Magnetic fields are unexpected in massive stars, due to the absence of a sub-surface convective dynamo. However, advances in instrumentation over the past three decades have led to their detection in a small but growing subset of these stars. Moreover, complementary theoretical developments have highlighted their potentially significant influence over the structure, evolution and circumstellar environments of massive stars. Here, we summarize a special session convened prior to the main conference, focused on presenting recent developments in the study of massive-star magnetic fields.

This report of the business meeting at the 2006 IAU GA is based on notes provided by Edward Tedesco, past president, and on the minutes taken by Petrus Jenniskens, secretary of Commission 15 in the triennium 2003 to 2006, with additional notes from the current secretary of Commission 15, Daniel Boice. For political reasons the incoming President, Walter Huebner, was unable to attend the General Assembly.

The five years that have passed since the last IAU Symposium devoted to massive stars have seen a veritable explosion of data on the high redshift universe. The tools developed to study massive stars in nearby galaxies are finding increasing application to the analysis of the spectra of star-forming regions at redshifts as high as z = 7. In this brief review, I consider three topics of relevance to this symposium: the determination of the metallicities of galaxies at high redshifts from consideration of their ultraviolet stellar spectra; constraints on the initial mass function of massive stars in galaxies at z = 2 − 3; and new clues to the nucleosynthesis of carbon and nitrogen in massive stars of low metallicity. The review concludes with a look ahead at some of the questions that may occupy us for the next five years (at least!).

Throughout their lives massive stars modify their environment through their ionizing photons and strong stellar winds. Here, I present coupled radiation-hydrodynamic calculations of the evolution of the bubbles and nebulae surrounding massive stars. The evolution is followed from the main sequence through the Wolf-Rayet stage and shows that structures are formed in the ISM out to some tens of parsecs radius. Closer to the star, instabilities lead to the breakup of swept-up wind shells. The photoevaporated flows from the resulting clumps interact with the stellar wind from the central star, which leads to the production of soft X-rays. I examine the consequences for the different observable structures at all time and size scales and evaluate the impact that the massive star has on its environment.

1. An application for admission to the Union as a National Member shall be submitted to the General Secretary by the proposing organization at least eight months before the next ordinary General Assembly.

Commission 51 met on 18 August 2006. President Karen Meech chaired the meeting and there were 16 members present, including vice-president Alan Boss, and OC member David Morrison.

We present results from a series of VLT/FORS narrow-band imaging and spectroscopic surveys of Wolf-Rayet (WR) stars in nearby spiral galaxies and compare observed populations in high- and low metallicity environments. The metal-rich galaxy M 83 is seen to host an exceptional WR content, with over 1000 WR stars being detected. N(WC)/N(WN) ~ 1.2 and late-type WC subtypes dominate the WC population. At low metallicity, ~100 stars has been identified within NGC 1313, with N(WC)/N(WN) ~ 0.5. In contrast to M83, the WC population of NGC 1313 comprises solely early subtypes plus a WO star (the first WO star to be identified beyond the Local Group). Consequently, the dominant WC subtype may serve as a crude metallicity diagnostic for WR galaxies.

In addition, the WR content of the blue compact dwarf galaxy NGC 3125 is examined. Previous UV and optical spectroscopic studies of knot A in NGC 3125 derive WR populations which differ by more than an order of magnitude. New VLT observations and archival HST spectroscopy reconcile this discrepancy via the use of LMC WR spectral templates and a reduced nebular-derived interstellar extinction. Empirical N(WR)/N(O) ratios for clusters within NGC 3125 are a factor of two higher than evolutionary synthesis predictions but are consistent with those observed for other young massive clusters.

A total of 16 among the new IAU members have asked to join Commission 20; they are: Jerome Berthier, Nicholas J. Cooper, Marco Delbò, Romina P. Di Sisto, Michael W. Evans, Tetsuharu Fuse, Ludmila Hudkova, Yurij N. Krugly, Elena N. Polyakhova, Zhanna Pozhalova, Alessandro Rossi, Qi Rui, Jonathan D. Shanklin, Slawomira E. Szutowicz, Gino Tuccari and Hong-Suh Yim. Moreover, two requests to join the Commission have been received by astronomers that are already IAU members: Peter De Cat and Ricardo A. Gil-Hutton.

In this review, the physical and wind properties of OB-stars are discussed, with particular emphasis on metallicity dependence and recent results from the flames survey of massive stars. We summarize the relation between spectral type and Teff, discuss the status quo of the “mass-discrepancy”, refer to the problem of “macro-turbulence” and comment on the distribution of rotational velocities. Observational constraints on the efficiency of rotational mixing are presented, and magnetic field measurements summarized. Wind properties are reviewed, and problems related to weak winds and wind-clumping highlighted.

Commission 25 is one of three Commissions under the umbrella of Division IX on Optical and Infrared Techniques. It is a technique oriented Commission.

