![]() | ![]() |
Astron. Astrophys. 339, 872-879 (1998) 4. Discussion and conclusionsThe CS(2-1) and CS(3-2) peak line temperatures
( The ratio of CS(3-2) to 13CO antenna temperature (using the 13CO value of MWW) is 0.08, about a factor 5 lower than the mean value found in the Cesaroni et al. sample. This may suggest that CS is depleted close to the ionization front, as also suggested by the LVG model. Our higher resolution observations of the CS(2-1), (3-2) and (5-4)
rotational transitions of the hotspot have confirmed that the
blister-type HII region has evacuated a cavity and
formed a sharp dense front at the edge of an extended molecular cloud,
particularly intense in the S-SW part. The morphology confirms that
A-NIR is the stellar source responsible for the heating source of the
dust emitting in the far IR and, in turn, of the hotspot , as
discussed by MWW. To estimate hydrogen densities we position-averaged
the spectra in different regions, to mitigate the effects of
undersampling at the higher frequency CS transitions, and compared the
resulting spectra with a set of LVG models at fixed temperature. We
thus found densities of order of
The mean electron density in source A is At the southern edge of source A, both the integrated line intensity (i.e., column density) and the line-width of CS(2-1) and (3-2) are enhanced. This effect is more pronunced at blue-shifted velocities, where the integrated intensity shows a sharp edge, almost bordering source A. Line profiles show some degree of asymmetry, consistent in some cases with a two-components Gaussian fit. We interpret these effects as an indication of shocked molecular gas in a shell around the blister being accelerated away and towards us. The line profiles associated with the NW part of our maps are consistent with a single component, and emission is observed at less blueshifted velocities. This molecular gas is thus likely to be associated with the remnant of the dense clump from which A-NIR originally formed. The coincidence of the NW clump with source B still leaves open the query if this non-thermal source is associated with it or not. ![]() ![]() ![]() ![]() © European Southern Observatory (ESO) 1998 Online publication: October 22, 1998 ![]() |