Difference: AAOmegaFileFormat (14 vs. 15)

Revision 152009-10-23 - RonHeald

  AAOmega File Format (or, which spectrum is which object?)
   Reduced File Extensions
   Combining Multiple AAOmega Data Sets containing a Common Subset of Targets
   Combining Control
   Fibre Table Columns
   Important Note on 2dF Fibre-Pivot Number and 2dfdr Fibre Number
   How to Access the Fibre Table Information 
  With Configure
   Within 2dfdr
   2dfinfo
   IRAF
   IDL
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+ File Extensions
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+ Reduced File Extensions
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+This table gives a summary of a AAOmega 2dfdr output file content, for either an individual reduced frame (....red.fits files) or a combined reduced frame (combined_frames.fits files). The file is a standard Multi-Extension FITS file (FITS MEF). The extensions can be accessed in a number of ways given below.
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+This table gives a summary of a AAOmega 2dfdr output file content, for either an individual reduced frame (*red.fits files like '21apr20006red.fits') or a combined reduced frame (combined_frames.fits files). The file is a standard Multi-Extension FITS file (FITS MEF). The extensions can be accessed in a number of ways given below.
 			 Extension 
			 IRAF format 
			 Contents
- Extension
+ Contents
  Combining Multiple AAOmega Data Sets containing a Common Subset of Targets
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+Instead of simply combining based on the fibre number in the reduced data frames (i.e. combine fibre 1 in frame 1 with fibre 1 in frame 2, etc.), the 2dfdr combine algorithm combines data based on object name. This has some advantages:
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+Combining of reduced files occurs in 'AUTO' reduction mode when all local object frames have been processed. It also can be done 'manually' using the Combine Reduced Runs... item in the 2dfdr Commands menu.
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+ Multiple configurations of the same field can be combined together in the case where some, but not all objects are in common.
  Only sky (S) and program (P) fibres are combined. This includes cases in which a fibre has been disabled part way though the observation of a field, so that only the good data is combined.
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+The 2dfdr combine algorithm combines data based on either object name or object location. That is, fibres having the same name (or location) are added and normalised to produce the output. This is to include all objects, whether they are contained within every frame or only a sub-set of the frames. The combine has the following features:
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+This can result in final combined data frames in which there are more spectra than the instrument can produce in one exposure. This is to include all objects, whether they are contained within every frame or only a sub-set of the frames. The first spectra will be all those from the first frame (including any unused/parked and sky fibres), while any additional spectra will be extra program (only) spectra from objects not present in the first frame. All the fibres extension information is properly propagated in this process.
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+ Multiple configurations of the same field can be combined together when objects are in common. Notice this can result in more spectra than the instrument can produce in one exposure.
 
 

 Only fibre types 'S' (sky) and 'P' (program) fibres are combined. This includes cases in which a fibre has been disabled part way though a field observation, so only good data is combined. Unused/parked fibres have all values set to zero.
 
 

 The first spectra will be all those from the first frame in the combine including unused/parked and sky fibres. Any additional spectra will be only sky and program spectra from objects in subsequent frames and not present in the first frame. If the data combined are all from the same configuration there will be no difference in the fibre count. 
 
 

 All the fibre table extension information is properly propagated. Additional fibres are numbered beginning from the last fibre of the first frame.
 

N.B. Currently the combined file exposure time is NOT set properly. Exposure time is given in only one place, the value of the FITS header keyword 'EXPOSED'. This exposure time applies to all fibres within the file. When files are combined, this keyword is copied from the first frame. To fix this situation the fibre table structure must be modified to have a new column. This column would give the actual exposure time (in seconds) for each fibre spectrum. See Exposure Time Handling in the bug list.

 Combining Control 

Control of the combining process is done using the widget on the  2dfdr GUI Combine tab. There are widgets to control 

Selecting whether the combine is done based on matching object name or object location is done with the COMBNAME argument list member. This appears as the Combine Matching Name widget on the Combine tab on the 2dfdr GUI. Setting Combine Matching Name to true causes that to happen. Setting it false causes the combine to be based on match object locations.
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+There are plans for an extra array to be added that gives the actual exposure time (in seconds) for each spectrum.
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+If the data combined are all from the same configuration there will be no difference between the new combining and the old fibre number combining (apart from that unused/parked fibres will have all their values set to zero).

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