SNR Estimates and Guidelines at McDonald

You can observe 30 minutes after sunset and until 30 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.

The default Flower 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.

If the seeing is below 0.6" then there is no benefit to exposures that are shorter than those recommended below.

Recommended exposure times - approximate:

Kmag	itime (sec) Seeing~0.6"	itime (sec) Seeing~0.8"	itime (sec) Seeing~1"	itime (sec) Seeing~1.2"	itime (sec) Seeing~1.6"	itime (sec) Seeing~2.0"
4	<10	<15	<20	<25	< 30	30
5	15	30	30	45	45	60
6	30	45	60	60	90	120
7	60	90	120	160	180	200
8	90	120	180	220	260	300
9	180	300	300	480	600	600
10	300	480	600	600	900	900
11	600	900	1200	infinity	infinity	infinity
12	900	1200	infinity	infinity	infinity	infinity
>13	1200	infinity	infinity	infinity	infinity	infinity

McD SNR Estimation:

Estimate your SNR with this equation:

SNR=(273*sqrt(itime*expnum)*10^(-0.2*(Kmag))) /(1.66*ln(seeing in ")+1.9)

For example, four 600s exposures on a K=10 target with 0.6" seeing will give you:

SNR=(273*sqrt(600*4)*10^(-0.2*10)) /(1.66*ln(0.6)+1.9) ~ 130

The same target with the same exposure time but in 1.0" seeing will give:

SNR=(273*sqrt(600*4)*10^(-0.2*10)) /(1.66*ln(1.0)+1.9) ~ 70

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