Galactic Metallicity Research Articles

An HST study of galactic inerstellar zinc and chromium

We present a survey of interstellar Zn II and Cr II absorption extracted from the Hubble Space Telescope Goddard High Resolution Spectrograph (HST GHRS) data archive. We find clear evidence for an enhanced depletion of Zn from the gas phase with increasing fractional abundance of molecular hydrogen f(H2). Our lower limit to the Galactic interstellar metallicity is approximately 65% of the solar value as determined by the measured Zn abundances in the lowest f(H2) sightlines, (N(Zn)/N(H(sup 0)(sub tot)) = -0.19 +/- 0.04. The correspondingly high depletion of Cr with respect to solar (N(Cr/N(H(sup 0)(sub tot)) = -1.44 +/- 0.26 indicates that there are significant amounts of dust present in these lines of sight. The Galactic abundances of Zn and Cr in the ISM provide a fundamental reference point which is used to understand the metal enrichment and dust formation history of damped Lyman alpha QSO absorption-line systems, normally believed to arise from intervening precursors to modern disk galaxies. Although the spread in Zn abundances is large for both the local ISM and in damped Lyman alpha systems, we still find a substantial difference (factor of 4-10) in metallicity between the two sets. This survey and future observations of more distant objects which probe the full extent of the Milky Way halo provide a more complete picture of the enrichment and depletion characteristics of present-day galaxies.

Yet another theory for the origin of halo globular clusters and spheroid stars

view Abstract Citations (30) References (50) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Yet Another Theory for the Origin of Halo Globular Clusters and Spheroid Stars Vietri, Mario ; Pesce, Enrico Abstract We consider the evolution of the gaseous, primordial (Z = 0) Galaxy, as cooling drives its gravitational collapse. We show that it is possible to form halo globular clusters (GCs) and early spheroid stars before gas acquires angular momentum and settles in a disk. Owing to their short cooling times (including collisional H_2_ cooling), denser than average condensations implode because of the pressure of the surrounding hot, tenuous medium. Small condensations (M < 5 X 10^4^ M_sun_) are then returned by the bounced shock to the hot phase, and large condensations (corresponding to GC masses M_*_ > 6 x 10^5^ M_sun_) fragment into stars in the dense shell behind the implosion shock before implosion is complete, thus generating the spheroid. Intermediate clouds, cooling to 100 K because of collisional excitation of H_2_, are compressed and left in approximate pressure equilibrium with the hot phase, then they fragment into stars and give rise to halo GCs. The upper limit to the GC mass, our major result, displays only a weak dependence (proportional to V_c_^1/2^) on Galactic parameters, making it a universal upper limit. The dependence upon overall Galactic metallicity is weak, so that current formation of GCs is allowed. Chemical homogeneity within protoclusters is naturally enforced by turbulent mixing in the cold phase, before fragmentation into stars. Mass ranges for halo GCs (assuming a reasonable star formation efficiency) and velocity dispersion for spheroid stars in agreement with observations are predicted. Publication: The Astrophysical Journal Pub Date: April 1995 DOI: 10.1086/175465 Bibcode: 1995ApJ...442..618V Keywords: Astronomical Models; Cooling Flows (Astrophysics); Early Stars; Galactic Evolution; Galactic Halos; Globular Clusters; Star Formation; Implosions; Interstellar Gas; Mathematical Models; Shock Fronts; Stellar Mass Accretion; Astrophysics; GALAXIES: COOLING FLOWS; GALAXY: GLOBULAR CLUSTERS: GENERAL; STARS: FORMATION full text sources ADS | data products SIMBAD (7) NED (7)

Age and Metallicity Distributions among Galactic Disk Stars

Observational studies of the relations between ages, metallicities and kinematics of disk stars in the solar neighbourhood are discussed with emphasis on the recent survey by Edvardsson et al. (1993), and galactic metallicity gradients inferred from these nearby stars are compared with gradients determined from distant B stars and open clusters.

Elemental Abundances of Sharp-Lined Pop I Main Sequence B, A, and F Stars and Pop II A Stars

The elemental abundances of late B and early A stars should be among the most reliably derived as these stars have well known atmospheric physics, and non-crowded optical spectra with lines of many species with good oscillator strengths. We obtained elemental abundances of sharp-lined stars from high dispersion, S/N &gt; 50, spectra taken at DAO and KPNO. We performed fine analyses using ATLAS6 and more recently ATLAS9 model atmospheres. Our papers (mostly in MNRAS) contain consistent studies of about 35 B3 to F7 superficially normal, Mercury-Manganese (HgMn), Am, and Field Horizontal Branch (FHB) A stars. The abundances of the normal main sequence B, A, and F stars are indicators of Galactic metallicity during the most recent epoch of Galactic history.

