bluuebunny/crossref_metadata_2025 huggingface dataset:
Number Counts of Clusters of Galaxies in X-ray and Submm Bands
Authors: Kitayama Tetsu , Sasaki Shin , Suto Yasushi
Published: July 2016

We compute the number counts of clusters of galaxies, the logN-logS relation, in several X-ray and submm bands on the basis of the Press—Schechter theory (Kitayama et al. 1998). We pay particular attention to a set of theoretical models which well reproduce the ROSAT 0.5–2 keV band logN-logS (Ebeling et al. 1997; Rosati et al. 1997), and explore possibilities to further constrain the models from future observations with ASCA and/or at submm bands. The latter is closely related to the European PLANCK mission and the Japanese LMSA project. We exhibit that one can break the degeneracy in an acceptable parameter region on the Ω0–σ8 plane by combining the ROSAT logN-logS and the submm number counts. Models which reproduce the ROSAT band logN-logS will have N(> S) ∼ (150–300)(S/10−12 erg cm−2 s−) −1.3 str−1 at S ≳ 10−12 erg cm−2 s−1 in the ASCA 2–10 keV band, and N(> Sv) ∼ (102–104)(Sv/100 mJy)−1.5 str−1 at Sv ≳ 100m J y in the submm (0.85mm) band. The amplitude of the logN-logS is very sensitive to the model parameters in the submm band. We also compute the redshift evolution of the cluster number counts and compare with that of the X-ray brightest Abell-type clusters (Ebeling et al. 1996). The results, although still preliminary, point to low density (Ω0 ∼ 0.3) universes. The contribution of clusters to the X-ray and submm background radiations is shown to be insignificant in any model compatible with the ROSAT logN-logS.
K Band Galaxy Counts in the South Galactic Pole Region
Authors: Minezaki T. , Kobayashi Y. , Yoshii Y. , Peterson B. A.
Published: July 2016

We carried out a K′ band survey during August and September, 1994, in the south galactic pole region that covers 180.8 arcmin2 to K = 19 and 2.21 arcmin2 to K = 21 by the ANU 2.3 m telescope at SSO, Australia, equipped with PICNIC, developed at NAOJ. New galaxy number counts from K = 13 to 22 were obtained, which provided the best determination of the galaxy counts from K = 17.5 to 19.0 because of our large survey area. They were very consistent with Gardner, Cowie, & Wainscoat (1993, ApJL, 415, 9) and other observations to K < 19, however, they were larger than the galaxy counts of Saracco et al. (1997, AJ, 114, 887) with similar area and depth of survey around that magnitudes.
Distribution and evolution of quasars
Authors: Nasiri S. , Rezania V.
Published: July 2016

In this paper we investigate: a) The evolution of quasars on the basis of gravitational contraction model of proto-galaxies. This is done by studying the number density of quasars given by Veron catalogue [1] in different luminosity classes. The order of classes increase with increasing the luminosity of corresponding quasars. It is shown that the decay of quasars is more sensible to their luminosities as expected by assuming that they are evolved from the contraction of slowly rotating proto-galaxies. The role of the angular momentum in the evolution of galaxies is emphasized by the results obtained from the size-luminosity relation of about 40,000 normal galaxies given by LEDA database [2]. In the model mentioned above the normal galaxies are assumed to be evolved from the contraction of relatively fast rotating proto-galaxies. b) The filamentary structures and voids of the large scale universe by plotting the entire sky map of quasars in the galactic coordinate. This is done by assuming that these objects are at cosmological distances. The result which is plotted in the following figure, seems to show some spatial correlations of quasars distribution. The region of missing quasars is due to the dust clouds in our galaxy which block our view of other quasars. Note the voids and clumpy distribution of quasars looking like filaments.
Measuring the Density Fluctuation From the Cluster Gas Mass Function
Authors: Shimasaku K.
Published: July 2016

We derive the gas mass function of clusters of galaxies to measure the density fluctuation spectrum on cluster scales. The baryon abundance confined in rich clusters is computed from the gas mass function and compared with the mean baryon density in the universe which is predicted by the BBN. This baryon fraction and the slope of the gas mass function put constraints on σ8 and the slope of the fluctuation spectrum. Adopting the density parameter of baryons Ωbh2 = 0.0175 ± 0.0075 and assuming that , we find for h = 0.7 ± 0.1. Our value of σ8 is independent of Ω0 and thus we can estimate Ω0 by combining σ8 as obtained in this study with those from Ω0-dependent analyses to date. Constraints are also derived for CDM and CHDM models.
Explosive Cosmogony and the Quasi-Steady State Cosmology
Authors: Burbidge G.
Published: July 2016

Modern cosmology began with the realization that there were solutions to Einstein's theory of gravity discovered by Friedmann and Lemaitre which when combined with the redshift distance relation of Hubble and others could be interpreted as showing that we live in an expanding universe. By 1930, the scientific establishment and many of the lay public believed this. It was then only elementary logic to argue that if time reversal was applied, the universe must originally have been so compact that we could talk of a beginning. Lemaitre tried to describe this state as the “Primeval Atom.” For a decade or so after the war, Gamow, Alpher and Herman and other leading physicists explored this dense configuration trying to make the chemical elements from protons and neutrons. They soon learned that this was not possible because of the absence of stable masses of five and eight, but they also realized that if such an early stage had occurred the universe would contain an expanding cloud of radiation which would preserve its black body form. Dicke and his colleagues in Princeton rediscovered this idea and decided to try and detect the radiation. Penzias and Wilson found such a radiation field, and COBE has demonstrated that it has a perfect black body form out to radio wavelengths. This history of the discovery together with the fact that the light elements D, He3 and He4 in about the right amounts can be made in a hot big bang has led to the widely held, but simplistic view, that the standard cosmology - the hot big bang - is correct.
A Pure Geometric Approach to Cosmology
Authors: Wanas M.I.
Published: July 2016

