I need to know does SDSS spectrum contains error spectrum as well?


The above link says, further HDU's contain error spectrum and than tells about the inverse variance. Does inverse variance contains error spectrum? If yes, how can I extract that, if not where can I find error spectrum?


1 Answer 1


The variance is the square of the standard deviation, so you can calculate 1$\sigma$ errors of the spectrum by taking the square root of one over the inverse variance of HDU1 (https://data.sdss.org/datamodel/files/SPECTRO_REDUX/RUN2D/PLATE4/spPlate.html#hdu1head).

(You will get infinity for bad pixels since their inverse variance is set to zero.)

  • $\begingroup$ Is there anyway to increase the level of sigma error? $\endgroup$ Jul 16, 2016 at 21:47
  • $\begingroup$ Absolutely right. The inverse variance is used because that is directly what you use to weight any fit to a model. $\endgroup$
    – ProfRob
    Jul 16, 2016 at 21:58
  • $\begingroup$ @syedali, like the 3sigma error? typically you assume a normal distribution and just multiply 1sigma by 3 (for example). see: en.wikipedia.org/wiki/… $\endgroup$
    – E. Douglas
    Jul 18, 2016 at 1:04

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