bluuebunny/crossref_metadata_2025_split huggingface dataset:
Discovery of a Stellar Association Surrounding the Massive Binary Sk–67°105 in the Large Magellanic Cloud
Authors: Ostrov P. G. , Niemela V. S. , Morrell N. I. 
Published: July 2016

Sk–67°105, a luminous O4f type stars in the Large Magellanic Cloud, is the exiting star of the H II region N 50 (DEM 193). Niemela & Morrell (1986) found this hot star to be a massive short period double lined spectroscopic binary. Because luminous OB stars are usually found in young stellar groups, we have searched for such an aggregate in the vicinity of Sk–67°105.Here we report, as a result of our search, the discovery of a new OB association in the LMC. We also find that Sk–67°105 is the most luminous star of a small compact cluster inside this OB association.
Analyses of the LMC Novae
Authors: Vanlandingham Karen M. , Schwarz Greg J. , Starrfield Sumner , Hauschildt Peter H. , Shore Steven N. , Sonneborn George 
Published: July 2016

In the past 10 years, 6 classical novae have been observed in the Large Magellanic Cloud (LMC). We have begun a study of these objects using ultraviolet spectra obtained by IUE and optical spectra from nova surveys. We are using the results of this study to further our understanding of novae and stellar evolution.Our study includes analysis of both the early, optically thick spectra using model atmospheres (Hauschildt et al. 1992), and the later nebular spectra using optimization of photoionization codes (Ferland 1996; James & Roos 1993). By analysing all the LMC novae in a consistent manner, we can compare their individual results and use their combined properties to calibrate Galactic novae. In addition, our studies can be used to determine the elemental abundances of the nova ejecta, the amount of mass ejected, and the contribution of novae to the ISM abundances. To date we have analysed Nova LMC 1988#1 (Schwarz et al. 1998) and Nova LMC 1990#1 (Vanlandingham et al. 1999), and have obtained preliminary results for Nova LMC 1991. The results of this work are presented in this poster.
Large Scale Structure of the Universe
Authors: Bahcall N.A. 
Published: July 2016

How is the universe organized on large scales? How did this structure evolve from the unknown initial conditions of a rather smooth early universe to the present time? The answers to these questions will shed light on the cosmology we live in, the amount, composition and distribution of matter in the universe, the initial spectrum of density fluctuations that gave rise to this structure, and the formation and evolution of galaxies, lusters of galaxies, and larger scale structures.To address these fundamental questions, large and accurate sky surveys are needed—in various wavelengths and to various depths. In this presentation I review current observational studies of large scale structure, present the constraints these observations place on cosmological models and on the amount of dark matter in the universe, and highlight some of the main unsolved problems in the field of large-scale structure that could be solved over the next decade with the aid of current and future surveys. I briefly discuss some of these surveys, including the Sloan Digital Sky Survey that will provide a complete imaging and spectroscopic survey of the high-latitude northern sky, with redshifts for the brightest ∼ 106 galaxies, 105 quasars, and 103.5 rich clusters of galaxies. The potentialities of the SDSS survey, as well as of cross-wavelength surveys, for resolving some of the unsolved problems in large-scale structure and cosmology are discussed.
Near-IR imaging and optical Spectroscopy of M 2-9
Authors: Arrieta A. , Torres-Peimbert S. 
Published: July 2016

IR OBSERVATIONS. We have extended previous infrared imaging studies (cf. Hora & Latter 1994 ApJ 437, 281; Kastner et al. 1996 ApJ 462, 777) through wide and narrow band filters.In these images: (a) JHK′ morphology is similar to the optical structure. The knots are brighter at the shorter wavelengths, while the core is brighter at K′. (b) [He I] 1.083 μm that traces the highly ionized region, is concentrated along the axial region and extends throughout the lobes (33″ × 9″). It shows the knots very prominently. (c) [Fe II] 1.644 μm, that traces the shock excited regions, extends []throughout the lobes; it is more prominent in the northern knot and it is very strong in the core. (d) The excited molecular H2 lines are concentrated on a wide ‘torus’ in the equatorial plane. This geometry is similar to that exhibited by most bipolar planetary nebulae where H2 has been detected (e.g., Kastner et al. 1996). No H2 emission is seen in the core. (e) Paγ shows emission in only in the core and the northern knot. (f) Brγ shows emission in the core and in knots N2, S2 and S3. (g) No significant emission in CO was obtained.
Evolutionary and Cosmological Corrections for High Redshift Galaxies
Authors: Möller C.S. , Alvensleben U. Fritze-v. , Fricke K.J. 
Published: July 2016

