Physical Properties and Kinematics of Dense Cores Associated with Regions of Massive Star Formation from the Southern Sky

Abstract

The results of spectral observations in the $\sim 84-92$ GHz frequency range of six objects in the southern sky containing dense cores and associated with regions of massive stars and star clusters formation are presented. The observations were carried out with the MOPRA-22m radio telescope. Within the framework of the local thermodynamic equilibrium (LTE) approximation, the column densities and abundances of the H${}^{13}$CN, H${}^{13}$CO${}^{+}$, HN${}^{13}$C, HC${}_3$N, c-C${}_3$H${}_2$, SiO, CH${}_3$C${}_2$H and CH${}_3$CN molecules are calculated. Estimates of kinetic temperatures ($\sim 30-50$ K), sizes of emission regions ($\sim 0.2-3.1$ pc) and virial masses ($\sim 70-4600M_{\odot }$) are obtained. The line widths in the three cores decrease with increasing distance from the center. In four cores, asymmetry in the profiles of the optically thick lines HCO${}^{+}$(1-0) and HCN(1-0) is observed, indicating the presence of systematic motions along the line of sight. In two cases, the asymmetry can be caused by contraction of gas. The model spectral maps of HCO${}^{+}$(1-0) and H${}^{13}$CO${}^{+}$(1-0), obtained within the framework of the non-LTE spherically symmetric model, are fitted into the observed ones. The radial profiles of density ($\propto r^{-1.6}$), turbulent velocity ($\propto r^{-0.2}$), and contraction velocity ($\propto r^{0.5}$) in the G268.42--0.85 core have been calculated. The contraction velocity profile differs from that expected both in the case of free fall of gas onto a protostar ($\propto r^{-0.5}$), and in the case of global core collapse (contraction velocity does not depend on distance). A discussion of the obtained results is provided.

49 pages, 10 figures

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