The First Delta a observations of three globular clusters

PAUNZEN, E.; ILLIENV, I.KH.; PINTADO, O.I.; BAUM, H.; MAITZEN, M.H.; NETOPIL, M.; ÖNEHAG., A.; ZEJDA, J.; FRAGA, L.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2014 vol. 443 p. 2492 - 2498

0035-8711

Globular clusters are main astrophysical laboratories to test and modify evolutionary models.Thought to be rather homogeneous in their local elemental distribution of members, resultssuggest a wide variety of chemical peculiarities. Besides different main sequences, believedto be caused by different helium abundances, peculiarities of blue horizontal-branch stars andon the red giant branch were found. This whole zoo of peculiar objects has to be explainedin the context of stellar formation and evolution. The tool of Da photometry is employedin order to detect peculiar stars in the whole spectral range. This three filter narrow bandsystem measures the flux distribution in the region from 4900 to 5600Å in order to findany peculiarities around 5200Å. It is highly efficient to detect classical chemically peculiarstars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way andMagellanic Clouds. We present Da photometry of 2266 stars from 109 individual frames forthree globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with publishedabundances, for three horizontal-branch stars, only, yield an excellent agreement. Accordingto the 3s detection limit of each globular cluster, about 3%of the stars lie in abnormal regionsin the diagnostic diagrams. The first observations of three widely different aggregates givevery promising results, which will serve as a solid basis for follow-up observations includingphotometric as well as spectroscopic studies.