On the hydrogen neutral outflowing disks of B[e] supergiants

(abridged) B[e] supergiants are known to possess geometrically thick dusty disks. Disk-forming wind models have, however, been found to be insufficient in reproducing the observed dust emission. This problem arises due to the severe assumption that, as for classical Be stars, the near-infrared excess emission originates in the disk. Modeling of the free-free and free-bound emission therefore results in an upper limit for the disk mass loss rate, hampering dust condensation in the disk. We propose a revised scenario for the non-spherical winds of B[e] supergiants: a normal B-type line-driven polar wind and an outflowing disk-forming wind that is neutral in hydrogen at, or very close to the stellar surface. We concentrate on the pole-on seen LMC B[e] supergiant R126 and calculate the line luminosities of the optical [OI] emission lines with an outflowing disk scenario. In addition, we compute the free-free and free-bound emission from a line-driven polar wind and model the spectral energy distribution in the optical and near-infrared. Good fits to the [OI] line luminosities are achieved for an outflowing disk that is neutral in hydrogen right from the stellar surface. Neutral thereby means that hydrogen is ionized by less than 0.1%. Consequently, the free-free and free-bound emission cannot (dominantly) arise from the disk and cannot limit the disk mass loss rate. The hydrogen neutral outflowing disk scenario therefore provides an ideal environment for efficient dust formation. The spectral energy distribution in the optical and near-infrared range can be well fitted with the stellar continuum plus free-free and free-bound emission from the polar line-driven wind. Our modeling further delivers minimum values for \dot{M}(disk) > 2.5d-5 M_sun/yr and for the density contrast between equatorial and polar wind of ~10.Comment: 9 pages, 8 figures, accepted for publication in A&

System thermal-hydraulic modelling of the phénix dissymmetric test benchmark

Phénix is a French pool-type sodium-cooled prototype reactor; before the definitive shutdown, occurred in 2009, a final set of experimental tests are carried out in order to increase the knowledge on the operation and the safety aspect of the pool-type liquid metal-cooled reactors. One of the experiments was the Dissymmetric End-of-Life Test which was selected for the validation benchmark activity in the frame of SESAME project. The computer code validation plays a key role in the safety assessment of the innovative nuclear reactors and the Phénix dissymmetric test provides useful experimental data to verify the computer codes capability in the asymmetric thermal-hydraulic behaviour into a pool-type liquid metal-cooled reactor. This paper shows the comparison of the outcomes obtained with six different System Thermal-Hydraulic (STH) codes: RELAP5-3D©, SPECTRA, ATHLET, SAS4A/SASSYS-1, ASTEC-Na and CATHARE. The nodalization scheme of the reactor was individually achieved by the participants; during the development of the thermal-hydraulic model, the pool nodalization methodology had a special attention in order to investigate the capability of the STH codes to reproduce the dissymmetric effects which occur in each loop and into pools, caused by the azimuthal asymmetry of the boundary conditions. The modelling methodology of the participants is discussed and the main results are compared in this paper to obtain useful guide lines for the future modelling of innovative liquid metal pool-type reactors

Neutral material around the B[e] supergiant star LHA 115-S 65: An outflowing disk or a detached Keplerian rotating disk?

B[e] supergiants are surrounded by large amounts of hydrogen neutral material, traced by the emission in the optical [OI] lines. This neutral material is most plausibly located within their dense, cool circumstellar disks, which are formed from the (probably non-spherically symmetric) wind material released by the star. Neither the formation mechanism nor the resulting structure and internal kinematics of these disks (or disk-like outflows) are well known. However, rapid rotation, lifting the material from the equatorial surface region, seems to play a fundamental role. The B[e] supergiant LHA 115-S 65 (S65) in the SMC is one of the two most rapidly rotating B[e] stars known. Its almost edge-on orientation allows a detailed kinematical study of its optically thin forbidden emission lines. With a focus on the [OI] lines, we test the two plausible disk scenarios: the outflowing and the Keplerian rotating disk. Based on high- and low-resolution optical spectra, we investigate the density and temperature structure in those disk regions that are traced by the [OI] emission to constrain the disk sizes and mass fluxes needed to explain the observed [OI] line luminosities. In addition, we compute the emerging line profiles expected for either an outflowing disk or a Keplerian rotating disk, which can directly be compared to the observed profiles. Both disk scenarios deliver reasonably good fits to the line luminosities and profiles of the [OI] lines. Nevertheless, the Keplerian disk model seems to be the more realistic one, because it also agrees with the kinematics derived from the large number of additional lines in the spectrum. As additional support for the presence of a high-density, gaseous disk, the spectrum shows two very intense and clearly double-peaked [CaII] lines. We discuss a possible disk-formation mechanism, and similarities between S65 and the group of LBVs.Comment: 13 pages, 12 figures, accepted for publication in A&

