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Hi all, sorry I have a problem with sky subtraction of 1D extracted wavelength calibrated spectra. Since sky spectrum is shifted with respect to the science objects, how can I apply sky subtraction with skytweak? can anybody help me? thanks a lot[color=red:d7b9a0aca9][Mod Note: Forwarded posting][/color:d7b9a0aca9]

The help is basically reading the help page for the task. The examples might help. If you have a more specific question I would be glad to answer.A question is why is the sky spectrum not correctly calibrated. It might be easier to measure any shift in the sky spectrum from one or more sky lines and then correct the sky spectrum prior to sky subtraction. There are two possible paths to doing this. One is use the RV package to determine a doppler shift and use DOPCOR to apply the correction. The other is use identify and dispcor. Or even simplier might be to determine either an pixel shift and edit the CRPIX1 keyword or a wavelength shift and edit the CRVAL1 keyword.Frank Valdes