Variability and polarization in the inner jet of 3C395

We present new results on the parsec-scale jet of the quasar 3C395, derived from VLBI polarization sensitive observations made in 1995.91 and 1998.50 at 8.4, 15.4 and 22.2 GHz. The observations show a complex one-sided jet extending up to 20 mas, with a projected magnetic field essentially aligned with the radio jet. The emission is strongly dominated, in total intensity and polarization, by the core and the inner jet region (of ~3 mas length). We have studied the details of this dominant region finding clear structural variations during this ~2.5 years period, in contrast with the apparent quietness of the jet structure inferred from lower resolution VLBI observations. We observe the ejection of a new component from the core and variations in the degree of polarization of the inner jet components. We estimate a high Faraday Rotation Measure close to the core, with a strong decrease along the inner jet.Comment: 7 pages, 4 figures, A&A in pres

Study of star-forming galaxies in SDSS up to redshift 0.4: I. Metallicity evolution

The chemical composition of the gas in galaxies versus cosmic time provides a very important tool for understanding galaxy evolution. Although there are many studies at high redshift, they are rather scarce at lower redshifts. However, low redshift studies can provide important clues about the evolution of galaxies, furnishing the required link between local and high redshift universe. In this work we focus on the metallicity of the gas of star-forming galaxies at low redshift, looking for signs of chemical evolution. To analyze the metallicity contents star-forming galaxies of similar luminosities and masses at different redshifts. With this purpose, we present a study of the metallicity of relatively massive (log(M_star/M_sun)>10.5) star forming galaxies from SDSS--DR5 (Sloan Digital Sky Survey--Data Release 5), using different redshift intervals from 0.04 to 0.4. We used data processed with the STARLIGHT spectral synthesis code, correcting the fluxes for dust extinction, estimating metallicities using the R_23 method, and segregating the samples with respect to the value of the [NII]6583/[OII]3727 line ratio in order to break the R_23 degeneracy selecting the upper branch. We analyze the luminosity and mass-metallicity relations, and the effect of the Sloan fiber diameter looking for possible biases. By dividing our redshift samples in intervals of similar magnitude and comparing them, significant signs of metallicity evolution are found. Metallicity correlates inversely with redshift: from redshift 0 to 0.4 a decrement of ~0.1 dex in 12+log(O/H) is found.Comment: 11 pages, 9 figures, Accepted for publication in A&

OTELO survey: optimal emission-line flux determination with OSIRIS/GTC

Emission-line galaxies are important targets for understanding the chemical evolution of galaxies in the universe. Deep, narrow-band imaging surveys allow to detect and study the flux and the equivalent widths (EW) of the emission line studied. The present work has been developed within the context of the OTELO project, an emission line survey using the Tunable Filters (TF) of OSIRIS, the first generation instrument on the GTC 10.4m telescope located in La Palma, Spain, that will observe through selected atmospheric windows relatively free of sky emission lines. With a total survey area of 0.1 square degrees distributed in different fields, reaching a 5 \sigma depth of 10^-18 erg/cm^2/s and detecting objects of EW < 0.3 A, OTELO will be the deepest emission line survey to date. As part of the OTELO preparatory activities, the objective of this study is to determine the best combination of sampling and full width at half maximum (FWHM) for the OSIRIS tunable filters for deblending H\alpha from [NII] lines by analyzing the flux errors obtained. We simulated the OTELO data by convolving a complete set of synthetic HII galaxies in EW with different widths of the OSIRIS TFs. We estimated relative flux errors of the recovered H\alpha and [NII]6583 lines. We found that, for the red TF, a FWHM of 12 A and a sampling of 5 A is an optimal combination that allow deblending H\alpha from the [NII]6583 line with a flux error lower than 20%. This combination will allow estimating SFRs and metallicities using the H\alpha flux and the N2 method, respectively.Comment: 16 pages, 9 figures. Some authors added. Accepted for publication in PAS

Low frequency noise due to magnetic inhomogeneities in submicron FeCoB/MgO/FeCoB magnetic tunnel junctions

We report on room temperature low frequency noise due to magnetic inhomogeneities/domain walls (MI/DWs) in elliptic submicron FeCoB/MgO/FeCoB magnetic tunnel junctions with an area between 0.0245 and 0.0675{\mu}m2. In the smaller area junctions we found an unexpected random telegraph noise (RTN1), deeply in the parallel state, possibly due to stray field induced MI/DWs in the hard layer. The second noise source (RTN2) is observed in the antiparallel state for the largest junctions. Strong asymmetry of RTN2 and of related resistance steps with current indicate spin torque acting on the MI/DWs in the soft layer at current densities below 5x10^5 A/cm2.Comment: 12 pages, 4 figure

Ca impurity in small mixed 4^4He-3^3He clusters

The structure of small mixed helium clusters doped with one calcium atom has been determined within the diffusion Monte Carlo framework. The results show that the calcium atom sits at the $^4$He-$^3$He interface. This is in agreement with previous studies, both experimental and theoretical, performed for large clusters. A comparison between the results obtained for the largest cluster we have considered for each isotope shows a clear tendency of the Ca atom to reside in a deep dimple at the surface of the cluster for $^4$He clusters, and to become fully solvated for $^3$He clusters. We have calculated the absorption spectrum of Ca around the $4s4p \leftarrow 4s^2$ transition and have found that it is blue-shifted from that of the free-atom transition by an amount that depends on the size and composition of the cluster.Comment: 24 pages, 11 figures. Accepted on Journal of Chemical Physic