Difference: AAOmegaFileFormat (6 vs. 7)
Revision 72007-04-23 - RonHeald
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AAOmega File Format (or, which spectrum is which object?) | ||||||||
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An Important Note on 2dF Fibre-Pivot Number and 2dfdr Fibre Number | ||||||||
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| < < | There are two very important, and very different, numbers to understand in order to recover the information for which object each fibres was allocated to: Fibre slit position AND 2dF Fibre-Pivot position. For the most part there is a one-to-one correspondence between these numbers. i.e. the fibre at AAOmega slit position 1 (at the bottom of the CCD image, ...red.fits[0][*,1]) will map directly to 2dF Pivot position 1, and fibre 400 will map to Pivot position 400. (Note 400 is a guide fibre and so maps to a blank space at the top of the CCD image, ...red.fits[0][*,400]). However, during manufacture or repair of the AAOmega slit units, it is possible for the order of fibres in each of the AAOmega slits to fall out of synchronization with the 2dF Pivot numbering (2 slit blocks on each plate are like this as of April 2007). It is not practical to mechanically alter either position so each of the conversion betwen the two is propagated in the binary table extension (Pivot position). | |||||||
| > > | There are two very important, and very different, numbers needed to recover the information for which object each fibre was allocated: Fibre slit position AND 2dF Fibre-Pivot position. For the most part there is a one-to-one correspondence between these number sets. i.e. the fibre at AAOmega slit position 1 (at the bottom of the CCD image, ...red.fits[0][*,1]) will map directly to 2dF Pivot position 1, and fibre 400 will map to Pivot position 400. (Note 400 is a guide fibre and so maps to a blank space at the top of the CCD image, ...red.fits[0][*,400]). However, during manufacture or repair of the AAOmega slit units, it is possible for the order of fibres in each of the AAOmega slits to fall out of synchronization with the 2dF Pivot numbering (2 slit blocks on each plate are like this as of April 2007). It is not practical to mechanically alter either position so each of the conversion betwen the two is propagated in the binary table extension (Pivot position). | |||||||
| In the primary image .fits[0] (and also the variance array .fits[1]) the fibre at the bottom of the image, which is the fibre at slit position 1 (...red.fits[0][*,1]), corresponds to the first row in the binary table extension .fits[2]). The table contains a column entry, PIVOT, which gives the 2dF pivot position for this fibre. This is the fibre number seen be the Configure software. The very top fibre in a CCD image corresponds to the very last entry in the binary table (which will be an AAOmega guide fibre in the case of a single AAOmega data set). There is ALWAYS a one-to-one correspondence between each spectrum position in the image and the binary table. There is typically a one-to-one correspondence between slit position and 2dF pivot position but with a number of known mismatches and discontinuities which are tracked via the PIVOT column of the binary table. | ||||||||
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| < < | -- RonHeald - 16 Apr 2007 | |||||||
| > > | -- RonHeald - 23 Apr 2007 | |||||||
View topic | History: r18 < r17 < r16 < r15 | More topic actions...
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