Author name code: collados ADS astronomy entries on 2022-09-14 author:"Collados, Manuel" OR author:"Collados Vera, Manuel" ------------------------------------------------------------------------ Title: The European Solar Telescope Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.; Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein, C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados, M.; the EST team Bibcode: 2022arXiv220710905Q Altcode: The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR, the French Télescope Héliographique pour l'Étude du Magnétisme et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope (DOT). With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems. 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: Generalized Fluid Models of the Braginskii Type Authors: Hunana, P.; Passot, T.; Khomenko, E.; Martínez-Gómez, D.; Collados, M.; Tenerani, A.; Zank, G. P.; Maneva, Y.; Goldstein, M. L.; Webb, G. M. Bibcode: 2022ApJS..260...26H Altcode: 2022arXiv220111561H Several generalizations of the well-known fluid model of Braginskii (1965) are considered. We use the Landau collisional operator and the moment method of Grad. We focus on the 21-moment model that is analogous to the Braginskii model, and we also consider a 22-moment model. Both models are formulated for general multispecies plasmas with arbitrary masses and temperatures, where all of the fluid moments are described by their evolution equations. The 21-moment model contains two "heat flux vectors" (third- and fifth-order moments) and two "viscosity tensors" (second- and fourth-order moments). The Braginskii model is then obtained as a particular case of a one ion-electron plasma with similar temperatures, with decoupled heat fluxes and viscosity tensors expressed in a quasistatic approximation. We provide all of the numerical values of the Braginskii model in a fully analytic form (together with the fourth- and fifth-order moments). For multispecies plasmas, the model makes the calculation of the transport coefficients straightforward. Formulation in fluid moments (instead of Hermite moments) is also suitable for implementation into existing numerical codes. It is emphasized that it is the quasistatic approximation that makes some Braginskii coefficients divergent in a weakly collisional regime. Importantly, we show that the heat fluxes and viscosity tensors are coupled even in the linear approximation, and that the fully contracted (scalar) perturbations of the fourth-order moment, which are accounted for in the 22-moment model, modify the energy exchange rates. We also provide several appendices, which can be useful as a guide for deriving the Braginskii model with the moment method of Grad. Title: Polarimetric characterization of segmented mirrors Authors: Pastor Yabar, A.; Asensio Ramos, A.; Manso Sainz, R.; Collados, M. Bibcode: 2022ApOpt..61.4908P Altcode: 2022arXiv220514640P We study the impact of the loss of axial symmetry around the optical axis on the polarimetric properties of a telescope with segmented primary mirror when each segment is present in a different aging stage. The different oxidation stage of each segment as they are substituted in time leads to non-negligible crosstalk terms. This effect is wavelength dependent and it is mainly determined by the properties of the reflecting material. For an aluminum coating, the worst polarimetric behavior due to oxidation is found for the blue part of the visible. Contrarily, dust -- as modeled in this work -- does not significantly change the polarimetric behavior of the optical system . Depending on the telescope, there might be segment substitution sequences that strongly attenuate this instrumental polarization. Title: Optical design of an image-slicer integral field unit with two output slits Authors: Dominguez-Tagle, Carlos; Lopez, Roberto; Collados, Manuel; Vaz Cedillo, Jacinto J. Bibcode: 2022JATIS...8a5002D Altcode: The optical design of an integral field unit (IFU) based on image-slicers represents an interesting design exercise because of the small size of the components and the critical parameters to reduce optical aberrations. When the IFU to be designed is also intended to substitute an IFU prototype that is already integrated into a spectropolarimeter, it becomes even more challenging. The main reason to upgrade the IFU prototype is to cover a larger field of view (FOV). One of the work packages of the European project "Getting Ready for the European Solar Telescope" (GREST) had as its objective to find the best option to design such an IFU. After analyzing the requirements and the design considerations, the optical design pointed toward an IFU that doubles the FOV, reaching a value of 40.5 arcsec2. The designed IFU is composed of two image-slicers coupled together, each one with eight mirrors of 1.8 mm × 100 μm that feed two slits to the spectrograph. Title: First Light of the Integral Field Unit of GRIS on the GREGOR Solar Telescope Authors: Dominguez-Tagle, C.; Collados, M.; Lopez, R.; Cedillo, J. J. Vaz; Esteves, M. A.; Grassin, O.; Vega, N.; Mato, A.; Quintero, J.; Rodriguez, H.; Regalado, S.; Gonzalez, F. Bibcode: 2022JAI....1150014D Altcode: 2022arXiv220614294D An Integral Field Unit (IFU) based on image slicers has been added to the GREGOR Infrared Spectrograph (GRIS). This upgrade to the instrument makes possible 2D spectropolarimetry in the near-infrared by simultaneously recording the full Stokes profiles of spectral lines (in a given spectral interval) at all the points in the field of view (FOV). It provides high-cadence spectropolarimetric observations at the instrument’s high spatial resolution and high polarization sensitivity at the GREGOR solar telescope. The IFU is ideal for observing the polarized spectrum of fast-evolving solar features at high spatial and spectral resolutions. The high observing cadence opens the possibility of time-series observations. The analysis of observations to this level of accuracy is essential for understanding the complex dynamics and interactions of solar plasma and magnetic fields. The image slicer of the IFU has eight slices of width 100μm, covering a total FOV of  6′′×3′′. It was designed and built within the framework of the European projects SOLARNET and GREST, as a prototype for future instruments of the European Solar Telescope (EST) and was integrated into GRIS. After two commissioning campaigns in 2017 and 2018, the IFU was finally installed at the end of September 2018 and offered to all observers who use the telescope. Title: 10th International Symposium on Advanced Optical Manufacturing and Testing Technologies: Large Mirror and Telescopes Authors: Rao, Chang-Hui; Veillet, Christian; Ma, Xiaoliang; Fan, Bin; Liu, Fengchuan; Collados Vera, Manuel Bibcode: 2021SPIE12070E....R Altcode: No abstract at ADS Title: Chromospheric Heating Mechanisms in a Plage Region Constrained by Comparison of Magnetic Field and Mg II h & k Flux Measurements with Theoretical Studies Authors: Anan, Tetsu; Schad, Thomas; Kitai, Reizaburo; Dima, Gabriel; Jaeggli, Sarah; Tarr, Lucas; Collados, Manuel; Dominguez-Tagle, Carlos; Kleint, Lucia Bibcode: 2021AGUFMSH44A..05A Altcode: The strongest quasi-steady heating in the solar atmosphere from the photosphere through the corona occurs in plage regions. As many chromospheric heating mechanisms have been proposed, important discriminators of the possible mechanisms are the location of the heating and the correlation between the magnetic field properties in the chromosphere and the local heating rate. We observed a plage region with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation, the Interface Region Imaging Spectrograph (IRIS) obtained spectra of the ultraviolet Mg II h & k doublet emitted from the same region. In the periphery of the plage region, within the limited field of view seen by GRIS, we find that the Mg II radiative flux increases with the magnetic field in the chromosphere. The positive correlation implies that magnetic flux tubes can be heated by Alfvén wave turbulence or by collisions between ions and neutral atoms relating to Alfvén waves. Within the plage region itself, the radiative flux was large between patches of strong magnetic field strength in the photosphere, or at the edges of magnetic patches. On the other hand, we do not find any significant spatial correlation between the enhanced radiative flux and the chromospheric magnetic field strength or the electric current. In addition to the Alfvén wave turbulence or collisions between ions and neutral atoms relating to Alfvén waves, other heating mechanisms related to magnetic field perturbations produced by interactions of magnetic flux tubes could be at work in the plage chromosphere. Title: Measurements of Photospheric and Chromospheric Magnetic Field Structures Associated with Chromospheric Heating over a Solar Plage Region Authors: Anan, Tetsu; Schad, Thomas A.; Kitai, Reizaburo; Dima, Gabriel I.; Jaeggli, Sarah A.; Tarr, Lucas A.; Collados, Manuel; Dominguez-Tagle, Carlos; Kleint, Lucia Bibcode: 2021ApJ...921...39A Altcode: 2021arXiv210807907A In order to investigate the relation between magnetic structures and the signatures of heating in plage regions, we observed a plage region with the He I 1083.0 nm and Si I 1082.7 nm lines on 2018 October 3 using the integral field unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. During the GRIS observation, the Interface Region Imaging Spectrograph obtained spectra of the ultraviolet Mg II doublet emitted from the same region. In the periphery of the plage region, within the limited field of view seen by GRIS, we find that the Mg II radiative flux increases with the magnetic field in the chromosphere with a factor of proportionality of 2.38 × 104 erg cm-2 s-1 G-1. The positive correlation implies that magnetic flux tubes can be heated by Alfvén wave turbulence or by collisions between ions and neutral atoms relating to Alfvén waves. Within the plage region itself, the radiative flux was large between patches of strong magnetic field strength in the photosphere or at the edges of magnetic patches. On the other hand, we do not find any significant spatial correlation between the enhanced radiative flux and the chromospheric magnetic field strength or the electric current. In addition to the Alfvén wave turbulence or collisions between ions and neutral atoms relating to Alfvén waves, other heating mechanisms related to magnetic field perturbations produced by interactions of magnetic flux tubes could be at work in the plage chromosphere. Title: Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere (Corrigendum) Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.; Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A. Bibcode: 2021A&A...652C...2C Altcode: No abstract at ADS 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: Magnetic field structures associated with chromospheric heating in a plage region Authors: Anan, T.; Schad, T.; Kitai, R.; Dima, G.; Jaeggli, S.; Collados, M.; Dominguez-Tagle, C.; Kleint, L. Bibcode: 2021AAS...23821222A Altcode: The strongest quasi-steady heating in the solar atmosphere occurs in the active chromosphere and in particular within plage regions. Our aim is to investigate the relation between magnetic structures and the signatures of heating in the plage regions so as to clarify what mechanisms are at work. We observed a plage region in NOAA active region 12723 in the near infrared He I triplet and Si I 1082.7 nm on 2018 October 3 using the Integral Field Unit mode of the GREGOR Infrared Spectrograph (GRIS) installed at the GREGOR telescope. At the same time, the Interface Region Imaging Spectrograph (IRIS) obtained spectra in the ultra-violet Mg II h & k doublet emitted from the same region. We applied the HAnle and ZEeman Light v2.0 inversion code (HAZEL v2.0) to the GRIS data to infer the photospheric and chromospheric magnetic field. We find that the radiative flux of the Mg II was large between patches of strong magnetic field strength in the photosphere, or at edges of the magnetic patches. On the other hand, the spatial correspondences between the Mg II flux and the magnetic field strength in the chromosphere and between the Mg II flux and the electric current are not so clear. In conclusion, chromospheric heatings in the plage region can be related to magnetic field perturbations produced by interactions of magnetic flux tubes. Title: Modeling of 3d Atmospheres of Cool Stars with the Mancha Code Authors: Perdomo, Andrea; Vitas, Nikola; Khomenko, Elena; Collados, Manuel Bibcode: 2021csss.confE.129P Altcode: The first results of the application of the MANCHA code to the case of stars beyond the solar case are presented: hydrodynamical simulations of stars of spectral type K0V and M0V compared with the solar case. Title: Temporal evolution of small-scale internetwork magnetic fields in the solar photosphere Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.; Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A. Bibcode: 2021A&A...647A.182C Altcode: 2021arXiv210200942C Context. While the longitudinal field that dominates in photospheric network regions has been studied extensively, small-scale transverse fields have recently been found to be ubiquitous in the quiet internetwork photosphere and this merits further study. Furthermore, few observations have been able to capture how this field evolves.
Aims: We aim to statistically characterize the magnetic vector in a quiet Sun internetwork region and observe the temporal evolution of specific small-scale magnetic features.
Methods: We present two high spatio-temporal resolution observations that reveal the dynamics of two disk-centre internetwork regions taken by the new GREGOR Infrared Spectrograph Integral Field Unit with the highly magnetically sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87 Å. We record the full Stokes vector and apply inversions with the Stokes inversions based on response functions code to retrieve the parameters characterizing the atmosphere. We consider two inversion schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in a field free medium, and scheme 2 (S2), with two magnetic models and a fixed 30% stray light component.
Results: The magnetic properties produced from S1 inversions returned a median magnetic field strength of 200 and 240 G for the two datasets, respectively. We consider the median transverse (horizontal) component, among pixels with Stokes Q or U, and the median unsigned longitudinal (vertical) component, among pixels with Stokes V, above a noise threshold. We determined the former to be 263 G and 267 G, and the latter to be 131 G and 145 G, for the two datasets, respectively. Finally, we present three regions of interest, tracking the dynamics of small-scale magnetic features. We apply S1 and S2 inversions to specific profiles of interest and find that the latter produces better approximations when there is evidence of mixed polarities. We find patches of linear polarization with magnetic flux density of the order of 130−150 G and find that linear polarization appears preferentially at granule-intergranular lane boundaries. The weak magnetic field appears to be organized in terms of complex `loop-like' structures, with transverse fields often flanked by opposite polarity longitudinal fields. Title: Influence of ambipolar and Hall effects on vorticity in three-dimensional simulations of magneto-convection Authors: Khomenko, E.; Collados, M.; Vitas, N.; González-Morales, P. A. Bibcode: 2021RSPTA.37900176K Altcode: 2020arXiv200909753K This paper presents the results of the analysis of three-dimensional simulations of solar magneto-convection that include the joint action of the ambipolar diffusion and the Hall effect. Three simulation runs are compared: one including both ambipolar diffusion and the Hall effect; one including only ambipolar diffusion and one without any of these two effects. The magnetic field is amplified from initial field to saturation level by the action of turbulent local dynamo. In each of these cases, we study 2 h of simulated solar time after the local dynamo reaches the saturation regime. We analyse the power spectra of vorticity, of magnetic field fluctuations and of the different components of the magnetic Poynting flux responsible for the transport of vertical or horizontal perturbations. Our preliminary results show that the ambipolar diffusion produces a strong reduction of vorticity in the upper chromospheric layers and that it dissipates the vortical perturbations converting them into thermal energy. The Hall effect acts in the opposite way, strongly enhancing the vorticity. When the Hall effect is included, the magnetic field in the simulations becomes, on average, more vertical and long-lived flux tube-like structures are produced. We trace a single magnetic structure to study its evolution pattern and the magnetic field intensification, and their possible relation to the Hall effect.

This article is part of the Theo Murphy meeting issue `High-resolution wave dynamics in the lower solar atmosphere'. Title: Joint action of Hall and ambipolar effects in 3D magneto-convection simulations of the quiet Sun. I. Dissipation and generation of waves Authors: González-Morales, P. A.; Khomenko, E.; Vitas, N.; Collados, M. Bibcode: 2020A&A...642A.220G Altcode: 2020arXiv200810429G The partial ionization of the solar plasma causes several nonideal effects such as the ambipolar diffusion, the Hall effect, and the Biermann battery effect. Here we report on the first three-dimensional realistic simulations of solar local dynamo where all three effects were taken into account. The simulations started with a snapshot of already saturated battery-seeded dynamo, where two new series were developed: one with solely ambipolar diffusion and another one also taking into account the Hall term in the generalized Ohm's law. The simulations were then run for about 4 h of solar time to reach the stationary regime and improve the statistics. In parallel, a purely MHD dynamo simulation was also run for the same amount of time. The simulations are compared in a statistical way. We consider the average properties of simulation dynamics, the generation and dissipation of compressible and incompressible waves, and the magnetic Poynting flux. The results show that, with the inclusion of the ambipolar diffusion, the amplitudes of the incompressible perturbations related to Alfvén waves are reduced, and the Poynting flux is absorbed, with a frequency dependence. The Hall effect causes the opposite action: significant excess of incompressible perturbations is generated and an excess of the Poynting flux is observed in the chromospheric layers. The model with ambipolar diffusion shows, on average, sharper current sheets and slightly more abundant fast magneto-acoustic shocks in the chromosphere. The model with the Hall effect has higher temperatures at the lower chromosphere and stronger and more vertical magnetic field concentrations all over the chromosphere. The study of high-frequency waves reveals that significant power of incompressible perturbations is associated with areas with intense and more vertical magnetic fields and larger temperatures. This behavior explains the large Poynting fluxes in the simulations with the Hall effect and provides confirmation as to the role of Alfvén waves in chromospheric heating in internetwork regions, under the action of both Hall and ambipolar effects. We find a positive correlation between the magnitude of the ambipolar heating and the temperature increase at the same location after a characteristic time of 102 s. Title: The dynamics of a solar arch filament system from the chromosphere to the photosphere Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.; Diercke, A.; Collados, M.; Gömöry, P.; Zhong, S.; Hou, Y.; Denker, C. Bibcode: 2020sea..confE.199G Altcode: We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph in the He I 10830 Å range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 Å and Fe I 6173 Å spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the chromosphere to the photosphere. The average Doppler velocities inferred at the upper chromosphere from the He I 10830 Å triplet reach velocities up to 20-24 km s-1, and in the lower chromosphere and upper photosphere the Doppler velocities reach up to 11 km s-1 and 1.5 km s-1 in the case of the Ca II 8542 Å and Si I 10827 Å spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (chromosphere and upper photosphere) shows that they follow the same line-of-sight (LOS) velocity patern, which confirms the observational evidence that the plasma drains toward the photosphere as proposed in models of AFSs. The observations and the nonlinear force-free field (NLFFF) extrapolations demonstrate that the magnetic field loops of the AFS rise with time. Title: Local dynamo in stars beyond the Sun: Study for a K0V star Authors: Perdomo García, A.; Vitas, N.; Khomenko, E.; Collados Vera, M. A. Bibcode: 2020sea..confE.206P Altcode: We present the first results of application of the MANCHA3D code (Felipe 2010; Khomenko et al. 2017, 2018) to a K0V cool star. Initially we run the code solving purely hydrodynamic equations until the stationary convection is reached. Then we produce the magnetic field generation and amplification by Biermann's battery seed and local dynamo. We find values around 100 Gauss for the amplified saturated magnetic field, similar to those found in Khomenko et al. (2017) for the solar case. Title: The European Solar Telescope (EST): Recent developments Authors: Quintero Noda, C.; Collados, M.; EST Team Bibcode: 2020sea..confE.207Q Altcode: The optical design has been updated to include an Adaptive Secondary Mirror that becomes part of the Multi-Conjugated Adaptive Optics (MCAO) system. This new concept allows simplifying the optical design reducing the number of optical surfaces before the instrument suite. The project has also announced a call for tenders for the Preliminary Design of three EST main systems: the primary mirror assembly, the telescope structure, pier and enclosure, and the adaptive secondary mirror. In terms of science capabilities, the Science Advisory Group (SAG) published an updated version of the Science Requirements Document in December 2019. The EST Project Office elaborated a database of instrument requirements based on that document. After discussing it with the newly formed EST Review Panel, we developed a tentative light distribution and instrument suite diagram. It was presented and approved by the SAG in June. We are now starting to create the instrument developers team to achieve the proposed performance. Our goal is to deliver the community the construction proposal of the telescope and the instruments by the end of 2022. Title: Photospheric magnetic topology of a north polar region Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M. Bibcode: 2020A&A...635A.210P Altcode: 2020arXiv200304267P
Aims: We aim to characterise the magnetism of a large fraction of the north polar region close to a maximum of activity, when the polar regions are reversing their dominant polarity.
Methods: We make use of full spectropolarimetric data from the CRisp Imaging Spectro-Polarimeter installed at the Swedish Solar Telescope. The data consist of a photospheric spectral line, which is used to infer the various physical parameters of different quiet Sun regions by means of the solution of the radiative transfer equation. We focus our analysis on the properties found for the north polar region and their comparison to the same analysis applied to data taken at disc centre and low-latitude quiet Sun regions for reference. We also analyse the spatial distribution of magnetic structures throughout the north polar region.
Results: We find that the physical properties of the polar region (line-of-sight velocity, magnetic flux, magnetic inclination and magnetic azimuth) are compatible with those found for the quiet Sun at disc centre and are similar to the ones found at low latitudes close to the limb. Specifically, the polar region magnetism presents no specific features. The structures for which the transformation from a line-of-sight to a local reference frame was possible harbour large magnetic fluxes (>1017 Mx) and are in polarity imbalance with a dominant positive polarity, the largest ones (>1019 Mx) being located below 73° latitude. Title: Evolution of Stokes V area asymmetry related to a quiet Sun cancellation observed with GRIS/IFU Authors: Kaithakkal, A. J.; Borrero, J. M.; Fischer, C. E.; Dominguez-Tagle, C.; Collados, M. Bibcode: 2020A&A...634A.131K Altcode: 2020arXiv200105465K A quiet Sun magnetic flux cancellation event at the disk center was recorded using the Integral Field Unit (IFU) mounted on the GREGOR Infrared Spectrograph (GRIS). The GRIS instrument sampled the event in the photospheric Si I 10827 Å spectral line. The cancellation was preceded by a significant rise in line core intensity and excitation temperature, which is inferred from Stokes inversions under local thermodynamic equilibrium (LTE). The opposite polarity features seem to undergo reconnection above the photosphere. We also found that the border pixels neighboring the polarity inversion line of one of the polarities exhibit a systematic variation of area asymmetry. Area asymmetry peaks right after the line core intensity enhancement and gradually declines thereafter. Analyzing Stokes profiles recorded from either side of the polarity inversion line could therefore potentially provide additional information on the reconnection process related to magnetic flux cancellation. Further analysis without assuming LTE will be required to fully characterize this event.

Movie associated to Fig. 2 is available at https://www.aanda.org Title: Tracking Downflows from the Chromosphere to the Photosphere in a Solar Arch Filament System Authors: González Manrique, Sergio Javier; Kuckein, Christoph; Pastor Yabar, Adur; Diercke, Andrea; Collados, Manuel; Gömöry, Peter; Zhong, Sihui; Hou, Yijun; Denker, Carsten Bibcode: 2020ApJ...890...82G Altcode: 2020arXiv200107078G We study the dynamics of plasma along the legs of an arch filament system (AFS) from the chromosphere to the photosphere, observed with high-cadence spectroscopic data from two ground-based solar telescopes: the GREGOR telescope (Tenerife) using the GREGOR Infrared Spectrograph in the He I 10830 Å range and the Swedish Solar Telescope (La Palma) using the CRisp Imaging Spectro-Polarimeter to observe the Ca II 8542 Å and Fe I 6173 Å spectral lines. The temporal evolution of the draining of the plasma was followed along the legs of a single arch filament from the chromosphere to the photosphere. The average Doppler velocities inferred at the upper chromosphere from the He I 10830 Å triplet reach velocities up to 20-24 km s-1, and in the lower chromosphere and upper photosphere the Doppler velocities reach up to 11 km s-1 and 1.5 km s-1 in the case of the Ca II 8542 Å and Si I 10827 Å spectral lines, respectively. The evolution of the Doppler velocities at different layers of the solar atmosphere (chromosphere and upper photosphere) shows that they follow the same line-of-sight (LOS) velocity pattern, which confirms the observational evidence that the plasma drains toward the photosphere as proposed in models of AFSs. The Doppler velocity maps inferred from the lower photospheric Ca I 10839 Å or Fe I 6173 Å spectral lines do not show the same LOS velocity pattern. Thus, there is no evidence that the plasma reaches the lower photosphere. The observations and the nonlinear force-free field (NLFFF) extrapolations demonstrate that the magnetic field loops of the AFS rise with time. We found flow asymmetries at different footpoints of the AFS. The NLFFF values of the magnetic field strength help us to explain these flow asymmetries. Title: Two-dimensional simulations of coronal rain dynamics. I. Model consisting of a vertical magnetic field and an unbounded atmosphere Authors: Martínez-Gómez, D.; Oliver, R.; Khomenko, E.; Collados, M. Bibcode: 2020A&A...634A..36M Altcode: 2019arXiv191106638M Context. Coronal rain often comes about as the final product of evaporation and condensation cycles that occur in active regions. Observations show that the condensed plasma falls with an acceleration that is less than that of free fall.
Aims: We aim to improve the understanding of the physical mechanisms behind the slower than free-fall motion and the two-stage evolution (an initial phase of acceleration followed by an almost constant velocity phase) detected in coronal rain events.
Methods: Using the MANCHA3D code, we solve the 2D ideal magnetohydrodynamic equations. We represent the solar corona as an isothermal vertically stratified atmosphere with a uniform vertical magnetic field. We represent the plasma condensation as a density enhancement described by a 2D Gaussian profile. We analyse the temporal evolution of the descending plasma and study its dependence on such parameters as density and magnetic field strength.
Results: We confirm previous findings that indicate that the pressure gradient is the main force that opposes the action of gravity and slows down the blob descent, and that larger densities require larger pressure gradients to reach the constant speed phase. We find that the shape of a condensation with a horizontal variation of density is distorted during its fall because the denser parts of the blob fall faster than the lighter ones. This is explained by the fact that the duration of the initial acceleration phase and, therefore, the maximum falling speed attained by the plasma, increases with the ratio of blob to coronal density. We also find that the magnetic field plays a fundamental role in the evolution of the descending condensations. A strong enough magnetic field (greater than 10 G in our simulations) forces each plasma element to follow the path given by a particular field line, which allows for the description of the evolution of each vertical slice of the blob in terms of 1D dynamics, without the influence of the adjacent slices. In addition, under the typical conditions of the coronal rain events, the magnetic field prevents the development of Kelvin-Helmholtz instability.

Movies associated to Figs. 1, 8 and 10 are available at https://www.aanda.org Title: An introductory guide to fluid models with anisotropic temperatures. Part 1. CGL description and collisionless fluid hierarchy Authors: Hunana, P.; Tenerani, A.; Zank, G. P.; Khomenko, E.; Goldstein, M. L.; Webb, G. M.; Cally, P. S.; Collados, M.; Velli, M.; Adhikari, L. Bibcode: 2019JPlPh..85f2002H Altcode: 2019arXiv190109354H We present a detailed guide to advanced collisionless fluid models that incorporate kinetic effects into the fluid framework, and that are much closer to the collisionless kinetic description than traditional magnetohydrodynamics. Such fluid models are directly applicable to modelling the turbulent evolution of a vast array of astrophysical plasmas, such as the solar corona and the solar wind, the interstellar medium, as well as accretion disks and galaxy clusters. The text can be viewed as a detailed guide to Landau fluid models and it is divided into two parts. Part 1 is dedicated to fluid models that are obtained by closing the fluid hierarchy with simple (non-Landau fluid) closures. Part 2 is dedicated to Landau fluid closures. Here in Part 1, we discuss the fluid model of Chew-Goldberger-Low (CGL) in great detail, together with fluid models that contain dispersive effects introduced by the Hall term and by the finite Larmor radius corrections to the pressure tensor. We consider dispersive effects introduced by the non-gyrotropic heat flux vectors. We investigate the parallel and oblique firehose instability, and show that the non-gyrotropic heat flux strongly influences the maximum growth rate of these instabilities. Furthermore, we discuss fluid models that contain evolution equations for the gyrotropic heat flux fluctuations and that are closed at the fourth-moment level by prescribing a specific form for the distribution function. For the bi-Maxwellian distribution, such a closure is known as the `normal' closure. We also discuss a fluid closure for the bi-kappa distribution. Finally, by considering one-dimensional Maxwellian fluid closures at higher-order moments, we show that such fluid models are always unstable. The last possible non Landau fluid closure is therefore the `normal' closure, and beyond the fourth-order moment, Landau fluid closures are required. Title: An introductory guide to fluid models with anisotropic temperatures. Part 2. Kinetic theory, Padé approximants and Landau fluid closures Authors: Hunana, P.; Tenerani, A.; Zank, G. P.; Goldstein, M. L.; Webb, G. M.; Khomenko, E.; Collados, M.; Cally, P. S.; Adhikari, L.; Velli, M. Bibcode: 2019JPlPh..85f2003H Altcode: 2019arXiv190109360H In Part 2 of our guide to collisionless fluid models, we concentrate on Landau fluid closures. These closures were pioneered by Hammett and Perkins and allow for the rigorous incorporation of collisionless Landau damping into a fluid framework. It is Landau damping that sharply separates traditional fluid models and collisionless kinetic theory, and is the main reason why the usual fluid models do not converge to the kinetic description, even in the long-wavelength low-frequency limit. We start with a brief introduction to kinetic theory, where we discuss in detail the plasma dispersion function Z(ζ), and the associated plasma response function R(ζ)=1+ζZ(ζ)=-Z^' }(ζ)/2. We then consider a one-dimensional (1-D) (electrostatic) geometry and make a significant effort to map all possible Landau fluid closures that can be constructed at the fourth-order moment level. These closures for parallel moments have general validity from the largest astrophysical scales down to the Debye length, and we verify their validity by considering examples of the (proton and electron) Landau damping of the ion-acoustic mode, and the electron Landau damping of the Langmuir mode. We proceed by considering 1-D closures at higher-order moments than the fourth order, and as was concluded in Part 1, this is not possible without Landau fluid closures. We show that it is possible to reproduce linear Landau damping in the fluid framework to any desired precision, thus showing the convergence of the fluid and collisionless kinetic descriptions. We then consider a 3-D (electromagnetic) geometry in the gyrotropic (long-wavelength low-frequency) limit and map all closures that are available at the fourth-order moment level. In appendix Ae provide comprehensive tables with Padé approximants of R(ζ) up to the eighth-pole order, with many given in an analytic form. Title: Science Requirement Document (SRD) for the European Solar Telescope (EST) (2nd edition, December 2019) Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.; Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.; Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse, K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.; Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller, T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno, J.; Utz, D.; Zuccarello, F. Bibcode: 2019arXiv191208650S Altcode: The European Solar Telescope (EST) is a research infrastructure for solar physics. It is planned to be an on-axis solar telescope with an aperture of 4 m and equipped with an innovative suite of spectro-polarimetric and imaging post-focus instrumentation. The EST project was initiated and is driven by EAST, the European Association for Solar Telescopes. EAST was founded in 2006 as an association of 14 European countries. Today, as of December 2019, EAST consists of 26 European research institutes from 18 European countries. The Preliminary Design Phase of EST was accomplished between 2008 and 2011. During this phase, in 2010, the first version of the EST Science Requirement Document (SRD) was published. After EST became a project on the ESFRI roadmap 2016, the preparatory phase started. The goal of the preparatory phase is to accomplish a final design for the telescope and the legal governance structure of EST. A major milestone on this path is to revisit and update the Science Requirement Document (SRD). The EST Science Advisory Group (SAG) has been constituted by EAST and the Board of the PRE-EST EU project in November 2017 and has been charged with the task of providing with a final statement on the science requirements for EST. Based on the conceptual design, the SRD update takes into account recent technical and scientific developments, to ensure that EST provides significant advancement beyond the current state-of-the-art. The present update of the EST SRD has been developed and discussed during a series of EST SAG meetings. The SRD develops the top-level science objectives of EST into individual science cases. Identifying critical science requirements is one of its main goals. Those requirements will define the capabilities of EST and the post-focus instrument suite. The technical requirements for the final design of EST will be derived from the SRD. Title: Spectropolarimetric Observations of an Arch Filament System with GREGOR Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.; Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.; Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O. Bibcode: 2019ASPC..526..217B Altcode: 2018arXiv180401789B We observed an arch filament system (AFS) in a sunspot group with the GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The AFS was located between the leading sunspot of negative polarity and several pores of positive polarity forming the following part of the sunspot group. We recorded five spectro-polarimetric scans of this region. The spectral range included the spectral lines Si I 1082.7 nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate on the silicon line which is formed in the upper photosphere. The line profiles are inverted with the code 'Stokes Inversion based on Response functions' to obtain the magnetic field vector. The line-of-sight velocities are determined independently with a Fourier phase method. Maximum velocities are found close to the ends of AFS fibrils. These maximum values amount to 2.4 km s-1 next to the pores and to 4 km s-1 at the sunspot side. Between the following pores, we encounter an area of negative polarity that is decreasing during the five scans. We interpret this by new emerging positive flux in this area canceling out the negative flux. In summary, our findings confirm the scenario that rising magnetic flux tubes cause the AFS. Title: Photospheric Magnetic Fields of the Trailing Sunspots in Active Region NOAA 12396 Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer, C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2019ASPC..526..291V Altcode: 2018arXiv180507752V The solar magnetic field is responsible for all aspects of solar activity. Sunspots are the main manifestation of the ensuing solar activity. Combining high-resolution and synoptic observations has the ambition to provide a comprehensive description of the sunspot growth and decay processes. Active region NOAA 12396 emerged on 2015 August 3 and was observed three days later with the 1.5-meter GREGOR solar telescope on 2015 August 6. High-resolution spectropolarimetric data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together with the chromospheric He I λ1083.0 nm triplet. These near-infrared spectropolarimetric observations were complemented by synoptic line-of-sight magnetograms and continuum images of the Helioseismic and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). Title: Recent advancements in the EST project Authors: Jurčák, Jan; Collados, Manuel; Leenaarts, Jorrit; van Noort, Michiel; Schlichenmaier, Rolf Bibcode: 2019AdSpR..63.1389J Altcode: 2018arXiv181100851J The European Solar Telescope (EST) is a project of a new-generation solar telescope. It has a large aperture of 4 m, which is necessary for achieving high spatial and temporal resolution. The high polarimetric sensitivity of the EST will allow to measure the magnetic field in the solar atmosphere with unprecedented precision. Here, we summarise the recent advancements in the realisation of the EST project regarding the hardware development and the refinement of the science requirements. Title: Three-dimensional simulations of solar magneto-convection including effects of partial ionization Authors: Khomenko, E.; Vitas, N.; Collados, M.; de Vicente, A. Bibcode: 2018A&A...618A..87K Altcode: 2018arXiv180701061K In recent decades, REALISTIC three-dimensional radiative-magnetohydrodynamic simulations have become the dominant theoretical tool for understanding the complex interactions between the plasma and magnetic field on the Sun. Most of such simulations are based on approximations of magnetohydrodynamics, without directly considering the consequences of the very low degree of ionization of the solar plasma in the photosphere and bottom chromosphere. The presence of a large amount of neutrals leads to a partial decoupling of the plasma and magnetic field. As a consequence, a series of non-ideal effects, i.e., the ambipolar diffusion, Hall effect, and battery effect, arise. The ambipolar effect is the dominant in the solar chromosphere. We report on the first three-dimensional realistic simulations of magneto-convection including ambipolar diffusion and battery effects. The simulations are carried out using the newly developed MANCHA3Dcode. Our results reveal that ambipolar diffusion causes measurable effects on the amplitudes of waves excited by convection in the simulations, on the absorption of Poynting flux and heating, and on the formation of chromospheric structures. We provide a low limit on the chromospheric temperature increase owing to the ambipolar effect using the simulations with battery-excited dynamo fields.

