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We present a study of short period, central helium-burning variable stars inthe Local Group dwarf spheroidal galaxy LeoI, including 106 RR Lyrae stars and51 Cepheids. So far, this is the largest sample of Cepheids and the largestCepheids to RR Lyrae ratio found in such a kind of galaxy. The comparison withother Local Group dwarf spheroidals, Carina and Fornax, shows that the perioddistribution of RR Lyrae stars is quite similar, suggesting similar propertiesof the parent populations, whereas the Cepheid period distribution in LeoIpeaks at longer periods (P \sim 1.26d instead of ~0.5d) and spans over abroader range, from 0.5 to 1.78d.  Evolutionary and pulsation predictions indicate, assuming a mean metallicitypeaked within -1.5<= [Fe/H]<=-1.3, that the current sample of LeoI Cepheidstraces a unique mix of Anomalous Cepheids (blue extent of the red--clump,partially electron degenerate central helium-burning stars) and short-periodclassical Cepheids (blue-loop, quiescent central helium-burning stars). Currentevolutionary prescriptions also indicate that the transition mass between thetwo different groups of stars is MHeF \sim 2.1 Mo, and it is constant for starsmetal-poorer than [Fe/H]\sim-0.7. Finally, we briefly outline the differentimplications of the current findings on the star formation history of LeoI.

On the central helium-burning variable stars of the LeoI dwarf spheroidal galaxy