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Astron. Astrophys. 342, 687-703 (1999)

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Search for optical microvariability in a large sample of Seyfert I galaxies *

P.O. Petrucci 1, A. Chelli 1, G. Henri 1, I. Cruz-González 2, L. Salas 3 and R. Mujica 4

1 Laboratoire d'Astrophysique, Observatoire de Grenoble, B.P. 53X, F-38041 Grenoble Cedex, France
2 Instituto de Astronomia, UNAM, Ap. 70-264, C.U., 04510 México, D.F., México
3 Instituto de Astronomia, UNAM, Ap. 877, 22830 Ensenada, México
4 Instituto Nacional de Astrofisica, Optica y Electronica, Ap. 51 y 216 Z.P., 72000 Puebla, México

Received 4 May 1998 / Accepted 22 October 1998

Abstract

We present results of an optical (I band) monitoring of a sample of 22 Seyfert I galaxies. We aimed to detect microvariability with time resolution from [FORMULA] 6 minutes down to 30 seconds for the most luminous one. It is the largest survey ever done in the search of rapid optical variations in Seyfert galaxies. We used differential photometry and a new method of analysis between galaxy and comparison stars light curves in order to minimize the influence of the intrinsic variabilities of the latter. We thus obtain precision on standard deviation measurements less than 1% and generally of the order of 0.5%. We obtain no clear detection of microvariability in any of these objects. In the hypothesis where optical microvariability could be due to synchrotron emission of a non thermal electrons population, we discuss the physical constraints imposed by these results.

Key words: accretion, accretion disks – radiation mechanisms: non-thermal – galaxies: active – galaxies: Seyfert – infrared: galaxies

* Based on observations taken at the Cananea and San Pedro del Mártir observatories in Mexico

Send offprint requests to: P.O. Petrucci

Correspondence to: Petrucci@obs.ujf-grenoble.fr

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© European Southern Observatory (ESO) 1999

Online publication: February 23, 1999
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