Showing papers in "Astrophysical Journal Supplement Series in 1979"
TL;DR: In this paper, a grid of LTE model atmospheres is presented for effective temperatures ranging from 5500 to 50,000 K, for gravities from the main sequence down to the radiation pressure limit, for abundances solar, 1/10 solar, and 1/100 solar.
Abstract: A grid of LTE model atmospheres is presented for effective temperatures ranging from 5500 to 50,000 K, for gravities from the main sequence down to the radiation pressure limit, for abundances solar, 1/10 solar, and 1/100 solar. The models were computed by use of a statistical distribution-function representation of the opacity of almost 10/sup 6/ atomic lines. For each model we tabulate the temperature structure, fluxes, UBV and uvby colors, bolometric correction, and Balmer line profiles. The solar abundance models are compared to narrow, intermediate (by Relyea and Kuruez), and wide (by Relyea and Kuruez and by Buser and Kuruez) band photometry and are found to be in good agreement with the observations for effective temperatures aboue 8000 K. Excellent agreement exists with the spectrophotometry and Balmer line profiles of Vega. A small systematic error in the colors of late A and F stars is probably due to an overestimate of convection in weakly convective models. This error does not seem to affect greatly the use of the predicted colors for differential studies. The solar model has approximately a 2% error in the V flux because molecular lines were not included.
1,861 citations
TL;DR: In this paper, the authors examined the initial mass function (IMF) and time history of the stellar birthrate in the solar neighborhood assuming a time-independent IMF, and the present-day mass function is constructed from the luminosity function, and a discussion of all the relevant observational quantities (luminosity function and scale heights, correction for non--main-sequence stars, and correction for main-sequence brightening) and the associated uncertainties is given.
Abstract: We examine the initial mass function (IMF) and time history of the stellar birthrate in the solar neighborhood assuming a time-independent IMF. The present-day mass function is constructed from the luminosity function, and a discussion of all the relevant observational quantities (luminosity function, mass-luminosity relation, scale heights, correction for non--main-sequence stars, and correction for main-sequence brightening) and the associated uncertainties is given. The observed total mass is not in serious disagreement with the dynamical mass (Oort limit) when the uncertainties are considered, and so there is no strong evidence for a local ''missing mass'' problem. The primary constraint on the birthrate history is the requirement that the derived IMF not exhibit an unphysical discontinuity at the mass where the main-sequence lifetime equals the age of the galactic disk. Considering the above uncertainties, the average past birthrate may be at most about 5 times larger or 3 times smaller than the present bithrate according to this constraint, and we favor a variation of less than a factor of 2. A discussion of 12 secondary constraints on the birthrate history is given, and it is concluded that these constraints are either consistent with the continuity constraint or else indeterminate. Ther is, inmore » particular, no evidence for a birthrate which depends on the square of the mean gas density. If the birthrate depends on some power of the mean gas density, the exponent must be small (< or approx. =0.5). Theoretical models for the birthrate history are also examined. Tables of various useful quantities such as cumulative number and mass distributions, present birthrates, and mass consumption rates are given.« less
1,436 citations
TL;DR: In this article, the authors obtained optical scanner data from 4270 to 6710 A with a resolution of 7 A for some 600 H..cap alpha.. emission stars listed in the compilation of T Tauri stars by Herbig and Rao and in the original H..Cap alpha.. surveys.
