Material for this report was collected by the President, Vice-President and Members of the Organizing Committee. The President is, however, responsible for the form in which the report now appears. A number of special abbreviations in the references are explained in the report of Committee 27a. In addition, 3rd Harvard = 3rd Harvard-Smithsonian Conference on Stellar Atmospheres (1968). The field of Commission 29 overlaps particularly with those of 9, 27a, 36, 44 and 45 whose reports should be consulted. Since the last IAU meeting 29 has co-sponsored the following meetings: IAU Colloquium No. 4 on Stellar Rotation (Columbus, Ohio, September 1969); IAU Symposium No. 36, Ultraviolet Stellar Spectra and Related Ground-Based Observations (Lunteren, June, 1969); Second Trieste Colloquium, Mass Loss from Stars (September, 1968). We are also co-sponsoring IAU Symposium No. 42 on White Dwarfs to be held in Scotland (August, 1970). The thanks of the commission are due to their representatives on the organizing committees of these meetings. Reports from some working groups are appended. The working group with Commission 44 has not felt it necessary to submit a report (its main activity was the organization of Symposium No. 36). Miss Underhill (Chairman) recommends that the working group on Tracings of High Dispersion Stellar Spectra be dissolved.

Two new and independent determinations of the absolute spectral energy distribution in αLyr have been completed during the last three years. The first of these by Hayes has been published in part (Wolff, Kuhi and Hayes, 1968). It was done at the Lick Observatory using the Crossley reflector and two ribbon-filament standard lamps. His published results are based on the old practical temperature scale which is based on a melting point for gold of 1336·16K. The new scale has been adjusted to agree as well as possible with the thermodynamic temperature scale and is based on 1337·59K for the melting point of gold. Hayes’ results have been adjusted to this new scale and are shown in Table 1. The numbers listed are — 2·5 log fv + const, when fv is the flux from αLyr in ergs s-1 cm-2 Hz-1. The results are normalized to 0·000 at λ5556.

The new calibration by Oke and Schild was carried out on Palomar Mountain. A four inch reflecting telescope was built and mounted with the prime focus scanner which was built for the 200-inch telescope. Three light sources were used (1) a ribbon-filament standard lamp calibrated with an accuracy of 2 % by the National Bureau of Standards was used from λ3300 to λ8000.

Systematic equivalent width comparisons as initiated by K. O. Wright during the Seventh General Assembly of the IAU in 1948 and continued by G. Cayrel de Strobel since the Twelfth General Assembly in 1964 are meeting less and less response from the astronomical community. Griffin has stressed systematic errors in spectrographic results. For instance he claims in his paper (M.N.R.A.S., 143, 319) that owing to the light thrown in the wings of the instrumental profiles, the observed equivalent widths of absorption lines in late type stellar spectra are 5 to 10 % less than the true values. Furthermore Griffin pointed out the weakness of purely spectrographic comparisons which are all affected by the same type of errors. What is really needed is to know the true equivalent width of a few lines as they can be obtained from an accurate double pass photoelectric scanner. Pagel suggested that this can be done by comparing spectra of integrated sunlight from sky or minor planets with scans obtained by solar spectrometers. Griffin prefers that a bright star be used for this purpose. A complete change in the activity of this working group could very well be decided if the primary object is to have true standards of equivalent widths and if these cannot be obtained from conventional high dispersion spectrography.

A. Peton (Meudon) à partir de spectres à petite dispersion, a évalué une période de 33 ans pour les variations de l’émission de HD4180, une classe B5 IV et des oscillations assez importantes de l’enveloppe absorbante sur 3–4 ans (non publ.).

F. R. Hickok (Dunlap) a étudié les structures fines et les vitesses radiales de ɸPer à grande dispersion de telle sorte que les courbes de vitesse sont plus détaillées, mais, la période ne change pas. Probablement binaire. Des difficultés sont soulignées (non publ.).

Des variations spectrales et de vitesse radiale ont été observées par M. Hack et P. Stenner (Trieste, dans l’enveloppe de ζTau (publ.) ainsi que par Van der Wel (Utrecht) pour la période 1964-66 (non publ.). A. M. Delplace (Meudon) a mis en évidence une relation très étroite entre les profils Balmer H et la période de 7 ans. L’enveloppe, en moyenne, est en récession (publ.).

