Year: 2000
Type: article
Abstract: 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 × 10 3 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 Δ T e / T e ~ 0.035 throughout much of the shell, although here again T e rises by ~14% a little to the southeast of the nucleus, an enhancement which may also extend northwest and southeast along P.A. = 135°. 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 Δ A v ~ ±0.1 mag. There appears to be evidence for a band of extinction with amplitude Δ A v ~ 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.
Source: The Astrophysical Journal
DOI: 10.1086/317140
Authors: L. Cuesta, J. P. Phillips
Institution: Instituto de Astrofísica de Canarias
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2035928721