Extragalactic 1 millimeter sources - Simultaneous observations at centimeter, millimeter, and visual wavelengths

Observations simultaneously made at visual (B, V, and R) wavelengths, at 1, 1.4, and 3.4 mm and at 1.3, 2, 6, and 20 cm of 9 QSOs and BL Lac objects are reported. The range of the millimeter-visual spectral index alpha sub mv was only 0.65-0.82, typical of optically thin synchrotron emission. This may indicate that the electrons radiating synchrotron emission in this portion of the spectrum are not subjected to large radiation losses, and therefore relativistic bulk motion with Doppler factors of about 10 are required. The visual spectral index is much more broadly distributed and typically larger than alpha sub mv. The spectral energy distributions have not changed much in the last two to five years except for 2251+15 and perhaps 0235+164. Only 1749+09 shows a sharp spectral break shortward of 1 mm. Sixteen other sources were observed at 1 mm, of which seven were detected.