Models for the structure and origin of bipolar nebulae
The appearance of bipolar nebulae-symmetric reflection nebulae centered on evolved, mass-losing stars-can most simply be accounted for in terms of an axisymmetric distribution of outflowing dust in which the dust is concentrated towards an equatorial plane and declines monotonically with latitude above that plane. The symmetrically placed ''horns'' that can be seen radiating out of some bipolar nebulae, notably GL 2688, are a natural consequence of such a dust distribution if, at some latitude, the radial optical depth to starlight falls rapidly below unity. Several models of bipolar nebulae are presented. These structural models for bipolar nebulae lead in turn to an investigation of how such a geometry might arise. Although nonradial pulsation, rotationally forced mass ejection by a single star, and mass loss from a common envelope binary are all considered, the most attractive origin for bipolar nebulae is a binary star system in which the primary is evolving up the red giant branch to the point at which its radius approaches its tidal radius. If this occurs before corotation of the primary with the secondary's orbit can be achieved, then matter from the primary's enveloped can be gravitationally ejected from the system by the secondary, the ejected material being concentrated toward the system's equatorial plane. Numerical models of this phenomenon show that gravitational ejection from an asynchronous binary system easily leads to terminal outflow velocities in the observed range (20--50 km s/sup -1/), and that the rate of mass loss and the time scale over which the mass ejection takes place are consistent with observations if the particle density in the outer layers of the primary's atmosphere from which the material is extracted is in the range 10/sup 14/--10/sup 15/ cm/sup -3/. If this hypothesis is applicable, bipolar nebulae will probably become planetary nebulae, as previously suggested on observational grounds.
- Research Organization:
- Department of Astronomy, Columbia University
- OSTI ID:
- 5425997
- Journal Information:
- Astrophys. J.; (United States), Vol. 249:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
BINARY STARS
THREE-BODY PROBLEM
NEBULAE
STAR EVOLUTION
ANGULAR MOMENTUM
COSMIC DUST
MATHEMATICAL MODELS
NUMERICAL ANALYSIS
PLANETARY NEBULAE
PULSATIONS
RED GIANT STARS
STELLAR WINDS
DUSTS
GIANT STARS
MANY-BODY PROBLEM
MATHEMATICS
STARS
640105* - Astrophysics & Cosmology- Galaxies