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Astron. Astrophys. 318, 376-382 (1997)

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The radio source OQ 208: parsec-scale morphology and spectral properties

C. Stanghellini 1, 7, M. Bondi 2, 3, D. Dallacasa 2, 4, C.P.O'Dea 5, S.A. Baum 5, R. Fanti 2, 6 and C. Fanti 2, 6

1 Istituto di Radioastronomia del CNR, C.P. 141, I-96017 Noto SR, Italy
2 Istituto di Radioastronomia del CNR, Via Gobetti 101, I-40129 Bologna, Italy
3 Nuffield Radio Astronomy Laboratories, Jodrell Bank, Macclesfield, Cheshire, SK11 9DL, UK
4 Joint Institute for VLBI in Europe, Postbus 2, 7990 AA Dwingeloo, The Netherlands
5 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218
6 Dipartimento di Fisica, Università degli Studi, via Irnerio 46, I-40126 Bologna, Italy
7 Visitor at the Space Telescope Science Institute, Baltimore.

Received 19 December 1995 / Accepted 22 July 1996

Abstract

We present results from global VLBI (Very Long Baseline Interferometry) observations at 5 GHz of the radio source OQ 208. The milliarcsecond (mas) morphology of the radio emission is described by an asymmetric compact double structure with a flux density ratio between the two components of about 10:1, and a projected total size of [FORMULA] 7 mas (i.e. [FORMULA] 7 pc). Both components are resolved by the present observations.

Multifrequency VLA (Very Large Array) observations are used to define the spectral shape and, together with literature data, to investigate the flux density variability at different frequencies. The integrated radio spectrum is peaked at about 4 GHz. The flux density is constant below the peak and slowly decreasing at frequencies above the peak.

On the basis of the mas morphology, spectral information and flux density variations, we favour the hypothesis that the radio source consists of two parsec-size lobes undergoing synchrotron radiative losses.

Key words: galaxies: OQ 208=Mkn 668 – galaxies: active – radio continuum: galaxies

Send offprint requests to: C. Stanghellini

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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