Some useful developments in the model physics are briefly presented, followed by model results on chemical enrichments and WR stars. We discuss the expected rotation velocities of WR stars. We emphasize that the (C+O)/He ratio is a better chemical indicator of evolution for WC stars than the C/He ratios. With or without rotation, at a given luminosity the (C+O)/He ratios should be higher in regions of lower metallicity Z. Also, for a given (C+O)/He ratio the WC stars in lower Z regions have higher luminosities. The WO stars, which are likely the progenitors of supernovae SNIc and of some GRBs, should preferentially be found in regions of low Z and be the descendants of very high initial masses. Finally, we emphasize the physical reasons why massive rotating low Z stars may also experience heavy mass loss.

We report on a comprehensive study of the wind properties of 115 O- and early B-type stars in the Galaxy and the Large Magellanic Clouds. This work is part of the VLT/FLAMES Survey of Massive Stars. The data is used to construct the empirical dependence of the mass-loss in stellar winds on the metal content of their atmospheres. The metal content of early-type stars in the Magellanic Clouds is discussed. Assuming a power-law dependence of mass loss on metal content, Ṁ ∝ Zm, we find m = 0.83 ± 0.16 from an analysis of the wind momentum luminosity relation (Mokiem et al. 2007b). This result is in good agreement with the prediction m = 0.69 ± 0.10 by Vink et al. (2001). Though the scaling agrees, the absolute empirical value of mass loss is found to be a factor of two higher than predictions. This may be explained by a modest amount of clumping in the outflows of the objects studied.

Present were the members Abe, Babadzhanov, Baggaley, Borovička, Bowell, Ceplecha, Consolmagno, Jenniskens, Kolomiets, Koten, Marsden, Porubčan, Spurný, Valsecchi, Watanabe, and Williams.

Knowledge of the nature and mass of the progenitor stars of core-collapse supernovae are critical elements to test theoretical models of stellar evolution and stellar explosions. Here we describe the current limits and restrictions that can be placed on the progenitor stars of type II SNe and those of Ib/c. There are detections of some type II-P SN progenitors but the exploding stars that produce type Ib/c have eluded discovery. We discuss implications of these quantitative limits and the conclusions that we can now draw.

The Program Group for the World-wide Development of Astronomy (PG-WWDA) is one of nine Commission 46 program groups engaged with various aspects of astronomical education or development of astronomy education and research in the developing world. In the case of PG-WWDA, its goals are to promote astronomy education and research in the developing world through a variety of activities, including visiting astronomers in developing countries and interacting with them by way of giving encouragement and support.

Although it has long been hypothesised that core-collapse supernovae may produce large quantities of dust, interest in this problem has recently been rekindled given the enormous dust masses inferred at very high redshifts (z ≳ 6), when conventional low-mass dust-producing stars would fail to contribute significantly to the universal dust budget. Emission due to warm dust peaks at mid-IR wavelengths. However, with the notable exception of SN 1987A, supernova studies in the mid-IR have been virtually non-existent until the advent of the Spitzer Space Telescope. On behalf of the Mid-Infrared Supernova Consortium, I briefly discuss recent exciting results from mid-IR studies of core-collapse supernovae using Spitzer and attempt to put the role of supernovae as major dust producers into perspective.

Division IX provides a forum for astronomers engaged in the innovation, development and calibration of optical instrumentation and observational procedures including data processing.

This chapter lists the Adhering Organizations of the 63 National Members of the International Astronomical Union. As of September 2008, the IAU had 7 members with Interim status, 21 members in Category I, 10 members in Category II, 11 members in Category III, 3 members in Category IV, 4 members in Category V, 1 member in Category VI, 5 members in Category VII, and 1 member in Category X.

In his address to the Commission, the outgoing president A. Milani explained what he considers have been done well in the past triennium, what has been done only in part, and what has not been done at all. Among the things in which the performance was rated good, he mentioned the successful sponsorship and/or co-sponsorship of four meetings (IAU Colloquia 196 and 197, and Symposia 229 and 236) which have been held in the previous period, as well as of the Symposium on exoplanets to be held next year in China. The only failure in this respect was the proposed meeting in India, which failed already at the proposal definition stage. Also, Milani expressed his satisfaction with the triennial report which has been compiled for the occasion, and his gratitude to the collaborating authors.

Massive stars played a key role in the early evolution of the Universe. They formed with the first halos and started the re-ionisation. It is therefore very important to understand their evolution. In this review, we first recall the effect of metallicity (Z) on the evolution of massive stars. We then describe the strong impact of rotation induced mixing and mass loss at very low Z. The strong mixing leads to a significant production of primary 14N, 13C and 22Ne. Mass loss during the red supergiant stage allows the production of Wolf-Rayet stars, type Ib,c supernovae and possibly gamma-ray bursts (GRBs) down to almost Z = 0 for stars more massive than 60 M⊙. Galactic chemical evolution models calculated with models of rotating stars better reproduce the early evolution of N/O, C/O and 12C/13C. Finally, the impact of magnetic fields is discussed in the context of GRBs.