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Proper motions and variability of the H2 knots in the HH 111 and 121 protostellar outflows

1998; Oxford University Press; Volume: 301; Issue: 1 Linguagem: Inglês

10.1046/j.1365-8711.1998.02146.x

1365-2966

K. E. K. Coppin, C. J. Davis, M. Micono,

Stellar, planetary, and galactic studies

The proper motions of molecular hydrogen knots in the HH 111 and HH 121 outflows have been measured. High tangential velocities, in the range 265–461 km s−1, are measured in both flows. These values exceed the dissociation speed limit for molecular hydrogen in shocks, and therefore indicate that the associated shock velocities are much lower than the shock pattern speeds and underlying jet speeds. The data seemingly support a variable flow velocity origin for the knots in the two outflows, though some of the knots could also be caused by Kelvin—Helmholtz instabilities. We also report on the marked variability in morphology and luminosity observed in a number of these knots. A molecular cooling time of the order of a few years is inferred, in line with theoretical predictions based on ‘typical’ jet densities and velocities.