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Author name code: guerreiro
ADS astronomy entries on 2022-09-14
author:"Guerreiro, Nuno" 

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Title: Hanle rotation signatures in Sr I 4607 Å
Authors: Zeuner, F.; Belluzzi, L.; Guerreiro, N.; Ramelli, R.;
   Bianda, M.
2022A&A...662A..46Z    Altcode: 2022arXiv220208659Z
  Context. Measuring small-scale magnetic fields and constraining
  their role in energy transport and dynamics in the solar atmosphere
  are crucial, albeit challenging, tasks in solar physics. To this aim,
  observations of scattering polarization and the Hanle effect in various
  spectral lines are increasingly used to complement traditional magnetic
  field determination techniques. <BR /> Aims: One of the strongest
  scattering polarization signals in the photosphere is measured in the
  Sr I line at 4607.3 Å when observed close to the solar limb. Here,
  we present the first observational evidence of Hanle rotation in the
  linearly polarized spectrum of this line at several limb distances. <BR
  /> Methods: We used the Zurich IMaging POLarimeter, ZIMPOL at the
  IRSOL observatory, with exceptionally good seeing conditions and long
  integration times. We combined the fast-modulating polarimeter with a
  slow modulator installed in front of the telescope. This combination
  allows for a high level of precision and unprecedented accuracy in
  the measurement of spectropolarimetric data. <BR /> Results: Fixing
  the reference direction for positive Stokes Q parallel to the limb,
  we detected singly peaked U/I signals well above the noise level. We
  can exclude any instrumental origins for such U/I signals. These
  signatures are exclusively found in the Sr I line, but not in the
  adjoining Fe I line, therefore eliminating the Zeeman effect as the
  mechanism responsible for their appearance. However, we find a clear
  spatial correlation between the circular polarization produced by the
  Zeeman effect and the U/I amplitudes. This suggests that the detected
  U/I signals are the signatures of Hanle rotation caused by a spatially
  resolved magnetic field. <BR /> Conclusions: A novel measurement
  technique allows for determining the absolute level of polarization
  with unprecedented precision. Using this technique, high-precision
  spectropolarimetric observations reveal, for the first time, unambiguous
  U/I signals attributed to Hanle rotation in the Sr I line.

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Title: Modeling the scattering polarization of the solar Ca I 4227
    Å line with angle-dependent partial frequency redistribution
Authors: Janett, Gioele; Ballester, Ernest Alsina; Guerreiro, Nuno;
   Riva, Simone; Belluzzi, Luca; del Pino Alemán, Tanausú; Bueno,
   Javier Trujillo
2021A&A...655A..13J    Altcode: 2021arXiv211011990J
  Context. The correct modeling of the scattering polarization signals
  observed in several strong resonance lines requires taking partial
  frequency redistribution (PRD) phenomena into account. Modeling
  scattering polarization with PRD effects is very computationally
  demanding and the simplifying angle-averaged (AA) approximation is
  therefore commonly applied. <BR /> Aims: This work aims to assess the
  impact and the range of validity of the AA approximation with respect
  to the general angle-dependent (AD) treatment of PRD effects in the
  modeling of scattering polarization in strong resonance lines, with a
  focus on the solar Ca I 4227 Å line. <BR /> Methods: Spectral line
  polarization was modeled by solving the radiative transfer problem
  for polarized radiation, under nonlocal thermodynamic equilibrium
  conditions, taking PRD effects into account in static one-dimensional
  semi-empirical atmospheric models presenting arbitrary magnetic
  fields. The problem was solved through a two-step approach. In step 1,
  the problem was solved for the intensity only, considering a multilevel
  atom. In step 2, the problem was solved including polarization,
  considering a two-level atom with an unpolarized and infinitely sharp
  lower level, and fixing the lower level population calculated at
  step 1. <BR /> Results: The results for the Ca I 4227 Å line show
  a good agreement between the AA and AD calculations for the Q/I and
  U/I wings' signals. However, AA calculations reveal an artificial
  trough in the line-core peak of the linear polarization profiles,
  whereas AD calculations show a sharper peak in agreement with the
  observations. <BR /> Conclusions: An AD treatment of PRD effects is
  essential to correctly model the line-core peak of the scattering
  polarization signal of the Ca I 4227 Å line. By contrast, in the
  considered static case, the AA approximation seems to be suitable
  to model the wing scattering polarization lobes and their magnetic
  sensitivity through magneto-optical effects.

