Figure 3.

Plot of the Hamilton echelle spectrum of the planetary nebula NGC 6572, obtained on Sept. 1, 1991, in the wavelength interval 5514–5545 Å, showing the [Cl iii] 5517.7 and 5537.9 Å lines, where the flux is in units of erg⋅cm⁻²⋅sec⁻¹⋅Å⁻¹. We note that the structure in the [Cl iii] emission lines is due to shell expansion within the nebula. Radial velocity and interstellar extinction corrections (C = 0.4) have not been applied to this spectral scan.