The first Delta a observations of three globular clusters
2014 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 443, no 3, 2492-2498 p.Article in journal (Refereed) Published
Globular clusters are main astrophysical laboratories to test and modify evolutionary models. Thought to be rather homogeneous in their local elemental distribution of members, results suggest a wide variety of chemical peculiarities. Besides different main sequences, believed to be caused by different helium abundances, peculiarities of blue horizontal-branch stars and on the red giant branch were found. This whole zoo of peculiar objects has to be explained in the context of stellar formation and evolution. The tool of Delta a photometry is employed in order to detect peculiar stars in the whole spectral range. This three filter narrow-band system measures the flux distribution in the region from 4900 to 5600 angstrom in order to find any peculiarities around 5200 angstrom. It is highly efficient to detect classical chemically peculiar stars of the upper main sequence, Be/Ae, shell and metal-weak objects in the Milky Way and Magellanic Clouds. We present Delta a photometry of 2266 stars from 109 individual frames for three globular clusters (NGC 104, NGC 6205, and NGC 7099). A comparison with published abundances, for three horizontal-branch stars, only, yields an excellent agreement. According to the 3 sigma detection limit of each globular cluster, about 3 per cent of the stars lie in abnormal regions in the diagnostic diagrams. The first observations of three widely different aggregates give very promising results, which will serve as a solid basis for follow-up observations including photometric as well as spectroscopic studies.
Place, publisher, year, edition, pages
2014. Vol. 443, no 3, 2492-2498 p.
techniques: photometric, stars: chemically peculiar, stars: horizontal branch, globular clusters: individual: NGC 104, globular clusters: individual: NGC 6205, globular clusters: individual: NGC 7099
IdentifiersURN: urn:nbn:se:uu:diva-237583DOI: 10.1093/mnras/stu1276ISI: 000342920400045OAI: oai:DiVA.org:uu-237583DiVA: diva2:769000