bluuebunny/crossref_metadata_2025 huggingface dataset:
Hβ Profile Variations in the Spectrum of Seyfert Galaxy NGC 5548 Nucleus
Authors: Chuvaev K. K.
Published: June 2019

The spectra of NGC 5548 galaxy nucleus obtained at the Crimean Aetrophysical observatory on 2.6-m Shain telescope from April till August 1985 showed strong variations of Hβ line profile. The profile being almost symmetrical in April became more and more asymmetrical in June-August, the flux in blue wing increased twofold in respect to the red one. Such variations of line profile were accompanied by continuum decrease.

We suppose, that the observed variations might be explained by the appearance of the absorbing matter located on the line of sight between the nucleus and the gas responsible for the intensity increase in the blue wing of Hβ line. This gas might have been ejected close to the line of sight direction.
Multifrequency Observations of the Seyfert Galaxy 3C 120 in 1983–1986
Authors: Maraschi L. , Chiappetti L. , Cristiani S. , Danziger D. , Falomo R. , Malkan M.A. , Tagliaferri G. , Tanzi E.G. , Treves A. , Warnsteker W.
Published: June 2019

3C 120 (z=0.033) has the optical spectrum typical of a Seyfert I Galaxy, however unlike most Seyfert Galaxies it exhibits strong radio emission with a compact component where VLBI observations indicated superluminal expansion. It could therefore be classified as a mini Radio Loud Quasar.
Bulk Relativistic Motion in a Complete Sample of Radio Selected AGN
Authors: Schalinski C.J. , Biermann P. , Eckart A. , Johnston K.J. , Krichbaum T.Ph. , Witzel A.
Published: June 2019

A complete sample of 13 flat spectrum radio sources is investigated over a wide range of frequencies and spatial resolutions. SSC-calculations lead to the prediction of bulk relativistic motion in all sources. So far 6 out of 7 sources observed with sufficient dynamic range by means of VLBI show evidence for apparent superluminal motion.
Polarimetric and Photometric Investigations of Lacertids
Authors: Hagen-Thorn V.A. , Yacovleva V.A.
Published: June 2019

At the Astronomical Observatory of Leningrad State University two observational programs of investigation of lacertids - photographic photometry and photoelectric polarimetry - are in progress for many years. Some results for OJ 287 and BL Lac are of interest: (1) existence of preferable direction of polarization, (2) correlations between the brightness and polarization parameters, and (3) high degree of polarization (~50%) of individual sources responsible for variability.
Relationships Between Seyfert Galaxies, QSOs, and BL LACs
Authors: Hutchings J.B.
Published: June 2019

In this review, I will deal principally with the optical morphology of these three types of object, and attempt to outline similarities and essential differences. By this, I mean to include studies of the types of host galaxy, nuclear and galaxy luminosities and colours, interactions with other galaxies, and the general associations with other galaxies. Where relevant, I will refer to morphology at other wavelengths (generally radio), spectroscopy, and UV or X-ray properties. However, I expect these areas to be covered much more fully by other reviews and papers in this volume.
Morphology and Spectroscopy of Markarian 231
Authors: Hutchings J.B. , Neff S.G.
Published: June 2019

Deep optical imaging of Mkn 231 reveals twin (tidal?) tails, a linear nuclear feature at green wavelengths, and a very blue region 4 arcsec south of the nucleus. Much of the central part of the galaxy is red, but there are complex areas of blue luminosity outside this, and a sharp edge to the luminosity at a distance of ~16 arcsec from the centre. Overall, the host galaxy appears to have a normal optical luminosity and blue colour (B-R ~0.7) despite being one of the most luminous galaxies known in the infrared. Radio emission in the system is extended on one side on a similar scale to the optical tails, but shows no detailed correspondence with optical structure; in particular there is no radio counterpart to the optical ‘jet’. Examination of IUE archival data indicate that the UV flux is very weak and the UV spectrum is peculiar for a Seyfert galaxy. The UV observations provide evidence for considerable nuclear extinction in the system, in accordance with previously published optical and infrared work, but the UV extinction is unlike Galactic absorption and may be more similar to that seen in the LMC. Recent optical spectra of Mkn 231 show changes in both the emission line spectrum and in the strong broad absorption lines (BAL), compared with previously published observations. This places strong limitations on the size of the nuclear continuum source. We suggest that Mkn 221 is a recently merged system which is currently undergoing star-formation, and discuss the connection with BAL QSOs.
The Nature of Liners
Authors: Heckman Timothy M.
Published: June 2019

LINER's (Low-Ionization Nuclear Emission-line Regions) are found in the majority of early-type (Sb or earlier) galaxies, and in some late-type and peculiar galaxies as well. Because they are so common but are not energized by normal stars, their nature is critical to our understanding of both the active galactic nucleus phenomenon and the evolution of normal galactic nuclei. After briefly reviewing the spectroscopic basis of the LINER classification, I summarize four alternative models for LINER's: 1) LINER's as “mini-Seyferts” in which the emission-line gas is photoionized by a more dilute version of the high-energy nonstellar continuum found in Seyfert nuclei. 2) LINER's as accretion flows of cooling gas originating in the halos of galaxies and/or in the intra-cluster medium. 3) LINER's as starburst-driven winds. 4) LINER's as colliding, shock-heated galaxies. After reviewing the evidence, I conclude that it is very likely that several (and possibly all) of the above models are needed to account for the diverse properties of LINER's. While LINER's would then not have a single unified explanation, they would have a direct bearing on many issues in extragalactic astronomy.
Superassociations in the Arms of Normal and Active Galaxies
Authors: Melnick Jorge
Published: June 2019

The properties of violent star formation regions in the arms of spiral galaxies are reviewed with the aim of providing the foundations on which models of nuclear starbursts can be built. It is argued that the classical examples of extranuclear starbursts, giant HII regions and Superassociations, are closely related but fundamentally different classes of objects; their properties are reviewed and discussed in detail.

