We present preliminary results of the determination of fundamental parameters of single O-type stars in the MiMeS survey. We present the sample and we focus on surface CNO abundances, showing how they change as stars evolve off the zero-age main sequence.

It is now well established that a fraction of the massive (M > 8 M⊙) star population hosts strong, organised magnetic fields, most likely of fossil origin. The details of the generation and evolution of these fields are still poorly understood. The BinaMIcS project takes an important step towards the understanding of the interplay between binarity and magnetism during the stellar formation and evolution, and in particular the genesis of fossil fields, by studying the magnetic properties of close binary systems. The components of such systems are most likely formed together, at the same time and in the same environment, and can therefore help us to disentangle the role of initial conditions on the magnetic properties of the massive stars from other competing effects such as age or rotation. We present here the main scientific objectives of the BinaMIcS project, as well as preliminary results from the first year of observations from the associated ESPaDOnS and Narval spectropolarimetric surveys.

The Magnetism in Massive Stars (MiMeS) project represents the largest systematic survey of stellar magnetism ever undertaken. Based on a sample of over 550 Galactic B and O-type stars, the MiMeS project has derived the basic characteristics of magnetism in hot, massive stars. Herein we report preliminary results.

In A- and late B-type stars, strong magnetic fields are always associated with Ap and Bp chemical peculiarities. However, it is not clear at what point in a star's evolution those peculiarities develop. Strong magnetic fields have been observed in pre-main sequence A and B stars (Herbig Ae and Be stars), and these objects have been proposed to be the progenitors of Ap and Bp stars. However, the photospheric chemical abundances of these magnetic Herbig stars have not been studied carefully, and furthermore the chemical abundances of 'normal' non-magnetic Herbig stars remain poorly characterized. To investigate this issue, we have studied the photospheric compositions of 23 Herbig stars, four of which have confirmed magnetic fields. Surprisingly, we found that half the non-magnetic stars in our sample show λ Bootis chemical peculiarities to varying degrees. For the stars with detected magnetic fields, we find one chemically normal star, one star with λ Boo peculiarities, one star displaying weak Ap/Bp peculiarities, and one somewhat more evolved star with somewhat stronger Ap/Bp peculiarities. These results suggests that Ap/Bp peculiarities are preceded by magnetic fields, and that these peculiarities develop over the pre-main sequence lives of A and B stars. The incidence of λ Boo stars we find is much higher than that seen on the main sequence. We argue that a selective accretion model for the formation of λ Boo peculiarities is a natural explanation for this remarkably large incidence.

We present results of the X-ray monitoring of V4046 Sgr, a close classical T Tauri star binary, with both components accreting material. The 360 ks long XMM observation allowed us to measure the plasma densities at different temperatures, and to check whether and how the density varies with time. We find that plasma at temperatures of 1–4 MK has high densities, and we observe correlated and simultaneous density variations of plasma, probed by O VII and Ne IX triplets. These results strongly indicate that all the inspected He-like triplets are produced by high-density plasma heated in accretion shocks, and located at the base of accretion flows.

We present a preliminary 3D potential field extrapolation model of the joint magnetosphere of the close accreting PMS binary V4046 Sgr. The model is derived from magnetic maps obtained as part of a coordinated optical and X-ray observing program.

Short period binary systems containing magnetic Ap stars are anomalously rare. This apparent anomaly may provide insight into the origin of the magnetic fields in theses stars. As an early investigation of this, we observed three close binary systems that have been proposed to host Ap stars. Two of these systems (HD 22128 and HD 56495) we find contain Am stars, but not Ap stars. However, for one system (HD 98088) we find the primary is indeed an Ap star, while the secondary is an Am star. Additionally, the Ap star is tidally locked to the secondary, and the predominately dipolar magnetic field of the Ap star is roughly aligned with the secondary. Further investigations of HD 98088 are planned by the BinaMIcS collaboration.

We present time-dependent, self-consistent diffusion calculations for Cr, Mn and Fe in a Teff = 12 000 K and logg = 4.0 stellar atmosphere. The temporal evolution of the chemical stratifications is followed for the zero field case and for magnetic fields of varying strength and direction relative to the stellar surface. Preliminary conclusions are preceded by a comparison of the present results to equilibrium solutions.

The atmospheres of upper mainsequence chemically peculiar stars (ApBp stars) are known to be strongly affected by atomic diffusion. In recent years, both observations and models have shown that, as expected, the classical picture of abundance stratification is far too simple. A new generation of observational and modelling tools is appearing to take into account the complexity of the situation. In this talk, I will give an overview on recent results concerning the models for ApBp stars atmospheres. I will evaluate the two main approaches to estimate quantitatively the abundance stratifications: those using the so-called equilibrium hypothesis vs. those calculating time-dependent diffusion.

