Warm Patches Research Articles

Formation and flow of dust grains in cool stellar atmospheres

Stars are considered which would have no mass loss in the absence of dust grains, but are sufficiently cool for grains to condense in the atmosphere. Stars of ‘high’ luminosity lose gas and dust together at a copious rate; stars of ‘medium’ luminosity lose mainly grains without gas, and the atmosphere may be denuded of grain-forming material. Formulae are given for mass flow rates and for final velocities. A servomechanism is suggested which may lead to fairly large (∼0.1 μ), scattering silicate grains. An instability is suggested for cool M giants and supergiants, which leads to a patchy distribution of surface temperature (grains in cool patches, high flux in warm patches).