SIMBAD references

We are in the process of performing a circular polarization analysis of 2, 4 and 6 cm VLBA data for a complete sample of 34 1 Jy Northern BL Lac objects based on the method developed by Homan & Wardle (1999). We present here our results to date for about 70% of the sample. We have detected circular polarization in the core regions of about 20% of these sources at 2 cm and 6 cm, and in a somewhat higher fraction, 30-35%, at 4 cm. The degrees of circular polarization are similar to those detected for compact AGN in previous studies, with typical values of a few tenths of percent.