Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003

We present an analysis of the pulsation behaviour of the Delta Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the framework of STEPHI XII campaign during 2003 June--July. 183 hours of high precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained following a classical scheme of multi-channel photometry. Observations in different filters were also obtained and analyzed. Six and three frequencies have been unambiguously detected above a 99% confidence level in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql respectively. A comparison of observed and theoretical frequencies shows that 7 Aql and 8 Aql may oscillate with p modes of low radial orders, typical among Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial oscillations have to be present in both stars as well. The expected range of excited modes according to a non adiabatic analysis goes from n=1 to n=6 in both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in Astronomical Journa

Preliminary results from the STEPHI2009 campaign on the open cluster NGC 1817

We present preliminary observational results of the multi-site STEPHI campaign on the cluster NGC 1817. The three observatories involved are San Pedro Martir (Mexico), Xing Long (China) and the Observatorio del Teide (Spain) - giving an ideal combination to maximise the duty cycle. The cluster has 12 known delta Scuti stars and at least two detached eclipsing binary systems. This combination of characteristics is ideal for extracting information about global parameters of the targets, which will in turn impose strict constraints on the stellar models. From an initial comparison with stellar models using the known fundamental parameters, and just the observed pulsation frequencies and measured effective temperatures, it appears that a lower value of initial helium mass fraction will most likely explain the observations of these stars.Comment: 4 pages, proceedings from HELAS IV meeting 2010, Lanzarot

Electron Correlation and the c-axis Dispersion of Cu d_z^2: a New Band Structure for High Temperature Superconductors

Previously we showed the major effect of electron correlation in the cuprate superconductors is to lower the energy of the Cu d_x^2-y^2/O p_sigma (x^2-y^2) band with respect to the Cu d_z^2/O' p_z (z^2) band. In our 2D Hubbard model for La_1.85Sr_0.15CuO_4 (LaSCO), the z^2 band is narrow and crosses the standard x^2-y^2 band just below the Fermi level. In this work, we introduce c-axis dispersion to the model and find the z^2 band to have considerable anisotropic 3D character. An additional hole-like surface opens up in the z^2 band at (0,0,2pi/c) which expands with doping. At sufficient doping levels, a symmetry allowed x^2-y^2/z^2 band crossing along the (0,0)-(pi,pi) direction of the Brillouin zone appears at the Fermi level. At this point, Cooper pairs between the two bands (e.g. (k uparrow x^2-y^2/k downarrow z^2)) can form, providing the basis for the Interband Pairing Theory of superconductivity in these materials.Comment: submitted to Phys. Rev. Lett. Related publications: Phys. Rev. B 58, 12303 (1998); Phys. Rev. B 58, 12323 (1998); cond-mat/9903088; cond-mat/990310

Pulsational frequencies of the eclipsing delta-Scuti star HD 172189

The eclipsing delta-Scuti star HD 172189 is a probable member of the open cluster IC 4756 and a promising candidate target for the CoRoT mission. The detection of pulsation modes is the first step in the asteroseismological study of the star. Further, the calculation of the orbital parameters of the binary system allows us to make a dynamical determination of the mass of the star, which works as an important constraint to test and calibrate the asteroseismological models. From a detailed frequency analysis of 210 hours of photometric data of HD 172189 obtained from the STEPHI XIII campaign we have identified six pulsation frequencies with a confidence level of 99% and a seventh with a 65% confidence level in the range between 100-300 uHz. In addiction, three eclipses were observed during the campaign, allowing us to improve the determination of the orbital period of the system.Comment: 6 pages, 7 figure

Superconducting transitions of intrinsic arrays of weakly coupled one-dimensional superconducting chains: the case of the extreme quasi-1D superconductor Tl(2)Mo(6)Se(6)

International audienceTl(2)Mo(6)Se(6) represents a model system for quasi-one-dimensional (quasi-1D) superconductors. We investigate its superconducting transition in detail by means of electrical transport experiments on high-quality single crystalline samples with onset T(c) = 6.8 K. Our measurements indicate a highly complex superconducting transition that occurs in different stages, with a characteristic bump in the resistivity and distinct plateau structures in the supercurrent gap imaged by V-I curves. We interpret these features as fingerprints of the gradual establishment of global phase coherence in an array of weakly coupled parallel 1D superconducting bundles. In this way, we demonstrate that superconducting Tl(2)Mo(6)Se(6) behaves like an intrinsic array of proximity or Josephson junctions, undergoing a complex superconducting phase-ordering transition at 4.5 K that shows many similarities to the Berezinskii-Kosterlitz-Thouless transition

Complex valence-space effective operators for observables: the Gamow-Teller transition

Nuclei in the vicinity of driplines have been receiving a lot of attention in nuclear structure studies. In the nuclei, the continuum coupling is crucial in reproducing weakly-bound and unbound phenomena. To calculate observables of the nuclei as open quantum systems, we have developed valence-space effective operators in the complex-energy Berggren basis using many-body perturbation theory. We focus on the Gamow-Teller $\beta$ decay in the {\it sd} shell. The two- plus three-nucleon force from the chiral effective field theory (EFT), named EM1.8/2.0, has been used. The Gamow shell model which takes the continuum coupling into account can properly reproduce experimental observations of weakly-bound and unbound states. The $\beta$-decay isospin asymmetry between the dripline nucleus $^{22}\rm Si$ and its mirror partner $^{22}\rm O$ is reproduced, in which the $s_{1/2}$ continuum plays a key role. Significant Thomas-Ehrman shift is seen through mirror energy differences between the mirror daughters $^{22}\rm Al$ and $^{22}\rm F$, in which the continuum effect plays an important role

Filling minimality of Finslerian 2-discs

We prove that every Riemannian metric on the 2-disc such that all its geodesics are minimal, is a minimal filling of its boundary (within the class of fillings homeomorphic to the disc). This improves an earlier result of the author by removing the assumption that the boundary is convex. More generally, we prove this result for Finsler metrics with area defined as the two-dimensional Holmes-Thompson volume. This implies a generalization of Pu's isosystolic inequality to Finsler metrics, both for Holmes-Thompson and Busemann definitions of Finsler area.Comment: 16 pages, v2: improved introduction and formattin

Molecular prevalence of Chlamydia and Chlamydia-like bacteria in Tunisian domestic ruminant farms and their influencing risk factors

Chlamydia and Chlamydia-like bacteria are well known to infect several organisms and may cause a wide range of diseases, particularly in ruminants. To gain insight into the prevalence and diversity of these intracellular bacteria, we applied a pan-Chlamydiales real-time PCR to 1,134 veterinary samples taken from 130 Tunisian ruminant herds. The true adjusted animal population-level prevalence was 12.9% in cattle, against 8.7% in sheep. In addition, the true adjusted herd-level prevalence of Chlamydiae was 80% in cattle and 25.5% in sheep. Chlamydiales from three familylevel lineages were detected indicating a high biodiversity of Chlamydiales in ruminant herds. Our results showed that Parachlamydia acanthamoebae could be responsiblefor bovine and ovine chlamydiosis in central-eastern Tunisia. Multivariable logistic regression analysis at the animal population level indicated that strata and digestive disorders variables were the important risk factors of bovine and ovine chlamydiosis. However, origin and age variables were found to be associated withbovine and ovine chlamydiosis, respectively. At the herd level, risk factors for Chlamydia positivity were as follows: abortion and herd size for cattle against breeding system, cleaning frequency, quarantine, use of disinfectant and floor type for sheep. Paying attention to these risk factors will help improvement of control programs against this harmful zoonotic disease