13 replies to this topic

[PilarQ]

Greetings,

So during this summer, I took my StarAnalyser 100 and measured the spectra of planetary nebulae.
Below, you will find the similarities and, more interestingly, the differences in those spectra.



First post here,

The gear used:
BPK15075 + flattener Baader Mk. III
ZWO ASI 1600MM-C
StarAnalyser 100 (at the distance of ~16cm to the sensor)
Photographed from bortle 8/9 in the city of Warsaw, Poland

Attached Thumbnails

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Edited by PilarQ, 17 December 2024 - 03:53 AM.

[gfamily]

I'm not seeing any results🙁

[PilarQ]

Sorry, didn't see that the file size was too large

[happylimpet]

Nice data, nicely presented. There are a few unlabelled peaks - are those stars lying over the spectra?

[PilarQ]

Yes, exacly. You can see them on the pictures below the plot. I used bigger readout row height to average the noise.

Also I just saw that vertical axis has a Name in polish, sorry for that.
Those are arbitrary units of TIFF pixel readout in 16B

Edited by PilarQ, 17 December 2024 - 04:46 AM.

[Organic Astrochemist]

Interesting choice of planetary nebulae. How did you choose them?

Based on your results, it looks clear to me that they are in order of temperature and excitation class C6, C15 and C22.

Lower energy Balmer lines are greatest in C6 (which has no He II 4686) and diminish in C15 and C22.

The ratio of [OIII] lines to H-beta is lowest in C6 and increases in C15 and C22. [OIII] requires higher energy and temperature.

The strength of He II 4686 is greatest in C22. It requires nearly twice the energy to remove an electron from helium than from hydrogen.

However, when I consult the literature, it's a bit of a mess. In part because different authors have used different excitation class numbers.

This reference would suggest EC 1, 1, and 4

https://www.aanda.or...2057.right.html

This one suggests C22 is hotter than C6

https://articles.ads...S&filetype=.pdf

FYI if you ask chatGPT to provide numerical values for the excitation classes, the results are not reliable. It suggests they are all roughly the same.

Thanks for sharing.

[jgraham]

Excellent work! I often use small planetary nebula to calibrate my SA100.

Nicely done!

[PilarQ]

Interesting choice of planetary nebulae. How did you choose them?

Being honest, I live in a pretty big light polluted city, so I chose because their small size gives them a high surface brightness. Additionally, small objects provide better spectral resolution on the SA100. Boring:)
 

Based on your results, it looks clear to me that they are in order of temperature and excitation class C6, C15 and C22.

I love that you made such an observation! However I'm not sure if this is true or not, but learning and teaching astronomy objects to mu pupils at school, I saw that the bigger the number of Messier or Caldwell object, the farther south it is.
And regarding what you've said about needed temperatures it is fascinating to me. I might sit during the holydays and try to calculate those using basic quantum physics and Saha ionization equation.
 

 

[robin_astro]

 

And regarding what you've said about needed temperatures it is fascinating to me. I might sit during the holydays and try to calculate those using basic quantum physics and Saha ionization equation.
 

Francois Teyssier has a nice worked example on his website, using a bit higher resolution spectra though as some of the key lines tend to be blended at the Star Analyser resolution.

http://www.astronomi...ie/NGC2392.html

(First step is to correct for interstellar extinction)

 

Cheers

Robin

[Organic Astrochemist]

Francois Teyssier has a nice worked example on his website, using a bit higher resolution spectra though as some of the key lines tend to be blended at the Star Analyser resolution.
http://www.astronomi...ie/NGC2392.html
(First step is to correct for interstellar extinction)

Cheers
Robin

Nope. First step is NOT to correct for interstellar extinction. I have tremendous respect for Robin and Francois, and it is precisely their formidable experience that makes something as non-trivial as correcting for interstellar extinction as something they might suggest as “a first step”

Look at the reference for excitation class by Gurzadyan & Egikyan (1991). The lines that were used H-beta, [OIII] 5007 and 4959 and HeII 4686. How much did the intensities of those lines change after Francois corrected for interstellar extinction? +/- 1%!

We’re talking about an SA 100 here and roughly estimating the excitation class.

Notice I didn’t suggest calculating the Balmer decrement, wherein the relative intensities of H-alpha and other lines might be significantly impacted by interstellar extinction.

[robin_astro]

Look at the reference for excitation class by Gurzadyan & Egikyan (1991). The lines that were used H-beta, [OIII] 5007 and 4959 and HeII 4686. How much did the intensities of those lines change after Francois corrected for interstellar extinction? +/- 1%!

 

Very true !  Thanks for pointing that out.

 

I should have made it clear that Francois' worked example includes measurements of other physical parameters which use  lines more widely spaced in wavelength where in the general case IS extinction could potentially have a significant impact.

 

Cheers

Robin

[Organic Astrochemist]

I don't think that all of the unlabeled peaks in your spectra are stars, there are a few other lines visible.
I took this spectrum of IC 418 with my Alpy600, Borg 55FL and ASI178MM system.

