518 research outputs found
La première église cistercienne (XIIe s.) de l'abbaye de Vauclair (Aisne)
No full textCourtois René. La première église cistercienne (XIIe s.) de l'abbaye de Vauclair (Aisne). In: Archéologie médiévale, tome 2, 1972. pp. 103-131
Fingering convection in accreting hydrogen white dwarf
No full textThe accretion of heavy material from debris disk on the surface of hydrogen-rich white dwarfs induces a double diffusivity instability known as the fingering convection. It leads to an efficient extra mixing which brings the accreted material deeper in the star than by considering only mixing in the surface dynamical convection zone, in a time scale much shorter than that of gravitational settling. We performed numerical simulations of a continuous accretion of heavy material having a bulk Earth composition on the two well studied DAZ and ZZ Ceti pulsators GD 133 and G 29-38. We find that the existence of fingering convection implies much larger accretion rates to explain the observed abundances than previous estimates based on the standard mixing length theory and gravitational settling only.Fil: Wachlin, Felipe Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Vauclair, S.. Centre National de la Recherche Scientifique; FranciaFil: Vauclair, G.. Centre National de la Recherche Scientifique; FranciaFil: Althaus, Leandro Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaAn International Conference in Memory of Professor Jean-Paul Zahn's Great Scientific AchievementsParísFranciaInstitut d'Astrophysique de Pari
On the possible existence of a self-regulating hydrodynamical process in slowly rotating stars
No full textThe lithium plateau observed in halo stars has long appeared as a
paradox in the general context of the lithium abundance behavior in stellar outer
layers. First, the plateau is flat, second, the lithium abundance dispersion is
extremely small. This seems in contradiction with the large lithium variations observed
in younger stars. It is also difficult to understand theoretically: as lithium
nuclei are destroyed by nuclear reactions at a relatively low temperature
(≅2.5 million degrees), the occurrence of macroscopic motions in the
stellar outer layers easily lead to lithium depletion at the surface. On the
other hand, if no macroscopic motions occur in the stellar gas, lithium is subject
to microscopic diffusion which, in the case of halo stars, should also lead
to depletion. Several ideas have been proposed to account for the lithium behavior in
halo stars. The most promising possibilities were rotational-induced mixing, which
could reduce lithium in the same way for all the stars (Vauclair [CITE]; Pinsonneault
et al. [CITE] and [CITE]) and mass-loss, which could oppose the
lithium settling (Vauclair & Charbonnel [CITE], [CITE]). In both cases however, the parameters should be tightly adjusted
to prevent any dispersion in the final results.
Vauclair ([CITE]) (Paper I) looked for a physical process
which could occur in slowly rotating stars and explain why the dispersion of the lithium
abundances in the halo stars' plateau is so small. She pointed out
that the -gradient terms which appear in the
computations of the meridional circulation velocity
(e.g. Mestel [CITE]) were
not introduced in previous computations of rotationally-induced mixing. This can lead
to a self-regulating process which reduces the efficiency of the
meridional circulation as well as the microscopic diffusion.
Here we present numerical computations of this process and its influence
on the lithium abundance variations in halo stars.
