Over the past 3 years the availability of abstracts, journal's table-of-content, bibliographic searches and even preprints on the Internet means that summaries such as this will be unnecessary. The AAS WWW bibliographical/abstract services (http://cfa-www.harvard.edu/aas/) accesses several useful sites: http://cfa-www.harvard.edu/aas-search.shtml for bibliographic searches of ApJ, ApJL, ApJS, AJ and PASP from 1988 to the present. The ADS abstract bibliographic service covering in addition A&A, A&AS, MNRAS, PASJ, RMexAyA, PASAus, IrishAJ, BASInd, BalAst and other journals is http://adsabs.harvard.edu/abstractjervice.html; http://adsabs.harvard.edu/toc.service.html is for table-of-content queries that are useful for browsing the same journals. Most of these services are also available through the CDS (http://cdsweb.u-strasbg.fr/CDS.html) in several different languages. From this site can also be obtained published tables from astronomical journals as well as other data that have been deposited by individuals. The SIMBAD database (http://cdsweb.u-strasbg.fr/Simbad.html) maintains its importance as a stellar database in particular. It is necessary to have a user account to access SIMBAD. The ApJ contents is now online at http://www.journals.uchicago.edu/ApJ/journal/contents/ApJ. Notable by its absence from these data bases is Nature from whose home page (http://www.nature.com) the TOC of the current year's issues only can be browsed after registering. Preprints can be obtained from http://xxx.lanl.gov/archive/astro-ph covering the years 1992 to the present. The various search engines also often turn up papers given at conferences or in other publications than the mainstream astronomical journals. Transition probabilities and term levels are an important area long neglected for the provision of digital data (with the honourable exception of CDROM 18 from R.L.Kurucz). The spectroscopic databases of the NIST (http://aeldata.phys.nist.gov/nist_atomicjpectra.html) now contain extensive data for some elements, in particular the transitional probabilities for the iron group elements. One assumes that the list of elements with gf values will be progressively increased. It is obvious from a perusal of these web sources as well as noting the rapid filling of library shelves, that the number of papers being published in astronomy and astrophysics continues its inexorable increase. This makes it even more difficult to do justice to all the work done over the past 3 years.

This report focuses on a few subjects where substantial progress has been achieved during the past three years. Several colleagues were asked to describe what they consider as the highlights in their field, and we are very grateful to them for their prompt and competent response. They covered the following topics: massive stars (A. Maeder), intermediate mass stars (P. Demarque), low mass objects (G. Chabrier), stellar convection (H. Spruit), atomic diffusion (G. Michaud), rotational mixing (J.-P. Zahn), helioseismology (S. Basu) and solar neutrinos (E. Schatzman). J.-P. Zahn was responsible for collecting and editing their contributions.

Consistently with a trend observed in recent past triennial reports, progress in the theory of stellar atmospheres continues to be made in two different directions: (i) the traditional areas of continuum and line radiation transfer, line blanketing, atomic physics and atmospheric structures controlled by the joint conditions of radiative and hydrostatic equilibrium, and (ii) in areas of emerging interest such as oscillations, winds and mass loss, chromospheres, coronae and magnetic phenomena.

This report covers research in the field of stellar classification in the period July 1993 to June 1996. It is divided into several sections which were written by experts in each subfield. I want to thank them for their effort and cooperation. To conserve space, all references are given with only one name followed by a + sign if there are additional authors.

The three special projects sponsored by Commission 27: the Information Bulletin on Variable Stars (IVBS), the Archives of Unpublished Observations of Variable Stars, and the General Catalogue of Variable Stars (GCVS) continue to serve the astronomical community. Katalin Oláh, Laszlo Szabados, András Holl, Zsolt Kővári and their colleagues have made the Bulletin available in electronic form, including back issues. In addition, Andras Holl succeeded in setting up a WWW home page for our commission. Chris Sterken and the Editorial Board strived to maintain high scientific standard of the IVBS. The Archives, under Ed Schmidt, increased to over three hundred files. Nikolai N. Samus and his co-workers published the final volume of the 4th edition of the GCVS. The Catalogue is also available electronically. All these people should be highly prized for their hard work for the IAU and astronomers at large.

