Showing papers in "Astrophysical Journal Supplement Series in 1989"
TL;DR: In this paper, an all-sky catalog of 4073 rich clusters of galaxies, each having at least 30 members within the magnitude range m3 to m3 +2 (m3 is the magnitude of the third brightest cluster member) and each with a nominal redshift less than 0.2.
Abstract: This is an all-sky catalog of 4073 rich clusters of galaxies, each having at least 30 members within the magnitude range m3 to m3 +2 (m3 is the magnitude of the third brightest cluster member) and each with a nominal redshift less than 0.2. The southern data have been collected from a survey of UK 1.2 m Schmidt telescope IIIa-J plates and films and have been reduced to the systems defined by the northern data previously published by G. O. Abell. A revised northern catalog, including Bautz-Morgan types and redshifts where known, is also included. Subject headings: galaxies: clustering — galaxies: redshifts — galaxies: structure
1,430 citations
TL;DR: The spectroscopic structure these PAHs and PAH-related materials produce in the UV portion of the interstellar extinction curve lie just below current detection limits but fall in the range detectable by the Hubble Space Telescope.
Abstract: A comprehensive study of the PAH hypothesis is presented, including the interstellar, IR spectral features which have been attributed to emission from highly vibrationally excited PAHs Spectroscopic and IR emission features are discussed in detail A method for calculating the IR fluorescence spectrum from a vibrationally excited molecule is described Analysis of interstellar spectrum suggests that the PAHs which dominate the IR spectra contain between 20 and 40 C atoms The results are compared with results from a thermal approximation It is found that, for high levels of vibrational excitation and emission from low-frequency modes, the two methods produce similar results Also, consideration is given to the relationship between PAH molecules and amorphous C particles, the most likely interstellar PAH molecular structures, the spectroscopic structure produced by PAHs and PAH-related materials in the UV portion of the interstellar extinction curve, and the influence of PAH charge on the UV, visible, and IR regions
1,182 citations
TL;DR: In this paper, a general-purpose code for evolving three-dimensional, self-gravitating fluids in astrophyics, both with and without collisionless matter, is described.
Abstract: A new, general-purpose code for evolving three-dimensional, self-gravitating fluids in astrophyics, both with and without collisionless matter, is described. In this TREESPH code, hydrodynamic properties are determined using a Monte Carlo-like approach known as smoothed particle hydrodynamics (SPH). Unlike most previous implementations of SPH, gravitational forces are computed with a hierarchical tree algorithm. Multiple expansions are used to approximate the potential of distant groups of particles, reducing the cost per step. More significantly, the improvement in efficiency is achieved without the introduction of a grid. A unification of SPH with the hierarchical tree method is a natural way of allowing for larger N within a Lagrangian framework. The data structures used to manipulate the grouping of particles can be applied directly to certain aspects of the SPH calculation. 75 refs.
1,034 citations
TL;DR: In this paper, the authors used the Very Large Array (VLA) to obtain H-76 alpha recombination line profiles for six sources using a 4.4 arcsec beam at 2 and 6 cm, and their radio continuum brightness distributions are presented in the form of contour plots.
Abstract: Seventy-five ultracompact (UC) H II regions are observed 0.4 arcsec resolution at 2 and 6 cm using the Very Large Array, and their radio continuum brightness distributions are presented in the form of contour plots. H-76 alpha recombination line profiles are obtained for six sources using a 4.4 arcsec beam. It is shown that these UC H II regions have electron densities of at least approximately 10,000 per cubic cm, emission measures of at least approximately 10 to the 7th pc cm to the -6th, and diameters no more than approximately 0.1 pc, consistent with their being small photoionized nebulae produced by O and B stars embedded in clouds of molecular gas and dust. At high angular resolution five different morphologies of the ionized gas are seen: spherical or unresolved (43 percent), cometary (20 percent), core-halo (16 percent), shell (4 percent), and irregular or multiply peaked (17 percent). Evidence is presented that the UC H II region phase of a massive star must last for a significant fraction of its main-sequence lifetime.
861 citations
TL;DR: In this paper, a total of 149 dark cloud positions were surveyed for evidence of dense cores in the (J,K) = (1,1) rotating inversion line of NH3.