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Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
    Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
   W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
   R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
   Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
   V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
   M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
   S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
   Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
   Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
   Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
   A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
   Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
   Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
   K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
   Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
   Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
   S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
   Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
   S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
   F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
   Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
   Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
   Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
   Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
   K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
   S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
   K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
   Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
   Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
   Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
2020A&A...642A...8R    Altcode:
  Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
  sensing instrument package of the ESA/NASA Solar Orbiter mission
  that will explore the inner heliosphere and observe the Sun from
  vantage points close to the Sun and out of the ecliptic. Solar Orbiter
  will advance the "connection science" between solar activity and the
  heliosphere. <BR /> Aims: With EUI we aim to improve our understanding
  of the structure and dynamics of the solar atmosphere, globally as well
  as at high resolution, and from high solar latitude perspectives. <BR />
  Methods: The EUI consists of three telescopes, the Full Sun Imager and
  two High Resolution Imagers, which are optimised to image in Lyman-α
  and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
  up to corona. The EUI is designed to cope with the strong constraints
  imposed by the Solar Orbiter mission characteristics. Limited telemetry
  availability is compensated by state-of-the-art image compression,
  onboard image processing, and event selection. The imposed power
  limitations and potentially harsh radiation environment necessitate
  the use of novel CMOS sensors. As the unobstructed field of view of
  the telescopes needs to protrude through the spacecraft's heat shield,
  the apertures have been kept as small as possible, without compromising
  optical performance. This led to a systematic effort to optimise the
  throughput of every optical element and the reduction of noise levels
  in the sensor. <BR /> Results: In this paper we review the design
  of the two elements of the EUI instrument: the Optical Bench System
  and the Common Electronic Box. Particular attention is also given to
  the onboard software, the intended operations, the ground software,
  and the foreseen data products. <BR /> Conclusions: The EUI will
  bring unique science opportunities thanks to its specific design,
  its viewpoint, and to the planned synergies with the other Solar
  Orbiter instruments. In particular, we highlight science opportunities
  brought by the out-of-ecliptic vantage point of the solar poles,
  the high-resolution imaging of the high chromosphere and corona,
  and the connection to the outer corona as observed by coronagraphs.

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Title: Small-scale heating events in the solar atmosphere: lifetime,
    total energy and magnetic properties
Authors: Guerreiro, Nuno; Haberreiter, Margit; Hansteen, Viggo;
   Schmutz, Werner
2018EGUGA..2014516G    Altcode:
  Small-scale heating events (SSHEs) are believed to play a fundamental
  role in the heating of the solar corona, the pervading redshifts in
  the transition region, and the acceleration of spicules. We present
  a method to identify and track SSHEs over their lifetime and apply
  it to two simulation models. We identify the locations where the
  energy dissipation is maximum inside the SSHEs volume and we trace the
  SSHEs by following the spatial and temporal evolution of the maximum
  energy dissipation inside the SSHEs volume. The method is effective
  in following the SSHE and allows us to determine their lifetime,
  total energy and properties of the plasma as well as the magnetic
  field orientation in the vicinity of the SSHEs. We conclude that
  the SSHEs that have the potential to heat the corona live less than
  4 minutes. Moreover, the typically energy release ranges from 1020
  erg to 1024 erg. In addition, the directional change of the magnetic
  field lines on both sides of the current sheet constituting the SSHEs
  at the time of the absolute maximum energy dissipation ranges from 5
  to 15 degree. This work is very relevant for the interpretation and
  the potential observational evidence of the SSHEs from upcoming data
  from the Spectral Imaging of the Coronal Environment instrument (SPICE)
  and the Extreme UV imager (EUI) onboard the Solar Orbiter Mission.