The pervasive connection of Close Binary Stars (CBS) with essentially every fundamental field of astronomy and astrophysics has required a huge number of papers on many topics to be considered for this report. As a consequence, most of the invited contributors were forced to use more space then alloted. This coupled with the tight contraints imposed by the crckapb style did require the Commission’s President to make possibly controversial and certainly painful choices on how and where to make some unavoidable cuts. In particular, I had to drop most of the authors’ names in the references throught the text. This much suffered but necessary decision resulted in a 20% reduction of the report length. I hope that only a minority of C42 members will not share my choice. Since the various contributions were already quite concise, the remaining alternative was that of dropping some of the science, a choice I did actually consider, I must confess, only briefly.

This report covers some of the developments in the field of Commission 34, between the summer of 1993 and 1996. My predecessor, Harm Habing, noted in the last report, published in 1994, “that the traditional way of reporting is no longer adequate and that we have to rethink the format of this periodic report”. Some limited progress towards this goal has since been made, and greater discretion is now granted to the organizing committees in the preparation of their reports. The main consequence, as far as Commission 34 is concerned, is that the present report is briefer than in the recent past and makes no pretence at being a comprehensive survey of the literature over the review period. Indeed, “Chemistry” and “Planetary Nebulae” are not covered at all, as they are the topics of recent IAU Symposia (nos. 178 and 180, respectively).

Notwithstanding the decline in the level of funding for astronomy in many countries, the number of papers published continues to grow triennium by triennium. The volume of current research is such that it is no longer practicable for Commission reports to provide a complete guide to everything published within the relevant field during a given triennium. Correspondingly, at the XXIInd General Assembly in the Hague it was resolved that future reports would be of a selective nature rather than general surveys of the literature.

This report coveres the period 1 July 1993 to 30 June 1996. In contrast to reports from previous triennia, which were written by commission officers, committee members, and chairs of working groups, all members of the comission were invited, through a newsletter, to volunteer to write sections on topics that interested them. About a dozen people volunteered, not all of whom were able to complete the reports they had suggested.

The report that follows gives glimpses into the enormous amount of work in cosmology over the past three years, both in theory and in observations. It is impossible to do justice, within the space allotted, to all the exciting work and some important topics like structure formation could not be covered. Nevertheless, the contributors to different sections have done a conscientious job and I thank them all. Some of them had to step in to fill the gaps at short notice.

During the period covered by this report, major progresses have been achieved in various fields of astronomical techniques and instruments. The era of large telescopes has been opened with the commissioning of the 2 Keck telescopes and the final construction phase for major facilities (ESO, JNLT, LBT, Gemini, etc). More than ten telescopes, with aperture larger than 8m, will be ready to scrutinize the sky, at the beginning of the next century. A Spanish project (GRANTBCAN) remains incompletely financed at this time. The power of these telescopes will be maximum when full diffraction limit capabilities will be available at their focus. The period 1994-1997 has seen major and spectacular achievements with realisation of several operationnal adaptative optic systems on 4m-class telescopes (ESO, CFHT). Diffraction limits have been reached at near-IR wavelength and partial correction, even in the visible, are bringing resolution comparable to space observations. All 8-10m projects require adaptative optics and have plans for it. In the meantime, 3-4m class telescopes are beeing equiped as well, so that AO will appear everywhere within the next 3 years. The necessary complement of adaptive optics, ie: the laser guide star, is thoroughly studied in order to provide full coverage for atmospheric compensation all over the sky. Projects of monochromatic and polychromatic laser stars are flourishing in relation with all telescopes with aperture of 3m-plus adaptative optics projects. Field coverage and achievable resolution require good pixel sampling and therefore large format detectors. Projects of very large format cameras for the visible and infrared are considered, up to 16kxl6k (MEGACAM at CFHT for 1.5 degrees field). Progress has been obtained in the industry to reduce gaps in between bootable CCDs, to reduce amplifiers noise and improve sensitivity. High angular resolution capabilities will gain another magnitude when the actual developments on interferometry with small telescopes will be tranfered to arrays of large telescopes (ESO, Keck, etc). Resolutions of 0.001 arc. sec will be available within 5 years leading to a gain of a factor 1000 compared to a 3.5m telescope operating today without adaptive optics.