Abstract: A total of 149 dark cloud positions were surveyed for evidence of dense cores in the (J,K) = (1,1) rotating inversion line of NH3. Clouds with strong emission were mapped to determine the position of the core, and maps of 41 cores are presented. The spectrum of the peak emission is fitted by least-squares analysis to determine the optical depth, velocity, intrinsic line width, and excitation temperature. Statistical equilibrium analysis is used to determine the density of the core and the kinetic temperature when possible. Most of the dense cores have temperatures of 10-15 K, densities of 2000-20,000/cu cm, and intrinsic linewidths of 0.2-0.9 km/s. The core masses range from about 0.5 solar in L1517B to 760 solar in L1031B, and their sizes range from 0.06 to 0.9 pc. The cores are not generally spherically shaped, wtih aspect ratios ranging from 1.1 to 4 4. Cores with stars have broader lines than cores without stars. 74 refs.
536 citations
427 citations
TL;DR: In this paper, the resonance lines of C IV, N V, and Si IV in a sample of 203 O stars observed using IUE in a high-resolution mode are presented, using a consistent set of radius, luminosity, and mass estimates.
Abstract: Measurements of the resonance lines of C IV, N V, and Si IV in a sample of 203 O stars observed using IUE in a high-resolution mode are presented. The data are discussed using a consistent set of radius, luminosity, and mass estimates. The ratio of the maximum observed velocity and the terminal (farfield) velocity is found to average at 3.0 for 131 stars with strong or saturated lines, and at 2.6 for all stars. An expression is given which is the best available predictor of O star mass loss rates, giving an accuracy better than a factor of two irrespective of luminosity class. The ionization fractions C(3+)/C and N(4+)/N are found to be independent of stellar effective temperature, but increase by a factor of about two from main sequence stars to supergiants. Two new possible ON stars are identified, and enhanced surface nitrogen abundance is confimed in ON stars. Discrete narrow absorption features are found to be virtually universal characteristic of O star P Cygni profiles. 208 references.
418 citations
TL;DR: In this paper, radio recombination line emission from nearly 500 radio continuum sources near the Galactic plane at declinations greater than 37 deg were examined for radio recombinations line emission to see if they might be H II regions.
Abstract: Nearly 500 radio continuum sources near the Galactic plane at declinations greater than 37 deg were examined for radio recombination line emission to see if they might be H II regions. A total of 462 were detected, about half of these for the first time. The data are presented in an extensive table. Among the newly discovered nebulae are several with recombination lines so narrow that their electron temperature must be less than 4600 K. 35 refs.
390 citations
351 citations
TL;DR: In this article, Li abundances or upper limits have been determined for 644 bright G-K giant stars selected from the DDO photometric catalog, and the evolutionary states of these giants and their average masses are discussed briefly.
Abstract: Lithium abundances or upper limits have been determined for 644 bright G-K giant stars selected from the DDO photometric catalog. Two of these giants possess surface lithium abundances approaching the cosmic value of the interstellar medium and young main-sequence stars, and eight more giants have Li contents far in excess of standard predictions. At least some of these Li-rich giants are shown to be evolved to the stage of having convectively mixed envelopes, either from the direct evidence of low surface carbon isotope ratios, or from the indirect evidence of their H-R diagram positions. Suggestions are given for the unique conditions that might have allowed these stars to produce or accrete new lithium for their surface layers, or simply to preserve from destruction their initial lithium contents. The lithium abundance of the remaining stars demonstrates that giants only very rarely meet the expectations of standard first dredge-up theories; the average extra Li destruction required is about 1.5 dex. The evolutionary states of these giants and their average masses are discussed briefly, and the Li distribution of the giants is compared to predictions of Galactic chemical evolution. 110 refs.
267 citations
TL;DR: In this paper, the data from the IRAS satellite were coadded for about 1150 early-type galaxies with apparent magnitudes brighter than 14 mag. The sample selection, averaging procedure, and errors are discussed.
Abstract: The data from the IRAS satellite were coadded for about 1150 early-type galaxies with apparent magnitudes brighter than 14 mag. The sample selection, averaging procedure, and errors are discussed. Results are reported of galaxies of large angular size compared with the IRAS beamwidth and for a sample of dwarf ellipticals in the Virgo cluster. At 60 and 100 microns, about 45 percent of the ellipticals and 68 percent of the S0 galaxies are detected, showing that a large fraction of these galaxies contain cool interstellar matter.
