Spectral Characteristics and Behavior Intrinsic to the Compact Variable in BL Lac Objects

The investigators propose to obtain IUE observations of the spectra of optically variable BL Lacertae objects for comparison with previous-epoch IUE observations to continue their originally proposed study of UV spectral variations in these sources. The initial-epoch observations demonstrated the detectability of objects in the class and serve to define the spectral characteristics for particular luminosity levels in the observed objects. The purposes of the study in progress are: (1) to determine the energy distribution in the spectrum intrinsic to the compact nonthermal source, (2) to study the variation of the spectral energy distribution as the optical luminosity varies, and (3) to determine redshifts and distances using emission lines which may become detectable relative to the continuum as the sources vary. Each determination will help to constrain proposed models for the source and emission mechanisms. Nearly simultaneous observations in optical and other wavelengths by cooperating ground-based observers and x-ray observations with HEAO-2 will serve to extend the spectral baseline of the study.