This chapter gives the main IAU scientific bodies (Division, Commissions and their Working Groups) in force until the end of the XVIIIth General Assembly. As a result of the adoption of Resolution B4 by this Assembly, a new Divisional structure was established (see Chapters II and IV of these Transactions), to take effect on 1 September 2012.

Recent progress in the seismic interpretation of field β Cep stars has resulted in improvements of the physical description in the stellar structure and evolution model computations of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismic study based on the discovery of numerous multi-periodic and mono-periodic B-type stars in the open cluster NGC 884 (χ Persei). Our study illustrates the current status of ensemble asteroseismology of this young open cluster.

Pollux is considered as an archetype of a giant star hosting a planet: its radial velocity (RV) presents sinusoidal variations with a period of about 590 d, which have been stable for more than 25 years. Using ESPaDOnS and Narval we have detected a weak (sub-gauss) magnetic field at the surface of Pollux and followed up its variations with Narval during 4.25 years, i.e. more than for two periods of the RV variations. The longitudinal magnetic field is found to vary with a sinusoidal behaviour with a period close to that of the RV variations and with a small shift in phase. We then performed a Zeeman Doppler imaging (ZDI) investigation from the Stokes V and Stokes I least-squares deconvolution (LSD) profiles. A rotational period is determined, which is consistent with the period of variations of the RV. The magnetic topology is found to be mainly poloidal and this component almost purely dipolar. The mean strength of the surface magnetic field is about 0.7 G. As an alternative to the scenario in which Pollux hosts a close-in exoplanet, we suggest that the magnetic dipole of Pollux can be associated with two temperature and macroturbulent velocity spots which could be sufficient to produce the RV variations. We finally investigate the scenarii of the origin of the magnetic field which could explain the observed properties of Pollux.

The President of the IAU, Prof. Robert Williams, welcomed the delegates and members to this first business session of the General Assembly. The President invited the General Secretary, Dr. Ian Corbett, to start the business session.

OB stars are known to exhibit various types of wind variability, as detected in their ultraviolet spectra, amongst which are the ubiquitous discrete absorption components (DACs). These features have been associated with large-scale azimuthal structures extending from the base of the wind to its outer regions: corotating interaction regions (CIRs). There are several competing hypotheses as to which physical processes may perturb the star's surface and generate CIRs, including magnetic fields and non radial pulsations (NRPs), the subjects of this paper with a particular emphasis on the former. Although large-scale magnetic fields are ruled out, magnetic spots deserve further investigation, both on the observational and theoretical fronts.

We have observed the giant star 31 Comae in April and May 2013 with the spectropolarimeter Narval at Pic du Midi Observatory, France. 31 Comae is a single, rapidly rotating giant with rotational period ~6.8 d and vsini ~ 67 km/s. We present measurements and discuss variability of the longitudinal magnetic field (Bl), spectral activity indicators Hα, CaII H&K, Ca II IR triplet and evolutionary status. Our future aim is to perform a Zeeman-Doppler imaging study for the star.

HD 206860 is a young planet (HN Peg b) hosting star of spectral type G0V and it has a potential debris disk around it. In this work we measure the longitudinal magnetic field of HD 206860 using spectropolarimetric data and we measure the chromospheric activity using Ca II H&K, H-alpha and Ca II infrared triplet lines.

We study the rotation-activity relationship for low-mass members of the young cluster h Persei, a ~13 Myr old cluster. h Per, thanks to its age, allows us to link the rotation-activity relation observed for main-sequence stars to the still unexplained activity levels of very young clusters.

We constrained the activity levels of h Per members by analyzing a deep Chandra/ACIS-I observation pointed to the central field of h Per. We combined this X-ray catalog with the catalog of h Per members with measured rotational period, presented by Moraux et al. (2013). We obtained a final catalog of 202 h Per members with measured X-ray luminosity and rotational period. We investigate the rotation-activity relation of h Per members considering different mass ranges. We find that stars with 1.3 M⊙ > M 1.4 M⊙ show significant evidence of supersaturation for short periods. This phenomenon is instead not observed for lower mass stars.

Although the κ mechanism of pulsations is known for early-type stars, opacities and the equation of state are still uncertain. Stellar models calculated for the OP data implemented with the new Kurucz opacities at log T < 5.2 were investigated for different chemical compositions of elements. The additional metallic opacity bump at log T ≈ 5.06 that occurs in the Kurucz data changes markedly the oscillation spectra of unstable modes. Basic properties of the new opacity bump and examples of seismic models are shown. B-type stars observed in the Galaxy, LMC and SMC were considered. The problem was studied using Dziembowski's computing codes for linear, non-adiabatic and non-radial oscillations.

With the increasing quality of asteroseismic observations it is important to minimize the random and systematic errors in mode parameter estimates. To this end it is important to understand how the oscillations relate to the directly observed quantities, such as intensities and spectra, and to derived quantities, such as Doppler velocity. Here I list some of the effects we need to take into account and show an example of the impact of some of them.

Optical interferometry is the only technique giving access to milli-arcsecond (mas) resolution at infrared wavelengths. For Cepheids, this is a powerful and unique tool to detect the orbiting companions and the circumstellar envelopes (CSE). CSEs are interesting because they might be used to trace the Cepheid evolution history, and more particularly they could impact the distance scale. Cepheids belonging to binary systems offer an unique opportunity to make progress in resolving the Cepheid mass discrepancy. The combination of spectroscopic and interferometric measurements will allow us to derive the orbital elements, distances, and dynamical masses. Here we focus on recent results using 2- to 6-telescopes beam combiners for the Cepheids X Sgr, T Mon and V1334 Cyg.

