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Author name code: martinez-gonzalez
ADS astronomy entries on 2022-09-14
author:"Martinez Gonzalez, Maria J." 

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Title: Mapping the Hidden Magnetic Field of the Quiet Sun
Authors: Trelles Arjona, J. C.; Martínez González, M. J.; Ruiz
   Cobo, B.
2021ApJ...915L..20T    Altcode: 2021arXiv210610546T
  The Sun is the only star where we can resolve the intricate magnetism
  that all convective stars harbor. Yet, more than 99% of its visible
  surface along the solar cycle (the so-called quiet Sun) is filled with
  a tangled, unresolved magnetism. These "hidden" fields are thought
  to store enough magnetic energy to play a role in the heating of
  the Sun's outer atmosphere, but its field strength is still not
  constrained. Previous investigations based on the Hanle effect in
  atomic lines claim a strong magnetization of about 100 G, while
  the same effect in molecules show a factor of 10 weaker fields. The
  discrepancy disappears if the magnetic field strength of the hidden
  field is not homogeneous in the solar surface. In this Letter, we
  prove using magnetohydrodynamical simulations that it is possible
  to infer the average field strength of the hidden quiet-Sun magnetic
  fields using multiline inversions of intensity profiles in the Zeeman
  regime. Using this technique with 15 spectral lines in the 1.5 μm
  spectral range, we reveal that the spatial distribution of the hidden
  field is strongly correlated with convection motions, and that the
  average magnetization is about 46 G. Reconciling our findings with
  the Hanle ones is not obvious and will require future work on both
  sides, since it implies an increase of the field strength with height,
  something that is physically questionable.

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Title: Empirical determination of atomic line parameters of the 1.5
    μm spectral region
Authors: Trelles Arjona, J. C.; Ruiz Cobo, B.; Martínez González,
   M. J.
2021A&A...648A..68T    Altcode: 2021arXiv210304160T
  Context. Both the quality and amount of astrophysical data are steadily
  increasing over time owing to the improvement of telescopes and their
  instruments. This requires corresponding evolution of the techniques
  used for obtaining and analyzing the resulting data. The infrared
  spectral range at 1.56 μm usually observed by the GRegor Infrared
  Spectrograph (GRIS) at the GREGOR solar telescope has a width of
  around 30 Å and includes at least 15 spectral lines. Normally, only a
  handful of spectral lines (five at most) are used in studies using GRIS
  because of the lack of atomic parameters for the others. Including more
  spectral lines may alleviate some of the known ambiguities between
  solar atmospheric parameters. <BR /> Aims: We used high-precision
  spectropolarimetric data for the quiet Sun at 1.56 μm observed with
  GRIS on the GREGOR along with the SIR inversion code in order to obtain
  accurate atomic parameters for 15 spectral lines in this spectral
  range. <BR /> Methods: We used inversion techniques to infer both solar
  atmospheric models and the atomic parameters of spectral lines which,
  under the local thermodynamic equilibrium approximation, reproduce
  spectropolarimetric observations. <BR /> Results: We present accurate
  atomic parameters for 15 spectral lines within the spectral range from
  15 644 to 15 674 Å. This spectral range is commonly used in solar
  studies because it enables the study of the low photosphere. Moreover,
  the infrared spectral lines are better tracers of the magnetic fields
  than the optical ones.

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Title: Photospheric magnetic topology of a north polar region
Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
2020A&A...635A.210P    Altcode: 2020arXiv200304267P
  <BR /> Aims: We aim to characterise the magnetism of a large fraction
  of the north polar region close to a maximum of activity, when the
  polar regions are reversing their dominant polarity. <BR /> Methods:
  We make use of full spectropolarimetric data from the CRisp Imaging
  Spectro-Polarimeter installed at the Swedish Solar Telescope. The data
  consist of a photospheric spectral line, which is used to infer the
  various physical parameters of different quiet Sun regions by means
  of the solution of the radiative transfer equation. We focus our
  analysis on the properties found for the north polar region and their
  comparison to the same analysis applied to data taken at disc centre
  and low-latitude quiet Sun regions for reference. We also analyse
  the spatial distribution of magnetic structures throughout the north
  polar region. <BR /> Results: We find that the physical properties
  of the polar region (line-of-sight velocity, magnetic flux, magnetic
  inclination and magnetic azimuth) are compatible with those found
  for the quiet Sun at disc centre and are similar to the ones found
  at low latitudes close to the limb. Specifically, the polar region
  magnetism presents no specific features. The structures for which
  the transformation from a line-of-sight to a local reference frame
  was possible harbour large magnetic fluxes (&gt;10<SUP>17</SUP> Mx)
  and are in polarity imbalance with a dominant positive polarity, the
  largest ones (&gt;10<SUP>19</SUP> Mx) being located below 73° latitude.

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Title: Science Requirement Document (SRD) for the European Solar
    Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
   Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
   Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
   K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
   Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
   T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
   J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S    Altcode:
  The European Solar Telescope (EST) is a research infrastructure
  for solar physics. It is planned to be an on-axis solar telescope
  with an aperture of 4 m and equipped with an innovative suite of
  spectro-polarimetric and imaging post-focus instrumentation. The EST
  project was initiated and is driven by EAST, the European Association
  for Solar Telescopes. EAST was founded in 2006 as an association
  of 14 European countries. Today, as of December 2019, EAST consists
  of 26 European research institutes from 18 European countries. The
  Preliminary Design Phase of EST was accomplished between 2008 and
  2011. During this phase, in 2010, the first version of the EST Science
  Requirement Document (SRD) was published. After EST became a project
  on the ESFRI roadmap 2016, the preparatory phase started. The goal
  of the preparatory phase is to accomplish a final design for the
  telescope and the legal governance structure of EST. A major milestone
  on this path is to revisit and update the Science Requirement Document
  (SRD). The EST Science Advisory Group (SAG) has been constituted by
  EAST and the Board of the PRE-EST EU project in November 2017 and has
  been charged with the task of providing with a final statement on the
  science requirements for EST. Based on the conceptual design, the SRD
  update takes into account recent technical and scientific developments,
  to ensure that EST provides significant advancement beyond the current
  state-of-the-art. The present update of the EST SRD has been developed
  and discussed during a series of EST SAG meetings. The SRD develops
  the top-level science objectives of EST into individual science
  cases. Identifying critical science requirements is one of its main
  goals. Those requirements will define the capabilities of EST and the
  post-focus instrument suite. The technical requirements for the final
  design of EST will be derived from the SRD.

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Title: High-resolution spectroscopy of Boyajian's star during optical
    dimming events
Authors: Martínez González, M. J.; González-Fernández, C.; Asensio
   Ramos, A.; Socas-Navarro, H.; Westendorp Plaza, C.; Boyajian, T. S.;
   Wright, J. T.; Collier Cameron, A.; González Hernández, J. I.;
   Holgado, G.; Kennedy, G. M.; Masseron, T.; Molinari, E.; Saario, J.;
   Simón-Díaz, S.; Toledo-Padrón, B.
2019MNRAS.486..236M    Altcode: 2019MNRAS.tmp..828M; 2018arXiv181206837M
  Boyajian's star is an apparently normal main-sequence F-type star
  with a very unusual light curve. The dipping activity of the star,
  discovered during the Kepler mission, presents deep, asymmetric,
  and aperiodic events. Here we present high-resolution spectroscopic
  follow-up during some dimming events recorded post-Kepler observations,
  from ground-based telescopes. We analyse data from the HERMES, HARPS-N,
  and FIES spectrographs to characterize the stellar atmosphere and
  to put some constraints on the hypotheses that have appeared in the
  literature concerning the occulting elements. The star's magnetism,
  if existing, is not extreme. The spots on the surface, if present,
  would occupy 0.02 per cent of the area, at most. The chromosphere,
  irrespective of the epoch of observation, is hotter than the values
  expected from radiative equilibrium, meaning that the star has some
  degree of activity. We find no clear evidence of the interstellar
  medium or exocoments being responsible for the dimmings of the light
  curve. However, we detect at 1-2σ level, a decrease of the radial
  velocity of the star during the first dip recorded after the Kepler
  observations. We claim the presence of an optically thick object with
  likely inclined and high impact parameter orbits that produces the
  observed Rossiter-McLaughlin effect.

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Title: Spectropolarimetric analysis of an active region
    filament. II. Evidence of the limitations of a single-component model
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio
   Ramos, A.
2019A&A...625A.129D    Altcode: 2019arXiv190410688D
  <BR /> Aims: Our aim is to demonstrate the limitations of using a
  single-component model to study the magnetic field of an active region
  filament. To do this, we analyzed the polarimetric signals of the He I
  10830 Å multiplet, which were acquired with the infrared spectrograph
  GRIS of the GREGOR telescope (Tenerife, Spain). <BR /> Methods: After
  a first analysis of the general properties of the filament using HAZEL
  under the assumption of a single-component model atmosphere, in this
  second part we focus our attention on the observed Stokes profiles
  and the signatures that cannot be explained with this model. <BR />
  Results: We have found an optically thick filament whose blue and
  red components have the same sign in the linear polarization as an
  indication of radiative transfer effects. Moreover, the circular
  polarization signals inside the filament show strong magnetic field
  gradients. We also show that even a filament with such high absorption
  still shows signatures of the circular polarization that is generated
  by the magnetic field below the filament. The reason is that the
  absorption of the spectral line decays very quickly toward the wings,
  just where the circular polarization has a larger amplitude. In order
  to separate the two contributions, we explore the possibility of a
  two-component model, but the inference becomes impossible to overcome
  because very many solutions are compatible with the observations.

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Title: Spectropolarimetric analysis of an active region
    filament. I. Magnetic and dynamical properties from single component
    inversions
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio
   Ramos, A.
2019A&A...625A.128D    Altcode: 2019arXiv190409593D
  <BR /> Aims: The determination of the magnetic filed vector in solar
  filaments is made possible by interpreting the Hanle and Zeeman
  effects in suitable chromospheric spectral lines like those of the
  He I multiplet at 10 830 Å. We study the vector magnetic field of an
  active region filament (NOAA 12087). <BR /> Methods: 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 10 830 Å multiplet and in the photosphere Si I 10 827
  Å line. As has been done in previous studies, only a single-component
  model was 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. <BR /> Results: Some results clearly point out
  that a more complex inversion had to be performed. First, the Stokes
  V map of He I does not show a clear signature of the presence of the
  filament. Second, the local azimuth map follows the same pattern as
  Stokes V; it appears that polarity of Stokes V is conditioning the
  inference to very different magnetic fields even with similar linear
  polarization signals. This indication suggests that the Stokes V could
  be dominated from below by the magnetic field coming from the active
  region, and not from the filament itself. This evidence, and others,
  will be analyzed in depth and a more complex inversion will be attempted
  in the second part of this series.

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Title: Diagnostic potential of the Ca II 8542 Å line for solar
    filaments
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio Ramos,
   A.; de la Cruz Rodríguez, J.
2019A&A...623A.178D    Altcode: 2019arXiv190206574D
  <BR /> Aims: In this study we explore the diagnostic potential of
  the chromospheric Ca II line at 8542 Å for studying the magnetic and
  dynamic properties of solar filaments. We have acquired high spatial
  resolution spectropolarimetric observations in the Ca II 8542 Å line
  using the CRISP instrument at the Swedish 1 m Solar Telescope. <BR />
  Methods: We used the NICOLE inversion code to infer physical properties
  from observations of a solar filament. We discuss the validity of
  the results due to the assumption of hydrostatic equilibrium. We have
  used observations from other telescopes such as CHROTEL and SDO, in
  order to study large scale dynamics and the long term evolution of the
  filament. <BR /> Results: We show that the Ca II 8542 Å line encodes
  information of the temperature, line-of-sight velocity and magnetic
  field vector from the region where the filament is located. The current
  noise levels only allow us to estimate an upper limit of 260 G for the
  total magnetic field of the filament. Our study also reveals that if we
  consider information from the aforementioned spectral line alone, the
  geometric height, the temperature and the density could be degenerated
  parameters outside the hydrostatic equilibrium approach.

