Author name code: gafeira
ADS astronomy entries on 2022-09-14
author:"Gafeira, Ricardo" 
------------------------------------------------------------------------  

Title: Magnetic properties of short-lived penumbral microjets
Authors: Tapia, Azaymi Siu; Bellot Rubio, L. R.; Gafeira, Ricardo;
   Orozco Suárez, David
Bibcode: 2022cosp...44.2520T
Altcode:
  Penumbral microjets (PMJs) are fast elongated brightenings above
  sunspots penumbrae. They are presumed to be related to photospheric
  magnetic reconnection processes and contribute to the heating of the
  plasma in the higher atmospheric layers. Studying the spectral and
  polarization properties of the shortest-living microjets requires
  the fastest temporal cadence possible and is currently a challenging
  task. In this work, we use fast spectropolarimetric measurements of
  the Ca II 8542 A line made with the CRISP instrument at the Swedish
  1 m Solar Telescope, and exploit the diagnostic capabilities of this
  line to retrieve the magnetic field configuration and its evolution
  at different atmospheric heights during PMJs. Our findings show that
  short-lived PMJs are associated with a transient perturbation in
  the photospheric magnetic field and sometimes they show clear but
  weaker changes in the chromospheric field as well. We will describe
  the different types of evolution that were identified. These results
  support the idea that PMJs may be the result of magnetic reconnection
  at low altitudes in sunspot penumbra.

Title: Exploring dynamic, small-scale quiet Sun magnetism at high
    S/N with the GREGOR/GRIS-IFU
Authors: Campbell, Ryan; Collados, Manuel; Quintero Noda, Carlos;
   Mathioudakis, Mihalis; Gafeira, Ricardo
Bibcode: 2022cosp...44.2510C
Altcode:
  We have taken advantage of the improvements to GREGOR (Kleint et
  al. 2020, A&amp;A, 641, A27), Europe's largest solar telescope,
  to reveal small-scale magnetism at the solar internetwork (IN) in
  unprecedented detail. The observations were carried out at solar disk
  centre with the highly magnetically sensitive Fe I line at 1565nm. Our
  observations suggest that GREGOR's overhaul has helped achieve a
  higher effective spatial resolution while our synthetic profiles
  produced from MHD simulations suggests this data have been obtained
  at the telescope diffraction limit in the near infrared. By observing
  with high signal-to-noise (S/N), and exceptional seeing conditions, we
  reveal that as much as 35% of the IN shows linear polarisation signal
  at the 5$\sigma$ level, the highest fraction of linear polarization
  ever recorded in the quiet Sun IN, while as much as 70% shows circular
  polarization. We use the Stokes inversion based on response functions
  (SIR) inversion code to retrieve the thermodynamic, kinematic and
  magnetic properties of the atmosphere. We statistically compare our
  results to previous GRIS-IFU observations (Campbell et al. 2021,
  647, A182) obtained in 2019, prior to GREGOR's overhaul, focusing on
  controversies surrounding the impact of noise on the retrieval of the
  magnetic inclination angle. We employ the new open-source SIR Explorer
  (SIRE) application to easily and efficiently study several dynamic,
  small-scale magnetic features. We see evidence for weak transverse
  and complex small-scale 'loop-like' structures, with transverse fields
  flanked between opposite polarity longitudinal fields. In the last part
  of the presentation, SIRE will be demonstrated live for the audience.

Title: DeSIRe: Departure coefficient aided Stokes Inversion based
    on Response functions
Authors: Ruiz Cobo, B.; Quintero Noda, C.; Gafeira, R.; Uitenbroek,
   H.; Orozco Suárez, D.; Páez Mañá, E.
Bibcode: 2022A&A...660A..37R
Altcode: 2022arXiv220202226R
  Future ground-based telescopes, such as the 4-metre class facilities
  DKIST and EST, will dramatically improve on current capabilities for
  simultaneous multi-line polarimetric observations in a wide range of
  wavelength bands, from the near-ultraviolet to the near-infrared. As a
  result, there will be an increasing demand for fast diagnostic tools,
  i.e., inversion codes, that can infer the physical properties of the
  solar atmosphere from the vast amount of data these observatories
  will produce. The advent of substantially larger apertures,
  with the concomitant increase in polarimetric sensitivity, will
  drive an increased interest in observing chromospheric spectral
  lines. Accordingly, pertinent inversion codes will need to take
  account of line formation under general non-local thermodynamic
  equilibrium (NLTE) conditions. Several currently available codes can
  already accomplish this, but they have a common practical limitation
  that impairs the speed at which they can invert polarised spectra,
  namely that they employ numerical evaluation of the so-called response
  functions to changes in the atmospheric parameters, which makes them
  less suitable for the analysis of very large data volumes. Here we
  present DeSIRe (Departure coefficient aided Stokes Inversion based on
  Response functions), an inversion code that integrates the well-known
  inversion code SIR with the NLTE radiative transfer solver RH. The
  DeSIRe runtime benefits from employing analytical response functions
  computed in local thermodynamic equilibrium (through SIR), modified
  with fixed departure coefficients to incorporate NLTE effects in
  chromospheric spectral lines. This publication describes the operating
  fundamentals of DeSIRe and describes its behaviour, robustness,
  stability, and speed. The code is ready to be used by the solar
  community and is being made publicly available.

