We investigate the theoretical scenario concerning the large sample of variables recently discovered in the dwarf , metal-poor irregular galaxy Leo A , focusing the attention on the ” Anomalous ” Cepheid phenomenon and its correlation with RR Lyrae stars , Classical and Population II Cepheids .
To this purpose , we make use of suitable stellar and pulsation models to depict the pulsational history of evolutionary structures with metallicity Z =0.0004 , finding that He-burning pulsators are expected only outside the mass interval \sim 0.8-1.7 M _ { \odot } .
Stars from \sim 1.8 to 4 M _ { \odot } , a mass range including both Anomalous and Classical Cepheids , populate with good approximation a common M _ { V } -log P _ { F } instability strip , independently of the previous occurrence of a He flash event , with periods and luminosities increasing with the stellar mass and with a lower luminosity level M _ { V,LE } \sim - 0.5 mag , as observed in Leo A .
The class of less massive pulsators ( M < 
0.8 M _ { \odot } , namely RR Lyrae stars and Population II Cepheids ) populate a distinct instability strip , where the magnitudes become brighter and the periods longer when decreasing the pulsator mass .
The dependence on metal content of this scenario has been investigated over the range Z =0.0002 to 0.008 .
One finds that the edges of the pulsational strip for the more massive class of pulsators appear independent of metallicity , but with the minimum mass of these bright pulsators which decreases when decreasing the metallicity , thus decreasing the predicted minimum luminosity and period .
Comparison with data for Cepheids in Leo A and in the moderately metal rich extragalactic stellar system Sextans A discloses an encouraging agreement with the predicted pulsational scenario .
On this basis , we predict that in a stellar system where both RR Lyrae stars and Cepheids are observed , their magnitude difference may help in constraining both the metal content and the distance .
The current classification of metal-poor Cepheids is shortly discussed , advancing the suggestion for an updated terminology abreast of the current knowledge of stellar evolution .