Rotational modulation of the linear polarimetric variability of the cool dwarf TVLM 513−-46546

Aims: We aimed to monitor the optical linear polarimetric signal of the magnetized, rapidly rotating M8.5 dwarf TVLM 513$-$46546. Methods: $R$- and $I$-band linear polarimetry images were collected with the ALFOSC instrument of the 2.56-m Nordic Optical Telescope on two consecutive nights covering about 0.5 and 4 rotation cycles in the $R$ and $I$ filters, respectively. We also obtained simultaneous intensity curves by means of differential photometry. The typical precision of the data is $\pm$0.46\% ($R$), $\pm$0.35\% ($I$) in the linear polarization degree and $\pm$9 mmag ($R$), $\pm$1.6 mmag ($I$) in the differential intensity curves. Results: Strong and variable linear polarization is detected in the $R$ and $I$ filters, with values of maximum polarization ($p^{*}$ = 1.30$\pm$0.35 \%) similar for both bands. The intensity and the polarimetric curves present a sinusoid-like pattern with a periodicity of $\sim$1.98 h, which we ascribe to structures in TVLM 513$-$46's surface synchronized with rotation. We found that the peaks of the intensity and polarimetric curves occur with a phase difference of 0.18$\pm$0.01, and that the maximum of the linear polarization happens nearly half a period (0.59$\pm$0.03) after the radio pulse. We discussed different scenarios to account for the observed properties of the light curves.Comment: Accepted for publication in Astronomy and Astrophysic

Simultaneous optical and near-infrared linear spectropolarimetry of the earthshine

Aims: We aim to extend our current observational understanding of the integrated planet Earth spectropolarimetry from the optical to the near-infrared wavelengths. Major biomarkers like O$_{\rm 2}$ and water vapor are strong flux absorbents in the Earth atmosphere and some linear polarization of the reflected stellar light is expected to occur at these wavelengths. Methods: Simultaneous optical ($0.4-0.9$ $\mu$m) and near-infrared ($0.9-2.3$ $\mu$m) linear spectropolarimetric data of the earthshine were acquired by observing the nightside of the waxing Moon. The data have sufficient spectral resolution (2.51 nm in the optical, and 1.83 and 2.91 nm in the near-infrared) to resolve major molecular species present in the Earth atmosphere. Results: We find the highest values of linear polarization ($\ge 10\%$) at the bluest wavelengths, which agrees with the literature. Linear polarization intensity steadily decreases towards red wavelengths reaching a nearly flat value beyond $\sim$0.8 $\mu$m. In the near-infrared, we measured a polarization degree of $\sim4.5 \%$ for the continuum. We report the detection of molecular features due to O$_{2}$ at $0.760, 1.25 \mu$m and H$_{2}$O at 0.653$-$0.725 $\mu$m, 0.780$-$0.825 $\mu$m, 0.93 and 1.12 $\mu$m in the spectropolarimetric data; most of them show high linear polarimetry degrees above the continuum. In particular, the broad H$_{2}$O 1.12 $\mu$m band displays a polarimetric intensity as high as that of the blue optical. These features may become a powerful tool to characterize Earth-like planets in polarized light.Comment: 4 pages, 3 figures. Accepted for publication as Letter in Astronomy and Astrophysics on 23/01/201

Trigonometric parallaxes of young field L dwarfs

(Abridged) We aim to determine the trigonometric parallaxes and proper motions of a sample of ten field L0-L5 dwarfs with spectroscopic evidence for low-gravity atmospheres. We obtained J and Ks imaging data using 2-4-m class telescopes with a typical cadence of one image per month between 2010 January and 2012 December. We also obtained low resolution optical spectra (R~300, 500-1100 nm) using the 10-m GTCs to assess the presence of lithium absorption in four targets and confirm their young age. Trigonometric parallaxes and proper motions were derived to typical accuracies of 1 mas and +/-10 mas/yr. All ten L dwarfs have large motions, and are located at distances between 9 and 47 pc. They lie above and on the sequence of field dwarfs in the absolute J and K_s magnitude versus spectral type and luminosity versus Teff diagrams, implying ages similar to or smaller than those typical of the field. The detection of atomic lithium in the atmosphere of 2MASS J00452143+1634446 is reported for the first time. Three dwarfs have locations in the HR diagram indicative of old ages and high masses consistent with the observed lithium depletion previously published. We did not find evidence for the presence of astrometric companions with minimum detectable masses typically >=25 Mjup and face-on, circular orbits with periods between 60-90 d and 3 yr around eight targets. The astrometric and spectroscopic data indicate that about 60-70% of the field L-type dwarfs in our sample with evidence for low-gravity atmospheres are indeed young-to-intermediate-age brown dwarfs of the solar neighborhood with expected ages and masses in the intervals 10-500 Myr and 11-45 Mjup. The peaked-shape of the H-band spectra of L dwarfs, a signpost of youth, appears to be present up to ages of 120-500 Myr and intermediate-to-high gravities.Comment: Accepted for publication in A&

De sindicato clandestino a organización: la UGT de Sevilla durante la Transición

Después de su legalización, la UGT de Sevilla celebró su primer Congreso en julio de 1978. Todavía entonces era un sindicato muy limitado, carente de una amplia estructura or-gánica. La Unión Provincial diseñó una estrate-gia de expansión atendiendo cuatro frentes simultáneos: en primer lugar, la adaptación del sindicato al nuevo régimen democrático; en segundo lugar, clarificar sus relaciones con el PSOE en el nuevo contexto; el tercer frente fue la expansión orgánica y militante; y por último, el diseño de las directrices de lo que sería su labor sindical en la capital y la provinciaAfter being legalized, the UGT (Social-ist General Workers Union) in Seville held its first Congress in July 1978. At the time, it re-mained a low-profile labour union lacking a clear organizational structure. The provincial UGT in Seville thus designed an expansion strategy consisting of four elements: adapting the labour union to a new democratic context; clarifying its relations with the Socialist Party (PSOE); expanding the union’s membership and structure in the province; and, finally, establish-ing guidelines for its future activit

Testing the existence of optical linear polarization in young brown dwarfs

Linear polarization can be used as a probe of the existence of atmospheric condensates in ultracool dwarfs. Models predict that the observed linear polarization increases withthe degree of oblateness, which is inversely proportional to the surface gravity. We aimed to test the existence of optical linear polarization in a sample of bright young brown dwarfs, with spectral types between M6 and L2, observable from the Calar Alto Observatory, and cataloged previously as low gravity objects using spectroscopy. Linear polarimetric images were collected in I and R-band using CAFOS at the 2.2 m telescope in Calar Alto Observatory (Spain). The flux ratio method was employed to determine the linear polarization degrees. With a confidence of 3$\sigma$, our data indicate that all targets have a linear polarimetry degree in average below 0.69% in the I-band, and below 1.0% in the R-band, at the time they were observed. We detected significant (i.e. P/$\sigma$ $\le$ 3) linear polarization for the young M6 dwarf 2MASS J04221413+1530525 in the R-band, with a degree of $\mathrm{p^{*}}$ = 0.81 $\pm$ 0.17 %.Comment: Accepted for publication in MNRA