Signal-to-Noise Calculations for the IRS

Basic Sensitivity Data

Basic Data on the Instrument and Detector

The information on this page should be used as a guide, not an indiscriminate indicator of the final S/N you will obtain at the telescope.  Slit losses will still occur (and be substantial) when the site seeing is not good. Strong OH emission lines (which vary through the night), and the need to ratio your object spectrum to a telluric absorption feature standard spectrum (whew!) will often be the limiting factors in how well you do in practice.  How well your ratio turns out will also depend on such nasty things as seeing variations (the tip-tilt system will help to stabilize these) and the frequency with which you measure telluric standards (tip-tilt will not stabilize this).

If you have questions or feedback regarding the IRS, please contact Bob Blum, or Brooke Gregory (