We present the results of our analysis of the RR Lyrae ( RRL ) variable stars detected in two transition-type dwarf galaxies ( dTrans ) , ESO294-G010 and ESO410-G005 in the Sculptor group , which is known to be one of the closest neighboring galaxy groups to our Local Group .
Using deep archival images from the Advanced Camera for Surveys ( ACS ) onboard the Hubble Space Telescope ( HST ) , we have identified a sample of RR Lyrae candidates in both dTrans galaxies [ 219 RRab ( RR0 ) and 13 RRc ( RR1 ) variables in ESO294-G010 ; 225 RRab and 44 RRc stars in ESO410-G005 ] .
The metallicities of the individual RRab stars are calculated via the period-amplitude- [ Fe/H ] relation derived by Alcock et al .
This yields mean metallicities of \langle [ Fe / H ] \rangle _ { ESO 294 } = -1.77 \pm 0.03 and \langle [ Fe / H ] \rangle _ { ESO 410 } = -1.64 \pm 0.03 .
The RRL metallicity distribution functions ( MDFs ) are investigated further via simple chemical evolution models ; these reveal the relics of the early chemical enrichment processes for these two dTrans galaxies .
In the case of both galaxies , the shapes of the RRL MDFs are well-described by pre-enrichment models .
This suggests two possible channels for the early chemical evolution for these Sculptor group dTrans galaxies : 1 ) The ancient stellar populations of our target dwarf galaxies might have formed from the star forming gas which was already enriched through “ prompt initial enrichment ” or an “ initial nucleosynthetic spike ” from the very first massive stars , or 2 ) this pre-enrichment state might have been achieved by the end products from more evolved systems of their nearest neighbor , NGC 55 .
We also study the environmental effects of the formation and evolution of our target dTrans galaxies by comparing their properties with those of 79 volume limited ( D _ { \odot } < 2 Mpc ) dwarf galaxy samples in terms of the luminosity-metallicity relation and the H i gas content .
The presence of these RRL stars strongly supports the idea that although the Sculptor Group galaxies have a considerably different environment from the Local Group ( e.g .
no giant host galaxies , loosely bound and very low local density ) , they share a common epoch of early star formation with the dwarf satellite galaxies in the Local Group .