METALLICITIES AND VELOCITIES OF OLD OPEN CLUSTERS

ABSTRACT We have obtinaed moderate resoluiton CCD spectra for giants in six old open clusters in the direction of the galactic anti-center (NGC 188, 6705 (M11), 6819, 6940, and IC 4756). Using cross correlation techniques, we determined radial velocities for stars in each cluster and used these values to compute a cluster mean accurate to ~10 km s-1. These means agree quite well with published values. We then used between 4 and 6 spectroscopic indices to measure the metallicity of each star and produce a mean cluster metallicity. Following the Galactic metallicity gradient, more distant clusters are metal poor compared with clusters closer to the solar neighborhood. We used our data, which is centered around the solar radius, to supplement published results by Friel and Janes (1993), and used the combined data set to better define the Galactic metallicity gradient. We found that delta[Fe/H]/deltaRgc = -0.097 ± 0.017 dex/kpc for Rgc > 7 kpc. This result agrees quite well with that of Friel and Janes and with that of other authors. We discuss a possible correlation between age and Mg-enhancement which is indicated by the differences between Fe and Mg line strength among cluster giants. We also briefly consider metallicity dependencies with age and height above the Galactic plane.

The magnesium Mg2 index as an indicator of metallicity in elliptical galaxies

view Abstract Citations (109) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Magnesium Mg/2 Index as an Indicator of Metallicity in Elliptical Galaxies Buzzoni, Alberto ; Gariboldi, Giorgio ; Mantegazza, Luciano Abstract A quantitative calibration of the Mg_2_ index [Faber et al.,AJ,82,941(1977)] is attempted deriving a metallicity scale for elliptical galaxies. The dependence of the index on stellar temperature,gravity and metallicity has been studied through spectroscopic observations of 87 standards applying the derived calibration to models for stellar population synthesis. Buzzoni's [ApJS, 71,817(1989)] computational code has been used to explore the behavior of the index versus age, IMF, and metallicity of simple stellar populations (SSPs) inferring galactic metallicity for the Davies et al. [ApJS, 69, 581(1987)] extensive observational database. It appears that ellipticals are old metal-rich systems, with age about 15 Gyr and (Fe/HI = +0.15. A large spread of nearly one order of magnitude is however derived for metallicity among single galaxies confirming that [Fe/H] is the driving parameter inducing the color spread in the galaxy population. Evolutionary behavior of Mg_2_ is briefly discussed giving its expected variations at early epochs for comparison with high-redshift galaxies. Publication: The Astronomical Journal Pub Date: June 1992 DOI: 10.1086/116197 Bibcode: 1992AJ....103.1814B Keywords: Elliptical Galaxies; Galactic Evolution; Magnesium; Metallicity; Interstellar Extinction; Star Distribution; Stellar Composition; Astrophysics; GALAXIES: ELLIPTICAL AND LENTICULAR; GALAXIES: ABUNDANCES; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (109) NED (3)

Inhomogeneous halo collapse and early Galactic chemical evolution - Globular cluster metallicities

A new solution to the observed Galactic globular cluster metallicity distribution is proposed by considering inhomogeneous collapse of a centrally condensed proto-Galaxy. In contrast to the standard one-zone model, it is shown that, for inhomogeneous models, the metallicity distribution can be reproduced without the need to decrease the nucleosynthetic yield for metal-poor stars. Chemical evolution in free fall is calculated analytically. A hybrid hydroparticle code is developed to study the effect of supernova induced pressure.

A survey of proper motion stars. IX - The galactic halo's metallicity gradient

view Abstract Citations (66) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Survey of Proper Motion Stars. IX. The Galactic Halo's Metallicity Gradient Carney, Bruce W. ; Aguilar, Luis ; Latham, David W. ; Laird, John B. Abstract Using data already presented for a survey of proper motion stars and the Bahcall, Schmidt, and Soneira (1983) model of the Galaxy, Galactic orbital parameters are computed, including planar and three-dimensional eccentricities, apo- and perigalacticon distances, and maximum distances reached above/below the plane, based on extreme values for R and the absolute value of Z over 15 azimuthal periods. The orbital data are used to bin the survey's stars by apogalacticon and maximum Z distances. In an attempt to isolate a halo population sample, analyses are restricted to those stars that lag behind the local standard of the rest's circular orbital velocity by 50, 100, 150, and 200 km/s. The mean metallicities of the stars in a variety of Rapo and Zmax bins are compared . Publication: The Astronomical Journal Pub Date: January 1990 DOI: 10.1086/115320 Bibcode: 1990AJ.....99..201C Keywords: Halos; Metallic Stars; Milky Way Galaxy; Sky Surveys (Astronomy); Stellar Motions; Heavy Elements; Kinetic Energy; Stellar Mass; Stellar Orbits; Astrophysics; GALAXIES: THE GALAXY; STARS: POPULATION II; STARS: HIGH-VELOCITY; STARS: PROPER-MOTION full text sources ADS | data products SIMBAD (744)

