Re: pileup parameters.

Bulent KIZILTAN <bulent_at_email.domain.hidden>I was wondering how the pileup parameters are defined:
>
>  4  pileup.<1>nregions
>  5  pileup.<1>g0
>  6  pileup.<1>alpha

g0 corresponds to \bar{g}_0 in my pileup paper
(see http://space.mit.edu/~davis/pileup2001.html) and alpha
corresponds to \alpha.  Briefly, g0
represents the branching ratio into good grades, and alpha is
associated with grade migration.  g0 should be fixed at a value near
1, and alpha should be free to vary--- a value near 0.5 is expected.

nregions is harder to define.  It basically represents the number of
3x3 pixel islands that are piled.  For a near on-axis point source fix
it to 1.0.

--John
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