To derive the following sensitivity values, we observed UKIRT faint standard stars on the night of Feb 26, 2013 and March 8, 2013.  The stars observed were FS138 for J, H, K, and HD129653 for L' and M'.  Aperture photometry was used to get the flux from the star.  To determine the sky noise, we measured the number of counts from empty regions of sky of the same size as the aperture used on the star, using the same sky annulus as on the standard stars.  The standard deviation of the counts in these sky regions was taken as the noise.  The integration times are those that were used for the acutal observation. The 5 sigma limit is how bright a star would have to be for its flux to be 5 times the sky noise.  The 5 sigma flux limits are:

 

Filter     Int.time     Magnitude Limit     

J               432 s     20.6                                  

H               128 s     18.5                                  

K               128 s     18.0                                  

L'               9.6 s     12.0                                  

M'               18 s     10.2                                  

 

   The calculated 5 sigma flux limits for 60 seconds of integration time are:

 

Filter     Magnitude Limit     

J               19.5                                  

H               18.1                                  

K               17.6                                  

L'               13.0                                  

M'               10.9                                  

 

 

   Exposure time necessary to be sky-noise limited. We define this as when the total noise (photon noise plus read noise) is double the 10 e- of read noise. Note that the minimum exposure time is 0.4 seconds, so all L' and M' imaging is photon noise limited.

 

Filter     Int.time

J               14 s     

H               1.5 s     

K               1.7 s     

L'               0.05 s     

M'               0.01 s     

 

   The magnitude zero point is value to be added to the instrumental magnitude to obtain the magnitude of a star: mag = -2.5 log (DN/s) + ZP. We derived these values via photometry on a set of standard stars in the MKO JHKL'M' filters. These values are appropriate for 3 microsecond pixel sampling, high well depth low gain setting of NSFCam.

 

Filter          Magnitude Zero Point     

J                    23.21                                  

H                    23.69                                  

K                    23.08                                  

L'                    22.03                                  

M'                    19.89                                  

 

 

 

Last modified 24 Sept 2013