[Previous] | [Session 14] | [Next]
T. Ueta, M. Meixner (UIUC), M. Bobrowsky (Orbital Sci. Corp.)
Proto-planetary nebulae (PPNe) are transitional post-asymptotic giant branch (AGB) stars (0.8 < M*/M\odot < 8.0) which have not yet reached the planetary nebula (PN) phase. The complete history of mass-loss in the AGB phase is imprinted on circumstellar neutral gas/dust shells surrounding the cool PPN central stars (T\rm eff < 104K). Therefore, studies of the circumstellar shells of PPN offer an opportunity to reveal the mass-loss history of the progenitor AGB star before the shells are processed by the hardened radiation or fast wind of a PN central star.
In this presentation, we report results from our HST WFPC2 snapshot survey of 27 PPNe and AGB stars, and these 0.1'' resolution images reveal the morphologies of PPN reflection nebulosities. Of the 27 sources, 21 are identified with remarkable reflection nebulosity, which comprises at least two distinct morphological groups: bipolar (9 sources) and star+elliptical (12 sources). The bipolar group is characterized by spectacular bipolar or quadrupolar nebulosities in which the central star is either obscured by a dust lane (e.g. IRAS~16342-3814, IRAS~17150-3224) or not (e.g. IRAS~19374+2359). The star+elliptical group is characterized by elliptical or multi-polar nebulosity with the central star prominently visible in the nebula core (e.g. IRAS~17436+5003, IRAS~22272+5435). Due to their broad dynamic range of surface brightness, the star+elliptical type nebulae would not have been seen without the high angular resolution of HST. We compare these results with a complementary mid-infrared survey of PPN dust shells (Meixner et al. 1998).
If you would like more information about this abstract, please follow the link to http://www.astro.uiuc.edu/. This link was provided by the author. When you follow it, you will leave the Web site for this meeting; to return, you should use the Back comand on your browser.
The author(s) of this abstract have provided an email address for comments about the abstract: ueta@astro.uiuc.edu