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Title: Magnetic topology of the north solar pole
Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M.
2018A&A...616A..46P    Altcode: 2018arXiv180409075P; 2018A&A...616A..46Y
  The magnetism at the poles is similar to that of the quiet Sun in the
  sense that no active regions are present there. However, the polar quiet
  Sun is somewhat different from that at the activity belt as it has a
  global polarity that is clearly modulated by the solar cycle. We study
  the polar magnetism near an activity maximum when these regions change
  their polarity, from which it is expected that its magnetism should be
  less affected by the global field. To fully characterise the magnetic
  field vector, we use deep full Stokes polarimetric observations of the
  15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as well as
  a quiet region at disc centre to compare their field distributions. In
  order to calibrate the projection effects, we observe an additional
  quiet region at the east limb. We find that the two limb datasets share
  similar magnetic field vector distributions. This means that close to a
  maximum, the poles look like typical limb, quiet-Sun regions. However,
  the magnetic field distributions at the limbs are different from the
  distribution inferred at disc centre. At the limbs, we infer a new
  population of magnetic fields with relatively strong intensities (
  600-800 G), inclined by 30° with respect to the line of sight, and
  with an azimuth aligned with the solar disc radial direction. This
  line-of-sight orientation interpreted as a single magnetic field gives
  rise to non-vertical fields in the local reference frame and aligned
  towards disc centre. This peculiar topology is very unlikely for such
  strong fields according to theoretical considerations. We propose
  that this new population at the limbs is due to the observation of
  unresolved magnetic loops as seen close to the limb. These loops have
  typical granular sizes as measured in the disc centre. At the limbs,
  where the spatial resolution decreases, we observe them spatially
  unresolved, which explains the new population of magnetic fields that is
  inferred. This is the first (indirect) evidence of small-scale magnetic
  loops outside the disc centre and would imply that these small-scale
  structures are ubiquitous on the entire solar surface. This result has
  profound implications for the energetics not only of the photosphere,
  but also of the outer layers since these loops have been reported to
  reach the chromosphere and the low corona.

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Title: Cosmic Magnetic Fields
Authors: Sánchez Almeida, J.; Martínez González, M. J.
2018cmf..book.....S    Altcode:
  Magnetic fields play an important role in many astrophysical
  processes. They are difficult to detect and characterize since
  often their properties have to be inferred through interpreting the
  polarization of the light. Magnetic fields are also challenging to
  model and understand. Magnetized plasmas behave following highly
  non-linear differential equations having no general solution, so that
  every astrophysical problem represents a special case to be studied
  independently. Hence, magnetic fields are often an inconvenient subject
  which is overlooked or simply neglected (the elephant in the room,
  as they are dubbed in poster of the school). Such difficulty burdens
  the research on magnetic fields, which has evolved to become a very
  technical subject, with many small disconnected communities studying
  specific aspects and details. The school tried to amend the situation
  by providing a unifying view of the subject. The students had a chance
  to understand the behavior of magnetic fields in all astrophysical
  contexts, from cosmology to the Sun, and from starbursts to AGNs. The
  school was planed to present a balanced yet complete review of our
  knowledge, with excursions into the unknown to point out present and
  future lines of research. The subject of Cosmic Magnetic Fields was
  split into seven different topics: cosmic magnetic field essentials,
  solar magnetic fields, stellar magnetic fields, the role of magnetic
  fields on AGN feedback, magnetic fields in galaxies, magnetic fields in
  galaxy clusters and at larger scales, and primordial magnetic fields
  and magnetic fields in the early Universe. The corresponding lectures
  were delivered by seven well known and experienced scientists that
  have played key roles in the major advances of the field during the
  last years: F. Cattaneo, P. Judge, O. Kochukhov, R. Keppens, R. Beck,
  K. Dolag, and F. Finelli. Their lectures were recorded and are freely
  available at the IAC website: http://iactalks.iac.es/talks/serie/19.

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Title: The First Post-Kepler Brightness Dips of KIC 8462852
Authors: Boyajian, Tabetha. S.; Alonso, Roi; Ammerman, Alex; Armstrong,
   David; Asensio Ramos, A.; Barkaoui, K.; Beatty, Thomas G.; Benkhaldoun,
   Z.; Benni, Paul; Bentley, Rory O.; Berdyugin, Andrei; Berdyugina,
   Svetlana; Bergeron, Serge; Bieryla, Allyson; Blain, Michaela G.;
   Capetillo Blanco, Alicia; Bodman, Eva H. L.; Boucher, Anne; Bradley,
   Mark; Brincat, Stephen M.; Brink, Thomas G.; Briol, John; Brown,
   David J. A.; Budaj, J.; Burdanov, A.; Cale, B.; Aznar Carbo, Miguel;
   Castillo García, R.; Clark, Wendy J.; Clayton, Geoffrey C.; Clem,
   James L.; Coker, Phillip H.; Cook, Evan M.; Copperwheat, Chris M.;
   Curtis, J. L.; Cutri, R. M.; Cseh, B.; Cynamon, C. H.; Daniels, Alex
   J.; Davenport, James R. A.; Deeg, Hans J.; De Lorenzo, Roberto; de
   Jaeger, Thomas; Desrosiers, Jean-Bruno; Dolan, John; Dowhos, D. J.;
   Dubois, Franky; Durkee, R.; Dvorak, Shawn; Easley, Lynn; Edwards, N.;
   Ellis, Tyler G.; Erdelyi, Emery; Ertel, Steve; Farfán, Rafael. G.;
   Farihi, J.; Filippenko, Alexei V.; Foxell, Emma; Gandolfi, Davide;
   Garcia, Faustino; Giddens, F.; Gillon, M.; González-Carballo,
   Juan-Luis; González-Fernández, C.; González Hernández, J. I.;
   Graham, Keith A.; Greene, Kenton A.; Gregorio, J.; Hallakoun, Na'ama;
   Hanyecz, Ottó; Harp, G. R.; Henry, Gregory W.; Herrero, E.; Hildbold,
   Caleb F.; Hinzel, D.; Holgado, G.; Ignácz, Bernadett; Ilyin, Ilya;
   Ivanov, Valentin D.; Jehin, E.; Jermak, Helen E.; Johnston, Steve;
   Kafka, S.; Kalup, Csilla; Kardasis, Emmanuel; Kaspi, Shai; Kennedy,
   Grant M.; Kiefer, F.; Kielty, C. L.; Kessler, Dennis; Kiiskinen,
   H.; Killestein, T. L.; King, Ronald A.; Kollar, V.; Korhonen, H.;
   Kotnik, C.; Könyves-Tóth, Réka; Kriskovics, Levente; Krumm, Nathan;
   Krushinsky, Vadim; Kundra, E.; Lachapelle, Francois-Rene; LaCourse,
   D.; Lake, P.; Lam, Kristine; Lamb, Gavin P.; Lane, Dave; Lau, Marie
   Wingyee; Lewin, Pablo; Lintott, Chris; Lisse, Carey; Logie, Ludwig;
   Longeard, Nicolas; Lopez Villanueva, M.; Whit Ludington, E.; Mainzer,
   A.; Malo, Lison; Maloney, Chris; Mann, A.; Mantero, A.; Marengo,
   Massimo; Marchant, Jon; Martínez González, M. J.; Masiero, Joseph R.;
   Mauerhan, Jon C.; McCormac, James; McNeely, Aaron; Meng, Huan Y. A.;
   Miller, Mike; Molnar, Lawrence A.; Morales, J. C.; Morris, Brett M.;
   Muterspaugh, Matthew W.; Nespral, David; Nugent, C. R.; Nugent,
   Katherine M.; Odasso, A.; O'Keeffe, Derek; Oksanen, A.; O'Meara,
   John M.; Ordasi, András; Osborn, Hugh; Ott, John J.; Parks, J. R.;
   Rodriguez Perez, Diego; Petriew, Vance; Pickard, R.; Pál, András;
   Plavchan, P.; Pollacco, Don; Pozo Nuñez, F.; Pozuelos, F. J.; Rau,
   Steve; Redfield, Seth; Relles, Howard; Ribas, Ignasi; Richards, Jon;
   Saario, Joonas L. O.; Safron, Emily J.; Sallai, J. Martin; Sárneczky,
   Krisztián; Schaefer, Bradley E.; Schumer, Clea F.; Schwartzendruber,
   Madison; Siegel, Michael H.; Siemion, Andrew P. V.; Simmons, Brooke D.;
   Simon, Joshua D.; Simón-Díaz, S.; Sitko, Michael L.; Socas-Navarro,
   Hector; Sódor, Á.; Starkey, Donn; Steele, Iain A.; Stone, Geoff;
   Strassmeier, Klaus G.; Street, R. A.; Sullivan, Tricia; Suomela, J.;
   Swift, J. J.; Szabó, Gyula M.; Szabó, Róbert; Szakáts, Róbert;
   Szalai, Tamás; Tanner, Angelle M.; Toledo-Padrón, B.; Tordai, Tamás;
   Triaud, Amaury H. M. J.; Turner, Jake D.; Ulowetz, Joseph H.; Urbanik,
   Marian; Vanaverbeke, Siegfried; Vanderburg, Andrew; Vida, Krisztián;
   Vietje, Brad P.; Vinkó, József; von Braun, K.; Waagen, Elizabeth
   O.; Walsh, Dan; Watson, Christopher A.; Weir, R. C.; Wenzel, Klaus;
   Westendorp Plaza, C.; Williamson, Michael W.; Wright, Jason T.; Wyatt,
   M. C.; Zheng, WeiKang; Zsidi, Gabriella
2018ApJ...853L...8B    Altcode: 2018arXiv180100732B
  We present a photometric detection of the first brightness dips of
  the unique variable star KIC 8462852 since the end of the Kepler space
  mission in 2013 May. Our regular photometric surveillance started in
  2015 October, and a sequence of dipping began in 2017 May continuing
  on through the end of 2017, when the star was no longer visible from
  Earth. We distinguish four main 1%-2.5% dips, named “Elsie,”
  “Celeste,” “Skara Brae,” and “Angkor,” which persist
  on timescales from several days to weeks. Our main results so far
  are as follows: (i) there are no apparent changes of the stellar
  spectrum or polarization during the dips and (ii) the multiband
  photometry of the dips shows differential reddening favoring non-gray
  extinction. Therefore, our data are inconsistent with dip models that
  invoke optically thick material, but rather they are in-line with
  predictions for an occulter consisting primarily of ordinary dust,
  where much of the material must be optically thin with a size scale
  ≪1 μm, and may also be consistent with models invoking variations
  intrinsic to the stellar photosphere. Notably, our data do not place
  constraints on the color of the longer-term “secular” dimming,
  which may be caused by independent processes, or probe different
  regimes of a single process.

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Title: Inference of the chromospheric magnetic field orientation in
    the Ca II 8542 Å line fibrils
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Martínez
   González, M. J.; Socas-Navarro, H.
2017A&A...599A.133A    Altcode: 2016arXiv161206088A
  Context. Solar chromospheric fibrils, as observed in the core of
  strong chromospheric spectral lines, extend from photospheric field
  concentrations suggesting that they trace magnetic field lines. These
  images have been historically used as proxies of magnetic fields
  for many purposes. <BR /> Aims: Use statistical analysis to test
  whether the association between fibrils and magnetic field lines is
  justified. <BR /> Methods: We use a Bayesian hierarchical model to
  analyze several tens of thousands of pixels in spectro-polarimetric
  chromospheric images of penumbrae and chromospheric fibrils. We
  compare the alignment between the field azimuth inferred from the
  linear polarization signals through the transverse Zeeman effect and
  the direction of the fibrils in the image. <BR /> Results: We conclude
  that, in the analyzed fields of view, fibrils are often well aligned
  with the magnetic field azimuth. Despite this alignment, the analysis
  also shows that there is a non-negligible dispersion. In penumbral
  filaments, we find a dispersion with a standard deviation of 16°,
  while this dispersion goes up to 34° in less magnetized regions.

