Millimeter-wave spectra and variability of bright, compact radio sources

Observations at 2.7 mm and at 1.5 cm were used to study the millimeter spectra and variability of 176 bright, compact radio sources. More than 20 percent of the flat-spectrum sources, but none of the steep-spectrum sources, were seen to vary at 1.5 cm by at least 30 percent over ten months. This is consistent with the hypothesis that flat-spectrum sources are compact and possibly beamed, while steep-spectrum sources are not. These data can also be used to choose sources for VLBI observations and for calibration of millimeter-wave observations.