bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Planetary Nebula
Authors: Capellaro E. , Turatto M. , Sabbadin F.
Published: July 2016

The object (α1950 = 18h04m.3; δ1950 = −8o56!4) was discovered in a 103a-E+RG 1 objective prism plate taken with the 92/67-cm Schmidt telescope of the Astrophysical Observatory of Asiago (Italy). It presents only the Hα emission and no stellar continuum; following Kohoutek (1965, 1969, 1972) it is a bona fide planetary nebula. This classification is confirmed by the appearance of the object in the red and infrared plates of the Near Infrared Photographic Survey of the galactic plane (Sabbadin, 1986): it is quite bright in the red plate and almost invisible in the infrared one.
Planetary Nebulae Near the Galactic Center I: Method of Discovery and Preliminary Results
Authors: Pottasch S. R. , Bignell C. , Olling R. , Zijlstra A. A.
Published: July 2016

A method is described for finding planetary nebulae. Use is made of the far infrared IRAS colors and radio continuum measurements. The method is applied here to a region within 15° of the galactic center. The first results are given, including 36 new PN. The characteristics of the nebulae are described. While they are generally similar to known nebulae, the method of selection gives an emphasis to younger objects. A substantial number of the new nebulae may be in the transition phase between OH/IR stars and PN.
Distances to Planetary Nebulae
Authors: Lutz Julie H.
Published: July 2016

Finding distances to planetary nebulae remains a frustrating undertaking, but significant progress has been made over the past several years. This review covers primarily work done on distances since 1980, with some references to earlier papers. Some interesting new methods have been tried recently and some methods that have been used for years have been refined. Missions such as the Hubble Space Telescope and Hipparcos may provide new data on distances. Advances in ground-based telescopes and instruments will make possible new studies of distances.
Planetary Nebulae and the Galactic Bulge
Authors: Feast M.W. , Kinman T.D. , Lasker B.S.
Published: July 2016

Fifteen new PN have been discovered in the region of Baade's Windows using an objective prism technique. Absolute spectrophotometry, excitation classes, radii and radial velocities have been obtained. Radial velocities were also measured for eight other PN in this region. After correction for solar motion and the circular velocity at the sun, the radial velocities of bulge PN (Vc) with |b| < 5°.5 show good evidence for a rotation of the bulge. If Vc=α + βΔℓ then,
Spectroscopic Distances to Central Stars of Planetary Nebulae
Authors: Méndez R. H. , Kudritzki R. P. , Herrero A. , Husfeld D. , Groth H. G.
Published: July 2016

We present spectroscopic distances for 22 central stars of planetary nebulae. These distances have been determined using information provided by our non-LTE model atmosphere analyses of the stellar H and He absorption line profiles. In this way, no assumptions about nebular properties are necessary.

Our spectroscopic distances turn out to be larger than many other frequently cited values. We show that our distances are not in contradiction with the available information about the interstellar extinction, and we describe additional evidence supporting them.
H2 and HI Emission Line Imaging of the Ring Nebula NGC 6720
Authors: Greenhouse M. A. , Hayward T. L. , Thronson H. A.
Published: July 2016

We present infrared emission line images of the v = 1 → 0 S(1) transition of molecular hydrogen and Brγ recombination line of atomic hydrogen which cover the entire extent of NGC 6720, the Ring Nebula. The maps presented here are the highest angular resolution images of these transitions yet produced for this object, and have very low relative positional uncertainty. As a result, we clearly resolve the spatial stratification of the ionized and shocked molecular zones within the nebula discussed previously by Beckwith et al. (1978). The relative spatial distribution of molecular and ionized hydrogen we observe is typical of several planetaries which exhibit shocked H2 emission (eg. see Zuckerman and Gatley 1987), and is similar to that predicted by the interacting-stellar-winds model of planetary nebulae formation (see Volk and Kwok 1985 and references therein).
The Display and Manipulation of PN Images on an IBM PC or Compatible
Authors: Hoey M. J. , Whelan D.
Published: July 2016

This paper describes PC_IMega, a menu driven program that allows digital images to be displayed and manipulated on an IBM PC or compatible microcomputer, running under PC-DOS versions 2 or 3 with 128k of RAM. A sixteen colour Enhanced Graphics Adaptor card gives a screen resolution of 640 × 350 pixels.
Kinematical Properties of Planetary Nebulae
Authors: Bianchi Luciana , Greving Michael , Barnstedt J. , Diesch Chr.
Published: July 2016

We present newly determined expansion velocities for a number of Planetary Nebulae (PNe) which have been observed with the ESO 1.4m CAT and the Coude' Echelle Spectrograph (CES), operated at a r.p. of 105, corresponding to a resolution of about 3km/s at Hα. Two detector systems have been used: the standard ESO Reticon and a two-dimensional photon-counting imaging detector developed at the A.I.T. (AIT-MCP-Camera).
Evidence of Expansion in the Central Region of NGC 2346
Authors: Banerjee D.P.K. , Anandarao B. G. , Desai J. N. , Jain S. K. , Mallik D.C.V.
Published: July 2016

