@misc{misc3a5b5e16,
title   = {Are all annular planetary nebulae really closed shells?},
author = {Monteiro, H. and Gruenwald, Ruth Bomfim and Morisset, C and Viegas, Sueli Maria Marino},
year = {2002},
booktitle   = {Reunión Regional Latinoamericana de Astronomía Unión Astronómica Internacional}
}