bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the dynamical reference frame through minor planet orbit correction using crossing point observations
Authors: Whipple Arthur L. , Duncombe Raynor L. , Hemenway Paul D.
Published: June 2019

We have begun a program to establish a dynamical reference frame based on the motions of minor planets. The program will utilize observations from the Hubble Space Telescope, and will ultimately tie the HIPPARCOS reference system to a dynamical base. Thirty-four minor planets, 20 of which are suitable for observation with the Hubble Space Telescope, have been selected. Ground based observations, particularly crossing-point observations with long focus reflectors, have been initiated.

A computer program to simultaneously solve for the corrections of the orbits of the 34 minor planets including the crossing-point observations, was successfully run. The observations are treated by the method of W. H. Jeffreys. Using simulated data, solutions with and without crossing point observations demonstrate the value of those observations to produce a homogeneous and coherent set of results.
Analysis of UTI determinations by VLBI within project IRIS
Authors: Schuh H.
Published: June 2019

Two series of UT1 data determined by VLBI within Project IRIS at 5 day intervals respectively on a daily basis have been subjected to an iterative spectral analysis. Various significant oscillations with periods less than two months could be detected in the IRIS UT1 data. Most of the periods between 18 and 63 days obviously correspond to short-period variations in global atmospheric data. The other significant variations with periods shorter than 35 days can be clearly identified as being due to the influence of zonal tides on the rotation of the earth. The results of the spectral analysis are compared with the theoretical periods and phases and with the amplitudes given by Yoder et al. (1981). The spectral analysis reveals very clearly the monthly (27.6d) and the fortnightly (13.7d) terms and also the smaller variations at 14.77 days and 9.13 days. A similar analysis of 8 subsets, each with two months of the daily UT1 determinations, indicates that the small 7.10 day term can already be extracted from the VLBI observations.
Atmospheric angular momentum and its relation to the length of day
Authors: Hull R. A. , McCarthy D. D. , Schwartz C. H.
Published: June 2019

The U.S. Naval Observatory is responsible for the determination and prediction of UT1-UTC. An investigation was begun to determine if atmospheric angular momentum (AAM) data could be useful in the National Earth Orientation Service (NEOS) combined solution and in the prediction of UT1-UTC. The investigation found AAM data to be useful possibly in the combined solution, but predictions of UT1-UTC were adversely affected when predictions of AAM data were introduced.
Chandler effect and nearly diurnal free wobble as determined from observations with a superconducting gravimeter
Authors: Richter Bernd , Zürn Walter
Published: June 2019

A continuous three year series of observations with the model TT40 superconducting gravimeter has been analysed for all frequency domains. The frequency of the nearly diurnal free wobble (NDFW) (1 + 1/(431.2 ± 3.2) cycles/sid.d.) and a damping factor (6208.5 days) are derived from this dataset. These results are not in agreement with the values predicted by the theoretical model presented by Wahr but match very closely the values derived from VLBI observations. A similar study of long period effects suggests furthermore that there is a strog correlation with the polar motion observed by other techniques. By comparing different drift models with respect to the ultra-long period of the gravity variations it is shown that the observed Chandler effect is not principally subjected to this type of instrumentally dependent parameter.
On the ellipticity of the core-mantle boundary from Earth nutations and gravity
Authors: Yoder C. F. , Ivins E. R.
Published: June 2019

A change in the core free nutation period from its hydrostatic value of 466d to about 433d has been inferred from analysis of both earth's annual nutation amplitude from Polaris VLBI data (Herring et al., 1986) and surface gravity in the diurnal tidal band (Zürn et al., 1986; Neuberg et al., 1986). Gwinn et al. (1986) interpret this shift as due to an excess nonhydrostatic ellipticity ed, equivalent to a change in the equatorial minus polar radius of 0.5 km. In this paper, the effect of a layer at the core-mantle boundary (CMB) on σf(and hence ed) is examined. Although the potential effect of this layer on σfis found to be large, constraints imposed from gravimetry limit changes in edto 10%. In addition, the annual nutation has a significant out-of-phase component. Mantle solid friction accounts for a large fraction of the out-of-phase nutation.
Disks in the Pre-Main Sequence Binary Environment
Authors: Mathieu Robert D.
Published: June 2019

The interaction of disks and young binary stars is discussed, with particular emphasis on disk structure, the existence of accretion at the stellar surfaces and binary orbital evolution.
The Barium Stars
Authors: Smith Verne V.
Published: June 2019

The Barium stars are reviewed in terms of their known binary nature and their quantitative abundance peculiarities. It is concluded that the most likely explanation of the 12C and s-process overabundances observed in the Barium stars is mass transfer from a companion, which is now a white dwarf, but was once a 4He-burning thermally-pulsing asymptotic giant branch star.
Symbiotic Binary Stars
Authors: Kenyon Scott J.
Published: June 2019

This paper briefly reviews the physical properties of symbiotic stars: long-period interacting binaries composed of a red giant primary star and a hot companion. Two types of binaries produce symbiotic optical spectra: semi-detached systems with a main sequence secondary and detached systems with a white dwarf secondary. Semi-detached symbiotics resemble cataclysmic variables and Algol binaries, but on a much larger scale, and undergo dwarf nova-like eruptions. Wind accretion powers detached systems; occasional thermonuclear runaways produce symbiotic novae - distant cousins of classical novae.
Photometric Analysis in Detached Close Binaries with Eccentric Orbits. The Case of RX Her
Authors: Giménez A. , García J. M. , Bravo A.
Published: June 2019

