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Data reduction

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. A preliminary version can be downloaded on SourceForge ( This version still needs lots of work, and is not as performant as the future release. 

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

 Open source
 Orders extracted
  22 to 57 
  22 to 56
  bias, flat
  overscan, bias, flat
 Slit tilt correction
 Wavelength calibration
Wavelength correct
using telluric lines
 Output file
fits table
(one value per column)
 fits spectrum
(one order per extension)
  C (parameters tunned in a Makefile) 
  IDL (parameters given as values in the command line)

  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