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Astron. Astrophys. 355, 688-698 (2000)


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Tomography of the low excitation planetary nebula NGC 40

F. Sabbadin 1, E. Cappellaro 1, S. Benetti 3, M. Turatto 1 and C. Zanin 2,4

1 Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy
2 Dipartimento di Astronomia, Universitá di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy
3 Telescopio Nazionale Galileo, Aptdo. Correos 565, 38700 Santa Cruz de la Palma, Canary Island, Spain
4 Institut für Astronomie der Leopold-Franzens-Universität Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria

Received 30 June 1999 / Accepted 19 November 1999

Abstract

Spatially resolved, long-slit echellograms at different position angles of the bright, low excitation planetary nebula NGC 40 indicate that the higher the gas excitation, the faster the radial motion, thus confirming the overturn of the Wilson law already suggested by Sabbadin & Hamzaoglu (1982).

New reduction procedures, giving the radial trends of the electron density and of the ionic and chemical abundances, were applied to NGC 40; they show that:

- the radial matter distribution has a sharp "bell" profile with peaks up to 4000 cm-3;

- the ionization structure is peculiar, indicating the presence of chemical composition gradients within the nebula: the innermost regions, hydrogen depleted, are essentially constituted of photospheric material ejected at high velocity by the WC8 nucleus.

Moreover, detailed H+, O[FORMULA] and N+ tomographic maps, giving the spatial ionic distributions at four position angles, are presented and discussed within the interacting winds evolutionary model.

Key words: ISM: planetary nebulae: individual: NGC 40 – ISM: kinematics and dynamics – ISM: abundances

Send offprint requests to: F. Sabbadin

© European Southern Observatory (ESO) 2000

Online publication: March 9, 2000

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