The Early Chemical Enrichment Histories of Two Sculptor Group Dwarf
  Galaxies as Revealed by RR Lyrae Variables
  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 <[Fe/H]>_{ESO294} = -1.77 +/- 0.03 and <[Fe/H]>_{ESO410}
= -1.64 +/- 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.
