![Evolutionary history of Leo I Evolutionary history of Leo I. The large panel represents the rate of star formation as a function of time, while the small panel indicates the chemical enrichment in the same time interval. Three vertical lines separate the four periods described in the legend.](/sites/default/files/styles/crop_square_2_2_to_320px/public/images/news/fig_english_f.png?itok=RB83N9-M)
Leo I is one of the youngest dwarf spheroidal (dSph) galaxies in the Local Group. Its relative isolation, extended and complex star formation history (SFH), and recent perigalacticon passage ( ∼ 1 Gyr ago) make of Leo I one of the most interesting nearby stellar systems. We derived its SFH from a deep Hubble Space Telescope colour-magnitude diagram and found that global star formation enhancements in Leo I occurred ∼ 13, 5.5, 2.0, and 1.0 Gyr ago, after which it was substantially quenched, most probably due to ram pressure stripping with the Milky Way halo. We interpreted the most ancient
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