Astronomy and Astrophysics – Astronomy
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004apj...606..483l&link_type=abstract
The Astrophysical Journal, Volume 606, Issue 1, pp. 483-496.
Astronomy and Astrophysics
Astronomy
10
Stars: Agb And Post-Agb, Stars: Winds, Outflows
Scientific paper
A remarkably linear, bipolar, knotty jet was recently discovered in Hen 2-90, an object classified as a young planetary nebula. Using two-dimensional, magnetohydrodynamic simulations, we investigate periodic variations in jet density and velocity as the mechanism for producing the jet and its knotty structures. From a detailed comparison between the Hα emission derived from our models and the observations, we find that a nonmagnetized jet with density or velocity variations does not reproduce in detail the observed structure of the Hen 2-90 jet-a magnetized jet with periodic velocity variations is required. This jet has a radius of 125 AU, an average velocity of 300 km s-1 with periodic variations (period = 43 yr) in the jet velocity of amplitude +/-15 km s-1, and a toroidal magnetic field with a characteristic strength of 0.6 mG. The average mass-loss rate in the jet has decreased by about a factor of 3 in 600 yr (i.e., from 4.7×10-7 Msolar yr-1 at 20" to 1.7×10-7 Msolar yr-1 at 1" from the center along the jet axis). The progenitor asymptotic giant branch wind is assumed to have a mass-loss rate of 1.5×10-6 Msolar yr-1 (derived from the round, tenuous, Hα halo surrounding the central source) and a typical expansion velocity of 10 km s-1. We find a fairly detailed similarity in the physical properties of the jet in Hen 2-90 with that in the young stellar object HH 34. This similarity suggests that the jets in both objects may be launched in a similar manner, namely, from an accretion disk, despite the fact that these objects are at very different evolutionary stages.
Lee Chin-Fei
Sahai Raghvendra
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