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GRACES Integration Time Calculator

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The current ITC is an IDL script that can be downloaded HERE. It is an alternative to the ITC below, and it is much more accurate. To install it, simply untar the file (please choose the location wisely). Then, open IDL (assuming yu have a access to a licence) and get to the directory where the file ITCv1.1.tar was untarred. Then type:



The script will prompt you a series of questions before it produces the plot showing the S/N estimation. All the parameters (target parameters, observing conditions, etc.) can be given as inputs. For more details, type:

IDL> ITC,/help

You should also have the IDL Astronomy User's Library

The plot shows the signal-to-noise ratio as a function of wavelength per (physical) pixel. If you want to know the results for the optical resolution element, or for the interpolated pixels after spectra extraction, this is how to do it:
Signal-to-noise ratio per optical resolution element - The optical resolution element is 1.74 pix for the 1-fiber mode and 2.88 pix for the 2-fiber mode. Open the file .dat, and plot the signal-to-noise curve multiplied by the square-root of the size of the optical resolution element in pixels.
Signal-to-noise ratio per interpolated pixels - Once the spectrum is extracted, the steps between each wavelength is 0.63 pix. To get the signal-to-noise ratio for each of these interpolated pixel, you need to multiply the curve by the square-root of 0.63.
In any doubt, contact

If you do not have access to an IDL licence, you can still use the webform ITC below, but bear in mind that this is based on older performances that are not relevant anymore. You can as well use the current sensitivity curves to deduce the estimated exposure time for your target. Finally, you can always contact one of the GRACES team member for more extended help.

Webform (OLD) ITC: (Note: If the form below is not working and you do not have an IDL license, please email

How to use the GRACES (old) ITC  

  1. Astronomical source definition: Enter the brightness (in mag) in the selected filter, and give a temperature for the model black body. It is currently not possible to use actual spectra of stars, galaxies or QSO. The GRACES ITC assumes photometric conditions. To correct for worse conditions, please refer to Gemini observing constraints for cloud cover and modify the brigthness accordingly. For instance, for CC70%, you must add 0.3 mag.
  2. Instrument (ESPaDOnS) configuration: Select the Olapa 1 amp option and choose the other options at your own taste. These option are the central wavelength (the wavelength at which the wavefront sensor will optimise guiding), the spectroscopic mode (star only or star+sky, see more here) and the readout mode. To choose a CCD readout speed, please refer to the Detector characteristics page.
  3. Details of observation: Enter either the required signal-to-noise ratio or the desired exposure time. Make sure you select between "calculate S/N only" and "calculate exposure time" accordingly.
  4. Observing condition constraints: Please refer to the Gemini observing constraints for image quality to determine the value to use under Image Quality. The three choices of Moon phases can be considered as equivalent to sky backgrounds of 20%, 50/80% (depending on the distance to the moon you choose) and Any.
  5. Click on the Calculate button.  

If the form below is not visible, use this link: ITC

When preparing a proposal using GRACES, PIs have to include Overheads in their estimation of the total requested time per target.

If the above form is not visible, use this link: ITC

Based on the ESPaDOnS' exposure time calculator (EETC).

																																																																																										Last update February 10, 2015 by GRACES team

Gemini Observatory Participants