The observations were performed in February 1996 with the 20-m radio telescope of Onsala Space Observatory in Sweden. The half-power beamwidth of the telescope is 40 at the CS and C34S frequencies (97981.00 MHz and 96412.98 MHz, respectively) and 35 at the CO frequency (115.3 GHz). The front-end was a 3 mm SIS receiver. The single side band system temperature referred to outside the atmosphere was 400 - 1000 K for CS, 200 - 300 K for C34S and 900 - 1900 K for CO observations depending on the weather conditions and source elevation. The backend was a 256 channel filterbank with 250 kHz resolution.
The observations were made mainly in the frequency switching mode with the frequency offset of 15 MHz. The CS spectra at the peak positions and a part of the C34S spectra were obtained using dual beam switching with a beam throw of 115. Initially, point CS maps with 40 spacing were obtained for all sources. Then, the mapping was continued according to the initial results and extended normally to 10% of the peak antenna temperature value. Pointing was checked periodically by observations of nearby SiO masers; the pointing accuracy was .
The standard chopper-wheel technique was used for the calibration. We express the results in the units of main beam brightness temperature () assuming the main beam efficiency () of 0.56 and 0.50 at the CS and CO frequencies, respectively (L.E.B. Johansson, private communication). The temperature scale was checked by observations of Orion A, which we observed also at SEST (Paper I). The comparison with the SEST data shows that the main beam temperatures in these lines agree to within a few percent at the two instruments (we have taken into account the different spectral resolutions in our SEST and Onsala observations).
Our source list is based on the Arcetri Atlas of galactic H2O masers (Comoretto et al. 1990; Palagi et al. 1993; Brand et al. 1994), which covers the declination range .The present observations were limited to the longitude range (approximately) and . We managed to observe almost all masers from this atlas satisfying these criteria; their coordinates are given in Table 1. A few objects (S 199, S 255) observed earlier at Metsähovi (Zinchenko et al. 1994) were omitted from the current list. NGC 281 was observed in C34S only since it was not detected in this line at Metsähovi.
We designate all the sources according to their galactic coordinates. The common identifications with some well known objects are given in the last column.
Probably not all of these sources are physically associated with the CS cores. However, in all cases where we obtained the CS maps, there are IRAS point sources located within the regions of the CS emission (Sect. 3). We consider this spatial coincidence as a sufficient indication of the physical relationship. In the other cases, where the CS maps have not been obtained, there are IRAS sources within 1 from the maser positions. Most probably they are physically related to the CS cores.
We have reduced the data and produced maps using the GAG (Groupe d'Astrophysique de Grenoble) software package. The measured spectra were fitted by one or more Gaussian components.
The next step in the data analysis was the derivation of the beam-averaged C34S column densities when possible. We have performed it in the LTE approximation. The column densities were found from the C34S line intensity integral assuming for the excitation temperature the value K (the dependence of the (CS) estimates on the assumed is rather weak; if increases to 20 K these estimates change by 35%).
We have calculated kinematic distances to our sources from the CS velocities according to the recommendations of Fich et al. (1989), i.e. for a flat rotation curve with kms-1 assuming a standard IAU value for R0 of 8.5 kpc. For some sources no solution could be found in the framework of this model.
The sizes, LTE masses, virial masses and mean densities were calculated as in Paper I using either these kinematic distances or, when available, spectrophotometric distances to the exciting stars of nearby H II regions. For Gaussian brightness distribution our procedure gives the size at the level. As in Paper II we use "deconvolved" sizes, being defined as where is the beam width at the same () level. Of course, this procedure accounts for the beam size only approximately because many cores are elongated or have rather complex brightness distribution. The density estimates have been corrected accordingly.
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