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Hot HB Stars in Globular Clusters: Physical Parameters and Consequences for TheoryAtmospheric parameters (T(sub eff), log g), masses and helium abundances are derived for 42 hot horizontal branch (HB) stars in the globular cluster NGC6752. For 19 stars we derive magnesium and iron abundances as well and find that iron is enriched by a factor of 50 on average with respect to the cluster abundance whereas the magnesium abundances are consistent with the cluster abundance. Radiation pressure may levitate heavy elements like iron to the surface of the star in a diffusive process. Taking into account the enrichment of heavy elements in our spectroscopic analyses we find that high iron abundances can explain part, but not all, of the problem of anomalously low gravities along the blue HB. The blue HB stars cooler than about 15,100 K and the sdB stars (T(sub eff) greater than or = 20,000 K) agree well with canonical theory when analysed with metal-rich ([M/H] = +0.5) model atmospheres, but the stars in between these two groups remain offset towards lower gravities and masses. Deep Mixing in the red giant progenitor phase is discussed as another mechanism that may influence the position of the blue HB stars in the (T(sub eff), log g)-plane but not their masses.
Document ID
20000084844
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Moehler, S.
(Erlangen-Nuernberg Univ. Bamberg, Germany)
Sweigart, A. V.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Landsman, W. B.
(Raytheon ITSS Greenbelt, MD United States)
Heber, U.
(Erlangen-Nuernberg Univ. Bamberg, Germany)
Date Acquired
August 19, 2013
Publication Date
January 1, 2000
Subject Category
Astrophysics
Distribution Limits
Public
Copyright
Other

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