Abstract: Optical scanner data from 4270 to 6710 A with a resolution of 7 A have been obtained for some 600 H..cap alpha.. emission stars listed in the compilation of T Tauri stars by Herbig and Rao and in the original H..cap alpha.. surveys. These are used to obtain spectral types, reddening corrections, and emission-line strengths and are combined with infrared broad-band measurements out to 3.5 ..mu..m to provide bolometric luminosities and effective temperatures. H-R diagrams are presented for the Taurus-Auriga complex, Orion, NGC 2264, NGC 7000/IC 5070, and the rho Ophiuchi association. The following conclusions are reached: Most H..cap alpha.. emission stars lie on convective tracks in the H-R diagram, and their distribution does not correspond to any published dynamical evolutionary tracks. Most H..cap alpha.. emission stars are of spectra type late K and luminosity class between III and V. Radii and masses derived from the H-R diagram lie between 1 and 5 R/sub sun/ and between 0.2 and 3 M/sub sun/, respectively. The value of d (log N)/d (log M) ranges from -1.35 to -2.9 and for the three best-observed groups is consistent with the -1.35 of the Salpeter initial mass function. Star formation is not coeval on amore » time scale of less than a10/sup 4/to approx.6 x 10/sup 6/ years. The overall efficiency of star formation is approx.10%.6.. The bulk of the extinction occurs within the dark clouds rather than in circumstellar envelopes. High-mass stars may therefore form preferentially in the dense cores of clouds, and low-mass stars may form throughout the cloud. It is very likely that all close pairs of T Tauri stars are binaries.« less
819 citations
TL;DR: In this article, the structure of fast shocks incident upon interstellar gas of ambient density from 10 to the 7th per cu cm, while focusing on the problems of formation and destruction of molecules and infrared emission in the cooling, neutral post shock gas.
Abstract: The paper analyzes the structure of fast shocks incident upon interstellar gas of ambient density from 10 to the 7th per cu cm, while focusing on the problems of formation and destruction of molecules and infrared emission in the cooling, neutral post shock gas. It is noted that such fast shocks initially dissociate almost all preexisting molecules. Discussion covers the physical processes which determine the post shock structure between 10 to the 4 and 10 to the 2 K. It is shown that the chemistry of important molecular coolants H2, CO, OH, and H2O, as well as HD and CH, is reduced to a relatively small set of gas phase and grain surface reactions. Also, the chemistry follows the slow conversion of atomic hydrogen into H2, which primarily occurs on grain surfaces. The dependence of this H2 formation rate on grain and gas temperatures is examined and the survival of grains behind fast shocks is discussed. Post shock heating and cooling rates are calculated and an appropriate, analytic, universal cooling function is developed for molecules other than hydrogen which includes opacities from both the dust and the lines.
777 citations
336 citations
TL;DR: In this paper, the optical and UV emission-line intensities and column densities of ions observable in the visible and UV wavelengths were derived for plane-parallel steady-state shock waves in the interstellar medium.
Abstract: Calculations of the optical and UV emission-line intensities and column densities of ions observable in the optical and UV are presented for plane-parallel steady-state shock waves in the interstellar medium. The range of shock velocities considered is from 50 to 200 km/s, and preshock densities are between 1 and 300 per cu cm. The ionization state of the preshock gas is found to be an important parameter, and several sets of elemental abundances corresponding to various amounts of depletion onto grains are used. The results are compared with observations of the Cygnus Loop, the Vela supernova remnant, and Herbig-Haro objects.
302 citations
268 citations
TL;DR: In this paper, a detailed evaluation of gamma ray line production in the interstellar medium is made, and the compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei.
Abstract: Gamma ray line emission from nuclear deexcitation following energetic particle reactions is evaluated. The compiled nuclear data and the calculated gamma ray spectra and intensities can be used for the study of astrophysical sites which contain large fluxes of energetic protons and nuclei. A detailed evaluation of gamma ray line production in the interstellar medium is made.
258 citations
167 citations
153 citations
TL;DR: In this paper, a sample of E and S0 galaxies is presented, consisting of 80 field galaxies, 35 galaxies in the Virgo cluster and 22 in the Coma cluster.
Abstract: New infrared (JHK) photometry is presented for a sample of E and S0 galaxies. The sample comprises 80 field galaxies, 35 galaxies in the Virgo cluster and 22 in the Coma cluster. The galaxies span a range of 6 mag in absolute magnitude. Multiaperture UBVR photometry for 107 field galaxies is also presented. The infrared data are combined with the new optical data or with published optical data give V-K colors. This paper describes the observational techniques and lists the new data only; analysis of the results is presented in a subsequent paper.
TL;DR: In this article, 120 mA resolution spectra of the cores and wings of the Ca II H and K lines in 43 stars covering a wide range of spectral type and luminosity class were obtained with the KPNO 4 m echelle spectrograph and blue image tube, and calibrated in absolute suface flux units using Willstrop's narrow-band photometry and the Barnes and Evans relations for stellar angular diameters.
