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

http://www.sdss.org/dr12/spectro/spectro_basics/#AbouttheSpectra

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?

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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.)

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  • $\begingroup$ Is there anyway to increase the level of sigma error? $\endgroup$ – Syed Ali Jul 16 '16 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 '16 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 '16 at 1:04

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