Concluding Remarks of the I.A.U. colloquium NO.108

Extract

The discussions during the colloquium clearly pointed to the recent rapid progress in applying the atmospheric models to the detailed diagnostics of stellar evolution.

The high–quality spectroscopic data now available enable us to evaluate the abundances of scarce elements and isotopes in the classical stellar atmospheres. Many of them are found to be useful to sound the mixing and the gravity settling phenomena in the stellar interior. Extensive contributions were presented about the former process in the AGB stars, and about the latter process in the Li–defficient F stars.

The evolutionary interactions between the stellar interior and the atmosphere become distinct when the mass-loss processes set in. It was pointed out that high–rate mass loss can influence the internal evolution and mixing on one side, and that on the other side the mixing (dredging–up) can change the abundances of heavy elements in the atmosphere and further modulate the mass–loss rate. Many speakers presented ample of observational data from UV to mm–wave range indicating occurences of substantial mass loss from various kinds of stars. Self consistent models with spherical geometry were proposed for stellar winds which are driven by the radiation pressure acting on ions or dust grains. This involves comprehensive calculation related to the molecular chemistry and the grain physics. So far as the flow is stationary and spherically symmetric, the escape velocity and the mass–loss rate determine the density structure of the wind in radiative equilibrium.