Electronic Resource
Palo Alto, Calif.
:
Annual Reviews
Annual Review of Astronomy and Astrophysics
40 (2002), S. 439-486
ISSN:
0066-4146
Source:
Annual Reviews Electronic Back Volume Collection 1932-2001ff
Topics:
Physics
Notes:
Abstract We review the state of observational and theoretical studies of the shaping of planetary nebulae (PNe) and protoplanetary nebulae (pPNe). In the past decade, high-resolution studies of PNe have revealed a bewildering array of morphologies with elaborate symmetries. Recent imaging studies of pPNe exhibit an even richer array of shapes. The variety of shapes, sometimes multiaxial symmetries, carefully arranged systems of low-ionization knots and jets, and the often Hubble-flow kinematics of PNe and pPNe indicate that there remains much to understand about the last stages of stellar evolution. In many cases, the basic symmetries and shapes of these objects develop on extremely short timescales, seemingly at the end of AGB evolution when the mode of mass loss abruptly and radically changes. No single explanation fits all of the observations. The shaping process may be related to external torques of a close or merging binary companion or the emergence of magnetic fields embedded in dense outflowing stellar winds. We suspect that a number of shaping processes may operate with different strengths and at different stages of the evolution of any individual object.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1146/annurev.astro.40.060401.093849
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