Absolute dimensions of the close binary RX Her are derived based on a new set of photometric elements obtained with a modified version of EBOP code. The observed properties of both components are in good agreement with theoretical evolutionary models. However the predicted apsidal motion rate is not concordant with the observational evidences.
Resonance Between Pulsation Modes Due to Tidal Perturbation
Authors: Kolláth Z. , Nuspl J.
Published: June 2019

The effect of tidal perturbation to stellar pulsation is a relatively underdeveloped problem in the theory of variable stars. We derive amplitude equations describing the resonances between pulsational modes and orbital motion taking into consideration the rotation of stars as well. In the case of δ Scuti stars the two-mode-tidal resonance was found to be the most powerful effect. If the difference between frequencies of excited and damped mode is close to the orbital frequency, parametric excitation of the damped mode may occur, while the other mode loses energy. We discuss this effect for a wide range of parameters.
Photometric Analysis of Wide and Narrow Hα Band Observations of R Canis Majoris
Authors: Edalati M. Taghi , Banks Timothy , Budding Edwin
Published: June 2019

Wide and narrow Hα lightcurves of R CMa were analysed using Wilson-Devinney (WD) and Information Limit Optimisation Technique (ILOT) approaches. A range of mass ratios, tested by both methods, led to an optimal estimate of around 0.45, at variance with the spectroscopic value. The distortion on the light curve affects the modelling, and so, in a second fitting, this was represented by a ‘hot spot’, associated with mass transfer effects. A semi-detached configuration was then derived. This is supported by the form of the Hα index variation, which has also been modelled. Although thus appearing as a ‘classical Algol’ system, R CMa retains its inherent peculiarity of low mass ratio with low period, which cannot be reconciled with conservative evolution scenarios.
Irregular Period Variations of Eclipsing Binaries
Authors: Herczeg Tibor J.
Published: June 2019

Considering a small number of representative systems among them U Cephei, SV Centauri, V471 Tauri, EM Cygni, the case is made for irregular period variations playing a substantial role in the observed changes of close binary periods.
Mass Exchange Via Pulsational Dumping from and F Supergiant
Authors: Parsons S. B. , Dempsey R. C. , Bopp B. W.
Published: June 2019

HD 207739 = V1914 Cyg, a tidally distorted F8 supergiant plus an obscured hot non-degenerate star, is presently in a state of episodic mass dumping onto an accretion shell around the hot component. Unrelated to the 141 day orbital cycle, the obscuration has a 50 day periodicity during which most of the UV flux diminishes rapidly, then gradually brightens. The more evolved yet less massive F supergiant is thus presumably shedding mass due to its pulsation.
Wind Driven Mass Transfer in Interacting Binaries
Authors: Tout Christopher A. , Hall Douglas S.
Published: June 2019

Stars in close binary systems can suffer two kinds of mass change: 1) mass transfer between the stars 2) mass loss completely from the system. Observational estimates indicate that these are of the same order. A simple explanation can be found if the mass loss, by stellar wind, from the Roche-filling star is the driving mechanism behind mass transfer. We find quantitative estimates for the necessary conditions and find that the mass transfer rate and the mass loss rate are indeed similar. We find that the radii of evolved semi-detached systems are more consistent with wind-driven evolution than the traditional nuclear-driven Roche-lobe overflow.
Tidal Circularization Among the Close Binaries in M67
Authors: Latham David W. , Mathieu Robert D. , Milone Alejandra A. E. , Davis Robert J.
Published: June 2019

In 1971 Roger Griffin and Jim Gunn began monitoring the radial velocities of most of the members brighter than the main-sequence turnoff in the old open cluster M67, primarily using the 200-inch Hale Telescope. In 1982 the torch was passed to Dave Latham and Bob Mathieu, who began monitoring many of the same stars with the 1.5-meter Tillinghast Reflector and the Multiple-Mirror Telescope on Mt. Hopkins. We have successively combined these two sets of data, plus some additional CORAVEL velocities kindly provided by Michel Mayor, to obtain 20 years of time coverage (e.g. Mathieu et al. 1986). Among the stars brighter than magnitude V = 12.7 we have already published orbits for 22 spectroscopic binaries (Mathieu et al. 1990). At Mt. Hopkins an extension of this survey to many of the cluster members down to magnitude V = 15.5 has already yielded thirteen additional orbital solutions, with the promise of many more to come.
The Contact Binary H235 in the Open Cluster NGC 752
Authors: Milone E. F. , Stagg C. R. , Sugars B.J.A. , Mcvean J.R. , Schiller S. J. , Kallrath J.
Published: June 2019

Photoelectric BVRI light and radial velocity curves of the 0.41d period eclipsing variable have been analyzed with a new, simplex-enhanced version of the Wilson-Devinney light curve program, and used to explore detached, semi-detached, and contact solutions. The system is best modeled as a W-type W UMa system, with contact parameter, f = 0.44, although at time of writing, we cannot rule out the possibility of an A-type system.
An Investigation of IR Triplet He I 10830 Å Profiles in Active Regions and the Quiet Chromosphere
Authors: Levkovsky V. , Papushev P. , Salakhutdinov R.
Published: June 2019