Title: Testing the Accuracy of Coimbra Astronomical Observatory
    Solar Filament Historical Series (1929-1941)
Authors: Lourenço, Ana; Gafeira, Ricardo; Bonifácio, Vitor; Barata,
   Teresa; Fernandes, João; Silva, Eva
Bibcode: 2021SoPh..296..155L
Altcode: 2021arXiv210805978L
  The present work aims to validate the positions of solar filaments
  published in the Annals of Coimbra University Astronomical Observatory,
  currently the Geophysical and Astronomical Observatory of the
  University of Coimbra, corresponding to years 1929 to 1941. The
  published Stonyhurst positions were obtained by an original method
  devised in the early 20th century that used a spherical calculator
  instrument, a wood-made model of the Sun. We used the digital images
  of the original spectroheliograms to measure the positions of the
  filaments, and heliographic coordinates were determined with the
  routines implemented in the Python package Sunpy. The correlation
  coefficients between both sets of coordinates are positive and highly
  significant. The results validate the method used at the Coimbra
  observatory and the published data. We conclude that the Coimbra solar
  filament catalogues are reliable and can therefore be considered for
  future solar activity studies.

Title: Diagnostic capabilities of spectropolarimetric observations for
    understanding solar phenomena. I. Zeeman-sensitive photospheric lines
Authors: Quintero Noda, C.; Barklem, P. S.; Gafeira, R.; Ruiz Cobo,
   B.; Collados, M.; Carlsson, M.; Martínez Pillet, V.; Orozco Suárez,
   D.; Uitenbroek, H.; Katsukawa, Y.
Bibcode: 2021A&A...652A.161Q
Altcode: 2021arXiv210605084Q
  Future ground-based telescopes will expand our capabilities for
  simultaneous multi-line polarimetric observations in a wide range of
  wavelengths, from the near-ultraviolet to the near-infrared. This
  creates a strong demand to compare candidate spectral lines to
  establish a guideline of the lines that are most appropriate for each
  observation target. We focused in this first work on Zeeman-sensitive
  photospheric lines in the visible and infrared. We first examined their
  polarisation signals and response functions using a 1D semi-empirical
  atmosphere. Then we studied the spatial distribution of the line core
  intensity and linear and circular polarisation signals using a realistic
  3D numerical simulation. We ran inversions of synthetic profiles, and
  we compared the heights at which we obtain a high correlation between
  the input and the inferred atmosphere. We also used this opportunity
  to revisit the atomic information we have on these lines and computed
  the broadening cross-sections due to collisions with neutral hydrogen
  atoms for all the studied spectral lines. The results reveal that
  four spectral lines stand out from the rest for quiet-Sun and network
  conditions: Fe I 5250.2, 6302, 8468, and 15 648 Å. The first three
  form higher in the atmosphere, and the last line is mainly sensitive to
  the atmospheric parameters at the bottom of the photosphere. However,
  as they reach different heights, we strongly recommend using at least
  one of the first three candidates together with the Fe I 15 648 Å line
  to optimise our capabilities for inferring the thermal and magnetic
  properties of the lower atmosphere.

Title: Machine learning initialization to accelerate Stokes profile
    inversions
Authors: Gafeira, R.; Orozco Suárez, D.; Milić, I.; Quintero Noda,
   C.; Ruiz Cobo, B.; Uitenbroek, H.
Bibcode: 2021A&A...651A..31G
Altcode: 2021arXiv210309651G
  Context. At present, an exponential growth in scientific data
  from current and upcoming solar observatories is expected. Most of
  the data consist of high spatial and temporal resolution cubes of
  Stokes profiles taken in both local thermodynamic equilibrium (LTE)
  and non-LTE spectral lines. The analysis of such solar observations
  requires complex inversion codes. Hence, it is necessary to develop
  new tools to boost the speed and efficiency of inversions and reduce
  computation times and costs. <BR /> Aims: In this work we discuss
  the application of convolutional neural networks (CNNs) as a tool to
  advantageously initialize Stokes profile inversions. <BR /> Methods:
  To demonstrate the usefulness of CNNs, we concentrate in this paper on
  the inversion of LTE Stokes profiles. We use observations taken with
  the spectropolarimeter on board the Hinode spacecraft as a test bench
  mark. First, we carefully analyse the data with the SIR inversion code
  using a given initial atmospheric model. The code provides a set of
  atmospheric models that reproduce the observations well. These models
  are then used to train a CNN. Afterwards, the same data are again
  inverted with SIR but using the trained CNN to provide the initial
  guess atmospheric models for SIR. <BR /> Results: The CNNs allow us
  to significantly reduce the number of inversion cycles when used to
  compute initial guess model atmospheres (`assisted inversions'),
  therefore decreasing the computational time for LTE inversions by
  a factor of two to four. CNNs alone are much faster than assisted
  inversions, but the latter are more robust and accurate. CNNs also
  help to automatically cluster pixels with similar physical properties,
  allowing the association with different solar features on the solar
  surface, which is useful when inverting huge datasets where completely
  different regimes are present. The advantages and limitations of machine
  learning techniques for estimating optimum initial atmospheric models
  for spectral line inversions are discussed. Finally, we describe a
  python wrapper for the SIR and DeSIRe codes that allows for the easy
  setup of parallel inversions. The tool implements the assisted inversion
  method described in this paper. The parallel wrapper can also be used
  to synthesize Stokes profiles with the RH code. <BR /> Conclusions:
  The assisted inversions can speed up the inversion process, but the
  efficiency and accuracy of the inversion results depend strongly on
  the solar scene and the data used for the CNN training. This method
  (assisted inversions) will not obviate the need for analysing individual
  events with the utmost care but will provide solar scientists with
  a much better opportunity to sample large amounts of inverted data,
  which will undoubtedly broaden the physical discovery space.

