiar interacting binary (Harmanec et al. 1980). The aim of this paper is to present the phase-dependent behaviour of the UV spectrum of the star.
Atomic hydrogen in the planetary nebula IC 4997
Authors: Giovanardi C. , Altschuler D.R. , Schneider S.E. , Silverglate P.R.
Published: June 2019

In the course of a sensitive search for atomic hydrogen emission associated with planetary nebulae having high velocities relative to Galactic HI (Schneider et al. 1986), we detected absorption in the spectrum of IC 4997 (PK 58-10.1). This is only the second definite detection of HI associated with a PN. The velocity of the feature coincides precisely with that expected if the gas is expanding with the measured optical expansion velocity of 14 km s−1 (Sabbadin 1984), strongly suggesting an association.
Dust formation in C-star shells
Authors: Sedlmayr E.
Published: June 2019

The formation of carbon grains is described by a chemical pathway from acetylene via polyaromatic hydrogens (PAHs). The proposed mechanism is in excellent agreement with the observations and provides in particular the observed low condensation temperature which cannot be explained by classical nucleation theory.
Interstellar Scintillations and Neutron Star Kinematics
Authors: Cordes J.M.
Published: June 2019

The interstellar scintillation technique for measuring neutron star speeds is described and results are given for 71 radio pulsars. The mean transverse neutron star speed is 100 km s−1 and the distribution extends to 300 km s−1. The transverse speed correlates with the z velocity derived independently using distance from the galactic plane, consistent with most neutron stars having been born near the galactic plane. A correlation of transverse speed with the quantity PP ∝ (magnetic moment)2 is a general property of the neutron star population. Monte Carlo simulations of the progenitors of neutron stars show that the velocity distribution is inconsistent with the disruption of binary systems solely by symmetric supernova explosions. Either explosions are asymmetric or there are additional accelerations of neutron stars after their formation.
A Deep Search for Young Pulsars in the Galactic Plane at 1400 MHz
Authors: Clifton T.R. , Jones A.W. , Lyne A.G.
Published: June 2019

A new survey of the Galactic plane for pulsars has now been completed at Jodrell Bank at the relatively high frequency of 1400 MHz (Clifton, T.R. and Lyne, A.G. 1986, Nature, 320, 43). A further 8 new objects have been detected. The properties of these are summarized below.
Progenitors of the Local Pulsars; Lower Mass Limit and Beaming Factor
Authors: Blaauw A.
Published: June 2019

Following up on an earlier paper on the local pulsar population (Blaauw 1985; Paper I), in which it was shown that the majority of their progenitors must be sought among the local field stars between 6 and 10 solar masses (types B2, B3) - the local OB associations accounting for a minority only of the pulsar population - we consider implications of two further restrictions: raising the lower limiting mass for neutron star formation, Mn, above 6 solar masses, and raising the beaming factor, f, above 0.3.
Does the Radio Luminosity of Pulsar Grow up in its Later Stage?
Authors: Lu T. , Zhu P. C. , Kui J. S.
Published: June 2019

In usual statistical analyses, because of diversities of proper parameters of pulsars, some interesting features might be smeared. In order to remove these diversities, we use the mean values for all quantities of pulsars, instead of values of individual pulsar, to do statistical analyses. logP/P3 - log τ and logL - logτ have been plotted, here τ P/2P and L denote the characteristic time scale and the radio luminosity of pulsars respectively. The most striking feature is that after its initial dropping to a dip at about τ∼106 yrs, the radio luminosity of pulsar appears to grow up evidently and then redrop again. This feature is difficult to be understood in usual models. However, two tentative interpretations have been given in this paper.
A Statistical Study of the Correlation Between Galactic SNRS and Spiral Arms
Authors: Li Z.W. , Wheeler J.C. , Bash F.N.
Published: June 2019

Based on the statistical studies of external galaxies, our Galaxy is expected to produce Type I and Type II supernovae in closely equal number. There are as of this writing 162 known galactic SNRs.

The basis for our investigation is the observations that SN II are tightly correlated with spiral galaxies and that SN I do not correlate with spiral arms, but are roughly of old disk population.

We seek a method by which a correlation of SNR with spiral arms can be determined. For this preliminary exercise we use only information on the positions of the SNR in galactic coordinates.

As a test, we compared the angular distribution of SNR and giant HII regions which are presumed to define the location of the spiral arms. To the eye, there did seem to have a correlation.

We thus faced a host of questions.

Do SN I still occur in spiral arms, implying that they have massive progenitors?

Is the rate of formation of SN I in Galaxy (and M31) considerably less than that of SN II?

Do SN I not produce long lived radio SNRs?

We have developed a quantitative approach to investigate these questions. Using the observed angular distributions of SNRs and giant HII region, we form a cumulative distribution with respect to angle. Two observed distributions can be compared then, and the Kolmogrov-Smirnov statistics was used to determine the probability that the two samples are not drawn from the same distribution.

