You can observe starting at 12 degree twilight until, at most, 50 minutes before sunrise.
Don't get more than 4000 counts in a single exposure on a source, or strong H-band persistence will remain for ~15 minutes.
Try to get at least 1000 counts in a single exposure for your A0 telluric stars.
Science exposures with less than 30 counts are not easily reduced with the pipeline.
For most observations at Gemini, follow the programs requested observing plan (nodding and exposure times). The requested exposure times should provide the desired snr for the worst conditions allowable by the program, and will otherwise provide even better snr for that program. If targets are brighter than K=7 mag, then double check that the exposure time will not cause persistence (aim for max of snr ~250-300).
The default Fowler number is 16 and this should be used whenever possible.
For exposure times under 30 seconds the fowler number will need to be reduced, but should still be the largest even number possible.
GST SNR Estimation:
Estimate your SNR with this equation:
SNR=(273*sqrt(itime*expnum)*10^(-0.2*(Kmag-2))) /(0.7227*ln(seeing in ")+2.12)
Simple ETC for clear weather and 6" seeing:
https://igrins-jj.firebaseapp.com/etc/simple
Empirical SNR estimates based on the peak counts in the continuum:
| Peak counts in single frame continuum: | ABBA SNR (per resolution element) | ABBA(x2) |
50 | 55 | 80 |
| 150 | 100 | 140 |
| 300 | 140 | 200 |
| 600 | 200 | 280 |
| 1000 | 250 | 360 |
