We report the first detections of OH+emission in planetary nebulae (PNe). As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the PACS and SPIRE instruments aboard the... Show moreWe report the first detections of OH+emission in planetary nebulae (PNe). As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the PACS and SPIRE instruments aboard the HerschelSpace Observatory, we performed a line survey in these PNe over the entire spectral range between 51μm and 672μm to look for new detections. The rotational emission lines of OH+ at 152.99, 290.20, 308.48, and 329.77μm were detected in the spectra of three planetary nebulae: NGC 6445,NGC 6720, andNGC 6781. Excitation temperatures and column densities derived from these lines are in the range of 27–47 K and 2E10–4E11cm^-2, respectively. In PNe, the OH+ rotational line emission appears to be produced in the photodissociation region (PDR) in these objects. The emission of OH+ is observed only in PNe with hot central stars (Teff>100 000 K), suggesting that high-energy photons may play a role in OH+ formation and its line excitation in these objects, as seems to be the case for ultraluminous galaxies. Show less
