Magnetized and Rotating Winds in Planetary Nebulae

Details Magnetized and Rotating Winds in Planetary Nebulae Magnetized and Rotating Winds in Planetary Nebulae

Nov 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998larm.confe..56g&link_type=abstract

"IX Latin American Regional IAU Meeting, "Focal Points in Latin American Astronomy", held in Tonantzintla, Mexico, Nov 9-13, 199

Astronomy and Astrophysics

Astronomy

Scientific paper

We present 2-dimensional magneto-hydrodynamical simulations of the evolution of planetary nebulae formed by two interacting stellar winds. Single stars with initial masses above 1.3 solar masses can achieve near-critical rotation rates during their ``superwind'' phase at the tip of the asymptotic giant branch (AGB). The resulting equatorially confined winds and leads to the typical hourglass shape found in many planetary nebulae, such as MyCn18. Following Chevalier & Luo (1994) and Rozyczka \& Franco (1996), we combine the effect of a magnetic field in the post-AGB wind with rotating AGB winds. We obtain highly collimated bipolar nebula shapes, reminiscent of M2-9 or He 2-437. For strong fields, ansae and jets in the polar regions of the nebula are formed, similar to those observed in IC 4593. Weaker fields are found to be able to account for the shapes of classical elliptical nebulae, e.g. NGC 6905, in the case of spherically symmetric AGB winds, which we propose for single stars with initial masses below 1.3 solar masses. Photoionization, via instabilities in the ionization-shock front, can generate irregularities in the shape of the simulated nebulae. In particular, it leads to the formation of cometary knots, similar to those seen in the Helix nebula (NGC 7293). This effect may also be responsible for large scale irregularities like those found in Sh 2-71 or WeSb 4. In this scenario, most planetary nebula morphologies can be obtained from single stars, and is consistent with the Galactic distribution of the different nebula types. Spherical and elliptical nebulae are ascribed to progenitor masses below 1.3 solar masses, with magnetic effects introducing ellipticities. Bipolar nebulae, on the other hand, are found to stem from progenitors with initial masses above 1.3 solar masses.

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