Étude de la variabilité spectroscopique d’un échantillon d’étoiles Wolf-Rayet de type WC9

Nous savons que la grande majorité des étoiles WC9 produit de la poussière à base de carbone. Cette dernière doit se former dans des zones de très haute densité afin de survivre à l’environnement hostile qu’est celui du vent d’une étoile WR. Les étoiles WC appartenant à un système binaire WR + O produisent de la poussière quand les vents des deux étoiles entrent en collision et forment une zone de choc pouvant augmenter la densité du gaz d’un facteur 1000. Par contre, plusieurs étoiles WC9 n’ont, à ce jour, montré aucun signe de la présence d’un compagnon. Le but du projet est de tenter d’identifier un mécanisme alternatif responsable de la formation de poussière dans les étoiles WC9 n’appartenant pas à un système binaire. Nous présentons les résultats d’une campagne d’observation visant à caractériser la variabilité spectroscopique d’un échantillon de huit étoiles WC9 et une étoile WC8d. Nos résultats indiquent que la majorité des étoiles montrent des variations à grande échelle dans la raie d’émission C III 5696, soit à un niveau d’au moins 5% du flux de la raie et que les structures dans le vent ont une dispersion de vitesses de l’ordre de 150-300 km/s. De manière générale, les variations de vitesse radiales sont anti-corrélées avec le coefficient d’asymétrie de la raie, ce qui semble infirmer la présence d’un compagnon. Des observations en photométrie de l’étoile WR103 montrent une période de 9.1 ± 0.6 jours qui s’accorde avec les variations spectroscopiques et qui ne semble pas, de manière évidente, d’origine binaire.We know that the majority of WC9 stars produces carbon-based dust. To survive in the hot and harsh environement that is the wind of a WR star, the dust grains must be formed in regions of very high density. We know that WC stars that are part of a WR + O system can produce dust at periastron passage where the collision of the two stellar winds is strong enough to produce shocks that compress the gas to densities up to a factor 103 higher than that of the WR star. However, so far, many WC9 stars have shown no signs of a companion. The goal of the current project is to identify a mechanism that could be responsible for the formation of dust in single WC9 stars. We present the results of an observing campaign which aimed to characterize the spectroscopic variability of eight WC9 stars and one WC8d star. Our results indicate that most stars show large scale variations of their C III 5696 emission line that reach at least 5% of the total line flux, and that the structures in the wind have a mean velocity dispersion of 150-300 km/s. In general, the radial velocity variations are anti-correlated with the skewness variations. This seems to indicate that the variations are not due to the presence of a companion. Photometric observations of WR 103 show a period of 9.1 ± 0.6 days that agrees with the spectroscopic variations and does not seem from binary origin

MOST detects corotating bright spots on the mid-O type giant {\xi} Persei

We have used the MOST (Microvariability and Oscillations of STars) microsatellite to obtain four weeks of contiguous high-precision broadband visual photometry of the O7.5III(n)((f)) star {\xi} Persei in November 2011. This star is well known from previous work to show prominent DACs (Discrete Absorption Components) on time-scales of about 2 d from UV spectroscopy and NRP (Non Radial Pulsation) with one (l = 3) p-mode oscillation with a period of 3.5 h from optical spectroscopy. Our MOST-orbit (101.4 min) binned photometry fails to reveal any periodic light variations above the 0.1 mmag 3-sigma noise level for periods of hours, while several prominent Fourier peaks emerge at the 1 mmag level in the two-day period range. These longer-period variations are unlikely due to pulsations, including gravity modes. From our simulations based upon a simple spot model, we deduce that we are seeing the photometric modulation of several co-rotating bright spots on the stellar surface. In our model, the starting times (random) and lifetimes (up to several rotations) vary from one spot to another yet all spots rotate at the same period of 4.18 d, the best-estimated rotation period of the star. This is the first convincing reported case of co-rotating bright spots on an O star, with important implications for drivers of the DACs (resulting from CIRs - Corotating Interaction Regions) with possible bright-spot generation via a breakout at the surface of a global magnetic field generated by a subsurface convection zone.Comment: 9 pages, 4 figures, 2 tables, MNRAS in pres

