Showing papers in "Astrophysical Journal Supplement Series in 1982"

The ionization equilibrium of astrophysically abundant elements

Abstract: The paper presents new calculations of ionization equilibrium fractions of 11 abundant elements (C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, Ni) as functions of temperature. Convenient coefficients for fitting the rates of collisional ionization, radiative recombination, and dielectronic recombination are also tabulated. Many of the ionization rates are based on recent experimental measurements of cross sections for collisional ionization and autoionization following inner-shell excitation. These rates are used elsewhere in computations of nonequilibrium ionization, radiative cooling, radiative shock models, and plasma emission diagnostics.

Stellar weak interaction rates for intermediate mass nuclei. III. Rate tables for the free nucleons and nuclei with A = 21 TO A = 60

Abstract: Stellar electron and positron emission rates and continuum electron and positron capture rates, as well as the associated neutrino energy loss rates, are tabulated for the free nucleons and 226 nuclei with masses between A = 21 and 60. These rates were calculated in accordance with the procedure described in Papers I and II of this series and are presented here in tabular form on an abbreviated temperature and density grid. Results of these calculations on a detailed temperature and density grid are available in computer readable form on magnetic tape upon request to MJN. The stellar weak rate calculation procedure is reviewed, and the results are discussed. Comparison of the stellar weak rates to terrestrial decay rates are made where possible.

X-ray nebular models

Abstract: Theoretical models are presented for the temperature and ionization structure of spherically symmetric, constant density, gaseous nebulae surrounding compact X-ray sources and for the optical, UV, and X-ray spectra emerging from the nebulae. The structure is determined by assuming a local balance between heating and cooling in the gas, and the radiation field is found by solving a simplified equation of transfer. The calculations include an accurate and comprehensive treatment of the atomic processes affecting the state of the gas and the radiation field. The destruction of line radiation during resonance scattering causes models to be significantly hotter and more highly ionized than previous models of the same type. Model results are presented for a wide variety of gas densities and X-ray source spectra, scaling laws which allow these results to be generalized to a wide variety of astrophysical solutions are discussed, and column densities of multiply charged species are tabulated.

Catalog of CO radial velocities toward galactic H II regions

Abstract: This is a catalog of 242 molecular cloud complexes which are associated with optical H II regions. CO observations were made toward all but five of the H II regions in the Sharpless catalog and toward 62 additional suspected H II regions, 33 of which are previously uncataloged. Radial velocities are tabulated for each molecular cloud complex found to be associated with an H II region. The CO antenna temperature and line width are given for the most intense CO line seen toward each source. The catolog also summarized previous CO observations as well as the optical distances to the stars exciting the H II regions. Radio-quiet H II regions (those with 1.4 GHz flux densities <100 mJy) are found to be well correlated with objects having no associated CO. A list of kinematically distinct complexes is tabulated to facilitate investigations of the motions of the complexes.

The kinetic chemistry of dense interstellar clouds

Abstract: A model of the time-dependent chemistry of dense interstellar clouds is formulated to study the dominant chemical processes in carbon and oxygen isotope fractionation, the formation of nitrogen-containing molecules, and the evolution of product molecules as a function of cloud density and temperature. The abundances of the dominant isotopes of the carbon- and oxygen-bearing molecules are calculated. The chemical abundances are found to be quite sensitive to electron concentration since the electron concentration determines the ratio of H3(+) to He(+), and the electron density is strongly influenced by the metals abundance. For typical metal abundances and for H2 cloud density not less than 10,000 molecules/cu cm, nearly all carbon exists as CO at late cloud ages. At high cloud density, many aspects of the chemistry are strongly time dependent. Finally, model calculations agree well with abundances deduced from observations of molecular line emission in cold dense clouds.

Carbon and nitrogen abundances in giant stars of the metal-poor globular cluster M92

Abstract: Zinn in 1973 and 1977 and Norris and Zinn in 1977 showed that in M92 and several other metal-poor globular clusters the G bands (mostly due to CH) in the spectra of asymptotic giant branch (AGB) stars are systematically weaker than those found in the less highly evolved subgiant branch (SGB) stars. If carbon is depleted in the atmospheres of evolved stars because material at the base of the envelope, processed through the CN cycle, has been mixed with the material above, then the atmospheric nitrogen abundance should be correspondingly increased. In this paper we test the hypothesis that C and N abundances in M92 giants are negatively correlated as the evolutionary state becomes more advanced. We find that this simple hypothesis is not adequate to describe the complex behavior of C and N in the cluster giants.