In addition, we have constructed Monte-Carlo models in which sample objects are distributed in a prescribed pattern in the spiral arms and the galactic disk. The parameters of the Monte-Carlo simulation, such as the opening angle of the spiral arms and the fraction of objects in the disk vs arm population, can be adjusted to obtain the best fit to the observed distribution.

We also study the influence of the selection effects, if the surface brightness of SNR falls below a threshold for detectability (as 1/r2).
Herculis X1: Results and Interpretation
Authors: Durouchoux Ph.
Published: June 2019

The hard X-ray spectrum of Her X1 was measured for the first time with a high-resolution (1.4 keV FWHM) germanium spectrometer (LEGS: GSFC/Saclay collaboration). The observation was performed near the peak of the 0B state in the 35 day cycle and 1.24 s pulsations were observed between the energies of 20 keV and 70 keV. The best fit energies are 35 keV for an absorption line and 39 keV for an emission line. These are significantly lower energies than those derived from previous experiments.
Line Radiation from Accreting Magnetized Neutron Stars
Authors: Wang D.Y.
Published: June 2019

A new non-thermal model on cyclotron line radiation from accreting magnetized neutron stars have been reviewed. Above the magnetic polar cap of accreting neutron stars, the maser instability may be excited by a part of non-thermal electrons, and the radiation with the frequency near electron cyclotron frequency and its second harmonic may be emitted as well. According to this model, the intensity and energy of line radiation will vary with pulsation phase of X-ray pulsars. These phenomen have been observed from Her X-1.
The X-ray Radiation Mechanism of the Compact (Neutron) Binary Stars
Authors: Yi Tong , Geng Fang , Xinjie Mao
Published: June 2019

Usually we think a X-ray source may be a compact(neutron) binary star on which the X-ray radiation might be generated by gravitational acceleration for the particles coming from the primary and going along magnetic field lines of the compact star to the poles. But, in the past, people don't consider well the problem of particle acceleration. It seems to be simplified for the situation only to consider the gravitation effect, because some electric-magnetic effect in a strong magnetic field could not be neglected. However, it is unreasonable to neglect the plasma turbulent waves in an electric-magnetic field, because strong enough turbulent waves such as Alfven waves, whistlers generated nearby the surface of neutron stars probably contribute energy to accelerate particles, which may be more important than gravitation sometimes. For a binary system with a neutron star if ion number density N > 1017 /cm3 in its surface atmosphere, the turbulent wavess will be stimulated that will accelerate the particles reaching a speed over 108cm/s. they strike the atmosphere of the compact star in the system, so that a shock wave is formed which turns part of kinetic energy to heat to form hot spots of about 108K to emit X-ray.
The Birth of Neutron Stars
Authors: Woosley S. E.
Published: June 2019

Presupernova models of massive stars are discussed and their explosion by either the “core bounce” or neutrino energy transport mechanism briefly reviewed. Special consideration is given to those attributes of the stellar evolution and explosion that might influence the properties of the neutron star remnant: its mass, rotation rate, magnetic field, and “kick” velocity.
Binary Pulsars: Observations and Implications
Authors: Taylor J. H.
Published: June 2019

The Galaxy contains a large number of neutron stars in gravitation-ally bound binary systems. Among the most fruitful of these to study have been the binary radio pulsars, of which seven are now known. Unlike the “accretion-powered” neutron stars located in mass-exchanging X-ray binary systems, the “rotation-powered” binary radio pulsars are found in dynamically simple, clean systems in which both stellar components have already completed their nuclear evolution, thereby shedding their atmospheres and most of their mass. In such circumstances the orbital parameters of the system and the rotational parameters of the pulsar can be determined with high precision from analysis of pulse timing data. These measurements constrain the component masses and yield an estimate of the pulsar's magnetic dipole moment, which turns out to be an essential parameter in understanding the evolution of the systems. In this paper I review the known facts concerning binary pulsars, and then briefly discuss some implications for our understanding of the place of neutron stars in stellar evolution.
Synchro-Curvature Radiation and Magnetic Pair Production of Relativistic Electrons in Strong Curved Magnetic Fields
Authors: An S.-Y.
Published: June 2019

Most of common curved magnetic fields with axial symmetry in astrophysics can be expressed in a local cylindrical coordinate system (R, φ, Z) as

where HO, RO and N are real constants. It has been known that the non-zero curvature of the magnetic field lines can impose an additional pitch angle on the electrons moving in the field (1).
Thermal Radiation from a Radio Pulsar: PSR1055-52
Authors: Brinkmann W. , Ögelman H.
Published: June 2019

The radiopulsar PSR1055-52 has been observed now by the Exosat observatory for about 105 sec, thus increasing the previously published data base (Brinkmann et al. 1985) by a factor of two. The pulsar was seen in the low energy telescope (0.04–2 keV) with the thin Lexan and Al/Par filters, but not in the Boron filter or with the ME experiment.