The effects of k-dependent self-energy in the electronic structure of correlated materials

It is known from self-energy calculations in the electron gas and sp materials based on the GW approximation that a typical quasiparticle renormalization factor (Z factor) is approximately 0.7-0.8. Band narrowing in electron gas at rs = 4 due to correlation effects, however, is only approximately 10%, significantly smaller than the Z factor would suggest. The band narrowing is determined by the frequency-dependent self-energy, giving the Z factor, and the momentum-dependent or nonlocal self-energy. The results for the electron gas point to a strong cancellation between the effects of frequency- and momentum-dependent self-energy. It is often assumed that for systems with a nar- row band the self-energy is local. In this work we show that even for narrow-band materials, such as SrVO3, the nonlocal self-energy is important.Comment: 7 pages, 6 figure

Observational effects of magnetism in O stars: surface nitrogen abundances

We investigate the surface nitrogen content of the six magnetic O stars known to date as well as of the early B-type star tau Sco. We compare these abundances to predictions of evolutionary models to isolate the effects of magnetic field on the transport of elements in stellar interiors. We conduct a quantitative spectroscopic analysis of the sample stars with state-of-the-art atmosphere models. We rely on high signal-to-noise ratio, high resolution optical spectra obtained with ESPADONS at CFHT and NARVAL at TBL. Atmosphere models and synthetic spectra are computed with the code CMFGEN. Values of N/H together with their uncertainties are determined and compared to predictions of evolutionary models. We find that the magnetic stars can be divided into two groups: one with stars displaying no N enrichment (one object); and one with stars most likely showing extra N enrichment (5 objects). For one star (Theta1 Ori C) no robust conclusion can be drawn due to its young age. The star with no N enrichment is the one with the weakest magnetic field, possibly of dynamo origin. It might be a star having experienced strong magnetic braking under the condition of solid body rotation, but its rotational velocity is still relatively large. The five stars with high N content were probably slow rotators on the zero age main sequence, but they have surface N/H typical of normal O stars, indicating that the presence of a (probably fossil) magnetic field leads to extra enrichment. These stars may have a strong differential rotation inducing shear mixing. Our results should be viewed as a basis on which new theoretical simulations can rely to better understand the effect of magnetism on the evolution of massive stars.Comment: 14 pages, 6 figures. Accepted by A&

Radial dependence of line profile variability in seven O9--B0.5 stars

Massive stars show a variety of spectral variability: presence of discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, radial velocity modulations. Our goal is to study the spectral variability of single OB stars to better understand the relation between photospheric and wind variability. For that, we rely on high spectral resolution, high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We investigate the variability of twelve spectral lines by means of the Temporal Variance Spectrum (TVS). The selected lines probe the radial structure of the atmosphere, from the photosphere to the outer wind. We also perform a spectroscopic analysis with atmosphere models to derive the stellar and wind properties, and to constrain the formation region of the selected lines. We show that variability is observed in the wind lines of all bright giants and supergiants, on a daily timescale. Lines formed in the photosphere are sometimes variable, sometimes not. The dwarf stars do not show any sign of variability. If variability is observed on a daily timescale, it can also (but not always) be observed on hourly timescales, albeit with lower amplitude. There is a very clear correlation between amplitude of the variability and fraction of the line formed in the wind. Strong anti-correlations between the different part of the temporal variance spectrum are observed. Our results indicate that variability is stronger in lines formed in the wind. A link between photospheric and wind variability is not obvious from our study, since wind variability is observed whatever the level of photospheric variability. Different photospheric lines also show different degrees of variability.Comment: 13 pages, 9 figures + appendix. A&A accepted. Figures degraded for arxiv submissio

Properties of WNh stars in the Small Magellanic Cloud: evidence for homogeneous evolution

We derive the physical properties of three WNh stars in the SMC to constrain stellar evolution beyond the main sequence at low metallicity and to investigate the metallicity dependence of the clumping properties of massive stars. We compute atmosphere models to derive the stellar and wind properties of the three WNh targets. A FUV/UV/optical/near-infrared analysis gives access to temperatures, luminosities, mass loss rates, terminal velocities and stellar abundances. All stars still have a large hydrogen mass fraction in their atmosphere, and show clear signs of CNO processing in their surface abundances. One of the targets can be accounted for by normal stellar evolution. It is a star with initial mass around 40-50 Msun in, or close to, the core He burning phase. The other two objects must follow a peculiar evolution, governed by fast rotation. In particular, one object is likely evolving homogeneously due to its position blue-ward of the main sequence and its high H mass fraction. The clumping factor of one star is found to be 0.15+/-0.05. This is comparable to values found for Galactic Wolf-Rayet stars, indicating that within the uncertainties, the clumping factor does not seem to depend on metallicity.Comment: 16 pages. A&A accepte

RBR thermistors array for AOB2

SiPLAB Report 04/06, FCT, University of Algarve,2006.This report describes an electronic circuit board for interfacing the RBR thermistor chain manufactured by Richard Bracker Research, Ontario (Canada), with the Acoustic Oceanographic Buoy (version 2) - AOB2. The interface consists on a set of bridge amplifiers and associated electronics for converting the NTC thermistor signals into temperature related values in the data acquisition CPU control of the AOB2. With this board the temperature measured along the RBR thermistor chain array can be monitored on real time together with the acoustic data via the wireless lan network to which the AOB2 is associated.This work was partially supported by projects RADAR (POCTI/CTA/47719/2002), UAB (POCI/MAR/59008/2004) and NUACE (POSI/CPS/47824/2002) from FCT, Portugal

Acoustic oceanographic buoy (version 2)

SiPLAB Report 05/05, FCT, University of Algarve,2005.This report describes an underwater acoustic data acquisition system, which uses a surface buoy and an underwater array of acoustic and non-acoustic sensors. The surface buoy includes a digital storage unit for the acquired data, a communications system for remote monitoring and data transmission, a digital processing unit for pre-processing of acquired data and a battery power supply. A user manual is included as an installation, setup and maintenance guide for the system and its practical applications. The developed hardware and software is described in detail. Detailed schematics and designs can be found in the final section of this document, these can be used to develop the system, perform maintenance, purchase spare parts or perform any type of modifications.Project RADAR (POCTI/CTA/47719/2002), funded by FCT, Portugal

UAN subsurface telemetry unit. Laboratory tests

SiPLAB Report 07/09, FCT, University of Algarve,2009.This document describes the laboratory tests performed on the Subsurface Telemetry Unit (STU) which was developped for the Underwater Acoustic Network EU-FP7 Project. The tests are separated into mechanical, energy, cable, electronics, acoustic acquisition, STU computer and the base station.This work was supported by project UAN (Underwater Acoustic Network) from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement # 225669

UAN - Fixed sub-surface notes (projects plan)

This document describes requirements for the Fixed Sub-Surface Nodes (FNO) two of which are to be developed for the Underwater Acoustic Network (UAN) project. The fixed nodes serve as sensor platforms which are to be deployed and work autonomously and cable-less on the sea floor. Communication with these nodes is to be acomplished by using underwater acoustic modems. A description of hardware and software is included in this document. Mechanical drawings can be found in the appendix.This work was supported by project UAN Underwater Acoustic Network) from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement # 225669