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Session 7 - Planetary & Other Nebulae.
Display session, Monday, June 09
South Main Hall,
This video shows the observed [O III] spatial structure of the jet and surrounding ovoid nebulosity in the R Aqr system as a function of 41 velocity planes spaced at 12 km s^-1 intervals (Fabry-Perot observations at the Palomar 60"). The ovoid nebulosity, due to an explosion \sim660 years ago, is modeled as a circular ring expanding at 55 km s^-1 as seen at an inclination angle i \simeq 70^\circ. The similarly inclined bipolar jet is modeled as a superposition of two opening helical structures -- a small-scale helix with an apex angle of 16^\circ which has undergone \sim2-5 turns, and a large-scale helix with an apex angle of 60^\circ which has undergone \sim 1/3 of a turn. One possible explanation for the small-scale jet structure is the following process (Koupelis amp; Van Horn, 1988, ApJ, 324, 93): a parcel of ejected dust and gas is emitted along the rotation axis of the rotating star-accretion disk system which anchors a magnetic field that is frozen into the rotating parcel as well as the central source; since the parcel is free to expand, its rotation rate decreases, and the field is twisted into a helix; the consequent increase in the azimuthal component of the magnetic field builds up a strong magnetic pressure behind the parcel and accelerates it along the jet. The large-scale structure of the jet may simply be due to precession of the accretion disk. Jet radial velocities are in the range \pm175 km s^-1, suggesting an outward accelerated flow maximum of \sim \pm512 km s^-1. The video shows the model and data for comparison.
