The low-excitation structures of planetary nebulae
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
Phillips, J. P. et al.
Fecha de publicación:
4
2001