Entanglement as a signature of quantum chaos

We explore the dynamics of entanglement in classically chaotic systems by considering a multiqubit system that behaves collectively as a spin system obeying the dynamics of the quantum kicked top. In the classical limit, the kicked top exhibits both regular and chaotic dynamics depending on the strength of the chaoticity parameter $\kappa$ in the Hamiltonian. We show that the entanglement of the multiqubit system, considered for both bipartite and pairwise entanglement, yields a signature of quantum chaos. Whereas bipartite entanglement is enhanced in the chaotic region, pairwise entanglement is suppressed. Furthermore, we define a time-averaged entangling power and show that this entangling power changes markedly as $\kappa$ moves the system from being predominantly regular to being predominantly chaotic, thus sharply identifying the edge of chaos. When this entangling power is averaged over initial states, it yields a signature of global chaos. The qualitative behavior of this global entangling power is similar to that of the classical Lyapunov exponent.Comment: 8 pages, 8 figure

Control interface concepts for CHARA 6-telescope fringe tracking with CHAMP+MIRC

This is the author accepted manuscript. The final version is available from SPIE via the DOI in this record.Cophasing six telescopes from the CHARA array, the CHARA-Michigan Phasetracker (CHAMP) and Michigan Infrared Combiner (MIRC) are pushing the frontiers of infrared long-baseline interferometric imaging in key scientific areas such as star- and planet-formation. Here we review our concepts and recent improvements on the CHAMP and MIRC control interfaces, which establish the communication to the real-time data recording & fringe tracking code, provide essential performance diagnostics, and assist the observer in the alignment and flux optimization procedure. For fringe detection and tracking with MIRC, we have developed a novel matrix approach, which provides predictions for the fringe positions based on cross-fringe information.This work was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program

Transverse Pressure and Strangeness Dynamics in Relativistic Heavy Ion Reactions

Transverse hadron spectra from proton-proton, proton-nucleus and nucleus-nucleus collisions from 2 AGeV to 21.3 ATeV are investigated within two independent transport approaches (HSD and UrQMD). For central Au+Au (Pb+Pb) collisions at energies above $E_{\rm lab}\sim$ 5 AGeV, the measured $K^{\pm}$ transverse mass spectra have a larger inverse slope parameter than expected from the default calculations. The additional pressure - as suggested by lattice QCD calculations at finite quark chemical potential $\mu_q$ and temperature $T$ - might be generated by strong interactions in the early pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions. This is supported by a non-monotonic energy dependence of $v_2/$ in the present transport model.Comment: Proceedings of Strange Quark Matter 200

The enigmatic B[e]-star Henize 2-90: The non-spherical mass loss history from an analysis of forbidden lines