The movies associated to Figs. 16 and 17 are available at https://www.aanda.org Title: Temporal evolution of arch filaments as seen in He I 10 830 Å Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker, C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg, A.; Diercke, A. Bibcode: 2018A&A...617A..55G Altcode: 2018arXiv180700728G
Aims: We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them.
Methods: We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 Å spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS.
Results: We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10 830 Å triplet. The arch filament expanded in height and extended in length from 13″ to 21″. The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km s-1. Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km s-1 in the chromosphere. The temporal evolution of He I 10 830 Å profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time.
Conclusions: We followed the arch filament as it carried plasma during its rise from the photosphere to the corona. The material then drained toward the photosphere, reaching supersonic velocities, along the legs of the arch filament. Our observational results support theoretical AFS models and aids in improving future models.

The movie associated to Fig. 3 is available at https://www.aanda.org/ Title: Magnetic topology of the north solar pole Authors: Pastor Yabar, A.; Martínez González, M. J.; Collados, M. Bibcode: 2018A&A...616A..46P Altcode: 2018arXiv180409075P; 2018A&A...616A..46Y The magnetism at the poles is similar to that of the quiet Sun in the sense that no active regions are present there. However, the polar quiet Sun is somewhat different from that at the activity belt as it has a global polarity that is clearly modulated by the solar cycle. We study the polar magnetism near an activity maximum when these regions change their polarity, from which it is expected that its magnetism should be less affected by the global field. To fully characterise the magnetic field vector, we use deep full Stokes polarimetric observations of the 15 648.5 and 15 652.8 Å FeI lines. We observe the north pole as well as a quiet region at disc centre to compare their field distributions. In order to calibrate the projection effects, we observe an additional quiet region at the east limb. We find that the two limb datasets share similar magnetic field vector distributions. This means that close to a maximum, the poles look like typical limb, quiet-Sun regions. However, the magnetic field distributions at the limbs are different from the distribution inferred at disc centre. At the limbs, we infer a new population of magnetic fields with relatively strong intensities ( 600-800 G), inclined by 30° with respect to the line of sight, and with an azimuth aligned with the solar disc radial direction. This line-of-sight orientation interpreted as a single magnetic field gives rise to non-vertical fields in the local reference frame and aligned towards disc centre. This peculiar topology is very unlikely for such strong fields according to theoretical considerations. We propose that this new population at the limbs is due to the observation of unresolved magnetic loops as seen close to the limb. These loops have typical granular sizes as measured in the disc centre. At the limbs, where the spatial resolution decreases, we observe them spatially unresolved, which explains the new population of magnetic fields that is inferred. This is the first (indirect) evidence of small-scale magnetic loops outside the disc centre and would imply that these small-scale structures are ubiquitous on the entire solar surface. This result has profound implications for the energetics not only of the photosphere, but also of the outer layers since these loops have been reported to reach the chromosphere and the low corona. Title: Development of a field-of-view scanning system (FoV-SS): test results and lessons learned Authors: Esteves, Miguel A.; Dominguez-Tagle, Carlos; Vaz Cedillo, Jacinto Javier; Grassin, Olivier; Vega Reyes, Nauzet; Gracia Temich, Felix; Collados Vera, Manuel Bibcode: 2018SPIE10706E..6IE Altcode: Here is presented the tests results and the lessons learnt concerning an opto-mechanical device to scan the GREGOR telescope field of view. The scanning is done by means of a set of mirrors and a mechanism which allows to keep the optical path length constant, regardless the portion of the field being scanned. This system is intended to feed a static image slicer used for solar observations. The tight level of tolerances required makes its design and tests a real challenging activity which produces a lot of unexpected lessons to learn. The story after the issues detection, the consequent root cause analysis, the additional tests and tools developed to study the phenomena, and the construction of the solutions and issue mitigation mechanisms provides a good background to elaborate some recommendations for future developments. Title: The real time MCAO solar prototype for the EST Authors: Montoya, Luzma M.; Velasco, Sergio; Sánchez Capuchino, Jorge; Collados Vera, Manuel; Rodríguez Ramos, Luis Fernando; De Cos Juez, Francisco J.; Asensio Ramos, Andrés. Bibcode: 2018SPIE10703E..48M Altcode: The European Solar Telescope (EST) will be equipped with a MCAO system to provide an excellent correction within one arcminute field of view (FOV). A prototype of this system will be built with the same requirements except for the frame rate. This prototype will allow to test and verify new concepts for Solar MCAO, as, e.g., the integration of neuronal networks in the reconstruction process. This prototype will work as follows: a high-resolution image of the sun will be created and perturbed by a turbulence simulator with different phase screens placed at different heights. MCAO correction will be performed by one pupil DM and four altitude DMs. Two wide field wavefront sensors will be used to perform the tomography. The calibration and control strategies are still to be defined in the lab for the future implementation on the EST MCAO system. A scientific camera will evaluate the performance on a 60" field. The prototype is currently under construction and it is expected to be finished by 2019. Title: Commissioning tests of an Integral Field Unit (IFU) at GREGOR solar telescope Authors: Dominguez-Tagle, C.; Collados, M.; Esteves, M. A.; Vega Reyes, N.; Vaz Cedillo, J. J.; López, R. L.; Paez, E.; Grassin, O.; Gracia, F. Bibcode: 2018SPIE10702E..2ID Altcode: We present the commissioning of an IFU based on image-slicers and a 2D-Field-of-View Scanning System (FoV-SS) for the GREGOR Infrared Spectrograph (GRIS). The prototype of the image-slicer has eight slices of 1.8 mm x 0.1 mm in Zerodur, covering an area of 20 arcsec2. The FoV-SS, equipped with three Degrees of Freedom (DoF), allows to scan a region of 1 arcmin2, feeding the image-slicer with different portions of the field of view. A batch of tests was done during the Assembly, Integration and Verification (AIV) at GREGOR telescope. Title: Adaptive optics for high precision polarimetry: preliminary tests of DM polarization Authors: Stangalini, M.; Faccini, D.; Pedichini, F.; Piazzesi, R.; Ermolli, I.; Giorgi, F.; Montoya, L. M.; Collados Vera, M. Bibcode: 2018SPIE10703E..4VS Altcode: The European Solar Telescope (EST) will provide spectro-polarimetric measurements of the solar atmosphere with unprecedented sensitivity and accuracy. To this purpose, its optical scheme, as well as its MCAO system, are designed to minimize the instrumental polarization. In the framework of the EST design, we have started a series of laboratory tests to characterize the effects of using deformable mirrors on polarization measurements. In this contribution, we will show the results of these tests. These results are not only relevant to solar physics, but also to a number of other astrophysical research fields where high precision polarimetry is becoming a fundamental tool, such as for example exoplanets detection, and star formation characterization. Title: High-resolution imaging and near-infrared spectroscopy of penumbral decay Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei, R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.; Diercke, A.; González Manrique, S. J. Bibcode: 2018A&A...614A...2V Altcode: 2018arXiv180103686V
Aims: Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us to scrutinize the velocity and magnetic fields of sunspots and their surroundings.
Methods: Active region NOAA 12597 was observed on 2016 September 24 with the 1.5-meter GREGOR solar telescope using high-spatial-resolution imaging as well as imaging spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal proper motions were estimated with local correlation tracking, whereas line-of-sight (LOS) velocities were computed with spectral line fitting methods. The magnetic field properties were inferred with the "Stokes Inversions based on Response functions" (SIR) code for the Si I and Ca I NIR lines.
Results: At the time of the GREGOR observations, the leading sunspot had two light bridges indicating the onset of its decay. One of the light bridges disappeared, and an elongated, dark umbral core at its edge appeared in a decaying penumbral sector facing the newly emerging flux. The flow and magnetic field properties of this penumbral sector exhibited weak Evershed flow, moat flow, and horizontal magnetic field. The penumbral gap adjacent to the elongated umbral core and the penumbra in that penumbral sector displayed LOS velocities similar to granulation. The separating polarities of a new flux system interacted with the leading and central part of the already established active region. As a consequence, the leading spot rotated 55° clockwise over 12 h.
Conclusions: In the high-resolution observations of a decaying sunspot, the penumbral filaments facing the flux emergence site contained a darkened area resembling an umbral core filled with umbral dots. This umbral core had velocity and magnetic field properties similar to the sunspot umbra. This implies that the horizontal magnetic fields in the decaying penumbra became vertical as observed in flare-induced rapid penumbral decay, but on a very different time-scale. Title: Partially Ionized Plasmas in Astrophysics Authors: Ballester, José Luis; Alexeev, Igor; Collados, Manuel; Downes, Turlough; Pfaff, Robert F.; Gilbert, Holly; Khodachenko, Maxim; Khomenko, Elena; Shaikhislamov, Ildar F.; Soler, Roberto; Vázquez-Semadeni, Enrique; Zaqarashvili, Teimuraz Bibcode: 2018SSRv..214...58B Altcode: 2017arXiv170707975B Partially ionized plasmas are found across the Universe in many different astrophysical environments. They constitute an essential ingredient of the solar atmosphere, molecular clouds, planetary ionospheres and protoplanetary disks, among other environments, and display a richness of physical effects which are not present in fully ionized plasmas. This review provides an overview of the physics of partially ionized plasmas, including recent advances in different astrophysical areas in which partial ionization plays a fundamental role. We outline outstanding observational and theoretical questions and discuss possible directions for future progress. Title: Rayleigh-Taylor instabilities with sheared magnetic fields in partially ionised plasmas Authors: Ruderman, M. S.; Ballai, I.; Khomenko, E.; Collados, M. Bibcode: 2018A&A...609A..23R Altcode: 2017A&A...609A..23R
Aims: In the present study we investigate the nature of the magnetic Rayleigh-Taylor instability appearing at a tangential discontinuity in a partially ionised plasma when the effect of magnetic shear is taken into account.
Methods: The partially ionised character of the plasma is described by the ambipolar diffusion in the induction equation. The dynamics of the plasma is investigated in a single-fluid approximation. After matching the solutions on both sides of the interface we derive a dispersion equation and calculate the instability increment using analytical methods for particular cases of parameters, and numerical investigation for a wide range of parameters.
Results: We calculated the dependence of the instability increment on the perturbation wavenumber. We also calculated the dependence of the maximum instability increment on the shear angle of the magnetic field for various values of the ionisation degree.
Conclusions: Our results show that the Rayleigh-Taylor instability becomes sensitive to the degree of plasma ionisation only for plasmas with small values of plasma beta and in a very weakly ionised state. Perturbations are unstable only for those wavenumbers that are below a cut-off value. Title: Signatures of the impact of flare-ejected plasma on the photosphere of a sunspot light bridge Authors: Felipe, T.; Collados, M.; Khomenko, E.; Rajaguru, S. P.; Franz, M.; Kuckein, C.; Asensio Ramos, A. Bibcode: 2017A&A...608A..97F Altcode: 2017arXiv170806133F
Aims: We investigate the properties of a sunspot light bridge, focusing on the changes produced by the impact of a plasma blob ejected from a C-class flare.
Methods: We observed a sunspot in active region NOAA 12544 using spectropolarimetric raster maps of the four Fe I lines around 15 655 Å with the GREGOR Infrared Spectrograph, narrow-band intensity images sampling the Fe I 6173 Å line with the GREGOR Fabry-Pérot Interferometer, and intensity broad-band images in G-band and Ca II H-band with the High-resolution Fast Imager. All these instruments are located at the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The data cover the time before, during, and after the flare event. The analysis is complemented with Atmospheric Imaging Assembly and Helioseismic and Magnetic Imager data from the Solar Dynamics Observatory. The physical parameters of the atmosphere at differents heights were inferred using spectral-line inversion techniques.
Results: We identify photospheric and chromospheric brightenings, heating events, and changes in the Stokes profiles associated with the flare eruption and the subsequent arrival of the plasma blob to the light bridge, after traveling along an active region loop.
Conclusions: The measurements suggest that these phenomena are the result of reconnection events driven by the interaction of the plasma blob with the magnetic field topology of the light bridge.

Movies attached to Figs. 1 and 3 are available at http://www.aanda.org Title: Detection of emission in the Si I 1082.7 nm line core in sunspot umbrae Authors: Orozco Suárez, D.; Quintero Noda, C.; Ruiz Cobo, B.; Collados Vera, M.; Felipe, T. Bibcode: 2017A&A...607A.102O Altcode: 2017arXiv170906773O Context. Determining empirical atmospheric models for the solar chromosphere is difficult since it requires the observation and analysis of spectral lines that are affected by non-local thermodynamic equilibrium (NLTE) effects. This task is especially difficult in sunspot umbrae because of lower continuum intensity values in these regions with respect to the surrounding brighter granulation. Umbral data is therefore more strongly affected by the noise and by the so-called scattered light, among other effects.
Aims: The purpose of this study is to analyze spectropolarimetric sunspot umbra observations taken in the near-infrared Si I 1082.7 nm line taking NLTE effects into account. Interestingly, we detected emission features at the line core of the Si I 1082.7 nm line in the sunspot umbra. Here we analyze the data in detail and offer a possible explanation for the Si I 1082.7 nm line emission.
Methods: Full Stokes measurements of a sunspot near disk center in the near-infrared spectral range were obtained with the GRIS instrument installed at the German GREGOR telescope. A point spread function (PSF) including the effects of the telescope, the Earth's atmospheric seeing, and the scattered light was constructed using prior Mercury observations with GRIS and the information provided by the adaptive optics system of the GREGOR telescope during the observations. The data were then deconvolved from the PSF using a principal component analysis deconvolution method and were analyzed via the NICOLE inversion code, which accounts for NLTE effects in the Si I 1082.7 nm line. The information of the vector magnetic field was included in the inversion process.
Results: The Si I 1082.7 nm line seems to be in emission in the umbra of the observed sunspot after the effects of scattered light (stray light coming from wide angles) are removed. We show how the spectral line shape of umbral profiles changes dramatically with the amount of scattered light. Indeed, the continuum levels range, on average, from 44% of the quiet Sun continuum intensity to about 20%. Although very low, the inferred levels are in line with current model predictions and empirical umbral models. The Si I 1082.7 nm line is in emission after adding more that 30% of scattered light so that it is very sensitive to a proper determination of the PSF. Additionally, we have thoroughly investigated whether the emission is a byproduct of the particular deconvolution technique but have not found any evidence to the contrary. Only the circular polarization signals seem to be more sensitive to the deconvolution strategy because of the larger amount of noise in the umbra. Interestingly, current umbral empirical models are not able to reproduce the emission in the deconvolved umbral Stokes profiles. The results of the NLTE inversions suggests that to obtain the emission in the Si I 1082.7 nm line, the temperature stratification should first have a hump located at about log τ = -2 and start rising at lower heights when moving into the transition region.
Conclusions: This is, to our knowledge, the first time the Si I 1082.7 nm line is seen in emission in sunspot umbrae. The results show that the temperature stratification of current umbral models may be more complex than expected with the transition region located at lower heights above sunspot umbrae. Our finding might provide insights into understanding why the sunspot umbra emission in the millimeter spectral range is less than that predicted by current empirical umbral models. Title: Flows along arch filaments observed in the GRIS `very fast spectroscopic mode' Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.; Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier, R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2017IAUS..327...28G Altcode: 2017arXiv170102206G A new generation of solar instruments provides improved spectral, spatial, and temporal resolution, thus facilitating a better understanding of dynamic processes on the Sun. High-resolution observations often reveal multiple-component spectral line profiles, e.g., in the near-infrared He i 10830 Å triplet, which provides information about the chromospheric velocity and magnetic fine structure. We observed an emerging flux region, including two small pores and an arch filament system, on 2015 April 17 with the `very fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS) situated at the 1.5-meter GREGOR solar telescope at Observatorio del Teide, Tenerife, Spain. We discuss this method of obtaining fast (one per minute) spectral scans of the solar surface and its potential to follow dynamic processes on the Sun. We demonstrate the performance of the `very fast spectroscopic mode' by tracking chromospheric high-velocity features in the arch filament system. Title: Numerical simulations of quiet Sun magnetic fields seeded by the Biermann battery Authors: Khomenko, E.; Vitas, N.; Collados, M.; de Vicente, A. Bibcode: 2017A&A...604A..66K Altcode: 2017arXiv170606037K The magnetic fields of the quiet Sun cover at any time more than 90% of its surface and their magnetic energy budget is crucial to explain the thermal structure of the solar atmosphere. One of the possible origins of these fields is the action of the local dynamo in the upper convection zone of the Sun. Existing simulations of the local solar dynamo require an initial seed field and sufficiently high spatial resolution in order to achieve the amplification of the seed field to the observed values in the quiet Sun. Here we report an alternative model of seeding based on the action of the Bierman battery effect. This effect generates a magnetic field due to the local imbalances in electron pressure in the partially ionized solar plasma. We show that the battery effect self-consistently creates from zero an initial seed field of a strength of the order of micro G, and together with dynamo amplification allows the generation of quiet Sun magnetic fields of a similar strength to those from solar observations. Title: High-frequency waves in the corona due to null points Authors: Santamaria, I. C.; Khomenko, E.; Collados, M.; de Vicente, A. Bibcode: 2017A&A...602A..43S Altcode: 2017arXiv170406551S This work aims to understand the behavior of non-linear waves in the vicinity of a coronal null point. In previous works we have shown that high-frequency waves are generated in such a magnetic configuration. This paper studies those waves in detail in order to provide a plausible explanation of their generation. We demonstrate that slow magneto-acoustic shock waves generated in the chromosphere propagate through the null point and produce a train of secondary shocks that escape along the field lines. A particular combination of the shock wave speeds generates waves at a frequency of 80 mHz. We speculate that this frequency may be sensitive to the atmospheric parameters in the corona and therefore can be used to probe the structure of this solar layer.

Movies attached to Figs 2 and 4 are available at http://www.aanda.org Title: Penumbral thermal structure below the visible surface Authors: Borrero, J. M.; Franz, M.; Schlichenmaier, R.; Collados, M.; Asensio Ramos, A. Bibcode: 2017A&A...601L...8B Altcode: 2017arXiv170502832B Context. The thermal structure of the penumbra below its visible surface (I.e., τ5 ≥ 1) has important implications for our present understanding of sunspots and their penumbrae: their brightness and energy transport, mode conversion of magneto-acoustic waves, sunspot seismology, and so forth.
Aims: We aim at determining the thermal stratification in the layers immediately beneath the visible surface of the penumbra: τ5 ∈ [1,3] (≈70-80 km below the visible continuum-forming layer)
Methods: We analyzed spectropolarimetric data (I.e., Stokes profiles) in three Fe I lines located at 1565 nm observed with the GRIS instrument attached to the 1.5-m solar telescope GREGOR. The data are corrected for the smearing effects of wide-angle scattered light and then subjected to an inversion code for the radiative transfer equation in order to retrieve, among others, the temperature as a function of optical depth T(τ5).
Results: We find that the temperature gradient below the visible surface of the penumbra is smaller than in the quiet Sun. This implies that in the region τ5 ≥ 1 the penumbral temperature diverges from that of the quiet Sun. The same result is obtained when focusing only on the thermal structure below the surface of bright penumbral filaments.
Conclusions: We interpret these results as evidence of a thick penumbra, whereby the magnetopause is not located near its visible surface. In addition, we find that the temperature gradient in bright penumbral filaments is lower than in granules. This can be explained in terms of the limited expansion of a hot upflow inside a penumbral filament relative to a granular upflow, as magnetic pressure and tension forces from the surrounding penumbral magnetic field hinder an expansion like this. Title: First tests on the Integral Field Unit for GRIS at GREGOR Authors: Dominguez-Tagle, C.; Collados, M.; Lopez, R. L.; Vaz Cedillo, J. J.; Esteves, M. A.; Paez, E.; Asensio Ramos, A. Bibcode: 2017sone.meetE..89D Altcode: The observation of the highly dynamic events in the chromosphere with current slit or filter spectropolarimeters is not adequate. With the sake of incresing the time, spectral and spatial coherence of the data, an integral field unit prototype has been developed for the GRIS spectrograph on the GREGOR telescope. In this talk, we present the first tests of the prototype. Title: Science with European Solar Telescope Authors: Matthews, Sarah; Collados, Manuel Bibcode: 2017psio.confE..78M Altcode: No abstract at ADS Title: The SOLARNET project Authors: Collados, M. Bibcode: 2017psio.confE...1C Altcode: No abstract at ADS Title: Micro-meteorological contribution to the SHABAR seeing retrieval Authors: Hartogensis, Oscar; Hammerschlag, Robert; Sliepen, Guus; Sprung, Detlev; von der Lühe, Oskar; Collados, Manuel Bibcode: 2017psio.confE.102H Altcode: No abstract at ADS Title: SOLARNET WP70: Turbulence characterisation and correction Authors: Collados, M. Bibcode: 2017psio.confE..98C Altcode: No abstract at ADS Title: Slipping reconnection in a solar flare observed in high resolution with the GREGOR solar telescope Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák, J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann, A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.; Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T. Bibcode: 2016A&A...596A...1S Altcode: 2016arXiv160500464S A small flare ribbon above a sunspot umbra in active region 12205 was observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference filter. Context observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode, and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is part of a larger one that extends through the neighboring positive polarities and also participates in several other flares within the active region. We reconstructed a time series of 140 s of Ca II H images by means of the multiframe blind deconvolution method, which resulted in spatial and temporal resolutions of 0.1″ and 1 s. Light curves and horizontal velocities of small-scale bright knots in the observed flare ribbon were measured. Some knots are stationary, but three move along the ribbon with speeds of 7-11 km s-1. Two of them move in the opposite direction and exhibit highly correlated intensity changes, which provides evidence of a slipping reconnection at small spatial scales.

Movies associated to Figs. 1 and 2 are available at http://www.aanda.org Title: Deep probing of the photospheric sunspot penumbra: no evidence of field-free gaps Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.; Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.; Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe, O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.; Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H. Bibcode: 2016A&A...596A...2B Altcode: 2016arXiv160708165B Context. Some models for the topology of the magnetic field in sunspot penumbrae predict regions free of magnetic fields or with only dynamically weak fields in the deep photosphere.
Aims: We aim to confirm or refute the existence of weak-field regions in the deepest photospheric layers of the penumbra.
Methods: We investigated the magnetic field at log τ5 = 0 is by inverting spectropolarimetric data of two different sunspots located very close to disk center with a spatial resolution of approximately 0.4-0.45''. The data have been recorded using the GRIS instrument attached to the 1.5-m solar telescope GREGOR at the El Teide observatory. The data include three Fe I lines around 1565 nm, whose sensitivity to the magnetic field peaks half a pressure scale height deeper than the sensitivity of the widely used Fe I spectral line pair at 630 nm. Before the inversion, the data were corrected for the effects of scattered light using a deconvolution method with several point spread functions.
Results: At log τ5 = 0 we find no evidence of regions with dynamically weak (B< 500 Gauss) magnetic fields in sunspot penumbrae. This result is much more reliable than previous investigations made on Fe I lines at 630 nm. Moreover, the result is independent of the number of nodes employed in the inversion, is independent of the point spread function used to deconvolve the data, and does not depend on the amount of stray light (I.e., wide-angle scattered light) considered. Title: Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.; Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.; Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1050B Altcode: 2016arXiv160901514B Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0 nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the arch filament system connect the sunspot with patches of magnetic polarity opposite to that of the spot. These patches do not necessarily coincide with pores, where the magnetic field is strongest. Instead, areas are preferred not far from the polarity inversion line. These areas exhibit photospheric downflows of moderate velocity, but significantly higher downflows of up to 30 km s-1 in the chromospheric helium line. Our findings can be explained with new emerging flux where the matter flows downward along the field lines of rising flux tubes, in agreement with earlier results. Title: Magnetic fields of opposite polarity in sunspot penumbrae Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.; Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld, T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.; Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar, A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier, K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M. Bibcode: 2016A&A...596A...4F Altcode: 2016arXiv160800513F Context. A significant part of the penumbral magnetic field returns below the surface in the very deep photosphere. For lines in the visible, a large portion of this return field can only be detected indirectly by studying its imprints on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe a narrow layer in the very deep photosphere, providing the possibility of directly measuring the orientation of magnetic fields close to the solar surface.
Aims: We study the topology of the penumbral magnetic field in the lower photosphere, focusing on regions where it returns below the surface.
Methods: We analyzed 71 spectropolarimetric datasets from Hinode and from the GREGOR infrared spectrograph. We inferred the quality and polarimetric accuracy of the infrared data after applying several reduction steps. Techniques of spectral inversion and forward synthesis were used to test the detection algorithm. We compared the morphology and the fractional penumbral area covered by reversed-polarity and three-lobed Stokes V profiles for sunspots at disk center. We determined the amount of reversed-polarity and three-lobed Stokes V profiles in visible and infrared data of sunspots at various heliocentric angles. From the results, we computed center-to-limb variation curves, which were interpreted in the context of existing penumbral models.
Results: Observations in visible and near-infrared spectral lines yield a significant difference in the penumbral area covered by magnetic fields of opposite polarity. In the infrared, the number of reversed-polarity Stokes V profiles is smaller by a factor of two than in the visible. For three-lobed Stokes V profiles the numbers differ by up to an order of magnitude. Title: Horizontal flow fields in and around a small active region. The transition period between flux emergence and decay Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke, A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert, M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A...3V Altcode: 2016arXiv160507462V Context. The solar magnetic field is responsible for all aspects of solar activity. Thus, emergence of magnetic flux at the surface is the first manifestation of the ensuing solar activity.
Aims: Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region.
Methods: The small active region NOAA 12118 emerged on 2014 July 17 and was observed one day later with the 1.5-m GREGOR solar telescope on 2014 July 18. High-resolution time-series of blue continuum and G-band images acquired in the blue imaging channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were complemented by synoptic line-of-sight magnetograms and continuum images obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Horizontal proper motions and horizontal plasma velocities were computed with local correlation tracking (LCT) and the differential affine velocity estimator (DAVE), respectively. Morphological image processing was employed to measure the photometric and magnetic area, magnetic flux, and the separation profile of the emerging flux region during its evolution.
