25. Commission de Photométrie Stellaire

Much material extending our knowledge of stellar magnitudes has accumulated during the last four years. In the appendix to this report will be found a list of recent catalogues, a summary of the discussion made at Mt Wilson by Seares and the formulae that he finds for the reduction of these catalogues to a fundamental system, until such time as a more extended discussion shall have furnished definitive corrections.</jats:p

28. Commission des Nébuleuses et des Amas Stellaires

1. Since the field covered by Commission No. 28 extends over the problems of three very different types of objects—external galaxies, galactic nebulae, and star clusters—it has been proposed occasionally that the Commission might well be subdivided, or possibly eventually split into three separate Commissions. As Trumpler points out, these three fields “have often been grouped together...more on a historical basis than on an actual similarity of the researches... which are more and more drifting apart.” But some members of the Commission have noted that a distinct difference also separates globular clusters and galactic clusters; and that planetary nebulae and dark absorbing clouds involve at times widely different types of investigations. The chairman of the Commission has made a canvass of the opinions of the members and finds that a large majority believe that no division or subdivision is advisable at this time. It is suggested that the organization or reorganization of a Commission should be left to the Union as a whole or to the Executive Committee.</jats:p

28. Commission des Nébuleuses et des Amas Stellaires

During the time elapsed since the last general assembly of the I.A.U., many activities have been pursued by the astronomers engaged in research work in the wide fields of problems concerning nebulae and clusters. In fact a number of important discoveries have been made and earlier work has been extended in a way to consolidate earlier views or revise them. The embarras de richesse in this field and the extremely short time available for the compilation of a report make it impossible to present anything else than a few short notes partly written by heart and only intended to express personal views on the question of how the research work on nebulae and clusters might be carried on.The following report is mainly restricted to work done since the last meeting of the I.A.U., but in a few cases it has been necessary to mention earlier results.</jats:p

25. Commission de Photométrie Stellaire

The following summarizes the activities of various members of the Commission in matters pertaining to stellar photometry during the interval 1932-35: La partie photométrique des trois derniers volumes du Catalogue Astrographique (zone de Catane entre +46° et +55°) est soigneusement dressée sur le système de Miss Leavitt (Harv. Annals, 81). L’erreur moyenne des grandeurs, d’après la réduction de 100 plaques (zones +51° à + 54°, entre 6h et I2h), n’est que de ± om.o8. Nos réductions photométriques ont été effectuées par la formuleD = a-bg+cg2-dg3,où D dénote le diamètre de l’image photographique et G=8m+g dénote la grandeur de l’étoile.</jats:p

25. Commission de Photométrie Stellaire

The committee of the Carte du Ciel in 1910 adopted the following convention : That for Ao stars between magnitudes 5·5 and 6·5 the mean photographic magnitude should equal the mean Harvard visual magnitude. As a corollary, the colour index of Ao stars would then be zero.The zero point of the photographic magnitudes of the International Polar Sequence was fixed as nearly as possible in accordance with this definition; but it was by no means certain that the magnitudes thus adopted for the few stars of the Sequence represented the zero point defined by all the Ao stars specified.</jats:p

28. Commission des Nébuleuses et des Amas Stellaires

During the past three years observational and theoretical work has been uncommonly extensive and fruitful in two of the fields within the interests of Commission 28—namely, the distribution of external galaxies and the analysis of diffuse nebulosity, the latter including interstellar absorbing material. Important work is also under way at a number of observatories in the interpretation of planetary nebulae. Studies of clusters, however, have been limited to a few active workers, and progress has not been rapid in the analysis of individual galaxies.</jats:p

33. Commission de la Statistique Stellaire

The following report, which has been drawn up partly on the basis of the reports of the members of the Commission, touches briefly and without any attempt at completeness a few points of the recent developments in certain important fields falling within the domain of the Commission.</jats:p