Galactic R Coronae Borealis Stars: The C-2 Swan Bands, The Carbon Problem, And The C-12/C-13 Ratio

Observed spectra of R Coronae Borealis (RCB) and hydrogen-deficient carbon (HdC) stars are analyzed by synthesizing the C-2 Swan bands (1, 0), (0, 0), and (0, 1) using our detailed line list and the Uppsala model atmospheres. The (0, 1) and (0, 0) C-2 bands are used to derive the C-12 abundance, and the (1, 0) (CC)-C-12-C-13 band to determine the C-12/C-13 ratios. The carbon abundance derived from the C-2 Swan bands is about the same for the adopted models constructed with different carbon abundances over the range 8.5 (C/He = 0.1%) to 10.5 (C/He = 10%). Carbon abundances derived from C I lines are about a factor of four lower than the carbon abundance of the adopted model atmosphere over the same C/He interval, as reported by Asplund et al., who dubbed the mismatch between adopted and derived C abundance as the "carbon problem." In principle, the carbon abundances obtained from C-2 Swan bands and that assumed for the model atmosphere can be equated for a particular choice of C/He that varies from star to star. Then, the carbon problem for C-2 bands is eliminated. However, such C/He ratios are in general less than those of the extreme helium stars, the seemingly natural relatives to the RCB and HdC stars. A more likely solution to the C-2 carbon problem may lie in a modification of the model atmosphere's temperature structure. The derived carbon abundances and the C-12/C-13 ratios are discussed in light of the double degenerate and the final flash scenarios.Robert A. Welch Foundation of Houston, TX F-634McDonald Observator

Effect of mantle and ocean tides on the Earth's rotation rate

Aims: We aim to compute the rate of increase of the length of day (LOD) due to the axial component of the torque produced by the tide generating potential acting on the tidal redistribution of matter in the oceans and the solid Earth. Methods: We use an extension of the formalism applied to precession-nutation in a previous work to the problem of length of day variations of an inelastic Earth with a fluid core and oceans. Expressions for the second order axial torque produced by the tesseral and sectorial tide-generating potentials on the tidal increments to the Earth's inertia tensor are derived and used in the axial component of the Euler-Liouville equations to arrive at the rate of increase of the LOD. Results: The increase in the LOD, produced by the same dissipative mechanisms as in the theoretical work on which the IAU 2000 nutation model is based and in our recent computation of second order effects, is found to be at a rate of 2.35 ms/cy due to the ocean tides, and 0.15 ms/cy due to solid Earth tides, in reasonable agreement with estimates made by other methods

Second order torque on the tidal redistribution and the Earth's rotation

This study presents a complete treatment of the second order torques on the Earth due to the action of each of the three parts of the degree 2 potential (V20: zonal; V21: tesseral; and V22: sectorial) on the deformations produced by the other parts, and the consequent effects on nutation. The work of Mathews et al. (2002, J. Geophys. Res., 107, B4) contained a treatment of the action of the tesseral potential on tidal deformations, taking into account the presence of the fluid core, and also of the contributions from mantle anelasticity and ocean tides to the deformations. We extend that work to include the actions of the zonal and sectorial potentials too. Our computations show that an almost complete cancellation takes place between reciprocal contributions; the largest net effect reaches -35 µas on the in-phase 18.6-yr nutation in longitude. The total effect found on the precession is 0.1 mas/cy in longitude and in obliquity. The cancellations would have been complete but for the fact that (i) the values of the compliances (deformability parameters) are not the same for deformations excited by the three parts of the degree 2 potential even for a nondissipative Earth and (ii) anelasticity and ocean tides make the contributions to the compliances complex (besides being unequal for the three parts) and thus give rise to out-of-phase components in the response to tidal forcing

Evolution of the mass, size, and star formation rate in high-redshift merging galaxies MIRAGE - A new sample of simulations with detailed stellar feedback

We aim at addressing the questions related to galaxy mass assembly through major and minor wet merging processes in the redshift range 1<z<2. A consequent fraction of Milky Way like galaxies are thought to have undergone an unstable clumpy phase at this early stage. Using the adaptive mesh refinement code RAMSES, with a recent physically-motivated implementation of stellar feedback, we build the Merging and Isolated high-Redshift Adaptive mesh refinement Galaxies (MIRAGE) sample. It is composed of 20 mergers and 3 isolated idealized disks simulations with global physical properties in accordance with the 1<z<2 mass complete sample MASSIV. The numerical hydrodynamical resolution reaches 7 parsecs in the smallest Eulerian cells. Our simulations include: star formation, metal line cooling, metallicity advection, and a recent implementation of stellar feedback which encompasses OB-type stars radiative pressure, photo-ionization heating, and supernovae. The initial conditions are set to match the z~2 observations, thanks to a new public code DICE. The numerical resolution allows us to follow the formation and evolution of giant clumps formed in-situ from Jeans instabilities triggered by high initial gas fraction. The star formation history of isolated disks shows stochastic star formation rate, which proceeds from the complex behavior of the giant clumps. Our minor and major gas-rich merger simulations do not trigger starbursts, suggesting a saturation of the star formation in a turbulent and clumpy interstellar medium fed by substantial accretion from the circum-galactic medium. Our simulations are close to the normal regime of the disk-like star formation on a Schmidt-Kennicutt diagram. The mass-size relation and its rate of evolution matches observations, suggesting that the inside-out growth mechanisms of the stellar disk do not necessarily require to be achieved through a cold accretion.Comment: 18 pages, 12 figures. Accepted in A&

Spectral geometry, homogeneous spaces, and differential forms with finite Fourier series

Let G be a compact Lie group acting transitively on Riemannian manifolds M and N. Let p be a G equivariant Riemannian submersion from M to N. We show that a smooth differential form on N has finite Fourier series if and only if the pull back has finite Fourier series on

Impact environnemental des pneumatiques déchiquetés utilisés pour la construction d’ouvrages en remblai

Les pneumatiques usagés sont employés comme matériau de construction pour des ouvrages de génie civil et de géotechnique depuis les années 80. S’agissant de déchets, leur impact sur l’environnement doit être évalué, au regard de l’application visée et de la réglementation en vigueur. Cet article porte sur l’impact environnemental de pneumatiques usagés déchiquetés, lorsqu'ils sont utilisés en mélange avec du sable, pour la construction d’ouvrages en remblai. Des essais de lixiviation, de percolation et au lysimètre ont été réalisés, sur le matériau vierge et sur son résidu après incendie. Les liquides collectés ont été l’objet d’analyses physico-chimiques, considérant deux cents composés, et écotoxicologiques sur une bactérie et un crustacé. Les mesures révèlent un impact très limité en contexte normal. Par contre, les résidus après incendie doivent être envoyés en installation de stockage pour déchets dangereux. / This article deals with the assessment of the environmental impact of shredded scrap tyres mixed with sand to built embankments. Tests of leaching, of percolation and in a lysimeter were performed on the raw material as well as on the tailing resulting from fire. The liquids were analysed looking for 200 compounds and their toxicity on a shellfish and a bacterium was assessed. Measurements confirm the limited consequences on the environment, except in the case of fire, where tailings must be considered as hazardous waste

Quantum limit of photothermal cooling

We study the problem of cooling a mechanical oscillator using the photothermal (bolometric) force. Contrary to previous attempts to model this system, we take into account the noise effects due to the granular nature of photon absorption. This allows us to tackle the cooling problem down to the noise dominated regime and to find reasonable estimates for the lowest achievable phonon occupation in the cantilever