This paper gives a description of the technique and equipment used to make solar observations in the near IR region with a coronagraph. Examination of active-region spectra in the neighborhood of the He 110830 Å line confirm that the the line is enhanced in sunspot umbrae. The line profiles of umbrae and faculae differ qualitatively. Flares show a decrease in the line depth in comparison to faculae, and in flare kernels the line undergoes an emission reversal. Simultaneous observations of spectra of chromospheric spicules at two heights above the solar surface reveal that the half-width of the 10830 line increases with height.
Magnetic Fields, Oscillations, and Heating in the Quiet Sun Temperature Minimum Region from Ultraviolet Observations at 1600 Å
Authors: Cook J. W.
Published: June 2019

The High Resolution Telescope and Spectrograph (HRTS) instrument has obtained broadband spectroheliograph images at 1600 Å of the solar temperature minimum region. I discuss HRTS observations of quiet areas and their relation with magnetic fields, five minute oscillations, and heating. The brightness temperature of solar fine structure elements composing the supergranular network is found to be linearly proportional to the local absolute value of magnetic field strength. There is evidence for a 250-s period oscillation occurring in 10-arcsec scale patches, which however is energetically unimportant to the local heating budget. A general nonmagnetic background heating and five minute oscillations occur globally, while the network bright points occur in magnetic regions, heated perhaps from partial dissipation of Alfvén waves (whose energy flux is linearly proportional to B) in individual elemental 1500-G (at the photosphere) flux tubes which expand to form the temperature minimum fine structure bright points.
Properties of Magnetic Features from the Analysis of Near-Infrared Spectral Lines
Authors: Solanki Sami K.
Published: June 2019

An overview is given of the structure and the physics of magnetic features in solar plages, as derived from observations of near-infrared lines. First, the diagnostic potential of near-infrared lines is compared with that of lines in the visible and at 12 μm. Then, the results on the magnetic and velocity structure of magnetic features obtained from 1.5 μm lines are described, discussed and compared with results of observations in the visible and with theoretical predictions. Finally, the past and present achievements of near-infrared investigations of Zeeman-split lines are summarized.
The Applicability of a 5–18 μm Array Camera to Solar Imaging
Authors: Gezari Daniel Y.
Published: June 2019

The anticipated requirements and operating conditions are considered for using a mid-infrared array camera in broad- and narrow-band solar imaging observations. The array camera system was designed for high-background 5–18 μm general astronomical imaging observations. The electronic and optical design of the camera, its photometric characteristics, examples of observational results, and the requirements for imaging in both high- and low-background solar applications are discussed.
Open Panel Discussion on Interstellar Grain Models
Authors: Martin P. G.
Published: June 2019

A summary of the open discussion is provided. Topics ranged over composite particles, the 10 μm silicate feature, HAC, predictions, the 2200 å feature, carbon depletion, and far ultraviolet extinction.
Interstellar Dust in Collected Interplanetary Dust Particles
Authors: Sandford Scott A.
Published: June 2019

During the past decade interplanetary dust particles (IDPs) have been collected in the earth's stratosphere. Isotopic studies of these particles have demonstrated that many of them are greatly enriched in deuterium and at least some of them carry this enrichment in smaller subcomponents. Deuterium enrichments of a similar magnitude are seen in simple molecules in interstellar clouds. Deuterium enrichment in IDPs can be taken as evidence for the presence of interstellar material. It is not clear at this time whether the carriers of the isotopic anomalies represent true, unaltered interstellar dust grains, or whether they represent an altered component with a molecular ‘memory’ of original interstellar grains. The spectra of different components in the collected dust provide suggestive matches to similar components evident in the astronomical spectra of dust in comets, dense molecular clouds, and emission nebulae. The known extraterrestrial nature of the particles, the possible presence of interstellar material in them, and their spectral similarity to many astronomical objects all argue that the collected IDPs provide useful analogs for the modelling of interstellar dust.
Summary of the Ussr Ground Based Observations of the 3 K-Anisotropy
Authors: Parijskij Y.N.
Published: June 2019

Complete review of all (about 80) measurments made in US, USSR, GB, GFR, Australia, may be found in Parijskij and Korolkov (1986). Here we present very short summary of the astrophysical motivations and main results obtained in USSR during the last 20 years through ground based observations of 3 K anisotrory.
Coherent Large-Scale Motions from a New Sample of Spiral Galaxies
Authors: Rubin Vera C.
Published: June 2019

“The stellar milky way, in the region of which, according to Argelander's admirable observations, the brightest stars of the firmament appear to be congregated, is almost at right angles with another milky way, composed of nebulae… the milky way composed of nebulae does not belong to our starry stratum, but surrounds it at great distance without being physically connected with it, passing almost in the form of a large cross through the dense nebulae of Virgo, especially the northern wing, through Coma Berenicis, Ursa Major, Andromeda's girdle, and Pisces Boreales”. These words, published 140 years ago by Alexander von Humboldt (1849), outline the program which brings us all to Hungary for this conference.
The High-energy X-ray Background and Limits on Large Scale Structure
Authors: Mészáros A. , Mészáros P.
Published: June 2019

