Efficiency

By measuring the signal from standard stars we can measure the efficiency of the entire system.

H Measurements

Measurements of two standard stars in H band were taken on June 9 UT on the Thirty Inch under good conditions. The total integrated flux over sky in a very large aperture was measured. Several different exposures at different times were used and the values converted to DN/sec. 
Star          DN/sec             Mag       Mzp
HD10560       48911 +/- 500       6.7     18.4 
SAO106-1024    1246 +/- 300      10.7     18.4
The magnitudes were taken from KPNO and UKIRT lists The Zero Point Magnitude Mzp is defined such that: 
     Mstar = Mzp - 2.5 Log10(DN/sec)

J Measurements

Measurements of two stars were taken in J band on July 29 UT. 
Star          DN/sec          Mag       Mzp
A28-0  (s1)  15079           8.46      18.6 
A29-0  (s13)  1458          10.23      18.1
The agreement between these two observations is very poor and not understood.

Theoretical

The Mzp of a perfect system is computed from the following factors: 
Filter  Lambda      DLambda       Flux 0Mag  Mzp 
       micron      micron      W/m^2/micron 
J       1.25        0.28          3.07E-09   19.8
H       1.65        0.30          1.12E-09   19.0
Ks      2.2         0.35          4.07E-10   18.4
The central wavelengths and bandwidths are taken from the IR consortium curves for our filter. The 0 Mag flux is taken from. Vega

Efficiency

The efficiency of the system is the difference between the observed Mzp and the perfect zp. From the above two numbers at H, we get a difference of 0.6 mag which implies that the efficiency is 58%! The difference at J is around 1.3 mag which is about 30%.

Compare to the theoretical value.

The product of this is 0.40.

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Last Revised September 15, 2000