Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 1985
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985a%26a...147..169g&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 147, no. 1, June 1985, p. 169-177.
Astronomy and Astrophysics
Astrophysics
56
Astronomical Photometry, Cosmology, Galactic Evolution, Globular Clusters, Chronology, Distance, Interstellar Extinction, Metallicity
Scientific paper
The ages of 26 globular clusters are derived using the literature data on main sequence photometry available today. Theoretical ZAHB and P-L-A calibrations of RR Lyrae absolute magnitudes are used for distance scales together with a globular cluster metallicity scale, a constant helium content, and the theoretical isochrones by Vandenberg (1983). The resulting two sets of ages both indicate the presence of a systematic age difference between the inner and outer halo clusters, with the latter older by about 3 Gyr on the mean. This suggests a picture of the galactic halo collapse in which the timescale of galactic collapse and star formation depended on the galactocentric distance. A mean age of 14.6 + or - 0.4 Gyr is obtained, along with a Hubble constant between 50 and 90 km/s/Mpc.
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