It is well known that standard Big-Bang cosmology suffers from certain problems, e.g. singularity, horizon, flatness, … In the present work it is claimed that the appearence of some of these problems is due to two main assumptions. The first is the assumption that the 4-dimentional Riemannian (RIE)-geometry gives a complete description of the cosmic space-time. The second is the assumption that the material distribution in the universe is described by a phenomenological (PH)-matter tensor. It is shown that, by relaxing these two assumptions, some of the problems of the standard Big-Bang cosmology could be avoided. The following table summarises some results in favour of the above claim. The absolute parallelism (AP)-geometry is used to construct some of the theories mentioned in the table.
Stratified NLTE Model Atmospheres for Hot Stars
Authors: Dreizler Stefan , Schuh Sonja L.
Published: July 2016

In most stellar atmosphere models, a homogeneous chemical composition is assumed, which is a good approximation for many stars. With the absence of convection and mass–loss, however, gravitational settling can produce a chemical stratification gradient. Typical examples are white dwarfs. In hot stars this diffusion process is modified by the radiative acceleration, resulting in levitation of ions with large radiative cross sections. The status of our program for self-consistent stratified non-LTE model atmospheres is presented.
NLTE Line-Blanketed Model Stellar Atmospheres
Authors: Lanz Thierry , Hubeny Ivan , Heap Sara R.
Published: July 2016

We briefly review the assumptions and methods required to construct NLTE line-blanketed model atmospheres of hot stars. We describe our new grid of NLTE model atmospheres covering the parameter range of O stars at various metallicities. We have applied these new models to the analysis of HST/STIS and FUSE UV spectra of O stars in the SMC. This analysis leads us to revise down the effective temperature scale of O-type stars.
NLTE Radiative Transfer in the Extended Atmospheres and Winds of Cool Stars
Authors: Bennett Philip D. , Harper Graham M. , Brown Alexander , Linsky Jeffrey L.
Published: July 2016

The mechanism responsible for driving the ubiquitous winds of cool giant and supergiant stars remains to be established. To this end, we are constructing semi-empirical models of the extended outer atmospheres (‘chromospheres’) and winds of selected red supergiants. These models are constrained by analyses of the UV line spectra of single stars, and of red supergiants in binaries that eclipse their main-sequence companions: the ζ Aur and VV Cep stars. These detached binaries are well-separated, with no evidence of mass transfer. The C II] 2325 Å line profiles of the binaries are similar to those of comparable single stars, suggesting that the chromospheres remain relatively unperturbed by binarity. However, it is unclear how much binarity disturbs the wind: binary observations suggest a gradual acceleration (β ∼ 3), but line profile analyses of single red supergiants imply a rapid acceleration (β < 1). To date, we have obtained extensive series of HST/GHRS and STIS observations of three eclipsing red supergiant binaries: ζ Aur, HR 2554 and VV Cep. In this paper, we focus on ζ Aur, and present observations and modelling results for this eclipsing binary.
Solar Surface Magnetoconvection
Authors: Stein Robert F. , Nordlund Åke
Published: July 2016

Magnetoconvection simulations on meso-granule and granule scales near the solar surface are used to study small scale dynamo activity, the emergence and disappearance of magnetic flux tubes, and the formation and evolution of micropores.

From weak seed fields, convective motions produce highly intermittent magnetic fields in the intergranular lanes which collect over the boundaries of the underlying meso-granular scale cells. Instances of both emerging magnetic flux loops and magnetic flux disappearing from the surface occur in the simulations. We show an example of a flux tube collapsing to kG field strength and discuss how the nature of flux disappearance can be investigated. Observed Stokes profiles of small magnetic structures are severely distorted by telescope diffraction and seeing.

Because of the strong stratification, there is little recycling of plasma and field in the surface layers. Recycling instead occurs by exchange with the deep layers of the convection zone. Plasma and field from the surface descend through the convection zone and rise again toward the surface. Because only a tiny fraction of plasma rising up from deep in the convection zone reaches the surface due to mass conservation, little of the magnetic energy resides in the near surface layers. Thus the dynamo acting on weak incoherent fields is global, rather than a local surface dynamo.
Convection and the Relevant Problems of Stellar Structure, Evolution and Oscillations
Authors: Xiong D. R. , Deng L.
Published: July 2016

The main results of stellar structure, evolution and oscillations given by our non-local statistical theory of convection are summarized in this paper. A main difficulty of convection theories, i.e. supersonic convection, is also discussed.
A New View of the Magnetic Sun
Authors: Title A.
Published: July 2016