C IV absorption in an unbiased sample of 33 QSOs: evidence for the intervening galaxy hypothesis

Abstract: We present new observations of 27 QSOs at redshifts z/sub em/roughly-equal2 with 2.5 A resolution and with uniform signal-to-noise ratio. Using some previously observed objects we define an unbiased, homogeneous sample of 33 QSOs with which we investigate the properties of the absorption line systems. Particular attention is paid to C IV lambdalambda1548, 1550 doublets. We find that:

A catalog of infrared magnitudes and h-i-velocity widths for nearby galaxies

Abstract: Integrated infrared (1.6 ..mu..m) magnitudes and 21 cm velocity widths are presented for 308 nearby spiral galaxies. Positions, types inclinations, diameters, H I velocities and flux density integrals, and distances are also listed. These data form the basis for a recent analysis of the velocity field in the Local supercluster.

A numerical model for stellar core collapse calculations.

Abstract: A method for calculating stellar core collapse is discussed which emphasizes physical approximations and numerical methods. Collapse is modeled in terms of hydrodynamics coupled to radiation transport of all neutrino types. The latter are not assumed to be in thermal equilibrium. Analytic approximations used for the equations of state are discussed. The overall approach includes all of the physical processes which we believe are important for stellar core collapse.

Global properties of irregular galaxies

Abstract: We present optical and radio observations of global properties for a sample of noninteracting irregular galaxies and a few comparison objects. Program galaxies were chosen primarily on the basis of their blue colors and thus may be expected to represent systems with high rates of star formation. The data consist of 40'' aperture photometry through intermediate-band filters, 25'' aperture spectrophotometry in the region 3500--5900 A, spectrophotometry of individual H II regions primarily from 4500--7500 A;o, and 21 cm H I observations. From the filter photometry we determine a Mg index and a reddening-free color parameter Q. An iterative population synthesis technique is applied to the large aperture spectra in order to separate H..beta.. emission from absorption, and a star formation rate (SFR) is estimated from the number of ionizing photons coupled with a Miller and Scalo initial mass function. Line fluxes are used to determine the abundance ratios O/H and N/sup +//S/sup +/, and the radio data give information on gas masses and kinematics.

Emission-line profiles in Seyfert 1 galaxies

Abstract: Observed profiles of H I, He I, and He II emission lines in 19 Seyfert 1 galaxies are presented. The data, reduced to energy units versus radial velocity, are given in accurate graphical form for comparison with theoretical models. The profiles are shown as directly observed and as corrected for the blending effects of other lines. Some implications of these profiles on current models of active galactic nuclei are discussed.

The cluster system of M33.

Abstract: We have compiled a catalog of more than 250 nonstellar objects found on high resolution (approx.6.''7 mm/sup -1/) direct plates of M33. Additional classification criteria were derived from low dispersion 4 m grism plates and multicolor photographs. BVR photometry of 60 of these objects, believed to be star clusters, is presented, especially in comparison to similar observations of clusters in other local Group galaxies. The M33 clusters populate a fairly uniform region between 0.0

Structure and variability of H. cap alpha. emission in early-type supergiants

Abstract: Line profiles and equivalent widths are presented for H..cap alpha.. and H..beta.. in a sample of O and B supergiants. By making reference to model atmospheres and stellar wind theory, emission line luminosities are derived and shown to correlate with the rate of mass loss. Variability is observed to occur on a dynamical time scale of 1/sup d/--10/sup d/. The nature of the variations suggests that the velocity of outflowing material fluctuates with an amplitude of approx.100 km s/sup -1/ and that the fluctuations are not globally symmetric. No evidence for rapid variations with time scales shorter than 6 hr was found. Previously published H..cap alpha.. profiles indicate that for the most luminous stars changes in emission line luminosity by as much as a factor of 3 have occurred on time scales of years or longer. In other stars the profile has varied continuously, but changes in overall strength by more than a factor of a 2 are not indicated. Variations of the mass loss rates of 10% to 30% were inferred for all stars which were observed 3 or more times. In most stars the photospheric absorption lines remained unchanged, but in several cases the He I lambda6678 profilemore » was asymmetric and varied with the same time scale as the H..cap alpha.. emission.« less

A photometric map of interstellar reddening within 300 parsecs.

Abstract: An observational program is described which has as its goal a high resolution, three-dimensional survey of the dust component of the interstellar medium in the solar neighborhood. A network of approx.3450 bright A and F stars was established in the northern hemisphere with the intent that the stars act as probes for the detection of interstellar reddening. In conjunction with empirical calibrations by Crawford, uupsilonby..beta.. photometries yielded precise intrinsic colors and absolute magnitudes that, in turn, allowed the determination of the color excess and the position of each star in a rectangular coordinate system centered on the Sun. The results are summarized in a series of plots where several dust concentrations are readily apparent. In order of galactic longitude, these regions correspond to the inner portions of the Ophiuchus, Cepheus, and Taurus cloud complexes. A bridge of absorbing material, passing through Cassiopeia and Perseus, connects the latter two concentrations; the Ophiuchus complex extends into Aquila. These concentrations are characterized by small-scale irregularities both in density and spatial event. Comparison of the present results with previous investigations shows that this study provides a more definitive map of the spatial distribution of interstellar dust within several hundred parsecs of the Sun.

