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...of this peak in the data is related to the richness of the horizontal branch, which is in turn related to the age and chemical composition of the stars in the cluster. A comparison of the observed M3 luminosity function with the van Rhijn function shows a depletion of stars, relative to fainter stars, for absolute magnitudes brighter than roughly MV = 3.5. This...
Many years ago, careful measurements of the average magnitudes and colours of RR Lyrae stars in the globular cluster M3 showed that all these stars fell within a narrow range of luminosity and colour (or surface temperature) or, equivalently, luminosity and radius. Also, every star falling in this narrow range of brightness and size was an RR Lyrae variable. Subsequent work has indicated that...
in star cluster: Globular clusters )...M13 in the constellation Hercules is the easiest to see and is the best known. At a distance of 22,000 light-years, it has been thoroughly investigated and is relatively poor in variables. M3 in Canes Venatici, 32,000 light-years away, is the cluster second richest in variables, with well more than 200 known. Investigation of these variables resulted in the placement of the RR Lyrae...
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