Supergiants and the Galactic metallicity gradient. II - Spectroscopic abundances for 64 distant F- to M-type supergiants

view Abstract Citations (57) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Supergiants and the Galactic Metallicity Gradient. II. Spectroscopic Abundances for 64 Distant F- to M-Type Supergiants Luck, R. Earle ; Bond, Howard E. Abstract The metallicity gradient in the Galactic disk from in situ stars with visual magnitude ranging from 6 to 10 is analyzed. Atmospheric parameters and detailed chemical abundances for 64 Population I supergiants of spectral types F through M and luminosity classes Ia through II have been determined. The derived Fe/H ratios ranging from -0.5 to + 0.7 show a mean value of +0.13 with an estimated uncertainty of + or - 0.2. A subset of 25 supergiants fainter than 7th magnitude lying in the direction of the Galactic center shows a Fe/H mean of +0.18 + or - 0.04, while a similar sample of 15 faint supergiants lying in the direction of the Galactic anticenter shows a lower Fe/H mean of +0.07 + or - 0.06. For a sample of bright supergiants analyzed by Luck and Lambert (1985), the mean abundance pattern for all 64 stars showed the following: deficient C and O along with enhancement of N, indicating mixing of CNO-cycled material to the stellar surfaces; an apparent Sr enhancement attributed to departures from LTE; and an essentially solar pattern of other chemical elements. Publication: The Astrophysical Journal Supplement Series Pub Date: November 1989 DOI: 10.1086/191386 Bibcode: 1989ApJS...71..559L Keywords: Abundance; F Stars; M Stars; Metallicity; Stellar Spectra; Supergiant Stars; Astronomical Photography; Spectral Line Width; Stellar Color; Stellar Luminosity; Astrophysics; STARS: ABUNDANCES; STARS: LATE-TYPE; STARS: SUPERGIANTS full text sources ADS | data products SIMBAD (158) Related Materials (1) Part 1: 1982ApJ...263..215L

Distribution of R- and S-Process Elements in the Galactic Halo

Current observational results for the abundances of the very heavy elements (Z&amp;gt;30) in Population II halo stars are reviewed. New high resolution, low noise spectra of many of these extremely metal-poor stars reveal general consistency in their overall abundance patterns. Below Galactic metallicities of [Fe/H] Ã −2, all of the very heavy elements were manufactured almost exclusively in r-process synthesis events. However, there is considerable star-to-star scatter in the overall level of very heavy element abundances, indicating the influence of local supernovas on element production in the very early, unmixed Galactic halo. The s-process appears to contribute substantially to stellar abundances only in stars more metal-rich than [Fe/H] Ã −2.

Supergiants and the galactic metallicity gradient. I - 27 late-type supergiants in the inner-arm regions

From an analysis of high-dispersion Kitt Peak echelle data, atmospheric parameters and chemical abundances have been derived for 27 supergiants of spectral type F through M. Since the star studied lie within about 1 kpc of the Sun, their abundances will form the local reference point for extensions of this study to larger distances. The derived (Fe/H) ratios range from -0.6 to +0.1 dex, show a mean value of -0.15 dex, and have an internal uncertainty of +- 0.2 dex.

The chemical composition of late-type supergiants. IV - Homogeneous abundances and galactic metallicity trends

In a recent series of papers by Luck and by Luck and Bond on the chemical composition of G and K lb supergiants, (Fe/H) ratios were determined from high-dispersion spectroscopic data for 54 stars. The main results were: (1) that supergiants in the solar neighborhood have about twice the iron content of the Sun ( = +0.3); and (2) that supergiants between 7.7 and 10.2 kpc from the galactic center show a steep radial metallicity gradient, d(Fe/H)/dR = -0.24 kpc/sup -1/.

New subdwarfs. III - On obtaining the vertical galactic metallicity gradient from the kinematics of nearby stars

New subdwarfs. III - On obtaining the vertical galactic metallicity gradient from the kinematics of nearby stars