Astronomy and Astrophysics – Astrophysics
Scientific paper
2007-08-22
Astronomy and Astrophysics
Astrophysics
26 pages, 4 figures, accepted by Astrophysical Journal
Scientific paper
10.1086/522616
It is known that there must be some weak form of transport (called cool bottom processing, or CBP) acting in low mass RGB and AGB stars, adding nuclei, newly produced near the hydrogen-burning shell, to the convective envelope. We assume that this extra-mixing originates in a stellar dynamo operated by the differential rotation below the envelope, maintaining toroidal magnetic fields near the hydrogen-burning shell. We use a phenomenological approach to the buoyancy of magnetic flux tubes, assuming that they induce matter circulation as needed by CBP models. This establishes requirements on the fields necessary to transport material from zones where some nuclear burning takes place, through the radiative layer, and into the convective envelope. Magnetic field strengths are determined by the transport rates needed by CBP for the model stellar structure of a star of initially 1.5 solar mass, in both the AGB and RGB phases. The field required for the AGB star in the processing zone is B_0 ~ 5x10^6 G; at the base of the convective envelope this yields an intensity B_E < 10^4 G (approximately). For the RGB case, B_0 ~ 5x10^4 to 4x10^5 G, and the corresponding B_E are ~ 450 to 3500 G. These results are consistent with existing observations on AGB stars. They also hint at the basis for high field sources in some planetary nebulae and the very large fields found in some white dwarfs. It is concluded that transport by magnetic buoyancy should be considered as a possible mechanism for extra mixing through the radiative zone, as is required by both stellar observations and the extensive isotopic data on circumstellar condensates found in meteorites.
Busso Maurizio
Calandra Andrea
Nollett Kenneth M.
Wasserburg Gerald J.
No associations
LandOfFree
Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms? does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms?, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Can Extra Mixing in RGB and AGB Stars Be Attributed to Magnetic Mechanisms? will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-135546