It is shown that giant HII regions are a homogeneous class of gravitationally bound objects ionized by starburst clusters and that the initial mass functions of these clusters change according to their chemical composition being flatter for metal poor systems. Superassociations are loose associations of associations which generally contain one or more giant HII regions. Star formation in superassociations is self-sustaining and therefore these structures may last much longer than individual giant HII regions.

Isolated superassociations or HII galaxies are shown to have the same global properties as giant HII regions in late type galaxies. In particular, the correlations between Hβ luminosity and emission line velocity width are similar for both classes. Since HII galaxies can be observed out to large distances this correlation provides a potentially powerful method to calibrate the extragalactic distance scale. A preliminary calibration gives HO = 95 ± 9 km/sec/Mpc.

The relations between the properties of giant HII regions and Superassociations with those of their parent galaxies are briefly discussed.
Circumstellar matter around the candidate protostar EL29
Authors: Zinnecker H. , Perrier C. , Chelli A.
Published: June 2019

Infrared speckle interferometric observations at 3.6 μm carried out at the ESO 3.6m telescope have indicated that EL29, a deeply embedded infrared source in the Ophiuchus dark cloud (Elias 1978), appears to have a core-halo structure (Zinnecker, Chelli and Perrier 1989). A fit to the data gave angular scales of order of 0.05 arcsec for the core and 3.5 arcsec for the halo (Gaussian FWHM) corresponding to linear diameters of 8 AU and 620 AU, respectively (for a distance to the cloud of 160 pc). New infrared speckle observations confirm that the core is resolved at the 2 sigma level, and carries about 90% of the total 3.6 μm flux (Fig. 1). Furthermore, there is evidence from a recent IRTF lunar occultation experiment in the K-band (2.2 μm) for an additional inner 6 milli-arcsec (~ 1 AU) core which carries about 75–85% of the total K-flux from this source (Simon et al 1986). Perhaps this inner core is the dust shell inside of which grains are destroyed by the radiation from a central object.
Star formation in CHA T1
Authors: Wesselius P. R. , Assendorp R. , Roede H.
Published: June 2019

In a region of 0.4 × 0.5 pc around HD 97300 the amount of mass in gas and dust is < 16 M⊙, while the stellar mass is 6–9 M⊙. Thus in this core of a collapsing cloud (Cha T1) several stars have been formed in a very efficient way.
OH0739-14: An old star blowing bubbles
Authors: Reipurth Bo
Published: June 2019

Two large bipolar bubbles emanating from the OH/IR star OH0739-14 have been discovered. Interference filter images show that the bubbles are emission-line objects, and longslit spectra reveal that the bubbles are expanding, with a radial velocity-difference between the bubblefronts of over 200 km/sec.
Discovery of FK comae and RS CVn systems by observation of their X-ray emission
Authors: Fleming Thomas A. , Gioia Isabella , Maccacaro Tommaso
Published: June 2019

We are currently working with a statistically complete, unbiased sample of 125 x-ray-bright stars which were serendipitously detected by the Einstein Observatory Medium Sensitivity Survey (MSS). A program of optical spectroscopy and photometry is currently underway to measure radial velocities, distances, and such stellar parameters as rotation, temperature, surface gravity, metallicity, chromospheric activity, and age and to correlate them with absolute x-ray luminosity. So far, the majority of the sample (which was defined at |bII| > 20o) appears to be composed of either flare stars (e.g. dMe, dKe) or active binary systems (e.g. cataclysmic variables, RS CVn, W UMa).
Some observations relevant to the theory of extended envelopes
Authors: Wolf B.
Published: June 2019

Recent observations of S Dor variables and B[e]-supergiants are reviewed. These objects belong to the visually and bolometrically brightest stars in the universe. They have gained considerable interest for their exceptional stellar wind properties and represent rare cases of hot blue stars which form dust envelopes. S Dor variables are characterized by major outbursts. The ejecta have been spatially resolved in some cases. These luminous emission line stars are supposed to represent a short-lived phase in the evolution of the very massive stars prior to becoming WR stars.
Evidence for disks around certain luminous Magellanic cloud stars from the study of FeII
Authors: Muratorio G. , Friedjung M.
Published: June 2019

Study of FeII emission lines in emission and absorption using both emission line self absorption curves and ultraviolet spectral synthetis, shows that line emission is produced in the case of certain luminous Magellanic Cloud stars, in a region not in front of the photosphere. This region is most easily understood as being a disk. Absorption lines of FeII are either produced by a wind, or if the disk inclination is small with respect to the line of sight, in layers associated with the disk. The presence of disks also helps one to explain the form of the continuous energy distribution.
Far infrared observations on the peculiar variable star R Aquarii
Authors: Anandarao B.G. , Pottasch S.R.
Published: June 2019

