Stroemgren photometry of globular clusters: M55 & M22

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dc.creatorRichter, P.
dc.creatorHilker, M.
dc.creatorRichtler, T.
dc.date1999-07-15
dc.date.accessioned2026-07-07T02:32:31Z
dc.date.available2026-07-07T02:32:31Z
dc.descriptionWe present Stroemgren CCD photometry for the two galactic globular clusters M55 (NGC 6809) and M22 (NGC 6656). We find average Stroemgren metallicities of -1.71 dex for M55 and -1.62 dex for M22. The determination of metal abundances in cluster giants with the Stroemgren m1 index in comparison with spectroscopic data from Briley et al. (1993) and Norris & Freeman (1982, 1983) shows that M55 and M22 have different distributions of cyanogen strengths. In M55, no CN abundance variations are visible among the giant-branch stars. In striking contrast, a large dispersion of cyanogen strengths is seen in M22. For M22 we find patchily distributed variations in the foreground reddening of E(B-V)=0.07, which explain the colour dispersion among the giant-branch stars. There is no evidence for a spread in iron within M22 since the variations in m1 are dominated by the large range in CN abundances, as already found by Anthony-Twarog et al. (1995). The difference between M55 and M22 may resemble the difference in integral CN band strength between M31 globular clusters and the galactic system. The colour-magnitude diagram of M55 shows the presence of a population of 56 blue-straggler stars that are more centrally concentrated than the red giant-branch stars.
dc.description9 pages, 9 figures, accepted for publication in A&A MJ
dc.identifierhttps://arxiv.org/abs/astro-ph/9907200
dc.identifierhttp://arxiv.org/abs/astro-ph/9907200
dc.identifier.urihttp://salesiana.dossiersoluciones.com/handle/123456789/14491
dc.subjectAstrophysics
dc.titleStroemgren photometry of globular clusters: M55 & M22
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