Abstract: We present 120 mA resolution spectra of the cores and wings of the Ca II H and K lines in 43 stars covering a wide range of spectral type and luminosity class. These spectra were obtained with the KPNO 4 m echelle spectrograph and blue image tube, and are calibrated in absolute suface flux units using Willstrop's narrow-band photometry and the Barnes and Evans relations for stellar angular diameters. We estimate an uncertainty of +- 15% in our flux scales. We derive chromospheric radiative loss rates in H and K lines, and discuss trenfs in these loss rates with effective temperature for dwarfs, giants and supergiants. We compare these loss rates with similar rates for the Mg II h and k lines, and discuss the doublet line ratios for H and K. The monochromatic surface fluxes for different features in the H and K lines are presented. From the surface fluxes at K/sub 1/ we derived the radiation temperature T/sub R/(K/sub 1/). The T/sub R/(K/sub 1/)/T/sub eff/ ratio is lower in giants than in dwarfs, as predicted by partial redistribution calculations, and this ratio appears to be an empirical age indicator among dwarfs. Asymmetries in the K line profile providemore » evidence for a solar-type supergranulation flow pattern in F5--K5 dwarfs and perhaps aslo in G and early K supergiants. Measurements of line widths at H/sub 1/, K/sub 1/, and K/sub 2/ are presented, together with FWHM data for the H and K lines. We find rough agreement between the measured K/sub 1/ widths and the gravity and chromospheric heating rate dependences in the scaling law proposed by Ayeres. Finally, we present data on emission lines in the wings of H and K, and discuss chromospheric radiative loss rates in the Hepsilon line compared with loss rates in the H and K lines.« less
TL;DR: In this paper, the potential electron-density diagnostics for the high-temperature component of solar flares were studied with reference to the wavelength region from 171 to 630 A. The specific ions discussed include Fe IX through Fe XV, Ni XI through Ni XVII, and ions in the beryllium, boron, carbon, and nitrogen isoelectronic sequences.
Abstract: Potential electron-density diagnostics for the high-temperature component of solar flares are studied with reference to the wavelength region from 171 to 630 A. The specific ions discussed include Fe IX through Fe XV, Ni XI through Ni XVII, and ions in the beryllium, boron, carbon, and nitrogen isoelectronic sequences. Line ratios that could be useful as density indicators under solar-flare conditions are indicated, available data for the ions considered are reviewed, and several theoretical intensity ratios are plotted. The results are employed to determine the electron-density distribution as a function of electron temperature for several spectra from two flares. For these flares it is found that the electron density increases from 10 billion to 500 billion per cu cm for a temperature increase from 1 million to 10 million K.
TL;DR: In this paper, a standard mean luminosity profile in the B band of the El galaxy NGC 3379 along its east-west x-axis is derived from four sets of medium and low-resolution photographic and photoelectric McDonald data.
Abstract: A standard mean luminosity profile in the B band of the El galaxy NGC 3379 along its east-west x-axis is derived from four sets of medium- and low-resolution photographic and photoelectric McDonald data. The 154 mean points cover a range in excess of 11 mag down to ..mu../sub B/=27.8 mag arcsec/sup -2/ (x=7'.3), with possible detection out to x=16'.3 (..mu../sub B/approx. =30.9).The profile is presented within +- 0.08 mag at all x>10'' by ..mu../sub 1/=14.076+3.0083 x/sup 1/4/ (x in arcsec). Near the center the galaxy is brighter than ..mu../sub 1/ by up to 0.35 mag; the excess can be represented by a Gaussian core ..mu../sub II/=18.565+0.03965 r/sup 2/ (r in arcsec) contributing 19.8% of the integrated magnitude B=11.97 within r* =12'' and 4.0% of the total magnitude B/sub T/=10.225 of the galaxy.This two-component model convolved by the appropriate point spread function represents the data within a standard deviation of 0.04 mag over the whole range. Other analytical formulae give generally poorer fits. There is no evidence for a tidal cutoff or a tidal extension.The integrated magnitudes derived from the model agree with aperture photometry (47 values) within 0.05 mag (s.d.).
