Spectropolarimetric analysis of an active region filament. I. Magnetic and dynamical properties from single component inversions

The determination of the magnetic filed vector in solar filaments is possible by interpreting the Hanle and Zeeman effects in suitable chromospheric spectral lines like those of the He I multiplet at 10830 A. We study the vector magnetic field of an active region filament (NOAA 12087). Spectropolarimetric data of this active region was acquired with the GRIS instrument at the GREGOR telescope and studied simultaneously in the chromosphere with the He I 10830 A multiplet and in the photosphere with the Si I 10827 A line. As it is usual from previous studies, only a single component model is used to infer the magnetic properties of the filament. The results are put into a solar context with the help of the Solar Dynamic Observatory images. Some results clearly point out that a more complex inversion had to be done. Firstly, the Stokes $V$ map of He I does not show any clear signature of the presence of the filament. Secondly, the local azimuth map follows the same pattern than Stokes $V$ as if the polarity of Stokes $V$ were conditioning the inference to very different magnetic field even with similar linear polarization signals. This indication suggests that the Stokes $V$ could be dominated by the below magnetic field coming from the active region, and not, from the filament itself. Those and more evidences will be analyzed in depth and a more complex inversion will be attempted in the second part of this series.Comment: 18 pages, 19 figures, accepted for publication in A&

Bayesian inference of solar and stellar magnetic fields in the weak-field approximation

The weak-field approximation is one of the simplest models that allows us to relate the observed polarization induced by the Zeeman effect with the magnetic field vector present on the plasma of interest. It is usually applied for diagnosing magnetic fields in the solar and stellar atmospheres. A fully Bayesian approach to the inference of magnetic properties in unresolved structures is presented. The analytical expression for the marginal posterior distribution is obtained, from which we can obtain statistically relevant information about the model parameters. The role of a-priori information is discussed and a hierarchical procedure is presented that gives robust results that are almost insensitive to the precise election of the prior. The strength of the formalism is demonstrated through an application to IMaX data. Bayesian methods can optimally exploit data from filter-polarimeters given the scarcity of spectral information as compared with spectro-polarimeters. The effect of noise and how it degrades our ability to extract information from the Stokes profiles is analyzed in detail.Comment: 16 pages, 5 figures, accepted for publication in Ap

Synthesis of periglacial processes in Galicia (Spain)

[Resumen] En esta comunicación, de carácter bibliográfico, los autores incluyen con un breve comentario las publicaciones que hacen referencia a fenómenos periglaciares en Galicia[Abstract] In this note, of bibliographical characteristic, the authors enclose with a brief commentary about the periglacial geomorphology publications in the country of the Galicia

Synthesis of geomorphological processes in the «Galaico-Astur» Bounds

[Resumen] En este trabajo se analizan los distintos procesos geomorfológicos que han intervenido en el modelado de formas en el sector Galaico-Astur. Actualmente, los procesos de índole dinámica (fluviales, marinos, etc.) y los edafogenéticos son los que muestran una mayor incidencia aunque condicionados por la influencia de factores estructurales y de orden climático; buena parte de su eficacia está favorecida, igualmente, por las acciones antrópicas. En lo que respecta a los procesos antiguos, éstos vuelven a revestir su mayor importancia dentro de la tipología dinámica; no obstante, ellos presentan una originalidad más contrastada al haber actuado bajo condiciones climáticas más rigurosas y extremas, y con niveles de base marinos muy diferentes.[Abstract] In this synthesis we analyse the several geomorphological processes that have contributed to model the landforms in the «Galaico-Astur» area. At present, the dynamic nature processes (fluvial, marine, etc.) show a greater incidence though they are conditioned by the inf1uén:~ of climatic and structural factors; most of their efficacy results also increased by antrhopactions. As regards the ancient processes, those of dynamic type are again the more important ones. Furthermore, they appear more stressed because their action was performed on different sea-marine levels and their effects were reinforced by extreme and severe climatic conditions

Estudio geomorfológico de las terrazas fluviales cuaternarias del Valle del Tajo (sector Aranjuez-Toledo)