We calculate the evolution of high redshift galaxies by spectral type with our unified chemically consistent spectrophotometric evolution code. This model takes into account the increasing initial metallicity of successive stellar generations using recently published metallicity dependent stellar evolutionary tracks, color calibrations and spectra (Möller et al. 1997).We analyse how the consideration of a realistic metallicity distribution affects the evolutionary and cosmological corrections in various bands as a function of redshift. For various spectral types of galaxies and various cosmological parameters we present the color and magnitude evolution as a function of redshift and compare them with observations.
Observational Evidence for the Stratification of Chemical Abundances in Stellar Atmospheres
Authors: Ryabchikova T. , Wade G. A. , Leblanc F. 
Published: July 2016

We present spectroscopic and photometric observational evidence for abundance stratification in stellar atmospheres. Attention is given to chemically peculiar (Ap) stars in which magnetic fields stabilize the atmosphere, allowing diffusion processes to establish abundance stratification during the early stages of star's life. The results of recent empirical modelling of chemically stratified atmospheres are briefly discussed, and a comparison is given with the predictions of self-consistent atmospheric models which include radiative diffusion.The importance of abundance stratification analysis is demonstrated for rapidly oscillating (roAp) stars in which the amplitudes of the radial velocity pulsations are different for the lines of different elements in different ionization stages. We also demonstrate that chemical stratification has important effects on the Zeeman Stokes IQUV profiles of Ap stars, indicating that stratification must be taken into account in detailed modelling of their magnetic fields.
A New Study of Some Galactic Planetary Nebulae
Authors: Meatheringham Stephen J. , Wood Peter R. , Faulkner D. J. 
Published: July 2016

AbstractExpansion velocities ([O III], [O II], and He II) have been measured for a sample of 64 Southern Planetary Nebulae (PN). The ratio of [O III] to [O II] expansion velocities is used to derive a typical ionized shell thickness of order ΔR/Rneb ≍ 0.12. Nebular electronic densities have been determined from the [O II]λλ3727, 3729 A doublet for 23 of these objects. These data are compared with previously published values. The Dopita et al. (1987) distance scale for Magellanic Cloud PN based on a correlation between observable nebular parameters is used to derive distances to 32 Galactic nebulae. These distances are compared with published values, and lead to the conclusion that the Dopita et al., Daub (1982) and Maciel (1984) distance scales agree well, but that the Shklovsky (1956) method yields distances that are too large. Nebular ionized masses are also calculated for a subset of 30 objects.
Wind Features and Wind Velocities
Authors: Grewing Michael 
Published: July 2016

Fast winds have been detected in the spectra of many nuclei of planetary nebulae (PNNi). The wind velocities range from about 600 km/s to roughly 4000 km/s. While these winds add little to the mass of the nebular shells they may significantly effect their internal kinematics.By studying the emission from the faint outer envelopes of PNe one can infer also the wind properties of the progenitors of the current nuclei. This will in the end allow to test quantitatively current models of the origin of PNe.
Mass Loss Rates in Central Stars of Planetary Nebulae
Authors: Perinotto M. 
Published: July 2016

Central stars of planetary nebulae (PNCS) frequently exhibit fast winds (cf. Cerruti-Sola and Perinotto, 1985; C.P. and Grewing, this volume). They may be important for the structure of the whole nebula as well as for the evolution of the central star. Their speed is typically two orders of magnitude higher than that of the classical optically visible nebula, which in turn expands a few times faster than the most external winds detected in few cases in the radio domain.I review here the status of art in the determination of the mass loss rates (M) associated with these fast winds. I restrict myself to the ‘observational’ determinations. Only at the end I will say something about the predictions of multi-scattering line radiation wind driven theory in connection with one best studied object: N6C 6543. This allows one to conclude that this theory may be the right explanation also for these winds.
Quantitative Two-Dimensional Classifications of Low Dispersion Objective Prism Spectra
Authors: Schmidt-Kaler Th. 
Published: July 2016

