## Calibrating visibility amplitudes

Begin by plotting the (squared) visibility amplitudes of the program star (Mizar, FKV0497) and its calibrator (FKV0509) for a selection of channels. The plot widgets as shown below are created using Calibrate|Visibility|PLOT. The one on the left is the general plot selection widget, the one on the right, the (data) index selection widget, is created when additional input is required as to the indices of the selected data. Create it by selecting "VisSq c/e" for the Y-axis variable.

Now, set all the fields just like in the widgets shown below. Remember to terminate your entry in a text field with <return>!

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Here is all the amplitude data for the E-W baseline (ob=1) for Mizar (FKV0497) and its calibrator (FKV0509). We selected only 20 channels redward of 530 nm since the blue channels have a very low sensitivity.

Use Calibrate|Visibilities|CALIBRATE to bring up the calibration widgets. The one on the right is created when you select a "seeing indicator" in the list of the widget on the left. Click on the images for further information.

The calibration in our example works as follows: after making the selection as indicated above, click on "Calibrate". The calibrator data is then smoothed with a kernel of 40 min, and calibration factors are interpolated at the epochs of the program source scans. The calibration is applied to all stars selected in the plot selection widget. This is done for every channel ("Loop" option selected). Below is the screen print after clicking on "Calibrate".
Solution calculated for OB= 1, Bl= 1, Ch= 2. (RMS [%] = 1.876)
Solution calculated for OB= 1, Bl= 1, Ch= 3. (RMS [%] = 2.050)
Solution calculated for OB= 1, Bl= 1, Ch= 4. (RMS [%] = 2.116)
Solution calculated for OB= 1, Bl= 1, Ch= 5. (RMS [%] = 2.217)
Solution calculated for OB= 1, Bl= 1, Ch= 6. (RMS [%] = 2.135)
Solution calculated for OB= 1, Bl= 1, Ch= 7. (RMS [%] = 2.690)
Solution calculated for OB= 1, Bl= 1, Ch= 8. (RMS [%] = 2.634)
Solution calculated for OB= 1, Bl= 1, Ch= 9. (RMS [%] = 2.333)
Solution calculated for OB= 1, Bl= 1, Ch= 10. (RMS [%] = 2.254)
Warning(CALCOEFFS): no valid data points found! OB= 1, Bl= 1, Ch=11
Solution calculated for OB= 1, Bl= 1, Ch= 12. (RMS [%] = 2.161)
Solution calculated for OB= 1, Bl= 1, Ch= 13. (RMS [%] = 2.450)
Solution calculated for OB= 1, Bl= 1, Ch= 14. (RMS [%] = 2.043)
Solution calculated for OB= 1, Bl= 1, Ch= 15. (RMS [%] = 2.098)
Solution calculated for OB= 1, Bl= 1, Ch= 16. (RMS [%] = 1.975)
Solution calculated for OB= 1, Bl= 1, Ch= 17. (RMS [%] = 2.306)
Solution calculated for OB= 1, Bl= 1, Ch= 18. (RMS [%] = 2.028)
Solution calculated for OB= 1, Bl= 1, Ch= 19. (RMS [%] = 2.225)
Solution calculated for OB= 1, Bl= 1, Ch= 20. (RMS [%] = 1.709)
Calibration applied for stars FKV0497 FKV0509 .

We now should look at the results by plotting VisSq c/e for the E-W baseline (output beam 1). Just click on "Plot|Screen". Below is what you should see. Repeat the same calibration process for output beams 2 and 3 (spectrometers 2 and 3, i.e. the C-W and C-E baselines), as well as the triple amplitudes. Don't forget to change the data type (button "Variable") to TripleAmp when calibrating the triple amplitudes!