We present a study of short period , central helium–burning variable stars in the Local Group dwarf spheroidal galaxy LeoI , including 106 RR Lyrae stars and 51 Cepheids .
So far , this is the largest sample of Cepheids and the largest Cepheids to RR Lyrae ratio found in such a kind of galaxy .
The comparison with other Local Group dwarf spheroidals , Carina and Fornax , shows that the period distribution of RR Lyrae stars is quite similar , suggesting similar properties of the parent populations , whereas the Cepheid period distribution in LeoI peaks at longer periods ( P \sim 1.26d instead of \sim 0.5d ) and spans over a broader range , from 0.5 to 1.78d .
Evolutionary and pulsation predictions indicate , assuming a mean metallicity peaked within –1.5 \lower 2.58 pt \hbox { $ \sim$ } \kern - 6.7 pt \raise 1.72 pt \hbox { $ < $ } [ Fe/H ] \lower 2.58 pt \hbox { $ \sim$ } \kern - 6.7 pt \raise 1.72 pt \hbox { $ < $ } –1.3 , that the current sample of LeoI Cepheids traces a unique mix of Anomalous Cepheids ( blue extent of the red–clump , partially electron degenerate central helium-burning stars ) and short-period classical Cepheids ( blue–loop , quiescent central helium-burning stars ) .
Current evolutionary prescriptions also indicate that the transition mass between the two different groups of stars is M _ { HeF } \sim 2.1 M _ { \odot } , and it is constant for stars metal–poorer than [ Fe/H ] \sim –0.7 .
Finally , we briefly outline the different implications of the current findings on the star formation history of LeoI .