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Title: How to infer the Sun's global magnetic field using the
    Hanle effect
Authors: Vieu, T.; Martínez González, M. J.; Pastor Yabar, A.;
   Asensio Ramos, A.
2017MNRAS.465.4414V    Altcode:
  We present a different approach to determine the characteristics
  of the global magnetic field of the Sun based on the study of the
  Hanle signals. The Hanle effect of a stellar dipole produces a surface
  asymmetric pattern of linear polarization that depends on the strength
  and geometry of this global field. Moreover, if the dipole is misaligned
  with respect to the rotation, the Hanle signals are modulated following
  the rotational period. We explore the possibility to retrieve those
  characteristics by comparing the computed theoretical signatures with
  actual observations. We show that this is possible, in the case of the
  Sr I line of the Sun, provided that the polarimetric sensitivity is of
  the order or below 10<SUP>-5</SUP>-10<SUP>-6</SUP>. The inference can
  be done either using the maps of resolved signals, in particular the
  spread of values obtained along different directions on the stellar
  disc, or using the disc-integrated signals.

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Title: Synthetic polarimetric spectra from stellar prominences
Authors: Felipe, T.; Martínez González, M. J.; Asensio Ramos, A.
2017MNRAS.465.1654F    Altcode: 2016arXiv161009282F
  Stellar prominences detected in rapidly rotating stars serve as probes
  of the magnetism in the corona of cool stars. We have synthesized the
  temporal evolution of the Stokes profiles generated in the He I 10
  830 and 5876 Å triplets during the rotation of a prominence around
  a star. The synthesis was performed with the HAZEL code using a cloud
  model in which the prominence is characterized by a slab located at a
  fixed latitude and height. It accounts for the scattering polarization
  and Zeeman and Hanle effects. Several cases with different prominence
  magnetic field strengths and orientations have been analysed. The
  results show an emission feature that drifts across the profile while
  the prominence is out of the stellar disc. When the prominence eclipses
  the star, the intensity profile shows an absorption. The scattering
  induced by the prominence generates linear polarization signals
  in Stokes Q and U profiles, which are modified by the Hanle effect
  when a magnetic field is present. Due to the Zeeman effect, Stokes V
  profiles show a signal with very low amplitude when the magnetic field
  along the line of sight is different from zero. The estimated linear
  polarization signals could potentially be detected with the future
  spectropolarimeter Mid-resolution InfRAreD Astronomical Spectrograph,
  to be attached to Gran Telescopio Canarias telescope.

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Title: Probing deep photospheric layers of the quiet Sun with high
    magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
   M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
   Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
   Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
   Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
   K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
   Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
   Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L    Altcode: 2016arXiv160506324L
  Context. Investigations of the magnetism of the quiet Sun are hindered
  by extremely weak polarization signals in Fraunhofer spectral
  lines. Photon noise, straylight, and the systematically different
  sensitivity of the Zeeman effect to longitudinal and transversal
  magnetic fields result in controversial results in terms of the strength
  and angular distribution of the magnetic field vector. <BR /> Aims:
  The information content of Stokes measurements close to the diffraction
  limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
  spatial straylight and photon noise into account. <BR /> Methods: Highly
  sensitive full Stokes measurements of a quiet-Sun region at disk center
  in the deep photospheric Fe I lines in the 1.56 μm region were obtained
  with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
  statistics and Stokes V asymmetries were analyzed and compared to a
  similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
  diagnostics based directly on the shape and strength of the profiles
  were applied to the GRIS data. We made use of the magnetic line ratio
  technique, which was tested against realistic magneto-hydrodynamic
  simulations (MURaM). <BR /> Results: About 80% of the GRIS spectra
  of a very quiet solar region show polarimetric signals above a 3σ
  level. Area and amplitude asymmetries agree well with small-scale
  surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
  analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
  range with some concentrations of kilo-Gauss fields. <BR /> Conclusions:
  The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
  are so far unique in the combination of high spatial resolution scans
  and high magnetic field sensitivity. Nevertheless, the unavoidable
  effect of spatial straylight and the resulting dilution of the weak
  Stokes profiles means that inversion techniques still bear a high risk
  of misinterpretating the data.

---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
   Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
   Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
   González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
   Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
   Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
   M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
   T.; Volkmer, R.
2016A&A...596A...5M    Altcode: 2018arXiv180410089M
  Context. Over the past 20 yr, the quietest areas of the solar surface
  have revealed a weak but extremely dynamic magnetism occurring
  at small scales (&lt;500 km), which may provide an important
  contribution to the dynamics and energetics of the outer layers of
  the atmosphere. Understanding this magnetism requires the inference
  of physical quantities from high-sensitivity spectro-polarimetric
  data with high spatio-temporal resolution. <BR /> Aims: We present
  high-precision spectro-polarimetric data with high spatial resolution
  (0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
  telescope to shed some light on this complex magnetism. <BR /> Methods:
  We used inversion techniques in two main approaches. First, we assumed
  that the observed profiles can be reproduced with a constant magnetic
  field atmosphere embedded in a field-free medium. Second, we assumed
  that the resolution element has a substructure with either two constant
  magnetic atmospheres or a single magnetic atmosphere with gradients of
  the physical quantities along the optical depth, both coexisting with
  a global stray-light component. <BR /> Results: Half of our observed
  quiet-Sun region is better explained by magnetic substructure within
  the resolution element. However, we cannot distinguish whether this
  substructure comes from gradients of the physical parameters along the
  line of sight or from horizontal gradients (across the surface). In
  these pixels, a model with two magnetic components is preferred, and
  we find two distinct magnetic field populations. The population with
  the larger filling factor has very weak ( 150 G) horizontal fields
  similar to those obtained in previous works. We demonstrate that the
  field vector of this population is not constrained by the observations,
  given the spatial resolution and polarimetric accuracy of our data. The
  topology of the other component with the smaller filling factor is
  constrained by the observations for field strengths above 250 G:
  we infer hG fields with inclinations and azimuth values compatible
  with an isotropic distribution. The filling factors are typically
  below 30%. We also find that the flux of the two polarities is not
  balanced. From the other half of the observed quiet-Sun area 50% are
  two-lobed Stokes V profiles, meaning that 23% of the field of view
  can be adequately explained with a single constant magnetic field
  embedded in a non-magnetic atmosphere. The magnetic field vector and
  filling factor are reliable inferred in only 50% based on the regular
  profiles. Therefore, 12% of the field of view harbour hG fields with
  filling factors typically below 30%. At our present spatial resolution,
  70% of the pixels apparently are non-magnetised.

---------------------------------------------------------
Title: Upholding the unified model for active galactic nuclei:
    VLT/FORS2 spectropolarimetry of Seyfert 2 galaxies
Authors: Ramos Almeida, C.; Martínez González, M. J.; Asensio Ramos,
   A.; Acosta-Pulido, J. A.; Hönig, S. F.; Alonso-Herrero, A.; Tadhunter,
   C. N.; González-Martín, O.
2016MNRAS.461.1387R    Altcode: 2016arXiv160602204R
  The origin of the unification model for active galactic nuclei (AGN)
  was the detection of broad hydrogen recombination lines in the optical
  polarized spectrum of the Seyfert 2 galaxy (Sy2) NGC 1068. Since
  then, a search for the hidden broad-line region (HBLR) of nearby
  Sy2s started, but polarized broad lines have only been detected
  in ∼30-40 per cent of the nearby Sy2s observed to date. Here we
  present new VLT/FORS2 optical spectropolarimetry of a sample of 15
  Sy2s, including Compton-thin and Compton-thick sources. The sample
  includes six galaxies without previously published spectropolarimetry,
  some of them normally treated as non-hidden BLR (NHBLR) objects in
  the literature, four classified as NHBLR, and five as HBLR based on
  previous data. We report ≥4σ detections of a HBLR in 11 of these
  galaxies (73 per cent of the sample) and a tentative detection in NGC
  5793, which is Compton-thick according to the analysis of X-ray data
  performed here. Our results confirm that at least some NHBLRs are
  misclassified, bringing previous publications reporting differences
  between HBLR and NHBLR objects into question. We detect broad Hα and
  Hβ components in polarized light for 10 targets, and just broad Hα
  for NGC 5793 and NGC 6300, with line widths ranging between 2100 and
  9600 km s<SUP>-1</SUP>. High bolometric luminosities and low column
  densities are associated with higher polarization degrees, but not
  necessarily with the detection of the scattered broad components.

---------------------------------------------------------
Title: Upholding the unified model for AGN: VLT/FORS2
    spectropolarimetry of Seyfert 2 galaxies
Authors: Ramos Almeida, Cristina; Martínez González, M.; Asensio
   Ramos, A.; Acosta Pulido, J.; Hönig, S.; Alonso-Herrero, A.;
   Tadhunter, C.; González-Martín, O.
2016agnw.confE..52R    Altcode:
  The origin of the unification model for AGN was the detection of broad
  hydrogen recombination lines in the optical polarized spectrum of the
  Seyfert 2 galaxy (Sy2) NGC 1068. Since then, a search for the hidden
  broad-line region (HBLR) of nearby Sy2s started, but polarized broad
  lines have only been detected in ~30-40% of the nearby Sy2s observed
  to date. Here we present new VLT/FORS2 optical spectropolarimetry
  of a sample of 15 Sy2s, including Compton-thin and Compton-thick
  sources. The sample includes six galaxies without previously published
  spectropolarimetry, some of them normally treated as non-hidden BLR
  (NHBLR) objects in the literature, and four Sy2s classified as NHBLR
  based on previous data. We report &gt;4sigma detections of a HBLR in
  11 of these galaxies (73% of the sample). Our results confirm that at
  least some NHBLRs were misclassified, bringing previous publications
  reporting differences between HBLR and NHBLR objects into question. We
  detect broad Ha and Hb components in polarized light for 9 targets,
  and just broad Ha for the other two. We do not find any correlation
  between the properties of the polarized spectra and the column densities
  measured from the X-rays or torus inclination, but a larger sample is
  required to confirm this.

---------------------------------------------------------
Title: On the Magnetism and Dynamics of Prominence Legs Hosting
    Tornadoes
Authors: Martínez González, M. J.; Asensio Ramos, A.; Arregui, I.;
   Collados, M.; Beck, C.; de la Cruz Rodríguez, J.
2016ApJ...825..119M    Altcode: 2016arXiv160501183M
  Solar tornadoes are dark vertical filamentary structures observed
  in the extreme ultraviolet associated with prominence legs and
  filament barbs. Their true nature and relationship to prominences
  requires an understanding of their magnetic structure and dynamic
  properties. Recently, a controversy has arisen: is the magnetic field
  organized forming vertical, helical structures or is it dominantly
  horizontal? And concerning their dynamics, are tornadoes really rotating
  or is it just a visual illusion? Here we analyze four consecutive
  spectro-polarimetric scans of a prominence hosting tornadoes on its
  legs, which helps us shed some light on their magnetic and dynamical
  properties. We show that the magnetic field is very smooth in all the
  prominence, which is probably an intrinsic property of the coronal
  field. The prominence legs have vertical helical fields that show
  slow temporal variation that is probably related to the motion of
  the fibrils. Concerning the dynamics, we argue that (1) if rotation
  exists, it is intermittent, lasting no more than one hour, and (2)
  the observed velocity pattern is also consistent with an oscillatory
  velocity pattern (waves).