We show that in slowly rotating stars, under some conditions, lithium can be depleted
by a factor of up to two with a dispersion smaller than 0.1 dex in the
middle part of the lithium plateau. We derive a primordial
lithium abundance of , consistent with the recent determinations of
D/H and 4He/H
Accretion from debris disks onto white dwarfs. Fingering (thermohaline) instability and derived accretion rates
No full textContext. Recent observations of a large number of DA and DB white dwarfs show evidence of debris disks, which are the remnants of old planetary systems. The infrared excess detected with Spitzer and the lines of heavy elements observed in their atmospheres with high-resolution spectroscopy converge on the idea that planetary material accretes onto these stars. Accretion rates have been derived by several authors with the assumption of a steady state between accretion and gravitational settling. The results are unrealistically different for DA and DB white dwarfs. Aims. When heavy matter is accreted onto stars, it induces an inverse μ-gradient that leads to fingering (thermohaline) convection. The aim of this letter is to study the impact of this specific process on the derived accretion rates in white dwarfs and on the difference between DA and DB. Methods. We solve the diffusion equation for the accreted heavy elements with a time-dependent method. The models we use have been obtained both with the IRAP code, which computes static models, and the La Plata code, which computes evolutionary sequences. Computations with pure gravitational settling are compared with computations that include fingering convection. Results. The most important result is that fingering convection has very important effects on DAs but is inefficient in DBs. When only gravitational settling is taken into account, the time-dependent computations lead to a steady state, as postulated by previous authors. When fingering convection is added, this steady state occurs much later. Conclusions. The surprising difference found in the past for the accretion rates derived for DA and DB white dwarfs disappears. The derived accretion rates for DAs are increased when fingering convection is taken into account, whereas those for DBs are not modified. More precise and developed results will be given in a forthcoming paperFil: Deal, M.. Université de Toulouse; FranciaFil: Deheuvels, S.. Université de Toulouse; FranciaFil: Vauclair, G.. Université de Toulouse; FranciaFil: Vauclair, S.. Université de Toulouse; FranciaFil: Wachlin, Felipe Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Astrofísica de la Plata; Argentina. Universidad Nacional de la Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentin
Supplemental material for Does candidate for plate fixation selection improve the functional outcome after midshaft clavicle fracture? A systematic review of 1348 patients
No full textSupplemental material for Does candidate for plate fixation selection improve the functional outcome after midshaft clavicle fracture? A systematic review of 1348 patients by M Vautrin, G Kaminski, B Barimani, J Elmers, V Philippe, S Cherix, E Thein, O Borens and F Vauclair in Shoulder & Elbow</p
Importance of fingering convection for accreting white dwarfs in the framework of full evolutionary calculations: the case of the hydrogen-rich white dwarfs GD133 and G29-38
No full textContext. A large fraction of white dwarfs show photospheric chemical composition that is polluted by heavy elements accreted from a debris disk. Such debris disks result from the tidal disruption of rocky planetesimals that have survived to whole stellar evolution from the main sequence to the final white dwarf stage. Determining the accretion rate of this material is an important step toward estimating the mass of the planetesimals and understanding the ultimate fate of the planetary systems. Aims. The accretion of heavy material with a mean molecular weight, μ, higher than the mean molecular weight of the white dwarf outer layers, induces a double-diffusive instability producing the fingering convection and an extra-mixing. As a result, the accreted material is diluted deep into the star. We explore the effect of this extra-mixing on the abundance evolution of Mg, O, Ca, Fe and Si in the cases of the two well-studied polluted DAZ white dwarfs: GD 133 and G 29-38. Methods. We performed numerical simulations of the accretion of material that has a chemical composition similar to the bulk Earth composition. We assumed a continuous and uniform accretion and considered a range of accretion rates from 104 g/s to 1010 g/s. Two cases are simulated, one using the standard mixing length theory (MLT) and one including the double-diffusive instability (fingering convection). Results. The double-diffusive instability develops on a very short timescale. The surface abundance rapidly reaches a stationary value while the depth of the zone mixed by the fingering convection increases. In the case of GD 133, the accretion rate needed to reproduce the observed abundances exceeds by more than two orders of magnitude the rate estimated by neglecting the fingering convection. In the case of G 29-38 the needed accretion rate is increased by approximately 1.7 dex. Conclusions. Our numerical simulations of the accretion of heavy elements on the hydrogen-rich white dwarf GD 133 and G 29-38 show that fingering convection is an efficient mechanism to mix the accreted material deeply. We find that when fingering convection is taken into account, accretion rates higher by 1.7 to 2 dex than those inferred from the standard MLT are needed to reproduce the abundances observed in G 29-38 and GD 133.Fil: Wachlin, Felipe Carlos. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Vauclair, G.. Universite de Toulouse; Francia. Centre National de la Recherche Scientifique; FranciaFil: Vauclair, S.. Centre National de la Recherche Scientifique; Francia. Universite de Toulouse;Fil: Althaus, Leandro Gabriel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; Argentin
High-resolution extreme ultraviolet spectroscopy of G191-B2B: structure of the stellar photosphere and the surrounding interstellar medium
No full textWe have continued our detailed analysis of the high-resolution (R= 4000) spectroscopic observation of the DA white dwarf G191-B2B, obtained by the Joint Astrophysical Plasmadynamic Experiment (J-PEX) normal incidence sounding rocket-borne telescope, comparing the observed data with theoretical predictions for both homogeneous and stratified atmosphere structures. We find that the former models give the best agreement over the narrow waveband covered by J-PEX, in conflict with what is expected from previous studies of the lower resolution but broader wavelength coverage Extreme Ultraviolet Explorer spectra. We discuss the possible limitations of the atomic data and our understanding of the stellar atmospheres that might give rise to this inconsistency. In our earlier study, we obtained an unusually high ionization fraction for the ionized He ii present along the line of sight to the star. In the present paper, we obtain a better fit when we assume, as suggested by Space Telescope Imaging Spectrograph results, that this He ii resides in two separate components. When one of these is assigned to the local interstellar cloud, the implied He ionization fraction is consistent with measurements along other lines of sight. However, the resolving power and signal-to-noise available from the instrument configuration used in this first successful J-PEX flight are not sufficient to clearly identify and prove the existence of the two components
Synergy between asteroseismology and exoplanet science: an outlook
No full textSpace-based asteroseismology has been playing an important role in the characterization of exoplanet-host stars and their planetary systems. The future looks even brighter, with space missions such as NASA's TESS and ESA's PLATO ready to take on this legacy. In this contribution, we provide an outlook on the synergy between asteroseismology and exoplanet science, namely, on the prospect of conducting a populational study of giant planets around oscillating evolved stars with the TESS mission
Investigating the effect of depression, stress, and attachment style on leftward cradling bias.
