Abstract. To provide a detailed comparison between the performances of the MOPRA and SEST telescopes at frequencies of 85-113 GHz we have repeated part of the spectral survey of molecular absorption lines which was carried out by Greaves & Nyman (1996) with the SEST 15-m telescope using SgrB2 as background source. They detected 17 transitions from 11 different molecules and their variants (HCO+, HCN, HNC, CN, CCH, C3H2, CS, SiO, N2H+, CH3OH and SO) with integration times of 0.25-3 hours. The result is a uniformly calibrated data set which provides an understanding of the chemistry in the absorption clouds located in the foregroud spiral arms (often called `spiral arm clouds'), although their dynamics are not well understood.
Observations. 1-6 June and 15-19 August 1997, BW = 128 MHz, 256 channels, position switching
| Line Calibrators* | R.A. (1950.0) | Dec. (1950.0) | SEST Spectra | |
|---|---|---|---|---|
| Orion SiO | 05h 32m 47.0s | -05d 24' 23" | here | |
| IRC+10216 | 09h 45m 15.0s | +13d 30' 45" | here | |
| M17SW | 18h 17m 30.0s | -16d 15' 19" | here | |
| Observed Sources | R.A. (1950.0) | Dec. (1950.0) | - | |
| SgrB2 | 17h 44m 10.6s | -28d 22' 03" | - | |
| Transition | Frequency (GHz) | TA* Peak (K) | V Peak (km/s) | TA* Int (K km/s) | Observing Method | Band | Emission Spectra | Absorption Spectra | |
|---|---|---|---|---|---|---|---|---|---|
| C3H2(2-1) | 85.338905 | - | - | - | on-off | LSB | 1 | ||
| H13CO+(1-0) | 86.7543 | - | - | - | on-off | LSB | 1 | ||
| SiO(v=0,2-1) | 86.847 | - | - | - | on-off | LSB | LRS | ||
| HCN(1-0) | 88.631 | - | - | - | on-off | USB | 1, 2 | 3, 4, 5 | |
| " | " | - | - | - | " | (+70 km/s) | 1, 2 | 3 | |
| HCO+(1-0) | 89.188518 | - | - | - | on-off | LSB | 1 | 2, 3 | |
| HNC(1-0) | 90.663543 | - | - | - | on-off | USB | 1 | ||
| 13CS(2-1) | 92.4943 | - | - | - | on-off | USB | 1, 2 | ||
| N2H+(1-0) | 93.174 | - | - | - | on-off | USB | 1 | ||
| " | " | - | - | - | " | (+70 km/s) | 1, 2 | ||
| " | " | - | - | - | " | (-70 km/s) | 1, 2 | ||
| C34S(2-1) | 96.413 | - | - | - | on-off | USB | LRS | ||
| CH3OH | 96.741 | - | - | - | on-off | USB | 1, 2, 3 | ||
| CS(2-1) | 97.980968 | - | - | - | on-off | USB | 1, 2, 3 | 4 | |
| SO(3-2) | 99.299879 | - | - | - | on-off | USB | 1, 2 | ||
| C18O(1-0) | 109.7822 | - | - | - | on-off | USB | 1, 1 | ||
| 13CO(1-0) | 110.201 | - | - | - | on-off | USB | 1, 2, 3 | ||
| CH3CN(6-5) | 110.383 | - | - | - | on-off | USB | 1, 2 | ||
| CN(1-0) | 113.490 | - | - | - | on-off | USB | 1, 2 | ||
| " | " | - | - | - | " | (+70 km/s) | 1, 2 | ||
| " | " | - | - | - | " | (-70 km/s) | 1, 2 | ||
| CO(1-0) | 115.271 | - | - | - | on-off | LSB | 1, 2 | ||
B. Koribalski