TL;DR: In this article, a sample including 279 binary galaxies over a wide range of separations is selected from the Uppsala general catalog using well-defined criteria, and the true angular separation distribution of the binary galaxies is reconstructed from the observed distribution and a statistical analysis of the selection criteria.
Abstract: A sample including 279 binary galaxies over a wide range of separations is selected from the Uppsala general catalog using well-defined criteria. The true angular separation distribution of the binary galaxies is reconstructed from the observed distribution and a statistical analysis of the selection criteria. Observational data are complied on the galaxies using optical as well as radio information. The associated 21 cm neutral-hydrogen studies result in the detection of l49 member galaxies (94 without observed optical redshifts). In addition to accurate radial velocities, H I studies provide global measurements on individual galaxies, including total indicative mass and mass-to-light ratios, to be compared with values obtained from a statistical study of the orbital parameters.
TL;DR: In this paper, a consistent set of 247 evolutionary sequences extending from the ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40, Z from 0,00001 to 0,10, and masses of 0.55 to 6.90 solar masses.
Abstract: A consistent set of 247 evolutionary sequences extending from the ZAMS to the red-giant branch is presented for Y from 0.10 to 0.40, Z from 0.00001 to 0.10, and masses of 0.55 to 6.90 solar masses. Each sequence is started from a homogeneous ZAMS model, and almost all are evolved to the base of the red-giant branch. It is shown that: (1) the relative position of the main sequence can be determined as a function of composition; (2) theoretical luminosity functions can be derived from the relative evolutionary time scales; (3) a dip in luminosity sometimes occurs at the base of the red-giant branch and is most pronounced at larger Z values; (4) metal-poor stars evolve farther up along the main sequence before turning off toward the red-giant branch; and (5) the onset of helium burning halts the evolution across the Hertzsprung gap for the most massive and most metal-poor models, so that the star remains blue during its phase of core-helium burning.
TL;DR: A search for new hard X-ray sources using data from the first complete view of the sky with the HEAO-A2 experiment discovered 47 new sources, detected 7 sources recently discovered with other experiments, and significantly reduced the size of the error boxes for 6 previously known sources as mentioned in this paper.
Abstract: A search for new hard X-ray sources using data from the first complete view of the sky with the HEAO-A2 experiment discovered 47 new sources, detected 7 sources recently discovered with other experiments, and significantly reduced the size of the error boxes for 6 previously known sources. Intensities and error boxes are given for each of these sources; identifications are suggested when an error contains an object similar to known X-ray sources. The new identifications consist of seven Type 1 Seyfert galaxies, including two whose Seyfert characteristics were discovered due to their location in an X-ray error box; one intermediate Seyfert galaxy; three Abell clusters; five N-galaxies; two bursting radio sources; and an additional three nearby galaxies with bright nuclei and narrow emission lines.
TL;DR: In this article, the authors presented a 1.2-5.5 micrometer infrared spectrophotometry (1.5% resolution) for 13 stars which have been extensively used as infrared calibration objects: alpha Lyr, alpha CMA, alpha UMi, beta Dra, and alpha Cet.
Abstract: Airborne infrared spectrophotometry (1.2-5.5 microns, 1.5% resolution) is presented for 13 stars which have been extensively used as infrared calibration objects: alpha Lyr, alpha CMA, alpha UMi, beta Dra, and mu Her; the K giants beta Gem, alpha UMa, alpha Boo, gamma-1 And, and alpha Tau; and the M giants beta And, beta Peg, and alpha Cet. These spectra, obtained using NASA's Kuiper Airborne Observatory and Lear Jet Observatory, are virtually free of the interfering effects of terrestrial absorptions. Absolute calibration of the spectrophotometry was based on the theoretical model of alpha Lyr by Schild, Peterson, and Oke (1971), which fits photometric measurements at shorter wavelengths. The resulting flux densities are compared with previous ground-based photometry.
TL;DR: In this article, a summary of the observations performed by the MIT 1-40-keV X-ray detectors on OSO 7 between October 1971 and May 1973 is presented. But this summary is limited to the 3-10-kV band.