TL;DR: In this paper, the pseudo-time-dependent gas-phase model of Herbst and Leung (1986) for the chemistry of dense interstellar clouds is extended to include hydrocarbons as complex as C9H2 and CH3C6H.
Abstract: The pseudo-time-dependent gas-phase model of Herbst and Leung (1986) for the chemistry of dense interstellar clouds is extended to include hydrocarbons as complex as C9H2 and CH3C6H, and organonitrogen compounds as complex as HC9N and CH3C7N. About 600 reactions are added to the model. Most of the reaction rate coefficients and product branching ratios are estimated based on analogous reactions involving smaller species or on theoretical considerations. Calculated abundances are compared with observations in TMC-1, showing generally good agreement. It is found that the observed C(n)H abundances in TMC-1 can be understood in terms of gas-phase production schemes, although the model contains predictions at early time that are too large. The calculated peak abundances for cyanopolyynes show a small but increasing tendency to be low compared with observation as molecular size increases. 72 references.
TL;DR: In this paper, the spectra of 59 QSOs were obtained with emission redshifts in the range z = 2.75-4.11 at a resolution of 4 A in the 3150-4700 A range and 6A in the 4600-7000 A range, and the resulting number density as a function of redshift was in a form consistent with either q 0 = 0 or 1/2 and no evolution in the properties of the absorbing objects.
Abstract: The spectra of 59 QSOs are obtained with emission redshifts in the range z = 2.75-4.11 at a resolution of 4 A in the 3150-4700 A range and 6 A in the 4600-7000 A range. The objects constitute an unbiased sample as far as Lyman-limit detection is concerned. Emission-line equivalent widths and fluxes are listed, and the new data are used to derive emission redshifts. A total of 37 Lyman-limit systems (LLSs) are identified in the 59 QSOs; three QSOs each have two LLSs. All the LLSs have tau at least 1.5. A hazard plot and the Kaplan-Meier estimator are used to show that the distribution of LLSs is Poissonian. The resulting number density as a function of redshift is in a form consistent with either q0 = 0 or 1/2 and no evolution in the properties of the absorbing objects. It is believed that most of the LLSs are produced by galaxies. About two-thirds of the LLSs have associated heavy-element absorption systems, usually identified by the C IV doublet, in these low-resolution spectra. 48 refs.
TL;DR: In this article, the authors analyzed the infrared flux densities of 182 galaxies, including 50 galaxies in the Virgo cluster, using IRAS data for 12, 25, 60, and 100 microns, and the results were compared with data listed in the Point Source Catalog (PSC, 1985).
Abstract: Infrared flux densities of 182 galaxies, including 50 galaxies in the Virgo cluster, were analyzed using IRAS data for 12, 25, 60, and 100 microns, and the results were compared with data listed in the Point Source Catalog (PSC, 1985). In addition, IR luminosities, L(IRs), colors, and warm dust masses were derived for these galaxies and were compared with the interstellar gas masses and optical luminosities of the galaxies. It was found that, for galaxies whose optical diameter measures between 5 and 8 arcmin, the PSC flux densities are underestimated by a factor of 2 at 60 microns, and by a factor of 1.5 at 100 microns. It was also found that, for 49 galaxies, the mass of warm dust correlated well with the H2 mass, and that L(IR) correlated with L(H-alpha), demonstrating that the L(IR) measures the rate of star formation in these galaxies.
TL;DR: In this article, a new grid of 450 theoretical models for old simple stellar populations is presented, which explores the influence of relevant parameters such as age, chemical composition, initial mass function, and stellar mass loss, on the integrated spectral energy distribution.
Abstract: A new grid of 450 theoretical models for old simple stellar populations is presented. Evolutionary synthesis explores the influence of relevant parameters such as age, chemical composition, initial mass function, and stellar mass loss, on the integrated spectral energy distribution. Ages range between 4 and 18 Gyr, and the metallicity Z ranges from 0.0001 to 0.03, with helium content Y = 0.23 and 0.25, respectively. Three values are considered for the initial mass function, assumed as a power law, N(M) proportional to M exp-s; s = 1.35, 2.35, and 3.35. The computational code takes into account in a quantitative way the contributions from all the relevant stellar evolutionary phases according to the theory of the stellar evolution. Thus, late stage in the life of low- mass stars, such as the horizontal branch and the asymptotic and postasymptotic giant branches are accounted for. Furthermore, a simplified treatment for the evolution of the horizontal branch is developed, and the influence of different morphologies are investigated. 109 refs.
