منابع مشابه
Horizontal Branch stars as AmFm / HgMn stars
Recent observations and models for horizontal branch stars are briefly described and compared to models for AmFm stars. The limitations of those models are emphasized by a comparison to observations and models for HgMn stars.
متن کاملGravonuclear Instabilities in Post-Horizontal-Branch Stars
We investigate the gravonuclear instabilities reported by Bono et al. (1997a,b) during the onset of helium-shell burning at the end of the horizontal-branch (HB) phase. These instabilities are characterized by relaxation oscillations within the helium shell which lead to loops in the evolutionary tracks. We find the occurrence of these instabilities depends critically on how the breathing pulse...
متن کاملCalibrating horizontal-branch stars with Hipparcos
Parallaxes from the Hipparcos satellite allow for the first time to calibrate parameters of horizontal-branch (HB) like stars based on geometric distances. We present absolute magnitudes and luminosities for 8 such stars. Using Teff and log g values available from the literature, we also can calculate the mass of the HB stars. We find an average value ofMHB = 0.38 ±0.07 M for stars with 7500< T...
متن کاملHorizontal Branch Stars and the Ultraviolet Universe
Extremely hot horizontal branch (HB) stars and their progeny are widely considered to be responsible for the “ultraviolet upturn” (or UVX) phenomenon observed in elliptical galaxies and the bulges of spirals. Yet, the precise evolutionary channels that lead to the production of these stars remain the source of much debate. In this review, we discuss two key physical ingredients that are require...
متن کاملRadiative Levitation in Hot Horizontal Branch Stars
There is now considerable evidence that horizontal branch (HB) stars hotter than about 11,500 K experience an enormous enhancement of their photospheric iron abundance due to radiative levitation. In globular clusters, the photospheric iron abundance can reach values of [Fe/H] ∼ +0.3, or up to two orders of magnitude higher than the cluster iron abundance. Model atmospheres which take into acco...
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ژورنال
عنوان ژورنال: Astronomy and Geophysics
سال: 2004
ISSN: 1366-8781,1468-4004
DOI: 10.1046/j.1468-4004.2003.45524.x