The Delta V-L dependence and virial equilibrium of dense molecular-cloud cores

Details The Delta V-L dependence and virial equilibrium of dense molecular-cloud cores The Delta V-L dependence and virial equilibrium of dense molecular-cloud cores

Jan 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998arep...42...11p&link_type=abstract

Astronomy Reports, Volume 42, Issue 1, January 1998, pp.11-21

Astronomy and Astrophysics

Astronomy

1

Scientific paper

The dependence of the HCO+ and H13CO+ linewidths on the size of the emission region (Delta V ~ 2.9L^(0.5+/-0.1)) has been found for a sample of 12 dense molecular-cloud cores associated with Sharpless H II regions. Estimates of the core masses calculated in an isothermal dust component approximation are low if the dust temperature decreases toward the core boundary. If the core density profiles are described by a power law p propto r^-Beta, the exponent Beta has an upper limit Beta_max, which varies from 0.5 to 1.3 for the cores in the sample. It is not possible to obtain model spectra that agree with the observational data for Beta > Beta_max. The core masses are close to the virial masses for Beta = 0.5, indicating that the cores may be close to a critical state at the threshold of gravitational instability. The observed correlation between Delta V and L cannot be explained by the radial dependence of the velocity dispersion that results from the logotropic equation of state, which has recently been successfully used to explain similar dependences for both massive and low-mass cores. This may also testify that the dense cores studied are close to the critical state, in which the Delta V propto P_ext^1/4 L^1/2 relation is independent of the equation of state (where P_ext is the external pressure on the core). In this case, the mean external pressure for the sample cores should be P_ext / k ~ 5.9 x 10^6 cm^3 K.

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