TL;DR: In this paper, a systematic search for CO emission from regions around 34 young open clusters in the outer Galaxy was conducted and it was found that some moderately young clusters have no associated CO emission.
Abstract: Results are presented from a systematic search for CO emission from regions around 34 young open clusters in the outer Galaxy. The clusters have well-determined distances ranging from about 1 to 5 kpc and ages not greater than about 100 Myr. It was found that some moderately young clusters have no associated CO emission. All the surveyed clusters younger than about 5 Myr have associated with them at least one molecular cloud more massive than 10,000 solar mass, while the molecular clouds associated with clusters older than about 10 Myr are not more massive than a few thousands solar masses. It was also found that molecular clouds are receding from young clusters at a rate of about 10 km/sec, and that they seem to be destroyed by their interaction with the stars. Sites of ongoing star formation were identified in a number of clouds associated with young clusters.
TL;DR: In this paper, the authors presented an analysis of microwave backgrond anisotropies at various angular scales and of expected large-scale bulk velocities and mass correlation functions for a variety of models which include baryons, radiation, cold dark matter (CDM), and massive and massless neutrinos.
Abstract: Calculations of microwave backgrond anisotropies at various angular scales and of expected large-scale bulk velocities and mass correlation functions are presented for a variety of models which include baryons, radiation, cold dark matter (CDM), and massive and massless neutrinos. Nearly 100 different models are considered. Open and flat models with both adiabatic and isocurvature initial conditions are calculated for models without massive neurinos. A set of flat models with both massive neutrinos and CDM with adiabatic initial conditions is also considered. Fitting functions for the mass transfer function and small-angle radiation correlation function are provided for all of the models. A discussion of the evolution of the perturbations is presented. Results are compared with some recent observations of large-scale velocities and limits on microwave background anisotropies. CDM and baryon models have difficulty satisfying observational limits, although they are not completely ruled out. Hybrid models with massive neutrinos and CDM satisfy current observational data. 42 refs.
TL;DR: In this paper, the authors discuss the limitations and usefulness of linear force-free magnetic field formulations, specific phenomenological and topological parameters of these formulations, and their usefulness, and the relationship of the integral and Fourier procedures is shown explicitly.
Abstract: This paper discusses the interconnection of the various linear force-free magnetic field formulations, the specific phenomenological and topological parameters of these formulations, and their usefulness. Particularly, the limitations and usefulness of linear force-free fields are discussed. Specific field configurations are related to magnetographic interpretation. The relationship of the integral and Fourier procedures is shown explicitly. The physical interpretation of linear force-free fields is shown by analytic models and from the Marshall Space Flight Center solar vector magnetograms.
TL;DR: In this paper, the authors presented astrometry, photometry, and morphological types derived from CCD images, for 463 galaxies in the 100 compact groups selected by Hickson, and some minor revisions to the membership of the original catalog are made, based on these new images.
Abstract: The paper presents astrometry, photometry, and morphological types, derived from CCD images, for 463 galaxies in the 100 compact groups selected by Hickson. Some minor revisions to the membership of the original catalog are made, based on these new images. The completeness of the catalog is considered as a function of group magnitude and Galactic latitude. At high Galactic latitude the catalog is estimated to be 90 percent complete for groups with total B(T) magnitude 13.0 or less. It is less complete at lower Galactic latitude because of obscuration and high stellar density. 28 refs.
TL;DR: In this paper, the complete millimeter-wave spectrum between 70 and 115 GHz of the Sgr B2 molecular cloud and the star-forming KL region of Orion has been surveyed with the NRAO 11 m telescope at a resolution of 1 MHz.
