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Astron. Astrophys. 324, 203-210 (1997)

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3. Observations

The observations were made during several runs in 1985, 1986 and 1996 with the MPIfR antenna employing a maser receiver during the 1985-1986 and a HEMT receiver during the 1996 periods. At the rest frequency of the ([FORMULA]) = (1,1) and (2,2) lines of NH3 (23694.496 MHz and 23722.631 MHz, respectively) and of the J=9-8 line of HC5 N (23963.888 MHz) the FWHP beam size is 40 [FORMULA]. The zenith system temperature was around 60 K in good weather conditions on an atmosphere corrected antenna temperature ([FORMULA]) scale. The observations were made using position switching, with an integration time of typically 3 minutes on source. Spectral information was obtained with a 1024-channel three-level autocorrelation spectrometer. We observed the NH3 (1,1) and (2,2) lines simultaneously by splitting the autocorrelator into two spectrometers of 512 channels with bandwidths of 6.25 MHz and channel spacings of 0.154 km s-1. The velocity resolution was 0.185 km s-1, i.e. a factor 1.2 larger than the channel spacing. We observed the HC5 N line with the autocorrelator split into two parts, each with a bandwidth of 3.12 MHz and a velocity resolution of 0.092 km s-1. The spectra from the two split parts were then co-added in order to reduce the noise. The intensity scale of the spectra was calibrated on the continuum sources NGC7027, 3C123 and 3C286, according to the flux densities given by Baars et al. (1977 ). The pointing accuracy was better than 10 [FORMULA], corresponding to a point source flux density error of [FORMULA] 15%. The calibration accounted for the dependence of the gain on the elevation. Total flux density uncertainties are of the order of 20%.

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998