A& A Supplement series, Vol. 121, January 1997, 119 - 138
Received March 18; accepted May 21, 1996
-ray loud
blazars.M. Villata
, C.M. Raiteri
, G.
Ghisellini
, G. De Francesco
,
S. Bosio
, G. Latini
, B. Bucciarelli
,
M. Chiaberge
, G.
Chiumiento
, A. Cora
, L. Lanteri
, M.G.
Lattanzi
, G. Massone
, A.
Peila
, F. Racioppi
, R.L. Smart
, F.
Scaltriti
- E. Anderlucci
Send offprint request: M. Villata (villata@to.astro.it)
Osservatorio Astronomico di Torino, Strada Osservatorio 20, I-10025 Pino
Torinese (TO), Italy
Istituto di Fisica Generale dell'Università, Via Pietro
Giuria 1, I-10125
Torino, Italy
The results of the optical monitoring between November 1994 and
November 1995 of twenty 
-ray loud blazars included in
the Torino blazar monitoring program are presented. All data
were taken with the 
REOSC astrometric telescope of
the Torino Astronomical Observatory, equipped with a 
pixels charge-coupled device (CCD) camera.
Observations have been carried out in the standard B, V
(Johnson), and R (Cousins) bands. Source magnitudes are
calculated with respect to reference stars in the same frame.
For half blazar fields it was possible to perform a photometric
calibration through the observation of Landolt's fields during
photometric nights. In the other cases either photometric
sequences from the literature were adopted or, when lacking,
magnitudes were simply normalized to their minimum value. Most
of the monitored objects show a more or less pronounced
brightness variability on both short and long time scales. In a
few cases also noticeable intranight variations were detected.
Data simultaneous to pointings of the Compton Gamma Ray
Observatory (CGRO) are present in our light curves: when the
data are available they will provide a useful
information in order to understand the possible correlations
between the optical and 
-ray emissions. For one source
(PKS 2254+074) we performed also photopolarimetry, deducing
magnitudes, amount of polarization, and position angle in the
UBVRI bands.
keywords: quasars: general -- gamma rays: theory