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Title: Small-scale heating events in the solar
    atmosphere. II. Lifetime, total energy, and magnetic properties
Authors: Guerreiro, N.; Haberreiter, M.; Hansteen, V.; Schmutz, W.
2017A&A...603A.103G    Altcode:
  Context. Small-scale heating events (SSHEs) are believed to play a
  fundamental role in understanding the process responsible for heating
  of the solar corona, the pervading redshifts in the transition region,
  and the acceleration of spicules. <BR /> Aims: We determine the
  properties of the SSHEs and the atmospheric response to them in 3D
  magnetohydrodynamics (3D-MHD) simulations of the solar atmosphere. <BR
  /> Methods: We developed a method for identifying and following
  SSHEs over their lifetime, and applied it to two simulation models. We
  identified the locations where the energy dissipation is greatest inside
  the SSHEs volume, and we traced the SSHEs by following the spatial
  and temporal evolution of the maximum energy dissipation inside the
  SSHEs volume. <BR /> Results: The method is effective in following the
  SSHEs. We can determine their lifetime, total energy, and properties of
  the plasma, as well as the magnetic field orientation in the vicinity
  of the SSHEs. <BR /> Conclusions: We determine that the SSHEs that have
  the potential to heat the corona live less than 4 min, and typically
  the energy they release ranges from 10<SUP>20</SUP> to 10<SUP>24</SUP>
  erg. In addition, the directional change of the field lines on the two
  sides of the current sheet constituting the SSHEs ranges from 5° to
  15° at the moment of the absolute maximum energy dissipation.

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Title: Lower solar atmosphere and magnetism at ultra-high spatial
    resolution
Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian,
   Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira,
   Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven
2016arXiv161202348C    Altcode:
  We present the scientific case for a future space-based telescope
  aimed at very high spatial and temporal resolution imaging of the
  solar photosphere and chromosphere. Previous missions (e.g., HINODE,
  SUNRISE) have demonstrated the power of observing the solar photosphere
  and chromosphere at high spatial resolution without contamination from
  Earth's atmosphere. We argue here that increased spatial resolution
  (from currently 70 km to 25 km in the future) and high temporal cadence
  of the observations will vastly improve our understanding of the
  physical processes controlling solar magnetism and its characteristic
  scales. This is particularly important as the Sun's magnetic field
  drives solar activity and can significantly influence the Sun-Earth
  system. At the same time a better knowledge of solar magnetism can
  greatly improve our understanding of other astrophysical objects.

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Title: Detection and characterization of small-scale heating events
    in the solar atmosphere from 3D-MHD simulations and their potential
    role in coronal heating
Authors: Guerreiro, Nuno; Haberreiter, Margit; Schmutz, Werner;
   Hansteen, Viggo
2016cosp...41E.750G    Altcode:
  Aiming at better understanding the mechanism(s) responsible for the
  coronal heating we focus on analyzing the properties of the magnetically
  generated small-scale heating events (SSHEs) in the solar atmosphere. We
  present a comprehensive method to detect and follow SSHEs over time
  in 3D-MHD simulations of the solar atmosphere. Applying the method
  we are able to better understand the properties of the SSHEs and how
  the plasma in their vicinity respond to them. We study the lifetime,
  energy and spectral signatures and show that the energy flux dissipated
  by them is enough to heat the corona. Ultimately, these results will
  be important for the coordinated scientific exploration of SPICE and
  EUI along with other instruments on board solar orbiter.

