Mass Loss Rates, Ionization Fractions, Shock Velocities and Magnetic Fields of Stellar Jets
Hartigan, P. (Rice), Morse, J. (STScI), and Raymond, J. (CfA)
In this paper we calculate emission line ratios from a series of planar radiative shock models
that cover a wide range of shock velocities, preshock densities, and magnetic fields.
The models cover the initial conditions relevant to stellar jets, and we
show how to estimate the ionization fractions and shock velocities in jets directly from
observations of the strong emission lines in these flows.
The ionization fractions in the HH 34, HH 47, and HH 111 jets are ~ 2%, considerably smaller than
previous estimates, and the shock velocities are ~ 30 km/s . For each jet the ionization fractions were
found from five different line ratios, and the estimates agree to within a factor of ~ 2. The
scatter in the estimates of the shock velocities is also small (+/- 4 km/s).
The low ionization fractions of stellar
jets imply that the observed electron densities are much lower than the total densities, so the
mass loss rates in these flows are correspondingly higher (>~ 2x10^{-7} Msun/yr).
The mass loss rates in jets are a significant fraction (1% - 10%)
of the disk accretion rates onto young stellar objects that drive the outflows.
The momentum and energy supplied by the
visible portion of a typical stellar jet are sufficient to drive a weak molecular outflow.
Magnetic fields in stellar jets are difficult to measure because the line ratios from a radiative shock
with a magnetic field resemble those of a lower velocity shock without a field. The observed line fluxes
can in principle indicate the strength of the field if the geometry of the geometry of the shocks in the
jet is well-known.
(Journal of publication: ApJ 436, 125, 1994