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Due to the use of an image slicer for the two fibers, the FEROS order
definition uses a special technique for finding and centering orders.
The definition of the orders is done in several steps.
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First, the position of the orders is defined near the middle of the
frame. A central cut through the orders is cross-correlated with a
template which should match as good as possible the cross-order
profile. Centering the peaks of the correlation function gives the
centers of the orders near the center of the CCD. If the template
consists of the profile of a double fiber, both fibers are centered
simultaneously. This is the normal way of operation.
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Second, the orders are followed along the main dispersion direction by
cross-correlating cuts taken at varying y-positions with a secondary
template extracted from the central cut.
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Finally, the detected x-y positions of all orders are fitted with a
polynomial. This is done for each order individually. The polynomial
coefficients are kept in a table for the further steps.
Order definition is done with the command DEFINE/FEROS.
Next: Background subtraction
Up: FEROS
Previous: Requirement for the FEROS
Petra Nass
1999-06-15