Updated Toulouse solar models including the diffusion-circulation coupling and the effect of μ-gradients

New solar models are presented, which have been computed with the most recent physical inputs (nuclear reaction rates, equation of state, opacities, microscopic diffusion). Rotation-induced mixing has been introduced in a way which includes the feed-back effect of the μ-gradient induced by helium settling. A parametrization of the tachocline region below the convective zone has also been added in the computations. The sound velocities have been computed in the models and compared to the seismic Sun. Our best model is described in some detail. Besides the new physical inputs, the most important improvement concerns the computations of μ-gradients during the solar evolution and their influence in slowing down rotation-induced mixing. This process can explain why lithium is depleted in the present Sun while beryllium is not, and meanwhile why ³He has not increased at the solar surface for at least 3 Gyrs.     

The Origin of Jets from Young Stars: Steady State Disk Wind Models Confronted to Observations

We discuss in this contribution constraints on the origin of mass-loss from young stars brought by recent observations at high angular resolution (0.1″ = 14 AU) of the inner regions of winds from T Tauri stars. Jet widths and collimation scales, the large extent of the velocity profile as well as the detection of rotation signatures agree with predictions from extended (R _e ≥ 1 AU) magneto-centrifugal disk wind ejection models. Detected poloidal and toroidal velocities imply large ejection efficiencies (ξ ? 0.05, λ ? 10), suggesting that thermal gradients (originating in an accretion heated disk corona for example) play an important role in accelerating the flow.     

New pyrolytic and spectroscopic data on Orgueil and Murchison insoluble organic matter: A different origin than soluble?

Pyrolysis with and without tetramethylammonium hydroxide (TMAH), vacuum pyrolysis, and solid state ¹⁵N nuclear magnetic resonance (NMR) were used to examine the macromolecular insoluble organic matter (IOM) from the Orgueil and Murchison meteorites. Conventional pyrolysis reveals a set of poorly functionalized aromatic compounds, ranging from one to four rings and with random methyl substitutions. These compounds are in agreement with spectroscopic and pyrolytic results previously reported. For the first time, TMAH thermochemolysis was used to study extraterrestrial material. The detection of aromatics bearing methyl esters and methoxy groups reveals the occurrence of ester and ether bridges between aromatic units in the macromolecular network.No nitrogen-containing compounds were detected with TMAH thermochemolysis, although they are a common feature in terrestrial samples. Along with vacuum pyrolysis results, thermochemolysis shows that nitrogen is probably sequestered in condensed structures like heterocyclic aromatic rings, unlike oxygen, which is mainly located within linkages between aromatic units. This is confirmed by solid state ¹⁵N NMR performed on IOM from Orgueil, showing that nitrogen is present in pyrrole, indole, and carbazole moieties.These data show that amino acids are neither derived from the hydrolysis of IOM nor from a common precursor. In order to reconcile the literature isotopic data and the present molecular results, it is proposed that aldehydes and ketones (1) originated during irradiation of ice in space and (2) were then mobilized during the planetesimal hydrothermalism, yielding the formation of amino acids. If correct, prebiotic molecules are the products of the subsurface chemistry of planetesimals and are thus undetectable through astronomical probes.     

A spatial analysis of structural controls on Karst groundwater geochemistry at a regional scale

The coupled spatial investigation of the geometrical and geochemical properties of a chalk karstic aquifer provides information on the degree to which geologic structure controls aquifer functioning and groundwater quality. Major ion concentrations in the chalk aquifer of the Haute-Normandie region (France) were measured at a high spatial resolution (more than 100 sampling sites over a 6000 km² area) and mapped. The first observation is a continuity of the geochemical properties, in spite of the karstic properties of the aquifer principal components analysis of geochemical maps revealed two types of spatial distributions: ions with an autochthonous origin (Ca²⁺, HCO₃), and ions with a principally allochthonous origin (Cl⁻, Na⁺, , ). Mg²⁺ was categorised as both autochthonous (chalk dissolution) and allochthonous (brought in by infiltration of Tertiary deposits). To better understand the spatial distribution of the geochemistry, the aquifer geochemistry was compared to the physical properties of the aquifer, in particular aquifer thickness (representing aquifer geometry) and piezometric level (representing aquifer flow). Use of spatial correlation between the geochemical and the geometrical properties provided insight regarding the directional structure of the data and give evidence of directional relations between geochemical and geometrical properties. The degree of mineralisation (principally composed of Ca²⁺ and ions) increased along the direction of flow, corresponding to an increase in chalk dissolution rate along the flowpath. The steepest mineralisation gradients were related to an increase in the Mg/Ca ratio, evidence of longer residence times and corresponding to zones where aquifer flow capacity is limited because of a decrease of the thickness of the flow section (anticlines or faults). These results highlight the dominant role played by the geometry and the structural context in controlling aquifer geochemistry.     