---------------------------------------------------------
Title: Active Region Filaments Might Harbor Weak Magnetic Fields
Authors: Díaz Baso, C. J.; Martínez González, M. J.; Asensio
   Ramos, A.
2016ApJ...822...50D    Altcode: 2016arXiv160304645D
  Recent spectropolarimetric observations of active region filaments have
  revealed polarization profiles with signatures typical of the strong
  field Zeeman regime. The conspicuous absence in those observations of
  scattering polarization and Hanle effect signatures was then pointed
  out by some authors. This was interpreted as either a signature of
  mixed “turbulent” field components or as a result of optical
  thickness. In this article, we present a natural scenario to explain
  these Zeeman-only spectropolarimetric observations of active region
  (AR) filaments. We propose a two-component model, one on top of
  the other. Both components have horizontal fields, with the azimuth
  difference between them being close to 90°. The component that lies
  lower in the atmosphere is permeated by a strong field of the order of
  600 G, while the upper component has much weaker fields, of the order of
  10 G. The ensuing scattering polarization signatures of the individual
  components have opposite signs, so its combination along the line of
  sight reduces—and even can cancel out—the Hanle signatures, giving
  rise to an apparent Zeeman-only profile. This model is also applicable
  to other chromospheric structures seen in absorption above ARs.

---------------------------------------------------------
Title: Inversion of Stokes profiles with systematic effects
Authors: Asensio Ramos, A.; de la Cruz Rodríguez, J.; Martínez
   González, M. J.; Pastor Yabar, A.
2016A&A...590A..87A    Altcode: 2016arXiv160405470A
  Quantitative thermodynamical, dynamical and magnetic properties of the
  solar and stellar plasmas are obtained by interpreting their emergent
  non-polarized and polarized spectrum. This inference requires the
  selection of a set of spectral lines that are particularly sensitive to
  the physical conditions in the plasma and a suitable parametric model
  of the solar/stellar atmosphere. Nonlinear inversion codes are then
  used to fit the model to the observations. However, the presence of
  systematic effects, like nearby or blended spectral lines, telluric
  absorption, or incorrect correction of the continuum, among others,
  can strongly affect the results. We present an extension to current
  inversion codes that can deal with these effects in a transparent
  way. The resulting algorithm is very simple and can be applied to any
  existing inversion code with the addition of a few lines of code as
  an extra step in each iteration.

---------------------------------------------------------
Title: Where are the solar magnetic poles?
Authors: Pastor Yabar, A.; Martinez Gonzalez, M. J.; Collados, M.
2015MNRAS.453L..69P    Altcode: 2018arXiv180409748P
  Regardless of the physical origin of stellar magnetic fields -
  fossil or dynamo induced - an inclination angle between the magnetic
  and rotation axes is very often observed. Absence of observational
  evidence in this direction in the solar case has led to generally assume
  that its global magnetic field and rotation axes are well aligned. We
  present the detection of a monthly periodic signal of the photospheric
  solar magnetic field at all latitudes, and especially near the poles,
  revealing that the main axis of the Sun's magnetic field is not aligned
  with the surface rotation axis. This result reinforces the view of our
  Sun as a common intermediate-mass star. Furthermore, this detection
  challenges and imposes a strong observational constraint to modern
  solar dynamo theories.

---------------------------------------------------------
Title: Estimating the magnetic field strength from magnetograms
Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz, R.
2015A&A...577A.125A    Altcode: 2015arXiv150307670A
  A properly calibrated longitudinal magnetograph is an instrument
  that measures circular polarization and gives an estimation of the
  magnetic flux density in each observed resolution element. This usually
  constitutes a lower bound of the field strength in the resolution
  element, given that it can be made arbitrarily large as long as it
  occupies a proportionally smaller area of the resolution element
  and/or becomes more transversal to the observer while still produce
  the same magnetic signal. However, we know that arbitrarily stronger
  fields are less likely - hG fields are more probable than kG fields,
  with fields above several kG virtually absent - and we may even have
  partial information about their angular distribution. Based on a set of
  sensible considerations, we derive simple formulae based on a Bayesian
  analysis to give an improved estimation of the magnetic field strength
  for magnetographs.

---------------------------------------------------------
Title: Spectro-Polarimetric Imaging Reveals Helical Magnetic Fields
    in Solar Prominence Feet
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
   A.; Beck, C.; de la Cruz Rodríguez, J.; Díaz, A. J.
2015ApJ...802....3M    Altcode: 2015arXiv150103295M
  Solar prominences are clouds of cool plasma levitating above
  the solar surface and insulated from the million-degree corona by
  magnetic fields. They form in regions of complex magnetic topology,
  characterized by non-potential fields, which can evolve abruptly,
  disintegrating the prominence and ejecting magnetized material
  into the heliosphere. However, their physics is not yet fully
  understood because mapping such complex magnetic configurations
  and their evolution is extremely challenging, and must often be
  guessed by proxy from photometric observations. Using state-of-the-art
  spectro-polarimetric data, we reconstruct the structure of the magnetic
  field in a prominence. We find that prominence feet harbor helical
  magnetic fields connecting the prominence to the solar surface below.

---------------------------------------------------------
Title: Constraining the shaping mechanism of the Red Rectangle
    through the spectro-polarimetry of its central star
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
   R.; Corradi, R. L. M.; Leone, F.
2015A&A...574A..16M    Altcode: 2014arXiv1410.6365M
  We carried out high-sensitivity spectro-polarimetric observations of
  the central star of the Red Rectangle protoplanetary nebula with the
  aim of constraining the mechanism that gives its biconical shape. The
  stellar light of the central binary system is linearly polarised since
  it is scattered on the dust particles of the nebula. Surprisingly,
  the linear polarisation in the continuum is aligned with one of the
  spikes of the biconical outflow. Also, the observed Balmer lines,
  as well as the Ca ii K lines, are polarised. These observational
  constraints are used to confirm or reject current theoretical models
  for the shaping mechanism of the Red Rectangle. We propose that the
  observed polarisation is not very likely to be generated by a uniform
  biconical stellar wind. Also, the hypothesis of a precessing jet does
  not completely match observations since it requires a larger aperture
  jet than for the nebula.

---------------------------------------------------------
Title: Hierarchical analysis of the quiet-Sun magnetism
Authors: Asensio Ramos, A.; Martínez González, M. J.
2014A&A...572A..98A    Altcode: 2014arXiv1410.5953A
  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 carried out a meta-analysis
  of the magnetism of the quiet Sun from Hinode observations using a
  hierarchical probabilistic method. This method allowed 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 that are due to noise and degeneracies. Our results
  imply that the magnetic fields are very weak, below 275 G with 95%
  probability, with a slight preference for horizontal fields, although
  the distribution is not far from a quasi-isotropic distribution.

---------------------------------------------------------
Title: Upper Limits to the Magnetic Field in Central Stars of
    Planetary Nebulae
Authors: Asensio Ramos, A.; Martínez González, M. J.; Manso Sainz,
   R.; Corradi, R. L. M.; Leone, F.
2014ApJ...787..111A    Altcode: 2014arXiv1404.2718A
  More than about 20 central stars of planetary nebulae (CSPNs) have
  been observed spectropolarimetrically, yet no clear, unambiguous
  signal of the presence of a magnetic field in these objects has
  been found. We perform a statistical (Bayesian) analysis of all the
  available spectropolarimetric observations of CSPN to constrain the
  magnetic fields in these objects. Assuming that the stellar field is
  dipolar and that the dipole axis of the objects is oriented randomly
  (isotropically), we find that the dipole magnetic field strength
  is smaller than 400 G with 95% probability using all available
  observations. The analysis introduced allows integration of future
  observations to further constrain the parameters of the distribution,
  and it is general, so that it can be easily applied to other classes of
  magnetic objects. We propose several ways to improve the upper limits
  found here.

---------------------------------------------------------
Title: A search for magnetic fields on central stars in planetary
    nebulae
Authors: Leone, F.; Corradi, R. L. M.; Martínez González, M. J.;
   Asensio Ramos, A.; Manso Sainz, R.
2014A&A...563A..43L    Altcode: 2014arXiv1401.6282L
  Context. 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. <BR /> Aims: 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. <BR /> Methods: 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. Twentythree planetary nebulae
  that span 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. <BR /> Results:
  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.

---------------------------------------------------------
Title: Granular-sized magnetic flux emergence
Authors: Martínez González, María Jesús
2014cosp...40E2017M    Altcode:
  It is believed that solar magnetic fields are created in the
  tachocline, the interface between the convection zone and the radiative
  interior. Due to buoyancy instabilities, they move upward and emerge
  into the solar atmosphere in the form of Ω-shaped flux tubes. The
  largest emerging active regions produce sunspots or pores, lasting
  from days or weeks to moths, and the ephemeral regions emerge to
  feed the quiet Sun at supergranular scales (the network), lasting
  from hours to days. A surprising finding in solar physics in the last
  few years was the discovery that, despite their stochastic character,
  the quietest areas of the quiet Sun are formed, at granular scales, by
  small dipoles that live for several minutes. Are these dipoles just the
  end tail of the same emergence phenomenon than active regions? or are
  they the result of a surface phenomenon? In this talk I review all the
  present knowledge of the smallest scale emergence phenomenon observed
  in the Sun and I put in in context on the solar global magnetism.

---------------------------------------------------------
Title: Polarisation and magnetic fields in cool stars and the Sun. A
    session in memory of Meir Semel
Authors: Martínez González, M. J.; Marsden, S. C.
2013AN....334..164M    Altcode: 2013csss...17..164M
  Astrophysical plasmas and magnetic fields are inextricably coupled
  to each other. But magnetic fields are elusive; they cannot be
  fully characterized with standard (spectroscopic) observational
  techniques. Fortunately, polarisation, the third fundamental property
  of light, encodes all the quantitative information on the magnetism
  of the objects we observe. This splinter session brought together the
  solar and stellar spectropolarimetric communities to discuss some of
  the fundamental unsolved questions of solar and stellar magnetism and
  the future of spectropolarimetric observations.

---------------------------------------------------------
Title: Hanle Effect for Stellar Dipoles and Quadrupoles
Authors: Manso Sainz, R.; Martínez González, M. J.
2012ApJ...760....7M    Altcode: 2012arXiv1209.6187M
  We derive exact expressions for the degree of lineal polarization over
  a resolved or integrated stellar disc due to resonance scattering
  and the Hanle effect from a dipolar or quadrupolar distribution of
  magnetic fields. We apply the theory of scattering polarization within
  the formalism of the spherical tensors representation for the density
  matrix and radiation field. The distribution of linear polarization
  over the stellar disk for different configurations of the magnetic
  field is studied and its topology discussed. For an unresolved dipole,
  the resulting polarization can be expressed in terms of just three
  functions (of the inclination angle and effective dipole strength)
  that are calculated numerically and their behavior discussed. Dipolar
  and (aligned) quadrupoles are considered in some detail, but the
  techniques here—in particular, the extensive use of the spherical
  tensor formalism for polarization—can easily be applied to more
  general field configurations.

---------------------------------------------------------
Title: Anomalous Circular Polarization Profiles in the He I 1083.0
    nm Multiplet from Solar Spicules
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
   R.; Beck, C.; Belluzzi, L.
2012ApJ...759...16M    Altcode: 2012arXiv1209.2589M
  We report Stokes vector observations of solar spicules and a prominence
  in the He I 1083 nm multiplet carried out with the Tenerife Infrared
  Polarimeter. The observations show linear polarization profiles that
  are produced by scattering processes in the presence of a magnetic
  field. After a careful data reduction, we demonstrate the existence of
  extremely asymmetric Stokes V profiles in the spicular material that
  we are able to model with two magnetic components along the line of
  sight, and under the presence of atomic orientation in the energy
  levels that give rise to the multiplet. We discuss some possible
  scenarios that can generate the atomic orientation in spicules. We
  stress the importance of spectropolarimetric observations across the
  limb to distinguish such signals from observational artifacts.

---------------------------------------------------------
Title: Resolving the Internal Magnetic Structure of the Solar Network
Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki,
   S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.;
   Schmidt, W.
2012ApJ...758L..40M    Altcode: 2012arXiv1209.2584M
  We analyze the spectral asymmetry of Stokes V (circularly polarized)
  profiles of an individual network patch in the quiet Sun observed
  by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the
  network elements contain substructure which is revealed by the spatial
  distribution of Stokes V asymmetries. The area asymmetry between the
  red and blue lobes of Stokes V increases from nearly zero at the core
  of the structure to values close to unity at its edges (single-lobed
  profiles). Such a distribution of the area asymmetry is consistent
  with magnetic fields expanding with height, i.e., an expanding
  magnetic canopy (which is required to fulfill pressure balance and
  flux conservation in the solar atmosphere). Inversion of the Stokes
  I and V profiles of the patch confirms this picture, revealing a
  decreasing field strength and increasing height of the canopy base
  from the core to the periphery of the network patch. However, the
  non-roundish shape of the structure and the presence of negative area
  and amplitude asymmetries reveal that the scenario is more complex than
  a canonical flux tube expanding with height surrounded by downflows.

