Sunday, February 21, 2016

Abell 78 where's the helium?

first, a more aesthetically pleasing version in Ha OIII OIII, then the helium:

abell-78-HOO-800w.jpg
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 shaped by the much faster helium wind.  note the filaments (not diffraction spikes) streaming from the central star.

faint ring in Ha (hydrogen):
abell-78-Ha.jpg

complex shell with inner jets and stream leading to outer shell (bottom) in OIII (oxygen)
abell-78-oiii.jpg

very faint in Helium II
abell-78-He.jpg

Ha OIII He image
abell-78-HOHe-bright.jpg
with the helium giving not much more than a magenta cast to the outer shell especially upper left

mosaic:
top: Ha OIII He
abell-78-narrow-band-mosaic.jpg
bottom: HOHe HOO HOO (bright)

a number of sources indicate that the inner ring is mostly made up of helium
http://www.noao.edu/...y/abell_78.html
https://en.wikipedia.org/wiki/Abell_78
http://www.astrosurf...78/abell78.html
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 my last 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
ASA DDM60
Ha 30x20 min bx2, OIII 48x20 min bx2 (best 26 used for RL doconvolution)
HeII 4x20 min bx2, 1x 40 min bx2, 59x20 min bx4
9/23/15-11/14/15
eastbluff, CA