An ISO and IUE study of planetary nebula NGC 2440

The infrared and ultraviolet spectra of planetary nebula NGC2440 are presented. The observations were made by the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). These data, in conjunction with published optical observations have been used to derive electron temperature and density. The electron temperature increases with increasing ionization potential, from 11 000 to 18 000 K. The electron density has a constant value of 4500 cm(-3) in agreement with previous determinations. The chemical abundance has been derived for the following elements; helium, carbon, nitrogen, oxygen, neon, sulfur and argon. The ionization correction factor turns out to be very small for all species except sulfur

Birth and early evolution of a planetary nebula

The final expulsion of gas by a star as it forms a planetary nebula --- the ionized shell of gas often observed surrounding a young white dwarf --- is one of the most poorly understood stages of stellar evolution. Such nebulae form extremely rapidly (about 100 years for the ionization) and so the formation process is inherently difficult to observe. Particularly puzzling is how a spherical star can produce a highly asymmetric nebula with collimated outflows. Here we report optical observations of the Stingray Nebula which has become an ionized planetary nebula within the past few decades. We find that the collimated outflows are already evident, and we have identified the nebular structure that focuses the outflows. We have also found a companion star, reinforcing previous suspicions that binary companions play an important role in shaping planetary nebulae and changing the direction of successive outflows.Comment: 9 pages + 3 figures. To appear in Nature, 2 April 199

Photoionization model analysis of the planetary nebula Hu1-2

We have obtained high resolution optical spectra of the planetary nebula Hu 1-2 in the wavelength region of 3700 Angstrom-10050 Angstrom, with the Hamilton Echelle Spectrograph (HES) at Lick Observatory. Diagnostic analysis indicates that the nebular gas can be represented by inhomogeneous shells of electron density N(epsilon)similar or equal to4000-10000 cm(-3), and a gas temperature of 12000-18000 K. Using the spherically symmetric photoionization model with appropriate abundances, we tried to accommodate the observed physical conditions and high electron temperatures. The chemical composition of the nebula was derived from calculations using a photoionization model which predicts the observed IUE, HES and ISO line intensities; and the composition was then compared to previous determinations. Model analysis confirms the semi-empirically determined abundance derivations carried out in earlier studies. He and N abundances are high, but those of C, O, Ne and S are very low

Abundance in the planetary nebulae NGC 6537 and He2-111

The ISO and IUE spectra of the bipolar planetary nebulae NGC 6537 and He2-111 are presented. These spectra are combined with the spectrum in the visual wavelength region from the nebulae to obtain a complete spectrum that is corrected for extinction. The chemical abundance of the nebulae is then determined and compared to previous determinations, The abundance of the two nebulae is quite similar. A comparison is then made with the abundance of two other bipolar planetary nebulae whose abundance is also determined with the help of ISO observations. It is shown that not all bipolar nebulae have similar abundance. NGC 6445 has a much lower nitrogen to oxygen ratio, similar to NGC 7027, but still not as low as the Orion nebula

Abundances of planetary nebulae NGC 7662 and NGC 6741

The ISO and IUE spectra of the elliptical nebulae NGC7662 and NGC6741 are presented. These spectra are combined with the spectra in the visual wavelength region to obtain a complete, extinction corrected, spectrum. The chemical composition of the nebulae is then calculated and compared to previous determinations. The abundances found are compared to determinations made in other nebulae using ISO data. A discussion is given to see if possible evolutionary effects can be found from the abundance differences