At present there are in use three different models to characterize the large scale structure of the universe. The clustering model (Soneira and Peebles, 1978) assumes that the superclusters are high density islands in a low density sea. The void model (Joeveer and Einasto, 1978), on the other hand, assumes that the voids are isolated low density islands in a high density sea. The sponge model (Gott et al., 1986) assumes that high and low density regions occupy equal volumes, and that the high and low density regions are both connected. The straightforward way to decide among these three models is the direct investigation of the spatial distribution of the galaxies. Nevertheless, there is an essentially different observational method that may also be useful to obtain some information about these models. The X-ray background radiation (XRB) is due either to the bremsstrahlung of hot intergalactic gas, or to the sum of the radiation of unresolved discrete sources (E.G. Boldt 1987). If the “discrete” origin is correct, then obviously the actual number of sources, and hence their total intensity, may vary from one part of the sky to another. Thus, in this case one has the possibility to estimate the number of sources in a given volume from the observed isotropy of the XRB. For example, Hamilton and Helfand (1987) suggest that the number of sources must be larger than 5000/(degree)2. Any such estimate needs several assumptions. In the previous works one usually assumed that the sources were distributed completely randomly; see, e.g. Fabian (1972). Nevertheless, if the XRB is generated by young galaxies (Bookbinder et al. 1980), it is not excluded that the sources of the SRB are also grouped similarly to galaxies. Because in this case the distribution of sources of the XRB is not completely random, one may expect a different type of fluctuations in the intensity of the XRB. In addition, since the grouping may be quite different for the three structure models, the expected fluctuations may also be different. There is a chance to discriminate among them using the observed isotropy of XRB. The basic observational datum concerning the isotropy of the XRB is well-known: the fluctuations in the intensity are smaller than 3%, if 3° × 3° pixels are used Shafer (1983).
Superclustering: Theory Versus Observations
Authors: Einasto Jaan , Einasto Maret , Saar Enn , Jones Bernard J. T. , Martinez Vicent J.
Published: June 2019

The spatial distribution of galaxies is compared with model distributions. It is demonstrated that giant and dwarf galaxies in the Local Supercluster occupy statistically identical regions. Various tests suggest that galaxy formation is biased since all unbiased model distributions are in conflict with observed distribution of galaxies. Multifractal analysis shows that a cold dark matter dominated universe with biased galaxy formation has a fairly constant fractal dimension over a broad range of scales. This contrasts with the observed distribution which does not show simple fractal features.
Quasar Absorption Lines: Evolution and Clustering
Authors: Sargent Wallace L.W.
Published: June 2019

A large new sample of absorption redshifts derived from the C IV doublet in the spectra of 56 QSOs has been used to study the evolution and clustering tendencies of the heavy element absorbers (thought to be galaxies). The new data have been compared with more extensive existing data for the more common Lyman α forest lines (thought to be produced by intergalactic clouds). Little or no clustering is observed in the Lyman α forest lines; moreover, there is no evidence for voids in their distribution. Clustering has been detected in the heavy element redshifts on scales Δv ≥ 200 km s−1 where relative motions of clouds within galaxies are unlikely to dominate. The degree of clustering inferred at z ≈ 2 is of the order expected on the simplest model for the evolution of galaxy clustering in cosmic time. The recent discovery of similar concentrations of absorption features extending over Δz ∼ 0.2 in the spectra of widely separated QSOs on the sky provides evidence for very large structures, probably filaments or sheets of galaxies, extending over 100 Mpc (co-moving). The Lyman α forest and heavy element redshifts evolve very differently. The Lyman lines show a rapid increase in density with increasing z, while the C IV doublets show a decrease. This result emphasizes that there are two discrete populations of absorbers. The decrease in C IV line density may be due to the effects of the onset of stellar nucleosynthesis in galaxies.
Galaxies Giving Rise to MgII Absorption Systems in Quasar Spectra
Authors: Bergeron Jacqueline
Published: June 2019

The properties of the MgII absorption line systems detected in quasar spectra are briefly summarized. If these absorption systems arise in intervening galaxies, one can estimate their characteristic size and luminosity, and predict their identification rate. Results of a search for the absorbers is presented for a sample of 13 MgII systems at 0.16 ≤ z ≤ 0.79. Strong constraints on the luminosity function are derived from the high actual identification rate and observed galaxy luminosities. Other properties of these absorbing galaxies are discussed, especially their spectral type and spatial environment.
Dark Matter in Single and Double Galaxies
Authors: van Albada T.S.
Published: June 2019

Analyses of rotation curves of spiral galaxies show that the amount of dark matter in a galaxy can exceed the amount of luminous matter by a factor of 4. Lenticular galaxies also appear to have dark halos, but conflicting results have been obtained for ellipticals. Data for double spiral galaxies confirm the results from rotation curves and suggest that the dark halos do not extend much beyond 5 optical radii R25.
Dark Matter in Dwarf Galaxies
Authors: Aaronson Marc , Olszewski Edward W.
Published: June 2019

We begin by reviewing the history of Aaronson's entry into the study of dark matter and velocity dispersions. A short review of mass estimations and dark matter in spirals, small groups of galaxies, dwarf irregulars, and dwarf spirals follows. We then discuss velocity dispersions in the five dwarf spheroidals Fornax, Carina, Sculptor, Draco, and Ursa Minor. A new velocity histogram for Draco and Ursa Minor is shown. We then end with some questions and theoretical and observational needs.
Gravitational Lenses
Authors: Burke Bernard F.
Published: June 2019