We present observations of the bipolar planetary nebula NGC 2346 carried out with the 1-m telescope at the Vainu Bappu Observatory in Kavalur, India using (1) a high resolution piezo-electric scanned Fabry-Pérot Spectrometer (with a velocity resolution of 10 km s−1) for line studies in the 6000 A - 7000 A spectral range and (2) a pressure scanned Fabry-Pérot spectrometer (with a velocity-resolution of 5 km s−1) in the green region. The nebula was observed in the H I 6563 A and [N II] 6583 A emission lines using a 15″ aperture and in the [O III] 5007 A line using an 8″ aperture centered on the bright central spot. A number of scans in each of these lines were co-added to improve the signal-to-noise ratio. The [O III] profile shows a well defined split between the blue and the red component, typical of an expanding shell. The [N II] profile does not show a well resolved split, although a pronounced suggestion of a split was observed in all the scans. The Hα profile was broad and asymmetric. The composite [O III] and [N II] profiles were decomposed into two individual Gaussians for obtaining the expansion velocity.
The Structure of NGC 2392
Authors: Hoey M. J.
Published: July 2016

This paper reports preliminary results of a recent detailed examination of the morphology of the planetary nebula, NGC 2392.
Long-Slit 2-Dimensional Spectra of the Giant Halos Around NGC 6543 and NGC 6826
Authors: Middlemass D. , Clegg R.E.S. , Walsh J. R.
Published: July 2016

We have observed the large, faint halos around NGC 6543 and NGC 6826 with the Isaac Newton Telescope, using IPCS and CCD (2-dimensional) detectors. Line intensities are measured every 1.5 arcsec over a total slit length of 3 arcmin (IPCS) or 2 arcmin (CCD). Several slit positions across the halos were observed, so as to obtain average properties of these two regions. Halo spectra are compared with spectra of the bright core, so as to distinguish between reflection by dust and genuine thermal emission; the halos are not reflection nebulae.
Expansion Velocities of Southern Planetary Nebulae K.C. Sahu
Authors: Sahu K. C. , Pottasch S. R.
Published: July 2016

We have undertaken a programme of kinematic study of southern planetary nebulae by obtaining high-resolution (R ≥ 50,000) spectra, using the ESO 1.5-m telescope + the Coudé Echelle Spectrograph. As first results of this study, this paper presents previously unknown expansion velocities of 16 planetary nebulae. This result increases the total number of planetary nebulae for which the expansion velocities are now known by about 10%. Further, reliable distance measurements and other physical properties are available for most of these sources. Hence this sample significantly improves the previously available data for statistical analysis related to the dynamics and evolution of planetary nebulae. Some preliminary results based on such statistical analysis are presented. The details of the results will be published in Astron. Astrophys.
Detection of an Extended Optical Halo around IC 418
Authors: Monk D. J. , Barlow M. J. , Clegg R.E.S.
Published: July 2016

Two-dimensional long slit AAT IPCS spectra of IC 418 (in the 3400–4400 A wavelength region) show faint extensions in the [O II] 3726, 3729 A and Hγ emission lines out to at least 60 arcsec south and 50 arcsec north of the central star, compared to the angular radius of only 6 arcsec for the bright nebula.
Kinematic Structure and Chemical Composition of the Double Shell PN NGC 3242
Authors: Sahu K. C. , Pottasch S. R. , Anandarao B. G. , Desai J. N.
Published: July 2016

Kinematic study of the multiple shell PN NGC 3242 was carried out by obtaining Hα and [O III] line profiles at 9 positions of the nebula using a high-resolution (R ≅ 50,000) Fabry-Pérot spectrometer. The positions cover both the bright inner shell and the faint outer shell. It is shown here that the two apparently continuous shells are kinematically separate: the faint outer shell was ejected ∼ 5000 years earlier and has less expansion velocity than the bright inner shell.
A Young Planetary Nebula with OH Molecules: NGC 6302
Authors: Payne H. E. , Phillips J. A. , Terzian Yervant
Published: July 2016

We report the results of a sensitive survey of planetary nebulae in all four ground state OH lines. Our results confirm that evolved planetary nebulae are not OH sources in general. However, we did detect one interesting object: an OH 1612 MHz maser in the young planetary nebula NGC 6302. This nebula may be in a brief evolutionary stage, similar to the young and compact planetary nebula Vy 2-2 where OH has already been detected.
Detection of OH Maser Emission at 1667 MHz from IC 4997
Authors: Tamura S. , Kazes I.
Published: July 2016

We report the first detection of OH emission at 1667 MHz from a planetary nebula, IC 4997 (Figure 1). OH emission in satellite line of 1612 MHz was detected already from planetary nebulae not only Vy 2-2 (Davis and Seaquist 1979), but also two IRAS objects which were distinguished from OH/IR stars as planetary nebulae (Pottasch et al 1987). OH observations of IC 4997 have been carried out with the large radio telescope at Nançay, France. Highly resolved optical emission lines were obtained at the Okayama Astrophysical Observatory, Japan.
Planetary Nebulae and the Pregalactic Helium Abundance
Authors: Maciel Walter J.
Published: July 2016

Recent work has emphasized the determination of the pregalactic helium abundance by mass Yp and the slope ΔY/ΔZ based on the chemical composition of both galactic and extragalactic H II regions (Pagel, 1987; Pagel et al., 1986).
The Peculiar Planetary Nebula M1-78
Authors: Pottasch S. R. , Zijlstra A. A. , Ukita N. , Manchado A. , Ratag M.
Published: July 2016

The question of whether M1-78 is a PN or a compact H II region is discussed. We have obtained new high resolution radio continuum maps, optical spectra and CO maps. Arguments for it being a PN include spectral information, far infrared continuum emission, and radio morphology. It is the strongest CO emitting PN known. Its abundances are peculiar: high helium and very low oxygen and nitrogen abundances. If it is a PN it must be within 4 kpc, but 21-cm absorption measurements indicate that it may be further away.
Magnesium Abundances in Planetary Nebulae and Interstellar Absorption of Mg II λ2800 A
Authors: Middlemass D.
Published: July 2016

