Fig. 4
Oxygen abundance profiles of Cepheids, B-stars, HII regions, and planetary nebulae (PN); data sources are in Table 1. The adopted solar value of log (O / H) + 12 = 8.73 is from Asplund et al. (2009). Model curves (from bottom to top, in all panels) represent the gaseous abundance profile at times 4, 8 and 12 Gyr (thick curve), respectively.
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