Showing papers in "Astrophysical Journal Supplement Series in 1984"

Supernovae of type I as end products of the evolution of binaries with components of moderate initial mass (M< or approx. =9 M/sub sun/)

Abstract: Analysis of the theory of evolution of low- and intermediate-mass binaries allows us to select promising scenarios that lead to presupernova systems consisting of an accreting electron-degenerate dwarf (made primarily either of oxygen, neon, and magnesium, of carbon and oxygen, or of helium) and a low-mass (Mroughly-equalM/sub sun/) star supplying hydrogen-rich matter at rates in the range approx.10/sup -9/-10/sup -6/ M/sub sun/ yr/sup -1/ or a heavy disk composed of helium or of C and O supplying matter at an as yet undetermined rate. Some of these scenarios have an estimated frequency of realization comparable with the observed frequency (approx.10/sup -2/ yr/sup -1/) of Type I supernovae (SNeI), but it is as yet impossible to identify conclusively a single one as the most likely explanation of the SNI pheomenon and to reject all other possibilities. It is therefore not excluded that SNeI are a mixture of products of different scenarios. Estimates of formation frequency are very preliminary, since some of them are strongly dependent on the distribution of unevolved binaries over the initial mass ratio q/sub 0/, especially for q/sub 0/roughly-equal0.1--0.3, and most of them require knowledge of the processes that occur during a common envelope stage, the understanding ofmore » which is still very rudimentary.« less

Photochemistry of the atmosphere of Titan: comparison between model and observations.

Abstract: The photochemistry of simple molecules containing carbon, hydrogen, nitrogen, and oxygen atoms in the atmosphere of Titan has been investigated using updated chemical schemes and our own estimates of a number of key rate coefficients. Proper exospheric boundary conditions, vertical transport, and condensation processes at the tropopause have been incorporated into the model. It is argued that the composition, climatology, and evolution of Titan's atmosphere are controlled by five major processes: (a) photolysis and photosensitized dissociation of CH_4 ; (b) conversion of H to H_2 and escape of hydrogen; (c) synthesis of higher hydrocarbons; (d) coupling between nitrogen and hydrocarbons; (e) coupling between oxygen and hydrocarbons. Starting with N_2, CH_4, and H_20, and invoking interactions with ultraviolet sunlight, energetic electrons, and cosmic rays, the model satisfactorily accounts for the concentrations of minor species observed by the Voyager IRIS and UVS instruments. Photochemistry is responsible for converting the simpler atmospheric species into more complex organic compounds, which are subsequently condensed at the tropopause and deposited on the surface. Titan might have lost 5.6 × 10^4 , 1.8 × 10^3, and 4.0 g cm^-2 , or the equivalent of 8,0.25, and 5 × 10^-4 bars of CH_4, N_2 , and CO, respectively, over geologic time. Implications of abiotic organic synthesis on Titan for the origin of life on Earth are briefly discussed.

The globular cluster system of the Galaxy. III: measurements of radial velocity and metallicity for 60 clusters and a compilation of metallicities for 121 clusters

Abstract: On a obtenu des spectrogrammes (121 A mm −1 ) pour 60 amas globulaires galactiques et 3 amas globulaires du PNM. Les vitesses radiales obtenues par la technique de correlation croisee ont une precision de ±20 km s −1 et sont en bon accord avec la plupart des mesures anterieures. On a mesure les largeurs pseudo-equivalentes des raies de l'hydrogene Hδ, Hγ et Hβ et de la raie Ca IIK, la bande G et les raies Mg Ib

A library of stellar spectra.

