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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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