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Hello IRAF users!
I have three questions about spectra processing and related applications.First question is about tasks which allow to perform calculation of shift of two spectra using cross-correlation or another method. I would like to compare two echelle spectra (order by order) and find shifts beetwen them but I don't know how it can be done.My second question about application which is able to shift spectral apertures. How can I calculate shift between two spectra (w/o dispersion solution) for next using with specshift?And last question. What application allow me to combine two spectra (echelle) so that produced spectrum contain not only combination of first spectra in apertures (I extract spectra with optimal extraction algorithm) but also combined sigmas, etc?Thanks in advance.

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Cheers, Eugene.

[quote:f360ee2beb]First question is about tasks which allow to perform calculation of shift of two spectra using cross-correlation or another method. I would like to compare two echelle spectra (order by order) and find shifts beetwen them but I don't know how it can be done. [/quote:f360ee2beb]I use the rvsao package for this. I would suspect RVSAO is lurking around on this site, but I seem to always end up compiling it myself. I use it to calculate shifts order by order on echelle data quite often. It can do it in pixels, velocity, or angstroms. THere's also xcor which comes with IRAF, but... I've never used it so I'm not sure if it'd play nicely with echelle spectra.[quote:f360ee2beb]My second question about application which is able to shift spectral apertures. How can I calculate shift between two spectra (w/o dispersion solution) for next using with specshift? [/quote:f360ee2beb]mmm, not sure about the shifting without dispersion solution. I think imshift could do it.[quote:f360ee2beb]And last question. What application allow me to combine two spectra (echelle) so that produced spectrum contain not only combination of first spectra in apertures (I extract spectra with optimal extraction algorithm) but also combined sigmas, etc?[/quote:f360ee2beb]scombine is the only thing I know of that can combine spectra. I'm not sure if it'll combine the extras like the sigmas, etc.I'd suggest reading the help pages on scombine and imshift.

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The re-born Mac IRAF web site: http://macsingularity.org

[quote:72f6bcbac7="sirmarcos"]
I use the rvsao package for this. I would suspect RVSAO is lurking around on this site, but I seem to always end up compiling it myself. I use it to calculate shifts order by order on echelle data quite often. It can do it in pixels, velocity, or angstroms.[/quote:72f6bcbac7]
Thanks. I know about this package but I have never used it.[quote:72f6bcbac7]
mmm, not sure about the shifting without dispersion solution. I think imshift could do it.
[/quote:72f6bcbac7]
I found a task specshift. [quote:72f6bcbac7]
scombine is the only thing I know of that can combine spectra. I'm not sure if it'll combine the extras like the sigmas, etc.
[/quote:72f6bcbac7]
Yes, scombine works only with primary spectra and not operate with sigmas. I have copied sigmas into separate files and work further with them.

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Cheers, Eugene.