Abstract: The complete millimeter-wave spectrum between 70 and 115 GHz of the giant Sgr B2 molecular cloud and the star-forming KL region of Orion has been surveyed with the NRAO 11 m telescope at a resolution of 1 MHz. The data are are presented. The NRAO survey of Sgr B2 complements that of Cummins, being more complete between 70 and 115 GHz and somewhat more sensitive. The NRAO survey of Orion-KL parallels that of the Onsala Space Observatory between 72 and 91 GHz, and is the first such survey of the 70-72 and 91-115 GHz regions. It is considerably more sensitive than the Onsala survey. In particular, many more unidentified lines are seen in the NRAO survey than in the previous ones, despite more recent spectroscopic data to aid in identifications. 8 refs.
TL;DR: The FRANEC (Frascati Raphson Newton Evolutionary Code) as discussed by the authors has been used to fit H-burning stars in globular clusters of low and intermediate metallicity.
Abstract: The main features of the latest version of the evolutionary code FRANEC (Frascati Raphson Newton Evolutionary Code) are presented along with a set of evolutionary tracks, associated isochrones suitable for H-burning stars in globular clusters of low and intermediate metallicity. The numerical algorithms and the physical inputs adopted in the code are described, and the fitting of the sun and comparisons of selected tracks with previous evaluations are made. The influence of the equation of state for partially ionized matter on the path followed by a star in the HR diagram is addressed. Fitting the globular clustes M68, M3, M5, and NGC 362 leads to the conclusion that an age of 16 Gyr for all these clusters is compatible with the present isochrones. 63 refs.
TL;DR: In this paper, the metal abundances of eight F-type supergiants in each of the Magellanic Clouds were determined using the results of high-resolution spectroscopy analysis of these stars, together with new Stromgren uvby and Cousins (1980) BVRI photometry.
Abstract: Metal abundances of eight F-type supergiants in each of the Magellanic Clouds were determined using the results of high-resolution spectroscopy analysis of these stars, together with new Stromgren uvby and Cousins (1980) BVRI photometry. It was found that the mean Fe abundance (Fe/H) for the SMC is -0.65 + or - 0.2 dex, and the mean Fe abundance for the LMC is -0.30 + or - 0.2 dex. The abundances of stars in both the SMC and LMC appear relatively uniform, and the abundances of the elements relative to Fe are very similar in both Magellanic Clouds and in Canopus (the carbon-to-iron abundances are the same for all three). It was also found that Nd and Sm are overabundant in both clouds, supporting the trends found by Spite et al. (1988) for the three SMC stars they studied. 140 refs.
TL;DR: In this paper, the MK spectral classification for late A-type stars is refined and the effects of rotation of spectral classification and uvby(beta) photometry for these stars are examined.
Abstract: The MK spectral classification for late A-type stars is refined and the effects of rotation of spectral classification and uvby(beta) photometry for these stars are examined. It is found that, for A3 stars, the 4417/4481 A wavelength ratio produces results that are inconsistent with the Stark broadening of the H lines. It is suggested that this ratio is not useful as a luminosity criterion at any spectral type. Self-consistent sequences of narrow- and broadline standards are established. The results of the refined classification system are compared with Stromgren photometry, showing a set of low-v sin i A-type stars with anomalously large delta(c sub 1) indices for their luminosity types. It is proposed that these stars are rapid rotators seen at fairly low inclination angles. 24 refs.
TL;DR: In this article, a method for separating the "veiling" continuum often present in T Tauri stars from the underlying photospheric spectrum is described, by means of goodness-of-fit tests.
Abstract: A method for separating the 'veiling' continuum often present in T Tauri stars from the underlying photospheric spectrum is described. Echelle observations from 5100 to 6800 A of the partially veiled T Tauri star BP Tau were analyzed to determine the shape of the veiling spectrum. The residuals of the fit indicate the deviation of the veiling spectrum from a simple continuum and identify the location and strength of any emission-line components. It is shown, by means of goodness-of-fit tests, that the spectrum of BP Tau can be decomposed into a normal stellar spectrum plus a smooth veiling continuum with only a few emission lines superposed. The continuum dominates the veiling spectrum in this spectral region; the veiling does not arise from numerous deep photospheric absorption lines that are filled in by weak emission.
TL;DR: In this article, the authors presented the complete set of observations from the first out-of-plane CO survey of the southern Milky Way, and a spatial map, obtained by integrating the CO emission over the entire observed spectral range, 333 km/s, summarizes the survey concisely.