High-resolution IUE images have provided line profiles of emission cut by interstellar absorption in the magnesium II lines λλ2795, 2802 A in nine objects. The underlying emission has been reconstructed in seven of these by fitting Gaussian profiles to the remaining line wings. Estimates of the ratio of intrinsic to observed emission ranging from 1.5 to 23 have been obtained. Photo-ionization models of IC 418, IC 4997 and NGC 2440 have been used to obtain Mg/H ratios from the corrected Mg II line strengths. The logarithmic magnesium abundances obtained were 7.6±0.12, 6.96±0.3 and 6.5±0.3 respectively. These results indicate that depletion of Mg into grains is less than previously thought and reduce the observed gradient in the magnesium abundance. The Mg depletion may be related to the C/O ratio within the nebula; carbon-rich planetary nebulae may have less magnesium depletion than those with C/0 < 1.
A Possible Subdivision of Type II Planetary Nebulae
Authors: Faúndez-Abans M. , Maciel W. J.
Published: July 2016

A revision is made of the classification scheme of planetary nebulae proposed by Peimbert (1978), taking into account the observed heavy-element abundances and radial abundance gradients (Faúndez-Abans and Maciel, 1986; 1987a). A subdivision is proposed of type II PN into the subtypes a and b, according to their nitrogen abundances relative to hydrogen (Faundez-Abans and Maciel, 1987b). Type IIa PN show a higher enrichment in nitrogen than type IIb, which present a nitrogen abundance close to the value of population I objects and a radial N/H gradient as well.
A Photoionization Model Study of NGC 7027
Authors: Gruenwald Ruth B. , Pequignot Daniel
Published: July 2016

The physical characteristics of NGC7027 and the nature of the observations available make it an exceptional object to check the ability of steady photoionization modelling to correctly predict the emission spectrum of nebulae. After a decade of atomic physics and observation improvements, a complete updating of the analysis performed by Pequignot et al (1978) (Astron. Astrophys. 63, 313) is in order.
Close-Binary and Pulsating Central Stars
Authors: Bond Howard E.
Published: July 2016

As a result of photometric-monitoring studies, 7 planetary-nebula nuclei are now known to be binaries with orbital periods less than one day. These systems were probably produced via a common-envelope interaction, during which a wide pair was converted to a close binary surrounded by an ejected red-giant envelope. The frequency of occurrence of such close binaries among PNNs is about 10–15%, showing that binary-star interactions are a significant production mechanism for planetary nebulae. The descendants of close-binary PNNs are probably the cataclysmic variables. Two CVs surrounded by nebulae resembling old planetaries, 0623+71 and GK Per, may provide the most direct evidence for the origin of CVs through PN ejection. The observed birth rate for close-binary PNNs is more than an order of magnitude higher than for CVs, possibly indicating that our census of the CV population is very incomplete. The nucleus of K 1-16 is a member of the GW Vir class of extremely hot pulsating pre-white dwarfs, and the only one known to be surrounded by a PN. These objects offer exciting opportunities for direct measurement of evolutionary timescales and for seismological investigations of the interiors of PNNs and their immediate descendants.
Binarity and Intrinsic Variability in Central Stars of PN
Authors: Méndez R. H.
Published: July 2016

1. Introduction. 2. A list of binary and multiple CSPN. 3. A radial velocity study of CSPN at high spectral resolution. 4. Spectroscopic binaries or intrinsic variables? 5. Concluding remarks.
Model Atmospheres and Quantitative Spectroscopy of Central Stars of Planetary Nebulae
Authors: Kudritzki R. P. , Méndez R.H.
Published: July 2016

It is a good tradition in IAU Symposia about PN to have a paper on model atmospheres. However, this is always a difficult task for the authors, because the majority of the PN researchers still believe that the best model atmosphere for a Central Star is a black body. Of course, this puts a theorist in stellar atmospheres into a somewhat desperate position. However, Central Stars of Planetary Nebulae (hereafter CSPN) - as all other stars - show spectral lines. And we will try to use the opportunity of this paper to convince that - as for all other stars - the quantitative analysis of these lines on basis of model atmospheres yields extremely valuable information about the physical nature of the stars.
The Central Star of NGC 7027
Authors: Walton N.A. , Pottasch S.R. , Reay N. K. , Spoelstra T.
Published: July 2016

We have detected the central star of NGC 7027 by imaging the nebula through a narrow band ‘continuum’ filter onto the IPCS detector at the 2.5m Isaac Newton Telscope. We obtain an apparent visual magnitude for the central star of mv = 17.7 ± 0.5 mags.

Assuming that the central star radiates approximately as a blackbody, which is reasonable for the case of a hot star, then Zanstra temperatures for the central star can be calculated. We find TZ(H) = 3.9 × 105K and Tz(HeII) = 2.6 × 105K. Using the correction due to Stasinska & Tylenda (1986) we estimate the central star of NGC 7027 to have a temperature, Teff = 3.1 × 105K.

The luminosity and radii are found assuming a distance of d=1.2 kpc., giving L = 12,600 L⊙ and R = 0.039 R⊙. Placing the central star on the Log L - Log T diagram and comparing with evolutionary tracks for central stars with various masses from Wood & Faulkner (1986), indicates that the central star of NGC 7027 must have a mass, M ≥ 0.8 M⊙.

