Halo Metallicity Research Articles

Lick slit spectra of thirty-eight objective prism quasar candidates and low metallicity halo stars

Lick Observatory slit spectra of 38 objects which were claimed to have pronounced UV excess and emission lines are presented. Eleven QSOs, four galaxies at z of about 0.1, 22 stars, and one unidentified object with a low S/N spectrum were found. Of 11 objects which Zhan and Chen (1987, 1989) suggested were QSO with z(prism) not greater than 2.8; eight are QSOs. Six of the QSOs show absorption systems, including +027A with a relatively strong associated C IV absorption system, and Q0008+008 with a damped Ly-alpha system with an H I column density of 10 exp 21/sq cm. The equivalent widths of the Ca II K line, the G band, and the Balmer lines in 10 stars with the best spectra are measured, and metallicities are derived. Seven of them are in the range -2.5 to -1.7, while the others are less metal-poor.

Subdwarf Studies. III. The Halo Metallicity Distribution

view Abstract Citations (222) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Subdwarf Studies. III. The Halo Metallicity Distribution Ryan, Sean G. ; Norris, John E. Abstract We have constructed the metallicity distribution of a sample of 372 kinematically selected halo stars, most having spectroscopically determined abundances, drawn from our southern subdwarf study and the northern program of Laird et al. [AJ, 95, 1843 (l988a); 96, 1908 (l988b)]. We find that the metallicity distribution of this sample is in very good agreement with the predictions of Hartwick's [ApJ, 209, 418 (1976)] simple model over 2.5 decades of abundance. In particular, we find no significant deficit of metal weak stars, in contradistinction to the earlier investigation of Bond [ApJ, 248, 606 (1981)]. We assess selection effects in the data, and disregard the most metal-rich 10% of the sample, which is probably contaminated by disk stars. We also compare several of Searle's [The Evolution of Galaxies and Stellar Populations (Yale University Press, New Haven, 1977)] stochastic models with the data. The field star data are not well fitted by that family of models, but we find very good agreement between the globular cluster metallicity distribution and a stochastic model with a mean of 10 enrichments per fragment. Previous studies have shown that, due to the small number of clusters available, the agreement between their metallicity distribution and that of the simple model is marginal. It is possible, but not established, that the clusters and the field stars have different parent distributions, a stochastic model producing the former, and a simple model the latter. Publication: The Astronomical Journal Pub Date: May 1991 DOI: 10.1086/115812 Bibcode: 1991AJ....101.1865R Keywords: GALAXIES: THE GALAXY; STARS: SUBDWARFS; STARS: POPULATION II; STARS: WEAK-LINE full text sources ADS | data products SIMBAD (372) Related Materials (3) Part 1: 1989AJ.....98.1693R Part 2: 1991AJ....101.1835R Part 4: 1991AJ....102..303R

Subdwarf studies. II - Abundances and kinematics from medium resolution spectra. III - The halo metallicity distribution

Stars previously identified as having UV excesses are observed at 1-A resolution in the Ca II K-line region. Comparisons of these data with other samples and with Monte Carlo simulations involving a single component halo have yielded estimates of halo velocity dispersions and rotation velocity, corrected for the kinematic biases in the sample. It is suggested that the data are not consistent with a model in which the halo formed from star formation in a dissipating, collapsing cloud; they are, however, reconcilable with the formation of the halo stars by numerous, independently evolving gas clouds. The metallicity distribution of a sample of 372 kinematically selected halo stars is then constructed, with a view to selection effects in the data. Good agreement is noted between the globular cluster metallicity distribution and a stochastic model with a mean of 10 enrichments/fragment.

A survey of proper-motion stars. X - The early evolution of the Galaxy's halo

view Abstract Citations (158) References (80) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Survey of Proper-Motion Stars. X. The Early Evolution of the Galaxy's Halo Carney, Bruce W. ; Latham, David W. ; Laird, John B. Abstract The recent history of work bearing on the early chemical/dynamical evolution of the Galaxy, and the relation of the halo population to the disk population(s) are discussed. In particular, the mean rotational velocity v(rot), and planar orbital eccentricity (e) are considered as functions of time, inferred from mean metallicity. For m/H less than about -1, signs of dynamicl evolution in mean v(rot) or mean e are not detected. It is argued that (e) for metal-poor stars is about 0.6, not 0.8 as previously believed, and is even lower in the three-dimensional case. It is pointed out that all the data are consistent with the high-velocity, low metallicity halo population having had a chemical and dynamical history almost independent of the Galactic disk. It is proposed that the halo was assembled from mergers of small satellites with the Galaxy along the lines discussed by Searle and Zinn (1978). It is further proposed that the Galactic bulge originated from the gaseous outflow from the Galaxy's halo and these fragments. Publication: The Astronomical Journal Pub Date: February 1990 DOI: 10.1086/115351 Bibcode: 1990AJ.....99..572C Keywords: Galactic Evolution; Halos; Sky Surveys (Astronomy); Stellar Motions; Angular Velocity; Chemical Evolution; Milky Way Galaxy; Astronomy; GALAXIES: THE GALAXY; STARS: POPULATION II; STARS: SUBDWARFS; STARS: HIGH-VELOCITY full text sources ADS | data products SIMBAD (86) Related Materials (12) Part 1: 1987AJ.....93..116C Part 2: 1987AJ.....94.1066C Part 3: 1988AJ.....95.1843L Part 4: 1988AJ.....96..378C Part 5: 1988AJ.....96..560C Part 6: 1988AJ.....96..567L Part 7: 1988AJ.....96.1908L Part 8: 1989AJ.....97..423C Part 10: 2001AJ....122.3419C Part 11: 2002AJ....124.1132G Part 12: 2002AJ....124.1144L Part 13: 2005AJ....129.1886C

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)

PROBING THE OUTER GALACTIC HALO.

ABSTRACT The paper discusses recent and continuing studies of the outer halo of our galaxy. A brief inventory is conducted of the stellar systems lying at distances exceeding 25 kpc from the galactic center. The spatial distributions of such systems and the field stars are reviewed, as well as the galactic mass estimates that follow from considerations of their kinematics. The question of a gradient in the halo's metallicity is addressed, plus the scant information available on the chemical abundance pattern of outer halo stars. Finally, the probability of differences in ages of outer halo systems is discussed.

The ages and distances of eight globular clusters

view Abstract Citations (88) References (100) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The ages and distances of eight globular clusters. Carney, B. W. Abstract Deblanketing vector slopes as a function of temperature are derived from photometric and spectrophotometric studies of field subdwarfs and model atmospheres. These vectors are used to transform the UBV data of globular cluster main-sequence mean points to effective temperatures. With the addition of subdwarf bolometric corrections, the clusters' ages and distances are derived by fitting to model isochrones and field subdwarf parallax data. Results show that globular clusters formed over a period of several billion years, with the mean halo metallicity in the solar region increasing slowly with time. It appears that the galactic disk formed about the time halo metallicity reached a nearly solar level, 6 to 8 billion years ago. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1980 DOI: 10.1086/190659 Bibcode: 1980ApJS...42..481C Keywords: Chronology; Cosmology; Distance; Globular Clusters; Stellar Evolution; Abundance; Atmospheric Models; Stellar Magnitude; Stellar Spectrophotometry; Stellar Temperature; Subdwarf Stars; Ubv Spectra; Variable Stars; Astrophysics full text sources ADS | data products SIMBAD (8)