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Astron. Astrophys. 321, 123-128 (1997)

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The optical variability of QSOs

II. The wavelength dependence * **

S. Cristiani 1, S. Trentini 1, F. La Franca 2 and P. Andreani 1

1 Dipartimento di Astronomia, Università di Padova, Vicolo dell'Osservatorio 5, I-35122 Padova, Italy
2 Dipartimento di Fisica, Università degli Studi "Roma Tre", Via della Vasca Navale 84, I-00146 Roma, Italy

Received 25 April 1996 / Accepted 9 October 1996


The long-term variability of a sample of 149 optically selected QSOs in the field of the Selected Area 94 has been studied in the R-band. The relations between variability and luminosity and between variability and redshift have been investigated by means of "robust" statistical estimators, allowing to disentangle the effects of the measurement errors. The results are compared with the corresponding properties of the variability in the B-band for the same sample. An anti-correlation between the R-band variability and the intrinsic luminosity is found, analogously to what is observed in the B-band. The amplitude of the R-band variability turns out to be smaller (of a factor [FORMULA]) than the B-band variability. The implications in terms of the black-hole, starburst and microlensing models are discussed.

Key words: quasars: general

* Based on material collected with the UKSTU, the ESO-La Silla and the Mount Palomar telescopes and on COSMOS scans.
** Table 1 is only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr ( or via http://cdsweb.u-strasbg.fr/Abstract.html

Send offprint requests to: S. Cristiani

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998