L.A. Willson – författare

Fundamental unsolved problems of stellar astrophysics include the effects of angular momentum on stellar structure and evolution, the nature and efficiency of the processes by which angular momentum is redistributed within and lost from stars, and the role that stellar rotation plays in enhancing or driving stellar mass loss. There appears to be a qualitative change in the nature and efficiency of these mechanisms near spectral type FO: hotter (more massive) stars typically retain more angular momentum at least until they reach the main sequence, while cooler stars typically spin down quickly. For the hotter stars, recent work suggests a strong link between the type of pulsation behavior, the mass loss rates, and the rotation velocity. If the same mechanisms are able to drive mass loss from the main sequence A stars, as has recently been proposed, then the current interpretations of a number of observations will be drastically affected: e. g. the ages of clusters may be incorrect by up to a factor of two, and the surface abundances of isotopes of He, Li and Be may no longer give constraints on cosmological nucleosynthesis. There are also effects on the evolution of the abundances of elements in the interstellar medium and on the general evolution of populations of stars. Thus the questions of the mechanisms of angular momentum and mass loss of stars more massive than the sun is important not only for stellar studies but for the foundations of much of modern astrophysics.

Stellar mass loss is an essential part of the cycling of material from the interstellar medium into stars and back, and must be understood if we are to model processes on galactic to cosmological scales. The study of stellar winds and the effects of stellar mass loss has reached a particularly exciting stage where observational capabilities are increasingly able to provide interesting constraints on models and theories. Recent resu1ts from theoretical and observational work for both hot and cool stars with substantial winds have led to the suggestion that a combination of pulsation with other mechanisms makes for particularly efficient mass loss from stars. This provided the original motivation for the organization of this workshop. The conference was organized along relatively conventional lines according to the types of objects being scrutinized. However the true unity of the proceedings comes from the interplay of the mechanisms involved. For example, for the cool, luminous Mira variables, pulsation leads to shock waves that extend the atmosphere, enhancing dust formation; radiation pressure on dust drives the wind, cooling the atmosphere and in some cases suppressing the shocks. Similarly for the Be stars, both pulsation (in this case, non-radial) and radiation pressure (due to UV resonance lines) are expected to be important, and this expectation is at least qualitatively borne out by the observations.

Fundamental unsolved problems of stellar astrophysics include the effects of angular momentum on stellar structure and evolution, the nature and efficiency of the processes by which angular momentum is redistributed within and lost from stars, and the role that stellar rotation plays in enhancing or driving stellar mass loss. There appears to be a qualitative change in the nature and efficiency of these mechanisms near spectral type FO: hotter (more massive) stars typically retain more angular momentum at least until they reach the main sequence, while cooler stars typically spin down quickly. For the hotter stars, recent work suggests a strong link between the type of pulsation behavior, the mass loss rates, and the rotation velocity. If the same mechanisms are able to drive mass loss from the main sequence A stars, as has recently been proposed, then the current interpretations of a number of observations will be drastically affected: e. g. the ages of clusters may be incorrect by up to a factor of two, and the surface abundances of isotopes of He, Li and Be may no longer give constraints on cosmological nucleosynthesis. There are also effects on the evolution of the abundances of elements in the interstellar medium and on the general evolution of populations of stars. Thus the questions of the mechanisms of angular momentum and mass loss of stars more massive than the sun is important not only for stellar studies but for the foundations of much of modern astrophysics.

Stellar mass loss is an essential part of the cycling of material from the interstellar medium into stars and back, and must be understood if we are to model processes on galactic to cosmological scales. The study of stellar winds and the effects of stellar mass loss has reached a particularly exciting stage where observational capabilities are increasingly able to provide interesting constraints on models and theories. Recent resu1ts from theoretical and observational work for both hot and cool stars with substantial winds have led to the suggestion that a combination of pulsation with other mechanisms makes for particularly efficient mass loss from stars. This provided the original motivation for the organization of this workshop. The conference was organized along relatively conventional lines according to the types of objects being scrutinized. However the true unity of the proceedings comes from the interplay of the mechanisms involved. For example, for the cool, luminous Mira variables, pulsation leads to shock waves that extend the atmosphere, enhancing dust formation; radiation pressure on dust drives the wind, cooling the atmosphere and in some cases suppressing the shocks. Similarly for the Be stars, both pulsation (in this case, non-radial) and radiation pressure (due to UV resonance lines) are expected to be important, and this expectation is at least qualitatively borne out by the observations.

Fundamental unsolved problems of stellar astrophysics include the effects of angular momentum on stellar structure and evolution, the nature and efficiency of the processes by which angular momentum is redistributed within and lost from stars, and the role that stellar rotation plays in enhancing or driving stellar mass loss. There appears to be a qualitative change in the nature and efficiency of these mechanisms near spectral type FO: hotter (more massive) stars typically retain more angular momentum at least until they reach the main sequence, while cooler stars typically spin down quickly. For the hotter stars, recent work suggests a strong link between the type of pulsation behavior, the mass loss rates, and the rotation velocity. If the same mechanisms are able to drive mass loss from the main sequence A stars, as has recently been proposed, then the current interpretations of a number of observations will be drastically affected: e. g. the ages of clusters may be incorrect by up to a factor of two, and the surface abundances of isotopes of He, Li and Be may no longer give constraints on cosmological nucleosynthesis. There are also effects on the evolution of the abundances of elements in the interstellar medium and on the general evolution of populations of stars. Thus the questions of the mechanisms of angular momentum and mass loss of stars more massive than the sun is important not only for stellar studies but for the foundations of much of modern astrophysics.