EDP Sciences
Free access
Volume 434, Number 3, May II 2005
Page(s) 895 - 907
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20042391

A&A 434, 895-907 (2005)
DOI: 10.1051/0004-6361:20042391

Optical follow-up of BL Lac candidates in the 2BL sample

R. Nesci, S. Sclavi and E. Massaro

Dipartimento di Fisica, Universitá La Sapienza, P.le Aldo Moro 2, 00185 Roma, Italy
    e-mail: roberto.nesci@uniroma1.it

(Received 18 November 2004 / Accepted 7 January 2005 )

We investigate the nature of the BL Lac candidates in the northern part of the 2BL sample (Londish et al. 2002, MNRAS, 334, 941) searching for optical variability by means of $R_{\rm C}$ band photometry with the Asiago 1.8 and Loiano 1.5 m telescopes during years 2002, 2003 and 2004. We also made aperture photometry of the candidates on the plates available on the web from the Palomar and UK Schmidt telescopes. No significant variability was detected for the majority of the objects without detected radio and/or X-ray emissions, while clear variability was found for the few sources of the sample with strong radio and/or X-ray emission, which is a constant feature of the "classical" BL Lacs. Some considerations on the nature of the 2BL sources are made, taking into account their most recent data available in proper motions catalogues (SuperCOSMOS, USNO-B1) and in the Sloan Digital Sky Survey.

Key words: galaxies: active -- galaxies: BL Lacertae objects: general

SIMBAD Objects

© ESO 2005