NASA/IPAC EXTRAGALACTIC DATABASE
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For refcode 1989A&A...211..261C:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1989A&A...211..261C A method to estimate the motion of unresolved VLBI components in extragalactic radio sources. The case of NRAO 140 P. Charlot, B.H. Hough, and J.-F. Lestrade Institut Geographique National/SGN, 2 Av. Pasteur, F-94160 Saint-Mande, France Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 238-700, 4800 Oak Grove Dr., Pasadena, CA 91109, USA Bureau des Longitudes, 77 Av. Denfert Rochereau, F-75014 Paris, France Received February 1, accepted August 2, 1988 Summary. We present a method for estimating the relative motion of two blended VLBI compact components from measurements of the motion of their brightness centroid. This technique requires substantial a priori information about the source components, including their flux densities and separate knowledge of the motion of one of the blended components. However, this is often the situation with well-studied superluminal radio sources. This technique can provide valuable astrophysical information on component velocities from various astrometric/geodetic experiments in which these sources are incidentally observed. The superluminal quasar NRAO 140 was observed as a calibrator/phase reference source in a VLBI experiment at {lambda}=6cm on radio stars in 1983. To test this technique, we have analyzed these observations with a priori information provided by the monitoring program of Marscher and his collaborators (Marscher and Broderick, 1985; Marscher et al., 1987). We do find superluminal motion for the blended component A2 at {lambda} = 6 cm with apparent velocity ~ 5c (H_0_ = 100 km/s/Mpc, q_0_ = 0.5, z = 1.258) as expected from results at {lambda} = 2.8 cm by Marscher and Broderick (1982) and Marscher (1988a, b). We also briefly compare our MEM and CLEAN hybrid maps of NRAO 140. Key words: interferometry - quasars: jets of - quasars: NRAO 140 - radio sources: general - VLBI methods and techniques
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