Abstract: Les spectres de 161 etoiles de classe spectrale O-M et de classe de luminosite V, III et I, ont ete incorpores a un catalogue papier et une bande magnetique de spectres stellaires

Reddening estimates for galaxies in the Second Reference Catalog and the Uppsala General Catalog

Abstract: On donne les estimations du rougissement basees sur la methode de Burstein et Heiles (densite de colonne HI, comptages de galaxies) pour environ 13000 galaxies du Catalogue General d'Uppsala, compile par Nilson et pour pres de 4350 galaxies du Second Catalogue de Reference, compile par de Vaucouleurs, de Vaucouleurs et Corwin, 1976, avec |b|≥9,7°

The evolution of cataclysmic and low-mass X-ray binaries.

Abstract: We present an observational study of the structure and evolution of cataclysmic and low-mass X-ray binaries, concentrating on the 124 systems for which orbital periods are known. The eruptive properties and mass transfer rates of these stars are found to be highly correlated wit their orbital periods, suggesting that both the eruptive activity and the long-term evolution are determined by the properties of the lobe-filling secondaries. The secondaries do not satisfy the commonly used theoretical models of low-mass zero-age main-sequence (ZAMS) stars, but are, in general consistent with the empirically derived properties of the lower main sequence. We show stars, that R/R/sub direct-sum/ = (M/M/sub direct-sum/)/sup 0.88/ for low-mass ZAMS stars in the field, in wide binaries and in cataclysmic binaries. For masses above 0.8 M/sub direct-sum/, the empirical ZAMS is in reasonable agreement with the models. But in this regime (corresponding to orbital periods > or approx. = 9 hr), the secondaries in cataclysmic binaries are found to be slightly evolved from ZAMS.

HI shells, supershells, shell-like objects, and «worms»

Abstract: We present photographic representations of the combination of two Hi surveys, so as to eliminate the survey boundaries at Vertical BarbVertical Bar = 10/sup 0/. We also present high-contrast photographs for particular velocities to exhibit weak Hi features. All of these photographs were used to prepare a new list of Hi shells, supershells, and shell-like objects. We discuss the structure of three shell-like objects that are associated with high-velocity gas, and with gas at all velocities that is associated with radio continuum loops I, II, and III. We use spatial filtering to find wiggly gas filaments: ''worms'': crawling away from the galactic plane in the inner Galaxy. The ''worms'' are probably parts of shells that are open at the top; such shells should be good sources of hot gas for the galactic halo.

Synthesis of complex molecules in dense interstellar clouds via gas-phase chemistry: a pseudo time-dependent calculation

Abstract: On presente un modele detaille pour la chimie en phase gazeuse des nuages interstellaires denses qui inclut, pour la premiere fois, des reactions qui produisent et qui detruisent un echantillon representatif d'especes moleculaires complexes. Dans le modele, qui comprend 200 especes et plus de 1800 reactions en phase gazeuse, un ensemble initial d'abondances atomiques et moleculaires evolue sous des conditions physiques constantes et en l'absence de photodissociations

A set of partition functions and equilibrium constants for 300 diatomic molecules of astrophysical interest

Abstract: Developpements polynomiaux de fonctions de partition et de constantes d'equilibre de 300 molecules diatomiques et des atomes dependants, pour des temperatures de 1000 a 9000 K

The HEAO A-1 X-ray source catalog

Abstract: The catalog of X-ray sources detected during the NRL Large Area Sky Survey (LASS) with the HEAO 1 satellite is presented. The catalog is derived from the first six months of data from HEAO 1 and includes sources detected during one full scan. Positions and intensities for a total of 842 different sources are included, with a limiting flux of 250 nJy at 5 keV. The catalog is more than 90 percent complete at a flux level equivalent to 1.5 microjoules at 5 keV for a Crab-like spectrum. Cross-references with published literature are provided and coincidental identifications are proposed for some of the sources which have been never studied before. A cross-sectional line drawing of the sensor module of HEAO I is also provided.

