At this time when astronomers are being surprised by the discovery of objects which emit a fabulously large amount of energy, that is the quasi-stellar radio sources and the quasi-stellar galaxies, and when by the means of space vehicles X rays, gamma rays and cosmic rays are being observed to come from the depths of interstellar space, one may ask why write a book about stars. Stars seem to be almost incidental when one looks at the universe in terms of exceedingly great energies. Nevertheless, stars exist. They are accessible to study and they have not yet revealed all their secrets. This is enough to arouse interest and to cause one to try to find answers to the questions which arise. The early type stars are particularly interesting because they are spendthrift stars pouring out their energy at a great rate. But their brilliance is also their undoing. They must evolve rather quickly, on an astrophysical scale. Thus by studying these stars we are studying a population in change. The implications from the local and from the cosmological viewpoint are important if one wishes to understand the details of stellar evolution and of galactic structure. Perhaps one of the simplest reasons for writing a book about the early type stars is to see if some of the conundrums pre sented by the spectra of these stars can be unravelled when all the available infor mation is brought together.

In this Symposium, researchers specializing in pulsation, rotation, magnetic fields and stellar winds are brought together for the first time in order to broaden our understanding of O and B stars. Thanks to advances in digital spectroscopy, new types of pulsating B stars have been discovered. The pulsations can be understood in terms of the recent revision of metal opacities, but the effects of rapid rotation and magnetic fields need further study. Observations in the UV and X-ray regions demonstrate that many B and Be stars show other activity, besides pulsation which is not yet understood. The reason for the enhanced mass loss in Be stars is a question which dominates the Symposium and which remains unanswered, although it is surely to be found in activity at or near the photosphere coupled with rotation. It is shown that the geometry of the circumstellar envelopes around Be stars is indeed a flattened disk as they can now be optically resolved. The variability of radiatively-driven winds from O and B stars are likely related to the rotation of the star. This underlines the central theme of the book: that the various phenomena seen in these stars cannot be studied in isolation.

On April 28 1986 Cornelis de Jager reached the age of 65 years. On April 30 he officially retired from the University of Utrecht where he has held a Chair for Stellar Astrophysics, later changed into Space Physics, since 1958. Cees de Jager, as he prefers to be called by his friends, has had an active and successful life in science. His interest in astronomy was raised by his father under the clear skies of Celebes (Indonesia). He started a study in physics and astronomy as a student of the late M. Minnaert in Utrecht during World War II. When in 1943 the occupying forces recruited students who did not want to sign the declaration of loyalty for their war-efforts, Cees and three fellow students went into hiding at the Observatory in Utrecht. During this very "quiet" period van de Hulst developed the theory of the 21 em radiation of neutral hydrogen and de Jager started the observations of variable stars in the pitch dark nights of a country at war. The study of Beta Cepheids rapid ly awoke his interest which was kept throughout the years. In 1958 he organized an international campaign to observe 12 Lac spectroscopically and photometrically, which was a great success.

Research on massive stars is undergoing a period of rapid progress, with long-held convictions being shown to be incomplete. While these stars are relatively few in number, they are the main driver of chemical and dynamical evolution in galaxies through their stellar winds and explosive deaths in core-collapse supernovae. Furthermore the impact of massive stars is widely recognized in many areas, as they are often used as tools to interpret the conditions and processes arising in different environments. In parallel, the development of new instrumentation, analysis techniques and dedicated surveys across all possible wavelengths have delivered large amounts of exquisite new data. These data are now providing a harsh test for the current state-of-the-art theoretical calculations of massive star birth, evolution and death. IAU Symposium 329 covers these topics and is therefore an invaluable resource for researchers in the field of massive stars and their evolution.

Ultraviolet Astronomy and the Quest for the Origin of Life addresses the use of astronomical observations in the ultraviolet range to better understand the generation of complex, life-precursor molecules. The origin of RNA is still under debate but seems to be related to the generation of pools of complex organic molecules submitted to heavy cycles of solution in water and drying. This book investigates whether these cycles require a planetary surface or may occur in space by examining both the theoretical and observational aspects of the role of UV radiation in the origin of life. This book offers the latest advances in these studies for astronomers, astrobiologists and planetary scientists. - Addresses both the theoretical and observational aspects of the role of Ultraviolet (UV) radiation in the origin of life - Builds on the requirements to produce prebiotic molecules in space and the implications for the origin of RNA - Investigates the use of ultraviolet observations related to planetary system formation, the evolution of young planetary disks, and the interaction of stars with planetary atmospheres