Observations and Models of the 'Helix' Nebula NGC 7293

R. E. S. Clegg, J. R. Walsh
1989 Symposium - International astronomical union  
Long-slit IPCS 2-dimensional spectra in radial directions across the inner and outer shells and across some of the brightest cometary globules are presented. The spectra show the ionization structure of the nebula quantitatively, with He II λ4686 A strong in the inner regions and [N II] λ6584 A prominent in the outer shell, almost due east of the central star. The "[Ne III] anomaly", previously reported for NGC 6720 and 7293 by Hawley and Miller, is clearly seen. It, together with the [O I]
more » ... with the [O I] λ6300 A flux, provide constraints on our photo-ionization models, as both depend on the concentration of neutral H in the background gas.
doi:10.1017/s0074180900138367 fatcat:nxyudie3fve45mwzuphxq2pqwi