Results: The computed growth rates for photometric area, magnetic area, and magnetic flux are about twice as high as the respective decay rates. The space-time diagram using HMI magnetograms of five days provides a comprehensive view of growth and decay. It traces a leaf-like structure, which is determined by the initial separation of the two polarities, a rapid expansion phase, a time when the spread stalls, and a period when the region slowly shrinks again. The separation rate of 0.26 km s-1 is highest in the initial stage, and it decreases when the separation comes to a halt. Horizontal plasma velocities computed at four evolutionary stages indicate a changing pattern of inflows. In LCT maps we find persistent flow patterns such as outward motions in the outer part of the two major pores, a diverging feature near the trailing pore marking the site of upwelling plasma and flux emergence, and low velocities in the interior of dark pores. We detected many elongated rapidly expanding granules between the two major polarities, with dimensions twice as large as the normal granules. Title: Upper chromospheric magnetic field of a sunspot penumbra: observations of fine structure Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados, M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar, H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.; Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A...8J Altcode: 2016arXiv160801988J
Aims: The fine-structure of the magnetic field in a sunspot penumbra in the upper chromosphere is to be explored and compared to that in the photosphere.
Methods: Spectropolarimetric observations with high spatial resolution were recorded with the 1.5-m GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The observed spectral domain includes the upper chromospheric Hei triplet at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å spectral lines. The upper chromospheric magnetic field is obtained by inverting the Hei triplet assuming a Milne-Eddington-type model atmosphere. A height-dependent inversion was applied to the Sii 10 827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic field.
Results: We find that the inclination of the magnetic field varies in the azimuthal direction in the photosphere and in the upper chromosphere. The chromospheric variations coincide remarkably well with the variations in the inclination of the photospheric field and resemble the well-known spine and interspine structure in the photospheric layers of penumbrae. The typical peak-to-peak variations in the inclination of the magnetic field in the upper chromosphere are found to be 10°-15°, which is roughly half the variation in the photosphere. In contrast, the magnetic field strength of the observed penumbra does not vary on small spatial scales in the upper chromosphere.
Conclusions: Thanks to the high spatial resolution of the observations that is possible with the GREGOR telescope at 1.08 microns, we find that the prominent small-scale fluctuations in the magnetic field inclination, which are a salient part of the property of sunspot penumbral photospheres, also persist in the chromosphere, although at somewhat reduced amplitudes. Such a complex magnetic configuration may facilitate penumbral chromospheric dynamic phenomena, such as penumbral micro-jets or transient bright dots. Title: Active region fine structure observed at 0.08 arcsec resolution Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.; Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.; Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.; Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann, T.; Kneer, F.; Nicklas, H.; Sobotka, M. Bibcode: 2016A&A...596A...7S Altcode: 2016arXiv160707094S Context. The various mechanisms of magneto-convective energy transport determine the structure of sunspots and active regions.
Aims: We characterise the appearance of light bridges and other fine-structure details and elaborate on their magneto-convective nature.
Methods: We present speckle-reconstructed images taken with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the 486 nm and 589 nm bands. We estimate the spatial resolution from the noise characteristics of the image bursts and obtain 0.08″ at 589 nm. We describe structure details in individual best images as well as the temporal evolution of selected features.
Results: We find branched dark lanes extending along thin (≈1″) light bridges in sunspots at various heliocentric angles. In thick (≳ 2″) light bridges the branches are disconnected from the central lane and have a Y shape with a bright grain toward the umbra. The images reveal that light bridges exist on varying intensity levels and that their small-scale features evolve on timescales of minutes. Faint light bridges show dark lanes outlined by the surrounding bright features. Dark lanes are very common and are also found in the boundary of pores. They have a characteristic width of 0.1″ or smaller. Intergranular dark lanes of that width are seen in active region granulation.
Conclusions: We interpret our images in the context of magneto-convective simulations and findings: while central dark lanes in thin light bridges are elevated and associated with a density increase above upflows, the dark lane branches correspond to locations of downflows and are depressed relative to the adjacent bright plasma. Thick light bridges with central dark lanes show no projection effect. They have a flat elevated plateau that falls off steeply at the umbral boundary. There, Y-shaped filaments form as they do in the inner penumbra. This indicates the presence of inclined magnetic fields, meaning that the umbral magnetic field is wrapped around the convective light bridge. Title: Probing deep photospheric layers of the quiet Sun with high magnetic sensitivity Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González, M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.; Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.; Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.; Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier, K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.; Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.; Schmidt, D.; Kiess, C.; Nicklas, H. Bibcode: 2016A&A...596A...6L Altcode: 2016arXiv160506324L Context. Investigations of the magnetism of the quiet Sun are hindered by extremely weak polarization signals in Fraunhofer spectral lines. Photon noise, straylight, and the systematically different sensitivity of the Zeeman effect to longitudinal and transversal magnetic fields result in controversial results in terms of the strength and angular distribution of the magnetic field vector.
Aims: The information content of Stokes measurements close to the diffraction limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of spatial straylight and photon noise into account.
Methods: Highly sensitive full Stokes measurements of a quiet-Sun region at disk center in the deep photospheric Fe I lines in the 1.56 μm region were obtained with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise statistics and Stokes V asymmetries were analyzed and compared to a similar data set of the Hinode spectropolarimeter (SOT/SP). Simple diagnostics based directly on the shape and strength of the profiles were applied to the GRIS data. We made use of the magnetic line ratio technique, which was tested against realistic magneto-hydrodynamic simulations (MURaM).
Results: About 80% of the GRIS spectra of a very quiet solar region show polarimetric signals above a 3σ level. Area and amplitude asymmetries agree well with small-scale surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss range with some concentrations of kilo-Gauss fields.
Conclusions: The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4 are so far unique in the combination of high spatial resolution scans and high magnetic field sensitivity. Nevertheless, the unavoidable effect of spatial straylight and the resulting dilution of the weak Stokes profiles means that inversion techniques still bear a high risk of misinterpretating the data. Title: Flow and magnetic field properties in the trailing sunspots of active region NOAA 12396 Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer, C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados, M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1090V Altcode: Improved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of active regions. We present an illustrative sample of multi-instrument data acquired during a two-week coordinated observing campaign in August 2015 involving, among others, the GREGOR solar telescope (imaging and near-infrared spectroscopy) and the space missions Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). The observations focused on the trailing part of active region NOAA 12396 with complex polarity inversion lines and strong intrusions of opposite polarity flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV spectral profiles in the photospheric Si I λ1082.7 nm line, the chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I λ1083.9 nm line. Carefully calibrated GRIS scans of the active region provided maps of Doppler velocity and magnetic field at different atmospheric heights. We compare quick-look maps with those obtained with the ``Stokes Inversions based on Response functions'' (SIR) code, which furnishes deeper insight into the magnetic properties of the region. We find supporting evidence that newly emerging flux and intruding opposite polarity flux are hampering the formation of penumbrae, i.e., a penumbra fully surrounding a sunspot is only expected after cessation of flux emergence in proximity to the sunspots. Title: Three-dimensional structure of a sunspot light bridge Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.; Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016A&A...596A..59F Altcode: 2016arXiv161104803F Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking.
Aims: We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay.
Methods: We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.
Results: The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-β), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution.

Movies associated to Figs. 2 and 13 are available at http://www.aanda.org Title: Inference of magnetic fields in the very quiet Sun Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.; Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.; Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.; González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.; Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman, T.; Volkmer, R. Bibcode: 2016A&A...596A...5M Altcode: 2018arXiv180410089M Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution.
Aims: We present high-precision spectro-polarimetric data with high spatial resolution (0.4'') of the very quiet Sun at 1.56 μm obtained with the GREGOR telescope to shed some light on this complex magnetism.
Methods: We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component.
Results: Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak ( 150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area 50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised. Title: Fitting peculiar spectral profiles in He I 10830Å absorption features Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.; Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.; Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016AN....337.1057G Altcode: 2016arXiv160300679G The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He I 10830 Å triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He I 10830 Å triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double-Lorentzian fitting technique using Levenberg-Marquardt least-squares minimization. This technique is very simple and much faster than inversion codes. Line-of-sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub- and supersonic downflow velocities of up to 32 km s-1 for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. Title: The European Solar Telescope (EST) Authors: Matthews, Sarah A.; Collados, Manuel; Mathioudakis, Mihalis; Erdelyi, Robertus Bibcode: 2016SPIE.9908E..09M Altcode: The European Solar Telescope (EST) is being designed to optimize studies of the magnetic coupling between the lower layers of the solar atmosphere (the photosphere and chromosphere) in order to investigate the origins and evolution of the solar magnetic field and its role in driving solar activity. In order to achieve this, the thermal, dynamic and magnetic properties of the solar plasma must be probed over many scale heights and at intrinsic scales, requiring the use of multi wavelength spectroscopy and spectropolarimetry at high spatial, spectral and temporal resolution. In this paper we describe some of the over-arching science questions that EST will address and briefly outline the main features of the proposed telescope design and the associated instrumentation package. Title: On the Magnetism and Dynamics of Prominence Legs Hosting Tornadoes Authors: Martínez González, M. J.; Asensio Ramos, A.; Arregui, I.; Collados, M.; Beck, C.; de la Cruz Rodríguez, J. Bibcode: 2016ApJ...825..119M Altcode: 2016arXiv160501183M Solar tornadoes are dark vertical filamentary structures observed in the extreme ultraviolet associated with prominence legs and filament barbs. Their true nature and relationship to prominences requires an understanding of their magnetic structure and dynamic properties. Recently, a controversy has arisen: is the magnetic field organized forming vertical, helical structures or is it dominantly horizontal? And concerning their dynamics, are tornadoes really rotating or is it just a visual illusion? Here we analyze four consecutive spectro-polarimetric scans of a prominence hosting tornadoes on its legs, which helps us shed some light on their magnetic and dynamical properties. We show that the magnetic field is very smooth in all the prominence, which is probably an intrinsic property of the coronal field. The prominence legs have vertical helical fields that show slow temporal variation that is probably related to the motion of the fibrils. Concerning the dynamics, we argue that (1) if rotation exists, it is intermittent, lasting no more than one hour, and (2) the observed velocity pattern is also consistent with an oscillatory velocity pattern (waves). Title: Solar adaptive optics: specificities, lessons learned, and open alternatives Authors: Montilla, I.; Marino, J.; Asensio Ramos, A.; Collados, M.; Montoya, L.; Tallon, M. Bibcode: 2016SPIE.9909E..1HM Altcode: First on sky adaptive optics experiments were performed on the Dunn Solar Telescope on 1979, with a shearing interferometer and limited success. Those early solar adaptive optics efforts forced to custom-develop many components, such as Deformable Mirrors and WaveFront Sensors, which were not available at that time. Later on, the development of the correlation Shack-Hartmann marked a breakthrough in solar adaptive optics. Since then, successful Single Conjugate Adaptive Optics instruments have been developed for many solar telescopes, i.e. the National Solar Observatory, the Vacuum Tower Telescope and the Swedish Solar Telescope. Success with the Multi Conjugate Adaptive Optics systems for GREGOR and the New Solar Telescope has proved to be more difficult to attain. Such systems have a complexity not only related to the number of degrees of freedom, but also related to the specificities of the Sun, used as reference, and the sensing method. The wavefront sensing is performed using correlations on images with a field of view of 10", averaging wavefront information from different sky directions, affecting the sensing and sampling of high altitude turbulence. Also due to the low elevation at which solar observations are performed we have to include generalized fitting error and anisoplanatism, as described by Ragazzoni and Rigaut, as non-negligible error sources in the Multi Conjugate Adaptive Optics error budget. For the development of the next generation Multi Conjugate Adaptive Optics systems for the Daniel K. Inouye Solar Telescope and the European Solar Telescope we still need to study and understand these issues, to predict realistically the quality of the achievable reconstruction. To improve their designs other open issues have to be assessed, i.e. possible alternative sensing methods to avoid the intrinsic anisoplanatism of the wide field correlation Shack-Hartmann, new parameters to estimate the performance of an adaptive optics solar system, alternatives to the Strehl and the Point Spread Function used in night time adaptive optics but not really suitable to the solar systems, and new control strategies more complex than the ones used in nowadays solar Multi Conjugate Adaptive Optics systems. In this paper we summarize the lessons learned with past and current solar adaptive optics systems and focus on the discussion on the new alternatives to solve present open issues limiting their performance. Title: Local seeing determination by thermal-CFD analysis to optimize the European Solar Telescope image quality Authors: Vega Reyes, N.; Cavaller, L.; Marco de la Rosa, J.; Baiges, J.; Pont, A.; Pérez-Sánchez, D.; Codina, R.; Grivel, C.; Collados, M. Bibcode: 2016SPIE.9912E..1CV Altcode: The European Solar Telescope, EST, ([1], [2]) is a 4-meter solar telescope to be built in the Canary Islands in the near future. In order to select the best configuration for the EST telescope facilities, thermal and CFD analyses have been carried out to evaluate the seeing degradation produced by the telescope environment. The aim of this study is to calculate the values of optical parameters in different configurations and to find out which one causes the lowest image quality degradation. Starting from the determination of seeing degradation along the optical path by CFD techniques, several configurations have been compared making it possible to decide the future development line for the EST. Title: Opto-mechanical design of an image slicer for the GRIS spectrograph at GREGOR Authors: Vega Reyes, N.; Esteves, M. A.; Sánchez-Capuchino, J.; Salaun, Y.; López, R. L.; Gracia, F.; Estrada Herrera, P.; Grivel, C.; Vaz Cedillo, J. J.; Collados, M. Bibcode: 2016SPIE.9912E..5PV Altcode: An image slicer has been proposed for the Integral Field Spectrograph [1] of the 4-m European Solar Telescope (EST) [2] The image slicer for EST is called MuSICa (Multi-Slit Image slicer based on collimator-Camera) [3] and it is a telecentric system with diffraction limited optical quality offering the possibility to obtain high resolution Integral Field Solar Spectroscopy or Spectro-polarimetry by coupling a polarimeter after the generated slit (or slits). Considering the technical complexity of the proposed Integral Field Unit (IFU), a prototype has been designed for the GRIS spectrograph at GREGOR telescope at Teide Observatory (Tenerife), composed by the optical elements of the image slicer itself, a scanning system (to cover a larger field of view with sequential adjacent measurements) and an appropriate re-imaging system. All these subsystems are placed in a bench, specially designed to facilitate their alignment, integration and verification, and their easy installation in front of the spectrograph. This communication describes the opto-mechanical solution adopted to upgrade GRIS while ensuring repeatability between the observational modes, IFU and long-slit. Results from several tests which have been performed to validate the opto-mechanical prototypes are also presented. Title: Daytime turbulence profiling for EST and its impact in the solar MCAO system design Authors: Marco de la Rosa, J.; Montoya, L.; Collados, M.; Montilla, I.; Vega Reyes, N. Bibcode: 2016SPIE.9909E..6XM Altcode: The European Solar Telescope (EST) is a 4-meter facility to be built in Canary Islands in the near future. Extensive daytime turbulence observation campaigns with the long baseline SHABAR instrument has been carried out in the two candidate sites from 2011 up to the end of 2014. The collected data together with nighttime turbulence data allow the site characterization and the computation of average turbulence profiles. These profiles can be used to feed numerical simulations in order to take important design decisions for the multiconjugate adaptive optics (MCAO) system in the telescope. This paper describes the main tasks developed in this context up to date. Title: Observational Detection of Drift Velocity between Ionized and Neutral Species in Solar Prominences Authors: Khomenko, Elena; Collados, Manuel; Díaz, Antonio J. Bibcode: 2016ApJ...823..132K Altcode: 2016arXiv160401177K We report the detection of differences in the ion and neutral velocities in prominences using high-resolution spectral data obtained in 2012 September at the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). A time series of scans of a small portion of a solar prominence was obtained simultaneously with high cadence using the lines of two elements with different ionization states, namely, Ca II 8542 Å and He I 10830 Å. The displacements, widths, and amplitudes of both lines were carefully compared to extract dynamical information about the plasma. Many dynamical features are detected, such as counterstreaming flows, jets, and propagating waves. In all of the cases, we find a very strong correlation between the parameters extracted from the lines of both elements, confirming that both lines trace the same plasma. Nevertheless, we also find short-lived transients where this correlation is lost. These transients are associated with ion-neutral drift velocities of the order of several hundred m s-1. The patches of non-zero drift velocity show coherence in time-distance diagrams. Title: Simulated interaction of magnetohydrodynamic shock waves with a complex network-like region Authors: Santamaria, I. C.; Khomenko, E.; Collados, M.; de Vicente, A. Bibcode: 2016A&A...590L...3S Altcode: 2016arXiv160408783S We provide estimates of the wave energy reaching the solar chromosphere and corona in a network-like magnetic field topology, including a coronal null point. The waves are excited by an instantaneous strong subphotospheric source and propagate through the subphotosphere, photosphere, chromosphere, transition region, and corona with the plasma beta and other atmospheric parameters varying by several orders of magnitude. We compare two regimes of the wave propagation: a linear and nonlinear regime. While the amount of energy reaching the corona is similar in both regimes, this energy is transmitted at different frequencies. In both cases the dominant periods of waves at each height strongly depend on the local magnetic field topology, but this distribution is only in accordance with observations in the nonlinear case.

Movies are available in electronic form at http://www.aanda.org Title: Flows in and around Active Region NOAA12118 Observed with the GREGOR Solar Telescope and SDO/HMI Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke, A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann, A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert, M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer, R.; von der Lühe, O.; Waldmann, T. Bibcode: 2016ASPC..504...29V Altcode: 2016arXiv160301109V Accurate measurements of magnetic and velocity fields in and around solar active regions are key to unlocking the mysteries of the formation and the decay of sunspots. High spatial resolution images and spectral sequences with a high cadence obtained with the GREGOR solar telescope give us an opportunity to scrutinize 3-D flow fields with local correlation tracking and imaging spectroscopy. We present GREGOR early science data acquired in 2014 July - August with the GREGOR Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series of blue continuum (λ 450.6 nm) images of the small active region NOAA 12118 were restored with the speckle masking technique to derive horizontal proper motions and to track the evolution of morphological changes. In addition, high-resolution observations are discussed in the context of synoptic data from the Solar Dynamics Observatory. Title: On the Robustness of the Pendulum Model for Large-amplitude Longitudinal Oscillations in Prominences Authors: Luna, M.; Terradas, J.; Khomenko, E.; Collados, M.; de Vicente, A. Bibcode: 2016ApJ...817..157L Altcode: 2015arXiv151205125L Large-amplitude longitudinal oscillations (LALOs) in prominences are spectacular manifestations of solar activity. In such events nearby energetic disturbances induce periodic motions on filaments with displacements comparable to the size of the filaments themselves and with velocities larger than 20 {km} {{{s}}}-1. The pendulum model, in which the gravity projected along a rigid magnetic field is the restoring force, was proposed to explain these events. However, it can be objected that in a realistic situation where the magnetic field reacts to the mass motion of the heavy prominence, the simplified pendulum model could be no longer valid. We have performed nonlinear time-dependent numerical simulations of LALOs considering a dipped magnetic field line structure. In this work we demonstrate that for even relatively weak magnetic fields the pendulum model works very well. We therefore validate the pendulum model and show its robustness, with important implications for prominence seismology purposes. With this model it is possible to infer the geometry of the dipped field lines that support the prominence. Title: Evershed flow observed in neutral and singly ionized iron lines Authors: Khomenko, E.; Collados, M.; Shchukina, N.; Díaz, A. Bibcode: 2015A&A...584A..66K Altcode: 2015arXiv151000334K The amplitudes of the Evershed flow are measured using pairs of carefully selected Fe i and Fe ii spectral lines that are close in wavelength and registered simultaneously. A sunspot belonging to the NOAA 11582 group was scanned using the spectrograph of the German Vacuum Tower Telescope (Observatorio del Teide, Tenerife). Velocities were extracted from intensity profiles using the λ-meter technique. The formation heights of the observed spectral lines were calculated using semi-empirical models of a bright and dark penumbral filament taking into account the sunspot location at the limb. Our objective is to compare azimuthally averaged amplitudes of the Evershed flow extracted from neutral and ion lines. We find measurable differences in the radial component of the flow. All five pairs of lines show the same tendency; the flow measured from the Fe i lines has an amplitude that is a few hundred ms-1 larger than that of the Fe ii lines. This tendency is preserved at all photospheric heights and radial distances in the penumbra. We discuss the possible origin of this effect. Title: Oscillations and Waves in Sunspots Authors: Khomenko, Elena; Collados, Manuel Bibcode: 2015LRSP...12....6K Altcode: A magnetic field modifies the properties of waves in a complex way. Significant advances have been made recently in our understanding of the physics of sunspot waves with the help of high-resolution observations, analytical theories, as well as numerical simulations. We review the current ideas in the field, providing the most coherent picture of sunspot oscillations as by present understanding. Title: Where are the solar magnetic poles? Authors: Pastor Yabar, A.; Martinez Gonzalez, M. J.; Collados, M. Bibcode: 2015MNRAS.453L..69P Altcode: 2018arXiv180409748P Regardless of the physical origin of stellar magnetic fields - fossil or dynamo induced - an inclination angle between the magnetic and rotation axes is very often observed. Absence of observational evidence in this direction in the solar case has led to generally assume that its global magnetic field and rotation axes are well aligned. We present the detection of a monthly periodic signal of the photospheric solar magnetic field at all latitudes, and especially near the poles, revealing that the main axis of the Sun's magnetic field is not aligned with the surface rotation axis. This result reinforces the view of our Sun as a common intermediate-mass star. Furthermore, this detection challenges and imposes a strong observational constraint to modern solar dynamo theories. Title: Full Stokes observations in the He i 1083 nm spectral region covering an M3.2 flare Authors: Kuckein, Christoph; Collados, Manuel; Sainz, Rafael Manso; Ramos, Andrés Asensio Bibcode: 2015IAUS..305...73K Altcode: 2015arXiv150205505K We present an exceptional data set acquired with the Vacuum Tower Telescope (Tenerife, Spain) covering the pre-flare, flare, and post-flare stages of an M3.2 flare. The full Stokes spectropolarimetric observations were recorded with the Tenerife Infrared Polarimeter in the He i 1083.0 nm spectral region. The object under study was active region NOAA 11748 on 2013 May 17. During the flare the chomospheric He i 1083.0 nm intensity goes strongly into emission. However, the nearby photospheric Si i 1082.7 nm spectral line profile only gets shallower and stays in absorption. Linear polarization (Stokes Q and U) is detected in all lines of the He i triplet during the flare. Moreover, the circular polarization (Stokes V) is dominant during the flare, being the blue component of the He i triplet much stronger than the red component, and both are stronger than the Si i Stokes V profile. The Si i inversions reveal enormous changes of the photospheric magnetic field during the flare. Before the flare magnetic field concentrations of up to ~1500 G are inferred. During the flare the magnetic field strength globally decreases and in some cases it is even absent. After the flare the magnetic field recovers its strength and initial configuration. Title: MCAO numerical simulations for EST: analysis and parameter optimization Authors: Montoya, Luzma; Montilla, Iciar; Collados, Manuel Bibcode: 2015aoel.confE..16M Altcode: No abstract at ADS Title: Analytical study of high altitude turbulence wide-field wavefront sensing: impact on the design and reconstruction quality of future solar AO systems Authors: Montilla, Iciar; Collados, Manuel; Montoya, Luzma; Tallon, Michel Bibcode: 2015aoel.confE..18M Altcode: No abstract at ADS Title: On the nature of transverse coronal waves revealed by wavefront dislocations Authors: López Ariste, A.; Luna, M.; Arregui, I.; Khomenko, E.; Collados, M. Bibcode: 2015A&A...579A.127L Altcode: 2015arXiv150503348L Context. Coronal waves are an important aspect of the dynamics of the plasma in the corona. Wavefront dislocations are topological features of most waves in nature and also of magnetohydrodynamic waves. Are there dislocations in coronal waves?
Aims: The finding and explanation of dislocations may shed light on the nature and characteristics of the propagating waves, their interaction in the corona, and in general on the plasma dynamics.
Methods: We positively identify dislocations in coronal waves observed by the Coronal Multi-channel Polarimeter (CoMP) as singularities in the Doppler shifts of emission coronal lines. We study the possible singularities that can be expected in coronal waves and try to reproduce the observed dislocations in terms of localization and frequency of appearance.
Results: The observed dislocations can only be explained by the interference of a kink and sausage wave modes propagating with different frequencies along the coronal magnetic field. In the plane transverse to the propagation, the cross-section of the oscillating plasma must be smaller than the spatial resolution, and the two waves result in net longitudinal and transverse velocity components that are mixed through projection onto the line of sight. Alfvén waves can be responsible for the kink mode, but a magnetoacoustic sausage mode is necessary in all cases. Higher (flute) modes are excluded. The kink mode has a pressure amplitude that is less than the pressure amplitude of the sausage mode, though its observed velocity is higher. This concentrates dislocations on the top of the loop.
Conclusions: To explain dislocations, any model of coronal waves must include the simultaneous propagation and interference of kink and sausage wave modes of comparable but different frequencies with a sausage wave amplitude much smaller than the kink one.

Appendix A is available in electronic form at http://www.aanda.org Title: Variation in sunspot properties between 1999 and 2014 Authors: Rezaei, R.; Beck, C.; Lagg, A.; Borrero, J. M.; Schmidt, W.; Collados, M. Bibcode: 2015A&A...578A..43R Altcode:
Aims: We study the variation in the magnetic field strength, area, and continuum intensity of umbrae in solar cycles 23 and 24.
Methods: We analyzed a sample of 374 sunspots observed from 1999 until 2014 with the Tenerife Infrared Polarimeter at the German Vacuum Tower Telescope and the Facility InfRared Spectropolarimeter at the Dunn Solar Telescope. The sample of field strength, area, and intensities was used to trace any long-term or cyclic trend of umbral properties in the last 15 years.
Results: Sunspots are systematically weaker, that is, have a weaker field strength and stronger continuum intensity, toward the end of cycle 23 than they had at the maximum of cycle 23. The linear trend reverses with the onset of cycle 24. We find that the field strength decreases in the declining phase of cycle 23 by about 112 (± 16) G yr-1, while it increases in the rising phase of cycle 24 by about 138 (± 72) G yr-1. The umbral intensity shows the opposite trend: the intensity increases with a rate of 0.7 (± 0.3)% of Ic yr-1 toward the end of cycle 23 and decreases with a rate of 3.8 (± 1.5)% of Ic yr-1 toward the maximum of cycle 24. The distribution of the umbral maximum field strength in cycle 24 is similar to that of cycle 23, but is slightly shifted toward lower values by about 80 G, corresponding to a possible long-term gradient in umbral field strength of about 7 ± 4 G yr-1. If instead of the maximum umbral field we consider the average value over the entire umbra, the distribution shifts by about 44 Gauss.
Conclusions: The umbral brightness decreases in the rising stage of a solar cycle, but increases from maximum toward the end of the cycle. Our results do not indicate a drastic change of the solar cycle toward a grand minimum in the near future. Title: Magnetohydrodynamic wave propagation from the subphotosphere to the corona in an arcade-shaped magnetic field with a null point Authors: Santamaria, I. C.; Khomenko, E.; Collados, M. Bibcode: 2015A&A...577A..70S Altcode: 2015arXiv150303094S
Aims: The aim of this work is to study the energy transport by means of Magnetohydrodynamic (MHD) waves propagating in quiet-Sun magnetic topology from layers below the surface to the corona. Upwardly propagating waves find obstacles, such as the equipartition layer with plasma β = 1, the transition region, and null points, and they get transmitted, converted, reflected, and refracted. Understanding the mechanisms by which MHD waves can reach the corona can give us information about the solar atmosphere and the magnetic structures.
Methods: We carried out two-dimensional numerical simulations of wave propagation in a magnetic field structure that consists of two vertical flux tubes with the same polarity separated by an arcade-shaped magnetic field. This configuration contains a null point in the corona, which significantly modifies the behavior of the waves as they pass near it.
Results: We describe in detail the wave propagation through the atmosphere under different driving conditions. We also present the spatial distribution of the mean acoustic and magnetic energy fluxes for the cases where these calculations are possible, as well as the spatial distribution of the dominant frequencies in the whole domain.
Conclusions: We conclude that the energy reaches the corona preferably along almost vertical magnetic fields, that is, inside the vertical flux tubes. This energy is acoustic in nature. Most of the magnetic energy stays concentrated below the transition region owing to the refraction of the magnetic waves and the continuous conversion of acoustic-like waves into fast magnetic waves in the equipartition layer located in the photosphere where plasma β = 1. However, part of the magnetic energy reaches the low corona when propagating in the region where the arcades are located, but waves are sent back downward into the lower atmosphere at the null-point surroundings. This phenomenon, together with the reflection and refraction of waves in the TR and the lower turning point, act as a re-feeding of the atmosphere, which keeps oscillating during all the simulation time even if a driver with a single pulse was used as initial perturbation. In the frequency distribution, we find that high frequency waves can reach the corona outside the vertical flux tubes.