First results on the peculiar Mira variable star R Aquarii obtained by the Infrared Astronomical Satellite (IRAS) in the far-infrared region (12–100 microns) are presented. A simple radiative transfer model for plane, isothermal and homogeneous layer is given to interpret the far-infrared excess radiation in terms of circumstellar dust emission. A two dust shell model with silicate grains is proposed to explain the observed fluxes. This model explains as well the low-resolution spectra (LRS) in the 8–20 micron region from IRAS. The equivalent sizes of the emitting regions (shells) in R Aquarii are found to be 0.1 arc sec and 3 arc sec at temperatures of 800 ± 80 K and 87 ± 8 K respectively. Silicate grains of size 1 micron seem to be compatible with the observations. There is no clear indication for the presence of an isolated dust cloud in R Aquarii to support the eclipsing-cloud hypothesis for explaining the minima observed at 44 yr interval.
Formation and destruction of dust grains in circumstellar regions
Authors: Fadeyev Yu. A.
Published: June 2019

The existence of circumstellar dust in late-type stars is connected with stellar pulsations since periodic shocks accompanying pulsations seem to be the most probable mechanism of the gas density increase needed for condensation of dust particles in outer layers of the stellar atmosphere. Most abundant solid materials formed in O-rich stars are forsterite (or enstatite), silicon monoxide and iron, whereas in C-rich stars these are carbon, silicon carbide, magnesium sulphur and iron. Application of the homogeneous nucleation theory shows that condensation proceeds at extremely high departures from thermal equilibrium due to a very long time between collisions of condensable monomers. The most efficient mechanism of destruction of dust grains is thermal evaporation caused by variations of the stellar effective temperature.
Helioseismology from the South Pole The 1984/85 campaign
Authors: Gelly B. , Fossat E. , Grec G. , Pomerantz M.
Published: June 2019

More than 700 hours of full disk line of sight solar velocity have been recorded at the Geographic South Pole between late november 1984 and early february 1985. This paper presents very briefly some preliminary result of the analysis of this data.
Intermediate degree solar oscillations
Authors: Duvall T. L. , Harvey J. W. , Pomerantz M. A.
Published: June 2019

Spectra of solar intensity oscillations in the degree range ℓ = 20–98 were obtained with a 92% duty cycle over a 50 hour period from the geographic South Pole. After correction for solar rotation, the spectra have been averaged over azimuthal order m and fit with Lorentzian functions to provide values of background noise, amplitude, frequency and line width for 636 oscillation modes. The background noise is nearly independent of frequency in the range containing strong p-modes. The amplitude envelope shows little dependence on ℓ value and a frequency dependence similar to that of Doppler oscillations but shifted to higher frequency. Line widths increase at higher frequency and at higher ℓ values.
Earth based observations of solar luminosity oscillations
Authors: Jiménez A. , Pallé P.L. , Hernández F. Pérez , Régulo C. , Cortés T. Roca , Domingo V. , Korzennik S.
Published: June 2019

Earth based multichannel photometry of integral sunlight has been obtained at Izaña (Tenerife) during 1984–1986. Power spectra of the solar luminosity variations of individual days show power in the 5 minute interval above noise at a level comparable to SMM datad). When combining contigous days of data the signature of p mode solar oscillations spectrum appears* although individual peak identification is difficult.
Search for solar g-modes from 1981 to 1985
Authors: P.L. Pallé , Cortés T. Roca
Published: June 2019

Analysis of solar velocity data obtained at Izaña (Tenerife) over the years 1981–1985, has shown the existence of significant signals in the frequency range 25–125 μHz. Several ways of analyzing the data have been used in order to interpret these as solar internal gravity modes of degree ℓ≤ 3.
The magnetic field inside the Sun
Authors: Dziembowski W. , Goode Philip R.
Published: June 2019

Duvall, Harvey and Pomerantz (1986) reported the existence of a ‘structural asymmetry’ inside the Sun. We show that this asymmetry is not a consequence of the Sun's rotation. We attribute the asymmetry, rather, to a toroidal magnetic field inside the Sun. Consistency requires a field of about one megagauss located in the lower part of the convection zone. Accounting for such a field would wreak havoc on our understanding of the solar dynamo and convection.
Seismological investigations of compact stars
Authors: Winget† D. E.
Published: June 2019

Since Landolt's discovery of the first ZZ Ceti star, the ranks of the compact pulsators have swollen to include planetary nebula nuclei, hot pre-white dwarf stars, hot and cool white dwarf stars, and possibly even neutron stars. The discovery of multi-periodic variations in these objects has helped to usher in a new era of rapid progress in the field of stellar seismology. For the compact stars this rapid progress is the result of a combination of four fortunate circumstances: their physical structure is relatively simple; typical amplitudes are small enough to be both readily observable and amenable to linear analysis; the wealth of observed periods in each object provides many independent clues to the underlying structure of the compact stars; and the periods are short enough that we can observe many cycles in a night, thereby completely resolving the period structure in many of these stars.

