By running the computers for one week we have been able to process all observed images (both singles and those that had been coadded from stacks) with the EFM method, and thus estimated the exponent, alfa, that the basic PSF must be raised to to model the halo around the Moon. Plotting the histogram of 9000 values for alfa we get:
We see a broad distribution from about 1.3 to 2.1. Inspection of the results reveals that only the images with alfa values very close to ~1.7 are any good. The lower values correspond to hazy or even partially cloudy nights. The values higher than ~1.7 have yet to be examined.
A typical (histogram equalized) image of the residuals for one of the images with alfa near 1.71 is here:
A ‘slice’ across the image shows this:
Upper panel is the slice – black being the image, red being the fitted halo; second panel is a detail view of panel one showing the DS, vertical dashed lines showing the limits to the sky on which the halo is fitted; third panel shows the difference between the black and red curves in panel two.
We see that the EFM method has been able to fit the sky so that it is essentially just noise – even on the BS (right) side of the disc, and that the DS has been revealed for a wide area onto the disc itself, only near the terminator is there a problem with the subtraction – the residual dips down.
The double peaked of the distribution near alpha ~ 1.7is very intriguing! Are all bands shown here or just V? Would be interesting to see if alpha is a function of filter.I wonder if we could also have a plot of alpha versus airmass (or zenith angle)?