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Astron. Astrophys. 321, 374-378 (1997)

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On the galaxy surrounding the BL Lacertae object MS 0205.7+3509 *

Renato Falomo 1, Jari Kotilainen 2, Tapio Pursimo 3, Aimo Sillanpää 3, Leo Takalo 3 and Jochen Heidt 4

1 Osservatorio Astronomico di Padova,v. Osservatorio 5, I-35122 Padova, Italy (falomo@astrpd.pd.astro.it)
2 International School for Advanced Studies (ISAS/SISSA), via Beirut 2-4, I-34014 Trieste, Italy (jkotilai@sissa.it)
3 Tuorla Observatory, University of Turku, Väisäläntie 20, FIN-21500 Piikkiö, Finland
(jarkot@utu.fi, tpursimo@utu.fi, aimosill@utu.fi, takalo@utu.fi)
4 Landessternwarte Königstuhl, D-69117 Heidelberg, Germany (jheidt@hp2.Lsw.uni-heidelberg.de)

Received 2 September 1996 / Accepted 22 November 1996


We present high spatial resolution optical images of the BL Lac object MS 0205.7+3509 in the R filter, that allow us to discuss and clarify its anomalous properties. The source was previously claimed to be surrounded by a nebulosity de-centered with respect to the bright nucleus. In addition the host was claimed to be a disc dominated galaxy, contrary to the large majority of the hosts of BL Lacs. We find that there is a companion galaxy at about [FORMULA] from MS 0205.7+3509, which is responsible for many of the anomalous properties reported for this source. The observations are discussed in the context of the microlensing hypothesis for BL Lacs.

Key words: BL Lacertae objects – galaxies: individual, MS 0205.7+3509

* Based on observations collected at the Nordic Optical Telescope, La Palma.

Send offprint requests to: Renato Falomo

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998