The gravitational lensing phenomenon is a new observational tool in cosmology. It appears to occur reasonably frequently; several thousand examples probably are observable with current radio and optical telescopes. A dozen or so reasonable candidates have been proposed, but it has become clear that one must apply strong tests to distinguish between real examples of lensing and chance associations. The dramatic double quasar 1146+111 has emphasized the need to be rigorous, and data is presented that casts further doubt on its status as a lens. There are a number of well-established cases, however, and these illustrate the varied character of possible lenses. Present observational programs should enlarge the number of established examples. Time-delay measurements are also in progress that give a new class of cosmological test; the original lensed quasar pair 0957+561 seems to have a differential time delay provisionally estimated at 600 ± 200 days for the two principal images.
Is the Giant Luminous Arc in A370 a Gravitational Lensing Effect?
Authors: Mellier Y.
Published: June 2019

A gravitational lensing model is proposed to explain the giant arc structure we observed in September 1985 in the distant cluster of galaxies Abell 370 (z=0.37.4).
Microwave Background Anisotropies in a Baryon-Dominated Universe
Authors: Suto Yasushi , Gouda Naoteru , Sasaki Misao
Published: June 2019

We have calculated the anisotropies of the cosmic microwave background radiation in a baryon-dominated model (BDM), using a gauge invariant method. The results on a 4.5′ angular scale are as follows (h = 0.5 and initially Zel'dovich power spectrum assumed):
Corona Borealis Supercluster
Authors: Kalinkov M. , Kuneva I. , Kopylov A.
Published: June 2019

A detailed investigation of the CrB supercluster of galaxies was initiated. More than 50 new radial velocities were determined. The observations were carried out with the 6-m telescope.
Cosmological Streaming Velocities & Large-Scale Density Maxima
Authors: Peacock J. A. , Lumsden S.L. , Heavens A.F.
Published: June 2019

We consider the statistical testing of models for galaxy formation against the observed peculiar velocities on 10–100 Mpc scales (the Rubin-Ford effect). If we assume that observers are likely to be sited near maxima in the primordial field of density perturbations (Peacock & Heavens 1985: MNRAS 217, 805; Bardeen et al. 1986: Ap. J. 304, 15), then the observed filtered velocity field will be biased to low values by comparison with a point selected at random. The streaming-velocity data constrain models for galaxy formation with large-scale damping (adiabatic perturbations) to have a damping length close to the Rubin-Ford scale (rD ∼ 20 h−1 Mpc) and are mildly non-linear (Ω0.6 σo ∼1), where σo is the current fractional rms density variation. The Figure illustrates the regions of parameter space allowed at the 10,5,1 & 0.1% levels; the results are nearly independent of n, the power index of the primordial spectrum. Thus, both purely baryonic universes and universes dominated by massive neutrinos can account for the observed velocities, provided 0.1 ≲ Ω ≲ 1. In particular, the canonical Ω = 1 massive-neutrino model yields the required velocities quite naturally (in contradiction to the conclusion of Vittorio et al. 1986: Nature 323, 132), while not violating the constraints on the isotropy of the microwave background. For further details of this work, see Peacock, Lumsden & Heavens 1987: MNRAS in press.
The Fractal Turbulence and the Origin of Large Scale Structure
Authors: Liu Y.-Z. , Deng Z.-G.
Published: June 2019

We have suggested a scenario of fractal turbulence which might explain the origin of galaxies and the observed large scale structure of the universe (Liu and Deng, 1987). Under the condition of the early universe, the cosmic fluid can be regarded as incompressible. If we assume that the density perturbations in the early universe are adiabatic and have the scale-free Zeldovich spectrum, we may obtain the spectrum of the velocity perturbations. Perturbations with scales less than horizon will undergo dissipative process by Thomson scattering. So, the cosmic fluid can be considered as a viscous fluid (Peebles, 1971). We can find the largest and smallest scale of the perturbations in the cosmic fluid by taking account of the Reynold's number on given scale and the scale of horizon. Using the present values of Hubble constant and the mean density of matter, we have found that on the scale of horizon the Reynold's number is just the order of 102. This result shows that perturbations with scale a little smaller than horizon may produce Karman vortices before recombination and the vortices might form fractal turbulence due to Thomson drag.
Fractal Dimension in the Large Scale Distribution of Galaxies
Authors: Deng Z.-G. , Wen Z. , Liu Y.-Z.
Published: June 2019

In this work, we start from the definition of fractal dimension and by the number counting of galaxies to investigate that if the large scale distribution of galaxies has really a fractal structure. A fractal dimension in a distribution of objects is defined as

where N(R) is the number of objects within scale R. To find out D from number counting we have to pay attention to that the distribution of galaxies could not be a regular fractal map. The N(R) would understand as a statistical average. To avoid the edge effect appearing in the number counting we compare it with that obtained from an average by many times Monte Carlo sampling which is a uniform distribution and would have Dr = 3. From eq. (1) we get
The Advent of Cosmological Gas Dynamic Simulations
Authors: Evrard August E.
Published: June 2019

