THE LINE WIDTH-SIZE RELATION IN MASSIVE CLOUD CORES

We report (CO)-C-13 and (CO)-O-18 line observations and maps in Orion A (L1641) and B (L1630). Together with already published observations, these data are used to study the line width-map size relation in mass ive star-forming regions. The nonthermal component of the line width ( Delta upsilon(NT)) in Orion cores follows the trend Delta upsilon(NT)s imilar to R(q) with q = 0.21 +/- 0.03, significantly different from q = 0.53 +/- 0.07 found in low-mass cores. These relations are analyzed in the context of an equilibrium model of a spherically symmetric dens e core which incorporates both thermal and nonthermal (''TNT'') motion s. The internal consistency of the TNT model and Delta upsilon(NT)-R d ata is shown. We present general formulae for the TNT model and apply them to the observational data. Differences in the slope and in the in tercept of the log Delta upsilon(NT)-log R relation between massive an d low-mass cores imply significant differences in density structure, p ressure profile, mass infall rate, and probably in the masses of stars which form. In particular, massive cores are denser and have steeper density profiles than low-mass cores. Visual extinction values predict ed by the TNT model for low mass and massive cores (3.3 and 16 mag, re spectively) are in good agreement with available observational estimat es for similar objects. The higher density and pressure in massive cor es lead to values for the infall time for 1 M. of similar to 7 x 10(4) yr, similar to 6 times shorter than in low-mass cores. Massive dense cores associated with embedded young stellar objects have physical pro perties almost identical to neighboring massive starless cores. Thus, the formation of a star or a small group of stars does not significant ly affect the initial physical conditions of the associated molecular cloud core. On the other hand, line widths of ammonia cores become nar rower as the distance from embedded young stellar clusters increases. In particular, the massive core farthest away from embedded clusters i s mostly thermal and its kinetic temperature is similar to 10 K, simil ar to 2 times lower than the typical kinetic temperature of massive co res.