THE NEAR-INFRARED-OPTICAL-ULTRAVIOLET EMISSION OF BL LACERTAE OBJECTS

Near-infrared, optical, and ultraviolet quasi-simultaneous observation s of 11 BL Lacertae objects are reported. For all but one source the d ereddened spectral flux distribution in the (8 x 10(13))-(2 x 10(15)) Hz frequency range can be described by a single power law f(n)u propor tional to nu(-alpha) with average spectral index <alpha> = 0.88 +/- 0. 42 (standard deviation) plus, where relevant, the contribution of the host galaxy. In most cases the nonsimultaneous soft X-ray fluxes obtai ned by the Einstein Observatory lie on or below the extrapolation of t he power law. The results are compared with the average spectral prope rties of other samples of BL Lac objects studied separately in the IR- optical and in the UV bands. The implications for existing models of t he objects are briefly discussed.