From what I have read, including The Physics and Dynamics of Planetary Nebulae by Grigor A. Gurzadyan, a lot can be understood by considering the ionization energies of the elements.
ChatGPT provided
Hydrogen (H):
1st Ionization Energy: 13.598 eV

Helium (He):
1st Ionization Energy: 24.587 eV
2nd Ionization Energy: 54.417 eV

Nitrogen (N):
1st Ionization Energy: 14.534 eV
2nd Ionization Energy: 29.602 eV
3rd Ionization Energy: 47.153 eV
Oxygen (O):
1st Ionization Energy: 13.618 eV
2nd Ionization Energy: 35.118 eV
3rd Ionization Energy: 54.934 eV

Argon (Ar):
1st Ionization Energy: 15.759 eV
2nd Ionization Energy: 27.629 eV
3rd Ionization Energy: 40.380 eV

ChatGPT also gave the relative elemental abundances in planetary nebulae as

He/H: 0.1–0.2
N/H: 0.001–0.01
O/H: 0.01–0.1
Ar/H: 0.0001–0.001

Also useful are Grotrian diagrams:
https://ned.ipac.cal...ian/frames.html

Hydrogen and Helium don't have low-lying electronic states, so the lines we see are transitions from and to excited states. Therefore energies close to their ionization energies are required to produce these lines, which are often produced as the ions H+ and He+ recombine with electrons. We see these over a large volume where H and He are ionized to H+ and He+ (13.6 and 24.6 eV respectively -- energy available to ionize other elements as well). In IC 418 and C6, we DON'T see He II lines because apparently there is insufficient ionizing photons to efficiently produce He+2 (54.4 eV). In IC 418 the most intense He I lines are from the lowest, most populated triplet excited states 3s (7065) and 3d (5875) your spectrum of C6 also shows the transition from 4d (4471). The transition from the singlet excited state 3d is also visible in both (6678).

Nitrogen is less abundant than oxygen (roughly ten times less). There is sufficient ionizing photons to form N+2, but these are destroyed more easily than O+2 by ionization to N+3 (47.2 eV) and by recombination back to N+ with electrons (higher recombination rate for N+2 than for O+2 ). The result is less [N III] than [O III] and more [N II] than [O II]. Unlike H and He, the lines [O III] and [N II] can be produced by collisions and do not require ionization of O+2 to O+3. or of N+ to N+2 followed by recombination.

Edited by Organic Astrochemist, 07 February 2025 - 02:52 PM.

[columbidae]

I don't think that all of the unlabeled peaks in your spectra are stars, there are a few other lines visible.
I took this spectrum of IC 418 with my Alpy600, Borg 55FL and ASI178MM system.
ic418_20250131_731_Jim Ley.png
From what I have read, including The Physics and Dynamics of Planetary Nebulae by Grigor A. Gurzadyan, a lot can be understood by considering the ionization energies of the elements.
ChatGPT provided
Hydrogen (H):
1st Ionization Energy: 13.598 eV

Helium (He):
1st Ionization Energy: 24.587 eV
2nd Ionization Energy: 54.417 eV

Nitrogen (N):
1st Ionization Energy: 14.534 eV
2nd Ionization Energy: 29.602 eV
3rd Ionization Energy: 47.153 eV
Oxygen (O):
1st Ionization Energy: 13.618 eV
2nd Ionization Energy: 35.118 eV
3rd Ionization Energy: 54.934 eV
Silicon (Si):
1st Ionization Energy: 8.151 eV
2nd Ionization Energy: 16.349 eV
3rd Ionization Energy: 33.484 eV
Argon (Ar):
1st Ionization Energy: 15.759 eV
2nd Ionization Energy: 27.629 eV
3rd Ionization Energy: 40.380 eV

ChatGPT also gave the relative elemental abundances in planetary nebulae as

He/H: 0.1–0.2
N/H: 0.001–0.01
O/H: 0.01–0.1
Si/H: 0.0001–0.001
Ar/H: 0.0001–0.001

Also useful are Grotrian diagrams:
https://ned.ipac.cal...ian/frames.html

Hydrogen and Helium don't have low-lying electronic states, so the lines we see are transitions from and to excited states. Therefore energies close to their ionization energies are required to produce these lines, which are often produced as the ions H+ and He+ recombine with electrons. We see these over a large volume where H and He are ionized to H+ and He+ (13.6 and 24.6 eV respectively -- energy available to ionize other elements as well). In IC 418 and C6, we DON'T see He II lines because apparently there is insufficient ionizing photons to efficiently produce He+2 (54.4 eV). In IC 418 the most intense He I lines are from the lowest, most populated triplet excited states 3s (7065) and 3d (5875) your spectrum of C6 also shows the transition from 4d (4471). The transition from the singlet excited state 3d is also visible in both (6678).

Nitrogen is less abundant than oxygen (roughly ten times less). There is sufficient ionizing photons to form N+2, but these are destroyed more easily than O+2 by ionization to N+3 (47.2 eV) and by recombination back to N+ with electrons (higher recombination rate for N+2 than for O+2 ). The result is less [N III] than [O III] and more [N II] than [O II]. Unlike H and He, the lines [O III] and [N II] can be produced by collisions and do not require ionization of O+2 to O+3. or of N+ to N+2 followed by recombination.

Even though Si has lower ionization energies, only [Si II] from Si+ is seen because Si+2 is like He. Ar is similar to O but less abundant.

Why don't the relative abundances provided add up to 1.0?

[Organic Astrochemist]

They’re just relative to hydrogen not the total so you wouldn’t expect them to add to 1.. nebulae (and the sun) are roughly 92% H 7% He and less than 1 % other atoms. Planetary nebulae might be more like 74%, 24% and 2%.

Curiously the spectrum reflects greater than solar abundance of nitrogen and perhaps helium because PN are made after stars eject C N and O.

Edited by Organic Astrochemist, 07 February 2025 - 03:34 PM.