BIPOLAR JETS IN PLANETARY-NEBULAE - AN ANALYTICAL MODEL

Authors
Citation
G. Pascoli, BIPOLAR JETS IN PLANETARY-NEBULAE - AN ANALYTICAL MODEL, Journal of astrophysics and astronomy, 14(2), 1993, pp. 65-82
Citations number
71
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Astronomy & Astrophysics
ISSN journal
0250-6335
Volume
14
Issue
2
Year of publication
1993
Pages
65 - 82
Database
ISI
SICI code
0250-6335(1993)14:2<65:BJIP-A>2.0.ZU;2-Z
Abstract
The various and hitherto partially unsolved problems relative to the o rigin of bipolar jets or highly collimated fast outflows in planetary nebulae are reviewed within the framework of a stationary magnetohydro dynamic model. In order to explain the observations of high polar velo cities and the presence of polar blobs or knots in planetary nebulae, theoretical models are proposed taking into account both a large scale azimuthal magnetic field and an anisotropic turbulent velocity field. The models predict equatorial-to-polar density ratios which are rathe r small, in the range 2 to 3. Conversely, the polar-to-equatorial velo city contrasts are higher, with typical values upto 10. Thus the ad ho c hypothesis implicit in the literature that the density contrast is v arying in inverse ratio to the velocity one, does not seem well adapte d to the bipolar jet phenomenon in planetary nebulae. We point out, th erefore, that the bipolar jets have to be considered as a transient as pect of a very complex phenomenon. The model can be applied to objects such as He 2-104 or Mz3, M2-9.