Les mesures de vitesse radiale (VR) ont été continuées par les trois techniques: prisme objectif, spectrographie à fente, interférométrie, avec des instruments en fonction à l’Observatoire de Haute Provence ainsi qu’à celui de l’ESO.

Grand Nuage de Magellan: Le travail de 13 champs est pratiquement achevé et sera publié dès que les mesures de spectres de fente pris au Chili seront complètement dépouillés.

Un catalogue comprenant 1765 étoiles galactiques et 469 étoiles du Grand Nuage de Magellan est achevé. Un supplément comprend environ 200 étoiles particulières de cette région.

The astronomical observatories which actively cooperate in the network of the system of the Bureau International de l’Heure, are, at present, about 70. Most of the astronomical time determinations are carried out by means of Danjon Astrolabes or transit instruments; 10 observatories dispose of a PZT and 5 others are installing or planning to have it. The results of their observations, ɸ(observed latitude) and Δ T (difference between local U.T.0 and U.T.C), are collected at the BIH and – contrary to the procedure used until 1967 – used to simultaneously obtain the instantaneous coordinates of the pole (x, y), referred to conventional international origin (CIO), and longitudes origin on the pole equator. As a consequence of the adoption of the above-mentioned conventional pole, the BIH had to change all conventional longitudes in order to keep the origin formerly defined (1967); they are now reported in BIH Annual Reports. A further change was operated on the constant of aberration which, at the beginning of 1968, from 20˝.47 was changed to 20˝.496. The BIH had therefore to operate a step of to U.T.1, at the beginning of January 1968, and so did the Greenwich Observatory, with a step of + 0.0069. Global corrections, due to these variations and to others occurred from 1955 to 1968 (in 1958, variation of the polar reference, from Cecchini’s to the mean pole of the date; in 1961, adoption of FK4 and of new longitudes), to the data of the past years (until 1968), are reported on Table 8 of the BIH Annual Report, 1968. The formula supplying the correction U.T.2 —U.T.1 remained unchanged, except for the variable t, which is expressed (since 1967) as a fraction of the Besselian year. Finally, stars coordinates in the catalogs used for time service were revised on the basis of observations made during the latest ten years (Neuchâtel, Greenwich and Mizusawa) and a catalog has been prepared, which includes 807 right ascensions for 1960, drawn from 20 catalogs, with more than 185000 observations of the U.S.S.R. (Pulkova) time service, which is also preparing a new catalog of proper motions. The unification of star positions and proper motions is recommended for the PZT.

The present report is drastically shorter and, therefore, different in form from previous reports. While galactic research has increased considerably in recent years, the financial situation in the IAU made it necessary to reduce the size of the reports to half their previous size. This obliged us to adopt an almost telegraphic style in our report. However, an extended version of the report, including also the necessary references, will be published by the University of Thessaloniki and distributed to members of Commission 33. Any other interested astronomer may write to ask for a copy.

The report has been prepared by G. Contopoulos (Sections I, V, VI) and S. McCuskey (Sections II, III, IV). In our work we have been helped by Drs Kerr (radio astronomy) and Haradze (Russian contributions). Dr Elvius has written the Report of the Committee “Selected Areas”. We could cover the literature up to the fall of 1969, plus work in progress, reported by members of our commission.

At the IAU Prague meeting it was considered desirable to continue to report on work performed in the Kapteyn Selected Areas (below referred to as SA) and other similar fields, as those belonging to the Parenago, Shajn and Cleveland plans, cf. also the main report of Commission 33.

A more detailed version of the present Report, including references to published work, will be distributed to those specially interested.

At the Abastumani Observatory, Chuadze has determined photographic B and V magnitudes for 4000 stars in SA 25,48,50,73,75,97,99, and 122. Kalandadze has continued her work in Fields III and IV of the Parenago Plan and will publish a catalogue for about 8000 stars in Taurus; Metrevili will publish similar data (photographic UBV and spectral types) for 3000 stars. In co-operation with the Golosseievo Observatory a development of the Parenago Plan with photometric studies of regions centered at open clusters has been initiated; a catalogue of B and V magnitudes for 12000 stars by Voroshilov et al. has been published.

