P. Cox 1, P.J. Huggins 2, F. Boulanger 1, D. Cesarsky 1, T. Forveille 3, & R. Bachiller 4
1 Institut d'Astrophysique Spatiale, Université de Paris XI, 91405 Orsay, France
2 Physics Department, New York University, 4 Washington Place, New York, NY 10003, USA
3 Observatoire de Grenoble, B.P. 53X, 38041 Grenoble Cedex, France
4 Observatorio Astronómico Nacional (IGN), Apt 1143, 28800 Alcalá de Henares, Spain
We will present ISO observations on the Helix, the nearest fully evolved planetary nebulae. The data which were obtained with ISOCAM, ISOPHOT and the LWS allow a detailed study of the physical conditions of the photodissociation region (mid-infrared H2 rotational lines, far-infrared cooling lines of [CII and [OI]), of the ionized gas (through the atomic lines) and of the nature of the dust in the envelope which was ejected during the AGB phase. These data are compare with maps in the CO(2-1) emission obtained with Catech Submillimeter Observatory and the IRAM 30-meter telescope.