Polarization of the changing-look quasar J1011+5442

If the disappearance of the broad emission lines observed in changing-look quasars were caused by the obscuration of the quasar core through moving dust clouds in the torus, high linear polarization typical of type 2 quasars would be expected. We measured the polarization of the changing-look quasar J1011+5442 in which the broad emission lines have disappeared between 2003 and 2015. We found a polarization degree compatible with null polarization. This measurement suggests that the observed change of look is not due to a change of obscuration hiding the continuum source and the broad line region, and that the quasar is seen close to the system axis. Our results thus support the idea that the vanishing of the broad emission lines in J1011+5442 is due to an intrinsic dimming of the ionizing continuum source that is most likely caused by a rapid decrease in the rate of accretion onto the supermassive black hole.Comment: Accepted for publication in Astronomy and Astrophysics Letter

DMRG study of the Bond Alternating \textbf{S}=1/2 Heisenberg ladder with Ferro-Antiferromagnetic couplings

We obtain the phase diagram in the parameter space $(J'/J, \gamma)$ and an accurate estimate of the critical line separating the different phases. We show several measuments of the magnetization, dimerization, nearest neighbours correlation, and density of energy in the different zones of the phase diagram, as well as a measurement of the string order parameter proposed as the non vanishing phase order parameter characterizing Haldane phases. All these results will be compared in the limit $J'/J\gg 1$ with the behaviour of the $\textbf{S}=1$ Bond Alternated Heisenberg Chain (BAHC). The analysis of our data supports the existence of a dimer phase separated by a critical line from a Haldane one, which has exactly the same nature as the Haldane phase in the $\textbf{S}=1$ BAHC.Comment: Version 4. 8 pages, 15 figures (12 figures in document

Evaluation of Cinnamon Essential Oil as a Preservative Agent in the Postharvest Stage of Strawberries (Fragaria Sp.)

This study proposes the use of cinnamon as an antimicrobial agent with the presence of cinnamic aldehyde, which has antibacterial and antifungal activity and inhibits the production of mycotoxins. Initially, microorganisms were isolated in damaged post-harvest strawberries, isolating colonies of Botritys sp. as the main causal agent of the deterioration of these fruits. The anti-fungal ability of the cinnamon essential oil (Cinnamomum zeynalicum) was evaluated ‘in vitro’ on the development of the isolated fungus, and ‘in vivo’ on fresh fruit at different storage temperatures, times and concentrations of AE. The results obtained showed that the most effective treatments ‘in vivo’ were 250 and 500 ppm of cinnamon essential oil. On-site analyses showed fruit stability in terms of color, texture, flavor, smell, pH and acidity, especially when there is a concentration of 500 ppm of cinnamon essential oil combined with the storage of the fruit at refrigeration temperature (5ºC), this being the most effective treatment to reduce fungal rot and loss of fruit quality. Keywords: cinnamon essential oil, postharvest, strawberry, antifungal activity, preservative. Resumen Está investigación plantea el uso de la canela como un agente antimicrobiano con la presencia de aldehído cinámico el mismo que posee actividad antibacterial, antifúngica e inhibe la producción de micotoxinas. De manera inicial se asilaron microorganismos en fresa postcosecha deteriorada, aislando colonias de Botritys sp. como el principal agente causal del deterioro de estas frutas. La capacidad antifúngica del aceite esencial de canela (Cinnamomum zeynalicum) fue evaluada ‘in vitro’ sobre el desarrollo del hongo aislado e ‘in vivo’ sobre fruta fresca a diferentes temperaturas de almacenamiento, tiempos y concentraciones de AE. Los resultados obtenidos demostraron que los tratamientos más efectivos ‘in vivo’ fueron 250 y 500 ppm de aceite esencial de canela. Los análisis in situ mostraron estabilidad de los frutos en cuanto a color, textura, sabor, olor, pH y acidez sobre todo cuando se tiene una concentración de 500 ppm de aceite esencial de canela combinado con el almacenamiento de la fruta a temperatura de refrigeración (5ºC) siendo el tratamiento más efectivo para reducir la pudrición fúngica y la pérdida de la calidad de los frutos. Palabras clave: aceite esencial de canela, post cosecha, fresa, actividad antifúngica, conservante

