Optical identifications of flat-spectrum sources in the GB2 1400-MHz survey

Optical identifications of flat-spectrum sources stronger than 0.16 Jy at 1400 MHz from the GB2 survey have been made on the basis of accurate radio positions determined with the NRAO interferometer and comparably accurate optical positions measured on Palomar Sky Survey prints. As expected, most of the identifications are stellar, and the percentage of empty fields increases at lower flux densities. The radio-optical spectral index distribution has a median of 0.69 and an rms width of 0.10, in agreement with values previously obtained from an independent sample of flat-spectrum sources stronger than 0.35 Jy at 2700 MHz. These results are interpreted in terms of radio-optical flux correlations in flat-spectrum sources.