Unveiling shocks in planetary nebulae

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]/Halpha. To investigate the occurrence of shocks in planetary nebulae (PNe), we have used all narrowband [O III] and Halpha images of PNe available in the HST archive to build their [O III]/Halpha ratio maps and to search for regions where this ratio is enhanced. Regions with enhanced [O III]/Halpha 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]/Halpha ratio which are found mostly around density bounded PNe, where the local contribution of [N II] emission into the F656N Halpha filter cannot be neglected.

13 pages, 9 figures, 3 tables; To appear in Astronomy & Astrophysics

References in corpus (3)

• Multiple and Precessing Collimated Outflows in the Planetary Nebula IC 4634
• Studies of NGC 6720 with Calibrated HST WFC3 Emission-Line Filter Images--I: Structure and Evolution
• Discovery of Multiple Shells Around the Planetary Nebula IC 418

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