We have combined deep photometry in the B , V and I bands from CTIO/MOSAIC of the Sculptor dwarf spheroidal galaxy , going down to the oldest Main Sequence Turn-Offs , with spectroscopic metallicity distributions of Red Giant Branch stars .
This allows us to obtain the most detailed and complete Star Formation History to date , as well as an accurate timescale for chemical enrichment . The Star Formation History shows that Sculptor is dominated by old ( > 10 Gyr ) , metal-poor stars , but that younger , more metal-rich populations are also present .
Using Star Formation Histories determined at different radii from the centre we show that Sculptor formed stars with an increasing central concentration with time .
The old , metal-poor populations are present at all radii , while more metal-rich , younger stars are more centrally concentrated .
We find that within an elliptical radius of 1 degree , or 1.5 kpc from the centre , a total mass in stars of 7.8 \times 10 ^ { 6 } M _ { \odot } was formed , between 14 and 7 Gyr ago , with a peak at 13 - 14 Gyr ago . We use the detailed Star Formation History to determine age estimates for individual Red Giant Branch stars with high resolution spectroscopic abundances .
Thus , for the first time , we can directly determine detailed timescales for the evolution of individual chemical elements .
We find that the trends in alpha-elements match what is expected from an extended , relatively uninterrupted period of star formation continuing for 6 - 7 Gyr .
The knee in the alpha-element distribution occurs at an age of 10.9 \pm 1Gyr , suggesting that SNe Ia enrichment began \approx 2 \pm 1Gyr after the start of star formation in Sculptor .