Title: 3D Solar Coronal Loop Reconstructions with Machine Learning
Authors: Chifu, Iulia; Gafeira, Ricardo
Bibcode: 2021ApJ...910L..10C
Altcode: 2021arXiv210309960C
  The magnetic field plays an essential role in the initiation and
  evolution of different solar phenomena in the corona. The structure
  and evolution of the 3D coronal magnetic field are still not very
  well known. A way to ascertain the 3D structure of the coronal
  magnetic field is by performing magnetic field extrapolations from
  the photosphere to the corona. In previous work, it was shown that by
  prescribing the 3D-reconstructed loops' geometry, the magnetic field
  extrapolation produces a solution with a better agreement between
  the modeled field and the reconstructed loops. This also improves
  the quality of the field extrapolation. Stereoscopy, which uses at
  least two view directions, is the traditional method for performing
  3D coronal loop reconstruction. When only one vantage point of the
  coronal loops is available, other 3D reconstruction methods must
  be applied. Within this work, we present a method for the 3D loop
  reconstruction based on machine learning. Our purpose for developing
  this method is to use as many observed coronal loops in space and time
  for the modeling of the coronal magnetic field. Our results show that
  we can build machine-learning models that can retrieve 3D loops based
  only on their projection information. Ultimately, the neural network
  model will be able to use only 2D information of the coronal loops,
  identified, traced, and extracted from the extreme-ultraviolet images,
  for the calculation of their 3D geometry.

Title: Revisiting the mass- and radius-luminosity relations for FGK
    main-sequence stars
Authors: Fernandes, João; Gafeira, Ricardo; Andersen, Johannes
Bibcode: 2021A&A...647A..90F
Altcode: 2021arXiv210311044F
  Context. Scaling relations are very useful tools for estimating
  unknown stellar quantities. Within this framework, eclipsing binaries
  are ideal for this goal because their mass and radius are known with
  a very good level of accuracy, leading to improved constraints on
  the models. <BR /> Aims: We aim to provide empirical relations for
  the mass and radius as function of luminosity, metallicity, and
  age. We investigate, in particular, the impact of metallicity and
  age on those relations. <BR /> Methods: We used a multi-dimensional
  fit approach based on the data from DEBCat, an updated catalogue
  of eclipsing binary observations such as mass, radius, luminosity,
  effective temperature, gravity, and metallicity. We used the PARAM
  web interface for the Bayesian estimation of stellar parameters,
  along with the stellar evolutionary code MESA to estimate the binary
  age, assuming a coeval hypothesis for both members. <BR /> Results:
  We derived the mass and radius-luminosity-metallicity-age relations
  using 56 stars, with metallicity and mass in the range −0.34 &lt;
  [Fe/H] &lt; 0.27 and 0.66 &lt; M/M<SUB>⊙</SUB> &lt; 1.8. With that,
  the observed mass and radius are reproduced with an accuracy of 3.5%
  and 5.9%, respectively, which is consistent with the other results
  in literature. <BR /> Conclusions: We conclude that including the
  age in such relations increases the quality of the fit, particularly
  in terms of the mass, as compared to the radius. On the other hand,
  as otherss authors have noted, we observed an higher dispersion on the
  mass relation than in that of the radius. We propose that this is due
  to a stellar age effect.

