Other
Scientific paper
May 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987aj.....93.1144m&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 93, May 1987, p. 1144-1165. NSERC-supported research.
Other
127
Astronomical Photometry, Charge Coupled Devices, Globular Clusters, Abundance, Color-Magnitude Diagram, Main Sequence Stars, Oxygen, Stellar Luminosity
Scientific paper
V and B photometry reaching V ≥ 24 mag for the metal-poor globular cluster M68 (= NGC 4590 = C1236-264) has been obtained with the prime-focus CCD camera at the CTIO 4 m telescope. The main-sequence turnoff region of M68 is particularly well defined, allowing for detailed matching of the observed color-magnitude diagram with theoretical isochrones. The authors adopt Y = 0.24, [Fe/H] = -2.0, E(B-V) = 0.07 mag, and (m-M)v = 15.25 mag. They find that the best fit is obtained for isochrones with enhanced oxygen abundance, [O/Fe] = 0.7, and an age of 14 billion years. The sensitivity of this age estimate to changes in the principal parameters is discussed in the text. Isochrones and predicted colors from a grid of oxygen-enhanced models computed specifically for this analysis are presented. The luminosity function on the main sequence continuously rises to faint magnitudes, like those found for other metal-poor globular clusters (e.g., M13 and M15). This is in contrast with clusters which are metal rich and have flat luminosity functions, such as 47 Tuc and M4.
Bell Roger A.
Hesser James Edward
McClure Robert D.
Stetson Peter B.
VandenBerg Don. A.
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