Radar experiments in isotropic and anisotropic geological formations (granite and schists)1

In order to understand various aspects of radar wave propagation, a survey of electromagnetic wave behaviour relative to the geological characteristics of the formations prospected was undertaken. The sites chosen for the tests were a granite quarry and an underground schist working. By investigating an electrically resistive isotropic site and a conductive anisotropic site, it was demonstrated that non-conventional use of a radar system (antennae raised, various orientations of the transmitter/receiver, etc.) could improve data quality, and could allow information other than reflector depth to be collected (volume scattering intensity, isotropy, etc.). By studying wave propagation velocities, we underlined the difficulties encountered in establishing a velocity versus depth law, despite recourse to seismic data processing, such as NMO corrections. The results of field experiments, complemented by laboratory measurements of dielectric permittivities, clearly showed anisotropy effects: in the case of a path that is perpendicular to the schistosity plane, an electromagnetic wave propagates more slowly and is more attenuated than a wave parallel to the schistosity plane.     

Complete determination of the magnetic field vector and of the electron density in 14 prominences from linear polarizaton measurements in the HeI D3 and Hα lines

The present paper is devoted to the interpretation of linear polarization data obtained in 14 quiescent prominences with the Pic-du-Midi coronagraph-polarimeter by J. L. Leroy, in the two lines Hei D₃ andH quasi-simultaneously. The linear polarization of the lines is due to scattering of the anisotropic photospheric radiation, modified by the Hanle effect due to the local magnetic field. The interpretation of the polarization data in the two lines is able to provide the 3 components of the magnetic field vector, and one extra parameter, namely the electron density, because the linear polarization of H is also sensitive to the depolarizing effect of collisions with the electrons and protons of the medium. Moreover, by using two lines with different optical thicknesses, namely Hei D₃, which is optically thin, and H, which is optically thick ( = 1), it is possible to solve the fundamental ambiguity, each line providing two field vector solutions that are symmetrical in direction with respect to the line of sight in the case of the optically thin line, and which have a different symmetry in the case of the optically thick line.It is then possible to determine without ambiguity the polarity of the prominence magnetic field with respect to that of the photospheric field: 12 prominences are found to be Inverse polarity prominences, whereas 2 prominences are found to be Normal polarity prominences. It must be noticed that in 12 of the 14 cases, the line-of-sight component of the magnetic field vector has a Normal polarity (to the extent that the notion of polarity of a vector component is meaningful; no polarity can be derived in the 2 remaining cases); this may explain the controversy between the results obtained with methods based on the Hanle effect with results obtained through the Zeeman effect. A dip of the magnetic field lines across the prominence has been assumed, to which the optically thick H line is sensitive, and the optically thin Hei D₃ line is insensitive.For the Inverse prominences, the average field strength is 7.5±1.2 G, the average angle,, between the field vector and the prominence long axis is 36° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 29° ± 20°, and the average electron density is 2.1 × 10¹⁰ ± 0.7 × 10¹⁰ cm^–3. For the Normal prominences, the average field strength is 13.2±2.0 G, the average angle,, between the field vector and the prominence long axis is 53° ± 15°, the average angle, , between the outgoing field lines and the solar surface at the prominence boundary is 0° ± 20° (horizontal field), and the average electron density is 8.7 × 10⁹ ± 3.0 × 10⁹ cm^–3.     

Assessment of the ecological status of Mediterranean French coastal waters as required by the Water Framework Directive using the Posidonia oceanica Rapid Easy Index: PREI

This paper describes the PREI (Posidonia oceanica Rapid Easy Index), a method used to assess the ecological status of seawater along Mediterranean French coasts. The PREI was drawn up according to the requirements of the Water Framework Directive (WFD 2000/60/EC) and was tested on 24 and 18 stations in PACA (Provence-Alpes-Côtes d’Azur) and Corsica, respectively. The PREI is based on five metrics: shoot density, shoot leaf surface area, E/L ratio (epiphytic biomass/leaf biomass), depth of lower limit, and type of this lower limit. The 42 studied stations were classified in the first four levels of status: high, good, moderate and poor. The PREI values ranged between 0.280 and 0.847; this classification is in accordance with our field knowledge and with our knowledge of the literature. The PREI was validated regarding human pressure levels (r² = 0.74). (http://eurex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2000:327:0001:0072:EN:PDF).