Hello,When extracting a spectrum using a reference image and the tracing is turned off, the algorithm uses the same aperture definition as for the reference image. My question is:Are extraction weights also applied in case optimal extraction was used for the reference image? I guess no. There is an option 'profiles' in 'apall' to do that, but I could not find how to save the profile image of a extraction. Can anyone help me with that? Thanks.Regards,
Valery

Hello Valary,There are two things here which are independent. First you can use the apertures from a reference image or from the object. You have chosen to use apertures from the reference image and that is fine.Second you can compute the normalized profile from which the weights are compute using a reference image or the object independent of how the apertures are define. This is controlled by the profiles parameter. Note it is the profile that may be determined from a profile image and not the actual weights which are derived from the profile and the signal in the target spectrum.When the profiles are used from the profile image, because of low S/N in the object, these are derived (or rederived) using the current apertures (which might be inherited from the reference) during the processing. In other words, there is nothing saved concerning the profiles.So if you have a very weak spectrum which you believe is well aligned with a stronger spectrum and has the same profile then you 1) use that spectrum for the apertures (to avoid having to center and trace on the weak spectrum) and 2) you can specify the stronger spectrum for (re)determining the weights as the weak spectrum is being extracted.I hope this clears up your questions.Yours,
Frank Valdes

Hello Frank,Thank you for the clarification. Things are clearer now I think. If I undersood it correctly, the profile image should be an image that contans a well-exposed object, and not the profile that is to be used for the extraction of the weak object. Then when I run "apall" interactivelly (with profile, but not reference image) , I will be let to define the aperture, the background regions, the trace and compute the profile from the profile image. Then the same background regions and trace will be used to subtract the background (if 'back+') on the weak spectrtum and the computed profile will be used to (re)compute the extraction weights using the counts in the weak spectrum. If this is correct, then it was not clear to me from the help pages.Anyway, is it possible to further specify not to re-determine the extrcation weights from the weak spectrum, but to just apply the same extraction weight as for the strong spectrum? Thas is what I would like to do, and further I do not want to subtract the background from my "weak spectrum". In fact, in my case it is not even an object spectrum. It is the normalized flat filed image that contains strong fringes in the red. I would like to extract the 1D fringe pattern that was used to flat field the object image. That's why I want to apply exactly the same weights as those used for extrcating the object.Regards,
Vallery