---------------------------------------------------------
Title: Analytical Calculation of Stokes Profiles of Rotating Stellar
    Magnetic Dipole
Authors: Martínez González, M. J.; Asensio Ramos, A.
2012ApJ...755...96M    Altcode: 2012arXiv1206.2502M
  The observation of the polarization emerging from a rotating star
  at different phases opens up the possibility to map the magnetic
  field in the stellar surface thanks to the well-known Zeeman-Doppler
  imaging. When the magnetic field is sufficiently weak, the circular
  and linear polarization profiles locally in each point of the star are
  proportional to the first and second derivatives of the unperturbed
  intensity profile, respectively. We show that the weak-field
  approximation (for weak lines in the case of linear polarization)
  can be generalized to the case of a rotating star including the
  Doppler effect and taking into account the integration on the stellar
  surface. The Stokes profiles are written as a linear combination of
  wavelength-dependent terms expressed as series expansions in terms of
  Hermite polynomials. These terms contain the surface-integrated magnetic
  field and velocity components. The direct numerical evaluation of these
  quantities is limited to rotation velocities not larger than eight
  times the Doppler width of the local absorption profiles. Additionally,
  we demonstrate that in a rotating star, the circular polarization
  flux depends on the derivative of the intensity flux with respect to
  the wavelength and also on the profile itself. Likewise, the linear
  polarization depends on the profile and on its first and second
  derivatives with respect to the wavelength. We particularize the
  general expressions to a rotating dipole.

---------------------------------------------------------
Title: Dead Calm Areas in the Very Quiet Sun
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
   A.; Hijano, E.
2012ApJ...755..175M    Altcode: 2012arXiv1206.4545M
  We analyze two regions of the quiet Sun (35.6 × 35.6 Mm<SUP>2</SUP>)
  observed at high spatial resolution (lsim100 km) in polarized light by
  the IMaX spectropolarimeter on board the SUNRISE balloon. We identify
  497 small-scale (~400 km) magnetic loops, appearing at an effective
  rate of 0.25 loop h <SUP>-1</SUP> arcsec<SUP>-2</SUP> further, we
  argue that this number and rate are underestimated by ~30%. However,
  we find that these small dipoles do not appear uniformly on the solar
  surface: their spatial distribution is rather filamentary and clumpy,
  creating dead calm areas, characterized by a very low magnetic signal
  and a lack of organized loop-like structures at the detection level
  of our instruments, which cannot be explained as just statistical
  fluctuations of a Poisson spatial process. We argue that this is an
  intrinsic characteristic of the mechanism that generates the magnetic
  fields in the very quiet Sun. The spatio-temporal coherences and the
  clumpy structure of the phenomenon suggest a recurrent, intermittent
  mechanism for the generation of magnetic fields in the quietest areas
  of the Sun.

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Title: Model Selection for Spectropolarimetric Inversions
Authors: Asensio Ramos, A.; Manso Sainz, R.; Martínez González,
   M. J.; Viticchié, B.; Orozco Suárez, D.; Socas-Navarro, H.
2012ApJ...748...83A    Altcode: 2012arXiv1201.5063A
  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 (S/Ns) favor models without gradients
  along the line of sight. If the observations show 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
  S/Ns 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.

---------------------------------------------------------
Title: Influence of phase-diversity image reconstruction techniques
    on circular polarization asymmetries
Authors: Asensio Ramos, A.; Martínez González, M. J.; Khomenko,
   E.; Martínez Pillet, V.
2012A&A...539A..42A    Altcode: 2011arXiv1111.2496A
  Context. Full Stokes filter-polarimeters are key instruments for
  investigating the rapid evolution of magnetic structures on the solar
  surface. To this end, the image quality is routinely improved using
  a-posteriori image reconstruction methods. <BR /> Aims: We analyze
  the robustness of circular polarization asymmetries to phase-diversity
  image reconstruction techniques. <BR /> Methods: We used snapshots of
  magneto-hydrodynamical simulations carried out with different initial
  conditions to synthesize spectra of the magnetically sensitive Fe
  i line at 5250.2 Å. We degraded the synthetic profiles spatially
  and spectrally to simulate observations with the IMaX full Stokes
  filter-polarimeter. We also simulated the focused/defocused pairs of
  images used by the phase-diversity algorithm for reconstruction and the
  polarimetric modulation scheme. We assume that standard optimization
  methods are able to infer the projection of the wavefront on the Zernike
  polynomials with 10% precision. We also consider the less favorable case
  of 25% precision. We obtain reconstructed monochromatic modulated images
  that are later demodulated and compared with the original maps. <BR />
  Results: Although asymmetries are often difficult to define in the
  quiet Sun due to the complexity of the Stokes V profiles, we show
  how asymmetries are degraded with spatial and spectral smearing. The
  results indicate that, although image reconstruction techniques reduce
  the spatial smearing, they can modify the asymmetries of the profiles,
  which are mainly caused by the appearance of spatially-correlated noise.

---------------------------------------------------------
Title: Analytical maximum likelihood estimation of stellar magnetic
    fields
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
   A.; Belluzzi, L.
2012MNRAS.419..153M    Altcode: 2011MNRAS.tmp.1583M; 2011arXiv1108.4366M
  The polarized spectrum of stellar radiation encodes valuable information
  on the conditions of stellar atmospheres and the magnetic fields
  that permeate them. In this paper, we give explicit expressions to
  estimate the magnetic field vector and its associated error from the
  observed Stokes parameters. We study the solar case where specific
  intensities are observed and then the stellar case, where we receive
  the polarized flux. In the second case, we concentrate on the explicit
  expression for the case of a slow rotator with a dipolar magnetic
  field geometry. Moreover, we also give explicit formulae to retrieve
  the magnetic field vector from the least-squares deconvolution (LSD)
  profiles without assuming mean values for the LSD artificial spectral
  line. The formulae have been obtained assuming that the spectral lines
  can be described in the weak-field regime and using a maximum likelihood
  approach. The errors are recovered by means of the Hermitian matrix. The
  bias of the estimators is analysed in depth.

---------------------------------------------------------
Title: Advection and dispersal of small magnetic elements in the
    very quiet Sun
Authors: Manso Sainz, R.; Martínez González, M. J.; Asensio Ramos, A.
2011A&A...531L...9M    Altcode:
  We track small magnetic structures on very quiet regions (internetwork)
  of the Sun. We follow the footpoints of small-scale magnetic loops that
  appear on the photosphere at granular scales using spectropolarimetric
  and magnetographic data obtained with Hinode. We find two different
  regimes for their wanderings. Within granules (where they appear),
  they seem to be passively advected by the plasma - which is
  justified by their relatively low magnetic flux (~10<SUP>16</SUP>
  Mx), and magnetic field strength (~200 G). The plasma flow thus
  traced is roughly laminar with a characteristic mean velocity of 2
  km s<SUP>-1</SUP> and very low vorticity. Once the magnetic markers
  reach intergranular lanes, they remain there and are buffeted by the
  random flows of neighbouring granules and turbulent intergranules,
  follow random walks, and disperse across the solar surface with a
  diffusion constant of 195 km<SUP>2</SUP> s<SUP>-1</SUP>. While on
  their intergranular random walking, they may fall close to whirlpools
  (on scales ≲400 km) associated with convective downdrafts, similar
  to the events recently reported in mesogranular and supergranular cell
  boundaries tracking magnetic bright points, which provides additional
  evidence that these events are ubiquitous on the solar surface.

---------------------------------------------------------
Title: Non-detection of Magnetic Fields in the Central Stars of the
    Planetary Nebulae NGC 1360 and LSS 1362
Authors: Leone, Francesco; Martínez González, María J.; Corradi,
   Romano L. M.; Privitera, Giovanni; Manso Sainz, Rafael
2011ApJ...731L..33L    Altcode: 2011arXiv1104.1042L
  The presence of magnetic fields is an attractive hypothesis for shaping
  planetary nebulae (PNe). We report on observations of the central star
  of the two PNe NGC 1360 and LSS 1326. We performed spectroscopy on
  circularly polarized light with the Focal Reducer and Low Dispersion
  Spectrograph at the Very Large Telescope of the European Southern
  Observatory. Contrary to previous reports, we find that the effective
  magnetic field, which is the average over the visible stellar disk of
  longitudinal components of the magnetic fields, is null within errors
  for both stars. We conclude that direct evidence of magnetic fields on
  the central stars of PNe is still missing—either the magnetic field
  is much weaker (&lt;600 G) than previously reported, or more complex
  (thus leading to cancellations), or both. Certainly, indirect evidence
  (e.g., MASER emission) fully justify further efforts to point out the
  strength and morphology of such magnetic fields.

---------------------------------------------------------
Title: The Magnetic Fields of the Quiet Sun
Authors: Sánchez Almeida, J.; Martínez González, M.
2011ASPC..437..451S    Altcode: 2011arXiv1105.0387S
  This work reviews our understanding of the magnetic fields observed
  in the quiet Sun. The subject has undergone a major change during the
  last decade (quiet revolution), and it will remain changing since the
  techniques of diagnostic employed so far are known to be severely
  biased. Keeping these caveats in mind, our work covers the main
  observational properties of the quiet Sun magnetic fields: magnetic
  field strengths, unsigned magnetic flux densities, magnetic field
  inclinations, as well as the temporal evolution on short time-scales
  (loop emergence), and long time-scales (solar cycle). We also summarize
  the main theoretical ideas put forward to explain the origin of the
  quiet Sun magnetism. A final prospective section points out various
  areas of solar physics where the quiet Sun magnetism may have an
  important physical role to play (chromospheric and coronal structure,
  solar wind acceleration, and solar elemental abundances).

---------------------------------------------------------
Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
    Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
   R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
   A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
2011ApJ...730L..37M    Altcode: 2011arXiv1103.0145M
  We present observational evidence for oscillations of magnetic flux
  density in the quiet areas of the Sun. The majority of magnetic
  fields on the solar surface have strengths of the order of or lower
  than the equipartition field (300-500 G). This results in a myriad of
  magnetic fields whose evolution is largely determined by the turbulent
  plasma motions. When granules evolve they squash the magnetic field
  lines together or pull them apart. Here, we report on the periodic
  deformation of the shapes of features in circular polarization observed
  at high resolution with SUNRISE. In particular, we note that the
  area of patches with a constant magnetic flux oscillates with time,
  which implies that the apparent magnetic field intensity oscillates
  in antiphase. The periods associated with this oscillatory pattern
  are compatible with the granular lifetime and change abruptly, which
  suggests that these oscillations might not correspond to characteristic
  oscillatory modes of magnetic structures, but to the forcing by granular
  motions. In one particular case, we find three patches around the same
  granule oscillating in phase, which means that the spatial coherence
  of these oscillations can reach 1600 km. Interestingly, the same kind
  of oscillatory phenomenon is also found in the upper photosphere.

