EDP Sciences
Free access
Volume 384, Number 3, March IV 2002
Page(s) 1062 - 1085
Section Diffuse matter in space
DOI http://dx.doi.org/10.1051/0004-6361:20020109

A&A 384, 1062-1085 (2002)
DOI: 10.1051/0004-6361:20020109

The 3-D ionization structure of the planetary nebula NGC 6565

M. Turatto, E. Cappellaro, R. Ragazzoni, S. Benetti and F. Sabbadin

Osservatorio Astronomico di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy

(Received 26 November 2001 / Accepted 21 January 2002 )

A detailed study of the planetary nebula NGC 6565 has been carried out on long-slit echellograms ( $\lambda$/ $\Delta\lambda=60\,000$, spectral range = $\lambda\lambda$3900-7750 Å) at six, equally spaced position angles. The expansion velocity field, the c(H $\beta$) distribution and the radial profile of the physical conditions (electron temperature and density) are obtained. The distance, radius, mass and filling factor of the nebula and the temperature and luminosity of the central star are derived. The radial ionization structure is analyzed using both the classical method and the photo-ionization code CLOUDY. Moreover, we present the spatial structure in a series of images from different directions, allowing the reader to "see" the nebula in 3-D. NGC 6565 results to be a young (2000-2500 years), patchy, optically thick triaxial ellipsoid ( a=10.1 arcsec, a/b=1.4, a/c=1.7) projected almost pole-on. The matter close to major axis was swept-up by some accelerating agent (fast wind? ionization? magnetic fields?), forming two faint and asymmetric polar cups. A large cocoon of almost neutral gas completely embeds the ionized nebula. NGC 6565 is in a recombination phase, because of the luminosity drop of the massive powering star, which is reaching the white dwarf domain ( $\log T_*\simeq 5.08$ K; $\log L_*/L_\odot\simeq 2.0$). The stellar decline started about 1000 years ago, but the main nebula remained optically thin for other 600 years before the recombination phase occurred. In the near future the ionization front will re-grow, since the dilution factor due to the expansion will prevail on the slower and slower stellar decline. NGC 6565 is at a distance of 2.0 ( $\pm$0.5) kpc and can be divided into three radial zones: the "fully ionized" one, extending up to 0.029-0.035 pc at the equator (0.050 pc at the poles), the "transition" one, up to 0.048-0.054 pc (0.080 pc), the "halo", detectable up to 0.110 pc. The ionized mass ( $\simeq$0.03  $M_\odot$) is only a fraction of the total mass ( $\ge$0.15  $M_\odot$), which has been ejected by an equatorial enhanced superwind of 4 ( $\pm$ $2) \times 10^{-5}~M_\odot$ yr -1 lasted for 4 ( $\pm$ $2) \times 10^3$ years.

Key words: planetary nebulae: individual: NGC 6565 -- ISM: kinematics and dynamics

Offprint request: M. Turatto, turatto@pd.astro.it

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