A unique isolated dwarf spheroidal galaxy at D=1.9 Mpc
  We present a photometric and spectroscopic study of the unique isolated
nearby dSph galaxy KKR25. The galaxy was resolved into stars with HST/WFPC2
including old red giant branch and red clump. 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 12.6 to 13.7 Gyr ago. These stars are mostly metal-poor, with a
mean metallicity [Fe/H]\sim -1 to -1.6 dex. About 60 per cent of the total
stellar mass was formed during this event. There are indications of
intermediate age star formation in KKR25 between 1 and 4 Gyr with no
significant signs of metal enrichment for these stars. Long-slit spectroscopy
was carried out using the Russian 6-m telescope of the integrated starlight and
bright individual objects in the galaxy. We have discovered a planetary nebula
(PN) in KKR25. This is the first known PN in a dwarf spheroidal galaxy outside
the Local Group. We have measured its oxygen abundance 12+log(O/H)=7.60+-0.07
dex and a radial velocity Vh=-79 km/s. We have analysed the stellar density
distribution in the galaxy body. The galaxy has an exponential surface
brightness profile with a central light depression. We discuss the evolutionary
status of KKR25, which belongs to a rare class of very isolated dwarf galaxies
with spheroidal morphology.
