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I How to check if stellar/galactic spectrum extraction went well?

  1. Jun 1, 2018 #1
    I've been doing some spectrum extractions in IRAF, stellar and galactic, and I was wondering if anyone here had any ideas on how to tell if the extraction/calibration/etc went well? I have a bunch of finished projects but I'm not sure about how to tell if they're any good or not. Let me know if anyone has any ideas. I could also post some images of the spectra themselves if that might help.
  2. jcsd
  3. Jun 2, 2018 #2


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    What constitutes "well'? Studies usually apply a standard of observed vs predicted measurement of some or another 'key' variables in a model of interest. If the model produces predictions that match observation to a particular level of statistical confidence, the model is deemed valid to that level of confidence. If not, it is considered either incomplete or just plain wrong. Of course, one can make an entire career [and living] out of trumpeting statistically anomalous data as 'proof' of some hare-brained idea. This forms the basis for using Bayesian statistics as a measure of credibility. Then again, it is possible to misapply Bayesian statistics: giving rise to the adage "figures don't lie, but, liars figure."
  4. Jun 2, 2018 #3


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    I'm not sure what you accept a priori as "well". For instance, do you accept manual extraction, but not necessarily anything automated (until proven reliable)? In that case, have you compared your automated results to a manual extraction -
    1. on some small but very random sample on the statistical universe of your data; and
    2. on some small, very well focused subset that you feel you understand deeply -- something of a calibration set?
    If so, what did the comparisons show?
  5. Jun 2, 2018 #4
    I assume your concern is about how well you have done the extraction, wavelength calibration and instrument correction. In that case I think the best approach is to obtain spectra of well studied stars and compare your results with published results. The details will depend on what type of spectrograph you are using and the type of result you are aiming for, flux calibrated or normalised for example.I think IRAF has some standard star data somewhere that could use.

    Regards Andrew
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