Thanks Peter I will try.

Best wishes
László

PS. I have another question. I have a planck curve fitting code but somehow the fitting results to the background I get (whatever approach I use) are all nonsensical. Is it possible that planck curves cannot be fit when only the Rayleigh side (wing) is available. Or is there some other code to do temperature fits in such cases?

-----Eredeti üzenet-----
Feladó: Starlink Software User Support [mailto:[log in to unmask]] Meghatalmazó Peter W. Draper
Küldve: Tuesday, July 03, 2018 1:51 PM
Címzett: [log in to unmask]
Tárgy: Re: asking for help

On Tue, 3 Jul 2018, Nemes L szl  wrote:

> I am struggling with an infrared laboratory emission spectrum from 
> laser induced carbon plasmas. I enclose a spectrum file. However hard 
> I try to find a reasonable background splat-vo always gives me a 
> background that when subtracted results in emission features negative 
> in the short wavelength section. I tried subtraction and division by 
> the background. The latter approach results in highly enhanced long 
> wavelength features (of course as the baseline there drops to near 
> zero). Maybe there is some problem with the experimental spectrum..? 
> What tricks I could use to get an acceptable background. Without it I cannot fit the bands. Could you advise me, please.
> The spectrum is displayed on nm scale.
>
> Best regards
>
Hi L szl ,

the only way that will work for this type of spectrum is to draw the background "by hand". Use the "Analysis->Spectrum from interpolation" 
tool.

Using this you click a series of points along the spectrum (obviously along the baseline in this case) and then generate a spectrum from these points that can be subtracted from the spectrum. There are various interpolants available, like polynomials, but humans prefer curve types like hermite or akima, you can play with the positioning of the points and the curve type to get the best effect.

Regards,

Peter.



>
> -----Eredeti  zenet-----
> Felad : Starlink Software User Support 
> [mailto:[log in to unmask]] Meghatalmaz  Peter W. Draper
> K ldve: Sunday, July 01, 2018 1:45 PM
> C mzett: [log in to unmask]
> T rgy: Re: asking for help
>
> On Sun, 1 Jul 2018, Nemes L szl  wrote:
>
>> I am trying to save a polynomial background fit to my spectrum in 
>> order to fit the background to a Planck curve. I do not see an option 
>> for saving the background as a file in Starlink Splat-VO. Could you 
>> help me please
>
> Hi L szl ,
>
> when you fit a background this is shown as a spectrum in the "Global 
> list of spectra:". To save it just select the name and use 
> "File->Save". When doing this choose a file format of text and you'll 
> get a file with the polynomial evaluated at the coordinate positions 
> of the spectrum it was fitted to.
>
> Regards,
>
> Peter.
>
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--
Peter W. Draper, http://astro.dur.ac.uk/~pdraper

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