Abundance anomalies in red giants
Scalo (1981) has reviewed observational information on abundances, luminosities, masses and other properties of peculiar red giants of the disk population. We have constructed theoretical models of 2, 3, 5 and 7M o stars allowing for the effect of rotation on mass loss and core size (ratio of surface rotational speed to break up speed of the order of 0.2) up to core helium exhaustion. These objects develop considerable mixing between the core and envelope, lose mass to an appreciable extent (30 to 40%) and display significant composition change in the surface layers.
We conclude that the chemical peculiarities of these red giants can be understood as a consequence of rotational mixing and mass-loss. We have treated the angular momentum transfer from the core to the envelope, as well as angular momentum (spin) loss from the surface. The extended mixing between the core and envelope, coupled with loss of mass from the outer layers, should result in more efficient meridional circulation and angular momentum transfer. Abundance anomalies can be seen as a natural consequence of these processes.
KeywordsMain Sequence Chemical Peculiarity Joule Dissipation Angular Momentum Transfer Intermediate Mass Star
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