---------------------------------------------------------
Title: Small Magnetic Loops Connecting the Quiet Surface and the
    Hot Outer Atmosphere of the Sun
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
   A.; Bellot Rubio, L. R.
2010ApJ...714L..94M    Altcode: 2010arXiv1003.1255M
  Sunspots are the most spectacular manifestation of solar magnetism,
  yet 99% of the solar surface remains "quiet" at any time of the solar
  cycle. The quiet sun is not void of magnetic fields, though; they
  are organized at smaller spatial scales and evolve relatively fast,
  which makes them difficult to detect. Thus, although extensive quiet
  Sun magnetism would be a natural driver to a uniform, steady heating of
  the outer solar atmosphere, it is not clear what the physical processes
  involved would be, due to lack of observational evidence. We report on
  the topology and dynamics of the magnetic field in very quiet regions of
  the Sun from spectropolarimetric observations of the Hinode satellite,
  showing a continuous injection of magnetic flux with a well-organized
  topology of Ω-loop from below the solar surface into the upper
  layers. At first stages, when the loop travels across the photosphere,
  it has a flattened (staple-like) geometry and a mean velocity ascent
  of ~3 km s<SUP>-1</SUP>. When the loop crosses the minimum temperature
  region, the magnetic fields at the footpoints become almost vertical and
  the loop topology resembles a potential field. The mean ascent velocity
  at chromospheric height is ~12 km s<SUP>-1</SUP>. The energy input rate
  of these small-scale loops in the lower boundary of the chromosphere
  is (at least) of 1.4 × 10<SUP>6</SUP>-2.2 × 10<SUP>7</SUP> erg
  cm<SUP>-2</SUP> s<SUP>-1</SUP>. Our findings provide empirical evidence
  for solar magnetism as a multi-scale system, in which small-scale
  low-flux magnetism plays a crucial role, at least as important as active
  regions, coupling different layers of the solar atmosphere and being
  an important ingredient for chromospheric and coronal heating models.

---------------------------------------------------------
Title: The stochastic, intermittent nature of quiet Sun magnetism
Authors: Martinez González, M. J.; Manso Sainz, R.; López Ariste,
   A.; Bellot Rubio, L. R.; Bianda, M.
2010iac..talk....1M    Altcode: 2010iac..talk..153M
  No abstract at ADS

---------------------------------------------------------
Title: Statistical Analysis of the very Quiet Sun Magnetism
Authors: Martínez González, M. J.; Manso Sainz, R.; Asensio Ramos,
   A.; López Ariste, A.; Bianda, M.
2010ApJ...711L..57M    Altcode: 2010arXiv1001.4551M
  The behavior of the observed polarization amplitudes with spatial
  resolution is a strong constraint on the nature and organization
  of solar magnetic fields below the resolution limit. We study the
  polarization of the very quiet Sun at different spatial resolutions
  using ground- and space-based observations. It is shown that 80% of the
  observed polarization signals do not change with spatial resolution,
  suggesting that, observationally, the very quiet Sun magnetism
  remains the same despite the high spatial resolution of space-based
  observations. Our analysis also reveals a cascade of spatial scales
  for the magnetic field within the resolution element. It is manifest
  that the Zeeman effect is sensitive to the microturbulent field usually
  associated with Hanle diagnostics. This demonstrates that Zeeman and
  Hanle studies show complementary perspectives of the same magnetism.

---------------------------------------------------------
Title: Spectropolarimetric multi line analysis of stellar magnetic
    fields
Authors: Ramírez Vélez, J. C.; Semel, M.; Stift, M.; Martínez
   González, M. J.; Petit, P.; Dunstone, N.
2010A&A...512A...6R    Altcode: 2010arXiv1001.1003R
  <BR /> Aims: In this paper we study the feasibility of inferring the
  magnetic field from polarized multi line spectra using two methods:
  The pseudo line approach and The PCA-ZDI approach. <BR /> Methods:
  We use multi line techniques, meaning that all the lines of a stellar
  spectrum contribute to obtain a polarization signature. The use of
  multiple lines dramatically increases the signal-to-noise-ratio of
  these polarizations signatures. Using one technique, the pseudo line
  approach, we construct the pseudo line as the mean profile of all the
  individual lines. The other technique, the PCA-ZDI approach proposed
  recently by Semel et al. (2006, ASPC, 358, 355) for the detection
  of polarized signals, combines principle components analysis (PCA)
  and the Zeeman Doppler imaging technique (ZDI). This new method has
  a main advantage: the polarized signature is extracted using cross
  correlations between the stellar spectra and functions containing
  the polarization properties of each line. is extracted using cross
  correlations between the stellar spectra and functions containing the
  polarization properties of each line." These functions are the principal
  components of a database of synthetic spectra. The synthesis of the
  spectra of the database are obtained using the radiative transfer
  equations in LTE. The profiles built with the PCA-ZDI technique are
  called multi Zeeman signatures. <BR /> Results: The construction of the
  pseudo line as well as the multi Zeeman signatures is a powerful tool
  in the study of stellar and solar magnetic fields. The information of
  the physical parameters that governs the line formation is contained
  in the final polarized profiles. We have shown in particular using
  inversion codes that the magnetic field vector can be properly inferred
  with both approaches despite the magnetic field regime.

---------------------------------------------------------
Title: The quiet Sun magnetic field observed with ZIMPOL on
    THEMIS. I. The probability density function
Authors: Bommier, V.; Martínez González, M.; Bianda, M.; Frisch,
   H.; Asensio Ramos, A.; Gelly, B.; Landi Degl'Innocenti, E.
2009A&A...506.1415B    Altcode:
  Context: The quiet Sun magnetic field probability density function (PDF)
  remains poorly known. Modeling this field also introduces a magnetic
  filling factor that is also poorly known. With these two quantities,
  PDF and filling factor, the statistical description of the quiet Sun
  magnetic field is complex and needs to be clarified. <BR />Aims:
  In the present paper, we propose a procedure that combines direct
  determinations and inversion results to derive the magnetic field
  vector and filling factor, and their PDFs. <BR />Methods: We used
  spectro-polarimetric observations taken with the ZIMPOL polarimeter
  mounted on the THEMIS telescope. The target was a quiet region at disk
  center. We analyzed the data by means of the UNNOFIT inversion code,
  with which we inferred the distribution of the mean magnetic field α
  B, α being the magnetic filling factor. The distribution of α was
  derived by an independent method, directly from the spectro-polarimetric
  data. The magnetic field PDF p(B) could then be inferred. By introducing
  a joint PDF for the filling factor and the magnetic field strength, we
  have clarified the definition of the PDF of the quiet Sun magnetic field
  when the latter is assumed not to be volume-filling. <BR />Results: The
  most frequent local average magnetic field strength is found to be 13
  G. We find that the magnetic filling factor is related to the magnetic
  field strength by the simple law α = B_1/B with B<SUB>1</SUB> = 15
  G. This result is compatible with the Hanle weak-field determinations,
  as well as with the stronger field determinations from the Zeeman effect
  (kGauss field filling 1-2% of space). From linear fits, we obtain the
  analytical dependence of the magnetic field PDF. Our analysis has also
  revealed that the magnetic field in the quiet Sun is isotropically
  distributed in direction. <BR />Conclusions: We conclude that the
  quiet Sun is a complex medium where magnetic fields having different
  field strengths and filling factors coexist. Further observations
  with a better polarimetric accuracy are, however, needed to confirm
  the results obtained in the present work. <P />Based on observations
  made with the French-Italian telescope THEMIS operated by the CNRS
  and CNR on the island of Tenerife in the Spanish Observatorio del
  Teide of the Instituto de Astrofísica de Canarias. Present address:
  Instituto de Astrofísica de Canarias, vía Láctea s/n, 38205 La
  Laguna, Tenerife, Spain.

---------------------------------------------------------
Title: Multiline Zeeman signatures through line addition
Authors: Semel, M.; Ramírez Vélez, J. C.; Martínez González,
   M. J.; Asensio Ramos, A.; Stift, M. J.; López Ariste, A.; Leone, F.
2009A&A...504.1003S    Altcode: 2009arXiv0906.4226S
  Context: To obtain a significant Zeeman signature in the polarised
  spectra of a magnetic star, we usually “add” the contributions
  of numerous spectral lines; the ultimate goal is to recover the
  spectropolarimetric prints of the magnetic field in these line
  additions. <BR />Aims: Here we want to clarify the meaning of these
  techniques of line addition; in particular, we try to interpret the
  meaning of the “pseudo-line” formed during this process and to
  find out why and how its Zeeman signature is still meaningful. <BR
  />Methods: We create a synthetic case of line addition and apply well
  tested standard solar methods routinely used in research on magnetism
  in the Sun. <BR />Results: The results are convincing and the Zeeman
  signatures well detected; Solar methods are found to be quite efficient
  for stellar observations. We statistically compare line addition
  with least-squares deconvolution and demonstrate that they both give
  very similar results, as a consequence of the special statistical
  properties of the weights. <BR />Conclusions: The Zeeman signatures
  are unequivocally detected in this multiline approach. We suggest
  that magnetic field detection is reliable well beyond the weak-field
  approximation. Linear polarisation in the spectra of solar type stars
  can be detected when the spectral resolution is sufficiently high.

---------------------------------------------------------
Title: Emergence of Small-scale Magnetic Loops Through the Quiet
    Solar Atmosphere
Authors: Martínez González, M. J.; Bellot Rubio, L. R.
2009ApJ...700.1391M    Altcode: 2009arXiv0905.2691M
  We investigate the emergence of magnetic flux in the quiet Sun
  at very small spatial scales, focusing on the magnetic connection
  between the photosphere and chromosphere. The observational data
  consist of spectropolarimetric measurements and filtergrams taken
  with the Hinode satellite and the Dutch Open Telescope. We find that
  a significant fraction of the magnetic flux present in internetwork
  regions appears in the form of Ω-shaped loops. The emergence rate
  is 0.02 loops per hour and arcsec<SUP>-2</SUP>, which brings 1.1
  × 10<SUP>12</SUP> Mx s<SUP>-1</SUP> arcsec<SUP>-2</SUP> of new
  flux to the solar surface. Initially, the loops are observed as
  small patches of linear polarization above a granular cell. Shortly
  afterward, two footpoints of opposite polarity become visible in
  circular polarization within or at the edges of the granule and start
  moving toward the adjacent intergranular space. The orientation of the
  footpoints does not seem to obey Hale's polarity rules. The loops are
  continuously buffeted by convective motions, but they always retain a
  high degree of coherence. Interestingly, 23% of the loops that emerge
  in the photosphere reach the chromosphere (16 cases out of 69). They
  are first detected in Fe I 630 nm magnetograms and 5 minutes later
  in Mg I b 517.3 nm magnetograms. After about 8 minutes, some of them
  are also observed in Ca II H line-core images, where the footpoints
  produce small brightness enhancements.

---------------------------------------------------------
Title: Centre to Limb Variation of the Internetwork Magnetism
Authors: Martínez González, M. J.; Asensio Ramos, A.; López
   Ariste, A.
2009ASPC..405..219M    Altcode:
  We analyse 1.5 μm spectropolarimetric observations of quiet
  regions at different positions on the solar surface. Neither the
  circular and linear polarization signals nor the area and amplitude
  asymmetries present a clear trend with the position on the Sun. This
  fact discards a network-like scenario for the internetwork magnetic
  fields. An isotropically distributed magnetic field would reproduce the
  observations, whatever its organisation (myriads of low-lying loops,
  turbulent field, etc.).

---------------------------------------------------------
Title: Bayesian Inversion of Stokes Profiles
Authors: Asensio Ramos, A.; Martínez González, M. J.;
   Rubiño-Martín, J. A.
2009ASPC..405..315A    Altcode:
  Inversion techniques are the most powerful methods to obtain information
  about the thermodynamical and magnetic properties of solar and stellar
  atmospheres. In the last years, we have witnessed the development of
  highly sophisticated inversion codes that are now widely applied to
  spectro-polarimetric observations. However, no realistic confidence
  intervals are obtained for the inferred parameters. Additionally, it
  is fundamental to apply efficient techniques to assess the ability
  of models to reproduce the observations and to know to what extent
  the models have to be refined or can be simplified. We propose the
  application of Bayesian techniques. The posterior distribution, that
  takes into account both the a-priori knowledge and the information
  given by the data, is efficiently sampled using a Markov Chain Monte
  Carlo method. We demonstrate the capabilities of the code with the
  aid of an interesting example.

