Initial Conditions and Motions in Star-Forming Dense Cores

Details Initial Conditions and Motions in Star-Forming Dense Cores Initial Conditions and Motions in Star-Forming Dense Cores

Aug 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999pcim.conf..227m&link_type=abstract

The Physics and Chemistry of the Interstellar Medium, Proceedings of the 3rd Cologne-Zermatt Symposium, held in Zermatt, Septemb

Physics

13

Scientific paper

We review properties of dense cores as traced by molecular spectral lines sensitive to gas density > 10 ^4 cm ^{-3}. Cores span a range of properties which can be classified according to the proportion of thermal and turbulent motions in their line widths. ``Thermal" or ``low-mass" cores are dominated by thermal motions, are found in complexes with little evidence of clustering, and have 0-2 associated stars. They have size ~ 0.05 pc, kinetic temperature 10 K, and visual extinction 3 - 10 mag. ``Turbulent" or ``massive" cores are dominated by turbulent motions, are found in complexes which have formed clusters, and have 1-100 assocated stars. They have size ~ 0.1 pc, kinetic temperature 15-100 K, and visual extinction 10-50 mag. Turbulent cores may form stars differently from thermal cores, by producing ``kernels" or quiescent condensations which are cut off from MHD waves in the core. The motions which form cores and stars are now becoming evident through spectroscopic observations of ``infall asymmetry." By comparing the spectral profiles of optically thick and thin lines, it is possible to discern inward motions toward cores which have formed groups of stars, single stars, and toward ``starless cores" which have not yet formed any star. On scales of a few 0.01 pc, such infall asymmetry shows central concentration indicative of gravitational infall, with speeds of order 0.1 km/s. However, on larger scales of 0.1 pc, infall asymmetry in some cores is more extended than expected from star-forming gravitational infall and faster than expected from ambipolar diffusion. If these motions are driven by pressure rather than gravity, they may arise from "turbulent cooling flows" associated with the local dissipation of turbulence.

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