VLBI observations of the water vapor masers in Cepheus A, S252A, GL 2789, GL 2139, CO 59.79+0.04, W33B, and U Orionis

We report VLBI observations with angular resolution of 0".003 of H2O maser sources associated with Cepheus A, S252A, GL 2789/V645 Cyg, GL 2139, CO 59.79+0.04, W33B, and U Ori. The absolute positions of the masers were measured to an accuracy of 0".3. Positional coincidences were found between two groups of maser spots and two very compact H II regions in Cep A, and between the maser spots and a stellar-like optical image in GL 2789. In the case of Cep A, we found that the line widths of individual maser components varied as the ⅓ power of the flux densities.