In this review I will discuss the current state of our understanding of these objects, with special emphasis on their distribution in the H-R diagram, range of pulsation properties, possible mode selection mechanisms, excitation of the pulsations, problems of convection, and particularly the measurement and interpretation of period changes. In addition to the results of recent research, I will review the techniques used to obtain them, pointing out both their strengths and weaknesses. I will close with a discussion of some of the important problems facing us in the study of these objects, and attempt to identify potentially fruitful directions for future research.
Variations of the solar limb brightness with the oscillations
Authors: Schmieder B. , Mein P.
Published: June 2019

The aim of this work is to compute the amplitude of the limb darkening fluctuations due to oscillations in order to compare with the observations made with the heliometer at the Pic du Midi (Rösch and Yerle 1983–1984). It is shown that 5 min oscillations lead to variation in the brightness gradient of less than 2%.
Experience in operating a limited global network of stations measuring full-disc oscillations of the Sun
Authors: Elsworth Y.P. , Isaak G.R. , Jefferies S.M. , McLeod C.P. , New R. , van der Raay H.B. , Palle P.L. , Regulo C. , Cortes T. Roca
Published: June 2019

Details are given about the operation of a two station network and of a new semi-automatic station which has recently been added. Comparison is made with predicted duty cycles. A possible way of quantifying the sky quality is also given.
Pulsar Surveys
Authors: Manchester R.N.
Published: June 2019

The current situation regarding pulsar surveys is briefly reviewed. Most of the known pulsars have been found by major radio surveys that were unbiased in the sense of more-or-less uniformly covering a given area of sky. The results from two recent such surveys, the Green Bank 390 MHz survey of Stokes et al. (1985) and the Jodrell Bank 1400 MHz survey of Clifton and Lyne (1986) are compared. Conclusions are drawn regarding the effect of observing frequency on the results of pulsar surveys and the galactic distribution of pulsars and interstellar electrons.
Millisecond Pulsar Surveys
Authors: Backer D. C.
Published: June 2019

In 1982 a new class of pulsars was defined by the discovery of a star with a millisecond rotation period, 1.6 ms. In the past 3.5 years two additional pulsars with millisecond periods have been discovered. The rapid spin of these pulsars is attributed to mass transfer in a low-mass binary progenitor system. This hypothesis is supported by the presence of companions in two of the three millisecond pulsars. These recent discoveries have led both to a deeper understanding of the final stages of stellar evolution in binary systems, and to closer ties between the observational study of neutron stars by radio, optical and X-ray techniques. In addition the millisecond pulsars provide precise astrophysical clocks that can be used to improve the solar-system ephemeredes and to search for a background of gravitational waves that may have been produced in the early stages of the visible universe. Old and ongoing searches for new millisecond pulsars are described in this paper.
A Modified Pulsar Model Green Function Period Distribution
Authors: Chen L.F. , Liang S.R.
Published: June 2019

The downward accelerated e− in the “unfavorable” zone, like that in the “favorable” one, will emit γ-photons, which in turn convert into e± pairs in some places near the surface of stars. But what happens, which is different from that in the “favorable” zone, is that some γ-photons will travel through a long distance before their conversion. This makes it possible that some γ-photons arrive at the “diode” district in the “favorable” zone. The magnetic conversion of pairs is much easier to happen than that occured in the “favorable” zone, where the γ-photons are created by the primary e− beam. The existence of dense e± plasma near the surface of stars makes the E, vanish at places where such plasma is present.
The Structure of Pulsar Nebulae
Authors: Chevalier R. A. , Emmering R. T.
Published: June 2019

We have found solutions to the problem of a relativistic pulsar wind interacting with a nebula moving at constant velocity vn. The wind is assumed to contain a toroidal magnetic field; the ratio of Poynting flux to particle flux in the wind is a constant σ. Under these assumptions, the wind is shocked at a radius rs that moves out at constant velocity. Solutions for the shocked wind are only possible if σ < σc = 1/(−1 + c/vn). For a given value of vn, rs → as σ → σc. Kennel and Coroniti (1984) have calculated similar models for the Crab Nebula but they assume that rs is a constant; i.e. they calculate steady-state models. The steady-state approximation is expected to be good close to the shock wave, but it breaks down in the outer parts of the nebula. For vn = 2000 km s−1 and rn/rg = 20, Kennel and Coroniti find σ = 0.003. For the same Crab Nebula pmeters, our time-dependent model yields σ = 0.0016. There may be times in the evolution of Crab Nebula or of other pulsar nebulae when a model with a shocked relativistic wind and a toroidal magnetic field cannot apply. It appears that a wide variety of structures are possible for pulsar nebulae.
The X-ray Spectra of Tycho and SN1006
Authors: Koyama K.
Published: June 2019

The supernova remnants (SNR) SN1006 and Tycho are considered to be originating from type I supernovae (SN). Therefore one may expect a large amount of heavy elements, particularly iron, in the SNRs. In fact, our recent analysis of new data on the X-ray spectrum Tycho shows strong line emission associated with ionized silicon, sulfur and iron. This result contradicts the results of previous analyses which did not require an overabundance of iron.
Population of Accreting Neutron Stars in External Galaxies
Authors: Trinchieri Ginevra
Published: June 2019

The X-ray observations of the Milky Way galaxy with non-imaging X-ray satellites (e.g. UHURU, HEAO1) has revealed a number of discrete, point -like bright sources clustered around the Galaxy's center (in the bulge region) and on the plane of the Galaxy (see for example Tanambaum and Tucker, 1984). The brightermost ones have been associated with close accreting binary systems, containing an evolved object (a white dwarf, a neutron star or a black hole) and a companion visible star. For sources with X-ray luminosities Lx≦1038 erg s−1, the compact object needs to be a neutron star or a black hole.
On the Origin of Neutron Stars in Globular Clusters
Authors: Grindlay Jonathan E.
Published: June 2019

