Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997hst..prop.7284f&link_type=abstract
HST Proposal ID #7284
Astronomy and Astrophysics
Astronomy
Hst Proposal Id #7284 Stellar Ejecta
Scientific paper
Photoionization models of gaseous nebulae are widely used across much of galactic and extragalactic astronomy, but the discordance in recent composition estimates in Orion and NGC 7009 {tentatively attributed to temperature fluctuations} and the imagery revealing surprising complexity in many other objects points to basic deficiencies. Fortunately, Nature has provided us with a nearly spherically symmetric, thin shell planetary nebula, Abell 39. There are no obvious geometrical or hydrodynamical complications -- this object appears to be strikingly simple. HST/STIS observations of Abell 39, to obtain the critical UV spectra, combined with ground-based optical spectra, offer a clean test of whether we can realistically expect to reproduce nebular spectra, or whether there are remaining fundamental problems not due to geometrical/dynamical issues. The answer to this question has profound implications to such diverse questions as galactic abundance gradients or the primordial helium abundance.
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