Movies related to Figs. 3, 7, and 11 are available in electronic form at http://www.aanda.org Title: Magnetic and Dynamical Photospheric Disturbances Observed During an M3.2 Solar Flare Authors: Kuckein, C.; Collados, M.; Manso Sainz, R. Bibcode: 2015ApJ...799L..25K Altcode: 2015arXiv150104207K This Letter reports on a set of full-Stokes spectropolarimetric observations in the near-infrared He i 10830 Å spectral region covering the pre-flare, flare, and post-flare phases of an M3.2 class solar flare. The flare originated on 2013 May 17 and belonged to active region NOAA 11748. We detected strong He i 10830 Å emission in the flare. The red component of the He i triplet peaks at an intensity ratio to the continuum of about 1.86. During the flare, He i Stokes V is substantially larger and appears reversed compared to the usually larger Si i Stokes V profile. The photospheric Si i inversions of the four Stokes profiles reveal the following: (1) the magnetic field strength in the photosphere decreases or is even absent during the flare phase, as compared to the pre-flare phase. However, this decrease is not permanent. After the flare, the magnetic field recovers its pre-flare configuration in a short time (i.e., 30 minutes after the flare). (2) In the photosphere, the line of sight velocities show a regular granular up- and downflow pattern before the flare erupts. During the flare, upflows (blueshifts) dominate the area where the flare is produced. Evaporation rates of ∼ {{10}-3} and ∼ {{10}-4} g cm-2 s-1 have been derived in the deep and high photosphere, respectively, capable of increasing the chromospheric density by a factor of two in about 400 s. Title: Fluid description of multi-component solar partially ionized plasma Authors: Khomenko, E.; Collados, M.; Díaz, A.; Vitas, N. Bibcode: 2014PhPl...21i2901K Altcode: 2014arXiv1408.1871K We derive self-consistent formalism for the description of multi-component partially ionized solar plasma, by means of the coupled equations for the charged and neutral components for an arbitrary number of chemical species, and the radiation field. All approximations and assumptions are carefully considered. Generalized Ohm's law is derived for the single-fluid and two-fluid formalism. Our approach is analytical with some order-of-magnitude support calculations. After general equations are developed, we particularize to some frequently considered cases as for the interaction of matter and radiation. Title: Modeling the effect of high altitude turbulence in wide-field correlating wavefront sensing and its impact on the performance of solar AO systems Authors: Montilla, I.; Tallon, M.; Langlois, M.; Béchet, C.; Collados Vera, M. Bibcode: 2014SPIE.9148E..6DM Altcode: Solar Adaptive Optics (AO) shares many issues with night-time AO, but it also has its own particularities. The wavefront sensing is performed using correlations to efficiently work on the solar granulation as a reference. The field of view for that measurement usually is around 10". A sensor collecting such a wide field of view averages wavefront information from different sky directions, and the anisoplanatism thus has a peculiar impact on the performance of solar AO and MCAO systems. Since we are entering the era of large solar telescopes (European Solar Telescope, Advanced Technology Solar Telescope) understanding this issue is crucial to evaluate its impact on the performance of future AO systems. In this paper we model the correlating wide field sensor and the way it senses the high altitude turbulence. Thanks to this improved modelling, we present an analysis of the influence of this sensing on the performance of each AO configuration, conventional AO and MCAO. In addition to the analytical study, simulations similar to the case of the EST AO systems with FRiM-3D (the Fractal Iterative Method for Atmospheric tomography) are used in order to highlight the relative influence of design parameters. In particular, results show the performance evolution when increasing the telescope diameter. We analyse the effect of high altitude turbulence correlation showing that increasing the diameter of the telescope does not degrade the performance when correcting on the same spatial and temporal scales. Title: MuSICa image slicer prototype at 1.5-m GREGOR solar telescope Authors: Calcines, A.; López, R. L.; Collados, M.; Vega Reyes, N. Bibcode: 2014SPIE.9147E..3IC Altcode: Integral Field Spectroscopy is an innovative technique that is being implemented in the state-of-the-art instruments of the largest night-time telescopes, however, it is still a novelty for solar instrumentation. A new concept of image slicer, called MuSICa (Multi-Slit Image slicer based on collimator-Camera), has been designed for the integral field spectrograph of the 4-m European Solar Telescope. This communication presents an image slicer prototype of MuSICa for GRIS, the spectrograph of the 1.5-m GREGOR solar telescope located at the Observatory of El Teide. MuSICa at GRIS reorganizes a 2-D field of view of 24.5 arcsec into a slit of 0.367 arcsec width by 66.76 arcsec length distributed horizontally. It will operate together with the TIP-II polarimeter to offer high resolution integral field spectropolarimetry. It will also have a bidimensional field of view scanning system to cover a field of view up to 1 by 1 arcmin. Title: Rayleigh-Taylor instability in prominences from numerical simulations including partial ionization effects Authors: Khomenko, E.; Díaz, A.; de Vicente, A.; Collados, M.; Luna, M. Bibcode: 2014A&A...565A..45K Altcode: 2014arXiv1403.4530K We study the Rayleigh-Taylor instability (RTI) at a prominence-corona transition region in a non-linear regime. Our aim is to understand how the presence of neutral atoms in the prominence plasma influences the instability growth rate, as well as the evolution of velocity, magnetic field vector, and thermodynamic parameters of turbulent drops. We perform 2.5D numerical simulations of the instability initiated by a multi-mode perturbation at the corona-prominence interface using a single-fluid magnetohydrodynamic (MHD) approach including a generalized Ohm's law. The initial equilibrium configuration is purely hydrostatic and contains a homogeneous horizontal magnetic field forming an angle with the direction in which the plasma is perturbed. We analyze simulations with two different orientations of the magnetic field. For each field orientation we compare two simulations, one for the pure MHD case, and one including the ambipolar diffusion in Ohm's law (AD case). Other than that, both simulations for each field orientation are identical. The numerical results in the initial stage of the instability are compared with the analytical linear calculations. We find that the configuration is always unstable in the AD case. The growth rate of the small-scale modes in the non-linear regime is up to 50% larger in the AD case than in the purely MHD case and the average velocities of flows are a few percentage points higher. Significant drift momenta are found at the interface between the coronal and the prominence material at all stages of the instability, produced by the faster downward motion of the neutral component with respect to the ionized component. The differences in temperature of the bubbles between the ideal and non-ideal case are also significant, reaching 30%. There is an asymmetry between large rising bubbles and small-scale down flowing fingers, favoring the detection of upward velocities in observations. Title: Rayleigh-Taylor instability in partially ionized compressible plasmas: One fluid approach Authors: Díaz, A. J.; Khomenko, E.; Collados, M. Bibcode: 2014A&A...564A..97D Altcode: 2014arXiv1401.5388D
Aims: We study the modification of the classical criterion for the linear onset and growth rate of the Rayleigh-Taylor instability (RTI) in a partially ionized (PI) plasma in the one-fluid description by considering a generalized induction equation.
Methods: The governing linear equations and appropriate boundary conditions, including gravitational terms, are derived and applied to the case of the RTI in a single interface between two partially ionized plasmas. The boundary conditions lead to an equation for the frequencies in which some have positive complex parts, marking the appearance of the RTI. We study the ambipolar term alone first, extending the result to the full induction equation later.
Results: The configuration is always unstable because of the presence of a neutral species. In the classical stability regime, the growth rate is small, since the collisions prevent the neutral fluid to fully develop the RTI. For parameters in the classical instability regime, the growth rate is lowered, but the differences with the compressible MHD case are small for the considered theoretical values of the collision frequencies and diffusion coefficients for solar prominences.
Conclusions: The PI modifies some aspects of the linear RTI instability, since it takes into account that neutrals do not feel the stabilizing effect of the magnetic field. For the set of parameters representative for solar prominences, our model gives the resulting timescale comparable to observed lifetimes of RTI plumes. Title: Magnetic, Thermal and Dynamical Evolution of AN M3.2 Two-Ribbon Flare Authors: Collados, Manuel; Kuckein, Christoph; Manso Sainz, Rafael; Asensio Ramos, Andres Bibcode: 2014cosp...40E.568C Altcode: On 2013, 17th May, a two-ribbon M3.2 flare took place in the solar atmosphere on the active region AR 11748. The flare evolution was observed at the German VTT of the Observatorio del Teide using the instrument TIP-II, with spectropolarimetric measurements of the photosphere (Si I at 1082.7 nm) and the chromosphere (Helium triplet at 1083 nm). Simultaneous spectroscopic data of the chromospheric spectral line of Ca II at 854.2 nm and filtergrams at Halpha were also obtained. The flare evolution as observed from the ground can be compared with the changes observed by AIA@SDO at different ultraviolet wavelengths. The ground observations covered several hours, including the pre-flare, impulsive, gradual and post-flare phases. We present maps of the magnetic field, thermal and dynamical properties of the region during its evolution from pre- to post-flare phase. Title: Rayleigh-Taylor instability in partially ionized prominence plasma Authors: Khomenko, E.; Díaz, A.; de Vicente, A.; Collados, M.; Luna, M. Bibcode: 2014IAUS..300...90K Altcode: 2013arXiv1310.7016K We study Rayleigh-Taylor instability (RTI) at the coronal-prominence boundary by means of 2.5D numerical simulations in a single-fluid MHD approach including a generalized Ohm's law. The initial configuration includes a homogeneous magnetic field forming an angle with the direction in which the plasma is perturbed. For each field inclination we compare two simulations, one for the pure MHD case, and one including the ambipolar diffusion in the Ohm's law, otherwise identical. We find that the configuration containing neutral atoms is always unstable. The growth rate of the small-scale modes in the non-linear regime is larger than in the purely MHD case. Title: 3D simulations of Rayleigh-Taylor instability in prominences including partial ionization effects Authors: Khomenko, Elena; Collados, Manuel; De Vicente, Angel; Luna, Manuel; Diaz, Antonio Bibcode: 2014cosp...40E1476K Altcode: We study the Rayleigh-Taylor instability (RTI) at a prominence-corona transition region in a non-linear regime. Our aim is to understand how the presence of neutral atoms in the prominence plasma influences the instability growth rate, and the evolution of velocity, magnetic field vector and thermodynamic parameters of turbulent drops. We perform 3D numerical simulations of the instability initiated by a multi-mode perturbation at the corona-prominence interface using a single-fluid MHD approach including a generalized Ohm's law. Pairs of simulations are compared, one of them done under ideal MHD conditions, and others include ambipolar diffusion (AD) in the Ohm's law. Other than that, the simulations of each pair are identical in their magnetic field orientation and thermal parameters. The numerical results in the initial stage of the instability are compared with the analytical linear calculations. We find that the configuration is always unstable in the AD case. The growth rate of the small-scale modes in the non-linear regime is up to 50% larger in the AD case than in the purely MHD case and the average velocities of flows are a few percent larger. Significant drift momenta are found at the interface between the coronal and the prominence material at all stages of the instability, produced by the faster downward motion of the neutral component with respect to the ionized component. The differences in temperature of the bubbles between the ideal and non-ideal case are also significant. Title: Preliminary performance analysis of the Multi-Conjugate AO system of the EST Authors: Montilla, Icíar; Béchet, Clémentine; Langlois, Maud; Tallon, Michel; Collados, Manuel Bibcode: 2013aoel.confE..44M Altcode: The European Solar Telescope (EST), a 4-meter diameter world-class facility, has been designed to measure the properties of the solar magnetic field with great accuracy and high spatial resolution. For that reason, it incorporates an innovative built-in Multi-Conjugate Adaptive Optics system (MCAO), featuring 4 high altitude DM's. It combines a narrow field high order wavefront sensor, providing the information to correct the ground layer, and a wide field lower order sensor to control the higher altitude mirrors. Using sensors collecting wide field of view information has several implications, i.e. it averages wavefront information from different sky directions, making the Strehl ratio to drop for low elevation observations. So far these effects have not been studied in MCAO. We analyze this effect by using the Fractal Iterative Method (FrIM), which incorporates a wide field Shack-Hartmann, and we performed end to end simulations of the EST MCAO system to analyze the performance of this system for a large range of elevations, as required in solar observations, and depending on the asterism geometry and number and height of DM's, in order to find the best system configuration. Title: MuSICa: the Multi-Slit Image Slicer for the est Spectrograph Authors: Calcines, A.; López, R. L.; Collados, M. Bibcode: 2013JAI.....250009C Altcode: Integral field spectroscopy (IFS) is a technique that allows one to obtain the spectra of all the points of a bidimensional field of view simultaneously. It is being applied to the new generation of the largest night-time telescopes but it is also an innovative technique for solar physics. This paper presents the design of a new image slicer, MuSICa (Multi-Slit Image slicer based on collimator-Camera), for the integral field spectrograph of the 4-m aperture European Solar Telescope (EST). MuSICa is a multi-slit image slicer that decomposes an 80 arcsec2 field of view into slices of 50 μm and reorganizes it into eight slits of 0.05 arcsec width × 200 arcsec length. It is a telecentric system with an optical quality at diffraction limit compatible with the two modes of operation of the spectrograph: spectroscopic and spectro-polarimetric. This paper shows the requirements, technical characteristics and layout of MuSICa, as well as other studied design options. Title: a High Resolution Integral Field Spectrograph for the European Solar Telescope Authors: Calcines, A.; López, R. L.; Collados, M. Bibcode: 2013JAI.....250007C Altcode: This paper presents the proposal of a high resolution, integral field spectrograph that is currently being designed for the 4-meter aperture European Solar Telescope that will be located in the Canary Islands. This instrument is optimized to study the solar chromosphere and photosphere to allow the investigation of several phenomena concentrated within these two layers. It will be able to observe simultaneously a bidimensional field of view of 80 arcsec2 that is reorganized, using an integral field unit, into 8 long slits of 200 arcsec length by 0.05 arcsec width. It will have the capability to observe different layers of the Sun at the same time due to its multi-wavelength capability that allows the observation of 5 visible and 3 near-infrared wavelength intervals from 3900 to 23,000 Å, with a spectral resolution of about 300,000. The designed instrument is telecentric and presents an optical quality limited by diffraction. Title: Dislocations in Magnetohydrodynamic Waves in a Stellar Atmosphere Authors: López Ariste, A.; Collados, M.; Khomenko, E. Bibcode: 2013PhRvL.111h1103L Altcode: 2013arXiv1308.0145L We describe the presence of wave front dislocations in magnetohydrodynamic waves in stratified stellar atmospheres. Scalar dislocations such as edges and vortices can appear in Alfvén waves, as well as in general magnetoacoustic waves. We detect those dislocations in observations of magnetohydrodynamic waves in sunspots in the solar chromosphere. Through the measured charge of all the dislocations observed, we can give for the first time estimates of the modal contribution in the waves propagating along magnetic fields in solar sunspots. Title: MHD wave propagation in the solar network Authors: Calvo Santamaria, I.; Khomenko, E.; Cally, P. S.; Collados, M. Bibcode: 2013hsa7.conf..806C Altcode: Magneto-acoustic and Alfvénic waves are ubiquitous in solar coronal loops, possibly being excited by photospheric motions. It is not clear, though, how these waves get so high, having obstacles such as the acoustic cut-off frequency, reflection and refraction of fast MHD waves and also the strongly reflecting transition region. In this contribution we report on 2D numerical modelling of waves in magnetic arcade structures extending from photospheric layers through the transition region to the corona. Waves in the arcade are excited by sub-photospheric p-modes. We discuss the behaviour of waves, their conversion and propagation properties and possible mechanisms allowing their escape through the transition region. Title: MuSICa at GRIS: a prototype image slicer for EST at GREGOR Authors: Calcines, A.; Collados, M.; López, R. L. Bibcode: 2013hsa7.conf..939C Altcode: This communication presents a prototype image slicer for the 4-m European Solar Telescope (EST) designed for the spectrograph of the 1.5-m GREGOR solar telescope (GRIS). The design of this integral field unit has been called MuSICa (Multi-Slit Image slicer based on collimator-Camera). It is a telecentric system developed specifically for the integral field, high resolution spectrograph of EST and presents multi-slit capability, reorganizing a bidimensional field of view of 80 arcsec^{2} into 8 slits, each one of them with 200 arcsec length × 0.05 arcsec width. It minimizes the number of optical components needed to fulfil this multi-slit capability, three arrays of mirrors: slicer, collimator and camera mirror arrays (the first one flat and the other two spherical). The symmetry of the layout makes it possible to overlap the pupil images associated to each part of the sliced entrance field of view. A mask with only one circular aperture is placed at the pupil position. This symmetric characteristic offers some advantages: facilitates the manufacturing process, the alignment and reduces the costs. In addition, it is compatible with two modes of operation: spectroscopic and spectro-polarimetric, offering a great versatility. The optical quality of the system is diffraction-limited. The prototype will improve the performances of GRIS at GREGOR and is part of the feasibility study of the integral field unit for the spectrographs of EST. Although MuSICa has been designed as a solar image slicer, its concept can also be applied to night-time astronomical instruments (Collados et al. 2010, Proc. SPIE, Vol. 7733, 77330H; Collados et al. 2012, AN, 333, 901; Calcines et al. 2010, Proc. SPIE, Vol. 7735, 77351X) Title: EST: the largest and most sensitive spectropolarimeter Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly, B.; Pérez, A. : Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team Bibcode: 2013hsa7.conf..808C Altcode: Magnetic field plays a crucial role to understand most phenomena happening in the solar atmosphere. Sunspots, flares, prominences, coronal mass ejections are well known examples of its interaction with the solar plasma. To study the properties of this interaction, one needs to analyze the imprint it leaves in the radiation through the polarization induced in spectral lines, via the Zeeman and Hanle effects. Outside sunspots, the polarization degree of the emitted light is usually well below one part in one thousand, which requires sophisticated techniques to measure it accurately. To further complicate the situation, telescopes use mirrors and these introduce undesired polarization which is two or three orders of magnitude larger than that caused by the magnetic field of solar structures. For this reason, present telescopes doing polarimetry require an adequate modelling to correct the measured data from these spurious effects. In addition, most of the magnetic field interactions with the plasma take place at small scales. The best achievable angular resolution is mandatory to adequately study magnetic phenomena. The European solar Telescope (EST) has been defined to overcome these difficulties. Here, some aspects of the design are described. Title: The European Solar Telescope Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly, B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team Bibcode: 2013MmSAI..84..379C Altcode: The European Solar Telescope (EST) is a project to design, build and operate an European Solar 4-meter class telescope to be located in the Canary Islands, with the participation of institutions from fifteen European countries gathered around the consortium EAST (European Association for Solar Telescopes). The project main objective up to the present has been the development of the conceptual design study (DS) of a large aperture Solar Telescope. The study has demonstrated the scientific, technical and financial feasibility of EST. The DS has been possible thanks to the co-financing allocated specifically by the EU and the combined efforts of all the participant institutions. Different existing alternatives have been analysed for all telescope systems and subsystems, and decisions have been taken on the ones that are most compatible with the scientific goals and the technical strategies. The present status of some subsystems is reviewed in this paper. Title: An integral field spectrograph for the 4-m European Solar Telescope Authors: Calcines, A.; Collados, M.; López, R. L. Bibcode: 2013MmSAI..84..416C Altcode: This paper presents the proposal of a high resolution, integral field spectrograph that is currently being designed for the 4-meter aperture European Solar Telescope. This instrument is optimized for the study of the solar chromosphere and photosphere to allow the investigation of magnetic phenomena concentrated within these two layers. It will observe a bidimensional field of view of 80 arcsec2 that is reorganized, using an integral field unit, into eight long slits of 200 arcsec length by 0.05 arcsec width. A new concept of image slicer has been specifically designed for this instrument. It is a telecentric system and, because of the symmetry of its layout, it presents several advantages, which are presented in this paper. The spectrograph will have capabilities to observe different layers of the Sun at the same time due to its multi-wavelength capability that allows the observation of 5 visible and 3 near-infrared wavelength intervals from 3900 to 23000 Å{}, with a spectral resolution of about 300,000. In addition, it is designed to offer two modes of operation: spectroscopic and spectro-polarimetric. The optical quality of the instrument is diffraction limited. Title: The GREGOR Solar Telescope on Tenerife Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.; Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G. Bibcode: 2012ASPC..463..365S Altcode: 2012arXiv1202.4289S 2011 was a successful year for the GREGOR project. The telescope was finally completed in May with the installation of the 1.5-meter primary mirror. The installation of the first-light focal plane instruments was completed by the end of the year. At the same time, the preparations for the installation of the high-order adaptive optics were finished, its integration to the telescope is scheduled for early 2012. This paper describes the telescope and its instrumentation in their present first-light configuration, and provides a brief overview of the science goals of GREGOR. Title: Simulations of Chromospheric Heating by Ambipolar Diffusion Authors: Khomenko, E.; Collados Vera, M. Bibcode: 2012ASPC..463..281K Altcode: 2012arXiv1202.2252K We propose a mechanism for efficient heating of the solar chromosphere based on non-ideal plasma effects. Three ingredients are needed for the work of this mechanism: (1) presence of neutral atoms; (2) presence of a non-potential magnetic field; (3) decrease of the collisional coupling of the plasma. Due to the decrease of collisional coupling, a net relative motion appears between the neutral and ionized components, usually referred to as “ambipolar diffusion.” This results in a significant enhancement of current dissipation as compared to the classical MHD case. We propose that the current dissipation in this situation is able to provide enough energy to heat the chromosphere by several kK on the time scale of minutes, or even seconds. In this paper, we show that this energy supply might be sufficient to balance the radiative energy losses of the chromosphere. Title: The GREGOR Solar Telescope Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F. Bibcode: 2012IAUSS...6E.203D Altcode: The 1.5-meter GREGOR solar telescope is a new facility for high-resolution observations of the Sun. The telescope is located at the Spanish Observatorio del Teide on Tenerife. The telescope incorporates advanced designs for a foldable-tent dome, an open steel-truss telescope structure, and active and passive means to minimize telescope and mirror seeing. Solar fine structure can be observed with a dedicated suite of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot Interferometer", and the "Grating Infrared Spectrograph". All post-focus instruments benefit from a high-order (multi-conjugate) adaptive optics system, which enables observations close to the diffraction limit of the telescope. The inclusion of a spectrograph for stellar activity studies and the search for solar twins expands the scientific usage of the GREGOR to the nighttime domain. We report on the successful commissioning of the telescope until the end of 2011 and the first steps towards science verification in 2012. Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from the Photosphere to the Corona Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera, M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.; Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M. Bibcode: 2012ASPC..463.....R Altcode: No abstract at ADS Title: Instrumental Capabilities of the EST Authors: Collados Vera, M.; EST Team Bibcode: 2012ASPC..463..413C Altcode: The EST has recently finished its conceptual design study. A number of instruments have been devised to make possible the observation of the solar photosphere and chromosphere with high spatial, spectral, and temporal resolution, as well as with high polarimetric sensitivity. To achieve these goals, the telescope is provided with a powerful MCAO system and a polarimetrically compensated optical design. In this paper, a summary of the present situation of the telescope and its different subsystems is outlined. Especial emphasis is put in the description of the instruments and of the flexible light distribution system. The latter will allow scientists to perform observations using all instruments at the same time or individually, to maximize the efficiency of the system. With this expected performance, EST will provide to the community with data of unprecedented quality to study solar magnetic phenomena at its finest scales. Title: Gregor@night: The future high-resolution stellar spectrograph for the GREGOR solar telescope Authors: Strassmeier, K. G.; Ilyin, I. V.; Woche, M.; Granzer, T.; Weber, M.; Weingrill, J.; Bauer, S. -M.; Popow, E.; Denker, C.; Schmidt, W.; von der Lühe, O.; Berdyugina, S.; Collados, M.; Koubsky, P.; Hackman, T.; Mantere, M. J. Bibcode: 2012AN....333..901S Altcode: We describe the future night-time spectrograph for the GREGOR solar telescope and present its science core projects. The spectrograph provides a 3-pixel resolution of up to R=87 000 in 45 échelle orders covering the wavelength range 390-900 nm with three grating settings. An iodine cell can be used for high-precision radial velocity work in the 500-630 nm range. The operation of the spectrograph and the telescope will be fully automated without the presence of humans during night-time and will be based on the successful STELLA control system. Future upgrades include a second optical camera for even higher spectral resolution, a Stokes-V polarimeter and a link to the laser-frequency comb at the Vacuum Tower Telescope. The night-time core projects are a study of the angular-momentum evolution of ``The Sun in Time'' and a continuation of our long-term Doppler imaging of active stars. Title: A retrospective of the GREGOR solar telescope in scientific literature Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.; Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.; Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa, M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann, T.; Wiehr, E.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..810D Altcode: 2012arXiv1210.3167D In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the ``historical'' context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes. Title: The 1.5 meter solar telescope GREGOR Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Waldmann , T. A. Bibcode: 2012AN....333..796S Altcode: The 1.5 m telescope GREGOR opens a new window to the understanding of solar small-scale magnetism. The first light instrumentation includes the Gregor Fabry Pérot Interferometer (GFPI), a filter spectro-polarimeter for the visible wavelength range, the GRating Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The excellent performance of the first two instruments has already been demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest solar telescope and number 3 in the world. Its all-reflective Gregory design provides a large wavelength coverage from the near UV up to at least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR is equipped with a high-order adaptive optics system, with a subaperture size of 10 cm, and a deformable mirror with 256 actuators. The science goals are focused on, but not limited to, solar magnetism. GREGOR allows us to measure the emergence and disappearance of magnetic flux at the solar surface at spatial scales well below 100 km. Thanks to its spectro-polarimetric capabilities, GREGOR will measure the interaction between the plasma flows, different kinds of waves, and the magnetic field. This will foster our understanding of the processes that heat the chromosphere and the outer layers of the solar atmosphere. Observations of the surface magnetic field at very small spatial scales will shed light on the variability of the solar brightness. Title: The GREGOR Fabry-Pérot Interferometer Authors: Puschmann, K. G.; Denker, C.; Kneer, F.; Al Erdogan, N.; Balthasar, H.; Bauer, S. M.; Beck, C.; Bello González, N.; Collados, M.; Hahn, T.; Hirzberger, J.; Hofmann, A.; Louis, R. E.; Nicklas, H.; Okunev, O.; Martínez Pillet, V.; Popow, E.; Seelemann, T.; Volkmer, R.; Wittmann, A. D.; Woche, M. Bibcode: 2012AN....333..880P Altcode: 2012arXiv1210.2921P The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50 arcsec × 38 arcsec is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25 arcsec × 38 arcsec. The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution of R ≈ 250,000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to ∼50 km on the solar surface. Title: GRIS: The GREGOR Infrared Spectrograph Authors: Collados, M.; López, R.; Páez, E.; Hernández, E.; Reyes, M.; Calcines, A.; Ballesteros, E.; Díaz, J. J.; Denker, C.; Lagg, A.; Schlichenmaier, R.; Schmidt, W.; Solanki, S. K.; Strassmeier, K. G.; von der Lühe, O.; Volkmer, R. Bibcode: 2012AN....333..872C Altcode: This paper describes the main characteristics of GRIS (GREGOR Infrared Spectrograph), the grating spectrograph installed in the recently inaugurated (May 2012) 1.5-meter GREGOR telescope located at the Observatorio del Teide in Tenerife. The spectrograph has a standard Czerny-Turner configuration with parabolic collimator and camera mirrors that belong to the same conic surface. Although nothing prevents its use at visible wavelengths, the spectrograph will be initially used in combination with the infrared detector of the Tenerife Infrared Polarimeter (TIP-II) in standard spectroscopic mode as well as for spectropolarimetric measurements. Title: Conceptual design of the data handling system for the European Solar Telescope Authors: Ermolli, Ilaria; Cauzzi, Gianna; Collados, Manuel; Paletou, Frederic; Reardon, Kevin; Aboudarham, Jean; Cirami, Roberto; Cosentino, Rosario; Del Moro, Dario; Di Marcantonio, Paolo; Giorgi, Fabrizio; Lafon, Martine; Pietropaolo, Ermanno; Romano, Paolo Bibcode: 2012SPIE.8448E..1SE Altcode: We present an overview of the conceptual design of the data handling unit of the ECS, the Control System for the European Solar Telescope (EST). We will focus on describing the critical requirements for this unit resulting from the overall design of the telescope, together with its architecture and the results of the feasibility analysis carried out to date. Title: Preliminary design of a multi-slit image slicer for EST Authors: Calcines, A.; López, R. L.; Collados, M. Bibcode: 2012SPIE.8446E..74C Altcode: Integral field spectroscopy is a modern technique used in Astronomy to obtain simultaneous spectral information of all points in a bidimensional field of view. This communication presents the preliminary design of a multi-slit image slicer to be coupled to the spectrographs of the 4 meters aperture European Solar Telescope. This integral field unit will provide the observation of an 80 arcsec2 field of view, rearranged into 8 slits of 200 arcsec length by 0.05 arcsec width. Different optical design alternatives with diffraction limited optical quality, as well as the design of a prototype for the GREGOR solar telescope, are presented. Title: Multi-purpose grating spectrograph for the 4-meter European Solar Telescope Authors: Calcines, A.; Collados, M.; Feller, A.; Gelly, B.; Grauf, B.; Hirzberger, J.; López Ariste, A.; Lopez, R. L.; Mein, P.; Sayéde, F. Bibcode: 2012SPIE.8446E..6TC Altcode: This communication presents a family of spectrographs designed for the European Solar Telescope. They can operate in four different configurations: a long slit standard spectrograph (LsSS), two devices based on subtractive double pass (TUNIS and MSDP) and one based on an integral field, multi-slit, multi-wavelength configuration. The combination of them composes the multi-purpose grating spectrograph of EST, focused on supporting the different science cases of the solar photosphere and chromosphere in the spectral range from 3900 Å to 23000 Å. The different alternatives are made compatible by using the same base spectrographs and different selectable optical elements corresponding to specific subsystems of each configuration. Title: Multi-conjugate AO for the European Solar Telescope Authors: Montilla, I.; Béchet, C.; Le Louarn, M.; Tallon, M.; Sánchez-Capuchino, J.; Collados Vera, M. Bibcode: 2012SPIE.8447E..5HM Altcode: The European Solar Telescope (EST) will be a 4-meter diameter world-class facility, optimized for studies of the magnetic coupling between the deep photosphere and upper chromosphere. It will specialize in high spatial resolution observations and therefore it has been designed to incorporate an innovative built-in Multi-Conjugate Adaptive Optics system (MCAO). It combines a narrow field high order sensor that will provide the information to correct the ground layer and a wide field low order sensor for the high altitude mirrors used in the MCAO mode. One of the challenging particularities of solar AO is that it has to be able to correct the turbulence for a wide range of observing elevations, from zenith to almost horizon. Also, seeing is usually worse at day-time, and most science is done at visible wavelengths. Therefore, the system has to include a large number of high altitude deformable mirrors. In the case of the EST, an arrangement of 4 high altitude DMs is used. Controlling such a number of mirrors makes it necessary to use fast reconstruction algorithms to deal with such large amount of degrees of freedom. For this reason, we have studied the performance of the Fractal Iterative Method (FriM) and the Fourier Transform Reconstructor (FTR), to the EST MCAO case. Using OCTOPUS, the end-to-end simulator of the European Southern Observatory, we have performed several simulations with both algorithms, being able to reach the science requirement of a homogeneous Strehl higher that 50% all over the 1 arcmin field of view. Title: Heating of the Magnetized Solar Chromosphere by Partial Ionization Effects