The formation of neutron stars in globular clusters is discussed in light of a number of recent results and, in particular, studies of the origin and evolution of the high luminosity x-ray binaries found in globular clusters. We argue that the neutron stars most probably arise from the accretion-induced collapse of white dwarfs in compact binary systems, themselves detectable as low luminosity cluster x-ray sources. The white dwarfs which can collapse are probably the remnants of relatively more massive stars than those presently found in globulars. This can account for the predominant occurrence of the high luminosity cluster sources in clusters of relatively high metallicity, since those clusters have recently been found to probably have flatter mass functions of their component stars.
Hardness Ratio in Evolving Low-Mass X-ray Binary Systems
Authors: Shaham J. , Tavani M.
Published: June 2019

Spectral observations of low-mass X-ray binaries (LMXBs) show that the soft component usually dominates over the hard one. These results provide additional support to an interpretation based on models of LMXBs in which the neutron star while, on the average, spinning up, is also experiencing a spinning down torque. Under these conditions, a fraction of the luminosity associated with the gravitational release of energy on the surface of the accreting neutron star may manifest itself as luminosity originating in the inner part of the accretion disk. It is probably possible to separate the two contributions; the stellar luminosity can be associated with the hard component of the spectrum and the disk luminosity, related to the exchange of energy due to the torque between the rapidly spinning neutron star and the accretion disk, can be associated with the soft spectral component.
The Problem of Solidification in Neutron Stars
Authors: Huang W.H. , Gao S.H.
Published: June 2019

The possibility existing crystal lattice in the interior of neutron stars is an interesting topic, Vela pulsar's glitches phenomenon is explained by means of this structure. There have been many articles in this respect in recent more than ten years. We are doing some work on the same topic.
A Model for the 1979 March 5 Gamma-Ray Transient
Authors: Alcock C. , Farhi E. , Olinto A.
Published: June 2019

We have constructed a model for the 1979 March 5 γ-ray burst (Cline et al. 1980; Evans et al. 1980). This event is characterized by a rapid rise (≤ 250 μs), an intense flash of duration ∼0.15s, followed by a decaying, lower intensity phase which lasted a few minutes, and was modulated with a period of 8s. The timing position error box includes a supernova remnant in the LMC, which suggests a distance of 55 kpc. At this distance the energy in the event is ∼1044 erg and the peak luminosity ∼107 greater than the Eddington limit for a 1.4 M⊙ object.
Radio Continuum Observations of Southern Planetary Nebulae Candidates
Authors: Van De Steene G.C. , Pottasch S.R.
Published: June 2019

In an attempt to find new Planetary Nebulae we have short radio continuum observations at 6 cm and 3 cm of 90 PN candidates with the Australian Compact Array. We selected the unidentified objects from the IRAS Point Source Catalogue on basis of their PN colors. Detection of radio continuum emission at the IRAS position almost certainly confirms that these objects are PN, because it indicates the presence of ionized gas. Therefore the 18 detected sources are considered new PN. Because of their high brightness temperatures, they are probably young PN.
Planetary Nebulae as a Research Field
Authors: Saurer W. , Weinberger R.
Published: June 2019

The “Astronomy and Astrophysics Abstracts”, edited twice a year by the “Astronomisches Recheninstitut” in Heidelberg, served as basis for the determination of some data concerning the development of planetary nebulae as a research field. From the numbered and unnumbered papers within the subject category 134 there it was, for example, possible to compare the development of the PN paper rate with that of the whole field of Astronomy; for the years 1986 to 1990, a list (including postal addresses) of all individuals (ca. 900!) who published at least one paper on PN was made. For these 5 years, we now know which scientist(s) published most, in how many countries research on PN is done, how the annual publication rate varies for a specific country etc. Below, we show two results of our statistics.
Model Atmospheres of Central Stars of PN
Authors: Kudritzki R.P. , Méndez R.H.
Published: June 2019

We review the work done in this field since the time of the Mexico Symposium on PN, five years ago. Although substantial progress has been achieved, a lot of work is still needed, and we pay attention to some remaining problems. We briefly describe some recent results about stellar and nebular properties, obtained with NLTE model atmosphere techniques.
Infrared Excess (IRE) as an Indicator of PN Distance
Authors: Jacoby George
Published: June 2019

The VLA observations presented by Pottasch et al. (1988, A&A 205, 248) and Ratag et al. (1990, A&A 233, 181) demonstrate that IRE (Pottasch et al. 1984, A&A 138, 10) correlates very well with F(6 cm) for the Galactic center PN, especially when IRE is large The correlation (see figure) can be approximated by:
Ring Nebulae Around Population I WR Stars: Is Their Origin Similar to the PNe?
Authors: Lozinskaya Tatiana A. , Dopita Michael A. , Chu You-Hua
Published: June 2019

Interference filter CCD images have been obtained in Hα and [O III] λ5007 for all population I WR stars in the LMC and SMC using the 2.4 m telescope at Siding Spring Observatory ANU. We have found new ring nebulae in the LMC around Br#13, 25, 31 and 56. Ring nebulae around Br 31 and Br 13 most probably represent stellar ejecta. Nebula around Br 56 is a filamentary wind-blown bubble type.
A Model of the Chemistry in the Neutral Shell of a Planetary Nebula
Authors: Gouldsworthy S. N. , Flower D. R.
Published: June 2019