The next move forward in simulations of cosmological structure is to include the hydrodynamics and thermal history of a gaseous component. The task is not an easy one. The dynamic range is wide in all interesting quantities (density, temperature, length-scales, time-scales, etc.). Generic initial mass distributions sampled from Gaussian random fields will, for many interesting power spectra, lead to a high degree of substructure present at all stages of the evolution. Grid-based hydrodynamic techniques currently lack the resolution necessary to evolve several levels of a clustering hierarchy simultaneously. A particle-based method known as SPH (Smoothed Particle Hydrodynamics, see Monoghan (1985) for a review) appears best suited for cosmological application. I have recently imbedded the technique into the P3M N-body code, described by Efstathiou et al. (1985) and used extensively by Efstathiou and collaborators, most recently in investigations of the cold dark matter scenario.
Rotation Profile of a String-Seeded Halo
Authors: Zurek W. H. , Quinn P. J.
Published: June 2019

We have used an N-body code to simulate the collapse of a wake left by a loop of cosmic string in a cold dark matter universe (Ω = 1, h = 0.5). Initial perturbations were introduced via the Zeldovich approximation in a high-resolution sphere of radius 1.5 Mpc (comoving) filled with a lattice of ∼ 104 points masses of 1.38 × 108M⊙. The top plot shows, at z = 24, a wake of a loop of Ms = 3 × 108M⊙ which has moved up and left through the center of the sphere with zeq velocity v = 0.01c directed at an 18° angle out of the plane of the figure. The collapsed object (center) is quite prolate. The outer shell of more massive particles is now also visible. The spherically averaged rotation profile of the “halo” is shown in the bottom diagram. The almost flat portion of the rotation curve corresponds to the size of the wake. There is also evidence for a soft core of ∼ 10 kpc in radius (our dynamical softening was 3 kpc). While the adopted initial velocity and mass are appropriate for loops with galaxy - galaxy separations, a one loop - one object correspondence is not a good approximation on the galactic scale. Moreover, baryons settling in the core of the halo would have steepened the profile and made it incompatible with observations. Halos seeded by several loops may have rotation profiles more compatible with those observed. The results of our simulations may be 10 applied - after an appropriate rescaling - to Abell clusters. There one loop typically seeds a single cluster. String-seeded Abell clusters should be therefore significantly prolate.
On the Interpretation of QSO Absorption Lines
Authors: Müller V. , Mücket J. P. , Gottlöber S. , Haubold H. J.
Published: June 2019

OSO absorption spectra may offer a clue to the distribution of intervening matter clouds at z = 0 … 3. We tackle 1) the question of the occurrence of metal absorption lines of different ionisation levels in the same redshift systems by investigating the radiation transport through an inhomogeneous temperature profile; 2) the clustering properties of the lines of the Lyα forest by a correlation analysis of 9 published high-resolution QSO-spectra with the result of a certain contribution of metal absorption lines as well as marginally significant positive correlation regions ξ ≈ 0.3.
The Rotation of Spiral Galaxies: Infall Model vs. Observations
Authors: Flores Ricardo A.
Published: June 2019

The infall model of the rotation of spiral galaxies predicts that the morphology of their velocity profiles and the relative abundance of dark matter (DM) in the intermediate region between, roughly, 3 and 5 scale lengths of their exponential disks is the result of the adiabatic contraction of the cores of their DM halos due to the dissipative infall of the gas destined to form the visible core of the galaxies. We compare the model with a few observations in a plane defined by two independent variables that can be calculated for the model and the observations. The model predicts substantially more DM interior to the optical radii of the galaxies than is allowed by the “maximum disk” hypothesis (i.e. the inner circular velocity is almost entirely due to the disk matter. However, a different version of the “maximum disk” idea might agree with the model: see the discussion by E. Athanassoula in these Proceedings). An analysis of the observations that is independent of this hypothesis indicates DM in abundance that agrees with the model. The data sample, unfortunately, is too small to draw yet any definitive conclusion on the validity of the model
Antibiased Galaxy Formation in the Pancake Scenario
Authors: Dekel A. , Braun E. , Shapiro P.
Published: June 2019

We reconsidered the timing problem of the neutrino-dominated cosmological scenario, i.e. the inferred young age for the large-scale structure versus the observationally indicated older age of galaxies and quasars. It can be resolved by 4 anti-biasing: of galaxy formation. By applying a variety of alternative prescriptions for galaxj formation to N-body simulations of the neutrino scenario, we find that the clustering of galaxies could be suppressed relative to the neutrinos to an extent that eliminate} the timing problem. It requires that galaxies form preferentially in the flat Sheets relative to the denser ‘filaments’ and compact clusters. This could emerge eithe from differences in the efficiency of galaxy formation itself, or due to feedback influence from a first generation of objects (e.g. quasars) which suppress the formatio: of incipient galaxies locally. Such an effect could be due to radiation pressure b Lα trapping in the ionized region at the vicinity of a quasar. We simulated various examples in order to quantify the requirements from such anti-biasing mechanisms and investigated their physical plausibility. Other aspects of the neutrino cosmology were studied in view of the proposed anti-biasing, concluding that we see no fata flaw in this picture.
The First Successful Attempts To Determine Stellar Parallaxes In The Light Of The Bessel/Struve Correspondence
Authors: Dick W. R. , Ruben G.
Published: June 2019

Among other items, the Bessel/Struve correspondence reflects the competition between the two astronomers in deriving a value of a stellar parallax significantly differing from zero. This paper summarizes the letters written between 1837 and 1840.
Rigorous Block-Adjustment Of The CPC2 Cape Zone
Authors: Zacharias N.
Published: June 2019

