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Data reduction

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Two pipelines were developed completely independently for GRACES data. One is called OPERA, the other DRAGRACES. Both are open source, but neither is supported by Gemini.

The OPERA pipeline


 
The Canada-France-Hawaii Telescope (CFHT) is about to complete (early 2017) the development of an alternative software reduction, name OPERA, that can reduce data from the ESPaDOnS spectrograph. That same pipeline can be adapted to also reduce GRACES data. The latest version can be downloaded on SourceForge (https://sourceforge.net/projects/opera-pipeline/).  

This document from CFHT, OPERAperformance.pdf, describes the performance of Opera in comparison with Libre-Esprit on Espadons data, which is also relevant for GRACES data reduction.

The DRAGRACES pipeline


Written in IDL, the pipeline can be found on the DR forum. It is barely more than a thousand lines long, and everyone is invited to download, use and modify it as needed. It is requested that no helpdesk ticket is sent regarding DRAGRACES, as questions and requests will be better addressed from the thread in the DR forum were the script can be found. 

New version available: v1.1 available on github here. This version has an improved wavelength solution, new scattered light correction, and various bug fixes including the fix for 2 fiber mode extraction.

 

Comparing both pipelines

 
  OPERA
 DRAGRACES
 Open source
 YES
 YES
 Orders extracted
  22 to 57 
  22 to 56
 Reduction
  bias, flat
  overscan, bias, flat
 Slit tilt correction
  YES
  YES
 Wavelength calibration
  YES
  YES
Wavelength correct
using telluric lines
  YES
  NO
 Output file
fits table
(one value per column)
 fits spectrum
(one order per extension)
 Language
  C (parameters tunned in a Makefile) 
  IDL (parameters given as values in the command line)


NOTES:
  1. The values given in the table are current, and will be updated as the pipelines are developed. Developement is expected by Gemini users who download the script, improve it, and share their work.

Do it yourself

The high-resolution spectrograph GRACES produces data that are comparable to any echelle spectrograph. It can be reduced reasonably well using IRAF.  However, for optimal resolution power (IRAF cannot deal with ESPaDOnS tilted slice image) and signal-to-noise, it is better to use a dedicated software. 

For any question about the raw data format, please contact graces_science@gemini.edu.