Radio observations of NGC 7027 have been taken using the Westerbork Radio Synthesis Telesocpe at 21cm. Self calibration techniques have been employed to give a radio continuum map of high dynamic range. These observations are being compared with a deep optical Hβ map to study the nature of the faint halo seen around NGC 7027 (Atherton et al. 1979)
Einstein X-ray Observations of Planetary Nebulae and their Implications
Authors: Tarafdar S. P. , Apparao K.M. V.
Published: July 2016

Central stars of nineteen planetary nebulae were observed for X-ray emission using the Einstein Observatory and four of them were detected. High resolution observations with the Einstein Observatory indicates that the X-ray source in NGC 246 is a point source. These planetary nebulae with positive observations turn out to be the nearest, have the least extinction and also have the largest size of the nebulae around them. It is possible that X-ray emission is observed from these planetary nebulae with larger ages because of the smaller extinction by the nebulae and also due to the settling of heavy elements in the central star which otherwise prevents escape of X-rays by providing opacity.
Nonradial Pulsational Analyses of the Pulsating Central Stars of Planetary Nebulae
Authors: Starrfield Sumner , Cox Arthur N.
Published: July 2016

We have performed nonradial pulsation analyses of the central star of the planetary nebula K1-16. K1-16 is a very unusual nebulae which appears to have ejected material that is very rich in helium. The central star shows no evidence for hydrogen in its spectrum and the helium and carbon lines are in emission. Grauer and Bond (Ap. J., 277, 211, 1984) discovered that it is pulsating with periods around 1700 sec. Although its spectral characteristics are similar to those of the PG1159-035 variables, it is pulsating in much longer periods than they are.
A Case Study of a WC Nucleus
Authors: Kaler J. B. , Shaw R. A. , Feibelman W. A.
Published: July 2016

We have examined the extraordinarily rich WC spectrum of the nucleus of He 2-99, an object closely akin to BD +30°3639. In all, we log 25 lines in the UV (λ1240-λ1950; λ2550-λ3150) and 89 in the optical between λ3610 and λ7065 (including a small number of nebular features). We provide a fundamental atlas for this class of star, wherein we give fluxes and identifications of the emission lines, including a detailed accounting of blends. The most powerful emissions are those of C III followed by C II and C IV. There is good indication that C I and even C V are present as well. Oxygen is well represented by O III; O II, O IV, and O V all appear present, but are generally confused by blends. Si III and Si IV appear, as do He I and He II. Other than N V, little case can be made for stellar nitrogen. The most serious barrier to analysis of the spectrum is the problem of coincidences and blends: there are few pure lines. Analysis of the nebular spectrum, which is severely contaminated by stellar line emission, indicates enrichment in carbon, but none in nitrogen.
The Kinematics of the Planetary Nebulae in the Large Magellanic Cloud
Authors: Meatheringham Stephen J. , Dopita Michael A. , Ford Holland. C. , Webster B. Louise
Published: July 2016

The radial velocities of a total of 94 Planetary Nebulae (PN) in the Large Magellanic Cloud (LMC) have been determined. The kinematics of the population of planetary nebulae is compared with the H I data in the context of a re-analysis of the survey by Rohlfs et al. (1984), taking into account the transverse velocity of the LMC. We find that the best solution for this transverse velocity is 275±65 km s−1, and that the LMC is near perigalacticon. This is consistent with a maximum Galactic mass of order 4.5 × 1011M⊙ out to 51 kpc the rotation curve obtained after correction for this velocity implies a mass of (4.6 × 0.3) × 109 M⊙ within a radius of 3 degrees, or about 6 × 109 M⊙, total. The rotation solution for the PN population is essentially identical with that of the H I, but the vertical velocity dispersion of 19.1 km s−1 is much greater than the value of 5.4 km s−1 found for the H I. This increase in velocity dispersion is consistent with it being the result of orbital heating and diffusion operating in the LMC in a manner essentially identical with that found for the solar neighbourhood.
Central Star and Nebular Masses for Magellanic Cloud Planetary Nebulae
Authors: Monk D. J. , Barlow M. J. , Clegg R. E. S.
Published: July 2016

AAT and IUE spectra of thirteen medium-excitation Magellanic Cloud planetary nebulae have been used to derive H I Zanstra effective temperatures and surface gravities for the central stars.
Progenitors of Planetary Nebulae
Authors: Kwok Sun
Published: July 2016

Over the past decade, we have come to realize that mass loss on the asymptotic giant branch (AGB) plays a significant role in the formation of planetary nebulae (PN). Mass ejected during the AGB can now be observed in haloes of PN and we believe that the main shell of PN is formed by the interaction of this material with a later-developed central-star wind. In this review, we show that the evolution from AGB to PN can be traced in a continuous infrared sequence. This sequence predicts properties of proto-PN which allow them to be identified.
IRAS 17516-2525: The Birth of a Planetary Nebula?
Authors: van der Veen W.E. , Habing H. J. , Geballe T. R.
Published: July 2016

IRAS 17516-2525 is a cool object at infrared wavelengths between 1 and 60μm. Spectroscopy in the wavelength ranges 2 - 2.5μm and 3 - 3.5μm shows the presence of Brα, Brγ, Pfγ emission lines and of a weak C2H2 absorption band, all clearly associated with the IRAS source. At the infrared position a faint star with a visual magnitude of about 20 is found.
The Shocking Truth About some “Proto-PN”
Authors: Goodrich R. W. , Bianchi Luciana
Published: July 2016

