Difference: AAOmegaFileFormat (2 vs. 3)

Revision 32007-04-15 - RonHeald

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AAOmega File Format (or, which spectrum is which object?)

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When analysing data from an AAOmega run, one needs to be able to map the combined spectra returned from the reduction task back to individual objects from the input catalogue. All the relevant information is contained within the combined output file(s). The page that follows attempts to describe how to recover this information. The process is simple, once one follows the logic. However, it can seem rather convoluted at first sight. Please send any questions, comments and suggestion you may have on how to make this information more digestible, to Rob

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< Sharp (rgs@aao.gov.au).

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> Sharp (rgs@aao.gov.au).

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< The table below gives a summary of the 2dfdr output file content, for either the individual frame ....red.fits files or a combined_frames.fits file. The file is a standard Multi-Extension FITS file (FITS MEF).

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> The table below gives a summary of the 2dfdr output file content, for either the individual frame ....red.fits files or a combined_frames.fits file. The file is a standard Multi-Extension FITS file (FITS MEF).

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	IRAF format	Contents

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Extension	IRAF format	Contents

Primary image	.fits[0]	WxN image containing the spectrum (W pixels long) for each fibre of the N spectra
First Extension	.fits[1]	WxN image containing the Variance array for the data
Second Extension	.fits[2]	FITS binary table, with N rows, one for each fibre. Each Row contains information for each object such as RA, Dec, 2dF Pivot number and more

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Seventh Extension .fits[7] Sky spectrum Stored as a FITS binary table, with W rows. Each row contains the one element of the 'typical' sky spectrum used in the data reduction ('typical' because for a combined frame it is not obvious how the final sky spectrum for each fibre should be represented here). Note: The variance information is correctly propagated, the sky spectrum is not presented here for this purpose.

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< These extension can be accessed in a number of ways. A number of example are provided below, if you have an alternate suggestion or an example that should be added to this list (or if something does not seem to work), please contact Rob Sharp (rgs@aao.gov.au).

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> The extension can be accessed in a number of ways. A number of examples are provided below.

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< The primary image in the MEF fits file is a WxN image where N is the number of spectra which are represented. This is 400 for AAOmega data, 392 science fibres and 8 guide fibres. Unused science fibres and Sky spectra, are included in the output file along with the guide fibres spectra, even though the spectra contain no information, as this is seen to simplify book keeping, and is a small disc space overhead. In the case where multiple sets of AAOmega datasets, which contained a subset of common objects, have been combined, the format is a little more complex, and is explained separately below.

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> The primary image in the MEF FITS file is a WxN image where N is the number of spectra which are represented. This is 400 for AAOmega data, 392 science fibres and 8 guide fibres. Unused science fibres and Sky spectra, are included in the output file along with the guide fibres spectra, even though the spectra contain no information, as this is seen to simplify book keeping, and is a small disc space overhead. In the case where multiple sets of AAOmega datasets, which contained a subset of common objects, have been combined, the format is a little more complex, and is explained separately below.

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An important note on 2dF Fibre-Pivot number and 2dfdr Fibre number

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An Important Note on 2dF Fibre-Pivot Number and 2dfdr Fibre Number

There are two very important, and very different, number which one must understand in order to recover the information on 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

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Binary Table columns

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Column	Column name	Description
1	Name	Object name, as given in the .fld file
2	RA	Right Ascension from the .fld file
3	Dec	Declination from the .fld file
4	X	2dF field plate X co-ordinate (in microns)
5	y	2dF field plate Y co-ordinate (in microns)
6	Xerr	Reported error in X in final fibre placement
7	Yerr	Reported error in Y in final fibre placement
8	Theta	Angle of fibre on field plate
9	Type	Fibre type (P-program, S - Sky, U-unused etc...)
10	Pivot	2dF fibre pivot number
11	Magnitude	Object magnitude, as given in the .fld file
12	PID
13	Comment	Comment from the .fld file
14	Retractor	2dF retractor number
15	Switch Field
16	Switch Partner	For cross beam switched data, the paired fibre is indicated (fibre slit position number)
17	Wlen

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Column	Column name	Description
1	Name	Object name, as given in the `.fld` file
2	RA	Right Ascension from the `.fld` file
3	Dec	Declination from the `.fld` file
4	X	2dF field plate X co-ordinate (in microns)
5	Y	2dF field plate Y co-ordinate (in microns)
6	Xerr	Reported error in X in final fibre placement
7	Yerr	Reported error in Y in final fibre placement
8	Theta	Angle of fibre on field plate
9	Type	Fibre type (P-program, S - Sky, U-unused etc...)
10	Pivot	2dF fibre pivot number
11	Magnitude	Object magnitude, as given in the `.fld` file
12	PID	???
13	Comment	Comment from the `.fld` file
14	Retractor	2dF retractor number
15	Switch Field	???
16	Switch Partner	For cross beam switched data, the paired fibre is indicated (fibre slit position number)
17	Wlen	???

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Example for accessing the fits Binary table information

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Examples Accessing the FITS Binary Table Information

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< This list is not exhaustive, if your favorite option is missing, send an e-mail to Rob Sharp (rgs@aao.gov.au) and we'll add it to the list.

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> This list is not exhaustive. If your favorite option is missing, send an e-mail to Rob Sharp (rgs@aao.gov.au) and we'll add it to the list.

With Configure

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