EDP Sciences
Free Access
Issue
A&A
Volume 436, Number 2, June III 2005
Page(s) 549 - 567
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361:20042447
Published online 30 May 2005


A&A 436, 549-567 (2005)
DOI: 10.1051/0004-6361:20042447

The 3-D shaping of NGC 6741: A massive, fast-evolving Planetary Nebula at the recombination-reionization edge

F. Sabbadin1, S. Benetti1, E. Cappellaro2, R. Ragazzoni3 and M. Turatto1

1  INAF - Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy
    e-mail: sabbadin@pd.astro.it
2  INAF - Osservatorio Astronomico di Capodimonte, via Moiariello 11, 80131 Napoli, Italy
3  INAF - Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Italy

(Received 29 November 2004 / Accepted 17 January 2005 )

Abstract
We infer the gas kinematics, diagnostics and ionic radial profiles, distance and central star parameters, nebular photo-ionization model, spatial structure and evolutionary phase of the Planetary Nebula NGC 6741 by means of long-slit ESO NTT+EMMI high-resolution spectra at nine position angles, reduced and analysed according to the tomographic and 3-D methodologies developed at the Astronomical Observatory of Padua (Italy).

NGC 6741 ( $\rm distance\simeq2.0$ kpc, $\rm age\simeq 1400$ yr, ionized mass $M_{\rm ion}\simeq 0.06~M_\odot$) is a dense (electron density up to 12 000 cm-3), high-excitation, almost-prolate ellipsoid ( $\rm0.036~pc \times 0.020~pc \times 0.018$ pc, major, intermediate and minor semi-axes, respectively), surrounded by a sharp low-excitation skin (the ionization front), and embedded in a spherical ( $\rm radius\simeq 0.080$ pc), almost-neutral, high-density ( $n{\rm (H\,I)}\simeq 7 \times10^3$ atoms cm-3) halo containing a large fraction of the nebular mass ( $M_{\rm halo}\ge 0.20~M_\odot$). The kinematics, physical conditions and ionic structure indicate that NGC 6741 is in a deep recombination phase, started about 200 years ago, and caused by the rapid luminosity drop of the massive ( $M_*=0.66{-}0.68~M_\odot$), hot (log $T_* \simeq 5.23$) and faint (log $L_*/L_\odot \simeq 2.75$) post-AGB star, which has exhausted the hydrogen-shell nuclear burning and is moving along the white dwarf cooling sequence. The general expansion law of the ionized gas in NGC 6741, $V_{\rm exp}$(km s $^{-1})=13 \times R\arcsec$, fails in the innermost, highest-excitation layers, which move slower than expected. The observed deceleration is ascribable to the luminosity drop of the central star (the decreasing pressure of the hot-bubble no longer balances the pressure of the ionized gas), and appears in striking contrast to recent reports inferring that acceleration is a common property of the Planetary Nebulae innermost layers. A detailed comparative analysis proves that the "U"-shaped expansion velocity field is a spurious, incorrect result due to a combination of: (a) simplistic assumptions (spherical shell hypothesis for the nebula); (b) unfit reduction method (emission profiles integrated along the slit); and (c) inappropriate diagnostic choice ($\lambda$4686 $\rm\AA $ of He II, i.e. a thirteen fine-structure components recombination line). Some general implications for the shaping mechanisms of Planetary Nebulae are discussed.


Key words: planetary nebulae: individual: NGC 6741 -- ISM: kinematics and dynamics

SIMBAD Objects



© ESO 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.