Star formation history and environment of the dwarf galaxy UGCA 92
  We present a quantitative star formation history of the nearby dwarf galaxy
UGCA 92. This irregular dwarf is situated in the vicinity of the Local Group of
galaxies in a zone of strong Galactic extinction (IC 342 group of galaxies).
The galaxy was resolved into stars with HST/ACS including old red giant branch.
We have constructed a model of the resolved stellar populations and measured
the star formation rate and metallicity as function of time. The main star
formation activity period occurred about 8 - 14 Gyr ago. These stars are mostly
metal-poor, with a mean metallicity [Fe/H] ~ -1.5 -- -2.0 dex. About 84 per
cent of the total stellar mass was formed during this event. There are also
indications of recent star formation starting about 1.5 Gyr ago and continuing
to the present. The star formation in this event shows moderate enhancement
from ~ 200 Myr to 300 Myr ago. It is very likely that the ongoing star
formation period has higher metallicity of about -0.6 -- -0.3 dex. UGCA 92 is
often considered to be the companion to the starburst galaxy NGC 1569.
Comparing our star formation history of UGCA 92 with that of NGC 1569 reveals
no causal or temporal connection between recent star formation events in these
two galaxies. We suggest that the starburst phenomenon in NGC 1569 is not
related to the galaxy's closest dwarf neighbours and does not affect their star
formation history.
