hi folks,
I am running my spectrograph program on a new spectrograph, and of course surprises showed up.
We have this IFU spectrograph with 1300 fibers, and I am trying to determine center, sigma and amplitude for all of these fibers (1300) at all wavelengths (4096).
It normally works fine, but when I get far from the center, sometimes the solution starts to bounce back and forth between two minima, like this:
center sigma amplitude
11.418597 3.937581 10316.810710
11.613498 2.697872 10862.134468
11.372858 3.896962 10279.177779
11.525734 2.393638 10785.292080
11.625337 2.765837 10744.202063
11.399946 3.849835 10366.270150
11.514934 2.317529 11099.356812
11.600127 2.718315 10819.541837
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this does not happen for the well focused central fibers which have a nice Gaussian profile
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I ran exactly the same fits using gnuplot and iraf, their solutions agree with each other and with my low sigma root solution, no bouncing ever.
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In root I normally use MIGRAD which is what I have always used and should be best. But I also tried SIMPLEX and I also tried using IMPROVE after running MIGRAD, I get the same problem, the solution bounces back and forth between these two minima.
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I know we have to get this thing focused over the entire ccd, period. But still it annoys me to see the solution jumping back and forth, it looks like I could do something to avoid this jumping - something that gnuplot and iraf apparently do
any ideas most welcome.
Antonio