i have a question about APALL

Mao yewei wrote on Jul 04, 2007

Dear all, i have a question when reducing slit spectra with IRAF.

In the task APALL, what does "width" mean? It says that "Profile centering width".
But i can't understand the meaning, or the essence.

My work is to reducing 2D-spectra of nearby galaxies, so the signal to noise ratio
of some outer areas far from the core is not high. When extracting weak
continuum, i decreased the value of "width" to 1,and found that it could obtain
higher S/N . idon't know whether my practice is proper.So i need some help.

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Valeev Azamat wrote on Jul 04, 2007

Read at first
help center1d

At every line across disparsion axis program
find (using center1d) real center of profile
in range (LINE +- 0.5 * width)

Is it answer to your question? May it help?

Azamat

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Mao yewei wrote on Jul 04, 2007

Thanks for your reply!

And do you know what's the proper value of "width"?

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Valeev Azamat wrote on Jul 04, 2007

Use default value. (5.0)
This value depent on matrix/instrument properties (read noise, gain,
scale...) and seeing in observing moment (I think), S/N value and so....

You may find the best value using this method:
setup apall.format="strip"
change width and see how change 2D-profile of spectra.
select the best value.

Cheers, Azamat :)

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Mao yewei wrote on Jul 04, 2007

i see!
thanks very much for helping me!

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Last post on Jul 04, 2007