No full textThe majority of women cradle infants to the left of their midline ? this phenomenon is known as leftward cradling bias. The right hemisphere's specialization for emotional processing is believed to explain the bias as it would facilitate emotional communication between the parent and child. Thus, it is of scientific and clinical interest to investigate the disruptors of leftward cradling bias. This study examined three possible disruptors of leftward cradling: stress, depression and attachment style. In total, after exclusion criteria were applied, 468 female students participated. Information was collected over the internet via surveys and using an imaginary cradling task, to facilitate obtaining a large sample. A hierarchical regression model was developed to concurrently examine the effect of depression, stress, and attachment style on leftward cradling bias. The hierarchical regression model was not statistically significant;; however, four points of interest were found in the data. First, depression was a significant predictor of reduced leftward cradling bias. This supports the findings of previous studies that depression disrupts leftward cradling bias (Alzahrani, 2012; Scola, Arciszewski, Measelle, & Vauclair, 2013; Vauclair & Scola, 2009; Weatherill et al., 2004). Second, stress was not a statistically significant predictor of reduced leftward cradling bias. This was surprising as stress has been shown to disrupt leftward cradling bias in the literature (Alzahrani, 2012;; Reissland, Hopkins, Helms, & Williams, 2009; Suter, Huggenberger, Blumenthal, & Schachinger, 2011; Suter, Huggenberger, & Schächinger, 2007). This lack of significance was attributed to the measure of daily stress used, indicating that future research should concentrate on major life stressors. Third, depression and stress were significantly correlated with each other. Thus, future research should take into account the interaction between them. Fourth, attachment style was not a significant predictor of reduced leftward cradling bias. However, it had a statistically significant correlation with depression and stress, which are connected to disrupted leftward cradling bias. Thus, the role between depression, stress, attachment style should be further explored
Asteroseismology of the planet-hosting star mu Arae. II. Seismic analysis
No full text16 pages, 8 figures, accepted in A&AAs most exoplanets host stars, HD 160691 (alias mu Ara) presents a metallicity excess in its spectrum compared to stars without detected planets. This excess may be primordial, in which case the star would be completely overmetallic, or it may be due to accretion in the early phases of planetary formation, in which case it would be overmetallic only in its outer layers. As discussed in a previous paper (Bazot and Vauclair 2004), seismology can help choosing between the two scenarios. This star was observed during eight nights with the spectrograph HARPS at La Silla Observatory. Forty three p-modes have been identified (Bouchy et al. 2005). In the present paper, we discuss the modelisation of this star. We computed stellar models iterated to present the same observable parameters (luminosity, effective temperature, outer chemical composition) while the internal structure was different according to the two extreme assumptions : original overmetallicity or accretion. We show that in any case the seismic constraints lead to models in complete agreement with the external parameters deduced from spectroscopy and from the Hipparcos parallax (L and Teff). We discuss the tests which may lead to a choice between the two typical scenarios. We show that the ``small separation'' seem to give a better fit for the accretion case than for the overmetallic case, but in spite of the very good data the uncertainties are still too large to conclude. We discuss the observations which would be needed to go further and solve this question
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