We present the results of nucleosynthesis computations in mass transport phenomena affecting the final evolutionary stages of a low mass star. We assume that the process starts near the H-burning shell, and is driven by magnetic mechanisms, according to recent suggestions [1]. This is due to the fact that magnetized bubbles are subject to a fast buoyancy, accompanied by a downward flow induced by the settling of the heavier non-magnetized envelope material. During its downward journey toward the H shell this envelope material can undergo further proton captures, so that the mixing process ultimately induces changes in the envelope isotopic ratios 12C/13C,17O/16O,18O/16O,26Al/27Al. In most conditions the circulation is such that 7Li is destroyed. Production of this nucleus can however occur in a region of the parameter space, if the fast-rising magnetic structures provide a rapid upward transport of the Be abundance, as present near the H shell or produced in the downflow. In normal low mass red giants (i.e. excluding the anomalous CJ stars and the super-Li rich objects) Li seems to be created only on the RGB, and then to undergo a slow destruction through extra-mixing processes

Slow and Fast extra-mixing in stars from magnetic Buoyancy

PALMERINI, SARA;BUSSO, Maurizio Maria
2009

Abstract

We present the results of nucleosynthesis computations in mass transport phenomena affecting the final evolutionary stages of a low mass star. We assume that the process starts near the H-burning shell, and is driven by magnetic mechanisms, according to recent suggestions [1]. This is due to the fact that magnetized bubbles are subject to a fast buoyancy, accompanied by a downward flow induced by the settling of the heavier non-magnetized envelope material. During its downward journey toward the H shell this envelope material can undergo further proton captures, so that the mixing process ultimately induces changes in the envelope isotopic ratios 12C/13C,17O/16O,18O/16O,26Al/27Al. In most conditions the circulation is such that 7Li is destroyed. Production of this nucleus can however occur in a region of the parameter space, if the fast-rising magnetic structures provide a rapid upward transport of the Be abundance, as present near the H shell or produced in the downflow. In normal low mass red giants (i.e. excluding the anomalous CJ stars and the super-Li rich objects) Li seems to be created only on the RGB, and then to undergo a slow destruction through extra-mixing processes
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11391/135405
Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus ND
  • ???jsp.display-item.citation.isi??? ND
social impact