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Age Gradient and the Second Parameter Problem in the Galactic Halo

1996; IOP Publishing; Volume: 463; Linguagem: Inglês

10.1086/177274

1538-4357

Harvey B. Richer, William E. Harris, Gregory G. Fahlman, R. A. Bell, Howard E. Bond, J. E. Hesser, S. T. Holland, C. Pryor, P. B. Stetson, Don A. VandenBerg, Sidney van den Bergh,

Gamma-ray bursts and supernovae

view Abstract Citations (77) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Age Gradient and the Second Parameter Problem in the Galactic Halo Richer, Harvey B. ; Harris, William E. ; Fahlman, Gregory G. ; Bell, Roger A. ; Bond, Howard E. ; Hesser, James E. ; Holland, Steve ; Pryor, Carlton ; Stetson, Peter B. ; Vandenberg, Don A. ; van den Bergh, Sidney Abstract We establish a framework for determining absolute ages of Galactic globular clusters and then use these ages to investigate the age-metallicity and age-Galactocentric distance relations for the 36 clusters with the most reliable age data. The clusters span Galactocentric distances from 4 through 100 kpc and cover a metallicity range from [Fe/H] = -0.6 to -2.3. Adopting currently plausible choices for the relation between cluster metallicity and horizontal-branch luminosity, and -enhancement ratios, we find that the majority of the globular clusters form an age distribution with a dispersion σ(t) of ∼109 yr, and a total age spread smaller than 4 Gyr. Clusters in the lowest metallicity group ([Fe/H] < -1.8) appear to be the same age to well within 1 Gyr at all locations in the Milky Way halo, suggesting that star formation began throughout the halo nearly simultaneously in its earliest stages. We find no statistically significant correlation between mean cluster age and Galactocentric distance (no age gradient) from 4 to 100 kpc. The correlation between cluster age and horizontal-branch type suggests that causes in addition to metallicity and age are required to understand the distribution of stars along the horizontal branches in globular cluster color-magnitude diagrams. Publication: The Astrophysical Journal Pub Date: June 1996 DOI: 10.1086/177274 arXiv: arXiv:astro-ph/9601072 Bibcode: 1996ApJ...463..602R Keywords: GALAXY: HALO; GALAXY: GLOBULAR CLUSTERS: GENERAL; STARS: ABUNDANCES; STARS: EVOLUTION; STARS: HORIZONTAL-BRANCH; Astrophysics E-Print: 26 pages, AASTeX v3.0 with 3 Postscript figures full text sources arXiv | ADS | data products SIMBAD (36)