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For the first time, we obtain chemical evolution models (CEMs) for Tucana andCetus, two isolated dwarf spheroidal galaxies (dSphs) of the Local Group. TheCEMs have been built from the star formation histories (SFHs) and themetallicity histories, both obtained independently by the LCID project fromdeep color-magnitude dia- grams. Based on our models, we find that the chemicalhistories were complex and can be divided into different epochs and scenarios.In particular, during 75 percent of the SFH, the galaxies behaved as closedboxes and, during the remaining 25 percent, either received a lot of primordialgas by accretion or they lost metals through metal-rich winds. In order todiscriminate between these two scenarios, abundances ratios in old stars areneeded. At t approximately 4.5 Gyr, the galaxies lost most of their gas due toa short-strong, well-mixed wind. We obtain very similar CEMs for both galaxies,although Cetus is twice as massive as Tucana. We conclude that the starformation in both galaxies began with only 1.5 percent of the baryonic massfraction predicted by lambda CDM.

Chemical history of isolated dwarf galaxies of the Local Group: I. dSphs: Cetus and Tucana