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GRACES Integration Time Calculator

The current ITC is an IDL script that can be downloaded HERE. It is an alternative to the ITC below, and is is much more accurate. To install iit, 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. To know calling sequence and the details, type:

IDL> ITC,/help

IMPORTANT NOTE: The three curves show the signal-to-noise as a function of wavelength per 1)sampling (0.63 pix), 2) pixel and 3) resolution element (1.74pix for 1-f and 2.88 pix for 2-f mode), from bottom up!

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.




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 aimed 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.  

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




Astronomical source definition

Point source with spatially integrated brightness mag in filter
Model black body spectrum with temperature K

Instrument (ESPaDOnS) configuration

CCD chip
Spectrum central wavelength: nm
Observing Mode:
CCD Readout Mode:

Details of observation

Total integration time to achieve a S/N ratio of (not yet implemented)
Total S/N ratio resulting from an exposure time of secs

Observing condition constraints

Image Quality: arcsec
Moon phase:
Angular distance from the Moon: deg
Zenith distance: deg


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

																																																														Last update February 10, 2015 by GRACES team