A model of the neutral region of a planetary nebula has been constructed, building on an existing program (Abgrall et al. 1992, Astr. Astrophys. 253, 525). It incorporates a large set of equations governing the formation and destruction of molecular species and also covers photo-dissociation/ionization reactions and cosmic ray interactions. The radiation field impinging on the nebula is modelled as a 105 K diluted Planck spectrum, truncated below 91.2 nm, augmented by spectral emission lines from the ionized region (data from G. Stasinska, private communication) and the hydrogen (2s→1s) two-photon continuum. The chemical species involved in the reactions are composed of seven elements — H, He, C, O, N, S and Fe — with H and He dominating the elemental abundances. The model considers a chemical environment which is carbon-rich (i.e. C/O > 1).
High Resolution Observations of CO in PNe
Authors: Shibata K.M. , Deguchi S. , Kasuga T. , Tamura S. , Hirano N. , Kameya O.
Published: June 2019

We have made aperture synthesis observations of 12CO(J=1−0) emission IRAS 21282+5050, CRL 618 and M 1–7 using the Nobeyama Millimeter Array (NMA). We observed with 3 or 2 configurations and obtained an angular resolution of 3″.2 × 3.1, 3″.6 × 3″.5 and 4″.3 × 3″.8.
Carbon- and Oxygen-Rich Progenitors of Planetary Nebulae
Authors: Habing H.J. , Blommaert J.A.D.L.
Published: June 2019

This review concerns stars on the Asymptotic Giant Branch that are about to develop into planetary nebulae (=PNe). They are still termed “stars”, and properly so, and yet they have already, in statu nascendi, the structure of a PN. There are two different kinds: oxygen-rich stars (spectral class: M) and carbon-rich stars (spectral class: C).
Planetary Nebulae from Miras?
Authors: Whitelock Patricia A. , Feast Michael W.
Published: June 2019

The properties of large amplitude AGB variables (Miras) are reviewed with particular emphasis on their relevance for evolution into PNe. We concentrate on recent observations in the LMC and Galactic Bulge. The available evidence is consistent with the idea that most Miras evolve into PNe and that most old disk stars go through the Mira and PNe phases. However, there are some suggestions that the most metal rich stars in the Galactic Bulge go through neither phase or do so very rapidly. The lifetime of a typical Bulge Mira must be more than 105 yrs and Miras outnumber PNe in the Bulge by about 10 to 1.
Dynamical Structures of Planetary Nebulae — Models Against Observations
Authors: Marten H. , Gesicki K. , Szczerba R.
Published: June 2019

Hydrodynamical calculations of Planetary Nebulae (PNe) over 25000 yrs of evolution which include timedependent effects of ionization as well as variable central stars winds and parameters consistent with stellar model calculations show a great variety of velocity and density structures which strongly deviate from the often assumed “homogeneous shells, expanding with constant velocities” (Marten & Schönberner, 1991, hereafter MS). By means of a static photoionization code we calculate the surface brightness in the 10 most prominent nebular emission lines for density structures of the model sequence “VS” as given by MS. The obtained radial emissivities are used together with the velocity and temperature structure of the ionized gas to calculate (thermally broadened) line profiles in order to derive “measured” expansion velocities. We compare the theoretical surface brightnesses with observations and demonstrate some difficulties in the interpretation of nebular expansion velocities, expansion distances and ages.
Rotation-Pulsation Coupling in the Bipolar Preplanetary Nebula, V Hya
Authors: Morris Mark , Barnbaum Cecilia
Published: June 2019

High-resolution optical spectra were taken of the carbon star V Hydrae at 10 different epochs spanning two stellar periods using the Hamilton Echelle Spectrograph at Lick Observatory. Velocities were determined at each epoch by performing a cross-correlation analysis against the spectra of standard stars with previously-determined velocities. The velocities of individual atomic absorption and emission lines, and their variations with phase, were also determined. The rising and falling of the photosphere is clearly in evidence, with an amplitude about the mean of ± 5 km s−1 and a phase consistent with the expectation that maximum light occurs at minimum radius. In addition, the spectra were subjected to a rotational broadening analysis, in which we determined V sin(i), where V is the presumed equatorial rotation velocity, by minimizing the differences between the spectra of V Hya and a number of artificially broadened comparison stars showing no evidence for broadening. Mechanisms other than stellar rotation, including both turbulence and opacity, were found to be unlikely contributors to the broadening. The very unusual rotation velocity (for a red giant) was found to vary between about 10 and 18 km s−1, with an average of ≈ 14 km s−1. The relative phase of the rotation velocity curve is consistent with the hypothesis that the pulsation leads to a periodically varying moment of inertia. The assumption of angular momentum conservation, coupled with the radial velocity and V sin(i) curves, permits a deduction of the equilibrium stellar radius: The similar magnitudes of the rotation and pulsation velocities imply that they are dynamically coupled, leading to a latitude–dependent circulation which probably affects the mass loss. This interaction should also have a strong effect on the convective structure of the envelope. The angular momentum implied for the V Hya atmosphere leads us to the conclusion that it is a common-envelope binary, and that it is a precursor of a binary nucleus in a bipolar planetary nebula.
Hα Profiles of Selected Candidates for Proto-Planetary Nebulae
Authors: Tamura S.
Published: June 2019