A numerical study of nonspherical black hole accretion. II - Finite differencing and code calibration

Abstract: We describe in detail our two-dimensional, axisymmetric computer code for calculating fully relativistic ideal gas hydrodynamics around a Kerr black hole. This code is being used to study fully dynamic inviscid fluid accretion onto black holes, as well as the evolution and developement of nonlinear instabilities in pressure-supported accretion disks. The numerical techniques are developed and discussed. A variety of alternate differencing schemes are compared on an analytic test bed. Some discussion is devoted to general issues in finite differencing. The working code is calibrated using analytically solvable accretion problems, including the radial accretion of dust and of fluid with pressure (Bondi accretion). Two-dimensional test problems include the spiraling infall of low angular momentum fluid, the formation of a pressure-supported torus, and the stable evolution of a torus.

Comparisons of a Standard Galaxy Model With Stellar Observations in Five Fields

Abstract: Modern data on the distribution of stellar colors and on the number of stars as a function of apparent magnitude in five directions in the Galaxy are analyzed. It is found that the standard model is consistent with all the available data. Detailed comparisons with the data for five separate fields are presented. The bright end of the spheroid luminosity function and the blue tip of the spheroid horizontal branch are analyzed. The allowed range of the disk scale heights and of fluctuations in the volume density is determined, and a lower limit is set on the disk scale length. Calculations based on the thick disk model of Gilmore and Reid (1983) are presented.

Pulsar polarization fluctuations. I. 1404 MHz statistical summaries.

Abstract: Observations de polarisation des pulsations individuelles des 11 pulsars PSR 0525+21, PSR 0823+26, PSR 0834+06 a , PSR 0919+06, PSR 0950+08 a , PSR 1133+16, PSR 1237+25, PSR 1929+10 a , PSR 1944+17, PSR 2016+28 et PSR 2020+28 a , a 1404 MHz avec le telescope de 3,05 m d'Arecibo

The HEAO 1 A-4 catalog of high-energy X-ray sources

Abstract: Results are reported from an all-sky survey carried out at high X-ray energies (13-180 keV) from August 1977 until January 1979 using data obtained with the UCSD/MIT Hard X-Ray and Low-Energy Gamma-Ray Instrument on the HEAO 1 satellite. Visual displays are presented which indicate qualitatively the location, intensities, and time variability of the detected high-energy X-ray sources. A model-dependent procedure for the quantitative analysis of the sky survey data is described. The results of this procedure are presented in tabular form and include fitted count rates in four broad energy bands for about 70 sources. All sources which were detected at a level of statistical significance of not less than about 6 sigma were clearly evident in the visual displays of sky survey data. The survey is therefore complete, except in regions of source confusion, down to an intensity level of about 1/75 of the Crab Nebula in the 13-80 keV band. Forty-four sources were detected in the 40-80 keV energy band, and 14 were detected in the 80-180 keV band. Although most of the detected sources are galactic, seven are extragalactic.

Blue and near-infrared surface photometry of spiral structure in 34 nonbarred grand design and flocculent galaxies

Abstract: On a examine les profils radiaux du disque et la structure des bras spiraux des 34 galaxies On donne les profils azimutaux et les diagrammes couleur-amplitude des bras spiraux On discute des modeles d'evolution de la couleur Ces modeles sont utilises pour determiner l'amplitude des spirales de densite stellaire sous jacentes et le renforcement relatif de la formation stellaire dans les bras en se basant sur les observations des amplitudes des bras et des variations de couleur

Planar numerical cosmology. II. The difference equations and numerical tests

Abstract: This paper is the second in a series describing a method for evolving inhomogeneous planar cosmological models on a computer. In Paper I we set forth our coordinate conditions, variables, and equations, and discussed the way our special gauge simplifies the numerical evolution. In this paper we focus on the architecture of the code. We describe the differencing techniques we use to solve the hydrodynamical and, especially, the Einstein equations. We also present the results of testing the code on problems in hydrodynamics, spatially homogeneous cosmologies, and linearized general relativistic perturbation theory. Appendices contain a discussion of Barton's method for monotonic transport and a new method for the solution of one-dimensional special relativistic similarity flow.

