TY - JOUR
T1 - Chemical composition of UV-bright star ZNG 4 in the globular cluster M 13
AU - Ambika, S.
AU - Parthasarathy, M.
AU - Aoki, W.
AU - Fujii, T.
AU - Nakada, Y.
AU - Ita, Y.
AU - Izumiura, H.
PY - 2004/4
Y1 - 2004/4
N2 - 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.
AB - 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.
KW - Galaxy: globular cluster: individual: M 13
KW - Stars: Population II
KW - Stars: abundances
KW - Stars: evolution
KW - Stars: horizontal-branch
KW - Stars: individual: ZNG 4
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U2 - 10.1051/0004-6361:20031759
DO - 10.1051/0004-6361:20031759
M3 - Article
AN - SCOPUS:1842582834
SN - 0004-6361
VL - 417
SP - 293
EP - 300
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
IS - 1
ER -