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Observing >> Variable Star Observing and Radio Astronomy

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lipman
super member


Reged: 03/20/09

Loc: San Carlos, CA
Measuring star temperature
      #6195114 - 11/14/13 05:59 PM

I have recently started using the Star Analyzer grating to take spectra, which I analyze with the RSPEC software. My son is using this for a school science fair experiment, and we have been playing around with an Excel model to fit the instrument response corrected RSPEC .dat files to a blackbody curve in order to determine star temperature. The file is here: https://www.dropbox.com/s/xocso5qfbplf4lq/RSPEC%20profile%20vs%20black%20body...

I am sharing it here in case anyone would like to use it, improve on it or critique it.

Paul


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robin_astro
sage


Reged: 12/18/05

Re: Measuring star temperature new [Re: lipman]
      #6197737 - 11/16/13 08:06 AM

Hi Paul,

I would recommend extracting the continuum from the spectrum first(ie use the spectrum with the lines removed) so that the absorption lines do not skew the fit. This is particularly important for cooler stars where the absorption lines will dominate the spectrum (and unfortunately also make it difficult to determine the continuum shape with any accuracy in low resolution spectra - try to fit the curve to the high spots in the spectrum rather than through the mean) Also be sure to limit the fit to wavelengths above the Balmer jump at 3646A

Do not be surprised though if your results deviate significantly from the text book values for Teff. Despite what some books say, star spectra are not in general particularly good fits to black body curves.

Incidentally, the 2 column dat files produced by RSpec are not unique to RSpec but can also generated and read by other spectral processing software such as Visual Spec and ISIS, IRAF,MIDAS etc. For maximum compatibility though it is a good idea to export dat files from RSpec with the constant bin size option selected. (This is not the default, I believe)


Cheers
Robin


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lipman
super member


Reged: 03/20/09

Loc: San Carlos, CA
Re: Measuring star temperature new [Re: robin_astro]
      #6199143 - 11/16/13 11:28 PM

Hi Robin,

Great point about deleting the absorption lines. That's next on my list!

Cheers,

Paul


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robin_astro
sage


Reged: 12/18/05

Re: Measuring star temperature new [Re: lipman]
      #6199599 - 11/17/13 09:58 AM

Paul,

There is an interesting article here on using the Star Analyser to estimate temperature from the spectrum using Visual Spec software
http://www.shelyak.com/dossier.php?id_dossier=18
Here they use an empirical correction factor to compensate for the effect of the star not being a perfect black body.

Cheers
Robin


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