---------------------------------------------------------
Title: Flux Cancellation in the Solar Photosphere: a near-IR Line
    of Mn I as a Diagnostic Tool
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
   A.; Trujillo Bueno, J.; Collados, M.
2009ASPC..405..215A    Altcode:
  Recently, \cite{asensio_2_asensio_mn07} pointed out that the near-IR
  line of Mn I at 15262.702 Å provides a new diagnostic window for
  exploring the magnetism of the quiet Sun. In contrast with previously
  considered Mn I lines located at visible wavelengths this near-IR
  line has the advantage that the shape of its intensity profile is very
  sensitive to the presence of magnetic fields. This enhanced magnetic
  sensitivity is produced by the coincidence of two favorable facts:
  the enhanced Zeeman sensitivity of near-IR lines and because this line
  is subjected to particularly strong Paschen-Back perturbations due to
  the hyperfine structure of manganese. Of great diagnostic interest is
  that the intensity profile itself give us information on the unsigned
  magnetic flux, while the polarization profiles are sensitive to the
  net flux. An application to spectropolarimetric observations with the
  Tenerife Infrared Polarimeter has allowed us to obtain the first flux
  cancellation map in an enhanced network region.

---------------------------------------------------------
Title: Multiline Zeeman signatures as demonstrated through the
    Pseudo-line
Authors: Semel, M.; Ramirez Velez, J. C.; Stift, M. J.; Martinez
   Gonzalez, M. J.; Lopez Ariste, A.; Leone, F.
2008arXiv0810.3543S    Altcode:
  In order to get a significant Zeeman signature in the polarised spectra
  of a magnetic star, we usually 'add' the contributions of numerous
  spectral lines; the ultimate goal is to recover the spectropolarimetric
  prints of the magnetic field in these line additions. Here we want to
  clarify the meaning of these techniques of line addition; in particular,
  we try to interpret the meaning of the 'pseudo-line' formed during
  this process and to find out why and how its Zeeman signature is still
  meaningful. We create a synthetic case of lines addition and apply
  well tested standard solar methods routinely used in the research
  on magnetism in our nearest star. The results are convincing and the
  Zeeman signatures well detected; Solar methods are found to be quite
  efficient also for stellar observations. The Zeeman signatures are
  unequivocally detected in this multiline approach. We may anticipate
  the outcome magnetic fields to be reliable well beyond the weak-field
  approximation. Linear polarisation in the spectra of solar type stars
  can be detected when the spectral resolution is sufficiently high.

---------------------------------------------------------
Title: PCA detection and denoising of Zeeman signatures in polarised
    stellar spectra
Authors: Martínez González, M. J.; Asensio Ramos, A.; Carroll,
   T. A.; Kopf, M.; Ramírez Vélez, J. C.; Semel, M.
2008A&A...486..637M    Altcode: 2008arXiv0804.4692M
  Aims: Our main objective is to develop a denoising strategy to
  increase the signal to noise ratio of individual spectral lines
  of stellar spectropolarimetric observations. <BR />Methods: 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. <BR />Results: 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
  techniques like line addition and least-squares deconvolution. Moreover,
  PCA is very robust and easy to compute.

---------------------------------------------------------
Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and
    6302 Å
Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.;
   Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez
   González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez
   Almeida, J.
2008ApJ...674..596S    Altcode:
  The reliability of quiet-Sun magnetic field diagnostics based on the
  Fe I lines at 6302 Å has been questioned by recent work. Here we
  present the results of a thorough study of high-resolution multiline
  observations taken with the new spectropolarimeter SPINOR, comprising
  the 5250 and 6302 Å spectral domains. The observations were analyzed
  using several inversion algorithms, including Milne-Eddington,
  LTE with 1 and 2 components, and MISMA codes. We find that the
  line-ratio technique applied to the 5250 Å lines is not sufficiently
  reliable to provide a direct magnetic diagnostic in the presence
  of thermal fluctuations and variable line broadening. In general,
  one needs to resort to inversion algorithms, ideally with realistic
  magnetohydrodynamic constrains. When this is done, the 5250 Å lines
  do not seem to provide any significant advantage over those at 6302
  Å. In fact, our results point toward a better performance with the
  latter (in the presence of turbulent line broadening). In any case,
  for very weak flux concentrations, neither spectral region alone
  provides sufficient constraints to fully disentangle the intrinsic
  field strengths. Instead, we advocate for a combined analysis of both
  spectral ranges, which yields a better determination of the quiet-Sun
  magnetic properties. Finally, we propose the use of two other Fe I
  lines (at 4122 and 9000 Å) with identical line opacities that seem
  to work much better than the others.

---------------------------------------------------------
Title: Near-IR internetwork spectro-polarimetry at different
    heliocentric angles
Authors: Martínez González, M. J.; Asensio Ramos, A.; López Ariste,
   A.; Manso Sainz, R.
2008A&A...479..229M    Altcode: 2007arXiv0710.5219M
  Aims:The analysis of near infrared spectropolarimetric data at the
  internetwork in different regions on the solar surface could offer
  constraints that reject current modeling of these quiet areas. <BR
  />Methods: We present spectro-polarimetric observations of very
  quiet regions for different values of the heliocentric angle for the
  Fe i lines at 1.56 μm, from disc centre to positions close to the
  limb. The spatial resolution of the data is 0.7{-}1”. We analyse
  direct observable properties of the Stokes profiles as the amplitude
  of circular and linear polarisation, as well as the total degree of
  polarisation. The area and amplitude asymmetries are also studied. <BR
  />Results: We do not find any significant variation in the properties of
  the polarimetric signals with the heliocentric angle. This means that
  the magnetism of the solar internetwork remains the same regardless
  of the position on the solar disc. This observational fact discards
  the possibility of modeling the internetwork as a network-like
  scenario. The magnetic elements of internetwork areas seem to be
  isotropically distributed when observed at our spatial resolution.

---------------------------------------------------------
Title: Internetwork magnetic field distribution from simultaneous
    1.56 μm and 630 nm observations
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.;
   Beck, C.
2008A&A...477..953M    Altcode: 2007arXiv0711.0267M
  Aims:We study the contradictory magnetic field strength distributions
  retrieved from independent analyses of spectropolarimetric observations
  in the near-infrared (1.56 μm) and in the visible (630 nm) spectral
  ranges in internetwork regions. <BR />Methods: To solve this apparent
  controversy, we present simultaneous and co-spatial 1.56 μm and 630 nm
  observations of an internetwork area. The properties of the circular
  and linear polarization signals, as well as the Stokes V area and
  amplitude asymmetries, are discussed. As a complement, we also used
  inversion techniques to infer the physical parameters of the solar
  atmosphere. As a first step, the infrared and visible observations
  are analysed separately to check their compatibility. Finally, the
  simultaneous inversion of the two data sets is performed. <BR />Results:
  The magnetic flux densities retrieved from the individual analysis
  of the infrared and visible data sets are strongly correlated. The
  polarity of the Stokes V profiles is the same at co-spatial pixels
  in both wavelength ranges. This indicates that both 1.56 μm and
  630 nm observations trace the same magnetic structures on the solar
  surface. The simultaneous inversion of the two pairs of lines reveals
  an internetwork full of sub-kG structures that fill only 2% of the
  resolution element. A correlation is found between the magnetic field
  strength and the continuum intensity: equipartition fields (B∼ 500
  G) tend to be located in dark intergranular lanes, whereas weaker
  field structures are found inside granules. The most probable unsigned
  magnetic flux density is 10 Mx/cm^2. The net magnetic flux density in
  the whole field of view is nearly zero. This means that both polarities
  cancel out almost exactly in our observed internetwork area.

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Title: Bayesian inversion of Stokes profiles
Authors: Asensio Ramos, A.; Martínez González, M. J.;
   Rubiño-Martín, J. A.
2007A&A...476..959A    Altcode: 2007arXiv0709.0596A
  Context: Inversion techniques are the most powerful methods to obtain
  information about the thermodynamical and magnetic properties of
  solar and stellar atmospheres. In the recent years, we have witnessed
  the development of highly sophisticated inversion codes that are now
  widely applied to spectro-polarimetric observations. The majority of
  these inversion codes are based on the optimization of a complicated
  non-linear merit function. The experience gained has facilitated the
  recovery of the model that best fits a given observation. However,
  and except for the recently developed inversion codes based
  on database search algorithms together with the application
  of Principal Component Analysis, no reliable and statistically
  well-defined confidence intervals can be obtained for the parameters
  inferred from the inversions. <BR />Aims: A correct estimation of the
  confidence intervals for all the parameters that describe the model is
  mandatory. Additionally, it is fundamental to apply efficient techniques
  to assess the ability of models to reproduce the observations and
  to determine to what extent the models have to be refined or can
  be simplified. <BR />Methods: Bayesian techniques are applied to
  analyze the performance of the model to fit a given observed Stokes
  vector. The posterior distribution, that takes into account both the
  information about the priors and the likelihood, is efficiently sampled
  using a Markov chain Monte Carlo method. For simplicity, we focus on
  the Milne-Eddington approximate solution of the radiative transfer
  equation and we only take into account the generation of polarization
  through the Zeeman effect. However, the method is extremely general
  and other more complex forward models can be applied, even allowing
  for the presence of atomic polarization. <BR />Results: We illustrate
  the method with different problems, from academic to more realistic
  examples. We show that the information provided by the posterior
  distribution is fundamental to understand and determine the amount
  of information available in the Stokes profiles in these particular
  cases. <P />Appendix A and B are only available in electronic form
  at http://www.aanda.org.

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Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å
Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados,
   M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González,
   M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J.
2007arXiv0710.1099S    Altcode:
  The reliability of quiet Sun magnetic field diagnostics based on the
  \ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We
  present here the results of a thorough study of high-resolution
  multi-line observations taken with the new spectro-polarimeter SPINOR,
  comprising the 5250 and 6302 Åspectral domains. The observations were
  analyzed using several inversion algorithms, including Milne-Eddington,
  LTE with 1 and 2 components, and MISMA codes. We find that the
  line-ratio technique applied to the 5250 Ålines is not sufficiently
  reliable to provide a direct magnetic diagnostic in the presence
  of thermal fluctuations and variable line broadening. In general,
  one needs to resort to inversion algorithms, ideally with realistic
  magneto-hydrodynamical constrains. When this is done, the 5250 Ålines
  do not seem to provide any significant advantage over those at 6302
  Å. In fact, our results point towards a better performance with the
  latter (in the presence of turbulent line broadening). In any case,
  for very weak flux concentrations, neither spectral region alone
  provides sufficient constraints to fully disentangle the intrinsic field
  strengths. Instead, we advocate for a combined analysis of both spectral
  ranges, which yields a better determination of the quiet Sun magnetic
  properties. Finally, we propose the use of two other \ion{Fe}{1} lines
  (at 4122 and 9000 Å) with identical line opacities that seem to work
  much better than the others.

---------------------------------------------------------
Title: Low-lying magnetic loops in the solar internetwork
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.;
   Solanki, S. K.
2007A&A...469L..39M    Altcode: 2007arXiv0705.1319M
  Aims:We study the structure of the magnetic field vector in the
  internetwork and search for the presence of small-scale loops. <BR
  />Methods: We invert 1.56 μm spectropolarimetric observations of
  internetwork regions at disc centre by applying the SIR code. This
  allows us to recover the atmospheric parameters that play a role in
  the formation of these spectral lines. We are mainly interested in the
  structure of the magnetic field vector. <BR />Results: We find that
  many opposite polarity elements of the internetwork are connected by
  short (2-6´´), low-lying (photospheric) loops. These loops connect
  at least the 10-20% of the internetwork flux visible in our data. Also
  we have some evidence that points towards a dynamic scenario that can
  be produced by the emergence of internetwork magnetic flux.

