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abstract
The large-scale morphology of the Helix Nebula is investigated using deep, narrow-band, CCD images obtained with the 30-cm, f/3.2, flat-field camera on Mt. Skinakas Observatory. A huge halo, covering an area of 36$\times$30$\arcmin$ around the main nebular body, is revealed at extremely low levels (3.7 \cdot 10$^{-17}$ ergs sec$^{-1}$cm$^{-2}$arcsec$^{-2}$) in the deep CCD images, obtained through narrow-band filters centered on the H$\alpha$+N[II], H$\beta$, [OIII] and [SII] lines.
The complex morphology of this nebula evident at both low and high light levels, along with the relatively-high expansion velocities of the various shells reported in the literature, suggests that the Helix Nebula must have undergone several, relatively-recent, mass-loss episodes. Also presented is clear evidence for an ongoing interaction between the expanding gaseous shells and the surrounding Interstellar Medium.