Title: Mimicking spectropolarimetric inversions using convolutional
    neural networks
Authors: Milić, I.; Gafeira, R.
Bibcode: 2020A&A...644A.129M
Altcode: 2020arXiv200602005M
  Context. Interpreting spectropolarimetric observations of the solar
  atmosphere takes much longer than the acquiring the data. The most
  important reason for this is that the model fitting, or "inversion",
  used to infer physical quantities from the observations is extremely
  slow, because the underlying models are numerically demanding. <BR />
  Aims: We aim to improve the speed of the inference by using a neural
  network that relates input polarized spectra to the output physical
  parameters. <BR /> Methods: We first select a subset of the data
  to be interpreted and infer physical quantities from corresponding
  spectra using a standard minimization-based inversion code. Taking
  these results as reliable and representative of the whole data set, we
  train a convolutional neural network to connect the input polarized
  spectra to the output physical parameters (nodes, in context of
  spectropolarimetric inversion). We then apply the neural network to
  the various other data, previously unseen to the network. As a check,
  we apply the referent inversion code to the unseen data and compare
  the fit quality and the maps of the inferred parameters between the
  two inversions. <BR /> Results: The physical parameters inferred by
  the neural network show excellent agreement with the results from
  the inversion, and are obtained in a factor of 10<SUP>5</SUP> less
  time. Additionally, substituting the results of the neural network back
  in the forward model, shows excellent agreement between inferred and
  original spectra. <BR /> Conclusions: The method we present here is
  very simple for implementation and extremely fast. It only requires a
  training data set, which can be obtained by inverting a representative
  subset of the observed data. Applying these (and similar) machine
  learning techniques will yield orders of magnitude acceleration in
  the routine interpretation of spectropolarimetric data.

Title: Temporal evolution of short-lived penumbral microjets
Authors: Siu-Tapia, A. L.; Bellot Rubio, L. R.; Orozco Suárez, D.;
   Gafeira, R.
Bibcode: 2020A&A...642A.128S
Altcode: 2020arXiv200715926S
  Context. Penumbral microjets (PMJs) is the name given to elongated
  jet-like brightenings observed in the chromosphere above sunspot
  penumbrae. They are transient events that last from a few seconds
  to several minutes, and their origin is presumed to be related to
  magnetic reconnection processes. Previous studies have mainly focused
  on their morphological and spectral characteristics, and more recently
  on their spectropolarimetric signals during the maximum brightness
  stage. Studies addressing the temporal evolution of PMJs have also
  been carried out, but they are based on spatial and spectral time
  variations only. <BR /> Aims: Here we investigate, for the first
  time, the temporal evolution of the polarization signals produced by
  short-lived PMJs (lifetimes &lt; 2 min) to infer how the magnetic field
  vector evolves in the upper photosphere and mid-chromosphere. <BR />
  Methods: We use fast-cadence spectropolarimetric observations of the
  Ca II 854.2 nm line taken with the CRisp Imaging Spectropolarimeter
  at the Swedish 1 m Solar Telescope. The weak-field approximation (WFA)
  is used to estimate the strength and inclination of the magnetic field
  vector. By separating the Ca II 854.2 nm line into two different
  wavelength domains to account for the chromospheric origin of the
  line core and the photospheric contribution to the wings, we infer
  the height variation of the magnetic field vector. <BR /> Results:
  The WFA reveals larger magnetic field changes in the upper photosphere
  than in the chromosphere during the PMJ maximum brightness stage. In
  the photosphere, the magnetic field inclination and strength undergo
  a transient increase for most PMJs, but in 25% of the cases the field
  strength decreases during the brightening. In the chromosphere, the
  magnetic field tends to be slightly stronger during the PMJs. <BR
  /> Conclusions: The propagation of compressive perturbation fronts
  followed by a rarefaction phase in the aftershock region may explain
  the observed behavior of the magnetic field vector. The fact that such
  behavior varies among the analyzed PMJs could be a consequence of the
  limited temporal resolution of the observations and the fast-evolving
  nature of the PMJs.

Title: Analysis of full-disc Ca II K spectroheliograms. III. Plage
    area composite series covering 1892-2019
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova,
   Natalie A.; Solanki, Sami K.; Banerjee, Dipankar; Barata, Teresa;
   Belik, Marcel; Gafeira, Ricardo; Garcia, Adriana; Hanaoka, Yoichiro;
   Hegde, Manjunath; Klimeš, Jan; Korokhin, Viktor V.; Lourenço, Ana;
   Malherbe, Jean-Marie; Marchenko, Gennady P.; Peixinho, Nuno; Sakurai,
   Takashi; Tlatov, Andrey G.
Bibcode: 2020A&A...639A..88C
Altcode: 2020arXiv200501435C
  Context. Studies of long-term solar activity and variability require
  knowledge of the past evolution of the solar surface magnetism. The
  archives of full-disc Ca II K observations that have been performed
  more or less regularly at various sites since 1892 can serve as an
  important source of such information. <BR /> Aims: We derive the plage
  area evolution over the last 12 solar cycles by employing data from all
  Ca II K archives that are publicly available in digital form, including
  several as-yet-unexplored Ca II K archives. <BR /> Methods: We analysed
  more than 290 000 full-disc Ca II K observations from 43 datasets
  spanning the period between 1892-2019. All images were consistently
  processed with an automatic procedure that performs the photometric
  calibration (if needed) and the limb-darkening compensation. The
  processing also accounts for artefacts affecting many of the images,
  including some very specific artefacts, such as bright arcs found
  in Kyoto and Yerkes data. Our employed methods have previously been
  tested and evaluated on synthetic data and found to be more accurate
  than other methods used in the literature to treat a subset of the data
  analysed here. <BR /> Results: We produced a plage area time-series
  from each analysed dataset. We found that the differences between the
  plage areas derived from individual archives are mainly due to the
  differences in the central wavelength and the bandpass used to acquire
  the data at the various sites. We empirically cross-calibrated and
  combined the results obtained from each dataset to produce a composite
  series of plage areas. The 'backbone' approach was used to bridge
  the series together. We have also shown that the selection of the
  backbone series has little effect on the final composite of the plage
  area. We quantified the uncertainty of determining the plage areas
  with our processing due to shifts in the central wavelength and found
  it to be less than 0.01 in fraction of the solar disc for the average
  conditions found on historical data. We also found the variable seeing
  conditions during the observations to slightly increase the plage
  areas during the activity maxima. <BR /> Conclusions: We provide the
  most complete so far time series of plage areas based on corrected
  and calibrated historical and modern Ca II K images. Consistent
  plage areas are now available on 88% of all days from 1892 onwards
  and on 98% from 1907 onwards. <P />The whole series described in
  the paper are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88</A>

