Astronomy and Astrophysics – Astrophysics
Scientific paper
1999-09-27
Astronomy and Astrophysics
Astrophysics
6 pages, 3 figures, to appear in the proceedings of: "The Galactic Halo: from Globular Clusters to Field Stars"; 35'th Liege I
Scientific paper
We study the ``jump'' in the blue horizontal--branch (BHB) distribution first detected by Grundahl et al. (1998) in the Galactic globular cluster (GC) M13. On the basis of Stromgren photometry for a sample of fourteen GC's we show that: 1) The jump is best characterized as a systematic shift, on a (u, u-y) color-magnitude diagram, from canonical zero-age HB (ZAHB) models, in the sense that the stars appear brighter and/or hotter than the models; 2) the jump is a ubiquitous phenomenon, ocurring over the temperature range 11,500 < Teff < 20,000K; 3) An analogous feature is present in (log g, log Teff) diagrams -- indicating a common physical origin for the two phenomena; 4) The physical mechanism responsible for the jump phenomenon is most likely radiative levitation of iron and other
Andersen Michael I.
Catelan Márcio
Grundahl Frank
Landsman Wayne B.
Stetson Peter B.
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