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| Paper: |
Studying the Fast Wind in PPNs via H2 |
| Volume: |
313, Asymmetrical Planetary Nebulae III |
| Page: |
175 |
| Authors: |
Hrivnak, B.J.; Kelly, D.M.; Su, K.Y.L. |
| Abstract: |
H2 emission can be used in proto-planetary nebulae (PPNs) to
trace the interaction of a fast wind from the star with the slowly
moving AGB wind. We review the results of recent surveys of
H2 in PPNs. In PPNs of F-G spectral types, it is almost
exclusively those with bipolar lobes and an optically-thick equatorial
structure (torus) that show H2 emission. On the other hand,
almost all PPNs of B spectral type show H2 emission. The
excitation mechanism is primarily collisional in the former case and
radiative in the latter. HST imaging shows that the emission comes from
the lobes in the F-G cases. A model for the evolution of H2
emission in PPNs is discussed. The fast wind appears to begin as early
as mid-G for PPNs with an optically-thick torus. |
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