A small number of bipolar planetaries -including M2-9, M1-91, GL 618, and M2-56- exhibit very strong emission lines of low ionization species such as [O I], [N I], [N II], and [S II]. Most previous authors have attempted to analyze the spectra of these objects assuming that they are photoionized by their central stars. Closer examination, however, suggests that a different excitation mechanism may be at work -that of shock heating.
HCN, The First Strong Maser in Carbon-Rich Stars
Authors: Omont A. , Guilloteau S. , Lucas R.
Published: July 2016

Maser emission has been observed at the frequency of the (0,2,0) J - 1 - 0 line of HCN (89088 MHz, energy 2050 K above the ground state) in 7 C-rich circumstellar envelopes: CIT 6, S Cep, IRC+ 50096, IRC+30374, FX Ser, AFGL 2513 and IRAS 17581-1744. This is the second molecule showing strong maser emission in millimeter lines, and the first strong maser ever observed in a C-rich circumstellar envelope. The emission is particularly strong (70 Jy) in CIT 6 because of its proximity (Guilloteau, Omont, and Lucas 1987). The masers in the stars have luminosities and linewidths (FWHM about 1 km/s) similar to CIT 6; they are also blueshifted by a few km/s with respect to the velocity of the star given by the central velocity of the ground-state HCN emission (Lucas, Guilloteau, and Omont 1987). These properties are somewhat similar to those of SiO masers in O-rich stars, although the intensities of HCN masers are weaker.
Lower Limit for NPN's Masses
Authors: Harpaz Amos
Published: July 2016

The lowest mass observed for a nucleus of a planetary nebula (NPN) is about 0.55 M⊙ (Weidemann and Koester, 1983, Schonberner, 1983). Hence, Lower mass WD's should have been produced without going through the phase of a visible PN ejection. Recently, Harpaz et al. (1987), have shown that very low mass WD's (up to 0.45 M⊙) can be formed by a single star evolution from red giant branch (RGB) stars, due to mass loss along the RGB. It turns out that WD's in mass range of 0.46–0.55 M⊙ formed by a single star evolution should be formed from the AGB, without an observable PN.
Some Hypothesized Observational Aspects of Magnetic Fields in Protoplanetary Nebulae
Authors: Pascoli G.
Published: July 2016

Polarization mapping of some reflection nebulae (e.g., NGC 6729) reveals parallel bands of polarization vectors across pre-main sequence stars (Ward-Thomson et al. 1985, Mon. Not. R. Astr. Soc., 215). These authors have suggested a model in which the bands would be. Explained by dust discs, the grains being aligned by toroidal magnetic fields ∼ 102 μG.
Evolutionary Tracks for Central Stars of Planetary Nebulae
Authors: Schönberner Detlef
Published: July 2016

Our understanding of the evolution of Central Stars of Planetary Nebulae (CPN) has made considerable progress during the last years. This was possible since consistent computations through the asymptotic giant branch (AGB), with thermal pulses and (in some cases) mass loss taken into account, became available (Schönberner, 1979, 1983; Kovetz and Harpaz, 1981; Harpaz and Kovetz, 1981; Iben, 1982, 1984; Wood and Faulkner, 1986). It turned out that the evolution depends very sensitively on the inital conditions on the AGB. More precisely, the evolution of an AGB remnant is a function of the phase of the thermal-pulse cycle during which this remnant was created on the tip of the AGB by the planetary-nebula (PN) formation process (Iben, 1984, 1987). This was first shown by Schönberner (1979), and then fully explored by Iben (1984). In short, two major modes of PAGB evolution to the white dwarf stage are possible, according to the two main phases of a thermally pulsing AGB star: the hydrogen-burning or helium-burning mode. If, for instance, the PN formation, i.e. the removal of the stellar envelope by mass loss, happens during a luminosity peak that follows a thermal pulse of the helium-burning shell, the remnant leaves the AGB while still burning helium as the main energy supplier (Härm and Schwarzschild, 1975). On the other hand, PN formation may also occur during the quiescent hydrogen-burning phase on the AGB, and the remnant continues then to burn mainly hydrogen on its way to becoming a white dwarf.
Planetary Nebulae with Massive Central Stars
Authors: Tylenda R.
Published: July 2016

The paper discusses the problem of planetary nebulae with massive nuclei from the point of view of their theoretical evolution and observational appearances. The available data suggest that NGC 2440, 6302, and 7027 have central stars with masses greater than 0.8 M⊙.
Star Formation and the Galaxy
Authors: Kerr F. J.
Published: July 2016

My task is to discuss the galactic context of star formation and to consider how large-scale phenomena in the Galaxy can influence the processes of star formation. This review, and the whole of the first session, are supposed to set the stage for the later consideration of protostellar and prestellar objects and smaller-scale effects in general.
Molecular Clouds
Authors: Thaddeus P.
Published: July 2016

To attempt to understand star formation without knowing the physical state of the dense interstellar molecular gas from which stars are made is an almost impossible task. Star formation has developed late as a branch of astrophysics largely for lack of observational data, and in particular, has lagged badly behind the study of the atomic and ionized components of the interstellar gas because spectroscopic techniques which work well at low density have an unfortunate tendency to fail when the density is high. Optical spectroscopy, which has been applied to the interstellar medium for over 70 years, has made little progress in regions of high density because of obscuration, and the same is true a fortiori of spacecraft spectroscopy in the UV; radio 21-cm and recombination line observations, although unhampered by obscuration, are unsatisfactory because the dense condensations are almost entirely molecular in composition.
The Large Scale Distribution of Radio Continuum in E and SO Galaxies
Authors: Ekers R.D.
Published: July 2016

