Issue |
Astron. Astrophys. Suppl. Ser.
Volume 133, Number 3, December II 1998
|
|
---|---|---|
Page(s) | 381 - 386 | |
DOI | https://doi.org/10.1051/aas:1998328 | |
Published online | 15 December 1998 |
The density and shock characteristics of NGC 2818*
1
Instituto de Astronomia y Meteorologia, Avenida Vallarta 2602, Col. Arcos Vallarta, C.P. 44130 Guadalajara, Jalisco, Mexico
2
Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain
Send offprint request to: J.P. Phillips
Received:
26
January
1998
Accepted:
26
June
1998
We report the results of narrow band imaging of the bipolar outflow source
NGC 2818 in transitions of [NII], [OIII], [SII], and HI. As a consequence, we
are able to assess the overall excitation properties of the shell, and determine
that line ratios towards the nebular periphery are anomalous, and
characteristic of planar shocks with velocity km s-1.
Pre-shock
densities are likely to be modest, and of order
cm-3.
The [SII] imaging is further used to derive a fully-sampled map of electron
density, whence it is clear that the density structure is rather complex and
related to various features within the excitation maps. Peak values
cm-3 occur close to the nucleus, although densities subsequently decline for
major axis displacements
arcsec. The minor axis distribution, on the other
hand, appears to be somewhat more extended and bilobal.
It is probable that complexities in the density mapping reflect the presence of
condensations and filaments within the primary shell structure, and that these
are also responsible for apparent variations in density as a function of
forbidden and permitted line transition.
Key words: planetary nebula: NGC 2818 / ISM: jets and outflows
© European Southern Observatory (ESO), 1998