High-resolution VLA observations of the radio jet in NGC 6251.

Abstract: Le jet de la radiogalaxie NGC 6251 a ete observe avec le VLA avec des resolutions de 1,15″ a 15″ a 1370, 1480, 1662 et 4885 MHz et de 50″ a 1446 et 1662 MHz. On a observe un contrejet dans la direction opposee au jet principal. On discute des implications des observations quant a la physique du jet

Observational studies of Cepheids. II - BVRI photometry of 112 Cepheids

Abstract: On presente plus de 4000 observations BVRI photoelectriques determinees differentiellement, ainsi que les courbes de lumiere resultantes, pour 112 cepheides accessibles d'observatoires de l'hemisphere Nord

Accurate integrations of the Roche model

Abstract: Integration precise du modele de Roche pour des systemes binaires serres en rotation synchrone. On obtient le rayon du volume binaires, les surfaces, les gravites moyennes et les gravites moyennes inverses en unites normalisees

The vertical structure and stability of alpha model accretion disks.

Abstract: A limit cycle driven by thermal instabilities in the accretion disk may account for the periodic outbursts of cataclysmis variables and certain x-ray transients. The outbursts will depend on specific properties of the vertical accreation disk structure such as convection, partial ionization opacity, and viscosity. As a step toward understanding the physical processes that determine the time-dependent nature of accretion disks, we have undertaken a parameter study of the vertically explicit structure corresponding to steady-state, ..cap alpha..-model, thin-disk accretion for accreting objects to 1 M. Solutions are presented for 10/sup 9/< or =r(cm< or =10/sup 11/; 10/sup -14/< or =M(M yr/sup -1/)< or =10/sup -7/; 10/sup -4/< or =..cap alpha..< or =1.0. Particular attention is paid to the role of convection in the vertical structure and to the location of critical points which represent the onset of thermal instability. Optically thin conditions are also examined in detail. The presence of molecules at low temperatures gives rise to double-valued, discontinuous solutions separated by ''forbidden'' regions. We show that the temperature in quiescence is likely to be low (T<2500 K) for the bulk of the matter. Quiescent temperatures of approx.6000 K are possible in thermal equilibrium only for r<7 x 10/sup 9/more » cm for ..cap alpha.. = 0.1. This will promote the storage of material in an outer, cold ring. Scaling laws are presented for the fundamental properties of the vertically explicit models, and these are used to derive time scales for various idealized phenomena. We present an ordering of three disk time scales.« less

The chemical composition and evolutionary state of the early R stars.

Abstract: A sample of 11 stars classified R0-R5 has been analyzed to determine (i) iron-peak metal abundances, (ii) abundances of elements produced by the s-process, (iii) the light element abundances (C,N, and O), and (iv)= the carbon isotopic ratio /sup 12/C//sup 13/C. Abundances are reported relative to the Sun. With the expection of HD 100764, which has an iron abundance 0.6 dex lower than the Sun's, the iron abundance of 10 stars is near solar. The s-process elements have no demonstrable enhancement in the sample, unlike the Ba II stars of the same temperature and the cooler carbon stars. The enhancement of carbon relative to the G-K giants found in the analysis of eight stars is 0.7 dex, with one star having Croughly-equal O (HD 113801), while another star (HD 95405) is probably not a carbon star (C/O = 0.87). Relative to the ordinary G-K giants, nitrogen is enhanced by a small amount (0.2 dex). In contrast, oxygen has nearly the value found in the Sun and in normal giants, except in the case of HD 100764 where O is probably as underabundant as Fe. The /sup 12/C//sup 13/C ratio ranges for near 4 to 14 for nine stars, indicating anmore » enrichment of /sup 13/C with respect to the majority of faint giants. For HD 156074 the oxygen isotopic ratios /sup 16/O//sup 17/O and /sup 16/O//sup 18/O do not have detectable departures from the solar system values. The lack of oxygen depletion indicates that the CNO cycle operating near equilibrium is not responsible for the fact that C/O>1 in these stars. Based on the early R stars' position in the H-R diagram, their space number densities, and their enhanced carbon abundances, it is here suggested that they result from mixing at the time of, or closely following, the helium core flash.« less