---------------------------------------------------------
Title: Turbulent fields in the quiet sun from Hanle and Zeeman
    effects with THEMIS
Authors: López Ariste, A.; Malherbe, J. M.; Manso Sainz, R.; Asensio
   Ramos, A.; Ramírez Vélez, J. C.; Martínez González, M.
2007sf2a.conf..596L    Altcode:
  The measurement of the Sr I line with full polarimetry and spatial
  resolution with THEMIS has provided the unexpected result of an apparent
  correlation between the Hanle effect signals and the Zeeman effect
  signals on this line. Traditionnally, Hanle effect signals in linear
  polarisation have been interpreted as the signature of unorganized,
  turbulent fields, while Zeeman effect signals -mostly in circular
  polarisation- were interpreted as structured fields. The correlation
  between both observed by THEMIS requires a change of mind respect to the
  picture of the quiet sun, with fewer structured fields and a turbulent
  field visible also in deep magnetograms. This picture is supported also
  by recent results with Mn lines with strong coupling with its hyperfine
  structure and of center-to-limb histograms of Zeeman amplitudes.

---------------------------------------------------------
Title: The Intrinsic Dimensionality of Spectropolarimetric Data
Authors: Asensio Ramos, A.; Socas-Navarro, H.; López Ariste, A.;
   Martínez González, M. J.
2007ApJ...660.1690A    Altcode: 2007astro.ph..1604A
  The amount of information available in spectropolarimetric data is
  estimated. To this end, the intrinsic dimensionality of the data is
  inferred with the aid of a recently derived estimator based on nearest
  neighbor considerations and obtained applying the principle of maximum
  likelihood. We show in detail that the estimator correctly captures the
  intrinsic dimension of artificial data sets with known dimension. The
  effect of noise in the estimated dimension is analyzed thoroughly,
  and we conclude that it introduces a positive bias that needs to be
  accounted for. Real simultaneous spectropolarimetric observations
  in the visible 630 nm and the near-infrared 1.5 μm spectral regions
  are also investigated in detail, showing that the near-infrared data
  set provides more information of the physical conditions in the solar
  atmosphere than the visible data set. Finally, we demonstrate that the
  amount of information present in an observed data set is a monotonically
  increasing function of the number of available spectral lines.

---------------------------------------------------------
Title: A Near-Infrared Line of Mn I as a Diagnostic Tool of the
    Average Magnetic Energy in the Solar Photosphere
Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste,
   A.; Trujillo Bueno, J.; Collados, M.
2007ApJ...659..829A    Altcode: 2006astro.ph.12389A
  We report on spectropolarimetric observations of a near-IR line of Mn I
  located at 15262.702 Å whose intensity and polarization profiles are
  very sensitive to the presence of hyperfine structure. A theoretical
  investigation of the magnetic sensitivity of this line uncovers several
  interesting properties. The most important one is that the presence
  of strong Paschen-Back perturbations due to the hyperfine structure
  produces an intensity line profile whose shape changes according to the
  absolute value of the magnetic field strength. A line ratio technique is
  developed from the intrinsic variations of the line profile. This line
  ratio technique is applied to spectropolarimetric observations of the
  quiet solar photosphere in order to explore the probability distribution
  function of the magnetic field strength. Particular attention is given
  to the quietest area of the observed field of view, which was encircled
  by an enhanced network region. A detailed theoretical investigation
  shows that the inferred distribution yields information on the average
  magnetic field strength and on the spatial scale at which the magnetic
  field is organized. A first estimation gives ~250 G for the mean field
  strength and a tentative value of ~0.4" for the spatial scale at which
  the observed magnetic field is horizontally organized.

---------------------------------------------------------
Title: Determination of field strengths in the quiet Sun
Authors: López Ariste, A.; Martínez González, M. J.; Ramírez
   Vélez, J. C.
2007A&A...464..351L    Altcode:
  The magnetism in the quiet regions of the solar photosphere carries
  information on the dynamo processes and its interaction with the
  convection of the outer layers of the sun. Unfortunately, the scales
  of the magnetic structures on these regions are mostly unresolved. It
  is therefore instrumental to tell apart the intrinsic field strengths
  in those regions from the flux through the resolution element. This
  disentanglement has been far from obvious, leading to opposing views
  of the magnetic topology in the unresolved structures of the quiet
  Sun. Our study contributes to the disentanglement of field strength from
  flux in the quiet Sun, at least, through the use of new observational
  constrains in the form of spectropolarimetry of Mn i lines observed
  in the solar spectrum.The chosen Mn lines present a strong coupling
  with hyperfine structure resulting in spectral features, present or
  absent as a function of field strength alone. We observe one of those
  lines simultaneously and co-spatially with the Fe i lines at 630 nm,
  at the core of the previous measurements.The inversion of the observed
  Fe lines results in either strong or weak fields depending on the
  initializations of the inversion algorithm. All the solutions show
  nevertheless equally good values for the σ parameter and are therefore
  equally valuable as solutions. The Mn however selects unambiguously
  strong or weak fields, sometimes agreeing with the inversions of the Fe
  lines, but half the time disagreeing with them.The Fe i lines at 630 nm,
  in the conditions found in the quiet Sun, carry no binding information
  on field strength. A proper analysis of quiet Sun magnetism should
  necessarily pass through its simultaneous and co-spatial observation
  with other lines imposing constraints on field strength, as the Mn i
  lines here analyzed. Ultimately, the magnetic topology of the quiet Sun
  shall arise from the coherent analysis of all these lines, sensitive
  to the Zeeman effect.

---------------------------------------------------------
Title: Internetwork magnetic fields observed in the visible.
Authors: Martínez González, M. J.
2007MmSAI..78...59M    Altcode:
  We present internetwork quiet Sun spectropolarimetric observations taken
  simultaneously at the Fe I lines at 630 and 525 nm. The magnetometry
  at 630 nm in these low flux regions of the Sun's photosphere has been
  put in doubt by a recent work. The 525 nm lines are supposed to give
  reliable results concerning the magnetic field strength in regions where
  the magnetic structures are not resolved. We study the compatibility
  of the results obtained in both spectral ranges to confirm or deny the
  affirmation that the 630 nm lines are not valid for recovering the
  magnetic field strength at the internetwork quiet Sun. We conclude
  that both the 630 nm and the 525 nm pair of lines give no trustable
  results concerning the magnetic field strength. However, the magnetic
  flux density is correctly recovered from both spectral ranges.

---------------------------------------------------------
Title: Internetwork magnetic fields
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.
2007msfa.conf..157M    Altcode:
  Spectropolarimetric observations of the internetwork obtained in the
  1.56 [mμ]m Fe I doublet are used to calculate the distributions of
  magnetic field strength, filling factor and magnetic flux density
  at different positions on the solar surface. We go one step further
  and describe what the observations show about the three-dimensional
  structure of the magnetic fields at the internetwork quiet Sun.

---------------------------------------------------------
Title: Internetwork Magnetic Field Distribution from Simultaneous
    Fe I 1.5 µ and Fe I 630 nm Observations
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.
2006ASPC..358...36M    Altcode:
  We took simultaneous observations in Fe I 1.5 µ and Fe I 630 nm of
  an internetwork region. We discuss the compatibility of the data in
  the two spectral ranges, and present results for the magnetic field
  distribution. We show that the larger contribution comes from hG
  field strengths.

---------------------------------------------------------
Title: On the validity of the 630 nm Fe I lines for magnetometry of
    the internetwork quiet Sun
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.
2006A&A...456.1159M    Altcode: 2006astro.ph..5446M
  Aims.The purpose of this work is to analyze the reliability of the
  magnetic field strengths inferred from the 630 nm pair of Fe i lines
  in internetwork quiet Sun regions.<BR /> Methods: .Some numerical
  experiments have been performed that demonstrate the inability
  of these lines to recover the magnetic field strength in such low
  flux solar regions.<BR /> Results: .It is shown how different model
  atmospheres, with magnetic field strengths ranging from a few hundred
  Gauss to kiloGauss, give rise to Stokes profiles that cannot be
  distinguished. The reasons for this degeneracy are discussed.<BR />

---------------------------------------------------------
Title: Campos magnéticos en el Sol en calma 

---------------------------------------------------------
Title: Campos magnéticos
en el Sol en calma 

---------------------------------------------------------
Title: Magnetic fields in the quiet sun;
Authors: Martínez González, María Jesús
2006PhDT.......335M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Magnetic flux in the internetwork quiet Sun
Authors: Khomenko, E. V.; Martínez González, M. J.; Collados, M.;
   Vögler, A.; Solanki, S. K.; Ruiz Cobo, B.; Beck, C.
2005A&A...436L..27K    Altcode:
  We report a direct comparison of the amplitudes of Stokes spectra of the
  Fe i 630 nm and 1.56 μm lines produced by realistic MHD simulations
  with simultaneous observations in the same spectral regions. The
  Stokes spectra were synthesized in snapshots with a mixed polarity
  magnetic field having a spatially averaged strength, &lt; B &gt;,
  between 10 and 30 G. The distribution of Stokes V amplitudes depends
  sensitively on &lt; B &gt;. A quiet inter-network region was observed
  at the German VTT simultaneously with TIP (1.56 μm) and POLIS (630
  nm). We find that the Stokes V amplitudes of both infrared and visible
  observations are best reproduced by the simulation snapshot with &lt;
  B &gt; = 20 G. In observations with 1 resolution, up to 2/3 of the
  magnetic flux can remain undetected.

---------------------------------------------------------
Title: Modeling the photometric and dynamical behavior of
    Super-Schmidt meteors in the Earth's atmosphere
Authors: Bellot Rubio, L. R.; Martínez González, M. J.; Ruiz
   Herrera, L.; Licandro, J.; Martínez-Delgado, D.; Rodríguez-Gil,
   P.; Serra-Ricart, M.
2002A&A...389..680B    Altcode:
  Faint meteors observed with Super-Schmidt cameras are re-examined
  in order to assess whether their dynamical and photometric behavior
  can be described by means of the single body theory. Velocities,
  decelerations and magnitudes are fitted simultaneously to synthetic
  curves resulting from integration of the appropriate set of differential
  equations. The parameters determined by this procedure are the ablation
  coefficient, the shape-density coefficient and the preatmospheric
  mass of each individual meteoroid. It turns out that 73% of the
  meteors analyzed here (with magnitudes in the range from +2.5 to -5)
  are reasonably well described by this theory, suggesting that they
  did not undergo significant fragmentation during their atmospheric
  flight. Nevertheless, we identify some systematic differences between
  observed and theoretical light curves of meteors for which the fit
  is good. Meteoroid bulk densities are estimated from the retrieved
  shape-density coefficients. The distributions of individual values
  are broad, indicating that objects of different densities coexist
  within the same meteoroid population. The average density is found to
  be 2400, 1400, and 400 kg m<SUP>-3</SUP> for A-type, B-type and C-type
  meteoroids, respectively. These results do not confirm the large values
  determined from quasicontinuous fragmentation models.

---------------------------------------------------------
Title: Modeling the dynamical and photometric behavior of faint
    meteors in the Earth's atmosphere
Authors: Bellot Rubio, Luis R.; Martínez González, María Jesús;
   Ruiz Herrera, Lola; Licandro, Javier; Martínez Delgado, David;
   Rodríguez Gil, Pablo; Serra-Ricart, Miquel
2001ESASP.495..525B    Altcode: 2001mete.conf..525B
  Faint meteors observed with Super-Schmidt cameras are re-examined
  in order to assess whether their dynamical and photometric behavior
  can be described by means of the single body theory. Velocities,
  decelerations and magnitudes are fitted simultaneously to synthetic
  curves resulting from integration of the appropriate set of differential
  equations. The parameters determined by this procedure are the ablation
  coefficient, the shape-density coefficient and the preatmospheric mass
  of the meteoroids. It turns out that 64% of the meteors analyzed here
  are reasonably well described by this theory, suggesting that they
  did not undergo significant fragmentation during their atmospheric
  flight. We identify some systematic differences between observed and
  theoretical light curves of meteors for which the fit is good. From
  the retrieved shape-density coefficients we derive meteoroid bulk
  densities. The average density turns out to be 1.0 g cm<SUP>-3</SUP>,
  with individual values ranging from 0.2 g cm<SUP>-3</SUP> to 1.4 g
  cm<SUP>-3</SUP>. This work represent a first step toward the analysis
  of low-light level video observations of very small meteoroids.