SIMBAD references

We present the results of optical spectroscopy and imaging with the SAO 6m telescope for the dwarf galaxy DDO 68 (UGC 5340 = VV 542), falling into the region of very low density of luminous (L>L_*) galaxies (Lynx-Cancer void). Its deep images in V,R bands and in the narrow Hα-filter show that this galaxy has the very irregular morphology, with a long curved tail on the South and a ring-like structure at the Northern edge. The latter consists of 5 separate regions, in three of which we could measure O/H by the classical T_e method. Their weighted mean oxygen abundance corresponds to 12+log (O/H)=7.21±0.03, coincident within uncertainties with those for I Zw 18. The (V-R) colour of DDO 68 is rather blue all over the galaxy, indicating the youth of its stellar populations. Comparing the (V-R)⁰ colour of the underlying exponential disk of 0.12±0.04mag with the PEGASE.2 models for the evolving stellar clusters, we give the first estimate of the ages of the oldest stellar population, which needs confirmation by the other colours and the photometry of resolved stars. These ages are in the range of 200-900Myr for continuous star formation law, and ∼100-115Myr for the instantaneous starburst. We discuss the properties and the possible youth of this nearby object (∼2.3 times closer than the famous young galaxy I Zw 18) in the context of its atypical environment.