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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, and are described further down on this page.

The recommended approach to get reliable results using GRACES is to compare extracted spectra using both OPERA and DRAGraces. OPERA is not supported by the Gemini observatory, but an internal version is run at the end of each GRACES run, and the extracted spectra are available through the Gemini Observatory Archive (GOA). See the Data Format page for information about these processed files. For any question regarding spectra reduced with OPERA, please email DRAGraces is a simple IDL script specialized for GRACES spectra. For any question or request about GRACES, please email

The OPERA pipeline

The Canada-France-Hawaii Telescope (CFHT) developed A software reduction, name OPERA, that is specialized  for ESPaDOnS spectrograph extraction. That same pipeline can be adapted to also reduce GRACES data. The latest version can be downloaded on SourceForge (  Reduced data from Opera is available on the GOA (more information on the Opera output can be found on the GRACES data format page).

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 is briefly discussed 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 sent directly to its author, André-Nicolas Chené

Newest version available: v1.3.1 available on github. This version has an improved way to handle the path to the data given to the option "dir", avoiding any confusions caused by how the path is written.

Older version available: v1.3 available on github. This version is modified to deal with the shift in the spectra on the detector post repair in late 2018. It can be used for spectra both pre- and post-repair and includes some other minor bug fixes.


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

Gemini Observatory Participants