Additive-Free Assemblies of Ramified Single-Walled Carbon Nanotubes

International audienceCarbon nanotubes (CNTs) are difficult to process, and their assembly in macroscopic materials that allow us to benefit from the exceptional properties of the nanotubes is of crucial interest for applications. The developed CNT processing procedures usually involve additives that remain in the final product and are known to diminish the properties of the CNT-based material. Here, we propose a multistep approach to process single-walled carbon nanotubes (SWNTs) and obtain macroscopic additive-free SWNT materials. High-quality dispersion purified SWNTs is first induced in polar solvent due to their preceding reduction reaction with an alkali metal. The partial debundling process occurring at this stage leads to ramified SWNTs. They can then be self-assembled by attractive intermolecular forces through a controlled destabilization of the dispersions by a simple oxidation. Swollen gels of SWNTs are formed at an air/solvent interface. After freeze-drying, the additive-free SWNT material shows a hierarchical structure with highly interconnected SWNTs. Thanks to the obtained ramification of the SWNTs, these latter are able to well entangle what guarantees the robustness of the obtained additive-free SWNT material. Moreover, this integrated process offers an increase of the accessible surface compared to that of the raw bundled SWNTs. The obtained assembled SWNTs show an improved adsorption capacity

Graphene modification for preparation of stable nanofluids

International audienceCarbon-based nanomaterials, such as carbon nanotubes or graphene, are recognized to be excellentcandidates for high performance materials. Graphene which is a layer of sp2 hybridized carbon atomswith a thickness of only one atom possesses various magnificent properties that are not shared byother materials [1]. Their excellent intrinsic thermal properties have, in particular, led a stronginterest for heat transfer applications [2]. However, dispersion of such material in water to preparestable nanofluids is highly difficult. And the dispersion issue is pointed out to be the main reason forthe reported disappointing and contradictory results in term of performance of such nanofluids [3].Indeed carbon nanoparticles are usually strongly hydrophobic and tend to separate from the liquidmedium, aggregate and sediment. Graphene being a new material, its efficient and controlled surfacemodification is still challenging. Our paper proposes different ways to chemically modify theproperties of graphenic materials in order to increase their hydrophilic character improving that waytheir dispersion. Chemical reactivity of graphene upon the applied treatments was deeply analyzedbased on the carried out multi-scale characterization of the modified graphene. We will discussgraphene reactivity in comparison with other nanostructured carbon materials. Rheologicalproperties of the prepared graphene dispersions will be presented and discussed regarding thepractical use of such dispersions under flowing conditions for heat transfer applications

CD169+macrophages in lymph node and spleen critically depend on dual RANK and LTbetaR signaling

CD169+ macrophages reside in lymph node (LN) and spleen and play an important role in the immune defense against pathogens. As resident macrophages, they are responsive to environmental cues to shape their tissue-specific identity. We have previously shown that LN CD169+ macrophages require RANKL for formation of their niche and their differentiation. Here, we demonstrate that they are also dependent on direct lymphotoxin beta (LT beta) receptor (R) signaling. In the absence or the reduced expression of either RANK or LT beta R, their differentiation is perturbed, generating myeloid cells expressing SIGN-R1 in LNs. Conditions of combined haploinsufficiencies of RANK and LT beta R revealed that both receptors contribute equally to LN CD169+ macrophage differentiation. In the spleen, the Cd169-directed ablation of either receptor results in a selective loss of marginal metallophilic macrophages (MMMs). Using a RANKL reporter mouse, we identify splenic marginal zone stromal cells as a source of RANKL and demonstrate that it participates in MMM differentiation. The loss of MMMs had no effect on the splenic B cell compartments but compromised viral capture and the expansion of virus-specific CD8+ T cells. Taken together, the data provide evidence that CD169+ macrophage differentiation in LN and spleen requires dual signals from LT beta R and RANK with implications for the immune response

Espaces de vie, espaces enjeux

Promeneurs du dimanche dans la campagne environnante, adolescents qui déambulent dans leur quartier, étudiants qui font la fête sous les fenêtres de riverains exaspérés, habitants expulsés et relogés dans le cadre d'opérations de rénovation urbaine, schémas directeurs visant à orienter l'occupation et le développement d'un territoire : l'espace est autant objet d'appropriation ordinaire que d'inscription dans des politiques publiques variées. Entendant la notion de mobilisation en un sens large, c'est cette diversité de rapports aux espaces et aux lieux que le présent ouvrage cherche à cerner. Comment se construisent les rapports aux espaces du quotidien ? Comment émergent des tensions, voire des conflits ? Comment les pratiques d'un espace sont-elles pensées par les pouvoirs publics lorsqu'ils les aménagent ? Comment les individus se réapproprient-ils ce même espace ? Quels rapports s'établissent entre leurs mobilisations et les régulations opérées par les pouvoirs publics ? Fruit d'une rencontre entre géographes, sociologues et politistes, ce livre s'est aussi ouvert aux architectes et aux urbanistes. Il invite à engager une réflexion interdisciplinaire sur les mobilisations relatives à l'espace et propose des perspectives et des outils pour développer un champ de recherche qui interpelle nombre de disciplines des sciences humaines et sociales