Optical spectra of BL Lacertae objects.

The paper presents a discussion of the spectroscopic properties of a sample of BL Lacertae objects. The BL Lac phenomenon covers a wide range of luminosities. The data indicate that the nuclear object can have optical luminosities ranging from less than that of a luminous giant elliptical galaxy to over 100 times the luminosity of such a galaxy. In all cases where a galaxy was detected, spectroscopic and direct photographic evidence indicate that it was an elliptical galaxy. Nearly three-fourths of the objects studied showed emission lines. These lines are typically weaker than those observed in QSOs, but stronger than those seen in some giant E galaxies.