Hubble Space Telescope Observations of New Rings in AGB Stars, PPN and PN

摘要

Many planetary nebulae (PNe) show rings and shells related to the remnants of the circumstellar envelopes of the asymptotic giant branch (AGB) phase. We have extensively analysed the Hubble Space Telescope (HST) archives and found ringlike structures in several PNe. Following the image analysis described in Corradi et al. (2004), and using unsharp masking techniques, it was possible to enhance the ring structures. In this study, we also find new rings in pre-planetary nebulae (PPNe) and some AGB and post-AGB stars.