Astron. Astrophys. 339, 872-879 (1998)

2. Observations

The multi-transition C³²S observations of the hotspot were carried out using the IRAM 30-m telescope on Pico Veleta in October 1996. We observed the CS , 3-2 and 5-4, with rest frequencies of 97.981, 146.969 and 244.936 GHz, respectively. The corresponding half power beam widths (HPBW) of the 30-m at those frequencies are , , and , respectively.

The front-end receivers employed SIS mixers with system temperatures in the ranges 230-350 K at 3 mm, 250-800 K at 2 mm (in a few spectra  K), and about 650-3000 K at 1.3 mm, after correction for atmosphere and telescope efficiency. Our spectrometers were two filter-banks with 1 MHz resolution (one of which was split into two parts to cover both the (2-1) and (3-2) lines) and two autocorrelators. The bandwidths used in the observations are listed in Table 1, together with the corresponding central frequencies and spectral resolutions.

Table 1. Frequency setups used for the transitions observed: the first number is the frequency at which the spectrum was centred, the second indicates the bandwidth, and the third is the spectral resolution. All values are in MHz

The integration time used for the single-scan varied from 2 to 4 minutes in total power mode, and beam chopping was carried out by using the wobbler (i.e. a nutating secondary). The intensity scale in our spectra is given in main beam brightness temperature, . The achieved sensitivities in this scale for integration times varying from 12 min to 44 min were 0.03 K to 0.066 K. The flux density to main beam brightness temperature ratio for a point source, , was 4.7 Jy/K (wavelength independent). The positions of source A and B (from TOHTFG) are listed in Table 2.

Table 2. Coordinates of radio continuum sources A and B

We obtained further data on the CS(2-1) transition in January 1998 with the 13.7-m telescope of the Five College Radio Astronomy Observatory ¹ (FCRAO) in New Salem (U.S.A.), using the new SEQUOIA 32 element focal plane array, although for the present observations only 12 elements were actually used.

The integration time used for the single-scan was about 23 minutes in frequency switching mode, using a frequency throw of 4 MHz. The HPBW at the frequency of the CS(2-1) line of the FCRAO telescope is about , and the map was carried out using Nyquist sampling. The main beam efficiency used to convert the antenna temperature, , to main beam brightness temperature is .

© European Southern Observatory (ESO) 1998

Online publication: October 22, 1998
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