Meridional circulation and diffusion in A and early F stars

Journal Article · Mon Apr 01 04:00:00 EST 1991 · Astrophysical Journal; (USA)

DOI:https://doi.org/10.1086/169853· OSTI ID:5759876

Charbonneau, P; Michaud, G ^[1]

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1. Montreal Universite, (Canada) Observatoire du Mont Megantic, Montreal (Canada)

Time-dependent two-dimensional calculations of diffusion in the presence of meridional circulation are presented for stellar models pertaining to FmAm stars. It is shown that, once the helium superficial convection zone (HSCZ) has disappeared, the meridional circulation has little influence on chemical separation. In stars rotating too rapidly to become FmAm stars, chemical separation remains possible under the HSCZ. Meridional circulation does not completely wipe out chemical separation at these velocities, and cannot by itself lead to the abundance patterns characteristic of Lambda Booti stars. Upper limits to turbulence are set. In the presence of meridional circulation, helium settling in stars rotating at the observed cutoff for FmAm stars remains possible for values of vertical turbulent diffusion coefficients of order 1000 sq cm/s under the helium convection zone. This sets extremely tight constraints on turbulence in stars with equatorial rotational velocities of 100 km/s or less. 52 refs.

• OSTI ID: 5759876
• Journal Information: Astrophysical Journal; (USA), Journal Name: Astrophysical Journal; (USA) Vol. 370; ISSN ASJOA; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics & Cosmology-- Stars & Quasi-Stellar
Radio & X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ABUNDANCE
CHEMICAL COMPOSITION
CONVECTION
DIFFUSION
ELEMENT ABUNDANCE
ELEMENTS
ENERGY TRANSFER
FINITE ELEMENT METHOD
FLUIDS
GASES
HEAT TRANSFER
HELIUM
LIMITING VALUES
MASS TRANSFER
MATHEMATICAL MODELS
NONMETALS
NUMERICAL SOLUTION
PHYSICS
RARE GASES
STAR MODELS
TIME DEPENDENCE
TURBULENCE
TWO-DIMENSIONAL CALCULATIONS