We review the interaction in intermediate and high mass stars between their evolution and magnetic and chemical properties. We describe the theory of Ap-star ‘fossil’ fields, before touching on the expected secular diffusive processes which give rise to evolution of the field. We then present recent results from a spectropolarimetric survey of Herbig Ae/Be stars, showing that magnetic fields of the kind seen on the main-sequence already exist during the pre-main sequence phase, in agreement with fossil field theory, and that the origin of the slow rotation of Ap/Bp stars also lies early in the pre-main sequence evolution; we also present results confirming a lack of stars with fields below a few hundred gauss. We then seek which macroscopic motions compete with atomic diffusion in determining the surface abundances of AmFm stars. While turbulent transport and mass loss, in competition with atomic diffusion, are both able to explain observed surface abundances, the interior abundance distribution is different enough to potentially lead to a test using asterosismology. Finally we review progress on the turbulence-driving and mixing processes in stellar radiative zones.

Discoveries of magnetic fields in pulsating B and Be stars have been claimed from low-resolution spectropolarimetric observations with FORS1 at VLT. We used the new generation of high-resolution spectropolarimeters, ESPaDOnS at CFHT and NARVAL at TBL, to check for the existence of these fields. We find that most of the claimed magnetic stars do not host a magnetic field. This work shows the importance of a critical analysis of FORS1 data when searching for weak magnetic fields in early-type stars and the advantage of using ESPaDOnS and NARVAL to study such type of stars.

In massive stars, magnetic fields are thought to confine the outflowing radiatively-driven wind, resulting in X-ray emission that is harder, more variable and more efficient than that produced by instability-generated shocks in non-magnetic winds. Although magnetic confinement of stellar winds has been shown to strongly modify the mass-loss and X-ray characteristics of massive OB stars, we lack a detailed understanding of the complex processes responsible. The aim of this study is to examine the relationship between magnetism, stellar winds and X-ray emission of OB stars. In conjunction with a Chandra survey of the Orion Nebula Cluster, we carried out spectropolarimatric ESPaDOnS observations to determine the magnetic properties of massive OB stars of this cluster.

Massive stars are those stars with initial masses above about 8 times that of the sun, eventually leading to catastrophic explosions in the form of supernovae. These represent the most massive and luminous stellar component of the Universe, and are the crucibles in which the lion's share of the chemical elements are forged. These rapidly-evolving stars drive the chemistry, structure and evolution of galaxies, dominating the ecology of the Universe - not only as supernovae, but also during their entire lifetimes - with far-reaching consequences. Although the existence of magnetic fields in massive stars is no longer in question, our knowledge of the basic statistical properties of massive star magnetic fields is seriously incomplete. The Magnetism in Massive Stars (MiMeS) Project represents a comprehensive, multidisciplinary strategy by an international team of recognized researchers to address the “big questions” related to the complex and puzzling magnetism of massive stars. This paper present the first results of the MiMeS Large Program at the Canada-France-Hawaii Telescope.

Atomic diffusion can have detectable effects in many kinds of stars, each time that mixing processes are not efficient enough to prevent the build up of abundance stratifications. In this talk, after presentation of some general aspects about diffusion processes in stars, I will discuss the role of radiative acceleration which is one of the important quantities determining diffusion velocities. I will also discuss some aspects specific to stellar atmospheres, in particular for stars exhibiting strong magnetic fields.

Four probable Ap members of the open cluster NGC 6475, were investigated through detailed spectrum synthesis. Cluster membership was confirmed for all four stars, however chemical abundance analysis shows that only three are truly Ap. Derived $v \sin i$  values and chemical abundances for 20 elements ranging form C to Eu are presented.

We present our current knowledge of the solar chemical composition based on the recent significant downward revision of the solar photospheric abundances of the most abundant metals very recently reviewed in detail by Asplund et al.  (2005a). These new solar abundances result from the use of a 3D hydrodynamical model of the solar atmosphere instead of the classical 1D hydrostatic models,accounting for departures from LTE, and improved atomic and molecular data. With these abundances, the new solar metallicity, Z, and Z/X, decrease to Z = 0.012 and Z/X = 0.0165 respectively, almost a factor of 2 lower than earlier widely used values. While resolving a number of longstanding problems, the new 3D-based solar photospheric composition also poses serious challenges for the standard solar model.

Main theoretical formulae and some computational results ofevolutionary segregation of Hg isotopes due to light-induced driftin the atmospheres of chemically peculiar stars have beenrepresented.


Time-resolved spectroscopic observations of non-radial oscillations in magnetic Apstars reveal unexpected and complex pulsation behaviour in spectral linesof individual chemical elements. This diverse rapid spectroscopic variability isclosely related to the presence of strong photospheric vertical abundance gradientsbuilt up by chemical diffusion. Consideration of chemical stratification and simultaneous interpretation of the pulsationalvariability of different chemical species have made it possible a tomographicmapping of the radial dependence of pulsationproperties of the atmospheres of roAp stars. Combination of the informationobtained using pulsation tomography with horizontal mapping using Doppler imagingopens a unique possibility to construct unprecedented three-dimensional maps of pulsationwaves, chemical spots and magnetic field in the atmospheres of peculiar A stars.


We present briefly some results of the ESO Large Program “First Stars"where it is shown that the abundance ratios of some light elements in theatmospheres of the extremely metal poor stars varies when the starevolves. This could be explained by a mixing with deep layers butsuch a mixing is not predicted by the theory.