Developments in instrumentation, numerical simulations, and theory are rapidly changing our view of solar magnetism. There are now observations that show magnetic field emerging on all convective scales. The emergence rate replaces the quiet Sun flux in less than 12 hours and even active region and sunspot fields are replaced in less than a month. There is evidence for local dynamo action suggesting that a bottom to a convection zone is not required for stellar magnetic activity. It is now recognized that 3D magnetic reconnection is fundamentally different from 2D. Time sequences of the one arc second spatial resolution TRACE images show that the temperature and density structure of the corona changes as fast as radiation and conduction allow. Because adjacent loops are observed in a range of temperatures that span at least 30 000 to 2 500 000 K, there is a inter mixture of temperatures regimes throughout the corona. Consequently, there is no line of sight through the corona that can be characterized by a single temperature and density. It would be surprising if other stars or other astrophysical systems with magnetic fields were simpler than the solar atmosphere.
Round Table Summary: Instrumentation and Data Processing
Authors: Adelman Saul J. , Bikmaev Ilfan , Gulliver Austin F. , Smalley Barry
Published: July 2016

During this round table Bikmaev described the systematic differences among equivalent width measurements and Gulliver discussed the reduction of high dispersion, high signal-to-noise CCD spectra. Smalley considered atmospheric extinction as it affects astronomical measurements while Adelman presented an overview of the ASTRA spectrophotometer.
Maser Observations of Cool Stars
Authors: Humphreys E.M.L.
Published: July 2016

SiO, H2O and OH masers are ubiquitous in the circumstellar envelopes (CSEs) of oxygen-rich, red giant stars. Radio interferometry allows the imaging of stellar maser emission down to sub-milliarcsecond scales. Such observations reveal asymmetry, inhomogeneity and apparent clumpiness in the extended atmosphere and surrounding envelope of the star. The studies place constraints on processes which are seldom included in models. Here, I review the observational data on stellar masers and discuss their implications for our understanding of the mass-loss and evolution of red giant stars.
Spectroscopic Survey of Planetary Nebulae
Authors: Acker A. , Köppen J. , Stenholm B.
Published: July 2016

Since 1984, we have undertaken a spectroscopic survey of planetary nebulae, both at La Silla (E.S.O.)., and at the Observatoire de Haute Provence (France), Up to now, the spectra of about 900 PN have been obtained; all 723 spectra observed at La Silla have been reduced and the line intensities have been measured for 250 of them; about one fourth of the 182 OHP spectra have been reduced.
The Photometric (UBV) Study of the Planetary Nebulae Variability in 1968–1987
Authors: Kostyakova E.B.
Published: July 2016

The photoelectric UBV-observations of planetary nebulae variability, begun in 1968 at Crimean Station of Sternberg State Astronomical Institute (USSR) and Skalnate Pleso Observatory (Czechoslovakia), were carried out during 20 years, 1987 inclusive.
Dust in Planetary Nebulae
Authors: Roche Patrick F.
Published: July 2016

The presence of dust in planetary nebulae can be deduced in several ways - from the observed depletions of condensable elements, internal extinction and, most directly, through the detection of infrared emission from the dust grains. We know that there is a substantial amount of dust in planetary nebulae, and that a significant fraction of the total luminosity emerges in the infrared through thermal emission in most objects. However, a number of questions still largely remain unsolved, and perhaps the most pressing of these are that we do not yet have a satisfactory understanding of the ultraviolet, optical or infrared properties of the dust grains and we also do not yet know exactly where the emitting grains are located within the nebulae; for example, are they mixed with the ionized gas, or in neutral inclusions or perhaps in a disk around the central star?
Molecules and Neutral Hydrogen in Planetary Nebulae
Authors: Rodríguez Luis F.
Published: July 2016

Molecules and/or neutral hydrogen have been detected in a modest number of planetary nebulae. However, when detected, these indicators of a significant neutral component can provide fundamental information on the total mass of the envelope, its chemistry and kinematics, and on the morphology and evolutionary status of the planetary nebula. A review of recent results is presented, giving emphasis to CO (carbon monoxide), H2 (molecular hydrogen), OH (hydroxil), and HI (neutral hydrogen). A major development of the last few years has been the capability to map with considerable angular resolution these species in planetary nebulae. In the best studied cases, the neutral component appears to be located surrounding the “waist” of a bipolar planetary nebulae. These is evidence suggesting that molecules and neutral hydrogen are not as uncommon in planetary nebula as the present statistics suggest. Indeed, the outer parts of a considerable fraction of the known planetary nebulae could be neutral. It is possible that a combination of good selection criteria and long integrations with the best telescopes could increase largely the number of known cases.
The Structure and Kinematics of Bipolar Planetary Nebulae
Authors: Weller W. G. , Heathcote S. R.
Published: July 2016

We have obtained high-dispersion, long-slit echelle spectra at closely spaced intervals across the face of the bipolar planetary nebulae NGC 2440, NGC 6302 and Mz-3. Deep monochromatic images of these objects in lines from high (HeII, [OIII]), intermediate (HI, [OII]) and low ([NII], [SII]) excitation species have also been acquired. Taken together, these data permit us to construct self-consistent spatio-kinematic models of these nebulae and to investigate the spatial variations of excitation conditions within them.
The Planetary ESO 166 - PN21
Authors: Ruiz María Teresa , R. Heathcote Stephen , Weller William G.
Published: July 2016

Long slit, high and low resolution, spectrograms of this object were obtained using the telescopes at CTIO. From the [N II] λ6584 line in the high resolution spectrum, we obtained a radial velocity difference between the front and back expanding shells at the center of the nebula of 56 km s−1 corresponding to an expansion velocity of 28 km s−1, From the low resolution spectra we found [S II] λλ6717/6731 line ratios indicating densities between 500 cm−3 and less than 200 cm−3. The temperature sensitive line ratios of [O III] and [N II] were not well determined due to the weakness of the λ4363 and λ5733 lines. A ionization structure is clearly seen with radial distance to the central star which shows that the inner shell (A2, A4, B2, B4) is not a projection of the outer one but a separate structure.
Thermal Infrared Emission by Dust in the Planetary Nebula NGC 3918
Authors: Harrington J. P. , Monk D.J. , Clegg R.E.S.
Published: July 2016

