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We present for the first time CCD Washington CT1 photometry for the unprecedented data base of some 3. 3 million stars distributed throughout the entire Small Magellanic Cloud (SMC) main body. We obtain ages and metallicities for representative field stellar populations and produce a star field age-metallicity relationship (AMR) from the birth of the galaxy until ∼ 1 Gyr ago, independent of any other previous approach. The SMC star field is featured by no gradients in age and metallicity, and by stellar populations younger than ∼ 2 Gyr more metal rich than Fe/H ∼ -0. 8 dex, which are confined to the innermost region (semi-major axis ≤ 1 ◦). When comparing this AMR with that for clusters with ages and metallicities in the same star field scales, we find that clusters and star fields have experienced two enhanced formation processes: the most recent peaked at an age of ∼3. 5 Gyr, and an earlier one detected at an age of ∼ 5-6 and 7. 5 Gyr for clusters and star fields, respectively.
Andrés E. Piatti (2012) studied this question.