Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1983
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1983apjs...51...29v&link_type=abstract
Astrophysical Journal Supplement Series, vol. 51, Jan. 1983, p. 29-65.
Astronomy and Astrophysics
Astrophysics
393
Globular Clusters, Main Sequence Stars, Metallicity, Star Clusters, Stellar Color, Stellar Evolution, Stellar Magnitude, Big Bang Cosmology, Galactic Evolution, Hertzsprung-Russell Diagram, Mass To Light Ratios, Milky Way Galaxy, Stellar Models, Ubv Spectra
Scientific paper
New stellar evolutionary sequences extending from the main sequence to the base of the red giant branch have been computed assuming two values of the helium abundance, Y = 0.2 and 0.3, for each of the adopted heavy-element abundances Z = 0.0001, 0.001, 0.003, 0.006, 0.01, and 0.0169 (solar). Main-sequence masses, in the range of 0.6 to 1.3 M_sun;, were chosen in order to produce turnoff luminosities similar to those observed for the galactic globular and old disk clusters. Color-magnitude diagrams were constructed and compared with the observations of all globular clusters for which main-sequence photometry is available. The color-magnitude of the old open cluster NGC 188 has been included in these comparisons. An extensive discussion of the metal content and the helium abundance of globular clusters is given. All of the globular clusters studied are predicted to have ages somewhere in the range of 15-18×109 yr. An excellent fit to the observations of NGC 188 has been achieved which yields an age of ≡10×109 yr for this open cluster if its metallicity is solar. This suggests that an age difference of perhaps as much as 8 billion yr may exist between the halo and the disk clusters. If 18×109 yr is the maximum age of the globulars, this lower limit to the age of the universe requires H0 ⪉ 60 km s-1 Mpc-1 for a Friedmann model with q0 = 0.
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