Abstract
We present results of an ongoing program at the European Southern Observatory Very Large Telescope for spectroscopy of BL Lac objects (BLLs) lacking a firm redshift estimate, and here we report on 15 objects. For 11 sources we confirm the BL Lac classification, and determine new redshifts for three objects, one with weak emission lines (PKS 1057 – 79, z = 0.569) and two with absorptions from the host galaxy (RBS 1752, z = 0.449; RBS 1915, z = 0.243); moreover, a subdamped Lyα system is detected in the direction of the BL Lac PKS 0823 – 223 (z ≥ 0.911). For the remaining eight BLLs, from the very absence of absorption lines of the host galaxy, lower limits to the redshift are deduced with z min in the interval 0.20-0.80. The remaining three sources are reclassified as a FSRQ (PKS 1145 – 676, z = 0.210; TXS 2346+052, z = 0.419) and a misclassified galactic star (PMNJ 1323 – 3652).
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