Jacqueline Bergeron

Reports on astronomy

Preface. Reports of Commissions. Ephemerides. Documentation and astronomical data. Astronomical telegrams. Celestial mechanics. Positional astronomy. Instruments and techniques. Solar activity. Solar radiation and structure. Atomic and molecular data. Physical study of comets, minor planets and meteorites. Physical study of planets and satellites. Rotation of the Earth. Positions and motions of minor planets, comets and satellites. Light of the night sky. Meteors and interplanetary dust. Photographic astrometry. Stellar photometry and polarimetry. Double and multiple stars. Variable stars. Galaxies. Stellar spectra. Radial velocities. Time. Structure and dynamics of the galactic system. Interstellar matter. Stellar constitution. Theory of stellar atmospheres. Star clusters and associations. Exchange of Astronomers. Radio astronomy. History of Astronomy. Close binary stars. Astronomy from Space. Stellar classification. Teaching of Astronomy. Cosmology. High energy astrophysics. The interplanetary plasma and the Heliosphere. Protection of existing and potential observatory sites. Bioastronomy: search for extraterrestrial life. Working Group for Planetary System Nomenclature: WGPSN. Working Group for the World Wide Development of Astronomy: WGWWDA.

Structure and Dynamics of the Galactic System

This report covers work published approximately from July 1, 1991 to June 30, 1993. The main reference has been the Astronomy and Astrophysics abstracts; some of the sections were written using the last 6 volumes available to each writer. Consequently, some of the references date back to 1990.

Stellar Photometry and Polarimetry

This is a summary of the essential work that was published since the previous report (McLean, 53.113.028), not a complete review. Most papers are cited by their volume, section, and reference number in Astronomy and Astrophysics Abstracts. Papers presented at the very successful IAU Colloquium 136 in Dublin (see report in IAU Information Bulletin 69, p. 26) are simply cited as (Dublin); they have just been published by Cambridge University Press.

Physical Study of Planets & Satellites

The study of the physical properties of planets and satellites has flourished since the beginning of direct space exploration in the 1960s. Although the pace of planetary exploration has declined since its peak (roughly from 1970 to 1986), this field remains strong and productive. The level of research activity was approximately the same as in the previous report period, with the publication of more than a thousand research papers. This activity is broadly international, and growth in planetary research has been especially notable in Europe. The two most important annual meetings of planetary scientists are the Division for Planetary Sciences (DPS) of the American Astronomical Society, held each autumn, and the Lunar and Planetary Science Conference, held each spring at Houston. Both meetings attract between 300 and 600 registrants, with a comparable number of papers presented. The primary journals for publication of planetary science are Icarus and the Journal of Geophysical Research, although many other astronomical and geoscience journals play an important role, as well as the two general-science journals Science and Nature.

Documentation and Astronomical Data

The scope of our commission may appear very broad, with ill-assorted topics. However, this is a wrong impression and I think that in the very near future the convergence of all our activities will appear clearer. With the development of computer resources and possibilities, all our activities lead to what we could call information science. Two books published lately (Intelligent Infomation Retrieval, A. Heck & F. Murtagh, Eds., Kluwer Acad. Publ., 1993 and Databases and On-line Data in Astronomy, M. Albrecht & D. Egret, Eds., Kluwer Acad. Publ., 1991) give a very good idea of this tendency.

Meteors and Interplanetary Dust

The organization of Commission 22 was disrupted by the untimely and much-lamented death of our President, Jan Stohl, in 1993 March. An appreciation of Jan appeared in the newsletter of the commission issued in 1993 April, and obituaries have been published in various other places. The Vice-President, Iwan Williams, assumed the duties of President thereafter, and with help from the OC has taken responsibility for the production of this report, and providing the formal sanction of the commission for various meetings associated with the 1994 General Assembly, and other conferences.

Double and Multiple Stars

The nature of research on double and multiple stars has changed drastically during the past several decades. Prior to then the research was mostly concerned with visual measures for the purposes of obtaining orbital elements and masses. Then came spectroscopic studies that (1) when combined with the visual orbital elements allowed the determination of orbits in three dimensions and (2) started an emphasis on the astrophysical and evolutionary natures of the components in such systems. Unfortunately except for a few nearby systems, the systems with large enough separations for spectroscopic measures of individual components were just those with orbital periods too long for visual determinations, while those systems with short enough periods for spectroscopic determinations were too closely-spaced for visual measurements.

