Sylvie Vauclair is not only a superb scientist, an excellent musician, a devoted mother, a passionate communicator of science to the public and a Chevalier de la Légion d'honneur, but, most importantly, a wonderful friend.

Hot massive stars are ideal indicators for present-day cosmic abundances. We review results from a non-LTE study of a larger sample of early B-type stars in the solar neighbourhood by Nieva & Przybilla (2012) and extend the analysis. Using comprehensive models with improved microphysics, novel analysis methodologies and high-quality spectra it is shown that the present-day chemical composition in massive stars out to several hundred parsec distance from the Sun is highly homogeneous. Abundances for about a dozen astrophysically important chemical elements are presented, including new preliminary data on aluminium, sulphur and argon. This establishes a cosmic abundance standard, which serves as a reference facilitating chemical peculiarities in other stars to be identified. Similarities and differences to the solar standard, and implications are discussed.

We provide an updated discussion of the sample of CEMP-s and CEMP-s/r stars collected from the literature. Observations are compared with the theoretical nucleosynthesis models of asymptotic giant branch (AGB) stars presented by Bisterzo et al. (2010, 2011, 2012), in the light of the most recent spectroscopic results.

We calibrate and then use the relation between equivalent width (EW) and full–width–half–maximum (FWHM) of metallic absorption lines in the spectra of RR Lyrae stars to estimate a new upper limit of Vrotsini ≤ 6 km.s−1 on their axial equatorial rotational velocities, and to derive the variations of macroturbulent velocities in their atmospheres during pulsation cycles. Finally, we present a simple way to estimate macroturbulent/rotational velocity from FWHM of the cross–correlation function.

We present a detailed atmospheric dynamics study of Blazhko and nonBlazhko RR ab stars, using a high-resolution spectroscopic survey. We derived the dynamical parameters: dynamical accelerations, radius variations, rise time, shock amplitudes, full width at half maximum, and their variation during the Blazhko modulation, and we highlight the relationship between period changes and variation in dynamical parameters over multi- Blazhko cycles. We discuss the origin of the Blazhko effect, giving a new empirical side for further theoretical models.

This is a non-exhaustive review of what we have learned from 10+ years of cluster studies with multi-object spectrographs at 10 m-class telescopes about what stars do with their birth-cloud lithium. This light and fragile element ties together Big-Bang and stellar physics, stellar atmospheric and interior modelling, it is a sensitive measure of our ability to quantitatively model Big-Bang Nucleosynthesis, stellar physics and Galactic chemical evolution. Progress has undoubtedly been made, but the picture that emerges is far from complete.

Mixing mechanisms bring the Li from the base of the convective zone to deeper and warmer layers where it is destroyed. These mechanisms are investigated by comparing observations of Li abundances in stellar atmospheres to models of stellar evolution. Observations in open cluster are especially suitable for this comparison, since their age and metallicity are homogeneous among their members and better determined than in field stars. In this work, we compare the evolution of Li abundances in three different clusters: the Hyades, NGC 752, and M 67. Our models are calculated with microscopic diffusion and transport of chemicals by meridional circulation, and calibrated on the Sun. These comparisons allow us to follow the evolution of Li abundance as a function of stellar mass in each cluster and as a function of the age by comparing this evolution in each cluster. We evaluate the efficiency of the mixing mechanisms used in the models, and we try to identifiy the lacking mechanisms to reproduce the observed evolution of Li abundance.

This paper first surveys how stellar magnetic fields are measured, and especially the impact of the most recent spectropolarimeters on our measurement capabilities. The two main types of stellar magnetism, dynamo and fossil fields, are discussed in a general way. This is followed by a broad survey of the current level of knowledge of magnetic fields in various classes of stars, from the pre-main sequence through main sequence stars, giants, and white dwarfs. Some of the hotter magnetic stars show clear abundance anomalies relative to the solar abundance ratios. The connection between magnetism and the atomic diffusion believed to be responsible for these anomalies is discussed, especially in the context of some new results from cluster A and B magnetic stars.

New spectral line polarisation observations of 7 bright Ap stars have been obtained with the ESPaDOnS and Narval high resolution spectropolarimeters (Silvester et al. 2012). The aim of this data set is produce a series of surface magnetic field and surface chemistry maps for these Ap stars. We present new magnetic maps for the Ap star α2 CVn using these new data and the MDI inversion code INVERS10. α2 CVn is the first Ap star to be observed during two separate epochs using high resolution phase resolved spectropolarimetric IQUV observations and as such allows us an insight into how stable the surface magnetic structure is over a decade timescale. We show that the new maps give a magnetic field structure consistent with the previous maps obtained by Kochukhov and Wade (2010) from lower quality MuSiCoS spectra taken a decade ago and that the field topology cannot be described by a dipolar or quadrupolar field.

