EXTINCTION IN LOW-IONIZATION BROAD ABSORPTION-LINE QUASI-STELLAR OBJECTS

Recently, Weymann et al. presented composite spectra of broad absorption line (BAL) QSOs as divided into two classes, those with spectra containing absorption from both high and low-ionization ionic species, and those showing only high-ionization absorption troughs. They showed that the spectral properties of the former class differed from those of the latter (and non-broad absorption line QSOs) in that their spectra contain stronger emission from Fe II and possibly Fe III, their continua are substantially redder, and Lyman-alpha and N v emission lines are weaker. In this contribution it is shown that correction for the extinction of a modest amount of dust can bring the spectra into coincidence. This extinction is not sufficient to explain the strong infrared-to-optical flux ratios seen in some of these objects. Differential k-corrections due to dust extinction are large enough that low-ionization BAL QSOs may be substantially underrepresented in magnitude-limited samples of QSOs.