| Abstract | The age of the SMC globular cluster NGC 121 is found from main-sequence isochrone fitting to be 12 + or - 2 x 10 to the 9th yr if a distance modulus that assumes M(v) = +0.6 for the field RR Lyrae variables near the cluster is used. If instead (m - M)0 = 19.3, then the cluster age is 9 + or - 2 x 10 to the 9th yr. The cluster is known to contain both RR Lyrae variables and a marginal carbon star; comparison with theoretical models indicates no significant inconsistencies in this joint occurrence at either modulus. The color-magnitude diagram for the mearby field also shows a faint, blue main-seqence turnoff and, in contrast to previous Magellanic Cloud field studies, the field lacks any evidence for the existence of a significant intermediate-age component. A new look at the chemical evolution of the Small Magellanic Cloud suggests that, unlike the galaxy, where the rate of enrichment has been steady after the initial phase, the enrichment in the SMC remaned small for a long interval before increasing rapidly sometime in the last 1-2 x 10 to the 9th yr. |
