3C 400.2 was observed in the 21-cm HI line using the Synthesis Telescope at the Dominion Radio Astrophysical Observatory (DRAO) (Roger et al. 1973; Veidt et al. 1985) in June 1995. The field of view is and the synthesized beam at the declination of 3C 400.2 is .
Spectral information on the HI 21-cm line was detected in a 128 channels digital spectrometer, which were spaced by 1.65 km s-1, covering the velocity range from -103.9 km s-1 to +105.6 km s-1 (all velocities are relative to the Local Standard of Rest).
The observed visibilities were calibrated and transformed into sky images using the standard software of DRAO. Radio continuum emission at 1420 MHz was subtracted from each line channel, and afterwards the HI line maps were corrected for the polar diagram of the antennas using a gaussian function of 105 arcmin FWHM. The data corresponding to shorter spacings were obtained from single dish HI observations carried out with the DRAO 26 m telescope using identical radial velocity and bandwidth parameters.
For presentation purposes, a constant background equal to the mean value of each channel map was subtracted from every map. Figure 2 shows the subtracted spectrum.
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