Spectroscopy of BL Lac Objects: New redshifts and mis-identified sources.

: Carangelo N, Falomo R, Kotilainen J, Treves A, Ulrich MH

: 2003

: HIGH ENERGY BLAZAR ASTRONOMY

: ASTR SOC P

: 299

: 302

: 4

: 1-58381-146-X

We are carrying out a program of high signal to noise optical spectroscopy of BL Lacs with unknown or tentative redshift. Here we report some preliminary results. New redshifts are measured for PKS0754+100 (z=0.266) and 1ES0715-259 (z=0.464). From lineless spectra of PG1553+113 and PKS1722+119 we set a lower limit of z>0.3 for both sources. In two cases (UM493 and 1620+103) stellar spectra indicate a wrong classification.