The Herschel Planetary Nebula Survey (HerPlaNS) is an imaging and spectroscopy survey of 11 planetary nebulae (PNe) in the far-IR using the PACS and SPIRE instruments aboard the Herschel Space Observatory. A line survey in these PNe over the entire spectral range between 51 μm and 672 μm revealed the first detections of OH+ emission in PNe. The rotational emission lines of OH+ at 152.99, 290.20, 308.48, and 329.77 μm were detected in the spectra of three PNe: NGC 6445, NGC6720, and NGC 6781. Excitation temperatures and column densities in the range of 27 - 47 K and 2×1010 - 4×1011 cm-2, respectively, were derived from these lines. In these objects, the OH+ rotational line emission is mostly likely produced in the photodissociation region (PDR). The emission of OH+ is observed only in PNe with hot central stars (Teff > 100000 K), with ring-like or torus-like structure. The fact that we do not detect OH+ in objects with Teff < 100000 K suggests that the hardness of the ionizing central star spectra (i.e. the production of soft X-rays, ≈ 100 - 300 eV) could be an important factor in the production of OH+ emission in PNe, as seems to be the case in recent OH+ detections in ultraluminous galaxies and supernovae remnants.
American Astronomical Society Meeting Abstracts #225
- Pub Date:
- January 2015