Yeh I can see the Evil HH really well in your data too
It is my understanding it is the H-Beta emission that imparts the blue to the Ha making it varying shades of magenta rather than red but as for the blue/cyan being presented in the the nebula in some images....I can't find any reference as to why this might be so in the natural RGB range..? The
La Silla 2.2m shot released recently shows the blue/cyan quite strongly but it was composed from 6 different filters (U, V, Ha, SII, Blue and Red)
. Manipulating colours for purely aesthetic reasons is perfectly legitimate (I do it often) but I don't understand what might be causing this blue otherwise? It can't be from Rayleigh scattering as this would surely be overwhelmed by the strong emission from such a large neb (wouldn't it?) so is there an explanation for this blue appearing in a natural RGB presentation coming from real physics occuring in the RGB range?
Mike