S5 0716+714 : GeV variability study

The GeV observations by Fermi-LAT give us the opportunity to characterize the high-energy emission (100 MeV - 300 GeV) variability properties of the BL Lac object S5 0716+714. In this study, we performed flux and spectral analysis of more than 3 year long (August 2008 to April 2012) Fermi-LAT data of the source. During this period, the source exhibits two different modes of flux variability with characteristic timescales of ~75 and ~140 days, respectively. We also notice that the flux variations are characterized by a weak spectral hardening. The GeV spectrum of the source shows a clear deviation from a simple power law, and is better explained by a broken power law. Similar to other bright Fermi blazars, the break energy does not vary with the source flux during the different activity states. We discuss several possible scenarios to explain the observed spectral break.Comment: 21 pages, 10 figures, Accepted for publication in Advances in Space Research journa

Sodium abundances in nearby disk stars

We present sodium abundances for a sample of nearby stars. All results have been derived from NLTE statistical equilibrium calculations. The influence of collisional interactions with electrons and hydrogen atoms is evaluated by comparison of the solar spectrum with very precise fits to the Na I line cores. The NLTE effects are more pronounced in metal-poor stars since the statistical equilibrium is dominated by collisions of which at least the electronic component is substantially reduced. The resulting influence on the determination of sodium abundances is in a direction opposite to that found previously for Mg and Al. The NLTE corrections are about -0.1 in thick-disk stars with [Fe/H] about -0.6. Our [Na/Fe] abundance ratios are about solar for thick- and thin-disk stars. The increase in [Na/Fe] as a function of [Fe/H] for metal-rich stars found by Edvardsson et al. (1993) is confirmed. Our results suggest that sodium yields increase with the metallicity, and quite large amounts of sodium may be produced by AGB stars. We find that [Na/Fe]ratios, together with either [Mg/Fe] ratio, kinematic data or stellar evolutionary ages, make possible the individual discrimination between thin- and thick-disk membership.Comment: 11pages, 11 figures. A&A accepte

Physical Conditions and Variability Processes in AGN Jets through Multi-Frequency Linear and Circular Radio Polarization Monitoring

Radio polarimetry is an invaluable tool to investigate the physical conditions and variability processes in active galactic nuclei (AGN) jets. However, detecting their linear and circular polarization properties is a challenging endeavor due to their low levels and possible depolarization effects. We have developed an end-to-end data analysis methodology to recover the polarization properties of unresolved sources with high accuracy. It has been applied to recover the linear and circular polarization of 87 AGNs measured by the F-GAMMA program from July 2010 to January 2015 with a mean cadence of 1.3 months. Their linear polarization was recovered at four frequencies between 2.64 and 10.45 GHz and the circular polarization at 4.85 and 8.35 GHz. The physical conditions required to reproduce the observed polarization properties and the processes which induce their variability were investigated with a full-Stokes radiative transfer code which emulates the synchrotron emission of modeled jets. The model was used to investigate the conditions needed to reproduce the observed polarization behavior for the blazar 3C 454.3, assuming that the observed variability is attributed to evolving internal shocks propagating downstream.Comment: 6 pages, 2 figure

On four numerical schemes for a unipolar degenerate drift-diffusion model

International audienceWe consider a unipolar degenerate drift-diffusion system where the relation between the concentration of the charged species c and the chemical potential h is $h(c) = log(c/(1−c))$. For four different finite volume schemes based on four different formulations of the fluxes of the problem, we discuss stability and existence results. For two of them, we report a convergence proof. Numerical experiments illustrate the behaviour of the different schemes

Galaxy evolution across the optical emission-line diagnostic diagrams?

The discovery of the M-sigma relation, the local galaxy bimodality, and the link between black-hole and host-galaxy properties, have raised the question whether AGN play a role in galaxy evolution. Several theoretical models implement AGN feedback to explain the observed galaxy luminosity function, and possibly the color and morphological transformation of spiral galaxies into passive ellipticals. To understand the importance of AGN feedback, a study of the AGN populations in the radio-optical domain is crucial. A mass sequence linking star-forming galaxies and AGN has been already noted in previous works, and it is now investigated as possible evolutionary sequence. We observed a sample of 119 intermediate-redshift (0.04<z<0.4) SDSS-FIRST radio emitters with the Effelsberg 100-m telescope at 4.85 and 10.45 GHz and obtained spectral indices. We find indications of spectral index flattening in high-metallicity star-forming galaxies, composite galaxies, and Seyferts. This "flattening sequence" along the [NII]-based emission-line diagnostic diagram is consistent with the hardening of galaxy ionizing field, due to nuclear activity. After combining our data with FIRST measurements at 1.4 GHz, we find that the three-point radio spectra of Seyferts and LINERs show substantial differences, attributable to small radio core components and larger (arcsecond sized) jet/lobe components, respectively. A visual inspection of FIRST images seems to confirm this hypothesis. Galaxies along this sequence are hypothesized to be transitioning from the active star-forming galaxies (blue cloud) to the passive elliptical galaxies (red sequence). This supports the suggestion that AGN play a role in shutting down star-formation, and allow the transition from one galaxy class to the other.Comment: 20 pages, 19 figures, accepted for publication in A&