Models of the dust grains in the planetary nebula NGC 3918 are presented. The models, which are calculated for four grain materials -graphite, amorphous carbon, silicate, and iron- have a size distribution of particles based on that found for the diffuse interstellar medium. The infrared spectrum of the nebula -described mainly by IRAS photometry corrected for line emission- can be matched either with graphite grains with a size range of 0.04 - 0.30 μm, or with amorphous carbon grains having a size range 0.0005 - 0.25 μm. The implied depletions of gas phase carbon are only 11% and 4%, respectively. It is shown that iron grains cannot be the dominant dust material.
Fluorescent H2 Emission in the Planetary Nebulae BD+30 3639 and Hb 12
Authors: Dinerstein H. L. , Carr J. S. , Harvey P. M. , Lester D. F.
Published: July 2016

We report results from a program of near-infrared spectroscopic observations of the H2 emission from planetary nebulae, being carried out at McDonald Observatory using an InSb array-detector spectrometer. Our observations employ both high spatial resolution (3″ diameter aperture) and high spectral resolution (λ/Δλ = 200–600), thus avoiding potential problems with line blending and spatial registration. These observations provide simultaneous measurements of H I recombination lines and H2 emission lines, thus accurately defining the relative extent and distribution of the ionized vs. molecular material. One-dimensional cuts through the compact planetary nebulae BD+30 3639 and Hubble 12, taken along east-west and north-south axes through the nebular centers, show that the H2 emission is concentrated in a ring or shell outside the ionized nebular core. The angular extent of the H2 emission in Hb 12, with a characteristic diameter of about 8–10″ arc seconds, is strikingly larger than the dimensions of the ionized core, which is less than 2″ in diameter.
Collisional Excitation of the 10830 He I Line and the Population of the 23S He I State in Gaseous Nebulae
Authors: Peimbert M. , Torres-Peimbert S.
Published: July 2016

From the study of the λλ5876, 7065 and 10830 He I line intensities in NGC 6572, NGC 6803, NGC 7009, NGC 7027, NGC 7662 and IC 418, it is found that the I(10830)/I(5876) ratio is weaker than expected. By considering estimates of the optical depth at λ10830 due to dust absorption and by determining the optical depth at λ10830 due to atomic absorption, it is argued that dust absorption of λ(10830) photons is not the cause for the low I(10830)/I(5876) ratios. By assuming that the 23S He0 state is depopulated only by radiative transitions to the 11S state and by triplet-singlet exchange collisions, it is found that its population is about a factor of two smaller than expected. This result is in agreement with a previous study of the λ3889, 4472, 5876, 6678 and 7065 line intensities in a group of thirteen Type I planetary nebulae. One of the main implications of the underpopulation of the 23S level is that the collisional effects in the N(He)/N(H) abundance ratios of planetary nebulae and 0-poor extragalactic H II regions are smaller than previously thought.
Emission Lines of CI and N II in Planetary Nebulae
Authors: Escalante V.
Published: July 2016

A model potential method (Caves and Dalgarno, 1972, J. Quant. Spect. Rad. Transf., 12, 1539) was used to calculate accurate non-hydrogenic radiative recombination rates and transition probabilities of singly excited states of CI and N II. The results can be used to determine the excitation mechanism of emission lines and to estimate N III concentrations in nebulae with CI and N II emission lines. In most nebulae, observed permitted lines of N II are produced by radiative recombination, but sometimes stronger recombination lines are missing in their spectra. The [CI] lines observed in NGC 7027 cannot be explained by simple radiative and dielectronic recombination. The low [CI] λλ9850 + 23/ λ8727 value may indicate that the emission is produced in high density (NeZ 105 cm−3) condensations where partial collisional deexcitation of metastable levels, takes place. N III concentrations were determined using published data of NGC 3242, NGC 3918, and NGC 6572. The procedure outlined by Wilkes et al. (1981, M.N.R.A.S., 197, 1) to determine N abundances from (N+ + N++)/He+ ratios does not always give consistent results with UV or [N II] data. The problem may be due to errors in the calculation of transition probabilities involving the doubly excited levels 2s2p33P0 and 3D0 of N II that affect the branching and effective recombination rate of the multiplet N II λ5680.
Magnitude Measurements of Central Stars of Planetary Nebulae
Authors: Gathier R. , Pottasch S. R.
Published: July 2016

Magnitudes have been measured for 44 faint central stars of planetary nebulae by imaging the star and nebula of a CCD detector. The nebula is suppressed by using a continuum filter. The remaining nebular continuum is then subtracted as background as long as the star can be clearly seen. This is true in 41 of the 44 cases observed. Zanstra temperatures are calculated from the observed magnitudes, and discussed.
Photometric and Spectroscopy Observations of Peculiar Nuclei of Planetary Nebulae
Authors: Jasniewicz G. , Acker A.
Published: July 2016

