Hi Paul, Bart & All,
First up, very, very nice image Bart. Congratulations.
Quote:
Originally Posted by Paul Haese
Resolution looks good Gray. I agree with the comments about the blue background cast. The histogram has blue to the right of the mid point. As Mike said, the cluster has mainly old main sequence stars and a smattering of blue stragglers. If you adjust the blue, the bulk of the stars looks white with notable blue stragglers and a few orange giants. Back ground comes up charcoal then.
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The thing that one has to bear in mind about "blue straggler" is that they are blue in a comparative sense and very rarely if ever actually "blue" -- ie have a B-V trace in the negatives. Most blue stragglers are currently believed to be merger remnant stars that are the result of two smaller stars colliding and/or merging or as a result of mass-transfer in a tight binary system. While stellar collisions/mergers are a vastly improbable event among the general population of stars in our galaxy, it is unlikely but does happen within the very, very dense cores of globular clusters and even in some dense open clusters where the distance between individual stars can be measured in light-hours as opposed to light-years.
Typically blue stragglers are F-type or at best very late A-type stars with a mass between 1 and 1.6 solar masses. The turn-off point (from the main sequence) for most genuine G.Cs is in the mid to late G-type (ie about 0.8 solar-masses). As I said, blue stragglers are generally not genuinely blue, but
comparatively blue and anomalously blue when compared to the other brighter member stars in the cluster (that are typically red AGB-tip stars). I would think that proper processing would render most of, if not nearly all these stragglers as white or very light yellow as opposed to blue. There might be a very few actually blue stars in a typical G.C that are, in the main, horizontal branch post AGB stars (and probably RR Lyrae-type variables) powered largely by the triple alpha process.
Best,
L.