Bibcode
DOI
Cuesta, L.; Phillips, J. P.
Bibliographical reference
The Astrophysical Journal, Volume 543, Issue 2, pp. 754-763.
Advertised on:
11
2000
Journal
Citations
18
Refereed citations
17
Description
We have observed the planetary nebula NGC 2440 in the transitions [O II]
λ3727, He II λ4686, [O III] λλ(4363+5007), H
I λλ(4861+6563), He I λ5876, [N II] λ6584,
[S II] λλ(6717+6731), and [S III] λ9061, as well as
in various continuum filters. As a result, we are able to evaluate the
excitation structure of the source and determine the projected
variations in density, extinction, and temperature. Density is found to
have a bilobal structure at the nucleus, where peak values approach
2×103 cm-3, and thereafter decline to ~500
cm-3 for distances ~+/-12" from the central star. Densities
for larger spatial offsets appear more uniform, although the maps reveal
evidence for appreciable small-scale clumping. Electron temperatures
appear to vary by no more than ΔTe/Te~0.035
throughout much of the shell, although here again Te rises by
~14% a little to the southeast of the nucleus, an enhancement which may
also extend northwest and southeast along P.A.=135deg.
Finally, it is noted that, as in the case of extinction and density, the
extinction is prone to small but quite rapid variations over the
projected surface of the source by of order ΔAv~+/-0.1
mag. There appears to be evidence for a band of extinction with
amplitude ΔAv~0.2 mag along the minor axis of the
exterior bilobal flow and for a possible extinction deficit associated
with the interior bilobal flow. We discuss possible scenarios for the
formation of this multipolar nebula in the context of the present
results.