Solar abundance corrections derived through 3D magnetoconvection simulations

We explore the effect of the magnetic field when using realistic three-dimensional convection experiments to determine solar element abundances. By carrying out magnetoconvection simulations with a radiation-hydro code (the Copenhagen stagger code) and through a-posteriori spectral synthesis of three Fe I lines, we obtain evidence that moderate amounts of mean magnetic flux cause a noticeable change in the derived equivalent widths compared with those for a non-magnetic case. The corresponding Fe abundance correction for a mean flux density of 200 G reaches up to ~0.1 dex in magnitude. These results are based on space- and time-averaged line profiles over a time span of 2.5 solar hours in the statistically stationary regime of the convection. The main factors causing the change in equivalent widths, namely the Zeeman broadening and the modification of the temperature stratification, act in different amounts and, for the iron lines considered here, in opposite directions; yet, the resulting $|\Delta\log\epsilon_{\odot}(Fe)|$ coincides within a factor two in all of them, even though the sign of the total abundance correction is different for the visible and infrared lines. We conclude that magnetic effects should be taken into account when discussing precise values of the solar and stellar abundances and that an extended study is warranted.Comment: ApJ accepte

Model selection for spectro-polarimetric inversions

Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios favor models without gradients along the line-of-sight. If the observations shows clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large signal-to-noise ratios favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future.Comment: 16 pages, 2 figures, 8 tables, accepted for publication in Ap

Solar Intranetwork Magnetic Elements: bipolar flux appearance

The current study aims to quantify characteristic features of bipolar flux appearance of solar intranetwork (IN) magnetic elements. To attack such a problem, we use the Narrow-band Filter Imager (NFI) magnetograms from the Solar Optical Telescope (SOT) on board \emph{Hinode}; these data are from quiet and an enhanced network areas. Cluster emergence of mixed polarities and IN ephemeral regions (ERs) are the most conspicuous forms of bipolar flux appearance within the network. Each of the clusters is characterized by a few well-developed ERs that are partially or fully co-aligned in magnetic axis orientation. On average, the sampled IN ERs have total maximum unsigned flux of several 10^{17} Mx, separation of 3-4 arcsec, and a lifetime of 10-15 minutes. The smallest IN ERs have a maximum unsigned flux of several 10^{16} Mx, separations less than 1 arcsec, and lifetimes as short as 5 minutes. Most IN ERs exhibit a rotation of their magnetic axis of more than 10 degrees during flux emergence. Peculiar flux appearance, e.g., bipole shrinkage followed by growth or the reverse, is not unusual. A few examples show repeated shrinkage-growth or growth-shrinkage, like magnetic floats in the dynamic photosphere. The observed bipolar behavior seems to carry rich information on magneto-convection in the sub-photospheric layer.Comment: 26 pages, 14 figure

The stellar spectral features of nearby galaxies in the near infrared: tracers of thermally pulsing asymptotic giant branch stars?

et al.We analyse the stellar absorption features in high signal-to-noise ratio (S/N) near-infrared (NIR) spectra of the nuclear region of 12 nearby galaxies, mostly spirals. The features detected in some or all of the galaxies in this sample are the TiO (0.843 and 0.886 μm), VO (1.048 μm), CN (1.1 and 1.4 μm), H2O (1.4 and 1.9 μm) and CO (1.6 and 2.3 μm) bands. The C2 (1.17 and 1.76 μm) bands are generally weak or absent, although C2 (1.76 μm) may be weakly present in the mean galaxy spectrum. A deep feature near 0.93 μm, likely caused by CN, TiO and/or ZrO, is also detected in all objects. Fitting a combination of stellar spectra to the mean spectrum shows that the absorption features are produced by evolved stars: cool giants and supergiant stars in the early- or thermally pulsing asymptotic giant branch (E-AGB or TP-AGB) phases. The high luminosity of TP-AGB stars, and the appearance of VO and ZrO features in the data, suggest that TP-AGB stars dominate these spectral features. However, a contribution from other evolved stars is also likely. Comparison with evolutionary population synthesis models shows that models based on empirical libraries that predict relatively strong NIR features provide a more accurate description of the data. However, none of the models tested accurately reproduces all of the features observed in the spectra. To do so, the models will need to not only improve the treatment of TP-AGB stars, but also include good quality spectra of red giant and E-AGB stars. The uninterrupted wavelength coverage, high S/N and quantity of features we present here will provide a benchmark for the next generation of models aiming to explain and predict the NIR properties of galaxies.The Brazilian authors thank CNPq and FAPERGS support. LCH acknowledges support by the Chinese Academy of Science through grant no. XDB09030102 (Emergence of Cosmological Structures) from the Strategic Priority Research Program and by the National Natural Science Foundation of China through grant No. 11473002. CRA is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934).Peer Reviewe