Although additional surveys with large Schmidt telescopes continue to yield small catches of additional planetaries (Kohoutek) one cannot escape the conclusion that most planetaries available to existing equipment have been detected. Much remains to be done with powerful Schmidt equipment in the southern hemisphere, especially in the Magellanic Clouds. A vast body of photometric and spectroscopic observation needs to be garnered for the numerous faint nebulae so far discovered.

Spectroscopic and spectrophotometric studies have been carried out for most bright planetaries (λ < 5800) but much remains to be done in the red and near infrared. Important advances have been made in the far infrared (~10μ) (Gillett, Low, Stein, Woolf) where a number of planetaries seem to show abnormally strong continua. This abnormally intense radiation has been attributed to non-thermal emission, effects of many faint lines, and to thermal emission by dust grains (Krishna Swamy, O’Dell) with perhaps the bulk of the evidence favoring the last-mentioned hypothesis. An increasing number of radio observations from 9·5 mm to 73 cm (Thompson, Colvin, Stanley, LeMarne, Kaftan-Kassim, Babieri and Ficarra, Terzian, L. Aller and Milne, Hughes) all indicate that planetaries are thermal sources.

During the period under review, theoretical work in the field of stellar constitution and evolution of stars has been effectively continued by several teams permanently working in Belgium, Denmark, France, German Democratic Republic, German Federal Republic, Italy, Japan, Poland, the United Kingdom, the U.S.A., the U.S.S.R. as well as by individual scientists in Argentina, Bulgaria, Czechoslovakia, India, Sweden and others. Most attention has been given during the past three years to analysis of late stages of stellar evolution, rotation, evolution of binaries, loss of mass on various stages of evolution, stellar stability, neutrino astrophysics, physical processes in the presupernovae stage. The discovery of pulsars has raised extremely the general interest for white dwarfs and neutron stars, and consequently the number of papers with new hypotheses concerning quasi-stellar sources has substantially dropped.

Many new evolutionary sequences of stellar models for various masses and different chemical compositions have been computed using improved numerical techniques and large computing programs. It is regretted that many of these results are difficult to compare mainly because of the differences in the input physics and the way the numerical results are being published. This is a field in which a closer international co-operation is highly desirable, especially on the following points: exchange of ideas on the programs presently under way and the planned programs in order to avoid unnecessary duplications: agreement on the numerical results which should be published; exchange of technical informations: (input physics, computing methods, detailed results of computations, opacity tables, etc.). Several attempts in this direction have been undertaken during the period under review (for example, Commission 35 Circular Letters NN 1–7 containing information on current work, publication by the U.S.S.R. Academy of Sciences of the Cox and Stewart’s Opacity Tables for 23 mixtures, several joint international projects for using the same programs, etc.), but the problem still remains to be solved.

This report has been prepared by the President with the assistance of the Vice-President, the Members of the Organizing Committee, V. V. Ivanov, P. Conti and of D. G. Hummer. The work of Commission 36 comes in contact with that of many commissions. Some subjects may be dealt with more fully in those reports; some subjects may have been “unlawfully” included here. Considerable choice has been exercised by the President about what to mention and in which section of the report to place it. The final product is only indicative of the large amount of work going on. An extensive bibliography has been compiled and will be distributed to commission members.

Commissions 12, 27, 29, 44 and 45 deal with observational material which our theories attempt to interpret, thus it is essential to study the reports of these commissions to appreciate the diversity of material for which theories are needed and against which theories may be checked. The theoretical treatment of the problems of planetary atmospheres, Commission 16, is not entirely divorced from that of stellar atmospheres. To set realistic inner boundary conditions on our atmosphere models and on our thinking, we must consider the material of Commission 35 while to set the outer boundary conditions we may consider the physical state of planetary nebulae which is one subject of Commission 34. When we wish to apply ideas about the interactions between radiation, atoms, ions and molecules we use material which lies in the province of Commission 14.

The data contained in this report have been taken from two sources: (1) Information received from astronomers active in the field of Commission 37 in response to a circular letter mailed July 1969; (2) Surveys of special fields, prepared by W. Becker on “Open star clusters and spiral structure”, by G. Larsson-Leander on “Clusters and stellar evolution”, by M. Walker on “Young clusters’, and by P. -B. Bouvier on “Dynamical models and numerical computations’. It is a pleasure to thank them and all of those who have contributed to the preparation of this report.