Photometric and spectroscopic observations of some bright central stars of planetary nebulae (PN) have been conducted between 1984 and 1987 with the following tools: differential photometer P7 (70-cm swiss telescope, La Silla c/o ESO); radial velocity scanner CORAVEL (1-m swiss telescope, Observatoire de Haute-Provence = OHP); spectrograph CARELEC with CCD detector (193-cm telescope, OHP).
Quantitative Investigations on Mass Outflow from Planetary Nebulae Nuclei
Authors: Cerrato S. , Bianchi L. , Grewing M. , Bässgen M. , Bässgen G.
Published: July 2016

Observed P-Cygni line profiles in the UV spectra of central stars of Planetary Nebulae (PNN) obtained with the IUE satellite has been fitted by theoretical profiles in order to determine mass loss rates.
Planetary Nebulae in the Magellanic Clouds
Authors: Barlow M. J.
Published: July 2016

The past few years have seen the study of Magellanic Cloud planetary nebulae cease to be an extragalactic sideshow and instead become one of the most quantitative branches of planetary nebula research, due largely to our ability to fully exploit the known distances to these systems since the launch of IUE and the advent of sensitive digital detectors mounted on large optical telescopes.
Thermal Pulses and the Formation of Planetary Nebula Shells
Authors: Renzini Alvio
Published: July 2016

Over the past decade a comprehensive, semiquantitative theoretical scenario for the final evolutionary stages of low and intermediate mass stars has been progressively elaborated and refined. It concerns the envelope ejection terminating the Asymptotic Giant Branch (AGB) phase, the AGB to Planetary Nebula (PN) transition, the fading and possible rejuvenation of PN nuclei, the formation processes of hydrogen-deficient stars, and the final production of white dwarfs (WD) of the DA and non-DA varieties (Renzini 1979, 1981a, 1981b, 1982, 1983, Iben & Renzini 1983, Iben et al. 1983, Iben 1984, 1985, 1987, Iben & Tutukov 1984, Iben & MacDonald 1985, 1986). In developing this scenario several important results of stellar evolution and hydrodynamical calculations have been incorporated, including in particular those of Paczynski (1971), Wood (1974), Härm & Schwarzschild (1975), Schönberner (1979, 1983), and Tuchman, Sack & Barkat (1979).
Stellar Evolution and the Planetary Nebula Formation Rate
Authors: Phillips J. P.
Published: July 2016

A knowledge of the formation rate of planetary nebulae is crucial to our understanding of a wide range of physical environments and processes, and as such has been fitfully investigated over the last forty or so years. The elemental composition of the interstellar medium, for instance, and in particular the seeding of the IS medium by CNO and s-process materials, turns out to be rather sensitively dependent upon the local rate of PN formation χ(PN) (Salpeter, 1978, Pottasch, 1984; Tinsley, 1978; and Wood et al, 1983). Similarly, and to varying degrees, the ionisation balance of the I.S. medium (cf. Pottasch, 1984; Salpeter, 1978), composition and number density of I.S. grains (Natta and Panagia, 1981), and ultimately the galactic star formation rate (cf. Miller and Scalo, 1979) can all (more or less directly) trace a dependency upon χ(PN). Finally, χ(PN) has proven historically important in establishing the evolutionary status of PN (cf. Abell and Goldreich, 1966), and is expected to be directly related to the rate of formation of white dwarfs, the death-rate of AGB-type stars (Mira variables, OH/IR sources), and the main-sequence turn-off rate in the mass range 2 ≲ M/M⊙ ≲ 10, some 1010 years ago.
The Presence of Water Masers in Color-Selected IRAS Sources
Authors: Lewis B. M. , Engels D.
Published: July 2016

Eder, Lewis, and Terzian (1987) examined ∼ 400 sources from the IRAS Point Source Catalogue with colors appropriate to OH/IR stars, for the presence of 1612 MHz emission. We examined a proportion of these objects at Effelsberg for the presence of water-maser emission. In sources with |bII| > 10° which are therefore relatively local, we find a 68% detection rate for water-masers among objects associated with 1612 MHz masers, as opposed to a 17% detection rate among sources with similar colors but without 1612 MHz emission. Those conditions in a circumstellar shell that favor the presence of water-masers also favor the presence of a 1612 MHz maser. These results are consistent with most Type II masers being associated with water-masers. Since Cooke and Elitzur (1985) show that water-masers are collisionally excited, this result excludes stirring of the envelope by a companion star with an associated loss of velocity coherence, as the primary cause for the existence of the color-analogue sources without 1612 MHz masers. We discuss an alternative scenario.
Two-Dimensional Hydrodynamical Models of Planetary Nebulae (PNe)
Authors: Igumenshchev I. V. , Shustov B. M. , Tutukov A. V.
Published: July 2016

To study the evolution of an expanding PNe formed by non-spherical stellar (super) wind we have computed seven evolutionary sequences for the dusty envelopes with mass 0.05 M⊙ taking angular distribution of mass loss and of the outflow velocity as parameters. In the case described below the gas velocity on the inner boundary is assumed: Vz=25 (1–0.4 (3 cos2 θ−1)12) km s−1 (where θ is the polar angle) with the density of ejected matter independent on θ. The mass loss rate on the (super) wind phase is 6 10−5 M⊙/yr the structure of the model at the moment of ionization breaks through PN in the polar direction is illustrated in Fig. 1. The density distribution in a meridional plane is shown in Fig. 1a together with the ionization boundary (the dashed line). Contours of equal emission measure nebula model are shown in Fig. 1b. After complete ionization of PN hydrogen distributions become smoother. We found that some of double-shell PNe may be the product of single mass loss event.
CCD Images of Three Planetary Nebulae with Binary Nuclei
Authors: Lutz Julie , Lame Nancy Jo
Published: July 2016