The objective prism (or grating) is the most efficient stellar spectrograph since it suffers no light losses at a slit and - compared to a slit spectrograph - only small losses in the camera optics. However, objective prism spectra have two principal disadvantages:(1)the spectral resolution (and consequently the sharpness of spectral features) depends on the seeing, which may vary from plate to plate.(2)quantitative measurements are difficult because of the difficulty in obtaining an exact photographic calibration; no comparison spectrum can be placed near the stellar spectra.
RR Lyrae Variable Stars and the Distance Scale
Authors: Clube S. V. M. , Dawe J. A. 
Published: July 2016

A statistical parallax algorithm (Clube and Dave, 1978a,b), using the technique of maximum likelihood, has been applied to a set of 103 ‘ab’ - RR Lyrae stars in the solar neighborhood (r 2&lt;kpc), using observational data from the Royal Greenwich Observatory Bulletins. A second set of 130 ‘ab’ - RR Lyrae stars has been kindly supplied to us by Dr. A. Heck (Université de Liège) to permit a comparison between our analyses. The purpose of this investigation was:(a) to investigate the variations of kinematical parameters and absolute luminosities of these stars as functions of Preston's index ΔS and of log (Period).(b) to identify those RR Lyrae stars in the solar neighborhood which most closely resemble those in the galactic halo, those near the galactic center, and those in the Magellanic Clouds.
The Position of the Sun in the HR Diagram
Authors: Barry Don C. 
Published: July 2016

Since the absolute magnitude of the Sun is known accurately and the solar spectrumdefinesspectral type G2 V, it would appear that the position of the Sun in the HR diagram is well established. However, the color of the Sun and its metallicity relative to other stars remains controversial. It is known from theory that stellar groups of differing composition will have different main sequences.The observed difference in the strength of the metallic lines in Coma stars relative to Hyades stars is caused by a systematic difference in [Fe/H] of less than 0.2 dex or 50%. Photographs and quantitative measures of the systematic differences between the Hyades and Coma spectra are presented. Visual comparison and quantitative analysis of the solar spectrum relative to Hyades and Coma spectra reveal that the Sun is metal rich similar to the Hyades stars rather than of normal disk metallicity as represented by Coma stars. Evidence is presented showing that the color and spectral line strengths of the Sun are more similar to stars classified G3 and G4 in the literature than G2. If the Hyades modulus is y = 3m.25, the (B-V) color of the Sun must be 0m.65 or redder for the Sun to be on or above the Hyades main sequence.
Rapid X-ray variability in active galactic nuclei
Authors: Barr P. , Mushotzky R. , Giommi P. , Clavel J. , Wamsteker W. 
Published: July 2016

SummaryRecent EXOSAT observations of active galactic nuclei are presented. Unlike earlier X-ray satellites (all of which flew in low earth orbit), the deep orbit of EXOSAT allows long continuous observations of celestial X-ray sources, uninterrupted by earth occultation etc. We present the results of EXOSAT observations of several AGN which have been seen to vary rapidly (timescale 0.2–6 hours). We also consider the implications of rapid variability in AGN. For Seyfert galaxies and quasars, we find a highly significant correlation between the timescale of variability and their X-ray luminosity. They are not, howwever, bounded either by the (classical) Eddington limit nor by efficiency arguments. We sugest, rather, that the emitting plasma is dominated by electron-positron pairs.
Non-Uniformities in the Hubble Flow: Results from a Survey of Elliptical Galaxies
Authors: Davies Roger L. , Burstein David , Dressler Alan , Faber S. M. , Lynden-Bell Donald , Terlevich Roberto , Wegner Gary 
Published: July 2016