The high-dispersion Hα line profiles of the candidate stars for proto-planetary nebulae(PPNs) are presented. Samples include mostly F supergiant stars. Volk and Kwok(1989) summarized four classes of stars which had been described in various literature as PPNs. They selected nearly one hundred new candidates of PPNs due to IRAS data. Our goal is to make clear the mass-losing phenomena and to establish the adequate models for the explaination of observed data from such stars. F supergiant stars also attract our attention to the spectroscopic variability in connection to their extended, rarefied and therefore complicated atmosphere. Observations were made at the Okayama Astrophysical Observatory with the 188-cm reflector and its coudé spectrograph. We used the intensified Reticon as the detector which has one dimensional array of 1024 pixels. The size of one pixel is 25 μm and corresponds to 0.13 Åand 5.9 km/sec at Hα. Our stellar samples are HD 46703, HD 56126, HD 112374, R CrB, HD 161796, 89 Her, IRAS 18095+2704, AFGL 2343, HD 187885, and UU Her. We obtained the Hα profiles and found a couple of absorption lines like the FeIλ6569, FeIIλ6516, and CIλ6587 among them. An express report and a short discussion about a part of these samples was already presented by Tamura and Takeuti(1991). Subsequent reports appeared and will appear in the articles of Tamura, Takeuti, and Zalewski(1992); Tamura and Takeuti (1992). We show various kinds of Hα profiles which consist of absorption and emission components and show clear evidence of activity in the extended atmosphere. We classify them into (i)P Cyg type profile, e.g. 89 Her, (ii)inverse P Cyg type profile, e.g. HD 187885, (iii)profiles with the central reversal at the bottom of absorption, e.g. HD 46703, (iv)profile with shoulder emission components, e.g. HD 56126, (v) asymmetric absorption profile, e.g. AFGL 2343. Concerning HD 161796 the Hα profile seems to have only an absorption component. It should be attributed to time variations, because the profile observed by Luck et al.(1990) is similar to (iv). In addition to a wide variety of the Hα profiles we have noticed their time variations ranging over different time spans, month, day, even in several ten minutes. Arellano Ferro(1985) noticed the change of Hα profiles of luminous yellow supergiants in various time scales too. We obtained radial velocities and compared with the expected values by the galactic rotation. We can recognize our sample stars are far from the galactic kinematics of disk members.
Shock Modelling of the Bipolar Outflow Source NGC 6537
Authors: Cuesta L. , Phillips J. P.
Published: June 2019

NGC 6537 is an unusual high excitation bipolar outflow source, with anomalous abundances indicative of a type I nebula. We have recently obtained a range of high resolution spectrophotometry for this source using the 2.5 m Isaac Newton Telescope (Observatorio del Roque de Los Muchachos, La Palma), together with narrow band optical imaging using the 2.6 m Nordic Optical Telescope (Observatorio del Roque de los Muchachos, La Palma). As a consequence, it is apparent that the source optical morphology is suggestive of the presence of an hyperbolic shock outflow surface, similar to those observed in other BPN (e.g. NGC 6302, Hb 5). Line ratio maps also indicate the presence of extremely strong [Nii] emission at the periphery of the outflow, whilst expansion velocities are of order ∼ 400 km sec−1. These large shell expansion velocities may in turn be driven by an extremely high velocity wind, which in this case appears to extend over a range ΔV ≥ 3000 km sec−1.
A Spectroscopic Study of Binary Star Planetary Nebulae
Authors: Walsh J.R. , Walton N.A. , Pottasch S.R.
Published: June 2019

A comprehensive spectrophotometric survey of the central stars of planetary nebulae with known or suspected binary star nuclei (BSPN) is underway. The aims of this programme are: to determine the nature of the companion to the ionising star of the nebula; to estimate the spectroscopic distance from the spectral type and magnitude of the companion and thence to determine the luminosity of the hot star; to compare the morphologies and excitation/abundance characteristics of BSPN with those of PN produced by single star evolution. The advantage of the distance determined from this simple method is that it is independent of any assumptions about the planetary nebula, in contrast to most other PN distance estimators.

To date 75 percent of known or suspected BSPN have been observed with the 2.5m Isaac Newton Telescope and the 1.5m ESO spectroscopic telescope at low and intermediate dispersions. A selection of preliminary results from the programme is presented, highlighting the binary central stars of NGC 246 and Abell 65.
New Light on UU Sagittae
Authors: Bell S.A. , Pollacco D.L.
Published: June 2019

New V and I band CCD photometry and medium resolution spectroscopy are used to derive the masses, luminosities and radii accurate to < 10% for the individual components of the eclipsing central star of the planetary nebula A63–UU Sge (M1 = 0.63 ± 0.06M⊙, R1 = 0.33 ± 0.01R⊙, M2 = 0.29 ± 0.04M⊙ and R2 = 0.53 ± 0.002R⊙). Emission lines from the secondary component and HeII and NV absorption features from the primary component are used to determine the first radial velocity curves of the system. Ultra–violet and optical spectra show that the temperature of the primary compoment is ∼ 105K – much larger than previously suspected. As the techniques used are essentially independent this is probably the most accurately known mass for a planetary nebula central star and therefore allows meaningful comparison to be made with evolutionary tracks for these objects.
The Active Phase of the Hot Component of Z Andromedae
Authors: Fernandez-Castro T. , Gonzalez-Riestra R. , Cassatella A. , Taylor A.R. , Seaquist E.R.
Published: June 2019