Beyond the extraordinary three dimensional map that Gaia will create for a billion of stars, it will reveal the origin and history of the Milky Way as the major goal. This does not weakness the fantastic impact of Gaia on the stellar physic. It will put constraints on the modeling of stars to an extreme that consequently new input physics will be mandatory to understand a Gaia HR diagram. Stars are formed in populations and evolve as collection of objects revealing important clues on how they formed, what kind of mass function is active during the star formation, how frequent is the star formation, all of this is imprinted in the intrinsic properties of stars that large surveys combined together like Gaia, Kepler, PLATO will revealed. The characterization of stars hosting planets is also a goal of such combination of large surveys and in particular of the measure of distances in the Galaxy. The launch of Gaia is for November of 2013 and the output catalogue is expected for 2020. Then will start the beginning of a new Astrophysics touching so many topics that a new age of astrophysics is then foreseen.

New observations of stellar pulsations, particularly from the CoRoT and Kepler space missions, have opened completely new possibilities for asteroseismic investigations for stars in large parts of the Hertzsprung-Russell diagram. Particularly dramatic has been the development of asteroseismology of stars showing solar-like oscillations, where hundreds of stars near the main sequence and tens of thousands of red giants can now be investigated. Although the analysis of the data have yielded extensive information about the global properties of the stars we are still only at the beginning of learning how to use the data for more profound studies of stellar interiors. Here I give a brief overview of the observations and discuss the potential contributions to the understanding of stellar physics.

I address the problem of estimating stellar parameters using asteroseismic data. In particular I focus on the biases introduced the differences existing between observed and theoretical oscillation frequencies introduced by a poor modelling of near-surface layers. I review some methods to evaluate this shift and discuss briefly some studies trying to take into account this effect while estimating stellar parameters.

This work concerns the study of the properties of convective cores in main-sequence models of solar-like pulsators and what information they may hold about stellar ages. We verified that the maximum absolute frequency derivative of particular combinations of frequencies, which we name “the slopes”, provides information on the relative size of the discontinuity in the sound-speed profile at the border of the convectively mixed region. Since the latter is related to the evolutionary state of stars, we show that for models with masses above 1.3M⊙, it may be possible to estimate the fraction of stellar main-sequence evolution from the slopes. Moreover, for models with masses below 1.2M⊙ we verified that it may be possible to use the slopes to discriminate against models with small amounts of core overshoot.

High precision photometry as performed by the CoRoT and Kepler satellites on-board instruments has allowed to detect stellar oscillations over the whole HR diagram. Oscillation frequencies are closely related to stellar interior properties via the density and sound speed profiles, themselves tightly linked with the mass and evolutionary state of stars. Seismic diagnostics performed on stellar internal structure models allow to infer the age and mass of oscillating stars. The accuracy and precision of the age determination depend both on the goodness of the observational parameters (seismic and classical) and on our ability to model a given star properly. They therefore suffer from any misunderstanding of the physical processes at work inside stars (as microscopic physics, transport processes...). In this paper, we recall some seismic diagnostics of stellar age and we illustrate their efficiency in age-dating the CoRoT target HD 52265.