Authors: Khomenko, E.; Collados, M. Bibcode: 2012ApJ...747...87K Altcode: 2011arXiv1112.3374K In this paper, we study the heating of the magnetized solar chromosphere induced by the large fraction of neutral atoms present in this layer. The presence of neutrals, together with the decrease with height of the collisional coupling, leads to deviations from the classical magnetohydrodynamic behavior of the chromospheric plasma. A relative net motion appears between the neutral and ionized components, usually referred to as ambipolar diffusion. The dissipation of currents in the chromosphere is enhanced by orders of magnitude due to the action of ambipolar diffusion, as compared with the standard ohmic diffusion. We propose that a significant amount of magnetic energy can be released to the chromosphere just by existing force-free 10-40 G magnetic fields there. As a consequence, we conclude that ambipolar diffusion is an important process that should be included in chromospheric heating models, as it has the potential to rapidly heat the chromosphere. We perform analytical estimations and numerical simulations to prove this idea. Title: Data handling and control of the European Solar Telescope Authors: Ermolli, I.; Bettonvil, F.; Cauzzi, G.; Cavaller, L.; Collados, M.; Di Marcantonio, P.; Grivel, C.; Paletou, F.; Romano, P.; Aboudarham, J.; Cirami, R.; Cosentino, R.; Giorgi, F.; Lafon, M.; Laforgue, D.; Reardon, K.; Sliepen, G. Bibcode: 2012MSAIS..19..380E Altcode: We describe some aspects of the facility operation that have been considered for the design of the data handling and control of the European Solar Telescope. The main sub-systems of the EST relevant for the control are summarized, together with some information on current solar data models. Title: Conceptual design of a high-resolution, integral field spectrograph for the European Solar Telescope Authors: Calcines, A.; Collados, M.; López, R. L. Bibcode: 2011hsa6.conf..660C Altcode: This communication presents the current status of the conceptual design of a high resolution, integral field spectrograph with multi-slit and multi-wavelength capabilities, designed for the 4 meter European Solar Telescope (EST). Title: Magneto-acoustic wave energy in sunspots: observations and numerical simulations Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C. Bibcode: 2011hsa6.conf..630F Altcode: We have reproduced some sunspot wave signatures obtained from spectropolarimetric observations through 3D MHD numericalsimulations. The results of the simulations arecompared with the oscillations observed simultaneously at different heights from the SiI lambda10827Å line, HeI lambda10830Å line, the CaII H core and the FeI blends at the wings of the CaII H line. The simulations show a remarkable agreement with the observations, and we have used them to quantify the energy contribution of the magneto-acoustic waves to the chromospheric heating in sunspots. Our findings indicate that the energy supplied by these waves is 5-10 times lower than the amount needed to balance the chromospheric radiative losses. Title: Venus transit 2004: Illustrating the capability of exoplanet transmission spectroscopy Authors: Hedelt, P.; Alonso, R.; Brown, T.; Collados Vera, M.; Rauer, H.; Schleicher, H.; Schmidt, W.; Schreier, F.; Titz, R. Bibcode: 2011A&A...533A.136H Altcode: 2011arXiv1107.3700H The transit of Venus in 2004 offered the rare possibility to remotely sense a well-known planetary atmosphere using ground-based absorption spectroscopy. Transmission spectra of Venus' atmosphere were obtained in the near infrared using the Vacuum Tower Telescope (VTT) in Tenerife. Since the instrument was designed to measure the very bright photosphere of the Sun, extracting Venus' atmosphere was challenging. We were able to identify CO2 absorption lines in the upper Venus atmosphere. Moreover, the relative abundance of the three most abundant CO2 isotopologues could be determined. The observations resolved Venus' limb, showing Doppler-shifted absorption lines that are probably caused by high-altitude winds. We demonstrate the utility of ground-based measurements in analyzing the atmospheric constituents of a terrestrial planet atmosphere using methods that might be applied in future to terrestrial extrasolar planets. Title: Performance simulations for the conceptual design of the European Solar Telescope (EST) Authors: Cavaller, L.; Collados, M.; Castro, J. Bibcode: 2011SPIE.8336E..0GC Altcode: 2011SPIE.8336E..15C The European Solar Telescope (EST) is a European collaborative project promoted by the European Association for Solar Telescopes (EAST) to build a high resolution 4m class solar telescope in the Canary Islands. Since 2008 to 2011 a Design Study has been developed to define the Conceptual Design of EST. During the Design Study, several preliminary performance simulations have been developed in order to demonstrate the feasibility of the proposed conceptual design and provide preliminary feedback for the defined top-down error budgets. Performance simulations developed during the Design study include structural FE, servo-control of telescope main axes, CFD analyses of wind load on the telescope, CFD analyses of local seeing, transient thermal analysis of the telescope structure and environment and AO performance. This paper presents a description of the conceptual design of EST and the results of the preliminary performance simulations, mainly focused to obtain the best telescope image quality. Title: Magnetoacoustic Wave Energy from Numerical Simulations of an Observed Sunspot Umbra Authors: Felipe, T.; Khomenko, E.; Collados, M. Bibcode: 2011ApJ...735...65F Altcode: 2011arXiv1104.4138F We aim at reproducing the height dependence of sunspot wave signatures obtained from spectropolarimetric observations through three-dimensional MHD numerical simulations. A magnetostatic sunspot model based on the properties of the observed sunspot is constructed and perturbed at the photosphere, introducing the fluctuations measured with the Si I λ10827 line. The results of the simulations are compared with the oscillations observed simultaneously at different heights from the He I λ10830 line, the Ca II H core, and the Fe I blends in the wings of the Ca II H line. The simulations show a remarkable agreement with the observations. They reproduce the velocity maps and power spectra at the formation heights of the observed lines, as well as the phase and amplification spectra between several pairs of lines. We find that the stronger shocks at the chromosphere are accompanied with a delay between the observed signal and the simulated one at the corresponding height, indicating that shocks shift the formation height of the chromospheric lines to higher layers. Since the simulated wave propagation matches very well the properties of the observed one, we are able to use the numerical calculations to quantify the energy contribution of the magnetoacoustic waves to the chromospheric heating in sunspots. Our findings indicate that the energy supplied by these waves is too low to balance the chromospheric radiative losses. The energy contained at the formation height of the lowermost Si I λ10827 line in the form of slow magnetoacoustic waves is already insufficient to heat the higher layers, and the acoustic energy which reaches the chromosphere is around 3-9 times lower than the required amount of energy. The contribution of the magnetic energy is even lower. Title: The Polarization Optics for the European Solar Telescope Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.; Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.; Snik, F.; Socas-Navarro, H. Bibcode: 2011ASPC..437..329B Altcode: EST, the European Solar Telescope, is a 4-m class solar telescope, which will be located at the Canary Islands. It is currently in the conceptual design phase as a European funded project. In order to fulfill the stringent requirements for polarimetric sensitivity and accuracy, the polarimetry has been included in the design work from the very beginning. The overall philosophy has been to use a combination of techniques, which includes a telescope with low (and stable) instrumental polarization, optimal full Stokes polarimeters, differential measurement schemes, fast modulation and demodulation, and accurate calibration, and at the same time not giving up flexibility. The current baseline optical layout consists of a 14-mirror layout, which is polarimetrically compensated and non-varying in time. In the polarization free F2 focus ample space is reserved for calibration and modulators and a polarimetric switch. At instrument level the s-, and p-planes of individual components are aligned, resulting in a system in which eigenvectors can travel undisturbed through the system. Title: Polarimetry with GREGOR Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.; Soltau, D.; Volkmer, R. Bibcode: 2011ASPC..437..351B Altcode: A brief description of the new 1.5-meter solar telescope GREGOR located at the Observatorio del Teide in Tenerife will be given. GREGOR will provide a spatial resolution of about 75 km on the Sun, and with its light collecting capability we will be able to study the development of small magnetic features with high cadence. From the beginning, it will be equipped with the GREGOR Fabry-Pérot Interferometer (GFPI) for the visible spectral range and with a GRating Infrared Spectrograph (GRIS). Both postfocus instruments can be combined with a polarimeter, and in both cases the light is modulated by two ferro-electric liquid crystals. A calibration unit can be inserted to determine the instrumental polarization. Because of the altazimuthal mount, time-dependent rotation of the polarimetric reference plane is introduced, and we have to develop a polarization model of the telescope. Measurements to verify this model are in preparation. Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise Balloon-Borne Solar Observatory Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.; Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández, L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.; Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer, T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.; Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.; Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.; Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez, P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.; Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S. Bibcode: 2011SoPh..268...57M Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter built by four institutions in Spain that flew on board the Sunrise balloon-borne solar observatory in June 2009 for almost six days over the Arctic Circle. As a polarimeter, IMaX uses fast polarization modulation (based on the use of two liquid crystal retarders), real-time image accumulation, and dual-beam polarimetry to reach polarization sensitivities of 0.1%. As a spectrograph, the instrument uses a LiNbO3 etalon in double pass and a narrow band pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four Stokes parameters at various points inside the spectral line. This allows vector magnetograms, Dopplergrams, and intensity frames to be produced that, after reconstruction, reach spatial resolutions in the 0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time cadences vary between 10 and 33 s, although the shortest one only includes longitudinal polarimetry. The spectral line is sampled in various ways depending on the applied observing mode, from just two points inside the line to 11 of them. All observing modes include one extra wavelength point in the nearby continuum. Gauss equivalent sensitivities are 4 G for longitudinal fields and 80 G for transverse fields per wavelength sample. The line-of-sight velocities are estimated with statistical errors of the order of 5 - 40 m s−1. The design, calibration, and integration phases of the instrument, together with the implemented data reduction scheme, are described in some detail. Title: Magneto-acoustic waves in sunspots from observations and numerical simulations Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C. Bibcode: 2011JPhCS.271a2040F Altcode: 2010arXiv1009.5512F We study the propagation of waves from the photosphere to the chromosphere of sunspots. From time series of cospatial Ca II H (including its line blends) intensity spectra and polarimetric spectra of Si I λ 1082.7 nm and He I λ 1083.0 nm we retrieve the line-of-sight velocity at several heights. The analysis of the phase difference and amplification spectra shows standing waves for frequencies below 4 mHz and propagating waves for higher frequencies, and allows us to infer the temperature and height where the lines are formed. Using these observational data, we have constructed a model of sunspot, and we have introduced the velocity measured with the photospheric Si I λ 1082.7 nm line as a driver. The numerically propagated wave pattern fits reasonably well with the observed using the lines formed at higher layers, and the simulations reproduce many of the observed features. The observed waves are slow MHD waves propagating longitudinally along field lines. Title: Numerical simulation of propagation of the MHD waves in sunspots Authors: Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky, V.; Collados, M. Bibcode: 2010HiA....15..354P Altcode: We present results of numerical 3D simulation of propagation of MHD waves in sunspots. We used two self consistent magnetohydrostatic background models of sunspots. There are two main differences between these models: (i) the topology of the magnetic field and (ii) dependence of the horizontal profile of the sound speed on depth. The model with convex shape of the magnetic field lines near the photosphere has non-zero horizorntal perturbations of the sound speed up to the depth of 7.5 Mm (deep model). In the model with concave shape of the magnetic field lines near the photosphere Δ c/c is close to zero everywhere below 2 Mm (shallow model). Strong Alfven wave is generated at the wave source location in the deep model. This wave is almost unnoticeable in the shallow model. Using filtering technique we separated magnetoacoustic and magnetogravity waves. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. The sunspot causes anisotropy of the amplitude distribution along the wavefront and changes the shape of the wavefront. The amplitude of the waves is reduced inside the sunspot. This effect is stronger for the magnetogravity waves than for magnetoacoustic waves. The shape of the wavefront of the magnetogravity waves is distorted stronger as well. The deep model causes bigger anisotropy for both mgnetoacoustic and magneto gravity waves than the shallow model. Title: Multi-layer Study of Wave Propagation in Sunspots Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C. Bibcode: 2010ApJ...722..131F Altcode: 2010arXiv1008.4004F We analyze the propagation of waves in sunspots from the photosphere to the chromosphere using time series of co-spatial Ca II H intensity spectra (including its line blends) and polarimetric spectra of Si I λ10,827 and the He I λ10,830 multiplet. From the Doppler shifts of these lines we retrieve the variation of the velocity along the line of sight at several heights. Phase spectra are used to obtain the relation between the oscillatory signals. Our analysis reveals standing waves at frequencies lower than 4 mHz and a continuous propagation of waves at higher frequencies, which steepen into shocks in the chromosphere when approaching the formation height of the Ca II H core. The observed nonlinearities are weaker in Ca II H than in He I lines. Our analysis suggests that the Ca II H core forms at a lower height than the He I λ10,830 line: a time delay of about 20 s is measured between the Doppler signal detected at both wavelengths. We fit a model of linear slow magnetoacoustic wave propagation in a stratified atmosphere with radiative losses according to Newton's cooling law to the phase spectra and derive the difference in the formation height of the spectral lines. We show that the linear model describes well the wave propagation up to the formation height of Ca II H, where nonlinearities start to become very important. Title: Magneto-acoustic Waves in Sunspots: First Results From a New Three-dimensional Nonlinear Magnetohydrodynamic Code Authors: Felipe, T.; Khomenko, E.; Collados, M. Bibcode: 2010ApJ...719..357F Altcode: 2010arXiv1006.2998F Waves observed in the photosphere and chromosphere of sunspots show complex dynamics and spatial patterns. The interpretation of high-resolution sunspot wave observations requires modeling of three-dimensional (3D) nonlinear wave propagation and mode transformation in the sunspot upper layers in realistic spot model atmospheres. Here, we present the first results of such modeling. We have developed a 3D nonlinear numerical code specially designed to calculate the response of magnetic structures in equilibrium to an arbitrary perturbation. The code solves the 3D nonlinear MHD equations for perturbations; it is stabilized by hyper-diffusivity terms and is fully parallelized. The robustness of the code is demonstrated by a number of standard tests. We analyze several simulations of a sunspot perturbed by pulses of different periods at a subphotospheric level, from short periods, introduced for academic purposes, to longer and realistic periods of 3 and 5 minutes. We present a detailed description of the 3D mode transformation in a non-trivial sunspot-like magnetic field configuration, including the conversion between fast and slow magneto-acoustic waves and the Alfvén wave, by calculation of the wave energy fluxes. Our main findings are as follows: (1) the conversion from acoustic to the Alfvén mode is only observed if the driving pulse is located out of the sunspot axis, but this conversion is energetically inefficient; (2) as a consequence of the cutoff effects and refraction of the fast magneto-acoustic mode, the energy of the evanescent waves with periods around 5 minutes remains almost completely below the level β = 1; (3) waves with frequencies above the cutoff propagate field aligned to the chromosphere and their power becomes dominating over that of evanescent 5 minute oscillations, in agreement with observations. Title: Current concept for the 4m European Solar Telescope (EST) optical design Authors: Sánchez Capuchino, J.; Collados, M.; Soltau, D.; López, R.; Rasilla, J. L.; Gelly, B. Bibcode: 2010SPIE.7652E..0SS Altcode: 2010SPIE.7652E..26S The European Solar Telescope (EST) is a 4-m class solar telescope to be located in the Canary Islands which is currently in its conceptual design study. EST is a pan-european project (with 29 partners, plus 7 collaborating institutions, from 14 countries) promoted by the European Association for Solar Telescopes (EAST). In the current concept, the main telescope and its transfer optics assemblies 14 mirrors to provide a Science Coudé Focus with an F/50 telecentric beam. It is diffraction-limited in a FOV of 1 arcmin with an unvignetted FOV of 2'x2'. The whole system is being optimized in throughput for several instruments observing simultaneously in a spectral range from 0.39 μm to 2.3 μm. Its innovative concept integrates an optical transfer stage assembling multiconjugated adaptive optics with optical field de-rotation and with a perfect balance of the whole system in terms of polarization being also time and wavelength invariant. Title: GREGOR telescope: start of commissioning Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. Bibcode: 2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the first time, that the entire light path has seen sunlight. The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system. This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with a multi-conjugate adaptive optics system that is presently under development at KIS. Title: European Solar Telescope: project status Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly, B.; Grivel-Gelly, C.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R. Bibcode: 2010SPIE.7733E..0HC Altcode: 2010SPIE.7733E..15C The European Solar Telescope is a project for a 4-meter class telescope to be located in the Canary Islands. EST is promoted by the European Association for Solar Telescopes (EAST). This is a consortium formed by a number of research organizations from fifteen European countries (Austria, Croatia, Czech Republic, France, Germany, Hungary, Italy, the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden, Switzerland, and United Kingdom). EST will specialize in high spatial and temporal resolution using diverse instruments that can efficiently produce two-dimensional spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights in the solar atmosphere. In this contribution, the status of the development of the Design Study of EST is presented, emphasizing the most important aspects of the optical design, mechanical structure, AO and MCAO systems for wavefront correction, instruments and polarization analysis. Title: Site-seeing measurements for the European Solar Telescope Authors: Berkefeld, Th.; Bettonvil, F.; Collados, M.; López, R.; Martín, Y.; Peñate, J.; Pérez, A.; Scharmer, G. B.; Sliepen, G.; Soltau, D.; Waldmann, T. A.; van Werkhoven, T. Bibcode: 2010SPIE.7733E..4IB Altcode: 2010SPIE.7733E.141B Seeing measurements are crucial for the optimum design of (multi-conjugate) adaptive optics systems operating at solar telescopes. For the design study of the 4-meter European Solar Telescope, to be located in the Canary Islands, several instruments have been constructed and operated, at the Observatorio del Roque de los Muchachos (La Palma) and at the Observatorio del Teide (Tenerife), to measure the properties of the ground layer and medium-high altitude turbulence. Several units of short (42.34 cm) and two long (323.06 cm) scintillometer bars are, or are to be, installed at both observatories. In addition to them, two wide-field wavefront sensors will be attached to the optical beams of the Swedish tower, on La Palma, and of the German VTT, on Tenerife, simultaneously used with the normal operation of the telescopes. These wavefront sensors are of Shack-Hartmann type with ~1 arcminute field of view. In this contribution, the instruments setup and their performance are described. Title: The heat stop for the 4-m European Solar Telescope EST Authors: Berrilli, F.; Egidi, A.; Del Moro, D.; Manni, F.; Cocciolo, M.; Scotto, A.; Volkmer, R.; Bettonvil, F. C. M.; Collados Vera, M.; Cavaller Marquez, L.; Sanchez Capuchino, J. Bibcode: 2010SPIE.7733E..2ZB Altcode: 2010SPIE.7733E..92B A study is presented for the realization of the heat stop for the 4-m European Solar Telescope EST, whose feasibility study will be completed in 2011. EST is an on-axis Gregorian telescope, equipped with a four-meter diameter primary mirror and primary focal length of about six meters. The heat stop, positioned at the primary focus, must be able to remove a heat load of 13 kW, while maintaining its surfaces very close to room temperature, to avoid the onset of seeing. In order to remove the heat, three configurations have been taken into consideration: 1) a flat 45° inclined heat rejecter, 2) a 45° conical heat rejecter and 3) a heat trap (made of a conical heat rejecter and a cylindrical heat absorber). All devices include an air removal system to avoid the formation of thermal plumes. Title: The polarization optics for the European Solar Telescope (EST) Authors: Bettonvil, F. C. M.; Collados, M.; Feller, A.; Gelly, B. F.; Keller, C. U.; Kentischer, T. J.; López Ariste, A.; Pleier, O.; Snik, F.; Socas-Navarro, H. Bibcode: 2010SPIE.7735E..6IB Altcode: 2010SPIE.7735E.214B EST (European Solar Telescope) is a 4-m class solar telescope, which is currently in the conceptual design phase. EST will be located at the Canary Islands and aims at observations with the best possible spectral, spatial and temporal resolution and best polarimetric performance, of the solar photosphere and chromosphere, using a suite of instruments that can efficiently produce two-dimensional spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights, and ranging from λ=350 until 2300 nm. In order to be able to fulfill the stringent requirements for polarimetric sensitivity and accuracy, from the very beginning the polarimetry has been included in the design work. The overall philosophy has been to use a combination of techniques, which includes a telescope with low (and stable) instrumental polarization, optimal full Stokes polarimeters, differential measurement schemes, fast modulation and demodulation, and accurate calibration. The current baseline optical layout consists of a 14-mirror layout, which is polarimetrically compensated and nonvarying in time. In the polarization free F2 focus ample space is reserved for calibration and modulators and a polarimetric switch. At instrument level the s-, and p-planes of individual components are aligned, resulting in a system in which eigenvectors can travel undisturbed through the system. Title: Data handling and control for the European Solar Telescope Authors: Ermolli, Ilaria; Bettonvil, Felix; Cauzzi, Gianna; Cavaller, Lluis; Collados, Manuel; Di Marcantonio, Paolo; Paletou, Frederic; Romano, Paolo; Aboudarham, Jean; Cirami, Roberto; Cosentino, Rosario; Giorgi, Fabrizio; Lafon, Martine; Laforgue, Didier; Reardon, Kevin; Sliepen, Guus Bibcode: 2010SPIE.7740E..0GE Altcode: 2010SPIE.7740E..13E We introduce the concepts for the control and data handling systems of the European Solar Telescope (EST), the main functional and technical requirements for the definition of these systems, and the outcomes from the trade-off analysis to date. Concerning the telescope control, EST will have performance requirements similar to those of current medium-sized night-time telescopes. On the other hand, the science goals of EST require the simultaneous operation of three instruments and of a large number of detectors. This leads to a projected data flux that will be technologically challenging and exceeds that of most other astronomical projects. We give an overview of the reference design of the control and data handling systems for the EST to date, focusing on the more critical and innovative aspects resulting from the overall design of the telescope. Title: Adaptive optics and MCAO for the 4-m European Solar Telescope EST Authors: Soltau, D.; Berkefeld, T.; Sánchez Capuchino, J.; Collados Vera, M.; Del Moro, D.; Löfdahl, M.; Scharmer, G. Bibcode: 2010SPIE.7736E..0US Altcode: 2010SPIE.7736E..27S A consortium of more than 20 European solar physics institution from 15 different countries is conducting a design study for a 4 m class solar telescope which shall be situated at the Canary Islands. In this paper we introduce the AO and MCAO design concept for EST. A ground layer deformable mirror is combined with an arrangement of four deformable layer mirrors. A combination of Shack-Hartmann wave front sensors with wide and narrow fields of view is used to control the system and to achieve a corrected field of view of one arcmin. Title: Current concept for the 4m European Solar Telescope (EST) optical design Authors: Sánchez-Capuchino, J.; Collados, M.; Soltau, D.; López, R.; Rasilla, J. L.; Gelly, B. Bibcode: 2010SPIE.7733E..36S Altcode: 2010SPIE.7733E..99S The European Solar Telescope (EST) is a pan-european project (with 29 partners, plus 7 collaborating institutions, from 14 countries) for the conceptual design study of a 4-meter class solar telescope promoted by the European Association for Solar Telescopes (EAST) to be located in the Canary Islands. The telescope, in the conceptual study, provides a Coudé focus with an F/50 telecentric beam. It is diffraction-limited in a FOV of 1 arcmin and it will be optimized in throughput for several instruments observing simultaneously in a spectral range from 0.39 μm to 2.3 μm. Its innovative concept integrates an optical transfer stage assembling multiconjugated adaptive optics with optical field de-rotation and with a perfect balance of the whole system in terms of polarization being time and wavelength invariant. Title: Feasibility study of high-resolution integral-field spectrographs for EST with multislit and multi-wavelength capabilities Authors: Calcines, Ariadna; Collados, Manuel; López, Roberto L. Bibcode: 2010SPIE.7735E..1XC Altcode: 2010SPIE.7735E..65C This communication shows the feasibility study of a new instrument designed for the 4 meter European Solar Telescope (EST) for high resolution spectro-polarimetric observations. This paper is specifically focused on the spectrographs that allow the simultaneous observation of 5 visible and 4 near-infrared wavelengths (complying with the science requirements), with 8 entrance slits of 200arcsec each fed by an integral field unit covering an area on the solar surface of 9 x 9 arcsec2. Title: Spectrograph capabilities of the European Solar Telescope Authors: Calcines, A.; Collados, M.; Feller, A.; Grauf, B.; Grivel-Gelly, C.; Hirzberger, J.; López Ariste, A.; López López, R.; Mein, P.; Sayède, F. Bibcode: 2010SPIE.7735E..20C Altcode: 2010SPIE.7735E..68C EST is a project for a 4-meter class telescope to be located in the Canary Islands. EST will be optimized for studies of the magnetic coupling between the photosphere and the chromosphere. This requires high spatial and temporal resolution diagnostics tools of properties of the plasma, by using multiple wavelength spectropolarimetry. To achieve these goals, visible and near-IR multi-purpose spectrographs are being designed to be compatible with different modes of use: LsSS (Long-slit Standard Spectrograph), multi-slit multi-wavelength spectrograph with an integral field unit, TUNIS (Tunable Universal Narrow-band Imaging Spectrograph), and new generation MSDP (Multi-channel Subtractive Double-pass Spectrograph). In this contribution, these different instrumental configurations are described. Title: European Solar Telescope: Progress status Authors: Collados, M.; Bettonvil, F.; Cavaller, L.; Ermolli, I.; Gelly, B.; Pérez, A.; Socas-Navarro, H.; Soltau, D.; Volkmer, R.; EST Team Bibcode: 2010AN....331..615C Altcode: In this paper, the present status of the development of the design of the European Solar Telescope is described. The telescope is devised to have the best possible angular resolution and polarimetric performance, maximizing the throughput of the whole system. To that aim, adaptive optics and multi-conjugate adaptive optics are integrated in the optical path. The system will have the possibility to correct for the diurnal variation of the distance to the turbulence layers, by using several deformable mirrors, conjugated at different heights. The present optical design of the telescope distributes the optical elements along the optical path in such a way that the instrumental polarization induced by the telescope is minimized and independent of the solar elevation and azimuth. This property represents a large advantage for polarimetric measurements. The ensemble of instruments that are planned is also presented. Title: GREGOR solar telescope: Design and status Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.; Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G. Bibcode: 2010AN....331..624V Altcode: The integration and verification phase of the GREGOR telescope reached an important milestone with the installation of the interim 1 m SolarLite primary mirror. This was the first time that the entire light path had seen sunlight. Since then extensive testing of the telescope and its subsystems has been carried out. The integration and verification phase will culminate with the delivery and installation of the final 1.5 m Zerodur primary mirror in the summer of 2010. Observatory level tests and science verification will commence in the second half of 2010 and in 2011. This phase includes testing of the main optics, adaptive optics, cooling and pointing systems. In addition, assuming the viewpoint of a typical user, various observational modes of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared Spectrograph (GRIS), and high-speed camera systems will be tested to evaluate if they match the expectations and science requirements. This ensures that GREGOR will provide high-quality observations with its combination of (multi-conjugate) adaptive optics and advanced post-focus instruments. Routine observations are expected for 2012. Title: Mode transformation and frequency change with height in 3D numerical simulations of magneto-acoustic wave propagation in sunspots Authors: Felipe, T.; Khomenko, E.; Collados, M. Bibcode: 2010arXiv1005.3684F Altcode: Three-dimensional numerical simulations of magnetoacoustic wave propagation are performed in a sunspot atmosphere with a computational domain covering from the photosphere to the chromosphere. The wave source, with properties resembling the solar spectrum, is located at different distances from the axis of the sunspot for each simulation. These results are compared with the theory of mode transformation and also with observational features. Simulations show that the dominant oscillation frequency in the chromosphere decreases with the radial distance from the sunspot axis. The energy flux of the different wave modes involved, including de Alfvén mode, is evaluated and discussed. Title: Numerical Simulation of Excitation and Propagation of Helioseismic MHD Waves in Magnetostatic Models of Sunspots Authors: Parchevsky, K.; Kosovichev, A.; Khomenko, E.; Olshevsky, V.; Collados, M. Bibcode: 2010arXiv1002.1117P Altcode: We present comparison of numerical simulations of propagation of MHD waves,excited by subphotospheric perturbations, in two different ("deep" and "shallow") magnetostatic models of the sunspots. The "deep" sunspot model distorts both the shape of the wavefront and its amplitude stronger than the "shallow" model. For both sunspot models, the surface gravity waves (f-mode) are affected by the sunspots stronger than the acoustic p-modes. The wave amplitude inside the sunspot depends on the photospheric strength of the magnetic field and the distance of the source from the sunspot axis. For the source located at 9 Mm from the center of the sunspot, the wave amplitude increases when the wavefront passes through the central part of the sunspot. For the source distance of 12 Mm, the wave amplitude inside the sunspot is always smaller than outside. For the same source distance from the sunspot center but for the models with different strength of the magnetic field, the wave amplitude inside the sunspot increases with the strength of the magnetic field. The simulations show that unlike the case of the uniform inclined background magnetic field, the p- and f-mode waves are not spatially separated inside the sunspot where the magnetic field is strongly non-uniform. These properties have to be taken into account for interpretation of observations of MHD waves traveling through sunspot regions. Title: NUMERICAL SIMULATION OF PROPAGATION AND SCATTERING OF THE MHD WAVES IN SUNSPOTS Authors: Parchevsky, K.; Kosovichev, A. G.; Khomenko, E.; Collados, M. Bibcode: 2009AGUFMSH23B1535P Altcode: We present comparison of numerical simulation results of MHD wave propagation in two different magnitostatic models of sunspots refferred to as "deep" and "shallow" models. The "deep" model has convex shape of magnetic field lines near the photosphere and non-zero horizorntal perturbations of the sound speed up to the bottom of the model (7.5 Mm). The "shallow" model has concave shape of the magnetic field lines near the photosphere and horizontally uniform sound speed below 2 Mm. Common feature of MHD waves behaviour in these two models is that for weak magnetic field (less than 1kG at the photosphere) waves reduce their amplitude when they reach the center of the sunspot and restore the amplitude when pass the center. For the "deep" model this effect is bigger than for the "shallow" model. The wave amplitude inside sunspots depends on the strength of the magnetic field. For the "shallow" model with photospheric magnetic field of 2.2 kG the wave amplitude inside the sunspot becomes bigger than outside (opposite to the weak magnetic field). The wave amplitude depends on the distance of the source from the sunspot center. For the "shallow" model and source distance of 9 Mm from the sunspot center the wave amplitude at some moment (when the wavefront passes the sunspot center) becomes bigger inside the sunspot than outside. For the source distance of 12 Mm the wave amplitude remains smaller inside the sunspot than outside for all moments of time. Using filtering technique we separated magnetoacoustic and magnetogravity waves. Simulations show that the sunspot changes the shape of the wave front and amplitude of the f-modes significantly stronger than the p-modes. It is shown, that inside the sunspot magnetoacoustic and magnetogravity waves are not spatially separated unlike the case of the horizontally uniform background model. Strong Alfven wave is generated at the wave source location in the "deep" model. This wave exists in the "shallow" model as well, but with much smaller amplitude. Title: Sunspot seismic halos generated by fast MHD wave refraction Authors: Khomenko, E.; Collados, M. Bibcode: 2009A&A...506L...5K Altcode: 2009arXiv0905.3060K Aims: We suggest an explanation for the high-frequency power excess surrounding active regions known as seismic halos.
Methods: We use numerical simulations of magneto-acoustic wave propagation in a magnetostatic sunspot model.