Acetylene bands observed in carbon stars : a laboratory study and an illustrative example of its application to IRC +10216.

Abstract: Acetylene (C/sub 2/H/sub 2/) has been identified as a constituent of the atmospheres of cool carbon stars based on Fourier transform stellar spectra in the near-infrared. To interpret these astrophysical data on a quantitative basis, a systematic laboratory study of the absorption spectrum of acetylene occurring in this spectral region has been made at a resolution of approx.0.03 cm/sup -1/, both at room temperature and at an elevated temperature of 160 /sup 0/C. Interpretation of the acetylene lines in the 3 ..mu..m region has led to the identification of 27 vibration-rotation bands which have been assigned to transitions between 41 different vibrational states of /sup 12/C/sub 2/H/sub 2/ and /sup 12/C/sup 13/CH/sub 2/, and absolute strengths were measured for 101 selected unblended spectral lines distributed among some of the stronger bands including the 0010/sup 0/0/sup 0/-0000/sup 0/0/sup 0/ band of /sup 12/C/sup 13/CH/sub 2/. In addition, the integrated strengths of the Q-branches of the 1000/sup 0/1/sup 1/-0000/sup 0/0/sup 0/ band at 4091 cm/sup -1/ and the 0100/sup 0/1/sup 1/-0000/sup 0/0/sup 0/ band at 2701 cm/sup -1/ of /sup 12/C/sub 2/H/sub 2/ were measured, and by comparing with the stellar data for IRC+10216, an estimate has been made for the acetylenemore » column density in the circumstellar shell of this carbon star.« less

A model of a sunspot chromosphere based on OSO 8 observations

Abstract: OSO 8 spectrometer observations of the H I, Mg II, and Ca II resonance lines of a large quiet sunspot during November 16-17, 1975, along with a C IV line of that event obtained by a ground-based spectrometer, are analyzed together with near-simultaneous ground-based Stokes measurements to yield an umbral chromosphere and transition region model. Features of this model include a chromosphere that is effectively thin in the resonance lines of H I and Mg II, while being saturated in Ca II, and an upper chromospheric structure similar to that of quiet-sun models. The similarity of the upper chromosphere of the sunspot umbra to the quiet-sun chromosphere suggests that the intense magnetic field plays only a passive role in the chromospheric heating mechanism, and the observations cited indicate that solar-type stars with large areas of ordered magnetic flux would not necessarily exhibit extremely active chromosphere.

X-ray and UV radiation from accreting nonmagnetic degenerate dwarfs. II

Abstract: Numerical calculations of X-ray and UV emission from accreting nonmagnetic degenerate dwarfs are reported, which span the entire range of accretion rates and stellar masses. Calculations include the effects of bremsstrahlung, Compton cooling, radiation pressure, albedo of the stellar surface, Compton degradation and free-free abscription of the X-ray spectrum by the accreting matter. Maximum X-ray luminosity for degenerate dwarfs undergoing spherical accretion is found to be 2.2 x 10 to the 36th ergs/s, which is little changed if accretion occurs radially over only a fraction of the stellar surface, so that the emitted radiation escapes without significant scattering. The temperature characterizing the X-ray spectra produced by degenerate dwarfs strongly depends on the stellar mass and the accretion rate, and it is suggested that the correlation between spectral temperature and luminosity is an important signature of degenerate X-ray sources.

The evolution of massive stars. ii: the influence of initial composition and mass loss

Abstract: We have studied the evolution of 15, 30, and 40 M/sub sun/ stars with compositions Y = 0.28 and Z = 0.01, 0.001, and 0.0002, and of 50 M/sub sun/ stars with Y = 0.28, Z = 0.0002. These models have been evolved from the zero-age main sequence through core helium burning and up to the point of carbon ignition. All models were evolved with and without the inclusion of mass loss. We have used a moderate mass loss rate with different efficiency factors for main-sequence and blue supergiant stars. Our results indicate that all massive stars ignite helium as blue supergiants. Stars with initial masses M/sub i/< or approx. =30 M/sub sun/ evolve redward very slowly and spend less than 1% of their total lifetimes as red supergiants. Above 30 M/sub sun/, the rate of redward evolution increases dramatically. The effect of a reduction in the initial metal content relative to solar abundances is to cause the models to be bluer and, in general, slightly more luminous at comparable stages of evolution. In the absence of mass loss, models with M/sub i/< or =30 M/sub sun/ and Z< or =0.001 do not become red supergiants prior to carbon ignition.more » Mass loss causes all models to evolve redward more rapidly during core helium burning.« less

A nuclear spectroscopic survey of field disk galaxies.

