Unveiling shocks in planetary nebulae^⋆

¹ Instituto de Astrofísica de Andalucía, IAA-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: mar@iaa.es
² Instituto de Astrofísica de Canarias, IAC, Vía Láctea s/n, 38205 La Laguna, Spain
³ Departamento de Astrofísica, Universidad de La Laguna, 38200 La Laguna, Tenerife, Spain
⁴ Departamento de Física Aplicada, Facultade de Ciencias, Campus Lagoas-Marcosende s/n, Universidade de Vigo, 36310 Vigo, Spain
⁵ Consejo Superior de Investigaciones Científicas (CSIC), c/ Serrano 117, 28006 Madrid, Spain
⁶ Departament de Física i Enginyeria Nuclear, EUETIB, Universitat Politècnica de Catalunya, Comte d’Urgell 187, 08036 Barcelona, Spain
⁷ Departament d’Astronomia i Meteorologia, Universitat de Barcelona, Av. Diagonal 647, 08028 Barcelona, Spain
⁸ Instituto de Ciencias Nucleares, UNAM, Ciudad Universitaria, 04510 Mexico City, Mexico

Received: 26 April 2013
Accepted: 25 July 2013

Abstract

The propagation of a shock wave into a medium is expected to heat the material beyond the shock, producing noticeable effects in intensity line ratios such as [O iii]/Hα. To investigate the occurrence of shocks in planetary nebulae (PNe), we have used all narrow-band [O iii] and Hα images of PNe available in the HST archive to build their [O iii]/Hα ratio maps and to search for regions where this ratio is enhanced. Regions with enhanced [O iii]/Hα emission ratio can be ascribed to two different types of morphological structures: bow-shock structures produced by fast collimated outflows and thin skins enveloping expanding nebular shells. Both collimated outflows and expanding shells are therefore confirmed to generate shocks in PNe. We also find regions with depressed values of the [O iii]/Hα ratio which are found mostly around density bounded PNe, where the local contribution of [N ii] emission into the F656N Hα filter cannot be neglected.