Δa Observations of Three Globular Clusters: NGC 104 NGC 6205 NGC 7099

PAUNZEN, E.; ILLIENV, I.KH.; PINTADO, O. I.

Florianopolis

Congreso; XIV Latin American Regional IAU Meeting; 2013

Sociedad Astronomica de Brasil

Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, new results suggest a wide variety of chemical peculiarities. The preselection of apparent peculiar stars for a detailed spectroscopic analysis is very important for globular cluster fields. Most regions are very dense and the target stars are, normally, very faint. Photometry could be one way out of the dilemma since it is very efficient. Up to now, only observations in the Johnson $UBV(RI)$ and Str{\"o}mgren $uvby\beta$ systems are able The tool of $\Delta a$ photometry is employed in order to detect chemically peculiar Population II stars. This three filter narrow band system measures the flux distribution in the region from 4900 to 5600\AA\, in order to find any peculiarities around 5200\AA. The first $\Delta a$ observations for 3 globular clusters: NGC~104, NGC~6205 and NGC~7099, give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.