Publications of the MPIfR
Optical & Infrared
Interferometry Group
Moraghan, A., Smith, M.D., Rosen, A.
Velocity study of axisymmetric protostellar
jets with molecular cooling
Monthly Notices of the Royal Astronomical Society
(MNRAS)
Vol. 371, Issue 3, pg.1448-1458 (2006)
Abstract
Jets of gas released from young stars excavate cavities and drive
bipolar outflows. The outflow properties may be related to the speed of
the jets. To test this, we study the propagation of supersonic
overdense jets through axisymmetric hydrodynamic simulations with
radiative cooling and chemistry, building on previous studies by
injecting molecular and atomic jets with a wide range of speeds,
between 50 and 300 km s-1, into both molecular and atomic media. We
show that the high collimation of outflows driven by molecular jets
holds for all jet speeds. At the higher speeds, we find that the jet
Mach number is the critical parameter which determines the shape of the
cavity and the cavity is filled with atomic gas. However, at low speeds
the jet material is the key factor with atomic jets producing much
wider cavities, whereas molecular jets produce narrow cool molecular
sheaths. A Mach disc is associated with the leading edge of the atomic
simulations, whereas oblique shocks which refocus the jet are found in
molecular flows. We also examine the mass spectra (distribution of mass
with radial velocity), generally finding quite shallow relationships
for all jet speeds (i.e the γ index is typically 1-2). Steep molecular
mass spectra are, however, associated with the
atomic-jet-molecular-medium combination. We conclude that the
properties of bipolar outflows possess signatures related to the jet
speed but are probably more sensitive to other factors.
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