I. Data overview and analysis demonstration with NGC 6781
1 Department of Physics and Astronomy, University of Denver, 2112 E. Wesley Ave., Denver CO 80210, USA
2 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara 252-5210, Japan
3 Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
4 Academia Sinica, Institute of Astronomy and Astrophysics, Taiwan
5 N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland
6 Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
7 Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels, Belgium
8 Rochester Institute of Technology, 54 Lomb Memorial Dr., Rochester NY 14623, USA
9 Department of Physics and Astronomy, Vanderbilt University, Nashville TN 37235, USA
10 Jodrell Bank Centre for Astrophysics, Alan Turing Building, Manchester M13 9PL, UK
11 ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
12 Leibniz-Institut für Astrophysik Potsdam (AIP), an der Sternwarte 16, 144 82 Potsdam, Germany
13 Department of Physics and Astronomy, Division of Astronomy & Space Physics, Uppsala University, Box 515, 751 20 Uppsala, Sweden
14 Department of Physics & Astronomy, Macquarie University, Sydney NSW 2109, Australia
15 Departamento de Física Teórica, Universidad Autónoma de Madrid, Cantoblanco 28049 Madrid, Spain
16 Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana IL 61801, USA
17 Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
18 Okayama Astrophysical Observatory (OAO), National Astronomical Observatory of Japan (NAOJ), 3037-5 Honjo, Kamogata, Asakuchi, 719-0232 Okayama, Japan
19 Jet Propulsion Laboratory, MS 183-900, California Institute of Technology, Pasadena CA 91109, USA
20 Instituto de Astronomía, Universidad Nacional Autónoma de México, Campus Ensenada, CP 22800 Baja California, México
21 Department of Astronomy, University of Washington, Seattle WA 98195-1580, USA
22 Physics Department, Technion, 32000 Haifa, Israel
23 Department of Physics and Astronomy, University of Rochester, Rochester NY 14618, USA
24 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS-65, Cambridge MA 02138, USA
25 School of Physics and Astronomy, EC Stoner Building, University of Leeds, Leeds LS2 9JT, UK
26 Center for Computational Relativity and Gravitation, Rochester Institute ofTechnology, Rochester NY 14623, USA
27 Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach, 1312 85741 Garching, Germany
Received: 10 January 2014
Accepted: 14 March 2014
Context. This is the first of a series of investigations into far-IR characteristics of 11 planetary nebulae (PNe) under the Herschel Space Observatory open time 1 program, Herschel Planetary Nebula Survey (HerPlaNS).
Aims. Using the HerPlaNS data set, we look into the PN energetics and variations of the physical conditions within the target nebulae. In the present work, we provide an overview of the survey, data acquisition and processing, and resulting data products.
Methods. We performed (1) PACS/SPIRE broadband imaging to determine the spatial distribution of the cold dust component in the target PNe and (2) PACS/SPIRE spectral-energy-distribution and line spectroscopy to determine the spatial distribution of the gas component in the target PNe.
Results. For the case of NGC 6781, the broadband maps confirm the nearly pole-on barrel structure of the amorphous carbon-rich dust shell and the surrounding halo having temperatures of 26−40 K. The PACS/SPIRE multiposition spectra show spatial variations of far-IR lines that reflect the physical stratification of the nebula. We demonstrate that spatially resolved far-IR line diagnostics yield the (Te, ne) profiles, from which distributions of ionized, atomic, and molecular gases can be determined. Direct comparison of the dust and gas column mass maps constrained by the HerPlaNS data allows to construct an empirical gas-to-dust mass ratio map, which shows a range of ratios with the median of 195 ± 110. The present analysis yields estimates of the total mass of the shell to be 0.86 M⊙, consisting of 0.54 M⊙ of ionized gas, 0.12 M⊙ of atomic gas, 0.2 M⊙ of molecular gas, and 4 × 10-3 M⊙ of dust grains. These estimates also suggest that the central star of about 1.5 M⊙ initial mass is terminating its PN evolution onto the white dwarf cooling track.
Conclusions. The HerPlaNS data provide various diagnostics for both the dust and gas components in a spatially resolved manner. In the forthcoming papers of the HerPlaNS series we will explore the HerPlaNS data set fully for the entire sample of 11 PNe.
Key words: infrared: stars / planetary nebulae: general / stars: winds, outflows / stars: mass-loss / planetary nebulae: individual: NGC 6781 / circumstellar matter
Herschel is an ESA Space Observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Table 2 and appendices are available in electronic form at http://www.aanda.org
© ESO, 2014