A Unified Theory for the Atmospheres of the Hot and Very Hot Jupiters: Two Classes of Irradiated Atmospheres

We highlight the importance of gaseous TiO and VO opacity on the highly irradiated close-in giant planets. The atmospheres of these planets naturally fall into two classes that are somewhat analogous to the M- and L-type dwarfs. Those that are warm enough to have appreciable opacity due to TiO and VO gases we term the ``pM Class'' planets, and those that are cooler we term ``pL Class'' planets. We calculate model atmospheres for these planets, including pressure-temperature profiles, spectra, and characteristic radiative time constants. We show that pM Class planets have hot stratospheres $\sim$2000 K and appear ``anomalously'' bright in the mid infrared secondary eclipse, as was recently found for planets HD 149026b and HD 209458b. This class of planets absorbs incident flux and emits thermal flux from high in their atmospheres. Consequently, they will have large day/night temperature contrasts and negligible phase shifts between orbital phase and thermal emission light curves, because radiative timescales are much shorter than possible dynamical timescales. The pL Class planets absorb incident flux deeper in the atmosphere where atmospheric dynamics will more readily redistribute absorbed energy. This will lead to cooler day sides, warmer night sides, and larger phase shifts in thermal emission light curves. Around a Sun-like primary this boundary occurs at $\sim$0.04-0.05 AU. The eccentric transiting planets HD 147506b and HD 17156b alternate between the classes. Thermal emission in the optical from pM Class planets is significant red-ward of 400 nm, making these planets attractive targets for optical detection. The difference in the observed day/night contrast between ups Andromeda b (pM Class) and HD 189733b (pL Class) is naturally explained in this scenario. (Abridged.)Comment: Accepted to the Astrophysical Journa

Simultaneous Radio to (Sub-) mm-Monitoring of Variability and Spectral Shape Evolution of potential GLAST Blazars

The Large Area Telescope (LAT) instrument onboard GLAST offers a tremendous opportunity for future blazar studies. In order to fully benefit from its capabilities and to maximize the scientific return from the LAT, it is of great importance to conduct dedicated multi-frequency monitoring campaigns that will result comprehensive observations. Consequently, we initiated an effort to conduct a GLAST-dedicated, quasi-simultaneous, broad-band flux-density (and polarization) monitoring of potential GLAST blazars with the Effelsberg and OVRO radio telescopes (11cm to 7mm wavelength). Here, we present a short overview of these activities which will complement the multi-wavelengths activities of the GLAST/LAT collaboration towards the 'low-energy' radio bands. Further we will give a brief outlook including the extension of this coordinated campaign towards higher frequencies and future scientific aims.Comment: 3 pages, to appear in the Proceedings of the First GLAST Symposium, Stanford University, February 200

Investigation of Frizzled-5 during embryonic neural development in mouse

Journal ArticleCellular and tissue--tissue interactions regulate development of the central nervous system (CNS) and a paramount question is what is the nature of the signals involved in these interactions. The vertebrate eye represents an excellent and challenging CNS model because it contains multiple cell and tissue types that must coordinate their development to form a functional unit. Eye development becomes apparent when the ventral diencephalic neuroepithelium evaginates to form the optic vesicles. The neural retina and retinal pigment epithelium become patterned in the distal and proximal domains of the optic vesicle, respectively. Adjacent extraocular tissues such as the surrounding mesenchyme, the overlying surface ectoderm and the ventral diencephalon regulate these patterning events. Interaction between the distal optic vesicle and surface (lens) ectoderm leads to invagination, formation of the optic cup, and subsequent development of the lens. Several genes have been shown to control optic cup morphogenesis and differentiation of ocular tissues

Fictive Impurity Approach to Dynamical Mean Field Theory: a Strong-Coupling Investigation

Quantum Monte Carlo and semiclassical methods are used to solve two and four site cluster dynamical mean field approximations to the square lattice Hubbard model at half filling and strong coupling. The energy, spin correlation function, phase boundary and electron spectral function are computed and compared to available exact results. The comparision permits a quantitative assessment of the ability of the different methods to capture the effects of intersite spin correlations. Two real space methods and one momentum space representation are investigated. One of the two real space methods is found to be significantly worse: in it, convergence to the correct results is found to be slow and, for the spectral function, nonuniform in frequency, with unphysical midgap states appearing. Analytical arguments are presented showing that the discrepancy arises because the method does not respect the pole structure of the self energy of the insulator. Of the other two methods, the momentum space representation is found to provide the better approximation to the intersite terms in the energy but neither approximation is particularly acccurate and the convergence of the momentum space method is not uniform. A few remarks on numerical methods are made.Comment: Errors in previous versions corrected; CDMFT results adde