Scientific Colloquium
March 23, 2007

"Collimating Stellar Ejecta"

Energetic and highly collimated flows are frequent in Young Steller Objects (YSOs)
where an accretion disk of charged particles and lots of angular momentum are
readily available.  As it turns out, outflows with similar
collimation geometries, energies, and outflow speeds are also found
at the other end of evolutionary tracks in the H-R diagram; i.e.,
when highly evolved AGB stars shed their outer layers.  I shall
review the growing evidence that reveals the nature of the outflows.
Single stars are not believed to harbor energy reserves capable of
driving the collimated flows unless potential energy is released
somehow from the stellar core, transported in a very organized way to
the surface, and released into the winds.  Far more popular among
theorists today is the notion of energy and momentum extracted from
the common envelope of a close binary system.  I will review the
theoretical notions and critically compare them to the data.

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