If we look at the radio properties of the nearby ellipticals we find a situation considerably different from that just described by van der Kruit for the spiral galaxies. For example NGC 5128 (Cen A), the nearest giant elliptical galaxy, is a thousand times more powerful a radio source than the brightest spiral galaxies and furthermore its radio emission comes from a multiple lobed radio structure which bears no resemblance to the optical light distribution (e.g. Ekers, 1975). The other radio emitting elliptical galaxies in our neighbourhood, NGC 1316 (Fornax A), IC 4296 (1333–33), have similar morphology. A question which then arises is whether at lower levels we can detect radio emission coming from the optical image of the elliptical galaxies and which may be more closely related to the kind of emission seen in the spiral galaxies.
Global Dynamics of the Interstellar Gas, Magnetic Field, and Cosmic Rays
Authors: Levy E. H.
Published: July 2016

I have been asked to review the physical principles which underlie the dynamical equilibrium and stability of a composite system of gas, magnetic field, and cosmic rays. What is of particular concern here are those aspects which control the distribution of magnetic field and cosmic rays, and thus influence the morphology of galaxies as seen in nonthermal radio emission.
The Kinematics within M31
Authors: Roberts Morton S. , Whitehurst Robert N. , Cram Tom R.
Published: July 2016

A new hydrogen line survey of M31 is described. A rotation curve of the galaxy is derived from these data. The northern half of the rotation curve can be traced to 27 kpc, the southern to 30 kpc. They are in general agreement; both sides show an extensive region of essentially constant rotational velocity.
The Three-Dimensional Distribution of Neutral Hydrogen in M31
Authors: Whitehurst Robert N. , Roberts Morton S. , Cram Thomas R.
Published: July 2016

Given the wealth of data, the rotation curve, and the necessity for out-of-plane hydrogen demonstrated in the preceding paper, it seems desirable to attempt to establish a systematic procedure for determining the three-dimensional distribution of hydrogen. Under the assumption of cylindrical rotation this is, in principle, possible for most of the galaxy.
A Warp in the HI Distribution at the Extreme NE and SW of M31
Authors: Emerson D.T. , Newton K.
Published: July 2016

Aperture synthesis observations of the neutral hydrogen in the extreme NE and SW regions of M31 have been made using the Cambridge Half-Mile Telescope, with an angular resolution of 3′.6 × 5′.5 and a resolution in radial velocity of 16 km/s (Newton and Emerson, 1977). These observations show that a warp in the HI distribution exists in opposite directions at each end of the galaxy.
The Large-Scale Distribution of HI in M33 and IC342
Authors: Baldwin J.E.
Published: July 2016

Distortions in the distribution of the HI in the outer parts of M33 are thought to be due to a warp in the HI plane. Measurements by Reakes and Newton with the Half Mile Telescope at Cambridge provide new evidence on the extent and kinematics of this gas. The integrated HI map with an angular resolution of 7 × 14 arcmin in shown in Fig 1a. The wings extend roughly symmetrically in outline to 70 arcmin (14 kpc) from the nucleus in the plane of the sky both to the NW and the SE. The radial velocity field in Fig lb shows large deviations from normal rotation in a plane in the outer parts. A model in which the gas rotates in circular orbits whose inclination and position angle of the major axis vary with radius, fits the HI distribution and kinematics quite well. Much larger extensions in R and z are required than in the model of Rogstad et al. (1976) and with a slower trend of i and P.A. with radius.
Material in the Vicinity of Galaxies
Authors: Burke Bernard F.
Published: July 2016

It is increasingly certain that the principal concentrations of neutral hydrogen gas are in spiral and irregular galaxies. The intergalactic medium (IGM) appears to be either a near-void with <ρ> ≲ 1.5 × 10−11 cm−3 from the 3C9 measurements of Gunn and Peterson (1965) or at best a hot, highly ionized gas with very little neutral hydrogen present (Field and Perrenod, 1977). In clusters of galaxies, the intracluster medium (ICM) also appears to be mostly hot and ionized, as suggested by X-ray observations (Jones et al. 1977) and by observations of head-tail radio galaxies. Even if most of the IGM and ICM were ionized, however, one might imagine that there exist high-density concentrations where the cooling rate is sufficient to allow recombination, particularly in the vicinity of galaxies. One might expect such condensations to be revealed either by 21-cm emission, or by absorption against a bright background continuum source.
The Photography of Groups of Galaxies
Authors: Vorontsov-Velyaminov B. A.
Published: July 2016

The method of combining several negatives together is at last coming into use. Forty years ago this method was used for the first time by Leontovsky in Leningrad. Putting together many negatives he was able to do photometry of M31 to fainter magnitudes than was possible photoelectrically. the method of preliminary baking of emulsions is more effective when it is done in a nitrogen atmosphere and still better in hydrogen. Spectacular results with the last method were obtained by A. Smith (1977). With a 70m exposure on IIIa-J plates there are no traces of the planetary nebula the Helix. After hydronization the same exposure reveals the overexposed image of this object. Arp and Lorre (1976) obtained striking results on IIIa-J emulsions using the process of deconvolution which improves the negatives. By means of some kind of filtration, removing faint stars and those of medium brightness etc., they improved the resolution of the extended images and obtained a better contrast. the authors published their photographs of the Stefan group and of the jet in M87. As a result of deconvolution it becomes evidence that NGC 7320 is much nearer to us than its apparent neighbouring galaxies because it is clearly resolved into HII regions and star clusters.
Optical Studies of Small Groups of Galaxies
Authors: Turner Edwin. L.
Published: July 2016

