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Typical NIRI Imaging Sensitivity Measurements

Sensitivity estimates can be obtained for a variety of filters and source spectra using the NIRI Integration Time Calculator (ITC). The NIRI ITC should be used for estimating exposure times needed for proposals. The information on this page is provided for guidance on data reductions and analysis.

Important caveat: these measurements are approximate only. Observing conditions vary, and the zero point, extinction, and background flux can change significantly in time.

The zero point is defined as the magnitude of an object that would yield 1 ADU/sec at an airmass of 1. They tend to be stable at the 3% level over many months.

Recommended exposure times are for imaging of faint objects using the f/6 camera (J through K) and f/32 (L' and M').

Approximate total throughput values are as measured for the entire system, including the telescope, instrument, and detector. These values are for aluminum coatings on the telescope optics and NIRI on the side port. A gain of 12.3 electrons/ADU was used for these calculations.

Filter	Center wavelength (痠)	Zero point (1 ADU/s)	Background (mag/arcsec)	Typical extinction	Recommended Exposure (s)	Approx. Total Throughput
J	1.25	24.05	15 to 16	0.05 to 0.1	60 to 120	27%
H	1.64	24.0	14 to 14.5	0.05 to 0.1	30 to 60	35%
Kprime	2.12	23.68	13.7 to 14.2	0.05 to 0.1	30	44%
Kshort	2.15	23.40	13.6 to 14.1	0.05 to 0.1	30
K	2.20	23.4	13.5 to 14.0	0.05 to 0.1	30	37%
L'	3.77	22.21	3.5	-	0.8	28%
M'	4.68	20.1	0.3	-	1.3	23%

Last update 2006 January 11 by Andrew Stephens, Joe Jensen and Tom Geballe