Abstract: The complete set of observations from the first out-of-plane CO survey of the southern Milky Way is presented. A spatial map, obtained by integrating the CO emission over the entire observed spectral range, 333 km/s, summarizes the survey concisely and can be compared with gamma-ray, IR, and other continuum data. The kinematic information is summarized in two longitude-velocity diagrams, which represent in one case the CO emission integrated over the whole latitude coverage of the survey, and in the other, to improve the contrast for the distant molecular clouds, over a narrower latitude region within 0.75 deg of the Galactic equator. The information is unfolded in a complete set of longitude-velocity contour diagrams, one for each latitude observed. 18 refs.
TL;DR: In this article, Graedel et al. used time-dependent models of the ion-molecule chemistry of dense interstellar clouds (Graedel, Langer, and Frerking, 1982) to calculate the abundances of key observational species used to interpret cloud properties.
Abstract: Revised time-dependent models of the ion-molecule chemistry of dense interstellar clouds (Graedel, Langer, and Frerking, 1982) are used to calculate the abundances of key observational species used to interpret cloud properties and study interstellar chemistry. Consideration is given to nitrogen-, oxygen-, and carbon-bearing molecules and isotopic ratios over a hydrogen density range of 1,000-50,000/cu cm and a temperature range of 10-40 K. The results for over 15 species, including C-13 variants, are presented in tables and graphs. The results are compared to abundance observations in TMC-1 and other interstellar clouds, showing that most observed abundances can be predicted by the models. 72 references.
TL;DR: In this article, the distribution of ionized gas in the nuclear regions of a statistically significant sample of 91 non-Seyfert spirals is reported, and it appears that nonthermal nuclear activity and nuclear star formation prefer different nuclear environments, with active nuclei tending to be found in intermediate-type and nuclear H II regions preferring late-type spirals.
Abstract: A study of the distribution of ionized gas in the nuclear regions of a statistically significant sample of 91 non-Seyfert spirals is reported. CCD interference band images isolating the bright emission-lines of H-alpha + forbidden N II (6548, 6583 A) have been used to map the distribution of ionized gas in the inner 1-2 kpc of these galaxies. The galaxies exhibit a rich variety of nuclear and circumnuclear emission-line structures ranging from no-detectable emission to bright stellar nuclei with complicated circumnuclear emission regions extending for many kiloparsecs. Trends with Hubble-type and low-ionization nuclear emission-line spectral type (LINER or H II region) have been discerned. In galaxies with nuclear H II regions, those regions are on average the brightest H II regions in their host galaxies. It appears that nonthermal nuclear activity and nuclear star formation prefer different nuclear environments, with active nuclei tending to be found in intermediate-type galaxies, and nuclear H II regions preferring late-type spirals. It is speculated that this preference may be related to the dynamical properties of the host galaxies. 53 refs.
TL;DR: In this paper, a nouvelles methodes numeriques a structure arborescentes ont recemment ete developpees pour resoudre les problemes gravitationnels a N corps: leur temps de calcul est de l'ordre de N logN ou N au lieu de N 2 mais ces methode approchees ont une precision limitee.
Abstract: De nouvelles methodes numeriques a structure arborescentes ont recemment ete developpees pour resoudre les problemes gravitationnels a N corps: leur temps de calcul est de l'ordre de N logN ou N au lieu de N 2 mais ces methodes approchees ont une precision limitee. Les calculs des erreurs commises sont presentes
TL;DR: In this article, a search for correlations of radio properties with various systemic and stellar parameters is performed, and significant correlations are found between the normalized radio luminosity L(6)/L(bol) and the normalized soft X-ray luminosity l(x)/L (bol).
Abstract: Observations of 77 RS CVn and related active binary systems were made with VLA at a continuum frequency of 4.86 GHz. The results are combined with other VLA observations to produce a total number of observed sources of 122. A search for correlations of radio properties with various systemic and stellar parameters is performed. Significant correlations are found between the normalized radio luminosity L(6)/L(bol) and the normalized soft X-ray luminosity L(x)/L(bol). It is suggested that the close correlation between low-level 6-cm emission and the hot component of the soft X-ray emission observed by the Einstein solid state spectrometer is caused by both emissions being produced by the same thermal electrons.