2. Instrument and observing technique
The observations were made during June and July 1996 using the 13.7 m radome enclosed radio telescope placed at the Itapetinga Radio Observatory. The radiotelescope resolution at the NH3(1,1) transition is 4.2 arc min. The receiver front-end consisted of a cooled HEMPT amplifier giving 50 db total gain. The single side band receiver temperature was typically 90 K and the total system temperature oscillated between 130 and 220 K. A circularly polarized corrugated horn was used in the observations. The aperture and beam efficiency were 0.37 and 0.63 respectively. The back-end was an acousto-optical spectrometer with 70 kHz resolution and total bandwidth of 41 MHz. The central frequency and frequency resolution were frequently checked by injecting monochromatic signals at the intermediate frequency stage. The spectra were taken using the ON-OFF total-power observing technique, switching between positions every 20 s. The signal was calibrated against a 15 K noise source and a room temperature load, to obtain the gain and correct for atmospheric attenuation (Abraham and Kokubun, 1992). Systematic observations of the transitions (J,K) = (1,1), (2,2) and (3,3) toward NGC 6334 and Orion A, which are well known NH3 sources, were performed in order to check the absolute intensity. The observations were made with the sources above in elevation and special care was taken to guarantee that the OFF position, generally 20' away in azimuth, fell outside the HII region. Also, we did not detect any absorption features, as would be observed if the molecular cloud were included in the OFF position and even small velocity gradients were present in the cloud.
© European Southern Observatory (ESO) 2000
Online publication: March 21, 2000