Abstract: On a obtenu les spectres des noyaux de 139 galaxies disques. On en a deduit les largeurs equivalentes des raies d'absorption et d'emission, ainsi que les couleurs et les magnitudes des noyaux. On a evalue les largeurs equivalentes Hα, en fonction du type morphologique et de la couleur du noyau. On a examine la correlation du rapport des flux [NII] a Hα avec les autres proprietes des noyaux

The Clark Lake Teepee-Tee telescope

Abstract: A new, fully steerable, decametric array for radio astronomy has been built at the Clark Lake Radio Observatory near Borrego Springs, California. This array is a 'T' of 720 conical spiral (teepee-shape) antennas, 3.0 km by 1.8 km. It is capable of operating between 15 and 125 MHz but has best sensitivity in the 25 to 75 MHz range. Both its operating frequency and beam position are adjustable in about 1 msec. A 1024-channel digital correlator has been built and attached to the array. This permits the simultaneous measurement of the complex visibility functions on 512 interferometer baselines between various portions of the array. After Fourier transformation these visibility data yield a 32 x 32 resolution element picture of the area of sky under observation, with frequency-dependent angular resolution ranging from 20 to 2.7 arcsec and a sensitivity of 1 Jy per beam. This system is described, and some initial observations are presented.

Stellar populations in the edge-on spiral galaxy NGC 4565. I: Surface brightness and color distributions

Abstract: Results are presented for photographic and photoelectric photometry of the edge-on Sb galaxy NGC 4565. Major-axis, minor-axis, and perpendicular surface brightness profiles are determined, along with color gradients parallel and perpendicular to the plane of the galaxy. It is found that the galaxy's light can be deconvolved naturally into five components: (1) a starlike nucleus located at the center of the bulge and the edge of the dust lane; (2) a thin disk containing the gas and dust, the young OB stars, and the spiral arms; (3) a thick disk that may be a locally isothermal sheet of old Population I metal-rich stars; (4) a bulge that merges smoothly into the thick disk at a radial distance of about 2.9 kpc; and (5) a corona whose light dominates the perpendicular profiles from about 2.9 to at least 8.2 kpc above the galactic plane.

A survey of interstellar neutral potassium. I - Abundances and physical conditions in clouds toward 188 early-type stars

Abstract: Observations of interstellar absorption in the resonance doublet 7664, 7698 A of neutral potassium toward 188 early-type stars at a spectral resolution of 8 km/s are reported. The 7664 A line is successfully separated from nearly coincident telluric O2 absorption for all but a few of the 165 stars for which K I absorption is detected, making possible an abundance analysis by the doublet ratio method. The relationships between the potassium abundances and other atomic abundances, the abundance of molecular hydrogen, and interstellar reddening are investigated.

Interplanetary gas. XXVIII - A study of the three-dimensional properties of interplanetary sector boundaries using disconnection events in cometary plasma tails

Abstract: Studies of the solar wind on the basis of cometary plasma tail observations are considered. Niedner and Brandt (1978, 1979) have concluded that the plasma tail frequently disconnects from the cometary head, and that these disconnection events (DEs) are produced by magnetic reconnection at sector boundary passages. They proposed that the disconnections are a natural combination of Alfven's model and the solar-wind sector structure first discovered by Wilcox and Ness (1965). The DEs can be utilized as probes of interplanetary sector structure. Correlations between DEs and sector boundaries observed at earth are considered, and sector boundary properties deduced from DEs are discussed. Attention is given to a review of the warped sheet model, the latitude extent of sector structure, the sector boundary tilt, and specific sources of error in the tilt angles derived from DEs.

An atlas of interstellar CA II and NA I profiles in the Carina nebula.

Abstract: Optical interstellar absorption line profiles in the spectra of 22 stars within the Carina Nebula, observed with the 4 m echelle spectrograph at resolving powers of 3--6 x 10/sup 4/, are presented. Radial velocities, equivalent widths, and representative column densities are given for resolved velocity components. As many as 12 distinct components spanning several hundred km s/sup -1/ are seen in a single line of sight. Large Ca II/Na I ratios are found for components with velocities >40 km s/sup -1/; one extreme case may correspond to a high-ionization feature associated with a WN-A star.