A preliminary classical plate adjustment (CPA) of the Cape zone (−40° ⩾δ⩾ −52°) of the Second Cape Photographic Catalogue (CPC2) has already been published (Nicholson et al 1984). A status report of the whole CPC2 project which provides a fourfold overlap of the entire southern hemisphere on 5820 plates with two exposures each, has been given elsewhere at this symposium (de Vegt et al 1987).
The Guide Star Catalog. II. Astrometric And Photometric Algorithms And Precision
Authors: Russell Jane L. , Lasker Barry M. , Jenkner Helmut
Published: June 2019

The algorithms used in photometric and astrometric calibration of the Guide Star Catalog, as well as the analyses of the related errors are discussed. The precision requirements of for relative positions and of for photometry are generally fulfilled.
Precise Proper Motions And Positions Of Stars From A Combination Of Fundamental Catalogues With The Hipparcos Catalogue
Authors: Wielen Roland
Published: June 2019

A combination of the HIPPARCOS catalogue with fundamental catalogues, such as the basic FK5, shall provide, for the common stars, proper motions (and derived positions) which are significantly more accurate (by a factor of up to 5) than those in the original catalogues. For many other stars, the ground-based observations would also be suited for improving the HIPPARCOS proper motions considerably.
The Contribution Of The Danjon Astrolabe To The Improvement Of The Fundamental Reference System at The Southern Hemisphere
Authors: Noël F.
Published: June 2019

An historic review is made of the observation programs with Danjon astrolabes which were carried out or are in progress at the southern hemisphere. The consistency of their results in the research of systematic errors of the FK4 Fundamental System, largely confirmed by other observation techniques, is shown. The Cape and Santiago astrolabe catalogues, the largest ones derived so far for southern stars, are briefly reviewed.
Vers Un Nouveau Catalogue General Astrolabes
Authors: Chollet F.
Published: June 2019

In the context of the future Hipparcos astrometric satellite which will give a high precision catalogue, the ground based astrometry will have new possibilities of research, particularly in the field of the stellar and the dynamical reference systems. The modern astrolabes should give, as new photoelectric meridian circles, an important contribution.

Since 1956, the Danjon astrolabe was used to determine the Earth rotation parameters. Very rapidly it was demonstrated (S. Débarbat, J. Kovalevsky, 1963) that this instrument was able to give very good planetary positions, relatively to the FK4. New studies shown, later, that it was also possible to observe the Sun (F. Laclare 1975, N. Leister 1979, F. Chollet 1981). The major contribution of the astrolabe was the observation of stellar catalogues (Billaud 1978) and now, the determination of the variations of the solar diameter.

In these conditions, it is now possible to use polyvalent astrolabes, able to give good positions of stars, planets and Sun. The Hipparcos catalogue, connected to the extragalactic reference system by VLBI, will constitute a very precise “interpolation system”. The main problem will be to save this high precision during a long time. Without other Hipparcos satellite or other method, this problem can be solved only by the ground based astrometric observations. At the same time, some other fields of research can be initiated if the astrometric observations are directly connected to Hipparcos catalogue, such as the local effects, the refraction, the motions of the vertical, which will improve in the future the ground based astrometric results.

Concerning the astrolabes, some studies are made in France to improve the instrument and the methods of reduction. At the same time, the astrolabe community has to use the same procedures of observation and reduction to be able to connect the results coming from several different stations.
Double Stars In The Astrographic Catalogue
Authors: Worley Charles E.
Published: June 2019

Nearly 20000 double stars have been detected from star positions listed in the Astrographic Catalogue. However, an examination of the various discoverer's efforts reveals that the past searches have been very incomplete. In fact, if the limits adopted by one discoverer were applied to the remainder of the catalogue, approximately 3·105 additional pairs would be found. Is such an endeavor justifiable scientifically?
Advances in Infrared Observations of Planetary Nebulae
Authors: M Rank David
Published: June 2019

The discovery of infrared continuum emission from NGC 7027 by Gillett, Low, and Stein in 1967 marked the beginning of far infrared observations of planetary nebulae. These early observations verified the predictions (Delmer, Gould, and Ramsey 1967) of infrared fine structure line emission from the SIV ion and also provided a surprise; namely, that the continuum radiation from planetary nebulae was not free-free emission from the gas, but rather that it was thermal emission from heated dust grains. In the ten years which have elapsed since 1967, numerous infrared emission lines have been observed and interpreted in many of the brighter planetary nebulae. In the middle infrared these lines were principally Ne II at 12.8μ, Gillett et al. (1969); SIV at 10.5μ, Holtz, et al. (1971), Gillett, et al. (1972), Aitken and Jones (1973); and AIII at 9.0μ Geballe and Rank (1973) and Gillett and Forrest (1973).
A Shortlived, Deep Convective Envelope for Highly Evolved, Blue Stars?
Authors: Sackmann I.-Juliana
Published: June 2019

