2 Observations

The observations were performed using the VLA in B-configuration at a frequency centred on 4860.1 MHz, on four occasions: 1994 July 8, 1994 July 30, 1995 October 9 and 1995 December 10. Data were taken in two contiguous bands of 50 MHz bandwidth centred at 4835 MHz and 4885 MHz. Exposure times were 2 minutes, resulting in a theoretical rms noise level of 0.10 mJy/beam; the median noise level of the maps is in fact about 0.1 mJy/beam (estimated from the rms in the bottom 20 pix² of each map). Phase calibration was performed typically once every 10-15 sources using point-source calibrators from the VLA Calibrator List (Perley 1982) during the 1995 observations, although only sporadic phase calibration is available for the 1994 observations. Flux densities were bootstrapped to the source 3C 48, using the value of 5.4 Jy at 4850 MHz from Baars et al. (1979). After calibration in AIPS, the data on each source in turn were mapped using the Caltech Difmap package (Shepherd et al. 1995), typically involving one pass of phase selfcalibration and one of amplitude self-calibration between passes through the CLEAN algorithm, using windows to build up flux in successively fainter parts of the source. A few sources (nearly all of them bright point sources) had residual offset corrections applied in addition. The final dataset was then read back into AIPS and the CLEAN algorithm was applied using the task IMAGR with the ROBUST parameter set to zero, giving a weighting scheme intermediate between natural and uniform weighting. In a few cases the Difmap CLEANed map was used as the final map. The combination of the two algorithms allowed easy interactive investigations of the data combined with deep and thorough CLEANing.

For each component of each object, the peak and extended fluxes have been measured by hand using the AIPS task TVSTAT. This procedure gives an indication of the flux, although it may not be totally reliable in cases where components are not well resolved from each other or when components are large and extended, and hence partially resolved out by the interferometer. Where a core was seen on the map, this was measured separately; otherwise a value is typically quoted for each lobe of a double source. 19 objects overlap with the sample observed in Paper I at 1.4GHz.

Basic observational parameters are given in Table 1, namely the date of the observation, details of the point-source response in the map, and comments about the data analysis. In Table 2 we present the flux and position measurements for the individual components, and indicate by an asterisk those cases in which the core is likely to be detected (although lacking spectral indices for each component we cannot identify the cores definitely). Figure 1 shows the maps of the sources. The noise level in each observation can be deduced from Fig. 1, in which the lowest contour is 2.8 times the rms noise level. In some cases only point sources are visible. In these cases, however, there is sometimes an indication of further resolved structure which the observations do not have the spatial frequency coverage to map properly.

A few, mostly small, sources were also mapped using the MERLIN interferometer at L-band ($\sim$1.4 GHz). The dates and details of these observations are given in Table 3, and the resulting maps in Fig. 2.

Acknowledgements

The Very Large Array is operated by Associated Universities for Research in Astronomy Inc. under agreement with the National Science Foundation. MERLIN is operated as a National Facility by the University of Manch ester on behalf of the UK Particle Physics and Astronomy Research Council.

  

Table 1: Objects observed, together with the major and minor axis (in arcseconds) and position angle (in degrees) of the restoring beam. Epochs are numbered as follows: 1=1994 July 8; 2=1994 July 30; 3=1995 October 9; 4=1995 December 10

 

Table 1: continued

 

Table 1: continued

  

Table 2: Positions of sources observed with the VLA, together with flux (mJy)es derived from the maps (see text). Both peak and integrated fluxes are given. Probable cores are indicated by an asterisk

 

Table 2: continued

 

Table 2: continued

 

Table 2: continued

 

Table 2: continued

 

Table 2: continued

  

Table 3: Log of the MERLIN observations

  

Figure 1: VLA maps of the sources observed. The bottom contour is indicated on the map (in mJy) in each case, and is always 2.8 times the rms noise level. The contour levels are (-1, 1, 1.4, 2.03, 3.05, 4.7, 7.6, 12.5, 21.2, 37, 67, 123, 235 , 457, 915, 1880, 4000) times the bottom contour

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

 

Figure 1: continued

  

Figure 2: MERLIN maps of six small sources observed in Paper I. Contours are given at $f\times$ (-1, 1, 2, 4, 8, 16, 32...) where f = 1 mJy/beam (4C+00.15), 0.5 mJy/beam (4C+03.14), 0.7 mJy/beam (4C+00.31), 0.5 mJy/beam (4C-02.63), 0.3 mJy/ beam (4C-03.65), 1.5 mJy/beam (4C+00.80)