We study colliding winds in the superluminous binary η Carinae by performing three-dimensional, Smoothed Particle Hydrodynamics (SPH) simulations. For simplicity, we assume both winds to be isothermal. We also assume that wind particles coast without any net external forces. We find that the lower density, faster wind from the secondary carves out a spiral cavity in the higher density, slower wind from the primary. Because of the phase-dependent orbital motion, the cavity is very thin on the periastron side, whereas it occupies a large volume on the apastron side. The model X-ray light curve using the simulated density structure fits very well with the observed light curve for a viewing angle of i = 54° and φ = 36°, where i is the inclination angle and φ is the azimuth from apastron.

The program of IAU scientific meetings is one of the most important means by which the IAU pursues its goal of promoting astronomy through international collaboration. A large fraction of the Union's budget is devoted to the support of the IAU scientific meetings. The Executive Committee (EC) places great emphasis on maintaining high scientific standards, coverage of a balanced spectrum of topics, and an appropriately international flavor for the programme of IAU Meetings. In that respect, the ICSU rules on non-discrimination in the access of qualified scientists from all parts of the world to any IAU meeting apply.

Commission 33 held a brief business session on 21 August within the science session organized jointly with its parent Division VII.

Division IV organizes astronomers studying the characterization, interior and atmospheric structure of stars of all masses, ages and chemical compositions.

A supergiants are objects in transition from the blue to the red (and vice versa) in the uppermost HRD. They are the intrinsically brightest “normal” stars at visual light with absolute visual magnitudes up to −9. They are ideal to study young stellar populations in galaxies beyond the Local Group to determine chemical composition and evolution, interstellar extinction, reddening laws and distances. We discuss most recent results on the quantitative spectral analysis of such objects in galaxies beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and Keck. We describe the analysis method including the determination of metallicity and metallicity gradients. A new method to measure accurate extragalactic distances based on the stellar gravities and effective temperatures is presented, the flux weighted gravity – luminosity relationship (FGLR). The FGLR is a purely spectroscopic method, which overcomes the uncertainties introduced by interstellar extinction and variations of metallicity, which plague all photometric stellar distance determination methods. We discuss the perspectives of future work using the giant ground-based telescopes of the next generation such as the TMT, the GMT and the E-ELT.

The International Astronomical Union (IAU) was founded in 1922 to “promote and safeguard astronomy . . . and to develop it through international co-operation”. The IAU is funded through its National Members. Almost all of the funds supplied from the dues are used for the development of astronomy.

I discuss observational clues concerning episodic mass-loss properties of massive stars in the time before the final supernova explosion. In particular, I will focus on the mounting evidence that LBVs and related stars are candidates for supernova progenitors, even though current paradigms place them at the end of core-H burning. Namely, conditions in the immediate circumstellar environment within a few 102 AU of Type IIn supernovae require very high progenitor mass-loss rates. Those rates are so high that the only known stars that come close are LBVs during rare giant eruptions. I will highlight evidence from observations of some recent extraordinary supernovae suggesting that explosive or episodic mass loss (a.k.a. LBV eruptions like the 19th century eruption of Eta Car) occur in the 5-10 years immediately preceding the SN. Finally, I will discuss some implications for stellar evolution from these SNe, the most important of which is the observational fact that the most massive stars can indeed make it to the ends of their lives with substantial H envelopes intact, even at Solar metallicity.

This paper reports the contributions made on the occasion of the Special Session entitled “Evolution of Massive Stars at Low Metallicity” which was held on Sunday, December 9, 2007 in Kauai (USA).

At the IAU XXV General Assembly in Sydney, 2003, a questionnaire on the perception of participation of “young astronomers” at IAU meeting was distributed. Following the conclusions from the analysis of this questionnaire, the IAU EC recommended in 2004 that the “young astronomers” concept at the next GA in Prague should be worked out with specific activities.