A 14, H 3-75 and K 1-2, three planetary nebulae with binary nuclei, were imaged with narrow-band [N II], Ha, [O III] and He II filters by using the TI CCD chip on the 0.9-m telescope at CTIO. The purpose of doing the observing was to see if planetaries with known binary nuclei exhibit particularly peculiar morphologies. In some cases (e.g., NGC 1514, NGC 3132), planetaries with binary nuclei have morphologies that are exhibited by a number of nebulae. In other cases (e.g., He 2-36, the nebulae with binary central stars have unique morphologies.
Initial Masses
Authors: Mallik D.C.V.
Published: July 2016

Planetary nebulae represent a transitory stage in the life of the majority of stars as they proceed towards the end of their nuclear evolution and descend to the domain of white dwarfs. The immediate precursors of the central stars are probably red giants which populate a part of the HR diagram far removed from the region inhabited by the central stars of well recognised nebulae. The problem of determining the initial masses is complicated by the widespread occurrence of massloss on the red giant branch. The total amount of mass lost by a star must depend upon a number of stellar parameters including the initial mass, but the exact nature of this dependence remains to be discovered and a unique relation between the final masses and initial main sequence masses is not yet available. Thus even though the mass distribution of the nuclei of planetary nebulae (NPN) has been derived in the last few years, it has not been possible to deduce from this an unambiguous initial mass distribution of the progenitors. Further, an observed sample always suffers from selection effects and, in the particular case of NPN mass distribution, this has led to irretrievable loss of information.
Binary Stars and Planetary Nebulae
Authors: Iben Icko , Tutukov Alexander V.
Published: July 2016

A non-negligible (∼ 15–20%) fraction of planetary nebulae is expected to be formed in close binaries in which one component fills its Roche lobe after the exhaustion of hydrogen or helium at its center. The nebula is ejected as a consequence of a frictional interaction between the stellar cores and a common envelope; the ionizing component of the central binary star may be a relatively high luminosity contracting star with a degenerate CO core, burning hydrogen or helium in a shell, or it may be a lower luminosity shell hydrogen-burning star with a degenerate helium core or a core helium-burning star. Even more exotic ionizing central stars are possible. Once the initial primary has become a white dwarf or neutron star, the secondary, after exhausting central hydrogen, will also fill its Roche lobe and eject a nebular shell in a common envelope event. The secondary becomes the ionizing star in a tight orbit with its compact companion. In all, there are roughly twenty different possibilities for the make-up of binary central stars, with the ionizing component being a post asymptotic giant branch star with a hydrogen- or helium-burning shell, a CO dwarf, a core helium-burning star, a shell helium-burning star with a degenerate CO core, a shell hydrogen-burning star with a degenerate helium core, or a helium degenerate dwarf, while its companion is a main sequence star, a CO degenerate dwarf, a helium star, a helium degenerate dwarf, or a neutron star. We estimate the occurrence frequency of several of these types and comment on the prior evolutionary history of 4 observed binary central stars.
Mass Distribution and Birth Rate of Central Stars of Planetary Nebulae: Comparison with White Dwarfs, and Influence of Selection Effects
Authors: Weidemann V.
Published: July 2016

The mass distribution of central stars (CPN) as derived by the Schönberner method (1981) M⊙ vs. age, v(exp) = const, for an enlarged local ensemble, as presented at the London Symposium, 1983, appears to be much narrower and more strongly peaked towards smaller masses than the one recently derived by Heap and Augensen (1987) (HA) using the same method, but IUE data and M⊙ (λ 1300) vs. age, corrected for individual v(exp). Whereas according to Schönberner 65% of all CPN have M < 0.64 M⊙, HA find only 44% below the same limit. We demonstrate that this discrepancy is entirely due to the fact, that HA use Daub and 0.9 × Cahn/Kaler distances, whereas Schönberner used 1.3 × CK. We list a number of arguments which favor the larger distances, especially the recent work by Méndez et al. (preprint, 1987) (Teff/g determinations) and investigations of Magellanic Cloud PN by Aller et al. (1987), Wood et al. (1987) and Barlow (1987) which all indicate a scale ≥. 1.4 × CK. If one uses Barlow's recalibration formula for optically thick PN, the distances for those - which mainly contribute to the massive CPN in the HA analysis - are increased so much as to remove most of them from the local ensemble. We thus obtain for the revised IUE ensemble 84% CPN with M < 0.64 M⊙, in better agreement with results for white dwarfs (70%) (cf. Weidemann, 1987).
Early Stages of Stellar Evolution
Authors: Strom S. E.
Published: July 2016

A wealth of new observational data made available through the advent of modern infrared and microwave techniques, have provided astronomers with their first glimpses into the current-epoch stellar wombs - dark interstellar clouds. As a consequence, the past ten years have witnessed major advances in our understanding of the early evolution of stars and the mechanisms which trigger star formation. A future, more detached view of this period might suggest that we have achieved
Collapse Dynamics and Collapse Models
Authors: Larson Richard B.
Published: July 2016

Although we now possess a wealth of information about the properties of molecular clouds and the circumstances in which stars form, we still have little direct information about the crucial question of how the material in molecular clouds actually becomes condensed into stars. In this report we shall discuss briefly the current status of theoretical attempts to understand this problem, based on calculations of the dynamics of collapsing clouds and protostars.
The Distribution of Light in Galaxies
Authors: Freeman K.C.
Published: July 2016

