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Since 1967, the main scientific events of the General Assemblies of the International Astronomical Union have been published in the separate series, Highlights of Astronomy. The present Volume 11 presents the major scientific presentations made at the XXIIIrd General Assembly, August 18-30, 1997, in Kyoto, Japan.

Ken Freeman I would like to pick out a few items that I found particularly interesting. The choice probably reflects my ignorance, because many of these topics are no doubt more known to most of you. I am fairly sure that some of them are basic and important. We will start with the first session. There were three closely related papers on the evolution of massive stars, the formation of open clusters and associations and the IMF. We learned that clusters appear to form in initially bound clouds 6 of masses between 10'+_10 M , but star formation is a destructive process. Most of the gas is@ lost and the remaining stars then find themselves in an unbound system, which naturally disperses on a dynamical time. As a result of this, star formation is typically a fairly inefficient process, at least on the scale of open clusters. However (as Heggie pointed out) it seems to be somewhat more efficient on smaller scales, as evidenced by the fairly high incidence of binary stars. To form a bound cluster requires a higher efficiency of star formation, typically 30% or more, and we see how the three papers of this morning session relate: the initial mass function and the timing of where and when the DB stars form dictate the likely fate of the system.

This volume of the Highlights of Astronomy contains the Invited Discourses and the proceedings or summaries of Joint Discussions, Special Sessions, and Working Group Meetings held at the XIInd IAU General Assembly in August 1994 in The Hague. While the three Invited Discourses are reproduced in the order of their appearance in the meeting programme, the Joint Discussions have been reordered according to their topics. Not included in this volume are the proceedings of the GA Symposia which will be published individually in the IAU Symposia series. I am most grateful to the authors of the invited discourses for preparing manuscripts in spite of heavy other commitments. It is a pleasure to express my appreciation of the work by Dr. Jacqueline Bergeron in organizing the XXIInd General Assembly, and I wish to thank all authors and meeting chairpersons for their cooperation and for providing their contributions in time to meet the customary publication schedule of this series. Special thanks are due to Ms. Monique Leger-Orine from the IAU office for considerable and patient assistance in the final editing, and to Dr. Tom Herbst from the Max­ Planck-Institute for Astronomy for permission to reproduce on the cover of this volume one of his IR images of Jupiter obtained just after the Comet Shoemaker-Levy 9 impact, one of the definite Highlights of Astronomy in 1994.

After the same pattern as the XIII th General Assembly of the International Astronom ical Union the present Volume of the Highlights in Astronomy contains the texts of the invited discourses given at the XIVth General Assembly held in Brighton, England, August 1970.

Transactions volume XIIIB bring the results of the administrative meetings and of the meetings of Commissions held during the General Assembly. The present volume is devoted to the most important scientific results of the General Assembly as presented in the Invited Discourses, Joint Discussions, and at Special Meetings.

This volume of the Highlights of Astronomy contains the Invited Discourses and the proceedings or summaries of Joint Discussions, Special Sessions, and Working Group Meetings held at the XIInd IAU General Assembly in August 1994 in The Hague.

Transactions volume XIIIB bring the results of the administrative meetings and of the meetings of Commissions held during the General Assembly. The present volume is devoted to the most important scientific results of the General Assembly as presented in the Invited Discourses, Joint Discussions, and at Special Meetings.

After the same pattern as the XIII th General Assembly of the International Astronom ical Union the present Volume of the Highlights in Astronomy contains the texts of the invited discourses given at the XIVth General Assembly held in Brighton, England, August 1970.

The Proceedings of the Symposia are published in separate Volumes, while the Transactions of the General Assembly and of the Extraordinary General Assembly contain short reports of the Commission meetings, the administrative sessions, and the opening ceremonies.

It has become a tradition in the Union to publish the Invited Discourses and the Proceedings of the Joint Discussions held at a Gene ral Assembly in a separate volume entitled HIGHLIGHTS OF ASTRONOMY. Part (TI) contains the proceedings of the four Joint Discussions and one Joint Meeting related essentially to stars and the structure of our Galaxy.

Since 1967, the main scientific events of the General Assemblies of the International Astronomical Union have been published in the separate series, Highlights of Astronomy. The present Volume 11 presents the major scientific presentations made at the XXIIIrd General Assembly, August 18-30, 1997, in Kyoto, Japan.

The present volume contains the texts of the three invited Di scourses and of the papers presented duri ng seven Joi nt Discussion Meetings and eight Joint Commission Meetings. The invited Discourses were arranged by the IAU Executive Committee and the Joint Discourses and Commission Meetings by the respective chairpersons.

The scientific meetings of the !AU are the !AU Symposia, !AU Colloquia, Regional Meetings in Astronomy held under the auspices of the !AU, the Commission Meetings, which may be Joint Meetings of Commissions, and !AU Joint Discussions.

It has become a tradition in the Union to publish the Invited Discourses and the Proceedings of the Joint Discussions held at a Gene ral Assembly in a separate volume entitled HIGHLIGHTS OF ASTRONOMY. Part (n) contains the proceedings of the four Joint Discussions and one Joint Meeting related essentially to stars and the structure of our Galaxy.

Since 1967, the main scientific events of the General Assemblies of the International Astronomical Union have been published in the separate series, Highlights of Astronomy. The present Volume 11 presents the major scientific presentations made at the XXIIIrd General Assembly, August 18-30, 1997, in Kyoto, Japan.

It has become a tradition in the Union to publish the Invited Discourses and the Proceedings of the Joint Discussions held at a Gene ral Assembly in a separate volume entitled HIGHLIGHTS OF ASTRONOMY. Part (TI) contains the proceedings of the four Joint Discussions and one Joint Meeting related essentially to stars and the structure of our Galaxy.

Since 1967, the main scientific events of the General Assemblies of the International Astronomical Union have been published in the separate series, Highlights of Astronomy. The present Volume 11 presents the major scientific presentations made at the XXIIIrd General Assembly, August 18-30, 1997, in Kyoto, Japan.

It is the customary practice to report the major events of a General Assembly -the Invited Discourses, Joint Discussions and Joint Commission Meetings in Highlights of Astronomy.

The scientific meetings of the !AU are the !AU Symposia, !AU Colloquia, Regional Meetings in Astronomy held under the auspices of the !AU, the Commission Meetings, which may be Joint Meetings of Commissions, and !AU Joint Discussions.