Z Andromeda is considered as the prototype of the symbiotic class. This system behaves essentially as the nearly uncontamined nucleus of a young planetary nebula. The parameters of its hot component (R=0,07 R0, T > 105 K) show that it lies close to the CSPN in the HR diagram (see Fernández–Castro et al. 1988). During the IUE lifetime (1978 onward), Z And experienced a phase of quiescence followed by an active phase which, starting in April 1984, lasted until about July 1986. Since then the star is recovering its quiescent appearance.
BZ Camelopardalis = 0623+71: The Cataclysmic Variable Inside a Bow-Shock Nebula
Authors: Shakhovskoy N.M. , Efimov Yu.S. , Andronov I.L. , Kolesnikov S.V.
Published: June 2019

The object BZ Cam = 0623+71 (Krautter et al., 1987) was observed at the telescope AZT-11 of the Crimean Astrophysical Observatory by using the UBVRI photometer-polarimeter of the Helsinki University (Korhonen et al., 1984). No significant linear polarization was found, the mean values have the upper limit of 0.2 per cent.
Further Models of Planetary Nebula Spectral Evolution
Authors: Volk K.
Published: June 2019

Studies of the total spectra of planetary nebulae (PN) show that they usually emit significant fractions of their total energy at infrared wavelengths. Many PN have IRAS observations but we do not understand their broad-band colours. To model these observations requires a combination of a photoionization treatment of the ionized region and a radiative transfer treatment of any neutral dust shell. Including the effects of the central star evolution and an assumed galactic distribution allows many observables to be simulated. I find that the Schönberner 0.64 M⊙ evolutionary track is too slow in the transition to high temperature to match the IRAS colours of PN if a typical AGB wind expansion speed is 10 km s−1. Accelerating the evolution track by a factor of 2 produces reasonable agreement. An equal mixture of carbon-rich and oxygen-rich sources with mass loss rates of 2 × 10−5 M⊙ yr−1 seems to reasonably match the general properties of the PN data from IRAS although the details are still unclear. These models strongly indicate that the post-AGB luminosity decline deduced by Knapp (1986) from radio CO line observations is not correct.
Morphology and Evolution of Planetary Nebulae
Authors: Stanghellini L. , Corradi R. L. M. , Schwarz H. E.
Published: June 2019

A large set of narrow-band images of planetary nebulae (PNe) have been studied together with the location of their nuclei (PNNi) on the logTeff – logL/L⊙ plane, in order to disclose possible correlations between the morphological class of the PNe and the evolutionary stage of their PNNi.
Dynamics of Agb Stars and Planetary Nebulae in the Galaxy
Authors: Dejonghe H.
Published: June 2019

The available kinematical data on OH/IR stars and PNs are reviewed. Dynamical models for the OH/IR stars are presented.
The Chemical Features of Galactic Planetary Nebulae
Authors: Amnuel P. R.
Published: June 2019

The chemical composition of 218 galactic planatary nebulae is investigated, all the nebulae are divided into four classes according to the masses of the nebulae and progenitor stars. The values of local abundances, galactic abundances and electron temperature gradients are found for each class of nebulae. The correlations between element abundances are also investigated. The results are compared with theorical predictions.
Galactic Ba Enrichment from TP-AGB Stars
Authors: Raiteri C. M. , Busso M. , Matteucci F. , Gallino R.
Published: June 2019

The production of the bulk of barium has long been ascribed to the main component of the s-process, whose astrophysical site has been envisaged in the convective He shell of Thermally Pulsing Asymptotic Giant Branch (TP-AGB) stars of low mass (1–3 M⊙; see Käppeler et al. 1990). The main neutron source is the 13C(α, n)16O reaction, operating at the thermal energy of kT = 12keV. We have calculated neutron captures in such environment with an updated nuclear physics, adopting the neutron capture cross sections of Beer, Voß, & Winters (1992) together with their temperature-dependence. Stellar models producing a mean neutron exposure of τ0 ≃ 0.30 mb−1 are able to reproduce the solar distribution of the s-abundances satisfactory, but the Ba isotopes show some overproduction. Such a strong indication suggests a revision of the Ba cross sections (see Gallino, Raiteri, & Busso 1992). Once that a suitable choice of σn, γ(Ba) is made, it is found that a r-contribution to solar Ba of the order of 10% can be expected.
Synthetic AGB Evolution in the LMC: The Abundances of PN
Authors: Groenewegen Martin , De Jong Teije
Published: June 2019

We have developed a model to calculate the evolution of AGB stars in a synthetic way. The evolution is started at the first thermal pulse (TP) and ends when the envelope mass has been lost due to mass loss or when the core mass reaches the Chandrasekhar mass.
Inertial Frame Determination from Hipparcos Observations of Minor Planets
Authors: Hestroffer D.
Published: June 2019

Observations of 48 minor planets by Hipparcos should lead to a good determination of the inertial reference frame. Analysis of one year observations showed periodic effects in the o-c due to a rotation between the Hipparcos system and the inertial system. By extending this result to a 2.5 years simulation and by studying the impact of added ground-based observations, it appears that the orbital elements of the Earth and the parameters of a rotation of the system can be obtained with an accuracy better than 5 mas.