Results: We propose that seismic halos can be caused by the additional energy injected by high-frequency fast mode waves refracted in the higher atmosphere due to the rapid increase of the Alfvén speed. Our model qualitatively explains the magnitude of the halo and allows us to make predictions of its behavior that can be checked in future observations. Title: The energy of waves in the photosphere and lower chromosphere. I. Velocity statistics Authors: Beck, C.; Khomenko, E.; Rezaei, R.; Collados, M. Bibcode: 2009A&A...507..453B Altcode: 2009arXiv0905.1011B Context: Acoustic waves are one of the primary suspects besides magnetic fields for the chromospheric heating process to temperatures above radiative equilibrium (RE).
Aims: We derived the mechanical wave energy as seen in line-core velocities on disc centre to obtain a measure of mechanical energy flux with height for a comparison with the energy requirements in a semi-empirical atmosphere model, the Harvard-Smithsonian reference atmosphere (HSRA).
Methods: We analyzed a 1-hour time series and a large-area map of Ca II H spectra on the traces of propagating waves. We analyzed the velocity statistics of several spectral lines in the wing of Ca II H, and the line-core velocity of Ca II H. We converted the velocity amplitudes into volume (∝ ρ v^2) and mass energy densities (∝ v^2). For comparison, we used the increase of internal energy (∝ R ρ Δ T) necessary to lift a RE atmosphere to the HSRA temperature stratification.
Results: We find that the velocity amplitude grows in agreement with linear wave theory and thus slower with height than predicted from energy conservation. The mechanical energy of the waves above around z ~ 500 km is insufficient to maintain on a long-term average the chromospheric temperature rise in the semi-empirical HSRA model. The intensity variations of the Ca line core (z ~ 1000 km) can, however, be traced back to the velocity variations of the lowermost forming spectral line considered (z ~ 250 km).
Conclusions: The chromospheric intensity, and hence, (radiation) temperature variations are seen to be induced by passing waves originating in the photosphere. The wave energy is found to be insufficient to maintain the temperature stratification of the semi-empirical HSRA model above 500 km. We will in a following paper of this series investigate the energy contained in the intensity variations to see if the semi-empirical model is appropriate for the spectra. Title: Flux Cancellation in the Solar Photosphere: a near-IR Line of Mn I as a Diagnostic Tool Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste, A.; Trujillo Bueno, J.; Collados, M. Bibcode: 2009ASPC..405..215A Altcode: Recently, \cite{asensio_2_asensio_mn07} pointed out that the near-IR line of Mn I at 15262.702 Å provides a new diagnostic window for exploring the magnetism of the quiet Sun. In contrast with previously considered Mn I lines located at visible wavelengths this near-IR line has the advantage that the shape of its intensity profile is very sensitive to the presence of magnetic fields. This enhanced magnetic sensitivity is produced by the coincidence of two favorable facts: the enhanced Zeeman sensitivity of near-IR lines and because this line is subjected to particularly strong Paschen-Back perturbations due to the hyperfine structure of manganese. Of great diagnostic interest is that the intensity profile itself give us information on the unsigned magnetic flux, while the polarization profiles are sensitive to the net flux. An application to spectropolarimetric observations with the Tenerife Infrared Polarimeter has allowed us to obtain the first flux cancellation map in an enhanced network region. Title: Observational Signatures of Numerically Simulated MHD Waves in Small-scale Flux Sheets Authors: Khomenko, E.; Collados, M.; Felipe, T. Bibcode: 2009ASPC..405..183K Altcode: 2008arXiv0801.3966K We present some results obtained from the synthesis of Stokes profiles in small-scale flux sheets with propagating MHD waves. To that aim, 2D flux sheets showing internal structure have been excited with 5 min period drivers, allowing non-linear waves to propagate inside the magnetic structure. The observational signatures of these waves in Stokes profiles of several spectral lines that are commonly used in spectropolarimetric measurements are discussed. Title: Influence of Coronal EUV Irradiance on the Stokes Profiles of the He I 10830 Å Multiplet Authors: Centeno, R.; Trujillo Bueno, J.; Uitenbroek, H.; Collados, M. Bibcode: 2009ASPC..405..297C Altcode: One of the most useful spectral windows for spectropolarimetric investigations of the solar chromosphere is the one provided by the spectral lines of the He I 10830 Å multiplet, whose polarization signals are sensitive to the Hanle and Zeeman effects. However, in order to be able to carry out reliable diagnostics of the dynamic and magnetic properties of the solar outer atmosphere it is crucial to have a good physical understanding of the sensitivity of the observed spectral line radiation to the various competing triggering mechanisms. Here we report a series of on-disk and off-the-limb non-LTE calculations of the 10830 Å absorption and emission profiles, focusing our investigation on their sensitivity to the EUV coronal irradiation and the model atmosphere used in the calculations. We show in what respects the on-disk case sensitivity of the polarization signals induced by the Zeeman effect to the EUV coronal irradiance, and investigate whether or not inversions based on the Milne-Eddington model are reliable. Concerning the off-the-limb case we demonstrate that the intensity ratio of the blue to the red components of the He I 10830 Å multiplet is a sensitive function of the amount of EUV coronal illumination. Therefore, measurements of this observable as a function of the distance to the limb and its confrontation with radiative transfer modeling might give us valuable information on the physical properties of the solar atmosphere and on the amount of EUV radiation penetrating the chromosphere from above. Title: A full-Stokes polarimeter for the GREGOR Fabry-Perot interferometer Authors: Balthasar, Horst; Bello González, N.; Collados, M.; Denker, C.; Hofmann, A.; Kneer, F.; Puschmann, K. G. Bibcode: 2009IAUS..259..665B Altcode: One of the first post-focus instruments of the new solar telescope GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the Göttingen Fabry-Perot interferometer at the Vacuum Tower Telescope (VTT) on Tenerife. This spectrometer is equipped with a full-Stokes polarimeter. The modulation is performed with two ferroelectric liquid crystals, one acting nominally as quarter-wave plate, and the other as half-wave plate. A modified Savart plate serves as polarimetric beam splitter. With the present liquid crystals, the optimum wavelength range of this polarimeter is between 580 and 660 nm. The spectro-polarimeter will benefit from the capabilities of the new telescope GREGOR which will provide a spatial resolution of about 0″.1 (75 km on the solar surface). Thus we will be able to investigate small magnetic features, and we will study their development with high cadence. Title: Theoretical Modeling of Propagation of Magnetoacoustic Waves in Magnetic Regions Below Sunspots Authors: Khomenko, E.; Kosovichev, A.; Collados, M.; Parchevsky, K.; Olshevsky, V. Bibcode: 2009ApJ...694..411K Altcode: 2008arXiv0809.0278K We use two-dimensional numerical simulations and eikonal approximation to study properties of magnetohydrodynamic (MHD) waves traveling below the solar surface through the magnetic structure of sunspots. We consider a series of magnetostatic models of sunspots of different magnetic field strengths, from 10 Mm below the photosphere to the low chromosphere. The purpose of these studies is to quantify the effect of the magnetic field on local helioseismology measurements by modeling waves excited by subphotospheric sources. Time-distance propagation diagrams and wave travel times are calculated for models of various field strengths and compared to the nonmagnetic case. The results clearly indicate that the observed time-distance helioseismology signals in sunspot regions correspond to fast MHD waves. The slow MHD waves form a distinctly different pattern in the time-distance diagram, which has not been detected in observations. The numerical results are in good agreement with the solution in the short-wavelength (eikonal) approximation, providing its validation. The frequency dependence of the travel times is in good qualitative agreement with observations. Title: Wave Propagation and Shock Formation in Different Magnetic Structures Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J. Bibcode: 2009ApJ...692.1211C Altcode: 2008arXiv0810.3613C Velocity oscillations "measured" simultaneously at the photosphere and the chromosphere—from time series of spectropolarimetric data in the 10830 Å region—of different solar magnetic features allow us to study the properties of wave propagation as a function of the magnetic flux of the structure (i.e., two different-sized sunspots, a tiny pore, and a facular region). While photospheric oscillations have similar characteristics everywhere, oscillations measured at chromospheric heights show different amplitudes, frequencies, and stages of shock development depending on the observed magnetic feature. The analysis of the power and the phase spectra, together with simple theoretical modeling, lead to a series of results concerning wave propagation within the range of heights of this study. We find that, while the atmospheric cutoff frequency and the propagation properties of different oscillating modes depend on the magnetic feature, in all the cases the power that reaches the high chromosphere above the atmospheric cutoff comes directly from the photosphere by means of linear vertical wave propagation rather than from nonlinear interaction of modes. Title: Magnetohydrostatic Sunspot Models from Deep Subphotospheric to Chromospheric Layers Authors: Khomenko, E.; Collados, M. Bibcode: 2008ApJ...689.1379K Altcode: 2008arXiv0808.3571K In order to understand the influence of magnetic fields on the propagation properties of waves, as derived from different local helioseismology techniques, forward modeling of waves is required. Such calculations need a model in magnetohydrostatic equilibrium as an initial atmosphere through which to propagate oscillations. We provide a method to construct such a model in equilibrium for a wide range of parameters, for use in simulations of artificial helioseismologic data. The method combines the advantages of self-similar solutions and current-distributed models. A set of models is developed by numerical integration of magnetohydrostatic equations from the subphotospheric to chromospheric layers. Title: High-resolution Ground-based European Solar Physics Authors: Collados, M. Bibcode: 2008LNEA....3..113C Altcode: This communication reviews some of the most challenging topics in high-resolution ground-based Solar Physics. The most powerful European facilities are described, together with their capabilities and skills gained in Europe using them. The reasons for a large-aperture solar telescope are outlined, based on present scientific needs, which have led to the joint project EST (European Solar Telescope), in which the most prestigious European Solar Physics research institutions participate. Some technical challenges of a such a large telescope are mentioned. Title: On the Possible Sources of Chromospheric Heating Authors: Beck, C.; Collados, M. Vera; Khomenko, E.; Rezaei, R. Bibcode: 2008ESPM...12.2.14B Altcode: The chromospheric temperature rise to values above the photospheric temperature cannot be due to radiative energy transport alone. We will outline different possibilities for the additional energy transport in the solar atmosphere by processes that require (or exclude) the presence of magnetic fields. We will discuss which of them could be identified and studied in detail using current data. To find the signature of the different heating processes and derive quantitative estimates of their efficiency, we analyzed simultaneous spectropolarimetric observations of photospheric magnetic fields (@630 nm) and intensity spectra of the chromospheric Ca II H line (396 nm). The mechanical energy flux at several height layers was derived from the velocity amplitudes of propagating acoustic waves seen in different spectral lines. The enhancement of chromospheric (radiation) temperature above the radiative equilibrium values was taken from an inversion of the Ca II H spectra with the SIR code assuming local thermal equilibrium (LTE) and complete redistribution (CRD). We compare the obtained energy values with each other and with the energy requirements demanded by theoretical/semi-empirical atmospheric models.

We find that the most important agent of chromospheric heating are propagating (magneto-)acoustic waves, which suffice to explain the brightenings in Ca II H spectra and their corresponding temperature enhancements. The energy contained in these intensity variations of the Ca II H line, however, is found to be insufficient to maintain a full-time and full-volume "hot" chromosphere. Additional energy transport mechanisms without a signature in the Ca II H spectra are thus necessary. Finally, we will outline which improvements are to be expected with future observations of higher quality (spatial resolution, enhanced polarimetric sensitivity, temporal cadence, other spectral lines) to be achieved with new ground-based telescopes like GREGOR or EST. Title: EST: The European Solar Telescope Authors: Collados, M. Bibcode: 2008ESPM...12..6.3C Altcode: The European Solar Telescope (EST) is a project for a 4 meter-class ground-based telescope, to be located in the Canary Islands. The project is promoted by the European Association for Solar Telescopes (EAST), a consortium formed by research organizations from 15 European countries. EST will be optimized for studies of magnetic coupling between the deep photosphere and upper chromosphere. The project has been approved for funds by the European Union, within the FP-7 framework, to produce the design of all systems and subsystems of the telescope during the next three years. This includes the optical and optomechanical design of the telescope itself and of the instruments and their control. MCAO will be included in the optical path in a natural way to compensate for atmospheric disturbances in an optimum way. The design of EST will strongly emphasize the use of a large number of visible and near-infrared instruments simultaneously which will influence the telescope design from the very beginning. This communication will center mainly on the scientific objectives that EST will address. Generally speaking, they involve understanding how the magnetic field emerges through the solar surface, interacts with the plasma dynamics to transfer energy between different regions, and finally releases it in the form of heat or as violent events in the solar chromosphere and corona. Among the many topics of interest, one may cite, as described in the EST Science Requirements Document: small-scale flux emergence in quiet sun regions, large-scale magnetic structures, magnetic flux cancellation processes, polar magnetic fields, magnetic topology of the photosphere and chromosphere, conversion of mechanical to magnetic energy in the photosphere, wave propagation from photosphere to chromosphere, energy dissipation in the chromosphere at small and large scales, etc. The present status and future perspectives of the project will also be outlined. Title: Multi-layer Study of Wave Propagation in Sunspots Authors: Felipe, T.; Khomenko, E.; Collados, M.; Beck, C. Bibcode: 2008ESPM...12.2.12F Altcode: Observations in different spectral lines give us information about the different layers of the solar atmosphere. Here we analyze the propagation of waves in sunspots from the photosphere to the chromosphere using time series of cospatial Ca II H intensity spectra and polarimetric spectra of Si I 10827 A and He I 10830 A multiplet. From the Doppler shifts of these lines we retrieve the temporal variations of the velocity along the line-of-sight at several heights. Phase spectra are used to get the relation between oscillatory signals measured at each spectral signature. Our analysis reveals standing waves for frequencies lower than 3.5 mHz and propagating waves for higher frequencies, which steepen into shocks in the chromosphere. Oscillations are detectable in Ca II H wings and they are propagated along line wing layers to the line core. Ca II H core forms at a lower height than the He I 10830 A line. A time delay of about 30 s is measured between the Doppler signals detected at both wavelengths. We also find that in "cold" sunspots the Si I 10827 A forms deeper than in the quiet sun. This type of measurements demonstrate the importance of simultaneous co-spatial observations at different wavelengths. Future infrastructures, such as GREGOR and EST, should include multi-wavelength capabilities to make possible the study of the photosphere-chromosphere connection with the highest spatial and temporal resolution. Title: Nonlinear Numerical Simulations of Magneto-Acoustic Wave Propagation in Small-Scale Flux Tubes Authors: Khomenko, E.; Collados, M.; Felipe, T. Bibcode: 2008SoPh..251..589K Altcode: 2008SoPh..tmp...32K; 2007arXiv0710.3335K We present results of nonlinear, two-dimensional, numerical simulations of magneto-acoustic wave propagation in the photosphere and chromosphere of small-scale flux tubes with internal structure. Waves with realistic periods of three to five minutes are studied, after horizontal and vertical oscillatory perturbations are applied to the equilibrium model. Spurious reflections of shock waves from the upper boundary are minimized by a special boundary condition. This has allowed us to increase the duration of the simulations and to make it long enough to perform a statistical analysis of oscillations. The simulations show that deep horizontal motions of the flux tube generate a slow (magnetic) mode and a surface mode. These modes are efficiently transformed into a slow (acoustic) mode in the vA<cS atmosphere. The slow (acoustic) mode propagates vertically along the field lines, forms shocks, and remains always within the flux tube. It might effectively deposit the energy of the driver into the chromosphere. When the driver oscillates with a high frequency, above the cutoff, nonlinear wave propagation occurs with the same dominant driver period at all heights. At low frequencies, below the cutoff, the dominant period of oscillations changes with height from that of the driver in the photosphere to its first harmonic (half period) in the chromosphere. Depending on the period and on the type of the driver, different shock patterns are observed. Title: First-Light Science Cases for the GREGOR Fabry-Perot Interferometer Authors: Denker, C.; Balthasar, H.; Bello González, N.; Collados, M.; Kneer, H. F. Nicklas; Puschmann, K. G. Bibcode: 2008ESPM...12..6.8D Altcode: The light-gathering capacity and resolving power of the 1.5-meter aperture GREGOR telescope will provide solar observations of the full Stokes vector with high temporal, spectral and spatial resolution. As one of the first-light instruments, the GREGOR Fabry-Perot Interferometer (GFPI) is well suited for observations with adaptive optics (AO) correction. Post-facto image correction (speckle masking imaging and deconvolution) will further enhance the data quality to approach the diffraction-limited resolution of the telescope. We will describe the GFPI optical design and its basic operating procedures. Instruments characteristics such as field-of-view, cadence, spectral resolution, and spectroscopic/polarimetric observing modes will result in boundary conditions, which have to be carefully considered in optimizing the scientific outcome of the first-light observations. We will present two science cases for quiet Sun and active region studies to illustrate the capabilities of this imaging spectro-polarimeter. Title: Seismology of Sunspots: An Interplay between Temperature and Magnetic Field Structures Authors: Olshevsky, V.; Khomenko, E.; Collados, M. Bibcode: 2008ESPM...12..3.2O Altcode: Using a numerical three-dimensional MHD modelling of magneto-acoustic wave propagation in a realistic magnetostatic sunspot model we investigate the influence of the magnetic field on the parameters measured by local helioseismology. We find that the variations of temperature as well as the presence of the magnetic field cause important changes to the wave travel times. Magnetic field speeds up the waves to considerable amount, while the temperature depression within a sunspot causes the opposite action. The calculated travel time differences between the unmagnetized and magnetized atmospheres lie in the range typically obtained from local helioseismology correlation analysis. Our numerical results are also in agreement with the analytical calculations of the travel times applying WKB technique. Title: European Solar Telescope (EST): project status Authors: Collados, Manuel Bibcode: 2008SPIE.7012E..0JC Altcode: 2008SPIE.7012E..17C The European Solar Telescope (EST) is a project for a large aperture (3-5 meters) ground-based telescope, to be located in the Canary Islands. EST will be optimized for studies of magnetic coupling between the deep photosphere and upper chromosphere. This will require diagnostics of the thermal, dynamic and magnetic properties of the plasma over many scale heights, by using multiple wavelength imaging, spectroscopy and spectropolarimetry. The design of EST will strongly emphasize the use of a large number of visible and near-infrared instruments simultaneously. To achieve these goals, EST will specialize in high spatial and temporal resolution using instruments that can efficiently produce twodimensional spectral information. In this communication, the present situation of the design is outlined, as well as the expected future phases and scheduling. Title: The participation of the Instituto de Astrofísica de Canarias in the European Solar Telescope Authors: Collados, M.; Calcines, A.; Diaz, J. J.; Gracia, F.; Grivel-Gelly, C.; López, R.; Mangharam, H.; Páez, E.; Perez, A.; Rasilla, J. L.; Rodríguez, L. F.; Sánchez-Capuchino, J.; Socas-Navarro, H. Bibcode: 2008SPIE.7012E..32C Altcode: 2008SPIE.7012E.105C This communication reviews the participation of the Instituto de Astrofísica de Canarias (IAC) in the design of the European Solar Telescope. Apart of being the coordinator institution of the whole project, and, as such, responsible for the project managing, the IAC leads several tasks like overall instrument definition or characterization of the atmospheric turbulence profile with height or the definition of adequate detectors. More in particular, the IAC will design and build two long-base SHABAR (SHAdow BAnd Ranger), instruments to measure medium-altitude seeing. The IAC is also responsible for the design, together with other institutions, of the design of grating spectropolarimeters suitable for multiwavelength high spatial and spectral resolution. Title: A high-resolution spectrograph for the solar telescope GREGOR Authors: Collados, Manuel; Calcines, A.; Díaz, J. J.; Hernnádez, E.; López, R.; Páez, E. Bibcode: 2008SPIE.7014E..5ZC Altcode: 2008SPIE.7014E.198C This communication shows the design, layout, mounting and start-up of a high-resolution grating spectrograph for VIS-NIR at GREGOR 1.5m Solar Telescope (Observatorio del Teide, Tenerife, Canary Islands). The instrument will be used together with the Tenerife Infrared Polarimeter (TIP-II). As special characteristics of the design, the following can be mentioned: The first folding mirror of the spectrograph can be placed in two positions to take into account the change of the optical axis introduced by the polarizing beamsplitter of TIP-II. This way the instrument is optimally aligned when used in situations with and without polarimeter. The second and third mirrors rotate the image of the entrance slit, making it parallel to the grating grooves. A system of prisms are used to adequately fit onto the detector the two orthogonal polarized beams generated by the polarimeter. Two output beams are possible, to make feasible simultaneous visible and near-infrared observations. Title: Error propagation in polarimetric demodulation Authors: Asensio Ramos, A.; Collados, M. Bibcode: 2008ApOpt..47.2541A Altcode: 2008arXiv0804.4708A The polarization analysis of light is typically carried out using modulation schemes. The light of an unknown polarization state is passed through a set of known modulation optics, and a detector is used to measure the total intensity passing the system. The modulation optics is modified several times, and, with the aid of several such measurements, the unknown polarization state of the light can be inferred. How to find the optimal demodulation process has been investigated in the past. However, since the modulation matrix has to be measured for a given instrument and the optical elements can present problems of repeatability, some uncertainty is present in the elements of the modulation matrix or covariances between these elements. We analyze in detail this issue, presenting analytical formulas for calculating the covariance matrix produced by the propagation of such uncertainties on the demodulation matrix, on the inferred Stokes parameters, and on the efficiency of the modulation process. We demonstrate that even if the covariance matrix of the modulation matrix is diagonal, the covariance matrix of the demodulation matrix is in general nondiagonal because matrix inversion is a nonlinear operation. This propagates through the demodulation process and induces correlations on the inferred Stokes parameters. Title: The Influence of Coronal EUV Irradiance on the Emission in the He I 10830 Å and D3 Multiplets Authors: Centeno, R.; Trujillo Bueno, J.; Uitenbroek, H.; Collados, M. Bibcode: 2008ApJ...677..742C Altcode: 2007arXiv0712.2203C Two of the most attractive spectral windows for spectropolarimetric investigations of the physical properties of the plasma structures in the solar chromosphere and corona are the ones provided by the spectral lines of the He I 10830 and 5876 Å (or D3) multiplets, whose polarization signals are sensitive to the Hanle and Zeeman effects. However, in order to be able to carry out reliable diagnostics, it is crucial to have a good physical understanding of the sensitivity of the observed spectral line radiation to the various competing driving mechanisms. Here we report a series of off-the-limb non-LTE calculations of the He I D3 and 10830 Å emission profiles, focusing our investigation on their sensitivity to the EUV coronal irradiation and the model atmosphere used in the calculations. We show in particular that the intensity ratio of the blue to the red components in the emission profiles of the He I 10830 Å multiplet turns out to be a good candidate as a diagnostic tool for the coronal irradiance. Measurements of this observable as a function of the distance to the limb and its confrontation with radiative transfer modeling might give us valuable information on the physical properties of the solar atmosphere and on the amount of EUV radiation at relevant wavelengths penetrating the chromosphere from above. Title: Channeling 5 Minute Photospheric Oscillations into the Solar Outer Atmosphere through Small-Scale Vertical Magnetic Flux Tubes Authors: Khomenko, E.; Centeno, R.; Collados, M.; Trujillo Bueno, J. Bibcode: 2008ApJ...676L..85K Altcode: 2008arXiv0802.0938K We report two-dimensional MHD simulations which demonstrate that photospheric 5 minute oscillations can leak into the chromosphere inside small-scale vertical magnetic flux tubes. The results of our numerical experiments are compatible with those inferred from simultaneous spectropolarimetric observations of the photosphere and chromosphere obtained with the Tenerife Infrared Polarimeter (TIP) at 10830 Å. We conclude that the efficiency of energy exchange by radiation in the solar photosphere can lead to a significant reduction of the cutoff frequency and may allow for the propagation of the 5 minute waves vertically into the chromosphere. Title: Multiline Spectropolarimetry of the Quiet Sun at 5250 and 6302 Å Authors: Socas-Navarro, H.; Borrero, J. M.; Asensio Ramos, A.; Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J. Bibcode: 2008ApJ...674..596S Altcode: The reliability of quiet-Sun magnetic field diagnostics based on the Fe I lines at 6302 Å has been questioned by recent work. Here we present the results of a thorough study of high-resolution multiline observations taken with the new spectropolarimeter SPINOR, comprising the 5250 and 6302 Å spectral domains. The observations were analyzed using several inversion algorithms, including Milne-Eddington, LTE with 1 and 2 components, and MISMA codes. We find that the line-ratio technique applied to the 5250 Å lines is not sufficiently reliable to provide a direct magnetic diagnostic in the presence of thermal fluctuations and variable line broadening. In general, one needs to resort to inversion algorithms, ideally with realistic magnetohydrodynamic constrains. When this is done, the 5250 Å lines do not seem to provide any significant advantage over those at 6302 Å. In fact, our results point toward a better performance with the latter (in the presence of turbulent line broadening). In any case, for very weak flux concentrations, neither spectral region alone provides sufficient constraints to fully disentangle the intrinsic field strengths. Instead, we advocate for a combined analysis of both spectral ranges, which yields a better determination of the quiet-Sun magnetic properties. Finally, we propose the use of two other Fe I lines (at 4122 and 9000 Å) with identical line opacities that seem to work much better than the others. Title: Internetwork magnetic field distribution from simultaneous 1.56 μm and 630 nm observations Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.; Beck, C. Bibcode: 2008A&A...477..953M Altcode: 2007arXiv0711.0267M Aims:We study the contradictory magnetic field strength distributions retrieved from independent analyses of spectropolarimetric observations in the near-infrared (1.56 μm) and in the visible (630 nm) spectral ranges in internetwork regions.
Methods: To solve this apparent controversy, we present simultaneous and co-spatial 1.56 μm and 630 nm observations of an internetwork area. The properties of the circular and linear polarization signals, as well as the Stokes V area and amplitude asymmetries, are discussed. As a complement, we also used inversion techniques to infer the physical parameters of the solar atmosphere. As a first step, the infrared and visible observations are analysed separately to check their compatibility. Finally, the simultaneous inversion of the two data sets is performed.
Results: The magnetic flux densities retrieved from the individual analysis of the infrared and visible data sets are strongly correlated. The polarity of the Stokes V profiles is the same at co-spatial pixels in both wavelength ranges. This indicates that both 1.56 μm and 630 nm observations trace the same magnetic structures on the solar surface. The simultaneous inversion of the two pairs of lines reveals an internetwork full of sub-kG structures that fill only 2% of the resolution element. A correlation is found between the magnetic field strength and the continuum intensity: equipartition fields (B∼ 500 G) tend to be located in dark intergranular lanes, whereas weaker field structures are found inside granules. The most probable unsigned magnetic flux density is 10 Mx/cm^2. The net magnetic flux density in the whole field of view is nearly zero. This means that both polarities cancel out almost exactly in our observed internetwork area. Title: Supersonic Downflows in the Photosphere Discovered in Sunspot Moat Regions Authors: Shimizu, T.; Martinez-Pillet, V.; Collados, M.; Ruiz-Cobo, B.; Centeno, R.; Beck, C.; Katsukawa, Y. Bibcode: 2007ASPC..369..113S Altcode: This paper reports on our new findings from the International Time Program observations at the Canaries islands, Spain, in July 2005. We have found small-scale photospheric events with extremely red-shifted Stokes V signals in sunspot moat regions. A preliminary estimate of the physical conditions for an observed Stokes V profile indicates the presence of a downward motion with a supersonic speed in the order of 10 km/s. With the currently evaluated observational information, we interprete the supersonic flows as downward motion from magnetic reconnection occurring at the upper chromosphere or lower photosphere. With coordinated observations of the Solar-B onboard telescopes, Stokes measurements by the SOT spectro-polarimeter would give new information for further understanding the nature of these events with strongly red-shifted Stokes V, and for discussing the physical conditions involving in possible magnetic reconnections in the lower solar atmosphere. Title: Multi-Line Quiet Sun Spectro-Polarimetry at 5250 and 6302 Å Authors: Socas-Navarro, H.; Borrero, J.; Asensio Ramos, A.; Collados, M.; Domínguez Cerdeña, I.; Khomenko, E. V.; Martínez González, M. J.; Martínez Pillet, V.; Ruiz Cobo, B.; Sánchez Almeida, J. Bibcode: 2007arXiv0710.1099S Altcode: The reliability of quiet Sun magnetic field diagnostics based on the \ion{Fe}{1} lines at 6302 Åhas been questioned by recent work. We present here the results of a thorough study of high-resolution multi-line observations taken with the new spectro-polarimeter SPINOR, comprising the 5250 and 6302 Åspectral domains. The observations were analyzed using several inversion algorithms, including Milne-Eddington, LTE with 1 and 2 components, and MISMA codes. We find that the line-ratio technique applied to the 5250 Ålines is not sufficiently reliable to provide a direct magnetic diagnostic in the presence of thermal fluctuations and variable line broadening. In general, one needs to resort to inversion algorithms, ideally with realistic magneto-hydrodynamical constrains. When this is done, the 5250 Ålines do not seem to provide any significant advantage over those at 6302 Å. In fact, our results point towards a better performance with the latter (in the presence of turbulent line broadening). In any case, for very weak flux concentrations, neither spectral region alone provides sufficient constraints to fully disentangle the intrinsic field strengths. Instead, we advocate for a combined analysis of both spectral ranges, which yields a better determination of the quiet Sun magnetic properties. Finally, we propose the use of two other \ion{Fe}{1} lines (at 4122 and 9000 Å) with identical line opacities that seem to work much better than the others. Title: Low-lying magnetic loops in the solar internetwork Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.; Solanki, S. K. Bibcode: 2007A&A...469L..39M Altcode: 2007arXiv0705.1319M Aims:We study the structure of the magnetic field vector in the internetwork and search for the presence of small-scale loops.
Methods: We invert 1.56 μm spectropolarimetric observations of internetwork regions at disc centre by applying the SIR code. This allows us to recover the atmospheric parameters that play a role in the formation of these spectral lines. We are mainly interested in the structure of the magnetic field vector.
