convective zone

convective zone

A zone in a star where convection is the main mode of energy transport. This occurs throughout a protostar on the Hayashi track, and beneath the surface of a main-sequence star, where the temperature is sufficiently low to enable the nuclei of hydrogen and heavier elements to recombine with free electrons to form atoms and negative ions. The presence of these atoms and ions and their ability to absorb photons increases the opacity of the medium to the passage of radiation from below and results in a steeper temperature gradient, thereby triggering turbulent convection. Stars rather more massive than the Sun, fusing hydrogen by the carbon cycle, have a convective zone at the core, which mixes the nuclear fusion region.

The surface convective zone of a sunlike or late-type star is almost certainly involved in the production of its magnetic field, and hence in the cycle of chromospheric activity (or in the Sun's case solar activity) and in the heating of the chromosphere and corona, but the details are still uncertain. See also granulation; stellar structure.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

convective zone

[kən′vek·div ‚zōn]

(astrophysics)

A region of instability just below the photosphere of the sun in which part of the heat is carried outward by convective currents.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.