(abridged) We study the optical spectrum of the exciting B[e] star Hen 2-90 based on new high-resolution observations that cover the innermost 2". Our investigation is splitted in two parts, a qualitative study of the presence of the numerous emission lines and the classification of their line profiles which indicate a circumstellar environment of high complexity, and a quantitative analysis of numerous forbidden lines, e.g. [OI], [OII], [OIII], [SII], [SIII], [ArIII], [ClII], [ClIII] and [NII]. We find a correlation between the different ionization states of the elements and the velocities derived from the line profiles: the highly ionized atoms have the highest outflow velocity while the neutral lines have the lowest outflow velocity. The recent HST image of Hen 2-90 reveals a bipolar, highly ionized region, a neutral disk-like structure and an intermediate region of moderate ionization. It seems that a non-spherical stellar wind model is a good option to explain the ionization and spatial distribution of the circumstellar material. We modelled the forbidden lines under the assumption of a non-spherically symmetric wind based on the HST image. We find that in order to fit the observed line luminosities, the mass flux, surface temperature, and terminal wind velocities need to be latitude dependent, which might be explained in terms of a rapidly rotating central star. A rotation speed of 75-80 % of the critical velocity has been derived. The total mass loss rate of the star was determined to be of order 3 10^{-5} M_sun/yr. Such a wind scenario and the fact that compared to solar abundances C, O, and N seem to be underabundant while S, Ar and Cl have solar abundances, might be explained in terms of a rapidly rotating post-AGB star.Comment: 16 pages, 13 figures, accepted for publication in A&A. Table 4 is included at the end of the paper. This table will only be available in the online version of the paper and will not appear in the printed versio

Exploring 4D Quantum Hall Physics with a 2D Topological Charge Pump

The discovery of topological states of matter has profoundly augmented our understanding of phase transitions in physical systems. Instead of local order parameters, topological phases are described by global topological invariants and are therefore robust against perturbations. A prominent example thereof is the two-dimensional integer quantum Hall effect. It is characterized by the first Chern number which manifests in the quantized Hall response induced by an external electric field. Generalizing the quantum Hall effect to four-dimensional systems leads to the appearance of a novel non-linear Hall response that is quantized as well, but described by a 4D topological invariant - the second Chern number. Here, we report on the first observation of a bulk response with intrinsic 4D topology and the measurement of the associated second Chern number. By implementing a 2D topological charge pump with ultracold bosonic atoms in an angled optical superlattice, we realize a dynamical version of the 4D integer quantum Hall effect. Using a small atom cloud as a local probe, we fully characterize the non-linear response of the system by in-situ imaging and site-resolved band mapping. Our findings pave the way to experimentally probe higher-dimensional quantum Hall systems, where new topological phases with exotic excitations are predicted

Examples of M5-Brane Elliptic Genera

We determine the modified elliptic genus of an M5-brane wrapped on various one modulus Calabi-Yau spaces, using modular invariance together with some known Gopakumar-Vafa invariants of small degrees. As a bonus, we find nontrivial relations among Gopakumar-Vafa invariants of different degrees and genera from modular invariance.Comment: 13 page

Multiplicity of Galactic Cepheids from long-baseline interferometry I. CHARA/MIRC detection of the companion of V1334 Cygni

We aim at determining the masses of Cepheids in binary systems, as well as their geometric distances and the flux contribution of the companions. The combination of interferometry with spectroscopy will offer a unique and independent estimate of the Cepheid masses. Using long-baseline interferometry at visible and infrared wavelengths, it is possible to spatially resolve binary systems containing a Cepheid down to milliarcsecond separations. Based on the resulting visual orbit and radial velocities, we can then derive the fundamental parameters of these systems, particularly the masses of the components and the geometric distance. We therefore performed interferometric observations of the first-overtone mode Cepheid V1334 Cyg with the CHARA/MIRC combiner. We report the first detection of a Cepheid companion using long-baseline interferometry. We detect the signature of a companion orbiting V1334 Cyg at two epochs. We measure a flux ratio between the companion and the Cepheid f = 3.10+/-0.08%, giving an apparent magnitude mH = 8.47+/-0.15mag. The combination of interferometric and spectroscopic data have enabled the unique determination of the orbital elements: P = 1938.6+/-1.2 days, Tp = 2 443 616.1+/-7.3, a = 8.54+/-0.51mas, i = 124.7+/-1.8{\deg}, e = 0.190+/-0.013, {\omega} = 228.7+/-1.6{\deg}, and {\Omega} = 206.3+/-9.4{\deg}. We derive a minimal distance d ~ 691 pc, a minimum mass for both stars of 3.6 Msol, with a spectral type earlier than B5.5V for the companion star. Our measured flux ratio suggests that radial velocity detection of the companion using spectroscopy is within reach, and would provide an orbital parallax and model-free masses.Comment: Published in A&