Updated NSFCam Backgrounds and Zero Points (October 1999)

Below are the results of recent measurements (October 27, 1999) of background count rates for NSFCam through the broad-band filters. Also given are the estimated Zero Point values for the filters. The ZP values for the L, L'_MK, M'_MK, and M filters are rough estimates only; the values for the other filters have been measured directly. Estimates of the sensitivity of NSFCam, using the values given here, can be calculated with the NSFCam Limiting Magnitude Calculator. Also available are a Signal-to-Noise Calculator and an Exposure Time Calculator. 
  Background = background count rate in electrons per square
      arcsecond per second (with a gain of 10 electrons/ADU).

  Zero Point = value to be added to the instrumental magnitude
      to obtain the intrinsic magnitude of a source:
               mag = -2.5 log (DN/s) + ZP
      These values correspond to an airmass of 1.0. Values for
      an airmass of 0.0 can be obtained by adding the extinction
      coefficient given below to the given ZP value.

 Filter  Background [magnitude/sq arcsec]    Zero Point Mag.    Extinction Coeff.
 ------  --------------------------------    ---------------    -----------------
  J_MK     5.6 x 10(3)  [ 15.4 ]               22.30              0.102
  H_MK     2.2 x 10(4)  [ 13.8 ]               22.19              0.059
  K'_MK    1.3 x 10(4)  [ 13.6 ]               21.42              0.088
  K_MK     1.2 x 10(4)  [ 13.7 ]               21.38              0.088
  L        7.0 x 10(6)  [  5.9 ]               20.5               0.150
  L'_MK    1.6 x 10(7)  [  4.8 ]               20.3               0.093
  M'_MK    4.7 x 10(7)  [  1.5 ]               18.1               0.193
  M        2.0 x 10(8)  [  0.3 ]               18.6               0.220
Assuming background-limited performance, signal-to-noise ratio scales directly with the source flux and with the square root of the total integration time. Questions about these values should be directed to Bobby Bus.

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