The distribution of light in galaxies is their most obvious and fundamental observable property. Hopefully it gives us some insight into their structure and dynamics. In this talk I will review some recent work on ellipticals and disk galaxies. In summary, the luminosity distributions for both these classes have several complexities, the dynamical significance of which is not yet clear. Both classes turn out to have roughly constant mean surface brightness. This may result from selection. However, if it is real, then it is important dynamically, and I will discuss this question at the end.
Radio Properties of the Nuclei in Elliptical, SO and Spiral Galaxies
Authors: Ekers R.D.
Published: July 2016

When Heeschen (1968) found that the nuclear sources in the two elliptical galaxies NGC 4278 and NGC 1052 contained flat spectrum unresolved sources he conjectured that these might be weaker versions of the compact optically thick and strongly variable sources found in the quasar nuclei. This conjecture appears to be correct since these are both now known to have diameters <0.1 pc (Cohen et al. 1971) and to be variable on time scales of order one year. This variability has recently been confirmed by observations with the VLA (Heeschen, private communication).
Galaxy Haloes and the Missing Mass Problem
Authors: van den Bergh Sidney
Published: July 2016

Available evidence on the mass-to-light ratios in binary galaxies, small clusters and in rich clusters is reviewed. The interpretation of the binary data remains ambiguous. The relative velocity of M81 and M82 implies thatm/LV> 12. The Local Group data also appear to favour the existence of some hidden mass associated with M31 and the Galaxy. In the Virgo cluster a significant fraction of the virial mass may be concentrated in the halo of M87. In Coma the missing mass was probably stripped from the haloes of the two dominant E galaxies and is now distributed throughout the cluster.

It is suggested that metal-poor stars in the galactic disc have a higher CNO abundance than do halo stars of similar metallicity. This may explain why globular cluster stars lie on taller red giant branches than do moderately high-velocity stars near the Sun. The dominant old red giant population in the disc of M31 appears to be similar to that in the Galaxy. Most of the red giants in M33, NGC 6822 and in the LMC lie on taller red giant branches than do those in the Galaxy and M31. This suggests that old evolved stars in these relatively low-luminosity galaxies have a lower heavy element abundance than do their counterparts in the galactic disc. The red giants in M32 appear to be intermediate between those in M31 and M33. This supports the idea that M32 was once much more luminous than it is at present.
Observations of high velocity HI clouds in the Local Group
Authors: Huchtmeier W.K.
Published: July 2016

High velocity clouds (HVC) of neutral hydrogen in or around our galaxy and the observations of intergalactic HI in the Local group: Magellanic stream (Mathewson et al., 1974, Astrophys. J. 190, p. 291), M 31 (Davies, R.D., 1975, Mon. Not. R. astr. Soc., 170, p. 45P), and in the Sculptor group of galaxies (Mathewson et al., 1975, Astrophys. J. 195, p. L97) motivated us to search for HVC-phenomena in a number of nearby late-type galaxies with the 100 m Effelsberg radio telescope which has a half power beam width of 8.5′ at the wavelength of 21 cm.
The Galactic Neighbourhood
Authors: Tammann G. A. , Kraan R.
Published: July 2016

Several properties of the 131 galaxies known within 9. 1 Mpc are investigated. 88 of these galaxies are concentrated into eight groups, leaving 33 percent of true field galaxies. There are E/S0 and S0 galaxies among the field galaxies; their types must be of cosmogonic origin. the groups have small velocity dispersion which limits the mean mass-to-light ratio for the different types of group galaxies to m/L < 20. Within the supergalactic plane the deviation from an ideal Hubble flow are small: the changes of ΔHO/ with distance and direction are not larger than ten percent; the radial component of the peculiar motion of field galaxies is <25 km s−1. the differential luminosity function of S/Im galaxies is well approximated by a Gaussian with and . the luminosity function of E/S0 galaxies is much flatter with a possible minimum, separating true E's and dwarf ellipticals (Reaves, 1977). the sample galaxies are strongly concentrated toward the supergalactic plane; at a distance of 4 Mpc of the plane the luminosity density drops to half its value. There is also a pronounced luminosity density decrease with increasing distance from the Virgo cluster centre; at a distance of 30 Mpc the density has decreased by more than a factor of 104. the best estimate of the mean luminosity density within a sphere of 30 Mpc radius centered on the Virgo cluster is 1.5 · 108 L⊙ Mpc−3.
The scatter in mass-to-luminosity ratios
Authors: Einasto Jaan
Published: July 2016

Mass-to-luminosity ratios of systems of galaxies as derived by different authors have a large scatter from ~ 10 to ~ 200. the observational data used by different authors differ only slightly, so the differences should lie in the treatment of the data. We have found that in most cases < M/L > differences can be explained in the following ways.
Stabilization of systems of galaxies by subclustering
Authors: Ozernoy L. M. , Reinhardt M.
Published: July 2016