Galaxies occur in a wide variety of systems ranging from binary pairs through small groups to rich clusters. These systems in turn possess a wide range of densities, with typical separations between bright (L ≫ L* = 3.4 × 1010 L⊙) galaxies varying from ≲ 10 kpc up to ~ 1 Mpc. Among the most common of these systems are small, loose groups containing ≲ 10 bright galaxies with separations ≳ 100 kpc. Such systems probably contain a substantial fraction of all galaxies (de Vaucouleurs 1975; van den Bergh 1962; Karachentseva 1973). Familiar examples include the Local Group and M81 group.
Hypergalaxies
Authors: Einasto Jaan
Published: July 2016

“Galaxies are like people: they depend on both genetics and environment” (van den Bergh 1975)
Cluster membership of Seyfert galaxies
Authors: Schmidt K.-H.
Published: July 2016

I would like to comment on very preliminary results concerning the cluster membership of Seyfert galaxies. Two years ago van den Bergh stated in a discussion of the bright classical Seyfert galaxies that these objects were mainly field galaxies. We extend this discussion to about seventy objects in the list of Drs Khachikian and Weedman (Astrophys. J., 192, 581, 1974). By a cross correlation of this list with Dr Abell's catalogue of rich clusters taking account both of the positions in the sky and the distances of the objects, we find only two certain cluster members - the well-known case NGC 1275 in the Perseus cluster and Markarian 298 in the Hercules cluster - and three probable or possible other cluster members. Taking into account the fact that only some fifty objects of Khachikian and Weedman fall within the distance range of the Abell catalogue, we find that only a few per cent of the Seyfert galaxies are members of Abell clusters. Within a factor of two, this percentage is the same as the percentage of cluster galaxies relative to all galaxies. Therefore, this result does not point to a pronounced field membership of the Seyfert galaxies.
The results of observations of double galaxies in the UBV system
Authors: Tomov Aleksander
Published: July 2016

In the Astronomical Observatory of the town of Belogradchik a one-channel electrophotometer in the UBV system with pulse counting has been installed at the 60-cm Cassegrain telescope. the photoamplifier used is of the type EMI 6256B (1). With this telescope the author has carried out observations of 80 double galaxies during the period 1974 to the middle of 1977, using the differential method of observation with 3 diaphragms (24″, 54″ and 135″) depending on its diameter.
Encounters of spherical galaxies: N-body simulations and comparison with theoretical predictions
Authors: Biermann Peter , Wielen Roland
Published: July 2016

We have studied hyperbolic encounters of spherical galaxies by self-consistent N-body simulations. Each galaxy is represented by a Plummer model. A galaxy contains up to 250 “particles”. the force between the particles is properly softened in order to avoid an unrealistic internal evolution due to close encounters of the particles. the results of these numerical experiments, carried out by R.W., are compared with theoretical predictions based on the impulsive approximation, made by P.B. in order to facilitate the assessment of such a comparison, the passing galaxy is here represented by a rigid gravitational field, moving on a straight line. in the table given below, we compare the relative mass loss, ΔM/M, and the relative change in the total internal energy of a galaxy, ΔE/E, for two cases. Both galaxies are of equal mass and size; the impact parameter is equal to the median radius of a galaxy (containing 50% of its mass in projection); the initial relative velocity would correspond to the orbital excentricity e as given, if the galaxies were mass points. While the agreement is fair with respect to the energy transfer ΔE, the theory predicts a mass loss of more than 10% (or 25 particles) in cases where no mass loss is observed in the N-body simulations the probable reason for this discrepancy is the failure of the impulsive approximation in these cases. A mass loss of the order of 1% or less cannot be ruled out in the N-body calculations, because of the limited number of particles. the significant increase of the internal energy of a galaxy during an encounter leads to an expansion of the outer parts of the galaxy. This expansion may finally lead to a mass loss as soon as the outer parts have expanded beyond the tidal radius of the galaxy caused by its cluster environment. the inelasticity of galactic encounters has implications for the dynamical evolution of groups and clusters of galaxies. the groups and clusters will shrink in radius because of the loss of orbital energy which is used to expand the individual galaxies. the final amount of collapse of the group or cluster is governed by the relative amount of the internal binding energies stored initially in the individual galaxies and released during the galactic encounters, in comparison to the binding energy of the group or cluster.
On the Magellanic Stream, the Mass of the Galaxy and the Age of the Universe
Authors: Lynden-Bell D.
Published: July 2016

The Magellanic stream has been fitted with high accuracy in both position and velocity by the tidal tearing of a Magellanic Cloud. To get the good fit to the high velocity at the stream's tip at a suitable distance from the Galaxy we need either a large mass for the Galaxy, or a large circular velocity for the Sun, or both. An extragalactic method of determining the circular velocity yields the high value of Vc = 294 ± 42 km/sec and an orbit of poor accuracy for the relative motion of the Galaxy and the Andromeda nebula. Very large masses are needed if Andromeda and the Galaxy were formed together. A new direct determination of Hubble's constant from the “superluminal” expansion observed in VLB radio sources gives an age of the Universe of 9 billion years. Either larger masses still or smaller distances within the local group are necessary to bring Andromeda back towards us in so short a time.
The stellar component of the Magellanic Stream
Authors: Kunkel William E.
Published: July 2016

