Astron. Astrophys. 321, 311-322 (1997)

2. Observations

The 133 and 157 GHz observations were made with the 12-m NRAO antenna at Kitt Peak. The beamwidth was at 133 GHz and at 157 GHz. The observations at both frequencies were performed with the 138-173 GHz dual polarisation SIS receiver in the position switching mode. The observations at 133 GHz were made during excellent weather conditions; typical system noise temperatures were 200 to 250 K. The system noise temperature at 157 GHz varied between 250-1000 K, depending on weather and elevation. The pointing accuracy was better than . The spectra were calibrated using the standard vane method. A 768-channel hybrid spectrometer was used at both frequencies, providing velocity resolution of 0.37 km s^-1 at 157 GHz and 0.22 km s^-1 at 133 GHz. See Slysh et al. (1995, 1996) for more information about the observations.

The 96 GHz observations were carried out in December 1994 using the 20-m millimetre-wave telescope of Onsala Space Observatory. The receiver was tuned to the rest frequency of the transition (96.74142 GHz). The main-beam efficiency and half-power beamwidth were 0.55 and , respectively. The pointing accuracy was . The observations were performed in a dual-beam switching mode with a beam separation of and a switch frequency of 2 Hz. A cryogenically cooled low-noise SIS mixer was used in the receiver. The single sideband receiver noise temperature was about 150 K. The system noise temperature, corrected for atmospheric absorption, rearward spillover and radome losses, varied between 290-900 K, depending on weather conditions and source elevation. The data were calibrated using the standard chopper-wheel method. The backend was a 256-channel filter spectrometer with 250 kHz frequency resolution. The line frequencies and strengths are presented in Table 1.

Table 1. Frequencies and line strengths of the transitions observed at 96 GHz (from Lees et al., 1973)

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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