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Title: Characterization of small-scale heating events in the solar
    atmosphere from 3D-MHD simulations and their potential role in
    coronal heating
Authors: Guerreiro, Nuno; Haberreiter, Margit; Hansteen, Viggo;
   Schmutz, Werner
2016EGUGA..1814407G    Altcode:
  Aiming at better understanding the mechanism(s) responsible for
  the coronal heating and the ubiquitous redshifts observed in the
  lower transition region we focus on analyzing the properties of
  small-scale heating events (SSHEs) in the solar atmosphere. We present
  a comprehensive method to follow SSHEs over time in 3D-MHD simulations
  of the solar atmosphere. Applying the method we are able to better
  understand the properties of the SSHEs and how the plasma in their
  vicinity respond to them. We present results for the lifetime, energy
  and spectral signatures of the SSHEs. Ultimately, these results will
  be important for the coordinated scientific exploration of SPICE and
  EUI along with other interments on board solar orbiter. ​

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Title: Characterisation of small-scale heating events in the solar
    atmosphere from 3D MHD simulations and their potential role in
    coronal heating
Authors: Haberreiter, M.; Guerreiro, N.; Hansteen, V. H.; Schmutz,
   W. K.
2015AGUFMSH31C2442H    Altcode:
  The physical mechanism that heats the solar corona is one of the still
  open science questions in solar physics. One of the proposed mechanism
  for coronal heating are nanoflares. To investigate their role in coronal
  heating we study the properties of the small-scale heating events in
  the solar atmosphere using 3D MHD simulations. We present a method
  to identify and track these heating events in time which allows us to
  study their life time, energy, and spectral signatures. These spectal
  signatures will be compared with available spectrosopic observations
  obtained with IRIS and SUMER. Ultimately, these results will be
  important for the coordinated scientific exploitation of SPICE and
  EUI along with other instruments onboard Solar Orbiter to address the
  coronal heating problem.

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Title: Small-scale Heating Events in the Solar
    Atmosphere. I. Identification, Selection, and Implications for
    Coronal Heating
Authors: Guerreiro, N.; Haberreiter, M.; Hansteen, V.; Schmutz, W.
2015ApJ...813...61G    Altcode:
  We present a comprehensive method to analyze small-scale heating
  events in detail in a 3D magnetohydrodynamics simulation for quiet-Sun
  conditions. The method determines the number, volume, and some general
  geometric properties of the small-scale heating events at different
  instants in a simulation with a volume of 16 × 8 × 16 Mm<SUP>3</SUP>,
  spanning from the top of the convection zone to the corona. We found
  that there are about 10<SUP>4</SUP> small-scale heating events at
  any instant above the simulated area of 128 Mm<SUP>2</SUP>. They
  occur mainly at heights between 1.5 and 3.0 Mm. We determine the
  average value of their projected vertical extent, which ranges from
  375 to 519 km over time, and we show that height, volume, and energy
  distribution of the events at any instant resemble power laws. Finally,
  we demonstrate that larger heating structures are a combination of much
  smaller heating events and that small-scale heating events dissipate
  enough energy to maintain the coronal energetic balance at any instant.

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Title: Numerical Simulations of Coronal Heating through Footpoint
    Braiding
Authors: Hansteen, V.; Guerreiro, N.; De Pontieu, B.; Carlsson, M.
2015ApJ...811..106H    Altcode: 2015arXiv150807234H
  Advanced three-dimensional (3D) radiative MHD simulations now reproduce
  many properties of the outer solar atmosphere. When including a domain
  from the convection zone into the corona, a hot chromosphere and corona
  are self-consistently maintained. Here we study two realistic models,
  with different simulated areas, magnetic field strength and topology,
  and numerical resolution. These are compared in order to characterize
  the heating in the 3D-MHD simulations which self-consistently
  maintains the structure of the atmosphere. We analyze the heating
  at both large and small scales and find that heating is episodic and
  highly structured in space, but occurs along loop-shaped structures,
  and moves along with the magnetic field. On large scales we find that
  the heating per particle is maximal near the transition region and that
  widely distributed opposite-polarity field in the photosphere leads
  to a greater heating scale height in the corona. On smaller scales,
  heating is concentrated in current sheets, the thicknesses of which are
  set by the numerical resolution. Some current sheets fragment in time,
  this process occurring more readily in the higher-resolution model
  leading to spatially highly intermittent heating. The large-scale
  heating structures are found to fade in less than about five minutes,
  while the smaller, local, heating shows timescales of the order of two
  minutes in one model and one minutes in the other, higher-resolution,
  model.