Results: We find that many opposite polarity elements of the internetwork are connected by short (2-6´´), low-lying (photospheric) loops. These loops connect at least the 10-20% of the internetwork flux visible in our data. Also we have some evidence that points towards a dynamic scenario that can be produced by the emergence of internetwork magnetic flux. Title: A Magnetic Map of a Solar Filament Authors: Merenda, L.; Trujillo Bueno, J.; Collados, M. Bibcode: 2007ASPC..368..347M Altcode: One of the most useful diagnostic tools for the detection of inclined magnetic fields in solar chromospheric and coronal structures is that based on the fact that the Hanle effect in forward scattering at the solar disk center creates linear polarization in some spectral lines, such as those of the He I 10830 Å multiplet. Here we show the preliminary results of an ongoing investigation on the magnetic field of a solar filament, based on the inversion of spectropolarimetric observations obtained with the Tenerife Infrared Polarimeter. Title: GREGOR: the New German Solar Telescope Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.; Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.; Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.; Wittmann, A. Bibcode: 2007ASPC..368..605B Altcode: 2007arXiv0704.2693B GREGOR is a new open solar telescope with an aperture of 1.5 m. It replaces the former 45-cm Gregory Coudé telescope on the Canary island Tenerife. The optical concept is that of a double Gregory system. The main and the elliptical mirrors are made from a silicon-carbide material with high thermal conductivity. This is important to keep the mirrors on the ambient temperature avoiding local turbulence. GREGOR will be equipped with an adaptive optics system. The new telescope will be ready for operation in 2008. Post-focus instruments in the first stage will be a spectrograph for polarimetry in the near infrared and a 2-dimensional spectrometer based on Fabry-Pérot interferometers for the visible. Title: Tenerife Infrared Polarimeter II Authors: Collados, M.; Lagg, A.; Díaz Garcí A, J. J.; Hernández Suárez, E.; López López, R.; Páez Mañá, E.; Solanki, S. K. Bibcode: 2007ASPC..368..611C Altcode: Since May 2005 the Tenerife Infrared Polarimeter II (TIP-II) has been operational at the Vacuum Tower Telescope on Tenerife. The core of the polarimeter is a 1024×1020 pixel infrared camera allowing for high precision measurements of the full Stokes vector with a pixel size of 0.18 arcsec, corresponding to the diffraction limit of the telescope at 1 μm. The polarimeter is able to reach a polarimetric accuracy of a few times 10-4, covering a wavelength range of 1 to 1.8 μm. With an upgrade in July 2006, the slit size has been increased to 77 arcsec allowing most active regions to be covered with a single scan. Here we present the technical details of the polarimeter and the camera. We also show some data illustrating the power of this new instrumentation. Title: Full-Stokes Observations and Analysis of He I 10830 Å in a Flaring Region Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Aznar Cuadrado, R.; Collados, M. Bibcode: 2007ASPC..368..467S Altcode: We present observations of the full Stokes vector in a flaring region, taken in the chromospheric He I 10830 Å multiplet. The data were recorded with the new Tenerife Infrared Polarimeter (TIP 2) at the German Vacuum Tower Telescope (VTT) during May 2005. The He profiles during the flare are extraordinary, showing extremely broad Stokes I absorption and very complex and spatially variable Stokes V signatures. We give first results on the line-of-sight velocities and the magnetic field vector values in the chromosphere for one observed Stokes profile by applying an inversion code to the He I lines. Title: On the Stokes V Amplitude Ratio as an Indicator of the Field Strength in the Solar Internetwork Authors: Khomenko, E.; Collados, M. Bibcode: 2007ApJ...659.1726K Altcode: The results of the determination of magnetic field strength from weak polarimetric signals in solar internetwork regions are contradictory. We investigate the origin of this contradiction with the help of MHD simulations. It is shown that the Stokes V amplitude ratio of the Fe I λλ15652-15648 lines is a good indicator of kG magnetic field concentrations, even for magnetic fields with a complex internal structure like those in MHD simulations. The Stokes V amplitude ratio of the Fe I λλ5247-5250 lines also shows a good correlation with magnetic field strength. However, in simulations with a flux level appropriate for the internetwork, it gives values corresponding to sub-kG fields. The reason is the rapid decrease of the field strength with height in kG magnetic field concentrations. These lines sample high regions of the atmosphere, where the field is already below kG levels. We also find that the Stokes V amplitude ratio of the Fe I λλ6301-6302 lines shows no correlation with the magnetic field strength. The reason lies in the large difference in the heights of formation of these two lines. The value of the magnetic field strength obtained from the Fe I λλ6301 and 6302 lines depends crucially on the treatment of gradients of the magnetic field, line-of-sight velocity, and temperature, even at a numerical spatial resolution of 20 km. Title: A Near-Infrared Line of Mn I as a Diagnostic Tool of the Average Magnetic Energy in the Solar Photosphere Authors: Asensio Ramos, A.; Martínez González, M. J.; López Ariste, A.; Trujillo Bueno, J.; Collados, M. Bibcode: 2007ApJ...659..829A Altcode: 2006astro.ph.12389A We report on spectropolarimetric observations of a near-IR line of Mn I located at 15262.702 Å whose intensity and polarization profiles are very sensitive to the presence of hyperfine structure. A theoretical investigation of the magnetic sensitivity of this line uncovers several interesting properties. The most important one is that the presence of strong Paschen-Back perturbations due to the hyperfine structure produces an intensity line profile whose shape changes according to the absolute value of the magnetic field strength. A line ratio technique is developed from the intrinsic variations of the line profile. This line ratio technique is applied to spectropolarimetric observations of the quiet solar photosphere in order to explore the probability distribution function of the magnetic field strength. Particular attention is given to the quietest area of the observed field of view, which was encircled by an enhanced network region. A detailed theoretical investigation shows that the inferred distribution yields information on the average magnetic field strength and on the spatial scale at which the magnetic field is organized. A first estimation gives ~250 G for the mean field strength and a tentative value of ~0.4" for the spatial scale at which the observed magnetic field is horizontally organized. Title: Multi-wavelength observations at the German VTT on Tenerife Authors: Beck, C.; Mikurda, K.; Bellot Rubio, L. R.; Kentischer, T.; Collados, M. Bibcode: 2007msfa.conf...55B Altcode: To study the small-scale dynamic processes of magneto-convection in the solar photosphere in more detail than currently achieveable, not only the spatial resolution has to be increased, but also the information content of observations. In order to do so, several wavelengths and spectral lines must be observed simultaneously. This is often achieved by coordinated campaigns at several telescopes with different post-focus instrumentation. The German Vacuum Tower Telescope (VTT) on Tenerife offers the possibility to operate several dedicated instruments spectrometers, polarimeters, imaging systems at the same time. We describe some of the possible combinations of post-focus instruments, and present examples of multi-wavelength data obtained recently. Title: Line ratio method applied to inter-network magnetic fields Authors: Khomenko, E.; Collados, M. Bibcode: 2007msfa.conf..303K Altcode: We investigate the validity of the Stokes V amplitude ratio as an indicator of the magnetic field strength in solar inter-network regions with the help ofMHD simulations. We show that the Stokes V amplitude ratio of the Fe I 15652-15648 Å lines and Fe I 5247-5250 Å lines show a good correlation with the magnetic field strength even for magnetic fields with a complex internal structure like those in MHD simulations. However, in the latter case, the amplitude ratio sub-estimates the magnetic field strength, always revealing sub-kG values. The Stokes V amplitude ratio of the Fe I 6301-6302 Å lines shows no correlation with the magnetic field strength. The reasons of this behaviour are explained. Title: Numerical modeling of MHD wave propagation in sunspots: a 3D case Authors: Olshevsky, V.; Khomenko, E.; Collados, M. Bibcode: 2007msfa.conf..347O Altcode: We present the first results of a 3D numerical modeling of linear MHD wave propagation in a realistic sunspot model. In our simulations, a piston located at the base of the photosphere generates waves with a certain period. The ratio between the acoustic and the Alfven speed, cS /vA, decreases from much larger than one at the photosphere to much lower than one in the chromosphere in our simulation domain. Waves propagate through the region where cS << vA, where mode transformation is observed. At a somewhat higher region, where cS = vA, the fast (magnetic) mode reflects back to the photosphere due to the vertical and horizontal gradients of vA. The slow (acoustic) mode propagates to the upper layers and increases its velocity amplitude. Unlike the 2D simulations, the Alfven mode is also generated by the piston and experiences transformations at the cS = vA layer. The behaviour of this mode requires further study. Title: New high resolution solar telescope GREGOR Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier, K.; Wittmann, A. D. Bibcode: 2007msfa.conf...39V Altcode: The 1.5m solar telescope GREGOR is being constructed at Tenerife, Spain. Its purpose is to observe with high spatial and spectral resolution small-scale dynamic magnetic features on the Sun. The telescope is completely open with retractable dome and actively cooled primary mirror made of silicon carbide to minimize thermal effects on the image quality. After completion it will be one of the most powerful solar telescopes. This paper presents a general overview of the telescope characteristics and the current status. Title: Wave propagation and shock formation in diverse magnetic structures Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J. Bibcode: 2007msfa.conf..245C Altcode: Velocity oscillations measured simultaneously at the photosphere and the chromosphere of different solar magnetic features (sunspots, pores and facular regions) allow us to study the properties of wave propagation as a function of the magnetic flux of the structure. While photospheric oscillations are similar everywhere, oscillations measured at chromospheric heights show different amplitudes, frequencies and stages of shock development depending on the observed magnetic feature. The analysis via power and phase spectra, together with simple theoretical modeling, lead to a series of results concerning wave propagation within the range of heights of this study. We find that, while the atmospheric cut-off frequency and the propagation properties of the different oscillating modes depend on the magnetic feature, in all the cases the power that reaches the high chromosphere comes directly from the photosphere by means of linear wave propagation rather than from non-linear interaction of modes. Title: Magnetic field inversions from Stokes profiles generated by MHD simulations Authors: Khomenko, E.; Collados, M. Bibcode: 2007MmSAI..78..166K Altcode: We report tests of inversion methods applied to complex Stokes spectra generated by realistic MHD simulations. The average magnetic field strength of the simulations used is of 30 and 140 G, which we believe is representative of quiet solar regions. The behaviour of the Fe I at 1.56 mu m and 630 nm lines is analyzed. The tests have been done with the original resolution of simulations (20 km) and also with resolution of 0.6'' and 1.4'' (after having conveniently degraded the images). Title: Polarimetry in the visible and near infrared Authors: Collados, M. Bibcode: 2007msfa.conf..143C Altcode: The various techniques used in the visible and near-infrared for the measurement of intrinsic polarization coming from solar regions are described. Their performance to allow for the acquisition of simultaneous spectropolarimetric data at several wavelengths is discussed. Any development of a future facility should take advantage of these capabilities to measure simultaneously different solar atmospheric layers with high spatial resolution. Title: Internetwork magnetic fields Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B. Bibcode: 2007msfa.conf..157M Altcode: Spectropolarimetric observations of the internetwork obtained in the 1.56 [mμ]m Fe I doublet are used to calculate the distributions of magnetic field strength, filling factor and magnetic flux density at different positions on the solar surface. We go one step further and describe what the observations show about the three-dimensional structure of the magnetic fields at the internetwork quiet Sun. Title: Oscillations and Wave Propagation in Different Solar Magnetic Features Authors: Centeno, R.; Collados, M.; Trujillo Bueno, J. Bibcode: 2006ASPC..358..465C Altcode: We present the results of the analysis of temporal series of spectro-polarimetric data measured simultaneously in the photospheric Si I 10827 Å line and the chromospheric He I 10830 Å triplet, on top of two different targets: a facular region and the umbra of a sunspot. The full Stokes inversion of both spectral features gives us the temporal variability of the physical conditions at two different regions in the solar atmosphere, allowing us to compare the LOS velocity oscillations at the photosphere and the chromosphere, and infer the main characteristics of wave propagation in both magnetic structures. Title: Measuring the Magnetic Vector with the He I 10830 Å Line: A Rich New World Authors: Solanki, S. K.; Lagg, A.; Aznar Cuadrado, R.; Orozco Suárez, D.; Collados, M.; Wiegelmann, T.; Woch, J.; Sasso, C.; Krupp, N. Bibcode: 2006ASPC..358..431S Altcode: The triplet of the He I transitions around 10830 Å not only shows a rich variety of Stokes profiles, but also allows the full magnetic vector in the upper chromosphere to be probed, thus revealing the magnetic structure of loops, current sheets, finely structured supersonic downflows, the chromospheric layers of sunspots (supporting the presence of uncombed fields in the penumbra), flares, and the quiet Sun. A very brief overview of some of the observations and results obtained so far is given. Title: Numerical Modeling of Magnetohydrodynamic Wave Propagation and Refraction in Sunspots Authors: Khomenko, E.; Collados, M. Bibcode: 2006ApJ...653..739K Altcode: We present numerical simulations of magnetoacoustic wave propagation from the photosphere to the low chromosphere in a magnetic sunspot-like structure. A thick flux tube, with dimensions typical of a small sunspot, is perturbed by a vertical or horizontal velocity pulse at the photospheric level. The type of mode generated by the pulse depends on the ratio between the sound speed cS and the Alfvén speed vA, on the magnetic field inclination at the location of the driver, and on the shape of the pulse in the horizontal direction. Mode conversion is observed to occur in the region in which both characteristic speeds have similar values. The fast (magnetic) mode in the region cS<vA does not reach the chromosphere and reflects back to the photosphere at a somewhat higher layer than the cS=vA line. This behavior is due to wave refraction, caused primarily by the vertical and horizontal gradients of the Alfvén speed. The slow (acoustic) mode continues up to the chromosphere along the magnetic field lines with increasing amplitude. We show that this behavior is characteristic for waves in a wide range of periods generated at different distances from the sunspot axis. Since an important part of the energy of the pulse is returned back to the photosphere by the fast mode, the mechanism of energy transport from the photosphere to the chromosphere by waves in sunspots is rather ineffective. Title: Internetwork Magnetic Field Distribution from Simultaneous Fe I 1.5 µ and Fe I 630 nm Observations Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B. Bibcode: 2006ASPC..358...36M Altcode: We took simultaneous observations in Fe I 1.5 µ and Fe I 630 nm of an internetwork region. We discuss the compatibility of the data in the two spectral ranges, and present results for the magnetic field distribution. We show that the larger contribution comes from hG field strengths. Title: On the validity of the 630 nm Fe I lines for magnetometry of the internetwork quiet Sun Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B. Bibcode: 2006A&A...456.1159M Altcode: 2006astro.ph..5446M Aims.The purpose of this work is to analyze the reliability of the magnetic field strengths inferred from the 630 nm pair of Fe i lines in internetwork quiet Sun regions.
Methods: .Some numerical experiments have been performed that demonstrate the inability of these lines to recover the magnetic field strength in such low flux solar regions.
Results: .It is shown how different model atmospheres, with magnetic field strengths ranging from a few hundred Gauss to kiloGauss, give rise to Stokes profiles that cannot be distinguished. The reasons for this degeneracy are discussed.
Title: Detailed design of the imaging magnetograph experiment (IMaX): a visible imager magnetograph for the Sunrise mission Authors: Álvarez-Herrero, A.; Belenguer, T.; Pastor, C.; González, L.; Heredero, R. L.; Ramos, G.; Reina, M.; Sánchez, A.; Villanueva, J.; Sabau, L.; Martínez Pillet, V.; Bonet, J. A.; Collados, M.; Jochum, L.; Ballesteros, E.; Medina Trujillo, J. L.; Ruiz, Cobo B.; González, J. C.; del Toro Iniesta, J. C.; López Jiménez, A. C.; Castillo Lorenzo, J.; Herranz, M.; Jerónimo, J. M.; Mellado, P.; Morales, R.; Rodríguez, J.; Domingo, V.; Gasent, J. L.; Rodríquez, P. Bibcode: 2006SPIE.6265E..4CA Altcode: 2006SPIE.6265E.132A In this work, it is described the Imaging Magnetograph eXperiment, IMaX, one of the three postfocal instruments of the Sunrise mission. The Sunrise project consists on a stratospheric balloon with a 1 m aperture telescope, which will fly from the Antarctica within the NASA Long Duration Balloon Program. IMaX will provide vector magnetograms of the solar surface with a spatial resolution of 70 m. This data is relevant for understanding how the magnetic fields emerge in the solar surface, how they couple the photospheric base with the million degrees of temperature of the solar corona and which are the processes that are responsible of the generation of such an immense temperatures. To meet this goal IMaX should work as a high sensitivity polarimeter, high resolution spectrometer and a near diffraction limited imager. Liquid Crystal Variable Retarders will be used as polarization modulators taking advantage of the optical retardation induced by application of low electric fields and avoiding mechanical mechanisms. Therefore, the interest of these devices for aerospace applications is envisaged. The spectral resolution required will be achieved by using a LiNbO 3 Fabry-Perot etalon in double pass configuration as spectral filter before the two CCDs detectors. As well phase-diversity techniques will be implemented in order to improve the image quality. Nowadays, IMaX project is in the detailed design phase before fabrication, integration, assembly and verification. This paper briefly describes the current status of the instrument and the technical solutions developed to fulfil the scientific requirements. Title: The new 1.5m solar telescope GREGOR: first light and start of commissioning Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens; Heidecke, Frank; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2006SPIE.6267E..0WV Altcode: 2006SPIE.6267E..29V The integration of the three main silicon carbide mirrors into the new 1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned during 2006. We expect first light at the end of 2006. A progress report about integration of the optics and mechanics and planning of the commissioning phase of the telescope and post focus instruments will be presented at the meeting. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg, the Astrophysikalische Institut Potsdam, the Institut fur Astronomie Gottingen and additional national and international Partners. Title: Site testing for the Advanced Technology Solar Telescope Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Streander, K. Bibcode: 2006SPIE.6267E..1TH Altcode: 2006SPIE.6267E..59H The Advanced Solar Technology Telescope (ATST) is a 4-m solar telescope being designed for high spatial, spectral and temporal resolution, as well as IR and low-scattered light observations. The overall limit of performance of the telescope is strongly influenced by the qualities of the site at which it is located. Six sites were tested with a seeing monitor and a sky brightness instrument for 1.5 to 2 years. The sites were Big Bear (California), Haleakala (Hawaii), La Palma (Canary Islands, Spain), Panguitch Lake (Utah), Sacramento Peak (New Mexico), and San Pedro Martir (Baja California, Mexico). In this paper we will describe the methods and results of the site survey, which chose Haleakala as the location of the ATST. Title: Determination of the Magnetic Field Vector via the Hanle and Zeeman Effects in the He I λ10830 Multiplet: Evidence for Nearly Vertical Magnetic Fields in a Polar Crown Prominence Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M. Bibcode: 2006ApJ...642..554M Altcode: The magnetic field is the key physical quantity responsible for the formation, stability, and evolution of solar prominences (ribbons of cool dense gas embedded in the hot tenuous corona). Therefore, it is important to obtain good empirical knowledge of the three-dimensional structure of prominence magnetic fields. Here we show how the magnetic field vector can be inferred via the physical interpretation of spectropolarimetric observations in the He I λ10830 multiplet. To this end, we have developed an inversion code based on the quantum theory of the Hanle and Zeeman effects and on a few modeling assumptions. We show an application to full Stokes vector observations of a polar crown prominence that, in the slit-jaw Hα image, showed nearly vertical plasma structures. Our results provide evidence for magnetic fields on the order of 30 G inclined by about 25° with respect to the local solar vertical direction. Of additional interest is that the inferred nearly vertical magnetic field vector appears to be slightly rotating around a fixed direction in space as one proceeds along the direction of the spectrograph's slit. While these results provide new light on the three-dimensional geometry of the magnetic fields that confine the plasma of polar crown prominences, they also urge us to develop improved solar prominence models and to pursue new diagnostic investigations. Title: Spectropolarimetric Investigation of the Propagation of Magnetoacoustic Waves and Shock Formation in Sunspot Atmospheres Authors: Centeno, Rebecca; Collados, Manuel; Trujillo Bueno, Javier Bibcode: 2006ApJ...640.1153C Altcode: 2005astro.ph.12096C Velocity oscillations in sunspot umbrae have been measured simultaneously in two spectral lines: the photospheric Si I λ10827 line and the chromospheric He I λ10830 multiplet. From the full Stokes inversion of temporal series of spectropolarimetric observations, we retrieved, among other parameters, the line-of-sight velocity temporal variations at photospheric and chromospheric heights. Chromospheric velocity oscillations show a 3 minute period with a clear sawtooth shape typical of propagating shock wave fronts. Photospheric velocity oscillations have basically a 5 minute period, although the power spectrum also shows a secondary peak in the 3 minute band that has been proven to be a predecessor for its chromospheric counterpart. The derived phase spectra yield a value of the atmospheric cutoff frequency around 4 mHz and give evidence for the upward propagation of higher frequency oscillation modes. The phase spectrum has been reproduced with a simple model of linear vertical propagation of slow magnetoacoustic waves in a stratified magnetized atmosphere that accounts for radiative losses through Newton's cooling law. The model explains the main features in the phase spectrum and allows us to compute the theoretical time delay between the photospheric and chromospheric signals, which happens to have a strong dependence on frequency. We find a very good agreement between this and the time delay obtained directly from the cross-correlation of photospheric and chromospheric velocity maps filtered around the 6 mHz band. This allows us to infer that the 3 minute power observed at chromospheric heights comes directly from the photosphere by means of linear wave propagation, rather than from nonlinear interaction of 5 minute (and/or higher frequency) modes. Title: A polarization model for the German Vacuum Tower Telescope from in situ and laboratory measurements Authors: Beck, C.; Schlichenmaier, R.; Collados, M.; Bellot Rubio, L.; Kentischer, T. Bibcode: 2005A&A...443.1047B Altcode: It is essential to properly calibrate the polarimetric properties of telescopes, if one wants to take advantage of the capabilities of high precision spectro-polarimeters. We have constructed a model for the German Vacuum Tower Telescope (VTT) that describes its time-dependent polarization properties. Since the coelostat of the telescope changes the polarization state of the light by introducing cross talk among different polarization states, such a model is necessary to correct the measurements, in order to retrieve the true polarization as emitted from the Sun. The telescope model is quantified by a time-dependent Mueller matrix that depends on the geometry of the light beam through the telescope, and on material properties: the refractive indices of the coelostat mirrors, and the birefringence of the entrance window to the vacuum tube. These material properties were determined experimentally in-situ by feeding the telescope with known states of polarization (including unpolarized light) and by measuring its response, and from measurements of an aluminum-coated sample in the laboratory. Accuracy can in our case be determined only for the combination of telescope and spectro-polarimeter used; for the instrument POLIS at the VTT, we estimate an accuracy of ±4-5× 10-3 for the cross talk correction coefficients. Title: Evidence for Fine Structure in the Chromospheric Umbral Oscillation Authors: Centeno, R.; Socas-Navarro, H.; Collados, M.; Trujillo Bueno, J. Bibcode: 2005ApJ...635..670C Altcode: 2005astro.ph.10740C Novel spectropolarimetric observations of the He I multiplet are used to explore the dynamics of the chromospheric oscillation above sunspot umbrae. The results presented here provide strong evidence in support of the two-component model proposed by Socas-Navarro and coauthors. According to this model, the waves propagate only inside channels of subarcsecond width (the ``active'' component), whereas the rest of the umbra remains nearly at rest (the ``quiet'' component). Although the observations support the fundamental elements of that model, there is one particular aspect that is not compatible with our data. We find that, contrary to the scenario as originally proposed, the active component remains through the entire oscillation cycle and harbors both the upflowing and the downflowing phase of the oscillation. Title: Determination of the Magnetic Field Vector in a Polar Crown Prominence via the Hanle and Zeeman Effects in the He I 10830 Å Multiplet. Authors: Merenda, L.; Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M. Bibcode: 2005ESASP.596E..18M Altcode: 2005ccmf.confE..18M No abstract at ADS Title: Simulations of - Acoustic Waves in Sunspots Authors: Khomenko, E. V.; Collados, M. Bibcode: 2005ESASP.596E..40K Altcode: 2005ccmf.confE..40K No abstract at ADS Title: Solar Site Survey for the Advanced Technology Solar Telescope. I. Analysis of the Seeing Data Authors: Socas-Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Hill, F.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Streander, K. Bibcode: 2005PASP..117.1296S Altcode: 2005astro.ph..8690S The site survey for the Advanced Technology Solar Telescope concluded recently after more than 2 years of data gathering and analysis. Six locations, including lake, island, and continental sites, were thoroughly probed for image quality and sky brightness. The present paper describes the analysis methodology employed to determine the height stratification of the atmospheric turbulence. This information is crucial, because daytime seeing is often very different between the actual telescope aperture (~30 m) and the ground. Two independent inversion codes have been developed to simultaneously analyze data from a scintillometer array and a solar differential image monitor. We show here the results of applying them to a sample subset of data from 2003 May that was used for testing. Both codes retrieve a similar seeing stratification through the height range of interest. A quantitative comparison between our analysis procedure and actual in situ measurements confirms the validity of the inversions. The sample data presented in this paper reveal a qualitatively different behavior for the lake sites (dominated by high-altitude seeing) and the rest (dominated by near-ground turbulence). Title: The new 1.5 solar telescope GREGOR: progress report and results of performance tests Authors: Volkmer, Reiner; von der Lühe, Oskar; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Halbgewachs, Clemens; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2005SPIE.5901...75V Altcode: The telescope structure including control system and the complete retractable dome of the new 1.5 m solar telescope GREGOR were assembled during 2004 at Izana on Tenerife, Spain. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fuer Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut fuer Astrophysik Goettingen and additional national and international Partners. Pointing, tracking and thermal tests were made to verify the proposed performance. The results of these tests and a progress report of the project will be presented. Title: Magnetic flux in the internetwork quiet Sun Authors: Khomenko, E. V.; Martínez González, M. J.; Collados, M.; Vögler, A.; Solanki, S. K.; Ruiz Cobo, B.; Beck, C. Bibcode: 2005A&A...436L..27K Altcode: We report a direct comparison of the amplitudes of Stokes spectra of the Fe i 630 nm and 1.56 μm lines produced by realistic MHD simulations with simultaneous observations in the same spectral regions. The Stokes spectra were synthesized in snapshots with a mixed polarity magnetic field having a spatially averaged strength, < B >, between 10 and 30 G. The distribution of Stokes V amplitudes depends sensitively on < B >. A quiet inter-network region was observed at the German VTT simultaneously with TIP (1.56 μm) and POLIS (630 nm). We find that the Stokes V amplitudes of both infrared and visible observations are best reproduced by the simulation snapshot with < B > = 20 G. In observations with 1 resolution, up to 2/3 of the magnetic flux can remain undetected. Title: On the fine structure of sunspot penumbrae. II. The nature of the Evershed flow Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Collados, M. Bibcode: 2005A&A...436..333B Altcode: 2005astro.ph..3677B We investigate the fine structure of the sunspot penumbra by means of a model that allows for a flux tube in horizontal pressure balance with the magnetic background atmosphere in which it is embedded. We apply this model to spectropolarimetric observations of two neutral iron lines at 1.56 μm and invert several radial cuts in the penumbra of the same sunspot at two different heliocentric angles. In the inner part of the penumbra we find hot flux tubes that are somewhat inclined to the horizontal. They become gradually more horizontal and cooler with increasing radial distance. This is accompanied by an increase in the velocity of the plasma and a decrease of the gas pressure difference between flux tube and the background component. At large radial distances the flow speed exceeds the critical speed and evidence is found for the formation of a shock front. These results are in good agreement with simulations of the penumbral fine structure and provide strong support for the siphon flow as the physical mechanism driving the Evershed flow. Title: The ATST Site Survey Authors: Hill, F.; Beckers, J.; Brandt, P.; Briggs, J. W.; Brown, T.; Brown, W.; Collados, M.; Denker, C.; Fletcher, S.