An interesting new phenomenon was encountered while evolving a star with a core mass, Mc of 0.8 M0 and with a small envelope mass (0.015 M0) away from the red giant branch towards the nuclei of planetary nebulae, while taking the helium shell flashes into account. It was found that the top of the intershell carbon pocket (the carbon-enriched region in between the hydrogen- and helium-burning shells left behind by the flash) was expanded outwards and cooled immensely; namely, cooled to near 20,000°K! This means that the intershell carbon pocket was lifted out to near the photosphere, right into the shallow outer convective envelope surrounding the hydrogen- and helium-ionization zones! The carbon opacity at these cool temperatures is great. It seems likely that all the layers from the outer regions of the intershell carbon pocket right up to the surface will become convective. This would be a totally new type of deep convective envelope with a vast number of fascinating implications. Careful checks of this new phenomenon are now underway. (Supported in part by the National Aeronautics and Space Administration [NSG 7195].)
The Effective Temperature of the Central Star, and a Criterion for Complete Absorption of Hydrogen Ionizing Photons by the Nebula
Authors: Pottasch S.R. , Wesselius P.R. , Wu C.-C. , Van Duinen R.J.
Published: June 2019

With the new measurements of the central star between 1500 Å and 3300 Å, practically the entire continuous emission has been measured or can be deduced if the nebula is optically thick for hydrogen and helium ionizing radiation. The effective temperature can then be found directly, if the ratio of the radius to the distance of the star is known. This latter quantity can be determined with different assumptions: that the brightness temperature in the visual is equal to the effective temperature is a reasonable assumption, with the advantage that even if it is not quite correct, the resultant effective temperature is only affected in a small way.
Chemical Abundances in Planetary Nebulae
Authors: Peimbert Manuel
Published: June 2019

PN can be divided into four types depending on their chemical composition. In order of decreasing heavy element abundances the types are: I) He and N rich, II) intermediate population, III) high velocity, and IV) halo population. The type II PN are overabundant in N and C relative to the Orion Nebula. Well defined gradients across the galactic disk of He, N and O are derived from type II PN; the oxygen gradient is similar to the metallicity gradient derived from GK giants and F main sequence stars. By comparing the O, Ne and S abundances of PN of types III and IV with the Fe abundances of stars of similar population it is found that the O, Ne and S enrichment in the Galaxy probably took place before the Fe enrichment.
Dust in Planetary Nebulae
Authors: S. Mathis John
Published: June 2019

In this review I shall concentrate on theoretical aspects of dust in planetary nebulae (PN), since Dr. Balick has reviewed observations in the preceding paper. I shall consider the questions, how much dust is there in PN? What is its composition? What effects does it have on the ionization structure? On the dynamics of the nebula?
Proto-Planetary Nebulae
Authors: Zuckerman B.
Published: June 2019

Although rare, planetary nebulae have been extensively studied by astronomers. This affection is certainly due in part to the beauty of the gaseous nebulae but it is also due to the belief that many, probably most, stars of intermediate mass (1–4 M) become planetary nebulae at least once during their lifetimes. If the planetary nebula is an (almost) inevitable stage in stellar evolution, it is important to determine its evolutionary precursors and followers. The latter are likely to be the white dwarfs and the former are generally believed to be red giants. With the advent of infrared and radio techniques it now appears possible, for the first time, to specify the immediate progenitors of planetary nebulae.
Oscillating Stars (MIRAS), Mass Loss and Formation of Planetary Nebulae (PN)
Authors: Tuchman I. , Sack N. , Barkat Z.
Published: June 2019

We report some results of an extensive study of dynamically and/or pulsationally unstable stellar envelopes at the red giant stage.
Radio Measurements of Possible Proto-Planetary Nebulae
Authors: Purton C.R. , Feldman P.A.
Published: June 2019

A number of objects which may be proto-planetary nebulae are being studied. They were found through a radio search of early-type emission-line stars, and the radio emission is believed to originate in extensive circumstellar ionised gas. The objects have an infrared spectrum which indicates the presence of dust, and a continuum radio spectrum characteristic of prolonged mass outflow from the central star. Of the five objects discussed here, Vy2-2, Hbl2, HD167362, Hl-36 and V1016 Cygni, a distance is available for only the last: for that object the calculated mass of the ionized gas is 0.02 M0 (see Ahem et al, 1977). If this is typical of the five, then they may represent the early stages of the low-mass planetary nebulae discussed by Wood and Cahn (1977). References: (1) Ahern, F.A., Fitzgerald, P.M., Marsh, K.A., and Purton, C.R. 1977, Astron, & Astrophys., in press. (2) Wood, P.R., and Cahn, J.H. 1977, Astrophys. J. 211, 499.
The Epoch of Galaxy Formation
Authors: Jones Bernard J.T. , Rees Martin J.
Published: June 2019

Unfortunately, there is as yet no direct observation of a forming galaxy, nor of a manifestly “young” galaxy. It is not even clear what such galaxies might look like. There are, however, some lines of attack that will yield indirect information about the environment in which galaxies formed. There is no lack of theories of galaxy formation, many of which provide quite different scenarios for the birth-process. the hope is that theories of galaxy formation may indicate what young galaxies ought to look like and thus guide us in our search for such objects.
Spectroscopic Binaries in the LMC
Authors: Niemela Virpi S.
Published: June 2019

Preliminary results are presented of an observing programme aimed to obtain estimates of the stellar masses from studies of spectroscopic binary systems in the Large Magellanic Cloud. These are the first steps with the final purpose to determine an empirical mass-luminosity relation in a galaxy other than our own.