Bibcode
Phillips, J. P.; Cuesta, L.; Ortega, V.
Referencia bibliográfica
Monthly Notices of the Royal Astronomical Society, Volume 322, Issue 4, pp. 866-876.
Advertised on:
4
2001
Número de citas
1
Número de citas referidas
1
Descripción
The low excitation properties of the planetary nebula (PN) NGC 6720 are
known to be unusual, and to imply large ring/core emission ratios. We
point out that such characteristics are by no means confined to this
source alone, and that high ratios may occur in a large fraction of
elliptical and circular PNe. Such trends may arise because of the
presence of thin low-excitation emission sheets `wrapped' within and
around the primary outflows. The widths of such shells are required to
be exceedingly small, and may (for certain cases) be of order
<<10-2pc. Such a mechanism appears capable of
explaining most of the observed emission properties, and may arise
through shock interaction between differing envelopes. Alternative
explanations in terms of bipolar or cylindrical outflows are shown to be
implausible.