SIMBAD references

The little studied PN, Sa 2-21 has been observed using the Manchester echelle spectrometer at the Anglo-Australian telescope. Narrow band, long-slit spectra were obtained at six positions over two perpendicular position angles in both the [N ii]λ6584 Å and [O iii]λ5007 Å emission lines. An [O iii] halo has been detected for the first time. A morphological modelling program was used to help determine the geometry, structure and kinematics of this ellipsoidal PN. It is proposed that the structure includes a pair of mid-latitude rings of [N ii] emission, not previously seen in elliptical PNe. Radial spokes of [O iii] emission have been detected in the main nebular shell indicating the presence of dynamical instabilities.