Clues from Spitzer/IRS spectra on the Compton thickness and the existence of the dusty torus

[Context]: Most of the optically classified low-ionisation, narrow emission-line regions (LINERs) nuclei host an active galactic nucleus (AGN). However, how they fit into the unified model (UM) of AGN is still an open question. [Aims]: The aims of this work are to study at mid-infrared (mid-IR) (1) the Compton-thick nature of LINERs (i.e. hydrogen column densities of NH> 1.5 × 1024 cm-2) and (2) the disappearance of the dusty torus in LINERs predicted from theoretical arguments. [Methods]: We have compiled all the available low spectral-resolution, mid-IR spectra of LINERs from the InfraRed Spectrograph (IRS) onboard Spitzer. The sample contains 40 LINERs. We have complemented the LINER sample with Spitzer/IRS spectra of PGQSOs, Type-1 Seyferts (S1s), Type-2 Seyferts (S2s), and StarBurst (SB) nuclei. We studied the AGN compared to the starburst content in our sample using different indicators: the equivalent width of the polycyclic aromatic hydrocarbon at 6.2 μm, the strength of the silicate feature at 9.7 μm, and the steepness of the mid-IR spectra. We classified the spectra as SB-dominated and AGN-dominated, according to these diagnostics and compared the average mid-IR spectra of the various classes. Moreover, we studied the correlation between the 12 μm luminosity, νLν(12 μm), and the 2−10 keV energy band X-ray luminosity, LX(2−10 keV). [Results]: In 25 out of the 40 LINERs (i.e. 62.5%), the mid-IR spectra are not SB-dominated, similar to the comparison S2 sample (67.7%). The average spectra of both SB-dominated LINERs and S2s are very similar to the average spectrum of the SB class. The average spectrum of AGN-dominated LINERs is different from the average spectra of the other optical classes, showing a rather flat spectrum at 6-28 μm. We find that the average spectrum of AGN-dominated LINERs with X-ray luminosities LX(2−10 keV) > 1041 erg/s is similar to the average mid-IR spectrum of AGN-dominated S2s. However, faint LINERs (i.e. LX(2−10 keV) < 1041 erg/s) show flat spectra different from any of the other optical classes. The correlation between νLν(12 μm) and LX(2−10 keV) for AGN nicely extends towards low luminosities only if SB-dominated LINERs are excluded and if the 2−10 keV band X-ray luminosity is corrected in Compton-thick LINER candidates. [Conclusions]: We find that LINERs proposed as Compton-thick candidates at X-ray wavelengths may be confirmed according to the X-ray to mid-IR luminosity relation. We show evidence that the dusty-torus disappear when their bolometric luminosity is below Lbol ≃ 1042 erg/s. We suggest that the dominant emission at mid-IR of faint LINERs might be a combination of an elliptical galaxy host (characterised by the lack of gas), a starburst, a jet, and/or ADAF emission. Alternatively, the mid-IR emission of some of these faint LINERs could be a combination of elliptical galaxy plus carbon-rich planetary nebulae. To reconcile the Compton-thick nature of a large number of LINERs without dusty-torus signatures, we suggest that the material producing the Compton-thick X-ray obscuration is free of dust.This research has been supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under the grant (project refs. AYA2013-42227-P, AYA 2012-39168-C03-01, and AYA 2010-15169) and by La Junta de Andalucia (TIC 114). AAH acknowledges support from grant AYA2012-31447. D.D. acknowledges support from grant 107313 from PAPIIT, UNAM. C.R.A. is supported by a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme (PIEF-GA-2012-327934).Peer Reviewe