The Planetary ESO 166 - PN21

Abstract

Long slit, high and low resolution, spectrograms of this object were obtained using the telescopes at CTIO. From the [N II] λ6584 line in the high resolution spectrum, we obtained a radial velocity difference between the front and back expanding shells at the center of the nebula of 56 km s⁻¹ corresponding to an expansion velocity of 28 km s⁻¹, From the low resolution spectra we found [S II] λλ6717/6731 line ratios indicating densities between 500 cm⁻³ and less than 200 cm⁻³. The temperature sensitive line ratios of [O III] and [N II] were not well determined due to the weakness of the λ4363 and λ5733 lines. A ionization structure is clearly seen with radial distance to the central star which shows that the inner shell (A2, A4, B2, B4) is not a projection of the outer one but a separate structure.