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Session 7 - Gas and Dust in the ISM.
Display session, Monday, June 10
Great Hall,
O'Dell and Handron(1996) have analyzed images of NGC 7239 (Helix Nebulae) produced by the Hubble Telescope. The images show many equal sized, dark globules with bright rims pointing in the direction of the central star and with thicknesses small compared to the radii of the globules. The sizes, optical depth properties, and locations of the globules are consistent with the idea that they are produced by a Rayleigh-Taylor instability of an accelerating, cold, optically thick nebular shell. However the number of globules predicted by the theory based on acceleration by a combination of gas pressure and ion rocket effect is much greater than the several thousand estimated by O'Dell and Handron. The instability is reconsidered to include acceleration due to a wind from the central star and a wider range of nebular and central star characteristics. Closer agreement between theory and observation results. The results are also applied to accelerating clouds in the vicinity of O stars and compared to regions containing "Elephant Trunks" such as the "Eagle" Nebula.
