Photoelectric intraday observations of BL Lacertae, 3C 66 A, B2 1652 + 39, and 3C 371

Abstract

A search for optical intraday variability in the sources BL Lac, 3C 66 A, B2 1652 + 39, and 3C 371 has failed to detect significant changes on a time scale ranging from 20 seconds to a few hours. Day-to-day changes in brightness are present in BL Lac, 3C 66 A, and 3C 371. The data suggest that as 3C 66 A and 3C 371 brighten, the U-B color index becomes more negative, while fairly large changes in U-B occur in BL Lac, which may or may not be accompanied by significant changes in V.