Steffen W, Espíndola M, Martínez S, Koning N. The 3D velocity structure of the planetary nebula NGC 7009. RevMexAA [Internet]. 2010 Nov. 22 [cited 2024 May 6];45(2). Available from: https://www.revistas.unam.mx/index.php/revmexaa/article/view/20594