Spectroscopy and direct imaging of the planetary nebula IC 4593¹

Spectroscopy of the planetary nebula IC 4593 leads to helium, oxygen, carbon, sulfur and argon abundances which are typical of non-type I planetaries. Nitrogen abundance is normal when UV data is used. Neon might be underabundant by a factor of 2. Images in various emission lines show that the nebula is composed of two internal structures dominated by gas dynamical effects, surrounded by a nearly spherical, clumpy and highly excited halo. There are many condensations, mostly beyond the halo, predominantly located to the southwest of the central star, form-ing sets of strings connected to the object's main body. The Hβ flux for the entire nebula is 3.1 × 10^-11 erg cm^-2 s^-1, 97% from the innermost structure, where the mass of ionized gas is ≃ 0. 72(D^kpc/4.3)² M⊙ (D^kpc, distance in kpc). The Hβ flux in the internal structures is larger to the northwest. The density, temperature and degree of excitation in the innermost region change with the azimuthal angle. We present some objections to the hypothesis that the structure of the outer north-western region of IC 4593 is caused by supersonic motion into the ISM. We suggest that the morphology of the planetary may be mainly due to different forms of mass loss from the central star.