We have used a new distance estimator for elliptical galaxies to determine the peculiar velocities, with respect to a uniform Hubble flow, of approximately 400 galaxies. The relative distances of five clusters in common with those of Aaronson et al. (1981, 1986), based on the infrared Tully-Fisher relation for spirals, are in good agreement.We do not see the reflex of the Local Group motion with respect to the microwave background out to recession velocities of 6000 km s−1. Rather, the frame of elliptical galaxies appears to be moving with respect to the microwave background with a velocity of 600 km s−1 towards 1 = 312°, b = +6°. This motion is consistent with a re-analysis of the Rubin et al. (1976) data on the magnitude-diameter relation for ScI galaxies and with the nearby and cluster samples of Aaronson et al. (1982, 1986).
Absorption Line Systems at z > 3 in the QSO 2000-330
Authors: Hunstead R.W. , Pettini M. , Blades J.C. , Murdoch H.S. 
Published: July 2016

This paper presents some preliminary results from analysis of our high-resolution (30–35 km/s FWHM) spectra of the Lyman α forest region in the z = 3.78 QSO 2000-330. These spectra were obtained at the Anglo-Australian Telescope over several observing seasons and have been analysed by fitting multiple-cloud Voigt profiles to Lyman series and heavy-element absorption lines. Two specific issues are addressed here:
(i)The distribution of column densities, N(H I), and velocity dispersions, b, for hydrogen clouds in the interval zabs = 3.43–3.78;(ii)Heavy-element abundances in a system at zabs = 3.1723.
Redshifts of New Galaxies
Authors: Arp Halton 
Published: July 2016

Observations increasingly demonstrate the spatial association of high redshift objects with larger, low redshift galaxies. These companion objects show a continuous range of physical properties - from very compact, high redshift quasars, through smaller active galaxies and finally to only slightly smaller companion galaxies of slightly higher redshift. The shift in energy distribution from high to low makes it clear that are seeing an empirical evolution from newly created to older, more normal galaxies.In order to account for the evolution of intrinsic redshift we must conclude that matter is initially born with low mass particles whose mass increase with time (age). This requires a physics which is nonlocal (Machian) and which is therefore more applicable to the cosmos than the Big Bang extrapolation of local physics. Ambartsumian's “superfluid” foresaw some of the properties of the new, low particle mass, protogalactic plasma which is required, demonstrating again the age-old lesson that open minded observation is much more powerful than theoretical assumptions.Since the ejected plasma, which preferentially emerges along the minor axis of the parent galaxy, develops into an entire galaxy, accretion disks cannot supply sufficient material. New matter must be created within a “white hole” rather than bouncing old matter off a “black hole”.
The Situation of Light Pollution in Germany
Authors: Hänel Andreas 
Published: July 2016

The central European climate in Germany is not ideal for serious astronomical observations. Increasing light pollution hampers thousands of amateur astronomers and millions of people from seeing starry skies and the Milky Way.To study the sources of light pollution, we estimate the increase of light pollution in Osnabrück, a town of about 160,000 inhabitants located in northwestern Germany. We try to extrapolate these statistical data to Germany and discuss possible reasons for increasing light pollution though the energy consumption stagnates. Some enthusiasts of the German amateur association “Vereinigung der Sternfreunde” have formed a working group DARK SKY to exchange information on this matter. Finally, we present some activities to make the public aware of the problem.
Chemical Models of Circumstellar Disks
Authors: Aikawa Yuri , Herbst Eric 
Published: July 2016

