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Session 77 - Irregular and Star Burst Galaxies.
Oral session, Thursday, June 11

[77.01] The Star Formation History of the Local Group Dwarf Galaxy Leo I

C. Gallart, W. Freedman (Carnegie Obs.), A. Aparicio (Inst. de Astrofisica de Canarias), G. Bertelli (Nat'l Council of Research, Rome, Italy), C. Chiosi (Padova U., Italy)

We present results on the star formation history of the Local Group dSph galaxy Leo I, obtained through the analysis of its deep HST color-magnitude diagram (CMD) using model CMDs computed from stellar evolutionary models. Our results show unambiguously that Leo I experienced a major increase of its star formation rate from about 6 Gyr ago to 2 Gyr ago. Some prior star formation possibly ocurred in another discrete episode of enhanced activity lasting 2-3 Gyr. Finally, a low level of star formation continued until 500-200 Myr ago.

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Program listing for Thursday