Abstract: This paper is a summary of the observations of the cosmic X-ray sky performed by the MIT 1-40-keV X-ray detectors on OSO 7 between October 1971 and May 1973. Specifically, mean intensities or upper limits of all third Uhuru or OSO 7 cataloged sources (185 sources) in the 3-10-keV range are computed. For those sources for which a statistically significant (greater than 20) intensity was found in the 3-10-keV band (138 sources), further intensity determinations were made in the 1-15-keV, 1-6-keV, and 15-40-keV energy bands. Graphs and other simple techniques are provided to aid the user in converting the observed counting rates to convenient units and in determining spectral parameters. Long-term light curves (counting rates in one or more energy bands as a function of time) are plotted for 86 of the brighter sources.
TL;DR: The most accurate values presently available for the rest frequencies of all known interstellar molecular transitions are presented and recommended for reference in future astronomical observations in the radio and microwave regions as discussed by the authors, and the recommended values have been carefully selected after critical evaluation of the spectroscopic literature.
Abstract: The most accurate values presently available for the rest frequencies of all known interstellar molecular transitions are presented and recommended for reference in future astronomical observations in the radio and microwave regions. The recommended values have been carefully selected after critical evaluation of the spectroscopic literature. Probable error limits along with the proper molecular and quantum mechanical labels are presented for each observed transition. Representative line antenna temperatures are also presented for a typical source as a convenience to users. References are cited to both the astronomical and the laboratory literature.
TL;DR: In this article, the Ca II infrared triplet line lambda8542 in 49 stars of spectral type F9--K3 was obtained with a silicon diode vidicon detector system on the KPNO McMath telescope.
Abstract: We have obtained profiles of the Ca II infrared triplet line lambda8542 in 49 stars of spectral type F9--K3 These data were obtained with a silicon diode vidicon detector system on the KPNO McMath telescope and have a spectral resolution of 014 A We find no evidence for distinct emission features in the lambda8542 lines, even for the most active chromosphere stars, but instead find that the line cores are filled in for active chromospheric stars compared to quiet chromosphere stars of the same spectral type We derive chromospheric radiative loss rates in the lambda8542 line and find good correlations with chromospheric radiative loss rates in the Ca II H and K lines and Mg II h and k lines and with the Wilson-Bappu K-line index Thus the lambda8542 line is a good diagnostic of chromospheric activity Computed lambda8542 line profiles for the seven stars for which model chromospheres are available are not in as good agreement with the data as we would like, and for the three modeled giants the addition of macroturbulence cannot account for discrepancies in the line cores We account for variability in the cap alpha Aur line profile as due to orbital motions of capmore » alpha Aur B, and we point out circumstellar features, indicating both outflowing and inflowing material, in six supergiants« less
TL;DR: An abundance analysis of 21 elements in 21 Hg-Mn, two Si-Cr, and six normal stars using model atmospheres and high-dispersion spectroscopy in the visible and UV as discussed by the authors.
Abstract: An abundance analysis has been conducted of 21 elements in 21 Hg-Mn, two Si-Cr, and six normal stars using model atmospheres and high-dispersion spectroscopy in the visible and UV. Manganese line strengths imply abundances that correlate well with stellar effective temperature. Within the studied sample of Hg-Mn stars there appears to be no correlation of abundances of any element with projected rotational velocity. Abundances in several Hg-Mn stars show patterns that are probably consistent with diffusion but difficult to reconcile with equilibrium nucleosynthesis. In general, no combination of gross stellar physical parameters is sufficient to characterize the patterns of line strengths observed in Hg-Mb Hg-Mn stars.
TL;DR: In this paper, the authors presented graphs and tables for 164 bright stars in the spectral region from 1200 to 3600 A. The spectra represent a subset of OAO 2 spectrometer data on file at the National Space Science Data Center.
Abstract: Ultraviolet stellar fluxes are presented in graphs and tables for 164 bright stars in the spectral region from 1200 to 3600 A. The spectra represent a subset of OAO 2 spectrometer data on file at the National Space Science Data Center. The monochromatic flux is given in units of erg per (sq cm-s-A) with a spectral resolution of about 22 A in the region from 3600 to 1850 A and of approximately 12 A in the region from 1850 to 1160 A.