Herschel Planetary Nebula Survey (HerPlaNS)
First detection of OH+ in planetary nebulae⋆
I. Aleman1, T. Ueta2,3⋆⋆, D. Ladjal2, K. M. Exter4, J. H. Kastner5, R. Montez Jr.6, A. G. G. M. Tielens1, Y.-H. Chu7, H. Izumiura8, I. McDonald9, R. Sahai10, N. Siódmiak11, R. Szczerba11, P. A. M. van Hoof12, E. Villaver13, W. Vlemmings14, M. Wittkowski15 and A. A. Zijlstra9
1 Leiden Observatory, University of Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
2 Department of Physics and Astronomy, University of Denver, 2112 E. Wesley Ave., Denver, CO 80210, USA
3 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yosinodai, Chuo-ku, Sagamihara, 252-5210 Kanagawa, Japan
4 Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
5 Chester F. Carlson Center for Imaging Science and Laboratory for Multiwavelength Astrophysics, Rochester Institute of Technology, 54 Lomb Memorial Drive, Rochester, NY 14623, USA
6 Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA
7 Department of Astronomy, University of Illinois, 1002 W. Green St., Urbana, IL 61801, USA
8 Okayama Astrophysical Observatory, National Astronomical Observatory of Japan, 3037-5 Honjo, Kamogata, Asakuchi, 719-0232 Okayama, Japan
9 Jodrell Bank Centre for Astrophysics, Alan Turing Building, The University of Manchester, M13 9PL, UK
10 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
11 N. Copernicus Astronomical Center, Rabianska 8, 87-100 Torun, Poland
12 Royal Observatory of Belgium, Ringlaan 3, 1180 Brussel, Belgium
13 Universidad Autónoma de Madrid, Dpto. Física Teórica, Módulo 15, Facultad de Ciencias, Campus de Cantoblanco, 28049 Madrid, Spain
14 Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
15 ESO, Karl Schwarzschild Str. 2, 85748 Garching bei München, Germany
Received: 29 October 2013
Accepted: 7 April 2014
Aims. We report the first detections of OH+ emission in planetary nebulae (PNe).
Methods. As part of an imaging and spectroscopy survey of 11 PNe in the far-IR using the PACS and SPIRE instruments aboard the Herschel Space Observatory, we performed a line survey in these PNe over the entire spectral range between 51μm and 672μm to look for new detections.
Results. 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, and NGC 6781. Excitation temperatures and column densities derived from these lines are in the range of 27–47 K and 2 × 1010–4 × 1011 cm-2, respectively.
Conclusions. 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.
Key words: astrochemistry / circumstellar matter / planetary nebulae: general / planetary nebulae: individual: NGC 6445 / planetary nebulae: individual: NGC 6720 / planetary nebulae: individual: NGC 6781
© ESO, 2014