Title: Magnetic properties of short-lived penumbral microjets
Authors: Siu-Tapia, A.; Bellot Rubio, L.; Orozco Suárez, D.;
   Gafeira, R.
Bibcode: 2020sea..confE.208S
Altcode:
  We investigate the temporal evolution of the polarization properties
  during penumbral microjets (PMJs). Studying the magnetic properties
  of these transients requires spectropolarimetric observations with
  the fastest temporal cadence possible and is currently a challenging
  task. In this work, we used fast temporal cadence spectropolarimetric
  measurements of the Ca II 8542 Å line from the CRISP instrument at the
  Swedish 1 m Solar Telescope, and exploited the diagnosis capabilities of
  this line to retrieve the magnetic field configuration and its evolution
  at different atmospheric heights during PMJs. Our findings show that
  the short-lived PMJs are associated to a transient perturbation in
  the photospheric magnetic field and sometimes they show clear but
  weaker changes in the chromospheric field as well. Here we describe
  the different types of evolution that were identified.

Title: VizieR Online Data Catalog: Plage area composite series
    (Chatzistergos+, 2020)
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki,
   S. K.; Banerjee, D.; Barata, T.; Belik, M.; Gafeira, R.; Garcia,
   A.; Hanaoka, Y.; Hegde, M.; Klimes, J.; Korokhin, V. V.; Lourenco,
   A.; Malherbe, J. -M.; Marchenko, G. P.; Peixinho, N.; Sakurai, T.;
   Tlatov, A. G.
Bibcode: 2020yCat..36390088C
Altcode:
  Annual, monthly, and daily values of the plage area composite series. <P
  />The archives included are those from the Arcetri (Ar), Baikal (Ba),
  Brussels (Br), Calern (CL), Catania (CT), Coimbra (Co), Kanzelhoehe
  (Ka), Kenwood (Ke), Kharkiv (Kh), Kislovodsk (Ki), Kodaikanal taken with
  the spectroheliograph (Ko), Kodaikanal taken with the Twin telescope
  (KT), Kodaikanal taken with the White-Light Active Region Monitor (WARM)
  telescope (KW), Kyoto (Ky), Manila (Ma), Mauna Loa (ML) taken with the
  Precision Solar Photometric Telescope (PSPT), McMath-Hulbert (MM), Mees
  (MS), Meudon taken with the spectroheliograph (MD1), Meudon taken with
  an interference filter (MD2), Mitaka taken with the spectroheliograph
  (Mi1), Mitaka taken with the Solar Flare Telescope with an interference
  filter (Mi2), Mt Wilson (MW), Pic du Midi (PM), SOlar Diameter Imager
  and Surface Mapper (SODISM) telescope on board the PICARD spacecraft
  (PS), Rome taken with the equatorial bar at Monte Mario (Ro), Rome taken
  with the PSPT (RP1), Rome taken with the PSPT with narrow bandwidth
  (RP2), Sacramento Peak (SP), San Fernando taken with the Cartesian
  Full-Disk Telescope (CFDT) 1 (SF1), San Fernando taken with the CFDT2
  (SF2), Schauinsland (Sc), Teide (Te) taken with the Chromospheric
  Telescope (ChroTel), Upice (UP), Valasske Mezirici (VM), Wendelstein
  (WS), and Yerkes (YR) sites <P />(3 data files).

Title: Mimicking spectropolarimetric inversion using convolutional
    neural networks
Authors: Milic, Ivan; Gafeira, Ricardo
Bibcode: 2019AAS...23422605M
Altcode:
  State of the art approach for the interpretation of
  spectropolarimetric observations of the solar atmosphere are the so
  called spectropolarimetric inversions. These methods fit a model
  atmosphere to the observed polarized spectrum and provide us with
  the maximum-likelyhood solution for the parameters of the underlying
  atmosphere. Inversions are extremely numerically demanding, because
  they fully take into account all the physical processes involved in
  the spectral line formation. This is especially pronounced in the case
  of spectral lines formed in the solar chromosphere. With the advent of
  next generation telescopes, such as DKIST, standard, minimization-based,
  inversions will simply be too slow. In this contribution we propose
  a way to accelerate the inversions by means of convolutional neural
  networks. We invert a small sub-set of the data using standard
  inversion approach and then train a convolutional neural network to
  generalize the results to the full data set. We analyze this method
  on different synthetic and observed data sets and compare the results
  with the results obtained by applying standard inversion methods. We
  find that, given an extensive enough data set, convolutional neural
  networks provide results that are very close to the ones obtained by
  standard inversion methods, in a fraction of time.

