Flat Compensation Consistency

["Mike Gutzwiller" <deepsky@fuse.net>]

I analyzed several star lists using the Flat Compensation program with encouraging results.  The lists were generated from five nights of data duringa week in the fall of 1996.  All were processed with the same set of flats and darks.  I used 8 regions and a background variation limit of 0.01.  With these limits I ended up with 100 to 200 stars in each region depending on the quality of the night.  Here are the compensation values I got:

 

    Night    371     373     374     376     377  Average Stdev

      X                 Camera 0

       0   0.000   0.024   0.024   0.038   0.016     0.020   0.014
      96   0.029   0.037  -0.001   0.011   0.018     0.019   0.015
     192   0.023   0.002  -0.002   0.023   0.007     0.011   0.012
     288   0.012   0.014   0.000   0.001   0.005     0.006   0.006
     384   0.006   0.019   0.002   0.001   0.002     0.006   0.008
     480  -0.015   0.001   0.021   0.005   0.007     0.004   0.013
     576  -0.006  -0.018   0.022  -0.005  -0.013    -0.004   0.015
     672  -0.058  -0.027  -0.039  -0.032  -0.020    -0.035   0.015
     768  -0.083  -0.015  -0.022  -0.032  -0.021    -0.035   0.028 

                        Camera 1

       0   0.000   0.055   0.073   0.046   0.051     0.045   0.027
      96   0.028   0.062   0.063   0.053   0.051     0.051   0.014
     192   0.030   0.038   0.032   0.033   0.031     0.033   0.003
     288   0.012   0.008   0.006   0.005   0.006     0.007   0.003
     384  -0.013  -0.024  -0.025  -0.024  -0.022    -0.022   0.005
     480  -0.011  -0.028  -0.030  -0.027  -0.033    -0.026   0.009
     576   0.002  -0.027  -0.027  -0.016  -0.020    -0.018   0.012
     672   0.026  -0.018  -0.006  -0.010  -0.006    -0.003   0.017
     768   0.041   0.009   0.002   0.001  -0.003     0.010   0.018 

                        Camera 2

       0   0.202   0.126   0.144   0.215   0.155     0.168   0.038
      96   0.162   0.135   0.098   0.126   0.128     0.130   0.023
     192   0.135   0.087   0.076   0.110   0.093     0.100   0.023
     288   0.086   0.063   0.048   0.063   0.044     0.061   0.017
     384   0.039   0.006   0.007   0.020   0.012     0.017   0.014
     480  -0.004  -0.016  -0.045  -0.015  -0.019    -0.020   0.015
     576  -0.038  -0.058  -0.072  -0.045  -0.065    -0.056   0.014
     672  -0.124  -0.160  -0.174  -0.145  -0.152    -0.151   0.019
     768  -0.194  -0.224  -0.201  -0.247  -0.231    -0.219   0.022
 

As you can see the values are quite consistent from one night to the next.  As expected the I cameras (0 and 2) are slightly worse than the V camera (1) since the I magnitudes are less well determined in the Tycho catalog.  Cameras 0 and 1 have fairly small compensation values but camera 2 has some whoppers with a range of 0.387 magnitudes from one side to the other!

 

There is some evidence from the table that night 371 is different from the others.  If we remove its data we get:

 

                     373     374     376     377        Average Stdev

      X                 Camera 0

       0           0.024   0.024   0.038   0.016           0.026   0.009
      96           0.037  -0.001   0.011   0.018           0.016   0.016
     192           0.002  -0.002   0.023   0.007           0.008   0.011
     288           0.014   0.000   0.001   0.005           0.005   0.006
     384           0.019   0.002   0.001   0.002           0.006   0.009
     480           0.001   0.021   0.005   0.007           0.009   0.009
     576          -0.018   0.022  -0.005  -0.013          -0.004   0.018
     672          -0.027  -0.039  -0.032  -0.020          -0.030   0.008
     768          -0.015  -0.022  -0.032  -0.021          -0.023   0.007 

                        Camera 1

       0           0.055   0.073   0.046   0.051           0.056   0.012
      96           0.062   0.063   0.053   0.051           0.057   0.006
     192           0.038   0.032   0.033   0.031           0.034   0.003
     288           0.008   0.006   0.005   0.006           0.006   0.001
     384          -0.024  -0.025  -0.024  -0.022          -0.024   0.001
     480          -0.028  -0.030  -0.027  -0.033          -0.030   0.003
     576          -0.027  -0.027  -0.016  -0.020          -0.023   0.005
     672          -0.018  -0.006  -0.010  -0.006          -0.010   0.006
     768           0.009   0.002   0.001  -0.003           0.002   0.005 

                        Camera 2

       0           0.126   0.144   0.215   0.155           0.160   0.039
      96           0.135   0.098   0.126   0.128           0.122   0.016
     192           0.087   0.076   0.110   0.093           0.092   0.014
     288           0.063   0.048   0.063   0.044           0.055   0.010
     384           0.006   0.007   0.020   0.012           0.011   0.006
     480          -0.016  -0.045  -0.015  -0.019          -0.024   0.014
     576          -0.058  -0.072  -0.045  -0.065          -0.060   0.012
     672          -0.160  -0.174  -0.145  -0.152          -0.158   0.012
     768          -0.224  -0.201  -0.247  -0.231          -0.226   0.019
 

In any case I believe the data supports the idea that we can compensate to the 0.01 magnitude level.

 

Mike G.