The δ Scuti pulsators occupy a region in the Hertzsprung-Russell diagram where several physical processes occur: the subsurface convection layers change from being deep and vigorous to being shallow and ineffective to transport energy. This transition has a large impact not only on pulsational stability but also on stellar evolution, activity, transport of angular momentum, mixing processes, etc.. It is therefore of great interest to understand how exactly the stellar structure changes with increasing temperature and mass. Theoretical models (Houdek et al. 1999; Samadi et al. 2002) predicted that the convection in the outer layers of δ Scuti stars is still efficient enough to excite solar-like oscillations. The Kepler target, HD 187547 (a.k.a. Superstar), was the first δ Scuti star to suggest that solar-like oscillations are indeed present in this type of stars (Antoci et al. 2011). There were several reasons to conclude that HD 187547 is a δ Scuti/solar-like hybrid pulsator. (1) The peaks at high frequencies are modes of pulsations approximately equidistantly spaced, as expected for high radial order pressure modes; these peaks are not combination frequencies as it is sometimes observed in δ Scuti stars. (2) The opacity mechanism cannot excite a continuous frequency range as observed in HD 187547 (Pamyatnykh 2000). (3) The identification as an Am star consistent with the low v sini, makes it very unlikely to be a δ Scuti/roAp hybrid, because strong large-scale magnetic fields, a necessity for roAp pulsators, have never been detected in Am stars (Auriere et al. 2010). (4) Although a large number of Am stars are found in binary systems, we find no evidence in the observed spectra for a companion, i.e. no significant RV shift over 170 days can be detected and the absorption lines can perfectly be reproduced by assuming a slowly-rotating chemically peculiar Am star. This means that the peaks at high frequencies are unlikely to be from a companion, because such a star would be an A or F-type star and would be visible in the spectrum and this is not the case. (5) The large separation Δν, which is the frequency difference between consecutive radial orders of the same degree l, predicts the frequency of maximum power (νmax) to be exactly where the mode with the highest amplitude in the supposed stochastic region is observed. Note that the Δν and νmax scaling relation is valid only for stochastic oscillations (e.g. Huber et al. 2011). (6) The statistical properties (Chang & Gough 1998) of the modes interpreted to be solar-like were very similar to what is expected for stochastic signals in general.

The space-borne missions CoRoT and Kepler have opened a new era in stellar physics, especially for evolved stars, with precise asteroseismic measurements that help determine precise stellar parameters and perform ensemble asteroseismology. This paper deals with the quality of the information that we can retrieve from the oscillations. It focusses on the conditions for obtaining the most accurate measurement of the radial and non-radial oscillation patterns. This accuracy is a prerequisite for making the best with asteroseismic data. From radial modes, we derive proxies of the stellar mass and radii with an unprecedented accuracy for field stars. For dozens of subgiants and thousands of red giants, the identification of mixed modes (corresponding to gravity waves propagating in the core coupled to pressure waves propagating in the envelope) indicates unambiguously their evolutionary status. As probes of the stellar core, these mixed modes also reveal the internal differential rotation and show the spinning down of the core rotation of stars ascending the red giant branch. A toy model of the coupling of waves constructing mixed modes is exposed, for illustrating many of their features.

Atomic diffusion – important in many contexts in stellar astrophysics and an important thread running through this meeting – is most spectacularly observable in the atmospheres of some A stars. The magnetic Ap stars and the non-magnetic Am stars show directly abundance anomalies caused by gravitational settling and radiative levitation. Over the last decade spectroscopic studies have begun to provide maps of abundance distributions in the magnetic Ap stars in three dimensions. Interestingly, high radial overtone p-mode pulsations in roAp stars have also given three-dimensional views of the stellar atmospheres with studies of rotational and line profile variations of pulsation amplitudes and phases. These detailed looks at the effects of microscopic atmospheric changes in the strongly non-LTE and magnetic upper atmospheric layers of Ap stars provide perhaps the most exciting challenge to atomic diffusion theory in terms of detailed explanation and prediction. Am stars were at one time thought not to pulsate because of gravitational settling of He from the He ii ionization zone that provides the κ-mechanism driving for δ Sct pulsations in A stars. In the last few years we have found with SuperWASP and Kepler observations that many Am stars do pulsate. More than half of all A stars pulsate at Kepler micromagnitude precision, yet there is a subset of A stars that truly do not pulsate at that level. Are these Am stars with the strongest signature of atomic diffusion? Is atomic diffusion the reason for the pulsational stability of these stars? The answers are not yet known.

Chemically peculiar stars are stage to a wide variety of physical phenomena, including diffusion, convection, magnetism and pulsation. Progress in the understanding of these objects, through the study of their oscillations, can help us to characterize these physical phenomena and better understand the way they are coupled in stars. A number of chemically peculiar A-type stars, known as rapidly oscillating Ap (roAp) stars, have been known to exhibit high frequency oscillations since the early 80s. Despite this, the mechanism responsible for driving these oscillations is not fully understood. Currently, the most widely accepted theory states that oscillations in this class of pulsators are excited by the opacity mechanism acting on the hydrogen ionization region, in an envelope where convection has been suppressed by a strong magnetic field. Nevertheless, this theory fails to correctly predict some of the observations for this class of pulsators. In this paper we briefly review the current status of understanding of the driving of pulsations in roAp stars. In particular, we shall emphasize the comparison between predictions of nonadiabatic models of roAp stars with observations of a subset of pulsators of this class for which stringent data on global parameters are available.

We report the discovery of a new class of non-radial pulsating stars that are the precursors of low-mass white dwarf stars.