RR Lyrae and short-period variable stars in the dwarf irregular galaxy NGC 6822

Abstract

We report the discovery of a large number of short-period variable stars in the dwarf irregular galaxy NGC6822, based on deep time-series imaging carried out with the ESO Very Large Telescope. In particular, we found a modest population of RR Lyrae stars tracing the presence of an old stellar component in NGC6822. Measurements of the average luminosity of RR Lyrae stars provide a new independent estimate of the distance to this galaxy based on a Pop.II indicator, (m-M)o=23.36 +/-0.17. In addition, our new data show a significant population of small-amplitude, short-period variable stars filling the instability strip starting at luminosities only a few tenths of a magnitude brighter than the RR Lyrae stars.