JHK observations of classical cepheids

Abstract: Nouvelle photometrie JHK de 69 Cepheides classiques galactiques. Les observations couvrant une phase entiere pour 23 de ces etoiles permettent de determiner les relations entre les amplitudes UBV et JHK

A study of the O'Connell effect in the light curves of eclipsing binaries

Abstract: L'effet O'Connell est le nom donne aux differences de hauteur entre les maxima dans les courbes de lumiere de certains systemes a eclipses

An augmented system of secondary standards for bright-star spectrophotometry.

Abstract: Etalonnages du systeme spectrophotometrique de Hayes-Latham pour 21 etoiles standard secondaires

The flare activity of AD Leonis

Abstract: Etude des eruptions de AD Leo a l'aide de techniques photometriques et d'analyse de ses courbes de lumiere

CCD surface photometry of field galaxies. I - Observations

Abstract: Images of 105 galaxies selected from a larger complete sample of intrinsically luminous galaxies have been obtained for the purpose of computing surface brightness profiles. The intensity profiles along the major and minor axes are computed by a method in which elliptical contours whose position angle and ellipticity are allowed to vary with radius are fitted to the true isophotes of a galaxy. The resulting profiles and ellipse parameters are listed for each object. An extensive comparison of the present photometry with that of other workers is made to assess the reliability of the data. For most objects, additional photometric information is given, including an isophotal radius and magnitude within a limiting isophote of 24.0 mag/sq arcsec, an approximate total magnitude, the effective radius containing one-half the total light, and the mean surface brightness inside this radius. A full analysis of the data is deferred to a second paper where the profiles will be decomposed into bulge and disk components.

An atlas of late-type stellar spectra, 2400-2778 inverse centimeters.

Abstract: Court atlas des spectres IR entre 2400 et 2778 cm −1 d'etoiles K, M, C et S. On donne les identifications moleculaires pour OH, CH, NH, SiO, CS et HCl. On donne les positions pour 174 raies atomiques probables du spectre de α Ori et α Tau. Soixante-douze raies de Na, Mg, Al, Si, K, Ca, Fe, Ti et Cr ont ete identifiees dans cette liste

A solar spectral line list between 10 and 200 Å modified for application to high spectral resolution X-ray astronomy

Abstract: A spectral line list for the 10-200 A range is developed from existing solar spectra for application to high spectral resolution measurements of astrophysical plasmas. The solar spectral line lists are merged into a single comprehensive list. The effect of the solar emission measure distribution is removed from the line intensities, which results in a set of emission rates for the lines that can be applied to many optically thin, low density high temperature plasmas in ionization equilibrium. In addition to the measured solar lines, 250 theoretical lines are added to this list. These lines fall in wavelength regions where the existing solar lists have few lines because of limitations in instrumental sensitivity. Also, some lines have been added because the sun has very little plasma at temperatures of about one million K, and consequently these lines are weak or absent in solar spectra. The entire list contains about 600 lines. Finally, predicted spectra of the two RS CVn stars, alpha Aur (Capella) and UX Ari, are presented at 1 and 0.25 A spectral resolution. Also, the solar spectrum is shown at 1 A resolution, and the emission rate spectrum (spectrum not modified by an emission measure distribution) is shown at very high spectral resolution. The predicted spectra for Capella and UX Ari are based on results obtained from the Einstein and International Ultraviolet Explorer (IUE) spacecraft.

Distant clusters of galaxies. I - Uniform photometry of 14 rich clusters

Abstract: On presente la photometrie photographique JF de 14 amas de galaxies riches dans le domaine des deplacements vers le rouge 0,18≤z≤0,39