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B. Balick, J. M. Wilson (University of Washington)
Deep Hubble images of NGC~6543 reveal a series of regularly spaced circular concentric ``rings'' that surround the famous Cat's Eye nebula. The rings seen in the lines of H\alpha, [O III], and [N II] but not the continuum. These photoionized rings are almost certainly the result of periodic spherical mass pulsations by the nucleus before the Cat's Eye formed.
A good fit to the observed H\alpha surface brightness distribution is obtained if the bubbles were ejected with constant mass, thickness, and ejection velocity. The model can be used to estimate the total mass of the rings, ~ 0.1M\sun, which lies between that of the core (~ 0.05 M\sun) and the surrounding halo (~0.5 M\sun). Assuming an ejection speed of 10 km s-1 the interpulse period is 1500 ±300 y, the same as the expansion age of the core itself.
Hubble images of other planetaries displayed on the poster, IC 418, NGC 7027, and Hubble 5 (a bipolar) show similar sets of multiple concentric rings. Hence, it appears, regular isotropic AGB mass pulses often precede the formation of brighter and more complex PN cores. However, the interpulse time scale, ~103 y, is a serious problem for extant models of core thermal pulses and surface pulsations. The cores of PNe seem to form in an abrupt change of mode of mass loss, as predicted by disrputive binary companion merger models.
A preprint is available from ftp://ftp.astro.washington.edu/pub/users/balick/6543paper. Financial support from NASA/STScI grant GO~7501 is very gratefully acknowledged.
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