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Observations of ultraluminous X-ray sources with the 6-m telescope of the SAO RAS

The nature of ultraluminous X-ray sources (ULXs) is not yet fully understood but it can be done in the most efficient way by analyzing its optical emission and environment. We present preliminary results of photometric and spectral studies of some newly identified ULX optical counterparts. Based on the X-ray catalog of ULX candidates by Liu 2011 we have unequivocally identified in the optical range more than 100 sources, for 49 of them we carried out a long slit spectroscopy. According to these results, the majority of the most brightest candidates (m$_V < 22^m$) turned out to be background objects of different types, but the observed parameters of other sources of the sample allow us to classify them as real ULX. Here we present results for ten selected sources.