@article{article9ae319da,
title   = {Three-Dimensional photoionization structure ande distances of planetary nebulae. IV. NGC 40},
author = {Monteiro, Hektor and Gonçalves, Diego Antonio Falceta},
year = {2011},
doi = {10.1088/0004-637X/738/2/174},
journal   = {The Astrophysical Journal}
}