Title: Slender Ca II H fibrils observed by SUNRISE/SuFI
Authors: Gafeira, Ricardo Jorge
Bibcode: 2018PhDT.......156G
Altcode:
  No abstract at ADS

Title: Erratum: Morphological Properties of
    Slender CaII H Fibrils Observed by sunrise II (<A
href="http://doi.org/10.3847/1538-4365/229/1/6">ApJS 229, 1, 6</A>)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..230...11G
Altcode:
  No abstract at ADS

Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
    with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
   Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
   A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
   Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....9J
Altcode: 2016arXiv161007449J
  We present observations of transverse oscillations in slender Ca II
  H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
  time series of high- (spatial and temporal-) resolution seeing-free
  observations in a 1.1 Å wide passband covering the line core of Ca
  II H 3969 Å from the second flight of the Sunrise balloon-borne solar
  observatory. The entire field of view, spanning the polarity inversion
  line of an active region close to the solar disk center, is covered with
  bright, thin, and very dynamic fine structures. Our analysis reveals
  the prevalence of transverse waves in SCFs with median amplitudes and
  periods on the order of 2.4 ± 0.8 km s<SUP>-1</SUP> and 83 ± 29 s,
  respectively (with standard deviations given as uncertainties). We
  find that the transverse waves often propagate along (parts of) the
  SCFs with median phase speeds of 9 ± 14 km s<SUP>-1</SUP>. While the
  propagation is only in one direction along the axis in some of the
  SCFs, propagating waves in both directions, as well as standing waves
  are also observed. The transverse oscillations are likely Alfvénic
  and are thought to be representative of magnetohydrodynamic kink
  waves. The wave propagation suggests that the rapid high-frequency
  transverse waves, often produced in the lower photosphere, can
  penetrate into the chromosphere with an estimated energy flux of ≈15
  kW m<SUP>-2</SUP>. Characteristics of these waves differ from those
  reported for other fibrillar structures, which, however, were observed
  mainly in the upper solar chromosphere.

Title: Morphological Properties of Slender Ca II H Fibrils Observed
    by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....6G
Altcode: 2016arXiv161200319G
  We use seeing-free high spatial resolution Ca II H data obtained by
  the SUNRISE observatory to determine properties of slender fibrils
  in the lower solar chromosphere. In this work we use intensity images
  taken with the SuFI instrument in the Ca II H line during the second
  scientific flight of the SUNRISE observatory to identify and track
  elongated bright structures. After identification, we analyze theses
  structures to extract their morphological properties. We identify
  598 slender Ca II H fibrils (SCFs) with an average width of around
  180 km, length between 500 and 4000 km, average lifetime of ≈400
  s, and average curvature of 0.002 arcsec<SUP>-1</SUP>. The maximum
  lifetime of the SCFs within our time series of 57 minutes is ≈2000
  s. We discuss similarities and differences of the SCFs with other
  small-scale, chromospheric structures such as spicules of type I and
  II, or Ca II K fibrils.

Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
    from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
   van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
   J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
   Suárez, D.; Riethmüller, T. L.; Schmidt, W.
Bibcode: 2017ApJS..229....7G
Altcode: 2017arXiv170102801G
  We report the detection of oscillations in slender Ca II H fibrils
  (SCFs) from high-resolution observations acquired with the Sunrise
  balloon-borne solar observatory. The SCFs show obvious oscillations in
  their intensity, but also their width. The oscillatory behaviors are
  investigated at several positions along the axes of the SCFs. A large
  majority of fibrils show signs of oscillations in intensity. Their
  periods and phase speeds are analyzed using a wavelet analysis. The
  width and intensity perturbations have overlapping distributions
  of the wave period. The obtained distributions have median values
  of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
  find that the fluctuations of both parameters propagate in
  the SCFs with speeds of {11}<SUB>-11</SUB><SUP>+49</SUP> km
  s<SUP>-1</SUP> and {15}<SUB>-15</SUB><SUP>+34</SUP> km s<SUP>-1</SUP>,
  respectively. Furthermore, the width and intensity oscillations have a
  strong tendency to be either in anti-phase or, to a smaller extent, in
  phase. This suggests that the oscillations of both parameters are caused
  by the same wave mode and that the waves are likely propagating. Taking
  all the evidence together, the most likely wave mode to explain all
  measurements and criteria is the fast sausage mode.