Using spectroscopic observations and photometric light curves of 280 nearby M dwarfs from the MEarth exoplanet transit survey, we examine the relationships between magnetic activity (quantified by Hα emission), rotation period, and stellar age (derived from three-dimensional space velocities). Although we have known for decades that a large fraction of mid-late-type M dwarfs are magnetically active, it was not clear what role rotation played in the magnetic field generation (and subsequent chromospheric heating). Previous attempts to investigate the relationship between magnetic activity and rotation in mid-late-type M dwarfs were hampered by the limited number of M dwarfs with measured rotation periods (and the fact that vsini measurements only probe rapid rotation). However, the photometric data from the MEarth survey allows us to probe a wide range of rotation periods for hundreds of M dwarf stars (from less than one to over 100 days). Over all M spectral types we find that magnetic activity decreases with longer rotation periods, including late-type, fully convective M dwarfs. We find that the most magnetically active (and hence, most rapidly rotating) stars are consistent with a kinematically young population, while slow-rotators are less active or inactive and appear to belong to an older, dynamically heated stellar population.

Cepheids are one of the most famous standard candles used to calibrate the Galactic distance scale. However, it is fundamental to develop and test independent tools to measure their distances, in order to reach a better calibration of their period-luminosity (P-L) relationship. We present here the first results obtained with the Integrated Parallax of Pulsation (IPoP) method, an extension of the classical Baade-Wesselink method that derives the distance by making a global modelisation of all the available data. With this method we aim to reach a 2% accuracy on distance measurements.

Cepheid masses are also an essential key for our comprehension of those objects. We briefly present an original approach to derive observational constraint on Cepheid masses. Unfortunately, it does not lead to promising results.

We examine the light curves of over 2700 stars observed in long cadence by the Kepler spacecraft as part of the Guest Observer program. Most of these stars are faint (Kepler magnitude > 14), and fall near or within the effective temperature and log g range of the γ Dor and δ Sct instability strips. We find that the pulsating stars are obvious from inspection of the light curves and power spectra, even for these faint stars. However, we find that a large number of stars are ‘constant’, i.e. show no frequencies in the 0.2 to 24 d−1 range above the 20 ppm level. We discuss the statistics for the constant stars, and some possible physical reasons for lack of pulsations. On the other hand, γ Dor and δ Sct candidates have been found in the Kepler data spread throughout and even outside of the instability regions of both types that were established from pre-Kepler ground-based observations. We revisit mechanisms to produce g- or p-mode pulsations in conditions when these modes are not expected to be unstable via the He-ionization κ effect (δ Sct) or convective blocking (γ Dor) pulsation driving mechanisms.

Convective envelopes in stars on the main sequence are usually connected only with stars of spectral types F5 or later. However, observations as well as theory indicate that the convective outer layers in hotter stars, despite being shallow, are still effective and turbulent enough to stochastically excite oscillations. Because of the low amplitudes, exploring stochastically excited pulsations became possible only with space missions such as Kepler and CoRoT. Here I review the recent results and discuss among others, pulsators such as δ Scuti, γ Doradus, roAp, β Cephei, Slowly Pulsating B and Be stars, all in the context of solar-like oscillations.

We present our joint efforts to study variable stars in open clusters. This includes a new catalogue, a photometric survey for new variables, and the database WEBDA. Our tools will shed more light on stellar variability in open clusters.

Various types of magnetic fields occur in stars: small scale fields, large scale fields, and internal toroidal fields. While the latter may be ubiquitous in stars due to differential rotation, small scale fields (spots) may be associated with envelop convection in all low and high mass stars. The stable large scale fields found in only about 10% of intermediate mass and massive stars may be understood as a consequence of dynamical binary interaction, e.g., the merging of two stars in a binary. We relate these ideas to magnetic fields in white dwarfs and neutron stars, and to their role in core-collapse and thermonuclear supernova explosions.

The meeting was attended by the President and Vice-President of the Commission, along with approximately 15 other members. The President reported on the election of new officers that took place at the end of March 2012, for four new members of the Organizing Committee as well as a new Vice-President, and thanked the outgoing members. Tomaz Zwitter (Slovenia) was elected as the new VP (2012–2015), and the new OC members for the period 2012–2018 are Alceste Bonanos (Greece), Alain Jorissen (Belgium), David Katz (France), and Matthias Steinmetz (Germany). The current VP, Dimitri Pourbaix, became the President through 2015.

Laboratory spectra showing Zeeman patterns in some FeH lines susceptible to be used as magnetic probes in cool stellar atmostpheres have been recorded in the laboratory, and molecular Landé factors obtained from analysis. These Landé factors have been used to model some lines recorded in Stokes V polarisation in sunspot spectra at the solar telescope THEMIS.

We report the results of spectropolarimetric study of the classical Cepheid η Aql. We found that the longitudinal magnetic field of η Aql sinusoidally varies with the radial pulsation period, while the amplitude B, mean field B0, and phases of maximum and minimum field change from year to year. We hypothesize that possible reasons of those variations are stellar axial rotation or dynamo mechanisms.