first, a more aesthetically pleasing version in Ha OIII OIII, then the helium:
Abell 78 is a rare type of planetary nebula who's exhausted central star ran out of hydrogen to burn (fuse) and collapsed, only to reignite--fusing helium rather than hydrogen at it's surface. this is reflected in the unusual shape of the planetary nebula: a smooth outer shell formed initially, followed by a complex inner shell formed by the much faster helium wind. note the filaments (not diffraction spikes) streaming from the central star.
faint ring in Ha:
complex shell with inner jets and stream leading to outer shell (bottom) in OIII
very faint in Helium II
Ha OIII He image
with the helium giving not much more than a magenta cast to the outer shell especially upper left
top: Ha OIII He
bottom: HOHe HOO HOO (bright)
a number of sources indicate that the inner ring is mostly made up of helium
i am at a loss to explain this as the helium was so faint relative the the Ha and OIII that i had to bin x 4 to pick anything up (this is what prompted the 4x binning further tested in this post).
the last link also makes the helium claim and includes the 2d spectrum of the nebula, but by my reading, the He line is much more faint than the Ha and OIII.
where is the all the helium? what am i missing? are they referring to He I? or the central star itself?
any input would be appreciated.
8" LX200R, SX Trius 694 binned x2 to 0.8"/px, binned x4 to 1.6"/px, (final image at .8"/px)
astrodon 5nm Ha, 3nm OIII, chroma 4 nm He
Ha 30x20 min bx2, O III 48x20 min bx2 (best 26 used for RL deconvolution)
He II 4x20 min bx2, 1x 40 min bx2, 59x20 min bx4
Edited by bill w, 08 February 2016 - 03:46 PM.