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We have characterized the pulsation properties of 164 candidate RR Lyraevariables (RRLs) and 55 candidate Anomalous and/or short-period Cepheids in LeoI dwarf spheroidal galaxy. On the basis of its RRLs Leo I is confirmed to be anOosterhoff-intermediate type galaxy, like several other dwarfs. We show that intheir pulsation properties, the RRLs representing the oldest stellar populationin the galaxy are not significantly different from those of five other nearby,isolated dwarf spheroidal galaxies. A similar result is obtained when comparingthem to RR Lyrae stars in recently discovered ultra-faint dwarf galaxies. Weare able to compare the period distributions and period-amplitude relations fora statistically significant sample of ab type RR Lyrae stars in dwarf galaxies(~1300stars) with those in the Galactic halo field (~14,000stars) and globularclusters (~1000stars). Field RRLs show a significant change in their perioddistribution when moving from the inner (dG<14 kpc) to the outer (dG>14kpc)halo regions. This suggests that the halo formed from (at least) two dissimilarprogenitors or types of progenitor. Considered together, the RRLs in classicaldwarf spheroidal and ultra-faint dwarf galaxies-as observed today-do not appearto follow the well defined pulsation properties shown by those in either theinner or the outer Galactic halo, nor do they have the same properties as RRLsin globular clusters. In particular, the samples of fundamental-mode RRLs indwarfs seem to lack High Amplitudes and Short Periods ("HASP":AV>1.0mag and P<0.48d) when compared with those observed in the Galactic halo field andglobular clusters. The observed properties of RRLs do not support the idea thatcurrently existing classical dwarf spheroidal and ultra-faint dwarf galaxiesare surviving representative examples of the original building blocks of theGalactic halo.

Homogeneous Photometry VI: Variable Stars in the Leo I Dwarf Spheroidal Galaxy