You are in: Instruments > AcqCam > Performance and Use > Sensitivity    

[Acq Cam image of NGC1097]

Acquisition Camera Sensitivity

Using the Acquisition Camera Integration Time Calculator (ITC) we have estimated the brightnesses of both point and uniform surface brightness sources that give a signal-to-noise ratio (S/N) of 5 in various integration times.

The details of how the ITC calculates limiting magnitudes is described in the "more info" links accessible from the ITC.

The ITC includes adjustments for observing conditions in its calculations. For the tables presented here, we assumed 70%-ile constraint for image quality and 50% conditions for sky transparency (CC and WV) and sky background . The meanings of the observing condition criteria are explained in detail in the observing condition constraints (see also the ITC help pages). We also assumed an airmass of less than 1.2 for the sensitivities presented here. Those applying for time on Gemini should use the ITC to make calculations using the most flexible set of criteria possible, as the joint probability of observing conditions used above or better is only 8.75%.

All magnitudes listed below result in a S/N of 5 in a total integration time as listed. For the hour-long integration, individual exposure times were 900s. In the other cases two exposures of half the listed total integration time were assumed. Observations are assumed to be dithered and sky subtraction noise is included. All individual exposures include the source. The ITC calculates the S/N in an aperture that maximizes S/N given the predicted image quality for the observing conditions and wavelength requested. The sensitivity values in the table below use the optimum ITC aperture. For uniform surface brightness sources, an aperture with an area of 1 square arcsec is used. A spectrum of an A0V star was assumed.

  Filter Name   point source mag   extended source  (3600sec)
mag / arcsec2
  1 sec   100sec  3600sec
B_G0152 20.0 23.0 25.0 25.4
V_G0153 20.8 23.7 25.7 26.1
R_G0154 20.3 23.2 25.2 25.6
I_G0155 20.1 22.9 24.8 25.3


During commissioning several standard star fields from Landolt 1992 were observed. The results listed below are from three photometric nights in June 2001. More data will be added as it becomes available. The zero points and colour terms are defined as

BLandolt = ZPB + CB(B-V)Landolt + maginstrumental
VLandolt = ZPV + CV(B-V)Landolt + maginstrumental
RLandolt = ZPR + CR(V-R)Landolt + maginstrumental
 ILandolt  = ZP+ CI(V-I) Landolt +  maginstrumental

   Filter Name      Mag Zero Point     Colour term 
B_G0152 27.4+/-0.1 0.24+/-0.06
V_G0153 28.2+/-0.1 0.14+/-0.01
R_G0154 27.5+/-0.1 0.28+/-0.04
I_G0155 27.0+/-0.1 0.08+/-0.01

[Science Operations home] [AcqCam home] [telescope home]

Last update March 5, 2003; Rodrigo Carrasco
Previous version October 23, 2002; Cláudia Winge