Abstract
We present a detailed model-atmosphere analysis of ZNG 4, a UV-bright star in the globular cluster M 13. From the analysis of a high resolution (R ≈ 45 000) spectrum of the object, we derive the atmospheric parameters to be T eff = 8500 ± 250 K, log g = 2.5 ± 0.5 and [Fe/H] = -1.5. Except for magnesium, chromium and strontium, all other even Z elements are enhanced with titanium and calcium being overabundant by a factor of 0.8 dex. Sodium is enhanced by a factor of 0.2 dex. The luminosity of ZNG 4 and its position in the color-magnitude diagram of the cluster indicate that it is a Supra Horizontal Branch (SHB) (post-HB) star. The underabundance of He and overabundances of Ca, Ti, Sc and Ba in the photosphere of ZNG 4 indicate that diffusion and radiative levitation of elements may be in operation in M 13 post-HB stars even at Teff of 8500 K. Detailed and more accurate abundance analysis of post-HB stars in several globular clusters is needed to further understand their abundance anomalies.
Original language | English |
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Pages (from-to) | 293-300 |
Number of pages | 8 |
Journal | Astronomy and Astrophysics |
Volume | 417 |
Issue number | 1 |
DOIs | |
Publication status | Published - 2004 Apr |
Externally published | Yes |
Keywords
- Galaxy: globular cluster: individual: M 13
- Stars: Population II
- Stars: abundances
- Stars: evolution
- Stars: horizontal-branch
- Stars: individual: ZNG 4
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science