2002A&A...384.1062T

A detailed study of the planetary nebula NGC 6565 has been carried out on long-slit echellograms (λ/Δλ=60000, spectral range = λλ3900-7750 Å) at six, equally spaced position angles. The expansion velocity field, the c(Hβ) 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 (logT<sub>*</sub>≃5.08K; logL<sub>*</sub>/L<sub>☉</sub>≃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 (±0.5) kpc and can be divided into three radial zones: the ``fully ionized'' one, extending up to 0.029-0.035pc at the equator (0.050pc at the poles), the ``transition'' one, up to 0.048-0.054pc (0.080pc), the ``halo'', detectable up to 0.110 pc. The ionized mass (≃0.03M_☉) is only a fraction of the total mass (≥0.15M_☉), which has been ejected by an equatorial enhanced superwind of 4(±2)x10^–5M_☉/yr lasted for 4(±2)x10³ years.