Physical Study of Comets. Minor Planets and Meteorites

The level of activity during the period covered, July 1990 to June 1993, was comparable, if not higher than in the previous period. Work continued on interpretation and modeling of the data from the 1986 apparition of comet P/Halley. Many of the research results reported in Bamberg (IAU Colloquium No. 116) were transferred to text book level (Mason 1990, Huebner 1990). Space mission research continued with the Giotto extended mission and preparation of CRAF and Rosetta. CRAF was eventually canceled, putting more importance on international collaboration for Rosetta. New lines of research were opened with the discovery of activity of 2060 Chiron, improved ground based CCD observations of distant comets, the spectacular breakup of the comet Shoemaker-Levy 1993e, and the detection of trans-Neptunian planetary bodies — potential Kuiper belt members. An important review of cometary science has been written by Festou et al. (1993). It contains a very complete list of references of literature up to 1992, including proceedings and monographs. Many international meetings as well as sections of larger Symposia dealt with the subjects of Commission 15. Most important for the community the Asteroids, Comets, Meteors series continued with its meetings in Flagstaff, USA, June 24-28, 1991 and in Belgirate, Italy, June 14-18, 1993 (IAU Symposium 160). Information on meetings relevant to Commission 15, can be also found in the IAU Information Bulletins and/or in the Astronomy and Astrophysics Abstracts.

Star Clusters and Associations

The last three years have been very productive for cluster research. More than 450 references for open clusters and more than 800 for globular clusters have been collected from the literature and Astronomy and Astrophysics Abstracts (Vol. 52 to 56). The observations present very broad scope thanks to the new instrumental facilities like infrared arrays and the X-ray and IR satellites. Our knowledge of how and where open clusters form has been considerably advanced with the advent of infrared arrays images which has revealed the presence of compact, centrally condensed clusters of newly formed stars embedded in, or closely associated with dense cores of giant molecular clouds. The present report tries to survey the activity in these domains, summarize the results and trends, and collect the information on the observed clusters and associations. But, owing to the large number of references, it is not possible to quote every paper. A higher priority has been given to the new data obtained for star clusters, which should help everybody to be easily informed of the observations made during the past three years. Therefore the traditional form of the report has been largely maintained. Abstracts and papers in conference proceedings have usually not been quoted here to save place and no attempt has been made to include unpublished material. For complete bibliographic information, the Astronomy and Astrophysics Abstracts, chapters 121 (young stellar objects), 131 (star formation), 152 (stellar associations), 153 (open clusters), 154 (globular clusters), and 156 (Magellanic Clouds) remain the best source. To improve the efficiency of literature retrieval, it would be important that the first keyword refers to open, respectively globular clusters, whatever the observational data may be (proper motions, radial velocity, photometry and so on). The database for stars in open clusters (Mermilliod 1992) offers an up-to-date bibliographic search facility based on keywords. Murtagh and Adorf (1993) have given a short report of the astronomical literature publicly accessible on-line. The subject of low-mass star formation in southern molecular clouds has been reviewed in a comprehensive ESO report edited by Reipurth (1991), which provides extensive references to the literature.

Light of the Night Sky

The diffuse components of the light of the night sky encompass a variety of physical phenomena over the full range of cosmic distance scales. From the Earth outward they include airglow in the Earth’s atmosphere, scattering and thermal emission from the interplanetary dust cloud (zodiacal light), integrated starlight, diffuse galactic light, and extragalactic background radiation. These components are necessarily observed together along the line of sight. Thus, the successful measurement of any one component requires knowledge of all the diffuse components. Moreover, the brightness of the diffuse sky background limits the detection of very faint objects, both extended and point-like. Thus, the spectral and spatial characteristics of the diffuse components have to be known in order to maximize detectability of very faint objects. Commission 21 is the only organization in which all of the diffuse components are studied and compared.