The problem of the Magellanic Stream (MS) is re-examined considering also stellar systems (globular clusters and dwarf spheroidal galaxies) lying between 25 and 250 kpc from the Galactic center (Kunkel and Demers 1976). the distribution of these systems is shown to be non-random, with a planar component whose inclination to the Local Group is 43°, and to the local supergalaxy exceeds 60°. the velocity distribution of members of the group shows a symmetry typical of debris associated with a disruptive event at perigalacticon of a victim moving in an elliptical orbit.
Radio haloes around galaxies and in clusters
Authors: Ginzburg V. L.
Published: July 2016

The question of whether or not our and other normal galaxies have some sort of halo - an extended region containing, in particular, cosmic rays - has been discussed for no less than 25 years. Such a “cosmic ray halo” (CRH) appears as a radio-halo, although the absence of the latter is not evidence against the presence of CRH. the point is that the relativistic electrons responsible for the radio emission from the radio-halo undergo synchrotron and Compton losses which are practically absent in the case of the cosmic-ray proton-nuclear component. Possibly because the discussion concerning the existence of the radio-halo in the Galaxy has lasted for years it has acquired a particular character. the latter is clearly reflected in the report by Baldwin (1976) who emphasized that: ȜIn this discussion so far I have avoided the use of the phrase Ȝradio-haloȝ. It arouses antagonism in otherwise placid astronomers and many sought to deny its existence …ȝ Such a situation evidently reflects the difficulties that arise in detecting the radio-halo of our own Galaxy when account is taken of other confusing galactic sources as well as of the metagalactic background.
Computer Simulations of Galaxy Clustering
Authors: Aarseth Sverre J.
Published: July 2016

The aim of the present work (performed in collaboration with J.R. Gott and E.L. Turner) is to account for the observed distribution of galaxies in terms of the gravitational instability picture. Specifically we assume that all the matter is contained in galaxies. the evolution of such a system can then be studied by N-body simulations once the initial conditions are specified. Our approach is essentially experimental; a variety of models are computed and the results are compared with observations.
Some Progress and Problems in the Upper Left of the HR Diagram
Authors: Walborn Nolan R.
Published: July 2016

The MK system of spectral classification does not include luminosity classes for types earlier than 09. Subsequent work with higher dispersions has allowed a luminosity classification for early O stars to be proposed. One of the principal criteria at types 09-B0 is the selective, negative luminosity effect in the Hell 4686 Å absorption line; a similar effect was found in the NIII 4634-4640-4642 Å absorption lines at 09-B0. These particular lines weaken markedly with increasing luminosity, while other HeII lines maintain a constant ratio to HeI (by definition), and other NIII lines strengthen considerably. These anomalous lines are the same ones which selectively appear in emission in Of stars, and the derived luminosity classification for earlier types is based upon the hypothesis that the negative absorption effect at 09-B0 is due to emission filling by the same mechanism producing the Of phenomenon, and that hence the latter may also be identified as a luminosity effect (Walborn 1971). One observes strong 4686 Å absorption and often weak 4640 Å emission [denoted ((f))] on the main sequence to the earliest types. As luminosity increases at a given spectral type, the HeII absorption weakens while the NIII emission increases [denoted (f)] and finally the most luminous stars have both 4686 and 4640 Å strongly in emission [denoted f]. A sequence of spectra all with types very near 07, but showing the marked changes with luminosity class in 4686 and 4640 Å, is illustrated by Walborn (1973). These effects show good agreement with other spectroscopic luminosity criteria such as SiIV absorption (Conti and Alschuler 1971) and Balmer-line strength (Crawford 1975, Morrison 1975), which are however less sensitive at the earliest types.
Carbon and Late Type M Stars as Population Indicators
Authors: Blanco V. M. , Hoag A.A. , McCarthy M. F.
Published: July 2016

The discovery of different ratios of carbon (C-type) to oxygen stars (M type) in the direction of the central regions of our own and the nearest galaxies, the Large and Small Magellanic Clouds, is the result of surveys made by Blanco, Blanco and Hoag (unpublished) who observed Baade's Window near NGC 6522 in the direction of our Galaxy's nuclear bulge and by Blanco, Blanco and McCarthy (in press) who observed selected regions in the center of the Large and Small Magellanic Clouds. We have observed each of these central regions with a combination of a grating and prism set in the converging beam of the prime focus of the CTIO 4 meter telescope (Hoag 1976). We used Eastman IV-N plates hypersensitized with silver nitrate solution; the spectral plates were exposed through a Wratten 89 filter for 60 min. We limited our spectral survey to M type stars later then M5 and to the carbon stars, using the criteria of Nassau and colleagues (1949). Thus far no S type stars have been discerned in central regions of the LMC or SMC at the dispersion used (2300 Å/mm).
Main Sequences Defined by Hyades and Field Stars
Authors: Upgren Arthur R.
Published: July 2016

This paper reviews the main sequences defined by members of the Hyades cluster and by the field stars in the solar neighborhood. For this purpose, the discussion is limited primarily to the stars of the lower portions of the main sequence, especially those of spectral classes K and early M. There are two reasons for emphasis on the faint red dwarf stars. First, the value of a parallax depends on its size or, more accurately, on the error in parallax divided by the parallax itself. Large parallaxes of high precision occur in large numbers only for stars inhabiting the lower main sequence. Furthermore, brighter stars of earlier spectral classes are more likely to be influenced by evolutionary effects which may differ between the Hyades and field stars, and which are difficult to calibrate.