Title: Slender Ca II H fibrils observed by SUNRISE 2
Authors: Gafeira, R.
Bibcode: 2017psio.confE..47G
Altcode:
  No abstract at ADS

Title: Ground-based Observations of Sunspots from the Observatory
of Coimbra: Evaluation of Different Automated Approaches to Analyse
    its Datasets
Authors: Carvalho, S.; Pina, P.; Barata, T.; Gafeira, R.; Garcia, A.
Bibcode: 2016ASPC..504..125C
Altcode:
  The Geophysical and Astronomical Observatory of the University
  of Coimbra (OGAUC) has a collection of solar observations
  (spectroheliograms) that span near nine decades, acquired
  uninterruptedly until today on a daily basis since 1926 and already
  in digital format. This extensive collection acquired with the
  same instrumentation must be processed altogether since its large
  temporal coverage can provide important inputs for the knowledge
  of the solar activity. Therefore, this work aims to evaluate the
  capability of some methods in the automatic detection of sunspots from
  spectroheliograms. The objective of this work is to define a strategic
  action, concerned with sunsposts detection, to be applied to all
  spectroheliograms datasets. The final detection results of different
  methods are compared to reference detections provided by an expert
  solar observer, in order to evaluate the performances on the detection
  of the contour of sunspots and also on the ability to differentiate the
  umbra and penumbra areas. According to the best detection performances
  (its accuracy but also computational time, among others), a processing
  chain will be implemented and applied to the whole data series of OGAUC.

Title: Temporal Evolution of Sunspot Areas and Estimation of Related
    Plasma Flows
Authors: Gafeira, R.; Fonte, C. C.; Pais, M. A.; Fernandes, J.
Bibcode: 2014SoPh..289.1531G
Altcode: 2013arXiv1310.7221G
  The increased amount of information provided by ongoing missions such as
  the Solar Dynamics Observatory (SDO) represents a great challenge for
  the understanding of basic questions such as the internal structure of
  sunspots and how they evolve with time. Here, we contribute with the
  exploitation of new data, to provide a better understanding of the
  separate growth and decay of sunspots, umbra, and penumbra. Using
  fuzzy sets to compute separately the areas of sunspot umbra and
  penumbra, the growth and decay rates for active regions NOAA 11117,
  NOAA 11428, NOAA 11429, and NOAA 11430 are computed from the analysis
  of intensitygrams obtained by the Helioseismic and Magnetic Imager
  onboard SDO. A simplified numerical model is proposed for the decay
  phase, whereby an empirical irrotational and uniformly convergent
  horizontal velocity field interacting with an axially symmetric and
  height-invariant magnetic field reproduces the large-scale features
  of the much more complex convection observed inside sunspots.

Title: Variation rate of sunspot area
Authors: Gafeira, R.; Fonte, C. C.; Pais, M. A.; Fernandes, J.
Bibcode: 2013MmSAI..84..428G
Altcode: 2012arXiv1211.6870G
  The emergence of the magnetic field lines through the photosphere has
  multiple manifestations and sunspots are the most prominent examples
  of this. One of the most relevant sunspot properties, to study both
  its structure and evolution, is the sunspot area: either total, umbra
  or penumbra area. Recent studies conclude that in active region NOAA
  11024 during the penumbra formation the umbra area remains constant
  and that the increase of the total sunspot area is caused exclusively
  by the penumbra growth. In this presentation the above conclusion
  is firstly tested, investigating the evolution of four different
  active regions. Hundreds of intensity images from the Helioseismic and
  Magnetic Imager are used, obtained by the Solar Dynamics Observatory,
  in order to describe the area evolution of the above active regions and
  estimate the increase and decrease rates for umbra and penumbra areas,
  respectively. A simple magnetohydrodynamic model is then tentatively
  used at first approximation to explain the observed results.

Title: The bimodal colors of Centaurs and small Kuiper belt objects
Authors: Peixinho, N.; Delsanti, A.; Guilbert-Lepoutre, A.; Gafeira,
   R.; Lacerda, P.
Bibcode: 2012A&A...546A..86P
Altcode: 2012arXiv1206.3153P
  Ever since the very first photometric studies of Centaurs and
  Kuiper belt objects (KBOs) their visible color distribution has been
  controversial. This controversy has triggered to a prolific debate on
  the origin of the surface colors of these distant icy objects of the
  solar system. Two scenarios have been proposed to interpret and explain
  the large variability of colors, hence surface composition. Are the
  colors mainly primordial and directly related to the formation region,
  or are they the result of surface evolution processes? To date, no
  mechanism has been found that successfully explains why Centaurs,
  which are escapees from the Kuiper belt, exhibit two distinct color
  groups, whereas KBOs do not. We readdress this issue using a carefully
  compiled set of B - R colors and H<SUB>R</SUB>(α) magnitudes (as
  proxy for size) for 253 objects, including data for 10 new small
  objects. We find that the bimodal color distribution of Centaurs is
  a size-related phenomenon, common to both Centaurs and small KBOs,
  i.e. independent of dynamical classification. Furthermore, we find that
  large KBOs also have a bimodal distribution of surface colors, albeit
  distinct from the small objects and strongly dependent on the "Haumea
  collisional family" objects. When plotted in B - R, H<SUB>R</SUB>(α)
  space, the colors of Centaurs and KBOs display a peculiar ? shape. <P
  />Table 3 and Appendix A are available in electronic form at
  <A href="http://www.aanda.org">http://www.aanda.org</A>Table
  3 is also available at the CDS via anonymous ftp
  to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A86">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A86</A>