This is a summary of the essential work that was published since the previous report (Young 1994), Reports on Astronomy Vol XXIIA, 229-238. This summary is not a complete review, and it certainly does not cover papers that appeared during the last couple of months. References are in terms of volume and reference number in Astronomy and Astrophysics Abstracts, and papers with no such citation numbers are given with their full bibliographic reference.

A new generation of major redshift surveys, with numbers of redshifts that far surpass those of earlier investigations, is getting under way. These surveys make use of fibre optics, but differ from earlier systems in that often hundreds - not just tens - of galaxies can be observed simultaneously, by means of improved fibre management techniques. One of the most prominent is the Sloan Digital Survey (63.013.080) which aims to provide photometry and redshifts for a million galaxies, using a dedicated 2.5 m telescope that is soon to commence operations. The Two-degree Field instrument on the 3.9 m Anglo-Australian Telescope (63.031.120) will have up to 400 fibres per field - while one field is being exposed, a robot will work on positioning a further 400 fibres, ready for the next exposure. Similarly the DENIS (63.036.281) and 2MASS surveys, mapping in the near-infrared, will require very large numbers of follow-up redshifts. Also, in terms of new technology, the 8.5 m Hobby-Eberly Telescope, a dedicated spectroscopic telescope, is soon to see first light; its low-resolution spectrograph should be able to service galaxies down to V = 23.5.

There have been many advances in radio astronomy during the last three years, and a sample of these are highlighted in the following Report. The coverage of all facets of radio astronomy is certainly not uniform, because much of the text has been provided as voluntary contributions by Commission 40 members, and the finished report will therefore be weighted according to individual interests. Nevertheless, hopefully this Report will show the enormous scope of today’s radio astronomy, and reflect some of the excitement of the latest findings.

Carol Lonsdale, Infrared Processing and Analysis Center, California Institute of Technology/JPL, Pasadena, CA, USA

During the triennium, Commission 6 continued to interact with the Central Bureau for Astronomical Telegrams (CBAT) under the very effective directorship of Brian Marsden. A widening of the associated astronomical subjects recorded in the IAU Circulars was noted. There is no doubt that these Circulars continue to play an important role for the fast dissemination of astronomical information. The trend towards a preference for electronic distribution by the recipients cannot be overlooked.

Since the last report, Commission 7 has supported IAU Symposium No. 172 “Dynamics, Ephemerides and Astrometry of the Solar System” (Paris, 1995) and co-supported IAU Colloquium No. 165 “Dynamics and Astrometry of Natural and Artificial Celestial Bodies” (Poznari, Poland, July 1996). During the 22nd General Assembly (The Hague, 1994), the Commission co-supported the joint discussions “Time scales: state of the art” and “Nutations” as well as the working group meeting “Near-Earth Objects Detection”.

The membership of the Commission stands, with the election of 18 IAU members and 12 historians at the XXII GA (1994), at 155 presently (Sept. 1996). Note the increase in membership, which is 24% and which hopefully may go to 30-35% by XXIII GA (1997). The Commission has put a message on WWW for all IAU members/presidents of various commissions to join the Commission 41 in a big way, so that it can extend its scope of activities further. Besides holding a Joint Discussion of its own (No. 17), Commission 41 is co-supporting JDs 8, 20 and 23.