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Recent improvements in globular cluster colour-magnitude diagrams, coupled with an increase in large-sample spectroscopic abundance studies of cluster giants, finally allow some attempts at a statistically meaningful comparison of the chemical compositions of red giant branch (RGB) and asymptotic branch (AGB) cluster stars. We review some of the extant data here, concluding that in a few clusters the AGB stars show on average smaller amounts of high-temperature proton-capture synthesis products (low oxygen, high sodium and aluminum) at their surfaces than do the first-ascent RGB stars. This suggests that those RGB stars with envelopes that have been enriched with proton-capture material also have high helium contents. Such stars after the He-flash then take up residence on the bluest parts of the horizontal branch (as a consequence of their high envelope helium), probably never to return to the AGB during subsequent evolutionary stages.
We develop a magnetohydrodynamical model of Alfven wave-driven wind in open magnetic flux tubes piercing the stellar surface of Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, and investigate the physical properties of the winds. The
The Galactic globular cluster NGC 1851 has raised much interest since HST photometry revealed that it hosts a double subgiant branch. Here we report on our homogeneous study into the cyanogen (CN) bandstrengths in the RGB population (17 stars) and AG
The space-borne missions CoRoT and Kepler opened up a new opportunity for better understanding stellar evolution by probing stellar interiors with unrivalled high-precision photometric data. Kepler has observed stellar oscillation for four years, whi
Asymptotic giant branch (AGB) stars play a key role in the enrichment of galaxies with heavy elements. Due to their large amplitude variability, the measurement of elemental abundances is a highly challenging task that has not been solved in a satisf
Blue hook (BHk) stars are a rare class of horizontal branch stars that so far have been found in only very few Galactic globular clusters (GCs). The dominant mechanism for producing these objects is currently still unclear. In order to test if the pr