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Abell 78 where's the helium?

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#1 bill w

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Posted 06 February 2016 - 03:02 PM

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 formed by the much faster helium wind.  note the filaments (not diffraction spikes) streaming from the central star. 

 

faint ring in Ha:

abell-78-Ha.jpg

 

complex shell with inner jets and stream leading to outer shell (bottom) in OIII

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 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
ASA DDM60
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
9/23/15-11/14/15
Eastbluff, CA


Edited by bill w, 08 February 2016 - 03:46 PM.

  • Ricky, polare70, nmoushon and 2 others like this

#2 BenB85

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Posted 06 February 2016 - 03:11 PM

Hi Bill, wish I could help you more, but it is a great series. The bottom left HOHe is my favorite compilation.



#3 Rick J

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Posted 06 February 2016 - 04:12 PM

Interesting.  I see I lost the inner jets due to glare from the central star in my LRGB image.  I wonder if I hold back the star if that might not show they are there after all.  Except for the jets the LRGB is little different which isn't all that common. 

 

What does it take to ionize helium?  Could it be the star just doesn't have the energy needed.  Bright often just means it is not hot enough to emit mostly in Uv so is bright to our eyes compared to really bright Uv stars.  I'd think they'd say ionized oxygen, helium etc. if that's what they meant.  Does He fall in the range of radio scopes?  I am not up on radio astronomy.

 

Rick



#4 freestar8n

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Posted 06 February 2016 - 06:27 PM

Nice presentation once again - and interesting topic.

I think the object is definitely H-deficient - but it's not clear to me what parts are truly "mostly helium".

Here are a few links I found:

http://www.esa.int/s...lanetary_nebula

http://adsabs.harvar...ApJ...266..298J

https://www.research...tary_structures

Note that much of the focus is on the knots themselves - which show well in the Oiii image - but don't show at all in the Ha. The outer elliptical shell shows about equally in Ha and He - and that may mean it is primarily He - if the He line is intrinsically much fainter.

So I think the main point is that regions are very H-deficient - and only 5 known planetaries are like that.

http://adsabs.harvar...ASPC...96..193H

That link says some of the knots are primarily He. But they are also bright in Oiii. I'm not sure what they are saying exactly - but I guess the He line is intrinsically faint.

Frank

#5 bill w

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Posted 06 February 2016 - 08:10 PM

Hi Bill, wish I could help you more, but it is a great series. The bottom left HOHe is my favorite compilation.

thanks ben



#6 bill w

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Posted 06 February 2016 - 08:23 PM

Interesting.  I see I lost the inner jets due to glare from the central star in my LRGB image.  I wonder if I hold back the star if that might not show they are there after all.  Except for the jets the LRGB is little different which isn't all that common. 

 

What does it take to ionize helium?  Could it be the star just doesn't have the energy needed.  Bright often just means it is not hot enough to emit mostly in Uv so is bright to our eyes compared to really bright Uv stars.  I'd think they'd say ionized oxygen, helium etc. if that's what they meant.  Does He fall in the range of radio scopes?  I am not up on radio astronomy.

 

Rick

thanks rick, missed your shot of it, very close match.  not sure how hot it has to be to ionize helium, but this one is supposed by be very hot as it's fusing He.  one fairly old article puts the temperature between 100,000-150,000K based on the UV spectrum.  the spectrum of the star itself shows crazy high energy stuff like O VI, with no H alpha. 


Edited by bill w, 06 February 2016 - 08:29 PM.


#7 bill w

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Posted 06 February 2016 - 08:28 PM

thanks for the links frank, will look into them. 

interestingly i ran into an very old paper on "helium rich" planetary nebulae while looking for objects to image with a helium filter.

poking around a bit more, i found that the helium signal was quite feeble in most of them.  turns out "helium rich" was defined be the ratio of helium to Ha.  i think these are now known as H- deficient (which you reference). 

 

Nice presentation once again - and interesting topic.

I think the object is definitely H-deficient - but it's not clear to me what parts are truly "mostly helium".

Here are a few links I found:

http://www.esa.int/s...lanetary_nebula

http://adsabs.harvar...ApJ...266..298J

https://www.research...tary_structures

Note that much of the focus is on the knots themselves - which show well in the Oiii image - but don't show at all in the Ha. The outer elliptical shell shows about equally in Ha and He - and that may mean it is primarily He - if the He line is intrinsically much fainter.

So I think the main point is that regions are very H-deficient - and only 5 known planetaries are like that.

http://adsabs.harvar...ASPC...96..193H

That link says some of the knots are primarily He. But they are also bright in Oiii. I'm not sure what they are saying exactly - but I guess the He line is intrinsically faint.

Frank



#8 polare70

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Posted 07 February 2016 - 05:25 AM

Very interesting !




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