Title: Mass-luminosity relation for FGK main sequence stars:
    metallicity and age contributions
Authors: Gafeira, Ricardo; Patacas, Carlos; Fernandes, João
Bibcode: 2012Ap&SS.341..405G
Altcode: 2012arXiv1205.5484G; 2012Ap&SS.tmp..234G
  The stellar mass-luminosity relation (MLR) is one of the most famous
  empirical "laws", discovered in the beginning of the 20th century. MLR
  is still used to estimate stellar masses for nearby stars, particularly
  for those that are not binary systems, hence the mass cannot be
  derived directly from the observations. It's well known that the MLR
  has a statistical dispersion which cannot be explained exclusively
  due to the observational errors in luminosity (or mass). It is an
  intrinsic dispersion caused by the differences in age and chemical
  composition from star to star. In this work we discuss the impact
  of age and metallicity on the MLR. Using the recent data on mass,
  luminosity, metallicity, and age for 26 FGK stars (all members of binary
  systems, with observational mass-errors ≤3 %), including the Sun,
  we derive the MLR taking into account, separately, mass-luminosity,
  mass-luminosity-metallicity, and mass-luminosity-metallicity-age. Our
  results show that the inclusion of age and metallicity in the MLR,
  for FGK stars, improves the individual mass estimation by 5 % to 15 %.

Title: Centaur-Sized KBOs Also Show Bimodal Colors
Authors: Peixinho, N.; Delsanti, A.; Guilbert-Lepoutre, A.; Gafeira,
   R.; Lacerda, P.
Bibcode: 2012epsc.conf..419P
Altcode: 2012espc.conf..419P
  Since the first color measurements of the surfaces of Centaurs
  and Kuiper Belt Objects (KBOs) their color distributions have been
  puzzling. Centaurs became known for splitting in two distinct color
  groups, whereas KBOs presented a rather continuous distribution of
  colors [Peixinho et al. 2003, A&amp;A 410, L29-L32]. Two decades after
  the discovery of the Kuiper Belt the mechanism responsible for the
  aforementioned distinct behavior remains unanswered. We have compiled
  a database of visible surface colors for 253 of these objects, of
  which 10 are new measurements, and analyzed the color distribution
  of Centaurs and KBOs as function of their absolute magnitudes,
  or size. We find evidence that Centaur-sized KBOs also exhibit two
  color groups. Such suggests that the 'color bimodality problem' is a
  size related phenomenon, shared both by Centaurs and KBOs of similar
  sizes, instead of a phenomenon related with dynamical class. We will
  also discuss other patterns seen among KBOs and the relations between
  spectral features and visible surface colors.

Title: VizieR Online Data Catalog: R absolute magnitudes of Kuiper
    Belt objects (Peixinho+, 2012)
Authors: Peixinho, N.; Delsanti, A.; Guilbert-Lepoutre, A.; Gafeira,
   R.; Lacerda, P.
Bibcode: 2012yCat..35460086P
Altcode: 2012yCat..35469086P
  Compilation of absolute magnitude H<SUB>Rα</SUB>, B-R color spectral
  features used in this work. For each object, we computed the average
  color index from the different papers presenting data obtained
  simultaneously in B and R bands (e.g. contiguous observations within
  a same night). When individual R apparent magnitude and date were
  available, we computed the H<SUB>Rα</SUB>=R-5log(r Delta), where R
  is the R-band magnitude, r and Delta are the helio- and geocentric
  distances at the time of observation in AU, respectively. When V and
  V-R colors were available, we derived an R and then H<SUB>Rα</SUB>
  value. We did not correct for the phase-angle α effect. This table
  includes also spectral information on the presence of water ice,
  methanol, methane, or confirmed featureless spectra, as available
  in the literature. We highlight only the cases with clear bands in
  the spectrum, which were reported/confirmed by some other work. The
  1st column indicates the object identification number and name or
  provisional designation; the 2nd column indicates the dynamical class;
  the 3rd column indicates the average H<SUB>Rα</SUB> value and 1-σ
  error bars; the 4th column indicates the average $B-R$ color and 1-σ
  error bars; the 5th column indicates the most important spectral
  features detected; and the 6th column points to the bibliographic
  references used for each object. <P />(3 data files).

Title: The Kuiper Belt Color Controversy Returns
Authors: Peixinho, N.; Delsanti, A.; Guilber-Lepoutre, A.; Gafeira,
   R.; Lacerda, P.
Bibcode: 2012LPICo1667.6131P
Altcode:
  We will discuss the colors of Centaurs and KBOs as a function of
  absolute magnitudes, i.e. size, from a database of 253 objects. We
  find a new interpretation for the bimodal color behavior of Centaurs
  and other relevant patterns among KBOs.