G. Alter reports that after a long delay the second edition of the Catalogue of Star Clusters and Associations. (G. Alter, J. Ruprecht, V. Vanýsek), which was discussed at a meeting of our commission at the Congress in Hamburg (1964) (Trans, IAU, 12B, 1966, 336), will now be published by Publishing House of the Hungarian Academy of Sciences. It is considerably enlarged, since it includes the contents of the annual Supplements published in B.A.C. between 1959 and 1967.

Radio astronomy continues to develop at explosive pace. In addition to containing many notable pieces of observational work carried out with improved sensitivity, angular resolution and spectral detail – and aided by data-handling techniques of increasing sophistication – the last three years have seen a flow of new and sometimes startling results. These are exemplified by the discovery of organic matter in the galaxy, and by the first observations pertaining to what are almost certainly neutron stars. The latter, of course, came with the dramatic discovery of pulsars, which are the subject of an Invited Discourse at this General Assembly.

Following the custom of this Commission, I have asked different members to review the work done in each of the main fields. On this occasion a special section has been added on pulsars; since the announcement of their discovery in February 1968, the rate of publication within so narrow a field could scarcely have been equalled in the history of science. As in the past, radio studies of the planets are incorporated in the Report to Commission 16.

The investigations on the history of astronomy proceed rapidly and concern all branches, viz. the history of astronomy in particular countries, the historical development of the astronomical problems, biographies of astronomers, history of observatories and of astronomical instruments etc. They are being made by professional astronomers and historians of science at observatories and institutions destined for the history of science. The president of Commission 41 cannot give a comprehensive review of all directions of investigations on the history of astronomy, because their results frequently have been published in publications not accessible to the author of this report. The present draft report is based mainly on information received by the president from members and consulting members. Besides, the present report contains short information on the results of international conferences, which were held independently of IAU.

This report differs from earlier ones because financial limitations require the length to be half that of the preceding one. Thus, bibliographical lists are severely limited and it has not been possible to refer to all published papers or to much of the unpublished work. It is hoped that a more extensive mimeographed report will be available to commission members and others interested by the time of the 1970 General Assembly.

For invaluable aid in preparing this report, I am deeply indebted to Drs. Batten, Herczeg, Katherine Kron, Larsson-Leander, Merrill, Plavec, and Cesevič. Most of these wrote sections of the report which appear only slightly altered to prevent duplication or to take account of very recent developments. Since it was necessary to review more than 1400 papers which appeared during the three-year interval, obviously this could not have been written without extensive collaboration. I am especially indebted to Drs. Merrill and Plavec for consultation in the difficult choice of matters to be eliminated.

This report emphasizes selected problems in plasma physics and magnetohydrodynamics that appear to be of substantial future interest in astrophysics. Because of space limitations, complete coverage is impossible and bibliographical references are drastically curtailed. More complete references to the papers in Sections B and C are available on application to the undersigned. Additional references should be easily available in the well known abstracting and review journals. I am grateful to the members of Commission 43 who supplied the information on which this report is based. I am particularly grateful to Professors Mestel, Lüst, and Kaplan for writing the three main sections of this report.

In view of the limitation on length set by the cost of producing the IAU Reports, the present report can only be a selection of the most important advances during the past three years and not a complete review of the field.

Attempting to pick out a few points of interest, since the last report improvements have been made in recording solar X-ray spectra and in high spatial resolution imaging; the OSO satellite programme continues to produce valuable data. The eclipse experiments planned for March 1970 will, if successful, provide a considerable amount of new information. The solar iron abundance is still a subject of interest in view of the revision of oscillator strengths used in the photospheric analyses. Further interplanetary observations have shown that the general nature of the solar wind at the Earth does not depend on the phase of the solar activity cycle, and have revealed large increases in the abundance of helium in the solar wind following solar flares.

Des classifications spectrales et des mesures photométriques ont été faites dans de nombreux Observatoires.

La classification à un seul paramètre, comme celle de Harvard, a été remplacée dans la plupart des cas par une classification bidimensionelle. La classification simplifiée est réservée aux étoiles faibles. Les classifications dans le système MK ont été faites dans de nombreux Observatoires et nous signalons les importantes listes d’Abastumani.

De nombreux astronomes ont recherché les étoiles riches ou pauvres en métaux, ce qui est l’amorce des classifications à trois paramètres. Des listes d’étoiles Am et Ap ont été publiées.