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#26 mwr

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Posted 27 January 2020 - 07:00 AM

Also one in the ARAS forum but again no fits file 

http://spectro-aras....it=ic418#p12101

Too bad. It would be nice to have a fits file with resolved lines for experimenting with convoluting and deconvoluting resolved and overlapped lines, respectively. Processing experimental data using Excel Solver could be interesting.  Bad seeing conditions at my observation site contribute substantially to line broadening and the contribution of coma to the line shape is probably rather small, so that the lines should be approximated by a Gaussian model (however, this has to be proved by a line shape analysis; some discussions on this topic can be found here: https://www.cloudyni...2nd-derivative/).

Has somebody done so far line deconvolution in astronomical spectroscopy using Excel Solver? I couldn't find so far a good review on this topic.



#27 robin_astro

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Posted 27 January 2020 - 07:44 AM

Too bad. It would be nice to have a fits file 

Indeed.  I encourage anyone to contribute  their spectra of any astronomical object to the BAA database provided they meet the quality standards  (good quality calibrated spectra in BeSS fits format) 

https://britastro.or...equirements.htm

You don't need to be a member of the BAA though new members are always welcome of course !

 

Cheers

Robin



#28 mwr

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Posted 28 January 2020 - 02:14 PM

[

 

 

I don't have a Star Analyser, but I bought a 100 /mm grating that fits in front of my 50mm dSLR lens and gives nice images (here of the Plough)

 

attachicon.gifU Maj.jpg

edit for spelling

Inspired by your nice wide field approach, I have tried to obtain a slitless spectrum of the large Orion Nebula M42. Thus, I have re-activated my 30 year old 28mm Tokina objective with the SA-100 as objective grating to keep M42 as small as possible on the sensor (16.4 Angström/pixel dispersion!). 30 x 1 sec untracked frames were stacked and the result can be almost called an "emission spectrum":

 

orion.jpg

 

Something of a nice didactic value with a minimalistic equipment (needless to say that my kids were totally unimpressed).

 

 


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#29 gfamily

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Posted 28 January 2020 - 04:07 PM

[

Inspired by your nice wide field approach, I have tried to obtain a slitless spectrum of the large Orion Nebula M42. Thus, I have re-activated my 30 year old 28mm Tokina objective with the SA-100 as objective grating to keep M42 as small as possible on the sensor (16.4 Angström/pixel dispersion!). 30 x 1 sec untracked frames were stacked and the result can be almost called an "emission spectrum":

 

attachicon.giforion.jpg

 

Something of a nice didactic value with a minimalistic equipment (needless to say that my kids were totally unimpressed).

Very nice - I may have to try something like this again - if we ever get some clear skies!



#30 mwr

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Posted 01 February 2020 - 05:27 AM

Bad seeing conditions at my observation site contribute substantially to line broadening and the contribution of coma to the line shape is probably rather small, so that the lines should be approximated by a Gaussian model (however, this has to be proved by a line shape analysis; some discussions on this topic can be found here: https://www.cloudyni...2nd-derivative/).

 

Finally I have found "Fityk", that is a quite comfortable peak fitting program https://fityk.nieto.pl/

 

One big advantage: It can read .dat-files created by RSpec or VSpec. Below is a SA-200 spectrum of NGC 7662 (blue snowball) that was recorded in the converging beam setup: 

 

fityk.jpg

 

The emission lines can be, indeed, fitted using a Gaussian model: 

 

fityk2.jpg

 

Of course, the fit isn't perfect, but the overlapping [OIII] lines are deconvoluted satisfactory (the theorectical line ratio of the non-resolved [OIII] lines  is about 1:3, which compares quite well with the result of the deconvolution).

 

The constraints of this approach are well known:

-the deconvolution is a so-called ill-posed problem, which means that many different functions solve a convolution equation within bounds of experimental data

-deconvolution delivers thus only meaningful results when the actual number of componets of the unresolved peak is known a priori and the fwhm of the lines due to the response function  of the system is known (which can be determined from the peak shape of a resolved peak)

-experimental spectral data can thus only be verfified, but the extraction of novel information is limited

 

Conclusion: It could be shown for my setup that the broadening of emission lines in a star analyser spectrum, that was recorded in a converging beam, is dominated by the seeing rather than by the spectral coma. Deconvolution is of limited value but a nice exercise for rainy days and cloudy nights.


Edited by mwr, 01 February 2020 - 05:28 AM.

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#31 robin_astro

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Posted 01 February 2020 - 06:59 AM

I am wondering in this case  if it is the apparent size of NGC7662 rather than the seeing that is swamping any aberrations and that the distribution of material in the PN is sufficiently uniform and symmetric to be an approximation to a gaussian.   The limitation then would be that with objects with less  symmetry the structure may be resolved as apparent spectral features.

 

Cheers

Robin


Edited by robin_astro, 01 February 2020 - 07:01 AM.

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#32 mwr

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Posted 01 February 2020 - 08:23 AM

I am wondering in this case  if it is the apparent size of NGC7662 rather than the seeing that is swamping any aberrations and that the distribution of material in the PN is sufficiently uniform and symmetric to be an approximation to a gaussian.   The limitation then would be that with objects with less  symmetry the structure may be resolved as apparent spectral features.

 

Cheers

Robin

Very good point!

I have also analysed the line shapes of IC 2149, IC 418 and IC 2003. The latter is definitely stellar with my equipment without any visible structural features : https://www.cloudyni...work/?p=9856129

 

The line shapes can be fitted well by a Gaussian model:

 

IC 2003:

 

ic_2003_fityk.jpg

 

IC 418:

 

ic418_fityk2.jpg

 

IC 2149:

 

2149.jpg


Edited by mwr, 02 February 2020 - 01:43 AM.



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