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&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.
Aims: In this work we discuss the application of convolutional neural networks (CNNs) as a tool to advantageously initialize Stokes profile inversions.
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.
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.
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.
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.
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.
Results: We derived the mass and radius-luminosity-metallicity-age relations using 56 stars, with metallicity and mass in the range −0.34 < [Fe/H] < 0.27 and 0.66 < M/M < 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.
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.
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.
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.
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 105 less time. Additionally, substituting the results of the neural network back in the forward model, shows excellent agreement between inferred and original spectra.
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.
Aims: Here we investigate, for the first time, the temporal evolution of the polarization signals produced by short-lived PMJs (lifetimes < 2 min) to infer how the magnetic field vector evolves in the upper photosphere and mid-chromosphere.
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.
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.
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.
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.
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.
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.
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.

The whole series described in the paper are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88 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.

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

(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 (ApJS 229, 1, 6) 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-1 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-1. 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-2. 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-1. 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}-11+49 km s-1 and {15}-15+34 km s-1, 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 HR(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, HR(α) space, the colors of Centaurs and KBOs display a peculiar ? shape.

Table 3 and Appendix A are available in electronic form at http://www.aanda.orgTable 3 is also available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/546/A86 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&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, 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=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 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 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.

(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.