[Resumen] En esta comunicación se analiza la morfología de los distintos niveles de terraza que pertenecientes al sistema fluvial Tajo-Jarama existen en el tramo comprendido entre Aranjuez y Toledo; igualmente se estudian las características sedimentológicas de los aluviones asociados a estas terrazas, así como otras formaciones detríticas de diferentes épocas geológicas que se advierten en esta zona de la Submeseta Sur. De esta manera se continuan las observaciones realizadas por nosotros hace unos años en las terrazas del Tajo, aguas arriba de Aranjuez y hasta las inmediaciones del embalse de Almoguera, en la provincia de Guadalajara (GONZALEZ MARTIN y ASENSIO AMOR, 1979), así como las investigaciones dedicadas a las deformaciones pseudo-tectónicas que en ocasiones afectan a los conjuntos sedimentarios fluviales (GONZALEZ MARTIN y ASENSIO AMOR, 1980)[Resumé] On étude dans ce travail les caracteres géomorphologiques des différents niveaux de terrasses dans la vallée du Tajo-Jarama (Aranjuez-Toledo). En meme temps, on analyse les caractéristiques sédimentologiques des materiaux associés aux ces formes morphologiques et des autres formations détritiques des ages tertiaires et quaternaires. De cette façon nous poursuivons les observations faites, il y a quelque temps, pour nous meme. D'un cote, le systeme de terrasses dans l'amont de Aranjuez et jusqu'a les environs de Almoguera (GONZALEZ MARTIN y ASENSIO AMOR, 1979). De l'autre, les recherches consacrées aux déformations pseudo-tectoniques visibles quelques fois dans ces ensambles sédimentaires quaternaires (GONZALEZ MARTIN y ASENSIO AMOR, 1980)

Hierarchical analysis of the quiet Sun magnetism

Standard statistical analysis of the magnetic properties of the quiet Sun rely on simple histograms of quantities inferred from maximum-likelihood estimations. Because of the inherent degeneracies, either intrinsic or induced by the noise, this approach is not optimal and can lead to highly biased results. We carry out a meta-analysis of the magnetism of the quiet Sun from Hinode observations using a hierarchical probabilistic method. This model allows us to infer the statistical properties of the magnetic field vector over the observed field-of-view consistently taking into account the uncertainties in each pixel due to noise and degeneracies. Our results point out that the magnetic fields are very weak, below 275 G with 95% credibility, with a slight preference for horizontal fields, although the distribution is not far from a quasi-isotropic distribution.Comment: 9 pages, 4 figures, accepted for publication in A&

A search for magnetic fields on central stars in planetary nebulae

One of the possible mechanisms responsible for the panoply of shapes in planetary nebulae is the presence of magnetic fields that drive the ejection of ionized material during the proto-planetary nebula phase. Therefore, detecting magnetic fields in such objects is of key importance for understanding their dynamics. Still, magnetic fields have not been detected using polarimetry in the central stars of planetary nebulae. Circularly polarized light spectra have been obtained with the Focal Reducer and Low Dispersion Spectrograph at the Very Large Telescope of the European Southern Observatory and the Intermediate dispersion Spectrograph and Imaging System at the William Herschel Telescope. Nineteen planetary nebulae spanning very different morphology and evolutionary stages have been selected. Most of central stars have been observed at different rotation phases to point out evidence of magnetic variability. In this paper, we present the result of two observational campaigns aimed to detect and measure the magnetic field in the central stars of planetary nebulae on the basis of low resolution spectropolarimetry. In the limit of the adopted method, we can state that large scale fields of kG order are not hosted on the central star of planetary nebulae.Comment: Paper accepted to be published in Astronomy and Astrophysics on 20/01/201

PCA detection and denoising of Zeeman signatures in stellar polarised spectra

Our main objective is to develop a denoising strategy to increase the signal to noise ratio of individual spectral lines of stellar spectropolarimetric observations. We use a multivariate statistics technique called Principal Component Analysis. The cross-product matrix of the observations is diagonalized to obtain the eigenvectors in which the original observations can be developed. This basis is such that the first eigenvectors contain the greatest variance. Assuming that the noise is uncorrelated a denoising is possible by reconstructing the data with a truncated basis. We propose a method to identify the number of eigenvectors for an efficient noise filtering. Numerical simulations are used to demonstrate that an important increase of the signal to noise ratio per spectral line is possible using PCA denoising techniques. It can be also applied for detection of magnetic fields in stellar atmospheres. We analyze the relation between PCA and commonly used well-known techniques like line addition and least-squares deconvolution. Moreover, PCA is very robust and easy to compute.Comment: accepted to be published in A&