We investigate the evolution of molecular abundances in circumstellar disks around young stars via numerical simulations. The results are compared with the composition of comets and radio observations of protoplanetary disks. First, we consider the molecular evolution in the midplane of the disk. Because of ionization by cosmic-rays or decay of radioactive nuclei, the molecular evolution in the region R ≳ 10 AU bears some similarity to that in molecular clouds. Considerable amounts of CO and N2, which come from the cloud core, are transformed, however, into CO2, CH4, NH3, and HCN. In regions where the temperature is low enough for these products to freeze onto grains, they accumulate in ice mantles. In the inner warmer regions of the disk, these molecules are desorbed from the mantles and transformed by gas-phase reactions into less volatile molecules, such as larger hydrocarbons, which then freeze out. Molecular abundances both in the gas phase and in ice mantles crucially depend on the temperature and thus vary significantly with the distance from the central star. Molecular abundances in ice mantles show reasonable agreement with the composition of comets. Our model suggests that comets formed in different regions of the disk having different molecular compositions.Secondly, we report two-dimensional (R, Z) distributions of molecules in circumstellar disks. In the Z-direction, which is perpendicular to the midplane, there is a steep gradient of density and radiation field. Since the density is lower in the regions removed from the midplane, there are significant amounts of gas-phase species in these regions, while most species are adsorbed onto grains in the midplane. Chemistry in the surface regions is also affected by the X-rays and UV radiation from the central star, and UV radiation from the interstellar field. The molecular abundances in these regions differ significantly from those in the midplane. Radicals such as CN are especially abundant near the disk surface. We obtain radial distributions of molecular column densities and averaged molecular abundances, which show reasonable agreement with the observational data at millimeter wavelengths.
The Light Elements: What is Known, What is Controversial
Authors: Spite F. 
Published: July 2016

The light elements are essential, because their primordial abundances are linked to the general parameters of the universe (at least in the Big Bang theory). Some of the light elements are fragile, and the interpretation of their abundances in stars requires a good knowledge of the stellar structure. The stellar abundances have to be known with a considerable accuracy, challenging the current level of representation of the stellar atmospheres. It is also difficult to reach accurate abundances in the gas : interstellar, H II regions, PN, intergalactic¨.On the other hand, the fragile light elements are important probes of the stellar interiors, and their observation helps to the determination of reliable models, which in turn will improve the accuracy of stellar abundances. A part of this symposium is devoted to this probing aspect.The talks (and many high quality posters) which build this symposium, cover all these aspects. I will try here to point out the controversial points and the reasonably well known facts. We expect from discussions, both formal and informal, a number of (eagerly awaited for) clarifications.
Evolution of D and 3He in the Galaxy
Authors: Tosi Monica 
Published: July 2016

The predictions of Galactic chemical evolution models for D and 3He are described in connection with those on the other Galactic quantities for which observational constraints are available.Models in agreement with the largest set of data predict deuterium depletions from the Big Bang to the present epoch smaller than a factor of 3 and do not allow for D/H primordial abundances larger than ∼ 4 × 10—5. Models predicting higher D consumption do not reproduce other observed features of our Galaxy.If both the primordial D and 3He are low, models assuming that 90% of low-mass stars experience an extra-mixing during the red giant phase reproduce all the 3He observed abundances. The same percentage allows to fit also the observed carbon isotopic ratios, thus supporting the self-consistency of the extra-mixing mechanism.
Solar Coronal Magnetic Fields
Authors: Hildebrandt J. , Kliem B. , Krüger A. 
Published: July 2016

A short compilation of various radio methods of the determination of magnetic fields in the solar corona is given which, completed by observations in other spectral ranges (e.g. the optical and X-ray ranges), results in a complex picture of the magnetic field. Some topics of interest are the following:
(1)Comparison with a standard reference magnetic field in the solar corona,(2)Possible evidence of substantial small-scale fluctuations of the magnetic field (e.g. in active regions),(3)Indication of magnetic fields substantially in excess of the standard distribution (e.g. in limb flare events).
Non-Axisymmetric Magnetic Structure Generation in Planets Sun and Galaxies
Authors: Starchenko S.V. 
Published: July 2016

The problem of preferential excitation of non-axially symmetric magnetic fields in most of the observed spiral galaxies and in planets as Uranus and Neptune is studied. It is suggested that a dynamo acting in a thin conductive shell is possible in these objects.It is shown that in this thin shell axisymmetric and non-axisymmetric magnetic field modes can be excited with equal efficiency. The preferential excitation of non-axially symmetric magnetic fields is possible, when the gradient of the angular velocity of rotation is comparatively small and has an essential component perpendicular to the shell.