Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990a%26a...235...35l&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 235, no. 1-2, Aug. 1990, p. 35-40. Research supported by MPI and CNR.
Astronomy and Astrophysics
Astrophysics
17
Astronomical Photometry, Bl Lacertae Objects, Near Infrared Radiation, Astronomical Spectroscopy, Color-Color Diagram, Correlation, Variability
Scientific paper
The J.H. K magnitudes of three bright BL Lac objects, measured during a monitoring program at the TIRGO observatory from 1986 to 1989, are presented and used to investigate the behavior of the spectral slope versus the flux level. In two objects, 1215 + 303 and 1219 + 285, the spectrum is steeper when the source is fainter, in agreement with the finding of Brown et al. (1989) on a sample of five objects. The third one, 1147 + 245, shows the opposite behavior: the difference is tentatively attributed to the relatively larger contribution in the third object by a flat spectral component, similar in nature to the one that in OVV quasars often emerges as an optical/UV excess. It is also noted that in at least two out of the three objects the J to K spectrum is often characterized by a negative curvature.
Lorenzetti Dario
Massaro Enrico
Perola Giuseppe Cesare
Spinoglio Luigi
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