<i>BVRI</i> photometry of BL Lacertae in 1993-1995
M. MaesanoIstituto Astronomico, Universitá “La Sapienza", via G.M. Lancisi 29, I-00161 Roma, ItalyF. MontagniIstituto Astronomico, Universitá “La Sapienza", via G.M. Lancisi 29, I-00161 Roma, ItalyE. MassaroIstituto Astronomico, Universitá “La Sapienza", via G.M. Lancisi 29, I-00161 Roma, ItalyR. NesciIstituto Astronomico, Universitá “La Sapienza", via G.M. Lancisi 29, I-00161 Roma, Italy
1997en
ABI
Abstract
The results of optical photometry of BL Lac over a time interval of two years in the B, V, R, I filters are presented. The source is found for most of the time in a low state. The mean colour indexes are similar to those observed in higher luminosity states, however a flattening of the spectral slope was present during three small amplitude outbursts. A brief comparison with the observations available in the literature and some considerations on the physical conditions driving the appearance of emission lines are made.
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Cited by 30 references