Infrared observations of hot massive stars and their environments provide adetailed picture of mass loss histories, dust formation, and dynamicalinteractions with the local stellar medium that can be unique to the thermalregime. We have acquired new infrared spectroscopy and imaging with thesensitive instruments onboard the SpitzerSpace Telescope in guaranteed and open time programs comprised of some of thebest known examples of hot stars with circumstellar nebulae, supplementing withunpublished Infrared Space Observatory spectroscopy. Here wepresent highlightsof our work on the environment around the extreme P Cygni-type star HDE316285,providing some defining characteristics of the star's evolution andinteractions with the ISM at unprecented detail in the infrared.

The Working Group Historical Instruments (WG-HI) was founded by the members of Commission 41 at the 2000 Manchester IAU XXIV General Assembly, with the main objectives to assemble a bibliography of existing publications relating to such instruments, and to encourage colleagues to carry out research and publish their results. Membership of the WG-HI has increased from three to nine people since its foundation. This clearly demonstrates the IAU members increasing interest in safeguarding old astronomical instruments and buildings as witness to their own country's cultural heritage and scientific progress.

As a result of the triennial reviews by the IAU Division presidents of their Commissions and Working Groups (Bye-Laws § V), the following structural changes have been proposed and approved by the Executive Committee.

We collect here the abstracts of five oral presentations for which the written contribution did not reach the editors in time for publication.

The meeting of the Working Group on Active B-type Stars consisted of a business meeting followed by a scientific meeting containing invited and contributed talks. The titles of the talks and their presenters are listed below. We plan to publish a series of articles containing summaries of these talks in Issue No. 39 of the Be Star Newsletter.

The meeting of the Working Group on standard stars (WG-SS) opened under the chairmanship of Corbally. Gray, as editor, gave a report on the Standard Stars Newsletter (SSN). Through a round of thanks given to Gray, it was recognized by the two dozen present that this publication is the major vehicle between WG-SS meetings for achieving its tasks, namely promoting and communicating work on standard stars. Copies of the newsletter can be downloaded from <http://stellar.phys.appstate.edu/ssn>.

Division VI gathers astronomers studying the diffuse matter in space between stars, ranging from primordial intergalactic clouds, via dust and neutral and ionized gas in galaxies, to the densest molecular clouds and the processes by which stars are formed.

Various experiments have definitely demonstrated that one-micron accuracy (0.″06) on the definition of stellar images on CdC plates cannot be claimed, as it was speculated back in 1999. More realistically, a 2-3 micron accuracy is achievable, getting worse toward the survey magnitude limit, with an average magnitude error of 0.3. The level of astrometric accuracy corresponds to a 0.″2 - 0.″3 error in position at Epoch 1900, which, once used as first Epoch for proper motion determination in combination with modern epoch observations, can produce errors at the level of 2-5 mas/yr, thereby allowing to detect stellar motions larger than 0.″01/yr, which at a distance of 500 pc from the Sun correspond to ~25-60 km/s tangential velocity. Therefore, the AC/CdC heritage collection can be regarded as a highly valuable first-epoch material, e.g., for the realization of a Tycho-2 extension to fainter magnitudes (~15 photographic), especially in selected areas where radial velocity data are available, for the exploration of stellar kinematics beyond our solar neighborhood.

Division VII provides a forum for astronomers studying our home galaxy, the Milky Way, which offers a unique laboratory for exploring the detailed structure of the stellar and gaseous components of galaxies and the process by which they form and evolve.

With a dynamical mass Mdyn ~ 1.3×105 M⊙ and a lower limit Mcl > 5 × 104 M⊙ from star counts, Westerlund 1 is the most massive young open cluster known in the Galaxy and thus the perfect laboratory to study massive star evolution. We have developed a comprehensive spectral classification scheme for supergiants based on features in the 6000–9000Å range, which allows us to identify > 30 very luminous supergiants in Westerlund 1 and ~ 100 other less evolved massive stars, which join the large population of Wolf-Rayet stars already known. Though detailed studies of these stars are still pending, preliminary rough estimates suggest that the stars we see are evolving to the red part of the HR diagram at approximately constant luminosity.