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Title: Identification and characterization of small-scale heating
    events in the solar atmosphere from 3D MHD simulations
Authors: Guerreiro, Nuno; Haberreiter, Margit; Schmutz, Werner;
   Hansteen, Viggo
2014cosp...40E1095G    Altcode:
  We studied the properties of small scale heating events (in the nano
  and micro-flare regime) in the solar atmosphere using existing 3D
  MHD simulations. We put forward a method for event identification
  and categorization. We determine the spatial extend of the events
  and their frequency and energy distributions. These results aim at
  improving the understanding of small scale heating events and their
  role for the heating of the solar corona.

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Title: The Cycling of Material between the Solar Corona and
    Chromosphere
Authors: Guerreiro, N.; Hansteen, Viggo; De Pontieu, B.
2013ApJ...769...47G    Altcode:
  Observations of transition region emission lines reveal the presence
  of redshifts in lines formed from the top of the chromosphere up
  to temperatures of about 2.5 × 10<SUP>5</SUP> K and blueshifts for
  temperatures above that. However, it is doubtful that the apparent large
  downward flows in the lower transition region represents an emptying of
  the corona, so some mechanism must be responsible for maintaining the
  mass balance between the corona and the lower atmospheric layers. We use
  a three-dimensional magnetohydrodynamics code to study the cycling of
  mass between the corona, transition region, and chromosphere by adding
  a tracer fluid to the simulation in various temperature intervals in the
  transition region. We find that most of the material seen in transition
  region emission lines formed at temperatures below 3 × 10<SUP>5</SUP> K
  is material that has been rapidly heated from chromospheric temperatures
  and thereafter is pushed down as it cools. This implies that the bulk
  of transition region material resides in small loops. In these loops,
  the density is high and radiative cooling is efficient.

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Title: Numerical Simulations of Spicule Acceleration
Authors: Guerreiro, N.; Carlsson, M.; Hansteen, V.
2013ApJ...766..128G    Altcode:
  Observations in the Hα line of hydrogen and the H and K lines of singly
  ionized calcium on the solar limb reveal the existence of structures
  with jet-like behavior, usually designated as spicules. The driving
  mechanism for such structures remains poorly understood. Sterling
  et al. shed some light on the problem mimicking reconnection events
  in the chromosphere with a one-dimensional code by injecting energy
  with different spatial and temporal distributions and tracing the
  thermodynamic evolution of the upper chromospheric plasma. They found
  three different classes of jets resulting from these injections. We
  follow their approach but improve the physical description by including
  non-LTE cooling in strong spectral lines and non-equilibrium hydrogen
  ionization. Increased cooling and conversion of injected energy into
  hydrogen ionization energy instead of thermal energy both lead to weaker
  jets and smaller final extent of the spicules compared with Sterling
  et al. In our simulations we find different behavior depending on
  the timescale for hydrogen ionization/recombination. Radiation-driven
  ionization fronts also form.

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Title: Spicules, mass flows and heating in the upper solar atmosphere
Authors: Guerreiro, Nuno Miguel Rodrigues
2013PhDT.......368G    Altcode:
  No abstract at ADS

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Title: Dark matter from cosmic defects on galactic scales?
Authors: Guerreiro, N.; Avelino, P. P.; de Carvalho, J. P. M.; Martins,
   C. J. A. P.
2008PhRvD..78f7302G    Altcode: 2008arXiv0807.4373G
  We discuss the possible dynamical role of extended cosmic defects on
  galactic scales, specifically focusing on the possibility that they may
  provide the dark matter suggested by the classical problem of galactic
  rotation curves. We emphasize that the more standard defects (such as
  Goto-Nambu strings) are unsuitable for this task but show that more
  general models (such as transonic wiggly strings) could in principle
  have a better chance. In any case, we show that observational data
  severely restricts any such scenarios.