Subclustering might help to solve the virial theorem paradox for systems of galaxies by hiding a major part of the potential energy in gravitationally bound subsystems. We have shown (Ozernoy and Reinhardt 1976, Astr. Astrophys., 52, 31) that even in groups of galaxies there is mass segregation, in the sense that bright group members tend to be concentrated towards the centre. Recently Wesson and Lermann (1977, Astrophys. Sp. Sci., 46, 327), realizing the importance of subclustering, proposed a quantitative method for estimating its effect on the stability of systems of galaxies. However, their assumption about the frequency of subsystems of multiplicity n is not in accord with Holmberg's (1962) result. the mean frequency of galaxies in pairs is 0.37 for the Turner and Gott groups (1976) and 0.23 for the de Vauceulours groups (1976), in good agreement with the value of 0.25 required by Holmberg's distribution. Assuming Holmberg's frequency of gravitationally bound subsystems and that they are homogeneously distributed throughout the system, we have for the ratio of the total potential energy of a system of N equal masses Ω to the potential energy calculated in the usual way neglecting subclustering Ωs, Ω/Ωs≈ 1+(Rc)/(N), if the velocity dispersion <σr2(n)> = constant. Here Rc is the effective radius of the system and  the mean distance of binaries. the assumption σr2(n) = const is reasonable for n ≤ 7, when Holmberg's distribution holds, since σr2(2) = 203 km s−1 according to Karachentsev (1974), and increases to only ≃ 1000 km s−1 for rich clusters. Since Karachentsev's data give an  = 33 kpc for HO = 55 km s−1 Mpc−1, we have Ω/Ωs≈ 4 for groups of galaxies with Rc≈ 1 Mpc and N = 10. Thus it seems that subclustering cannot remove the mass discrepancy for rich clusters and for groups only in moderate cases.
Markarian galaxies with double and multiple nuclei
Authors: Khachikian E.
Published: July 2016

Saakian, Petrosian and I have studied the central regions of Markarian galaxies using observations made with the SAO 6-metre telescope and the 2.6 m and 0.5 m telescopes of the Burakan Observatory. in a paper soon to be published, we show that in those galaxies which have strong ultraviolet excesses, i.e. Markarian Galaxies, double or multiple nuclei are found with a significantly greater frequency than they are in ordinary galaxies. This result suggests that these are among the most active nuclei. the photographs in our paper show the 60 examples of double or multiple nuclei found in the first 8 lists of Markarian galaxies.
Gas in Galaxy Clusters
Authors: Silk Joseph
Published: July 2016

Gaseous matter almost certainly cannot account for a significant amount of the binding mass in the cores of rich clusters. Implications of the variety of upper limits are well known (Tarter and Silk 1974), and will not be described here. However intracluster gas provides important clues to the evolution of galaxy clusters, and the present review is devoted to elucidating its role.
The Local Supercluster
Authors: de Vaucouleurs G.
Published: July 2016

The first quantitative evidence for a large scale density excess or “metagalactic cloud” including the Local Group was obtained by Holmberg (1937) and confirmed by Reiz (1941). the present concept of the Local Supercluster (LSC) as a flattened aggregate of field galaxies, small groups and larger clouds centered at the Virgo cluster was formulated 25 years ago (de Vaucouleurs 1953) even before large-scale superclustering was recognized as a general phenomenon. See review papers in Vistas in Astronomy (1956), Soviet Astronomy (1960), Science (1970), Publ. Astron. Soc. Pacific (1971), and IAU Symp. No. 63 (Abell 1974).
Absolute Magnitudes by Statistical Parallaxes
Authors: Heck André
Published: July 2016

Our algorithm for stellar luminosity calibrations (based on the principle of maximum likelihood) allows the calibration of relations of the type:

Where n is the size of the sample at hand,

Mi, are the individual absolute magnitudes,

Cijare observational quantities (j = 1, …, N), and

qjare the coefficients to be determined.

If we put N = 1 and CiN= 1, we havethe mean absolute magnitude of the sample. As additional output, the algorithm provides us also with the dispersion in magnitude of the sample σM, the mean solar motion (U, V, W) and the corresponding velocity ellipsoid (σu, σV, σw).
HR Diagrams Derived from the Michigan Spectral Catalogue
Authors: Houk Nancy , Fesen Robert
Published: July 2016

In this paper we present some HR diagrams constructed using data from theMichigan Spectral Catalogues. Houk (1975) has been systematically reclassifying the Henry Draper stars on the MK system, from the south pole northward. Objective-prism plates, with a reciprocal dispersion of 108 Å/mm, have been taken with the Michigan Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory in Chile. The spectra are classified visually from the plates, and the results are put onto IBM cards and magnetic tape from which the catalogues are produced.
The HR Diagram for Luminous Stars in Nearby Galaxies
Authors: Humphreys Roberta M.
Published: July 2016

HR diagrams for the stellar populations in other galaxies play a fundamental role in our understanding of the progress of stellar evolution and the effects of possible variations in chemical composition. It is important to compare what little information we have about stars in other galaxies with the same types of stars in our own Milky Way. Basically we are asking - are they the same, and how universal are the processes we observe in our Galaxy?
The Vogt-Russell Theorem, and New Results on an Old Problem
Authors: Kähler Helmuth
Published: July 2016

Half a centry ago Henry Norris Russell and Heinrich Vogt independently made a conjecture concerning the structure of spherical stars which are in hydrostatic and thermal equilibrium (Russell, 1927; Vogt, 1926). This conjecture has later come to be known as the Vogt-Russell theorem and is usually formulated as follows: The structure of a star is uniquely determined by the mass and the composition. In other words, the statement claims the existence and uniqueness of a stellar equilibrium configuration for given parameters mass and composition, and you may find what is called a mathematical proof in many textbooks on stellar structure.