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lecinski, A.; Lin, H.; Oncley, S.; Penn, M.; Radick, R.; Rimmele, T.; Socas-Navarro, H.; Soltau, D.; Streander, K. Bibcode: 2005AGUSMSP34A..04H Altcode: The Advanced Technology Solar Telescope (ATST) will be the world's largest aperture solar telescope, and is being designed for high resolution, IR, and coronal research. It must be located at a site that maximizes the scientific return of this substantial investment. We present the instrumentation, analysis and results of the ATST site survey. Two instrumentation sets were deployed at each of six sites to measure seeing as a function of height, and sky brightness as a function of wavelength and off-limb position. Analysis software was developed to estimate the structure function Cn2 as a function of height near the ground, and the results were verified by comparison with in-situ measurements. Additional software was developed to estimate the sky brightness. The statistics of the conditions at the sites were corrected for observing habits and the annualized hours of specific observing conditions were estimated. These results were used to identify three excellent sites suitable to host the ATST: Haleakala, Big Bear and La Palma. Among them, Haleakala is proposed as the optimal location of the ATST, La Palma and Big Bear being viable alternative sites. Title: Observation and Modeling of Anomalous CN Polarization Profiles Produced by the Molecular Paschen-Back Effect in Sunspots Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M. Bibcode: 2005ApJ...623L..57A Altcode: 2005astro.ph..5076A We report novel spectropolarimetric observations of sunspots carried out with the Tenerife Infrared Polarimeter in a near-IR spectral region around 15410 Å, which is known to contain two groups of prominent OH lines that show circular polarization signals of opposite polarity. Surrounding these well-known OH lines, we have discovered the presence of CN lines of the Δv=1 band that show anomalous polarization profiles. Although the Stokes V signals of the OH lines are antisymmetric and of a sizable amplitude, the CN lines show almost negligible circular polarization. On the contrary, the linear polarization signals turn out to be much stronger in the CN lines than in the OH lines. Interestingly, these CN lines present striking antisymmetric linear polarization profiles, which we are able to explain and model via the Paschen-Back effect theory for diatomic molecules. The presence of such peculiar CN lines in the same spectral region of the OH lines may be useful to improve our empirical knowledge of solar magnetic fields via the simultaneous observation and modeling of the transverse and longitudinal Zeeman effects in two different molecular species. Title: The Hanle and Zeeman Effects in Solar Spicules: A Novel Diagnostic Window on Chromospheric Magnetism Authors: Trujillo Bueno, J.; Merenda, L.; Centeno, R.; Collados, M.; Landi Degl'Innocenti, E. Bibcode: 2005ApJ...619L.191T Altcode: 2005astro.ph..1533T; 2005astro.ph..1533B An attractive diagnostic tool for investigating the magnetism of the solar chromosphere is the observation and theoretical modeling of the Hanle and Zeeman effects in spicules, as shown in this Letter for the first time. Here we report on spectropolarimetric observations of solar chromospheric spicules in the He I λ10830 multiplet and on their theoretical modeling accounting for radiative transfer effects. We find that the magnetic field in the observed (quiet-Sun) spicular material at a height of about 2000 km above the visible solar surface has a strength of the order of 10 G and is inclined by approximately 35deg with respect to the local vertical direction. Our empirical finding based on full Stokes vector spectropolarimetry should be taken into account in future magnetohydrodynamical simulations of spicules. Title: Some properties of an isolated sunspot Authors: Balthasar, H.; Collados, M. Bibcode: 2005A&A...429..705B Altcode: We present an investigation of a single sunspot observed in the neutral Fe line at 1089.6 nm with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope on Tenerife. Using the SIR code, we obtain maps of the magnetic field strength, inclination and azimuth, and Doppler velocities. The magnetic field strength drops from 2800 G in the umbra to about 700 G at the outer penumbral boundary, where we encounter an average magnetic inclination of 72o. Comparing the magnetic flux passing through different areas, we conclude that the inner penumbra must be deep, while the outer penumbra could be shallow. Assuming that the magnetic field strength encountered at the outer penumbral boundary forms a smooth surface through which the total flux of the spot passes, it would be approximately an ellipsoidal cap with a top height of 5250 km. This scenario leads to an average vertical magnetic gradient of 0.4 G km-1. Evershed Doppler velocities are about 2 km s-1. Two penumbral locations related to dark intensity features exhibit a steeper and slightly stronger magnetic field than elsewhere in the penumbra, and one of them is connected to an interruption of the Evershed effect. Title: Two magnetic components in sunspot penumbrae Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M. Bibcode: 2004A&A...427..319B Altcode: The magnetic and kinematic configuration of sunspot penumbrae is investigated by performing an inversion of the Stokes profiles of three infrared lines at 1565 nm. We use a two-component model atmosphere to describe, at least to first order, the unresolved structure of the penumbra. The observed Stokes profiles are successfully fitted, including those exhibiting abnormal shapes. The results of the inversion are consistent with the idea that the penumbra is formed by almost horizontal flux tubes embedded in a more vertical background magnetic field, as proposed by Solanki & Montavon (\cite{Sol93}). The tubes possess weaker fields than the background except in the very outer penumbra, and carry most of the Evershed flow. We characterize the radial variation of the magnetic field vector and the velocity vector in these atmospheric components. In the middle penumbra and beyond, the magnetic field and the flow in the tubes are seen to return to the solar surface. Everywhere in the penumbra, there is a perfect alignment of the magnetic field vector and the velocity vector in the component describing the penumbral flux tubes. We find that the Evershed flow is supercritical in many places of the outer penumbra, and supersonic at some locations near the outer sunspot boundary. Based on these inversions, we suggest that the azimuthal fluctuations in the average magnetic field inclination and strength inferred from simple one-component models are caused by fluctuations in the filling factor (i.e., the fractional area of the resolution element occupied by flux tubes), not by changes in the intrinsic magnetic and kinematic properties of the background or the flux-tube atmospheres. Also, we confirm the jump of magnetic field azimuth proposed by Müller et al. (\cite{Mul02}) to explain the observed net circular polarization of infrared lines. Title: Progress report of the 1.5 m solar telescope GREGOR Authors: Volkmer, Reiner; von der Lühe, Oskar F.; Kneer, Franz; Staude, Jürgen; Berkefeld, Thomas; Caligari, Peter; Schmidt, Wolfgang; Soltau, Dirk; Nicklas, Harald; Wiehr, Eberhardt; Wittmann, Axel; Balthasar, Horst; Hofmann, Axel; Strassmeier, Klaus; Sobotka, Michal; Klvana, Miroslav; Collados, Manuel Bibcode: 2004SPIE.5489..693V Altcode: GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen and other national and international Partners. The refurbishment of the building is almost finished. The manufacturing of the telescope structure and the optics is still in progress. After the integration of the new complete retractable dome in July 2004 the telescope structure, optic and post focus instruments will be assembled during the rest of the year. First light is planned during May 2005. Title: Solar site testing for the Advanced Technology Solar Telescope Authors: Hill, Frank; Beckers, Jacques; Brandt, Peter; Briggs, John; Brown, Timothy; Brown, W.; Collados, Manuel; Denker, Carsten; Fletcher, Steven; Hegwer, Steven; Horst, T.; Komsa, Mark; Kuhn, Jeff; Lecinski, Alice; Lin, Haosheng; Oncley, Steve; Penn, Matthew; Rimmele, Thomas R.; Socas-Navarro, Hector; Streander, Kim Bibcode: 2004SPIE.5489..122H Altcode: The location of the Advanced Technology Solar Telescope (ATST) is a critical factor in the overall performance of the telescope. We have developed a set of instrumentation to measure daytime seeing, sky brightness, cloud cover, water vapor, dust levels, and weather. The instruments have been located at six sites for periods of one to two years. Here we describe the sites and instrumentation, discuss the data reduction, and present some preliminary results. We demonstrate that it is possible to estimate seeing as a function of height near the ground with an array of scintillometers, and that there is a distinct qualitative difference in daytime seeing between sites with or without a nearby lake. Title: The imaging magnetograph eXperiment for the SUNRISE balloon Antarctica project Authors: Martinez Pillet, Valentin; Bonet, Jose A.; Collados, Manuel V.; Jochum, Lieselotte; Mathew, S.; Medina Trujillo, J. L.; Ruiz Cobo, B.; del Toro Iniesta, Jose Carlos; Lopez Jimenez, A. C.; Castillo Lorenzo, J.; Herranz, M.; Jeronimo, J. M.; Mellado, P.; Morales, R.; Rodriguez, J.; Alvarez-Herrero, Alberto; Belenguer, Tomas; Heredero, R. L.; Menendez, M.; Ramos, G.; Reina, Manuel; Pastor, C.; Sanchez, A.; Villanueva, J.; Domingo, Vicente; Gasent, J. L.; Rodriguez, P. Bibcode: 2004SPIE.5487.1152M Altcode: The SUNRISE balloon project is a high-resolution mission to study solar magnetic fields able to resolve the critical scale of 100 km in the solar photosphere, or about one photon mean free path. The Imaging Magnetograph eXperiment (IMaX) is one of the three instruments that will fly in the balloon and will receive light from the 1m aperture telescope of the mission. IMaX should take advantage of the 15 days of uninterrupted solar observations and the exceptional resolution to help clarifying our understanding of the small-scale magnetic concentrations that pervade the solar surface. For this, IMaX should act as a diffraction limited imager able to carry out spectroscopic analysis with resolutions in the 50.000-100.000 range and capable to perform polarization measurements. The solutions adopted by the project to achieve all these three demanding goals are explained in this article. They include the use of Liquid Crystal Variable Retarders for the polarization modulation, one LiNbO3 etalon in double pass and two modern CCD detectors that allow for the application of phase diversity techniques by slightly changing the focus of one of the CCDs. Title: Thermal-magnetic relation in a sunspot and a map of its Wilson depression Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.; Borrero, J. M.; Berdyugina, S. Bibcode: 2004A&A...422..693M Altcode: We present relations between thermal and magnetic quantities in a simple, isolated sunspot, as deduced from the inversion of 1.56 μm spectropolarimetric data. We used a combination of two infrared Fe I lines at 15 648.5 Å and 15 652.8 Å/ in the inversions. Due to the high Zeeman sensitivity of these lines, we can study this relationship in the entire sunspot. The relevant parameters were derived both as a function of location within the sunspot and of height in the atmosphere using an inversion technique based on response functions. In this paper we relate the magnetic vector with temperature. We find a non-linear relationship between the various components of the magnetic vector and temperature, which confirm the results from earlier investigations. We also computed the Wilson depression and the plasma β for the observed sunspot and compare our results with earlier findings. Title: Latest Results from the ATST Site Survey Authors: Hill, F.; Collados, M.; Navarro, H.; Beckers, J.; Brandt, P.; Briggs, J.; Brown, T.; Denker, C.; Hegwer, S.; Horst, T.; Komsa, M.; Kuhn, J.; Lin, H.; Oncley, S.; Penn, M.; Rimmele, T.; Soltau, D.; Streander, K. Bibcode: 2004AAS...204.6909H Altcode: 2004BAAS...36..795H We present the latest results and current status of the site survey portion of the Advanced Technology Solar Telescope (ATST) project. The ATST will provide high resolution solar data in the visible and IR. The site is a major factor determining the performance of the telescope. The most critical site characteristics are the statistics of daytime seeing quality and sky clarity. These conditions are being measured by a suite of instruments at three sites (Big Bear, Haleakala, La Palma). These sites were chosen from a set of six that have been tested starting in November 2001. The instrumentation includes a solar differential image motion monitor, an array of scintillometers, a miniature coronagraph, a dust monitor, and a weather station. The analysis of the data provides an estimate of the seeing as a function of height near the ground. We will present the latest results of the analysis of the survey data set. Title: Detection of Polarization from the E4Π-A4Π System of FeH in Sunspot Spectra Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Collados, M. Bibcode: 2004ApJ...603L.125A Altcode: 2004astro.ph..1597A; 2004astro.ph..1597R Here we report the first detection of polarization signals induced by the Zeeman effect in spectral lines of the E4Π-A4Π system of FeH located around 1.6 μm. Motivated by the tentative detection of this band in the intensity spectrum of late-type dwarfs, we have investigated the full Stokes sunspot spectrum and have found circular and linear polarization signatures that we associate with the FeH lines of the E4Π-A4Π band system. We investigate the Zeeman effect in these molecular transitions and point out that in Hund's case (a) coupling, the effective Landé factors are never negative. For this reason, the fact that our spectropolarimetric observations indicate that the Landé factors of pairs of FeH lines have opposite signs prompts us to conclude that the E4Π-A4Π system must be in intermediate angular momentum coupling between Hund's cases (a) and (b). We emphasize that theoretical and/or laboratory investigations of this molecular system are urgently needed for exploiting its promising diagnostic capabilities. Title: Successful Measurement of the Full Magnetic Vector Near the Base of the Solar Corona Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Landi Degl'Innocenti, E.; Collados, M. Bibcode: 2003AGUFMSH41D..05S Altcode: The measurement of coronal fields has in the past generally been restricted to the field strength or to only some of the components of the magnetic vector. We present here a technique for measuring the full magnetic vector near the base of the solar corona. As an application we report on observations of a developing active region with ongoing magnetic flux emergence. The data allow the first measurement of the 3-D structure of magnetic loops. They also provide the first detection of an electric current sheet located near the base of the solar corona. Such current sheets or tangential discontinuities of the coronal magnetic field have long been thought to be a major source of coronal heating. Title: Three dimensional structure of a regular sunspot from the inversion of IR Stokes profiles Authors: Mathew, S. K.; Lagg, A.; Solanki, S. K.; Collados, M.; Borrero, J. M.; Berdyugina, S.; Krupp, N.; Woch, J.; Frutiger, C. Bibcode: 2003A&A...410..695M Altcode: The magnetic, thermal and velocity structure of a regular sunspot, observed close to solar disk center is presented. Spectropolarimetric data obtained with the Tenerife Infrared Polarimeter (TIP) in two infrared FeI lines at 15 648.5 Å and 15 652.8 Å are inverted employing a technique based on response functions to retrieve the atmospheric stratification at every point in the sunspot. In order to improve the results for the umbra, profiles of Zeeman split OH lines blending the FeI 15 652.8 Å are also consistently fit. Thus we obtain maps of temperature, line-of-sight velocity, magnetic field strength, inclination, and azimuth, as a function of both location within the sunspot and height in the atmosphere. We present these maps for an optical depth range between log tau5 = 0 and log tau5 = -1.5, where these lines provide accurate results. We find decreasing magnetic field strength with increasing height all over the sunspot, with a particularly large vertical field gradient of ~ -4 G km-1 in the umbra. We also observe the so called ``spine'' structures in the penumbra, i.e. extended radial features with a stronger and more vertical magnetic field than the surroundings. Also we found that the magnetic field zenith angle increases with height. From the velocity map it is clear that the Evershed flow avoids the spines and mostly concentrates in the more inclined intervening field. The field inclination at a few locations in the outer penumbra in lower layers goes beyond 90o. These locations coincide with the strongest flows in the velocity map. Title: Three-dimensional magnetic field topology in a region of solar coronal heating Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Collados, M. Bibcode: 2003Natur.425..692S Altcode: Flares and X-ray jets on the Sun arise in active regions where magnetic flux emerges from the solar interior amd interacts with the ambient magnetic field. The interactions are believed to occur in electric current sheets separating regions of opposite magnetic polarity. The current sheets located in the corona or upper chromosphere have long been thought to act as an important source of coronal heating, requiring their location in the corona or upper chromosphere. The dynamics and energetics of these sheets are governed by a complex magnetic field structure that, until now, has been difficult to measure. Here we report the determination of the full magnetic vector in an interaction region near the base of the solar corona. The observations reveal two magnetic features that characterize young active regions on the Sun: a set of rising magnetic loops and a tangential discontinuity of the magnetic field direction, the latter being the observational signature of an electric current sheet. This provides strong support for coronal heating models based on the dissipation of magnetic energy at current sheets. Title: Quiet-Sun inter-network magnetic fields observed in the infrared Authors: Khomenko, E. V.; Collados, M.; Solanki, S. K.; Lagg, A.; Trujillo Bueno, J. Bibcode: 2003A&A...408.1115K Altcode: This paper presents the results of an investigation of the quiet Sun's magnetic field based on high-resolution infrared spectropolarimetric observations obtained with the Tenerife Infrared Polarimeter (TIP) at the German VTT of the Observatorio del Teide. We observed two very quiet regions at disc centre. The seeing was exceptionally good during both observing runs, being excellent during one of them. In both cases the network was intentionally avoided to the extent possible, to focus the analysis on the characteristics of the weak polarization signals of the inter-network regions. We find that the Stokes V profile of Fe I 15648 Å line in almost 50% of the pixels and Stokes Q and/or U in 20% of the pixels have a signal above 10-3 (in units of continuum intensity Ic), which is significantly above the noise level of 2-3 x 10-4. This implies that we detect fluxes as low as 2 x 1015 Mx/px. We find evidence that we have detected most of the net flux that is in principle detectable at 1'' resolution with the Zeeman effect. The observed linear polarization resulting from the transverse Zeeman effect indicates that the magnetic fields have a broad range of inclinations, although most of the pixels show polarization signatures which imply an inclination of about 20o. Nearly 30% of the selected V-profiles have irregular shapes with 3 or more lobes, suggesting mixed polarities with different LOS velocity within the resolution element. The profiles are classified using a single value decomposition approach. The spatial distribution of the magnetic signal shows that profiles of different classes (having different velocities, splitting, asymmetries) are clustered together and form patches, close to the spatial resolution in size. Most of the field is found to be located in intergranular lanes. The statistical properties of the mainly inter-network field sampled by these observations are presented, showing that most of the observed fields are weak with relatively few kG features. The field strength distribution peaks at 350 G and has a FWHM of 300 G. Other parameters, such as profile asymmetries, filling factors and line-of-sight velocities are also determined and discussed.

Based on observations with the German Vacuum Tower Telescope (VTT) operated by the Kiepenheuer-Institut für Sonnenphysik at the Spanish Observatorio del Teide of the Instituto de Astrofísica de Canarias (IAC). Title: Understanding internetwork magnetic fields as determined from visible and infrared spectral lines Authors: Bellot Rubio, L. R.; Collados, M. Bibcode: 2003A&A...406..357B Altcode: We present numerical experiments aimed at understanding why near-infrared observations systematically deliver weak magnetic fields in the internetwork, whereas analyses based on visible lines indicate that kG fields are ubiquitous. Synthetic noisy Stokes V profiles of the iron lines at 6302 Å and 1.565 mu m have been produced under varying conditions in an effort to simulate polarized spectra coming from the internetwork. An inversion technique has been applied to the profiles, as it is usually done with real observations, in order to derive the distribution of magnetic fields in the simulated region. Our results show that infrared lines yield distributions which are very similar to those used as input for the simulation, while visible lines are to a large extent affected by noise. Analyses based on the Fe I lines at 6302 Å may lead to an overabundance of kG fields if the signal-to-noise ratio in Stokes V is poorer than about 10. A particular example is shown where strong fields are retrieved in nearly 30% of the pixels of a simulated internetwork region in which only fields of 200 G exist. Title: Magnetoacoustic Waves in Sunspots Authors: Khomenko, E. V.; Collados, M.; Bellot Rubio, L. R. Bibcode: 2003ApJ...588..606K Altcode: Observed variations of the magnetic field strength in sunspot umbrae consist of intrinsic oscillations and ``false'' oscillations due to time-dependent opacity effects. Here we present an approach intended for the separation of these components. We develop a mathematical formalism based on the analytical solution of the MHD equations including gravity, inclination of the magnetic field, and effects of nonadiabaticity. The theoretical results are compared with observations in the near-infrared at 1.56 μm by Bellot Rubio and coworkers using the Tenerife Infrared Polarimeter. It is shown that part of the detected field strength variations can be intrinsic magnetic field oscillations caused by magnetoacoustic waves. Title: Field-aligned Evershed flows in the photosphere of a sunspot penumbra Authors: Bellot Rubio, L. R.; Balthasar, H.; Collados, M.; Schlichenmaier, R. Bibcode: 2003A&A...403L..47B Altcode: We determine the inclinations of the vector magnetic field and flow velocity in a sunspot penumbra by interpreting full Stokes profiles of three infrared lines observed with the Tenerife Infrared Polarimeter. It is shown that analyses based on one-component atmospheres deliver flow velocities which are more horizontal than the average magnetic field by up to 10 deg. This apparent violation of the concept of frozen-in magnetic fields is solved as soon as two magnetic atmospheres are allowed to coexist in the resolution element. The magnetic field and velocity in the atmospheric component carrying the Evershed flow are found to be aligned to within +/- 2 deg all the way from the inner to the outer penumbra. This is the first observational confirmation of magnetic fields being frozen into the plasma in sunspots. Our results indicate that sunspot penumbrae can be understood in terms of inclined flux tubes embedded in a more vertical background field. The flux tubes carry most of the Evershed flows and return to the solar surface in the middle penumbra and beyond. The background atmosphere is essentially at rest in the inner penumbra, and harbors small flows in the outer penumbra. Title: Inverting Scintillometer Array Data to Estimate Cn2(h) for the ATST Site Survey Authors: Hill, F.; Collados, M. Bibcode: 2003SPD....34.2020H Altcode: 2003BAAS...35..848H One of the instruments developed for the Advanced Technology Solar Telescope (ATST) site survey is a non-redundant array of six scintillometers known as a ShaBaR (SHAdow BAnd Ranging) system, developed by J. Beckers. The ShaBaR provides an estimate of Cn2(h), the turbulence structure function, in the Earth's atmosphere. We can use the estimate of Cn2(h) to infer the value of r0, the Fried parameter, at any height above the ground up to the maximum range of the ShaBaR. In this poster, we present two methods of extracting the estimates by 1) inverting the data via a kernel function derived from the theory of atmospheric turbulence, and 2) assuming a modified Hufnagel-Valley model of Cn2(h). We also show a series of simulations that has been produced and used to test the accuracy and precision of the methods. Title: Stokes polarimeters in the near-infrared Authors: Collados, Manuel V. Bibcode: 2003SPIE.4843...55C Altcode: In this contribution, the main characteristics of near infrared spectropolarimetric measurements are described, putting especial emphasis on the techniques to minimize the crosstalk between the Stokes parameters. Title: Liquid crystal optical retarders for IMaX to fly with SUNRISE Authors: Jochum, Lieselotte; Herrero, Pilar; Collados, Manuel; Martinez Pillet, Valentin; Rodriguez, Javier; Lopez, Manuel Bibcode: 2003SPIE.4843...30J Altcode: The Instituto de Astrofísica de Canarias (IAC), Spain, together with the Spanish company Tecdis Displays Ibérica, S.A., are developing voltage tunable optical retarders using liquid crystals as phase retarding medium. The ROCLIs are built for being used in the Imaging Magnetograph eXperiment (IMaX), which is one of the instruments aboard of the SUNRISE balloon mission (details about IMaX are described in a different paper in this session). A big advantage of using voltage tuned retarder plates is that no mechanisms are needed, which reduces significantly failure risk, weight, power and cost, aspects of particular importance in the SUNRISE balloon mission and for many future space borne applications. A set of prototypes has already been fabricated by Tecdis S.A. and is being characterized in the IAC laboratories. The purpose of these prototypes is to evaluate and demonstrate conceptually the suitability of the chosen liquid crystal for our use in IMaX. First results are very promising. In this paper we will present a full technical description of the ROCLIs for IMaX together with the laboratory test and verification results. Title: IMax: a visible magnetograph for SUNRISE Authors: Jochum, Lieselotte; Collados, Manuel; Martínez Pillet, Valentin; Bonet, Jose A.; del Toro Iniesta, Jose Carlos; Lopez, Antonio; Alvarez-Herrero, Alberto; Reina, Manuel; Fabregat, Juan; Domingo, Vicente Bibcode: 2003SPIE.4843...20J Altcode: The description of the Imaging Magnetograph eXperiment (IMaX) is presented in this contribution. This is a magnetograph which will fly by the end of 2006 on a stratospheric balloon, together with other instruments (to be described elsewhere). Especial emphasis is put on the scientific requirements to obtain diffraction-limited visible magnetograms, on the optical design and several constraining characteristics, such as the wavelength tuning or the crosstalk between the Stokes parameters. Title: The structure of the penumbra Authors: Balthasar, H.; Bellot Rubio, L.; Collados, M. Bibcode: 2003AN....324..390B Altcode: No abstract at ADS Title: Structure of a simple sunspot from the inversion of IR spectral data Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.; Berdyugina, S. V.; Frutiger, C.; Krupp, N.; Woch, J. Bibcode: 2003AN....324..388M Altcode: Analysis of spectral data of two neighboring infrared lines, Fe i 15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out for a simple sunspot when it was near the solar disk center (mu = 0.92), to understand the basic structure of sunspot magnetic field. Inversions of Stokes profiles are carried out to derive different atmospheric parameters both as a function of location within the sunspot and height in the atmosphere. As a result of the inversion we have obtained maps of magnetic field strength, temperature, line-of-sight velocity, field inclination and azimuth for different optical depth layers between log (tau_ {5}) = 0 and log (tau_ {5}) = -2.0 . In this paper we present few results from our inversion for a layer averaged between log (tau_ {5}) from 0.0 to -0.5. Title: Modeling the Fine Structure of a Sunspot Penumbra through the Inversion of Stokes Profiles Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.; Collados, M.; Bellot Rubio, L. R. Bibcode: 2003ASPC..286..235B Altcode: 2003ctmf.conf..235B No abstract at ADS Title: New Spectropolarimetric Observations of Solar Coronal Filaments in the He I 10830 Å Multiplet Authors: Collados, M.; Trujillo Bueno, J.; Asensio Ramos, A. Bibcode: 2003ASPC..307..468C Altcode: No abstract at ADS Title: Thermal-magnetic relation of a sunspot as inferred from the inversion of 1.5 μm spectral data Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Krupp, N.; Woch, J.; Collados, M.; Berdyugina, S.; Frutiger, C. Bibcode: 2002ESASP.505..501M Altcode: 2002IAUCo.188..501M; 2002solm.conf..501M We present the thermal-magnetic relation in a simple, isolated sunspot deduced from the inversion of 1.56 μm spectropolarimetric data. Due to the high Zeeman sensitivity of the g = 3, Fe I 1.5648 μm line, we can study this relationship in the entire sunspot. An inversion technique based on response functions is used to derive various parameters, both as a function of location within the sunspot and of height in the atmosphere. In this paper we attempt to relate field strength, vertical and radial field components and the field inclination with temperature. Title: THEMIS and DOT joint observations on NOAA 9716 Authors: Briand, C.; Collados, M.; Sütterlin, P. Bibcode: 2002ESASP.505..361B Altcode: 2002IAUCo.188..361B; 2002solm.conf..361B Ephemeral magnetic emergence has been detected in a decaying β region observed in December 2001 simultaneously with the DOT and THEMIS. We present here the main characteristics of this phenomenon. Also the time evolution of a small group of pores is shown together with the time evolution of an horizontal magnetic field overlying them. Title: Statistical properties of magnetic fields in intranetwork Authors: Khomenko, E. V.; Collados, M.; Lagg, A.; Solanki, S. K.; Trujillo Bueno, J. Bibcode: 2002ESASP.505..445K Altcode: 2002IAUCo.188..445K; 2002solm.conf..445K We report a study of the quiet sun's magnetic field based on high-resolution infrared spectropolarimetric observations (TIP/VTT). We find that in almost 50% of the pixels Stokes V and in 15% the Stokes Q and/or U profiles have a signal above 10-3. The statistical properties of the mainly intranetwork field sampled by these observations are presented, showing that most of the observed fields are weak (the field strength distribution peaks at 350 G and has a FWHM of 300 G) with very few kG features. The magnetized regions occupy a very small fill fractions (about 2%). The field changes properties on granular spatial scales and the size of the patches formed by similar profiles is close to 1". Most of the parameters of the observed polarization profiles show correlations with granulation parameters. Title: Infrared spectropolarimetry of sunspots Authors: Collados, M. Bibcode: 2002AN....323..254C Altcode: Recently a number of works have given interesting results on the penumbral fine structure of sunpots (del Toro Iniesta, Bellot Rubio & Collados 2001; Schlichenmaier & Collados 2002), where, for instance, cold supersonic Evershed downflows were observed. In addition, there are recent results that show the existence of shock wave trains propagating in umbral chromospheres with a 3-min period, where the photospheric driving signal has also been detected. The phase difference between the photospheric and chromospheric signals in the 5.5-6.5 mHz band (3 minute) allows to infer that an upward propagation of the slow magnetoacoustic mode, with an increasing velocity amplitude (due to the rapid decrease of density) and reaching the non-linear regime, is giving rise to shock fronts. All these results show that the umbra and the penumbra have a dynamical behaviour which is far from being near an equilibrium situation. Title: Spectropolarimetry in a sunspot penumbra. Spatial dependence of Stokes asymmetries in Fe I 1564.8 nm Authors: Schlichenmaier, R.; Collados, M. Bibcode: 2002A&A...381..668S Altcode: Stokes profiles of sunspot penumbrae show distinct asymmetries, which point to gradients in the velocity field and in the magnetic field. We present spectropolarimetric measurements of the Stokes vector in the neutral iron triplet at 1564.8 nm taken with the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT) in Tenerife. We report on the peculiarities of the profiles of circularly and linearly polarized light for spots at different heliocentric angles. We elaborate on the spatial dependence of Stokes asymmetries within the penumbra and find for profiles of circularly polarized light: (1) In the center-side penumbra the amplitude difference of Stokes-V exhibits a sign reversal on a radial cut, i.e., in the inner (outer) penumbra the red (blue) lobe is broader and shows a smaller amplitude than the blue (red) lobe. (2) In the outer limb-side penumbra (beyond the magnetic neutral line) the red lobe is broader and of less amplitude than the blue lobe. (3) Along the magnetic neutral line we find abnormal Stokes-V profiles, which consist of more than 2 lobes. This indicates the presence of two polarities. For small heliocentric angles abnormal profiles are also seen beyond the magnetic neutral line in the outer penumbra. (4) Maps of the net circular polarization have the tendency to be antisymmetric with respect to the axis that connects disk center with spot center. This finding is striking, because corresponding maps for Fe I 630.25 are symmetric. For linearly polarized profiles we extract the following features: (5) On the center-side penumbra at a heliocentric angle of 56o a Doppler-shift as high as 5 km s-1 can be directly measured by the splitting of the pi -component of the linearly polarized component. (6) In limb-side penumbrae, the profiles of the pi -component show the typical asymmetry properties of the Evershed flow as observed in Stokes-I of magnetically insensitive lines. (7) In the outer center- and limb-side penumbrae the center of the pi -component is blue-shifted relative to the zero-crossing of the V-profile. Motivated by the moving tube model of Schlichenmaier et al. (\cite{schlichenmaier+jahn+schmidt1998b}), we construct simple model atmospheres featuring hot upflows and cool outflows and calculate corresponding synthetic V-profiles. These profiles are compared with our measured ones and with observed V-profiles in Fe I 630.25 from other authors. We find that the synthetic V-profiles can reproduce all essential characteristics of observed V-profiles for both lines. Title: Selective absorption processes as the origin of puzzling spectral line polarization from the Sun Authors: Trujillo Bueno, J.; Landi Degl'Innocenti, E.; Collados, M.; Merenda, L.; Manso Sainz, R. Bibcode: 2002Natur.415..403T Altcode: 2002astro.ph..1409T Magnetic fields play a key role in most astrophysical systems, from the Sun to active galactic nuclei. They can be studied through their effects on atomic energy levels, which produce polarized spectral lines. In particular, anisotropic radiation `pumping' processes (which send electrons to higher atomic levels) induce population imbalances that are modified by weak magnetic fields. Here we report peculiarly polarized light in the HeI 10,830-Å multiplet observed in a coronal filament located at the centre of the solar disk. We show that the polarized light arises from selective absorption from the ground level of the triplet system of helium, and that it implies the presence of magnetic fields of the order of a few gauss that are highly inclined with respect to the solar radius vector. This disproves the common belief that population imbalances in long-lived atomic levels are insignificant in the presence of inclined fields of the order of a few gauss, and opens up a new diagnostic window for the investigation of solar magnetic fields. Title: Penumbral finestructure: need for larger telescopes Authors: Balthasar, H.; Sütterlin, P.; Collados, M. Bibcode: 2001AN....322..367B Altcode: We obtained at the same time G-band images at the Dutch Open Telescope (DOT) on La Palma and spectropolarimetric data in the near infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The spectropolarimetric data show interesting correlations. Bright filaments have a smaller magnetic field s trength, and higher Evershed velocities occur in dark structures. This result is in agreement with some previous observations, but also in contradiction to others. However, we suffer from the fact that the resolution limit of the VTT at a wavelength of 1.565 μm corresponds to 400 km. Spatial power spectra derived from the DOT data indicate a typical width of 250 km for penumbral filaments. Obviously a solar telescope with an aperture of at least 1.5~m is needed to obtain sophisticated results for penumbral structures. Title: Observation of Convective Collapse and Upward-moving Shocks in the Quiet Sun Authors: Bellot Rubio, Luis R.; Rodríguez Hidalgo, Inés; Collados, Manuel; Khomenko, Elena; Ruiz Cobo, Basilio Bibcode: 2001ApJ...560.1010B Altcode: We present spectropolarimetric evidence of convective collapse and destruction of magnetic flux by upward-moving fronts in the quiet Sun. The observational material consists of time series of the full Stokes vector of two infrared spectral lines emerging from regions associated with Ca II K network points. The amplitude of the circular polarization profiles of a particular spatial point is seen to increase while the profiles are redshifted. It then decreases during a much shorter phase characterized by large blueshifts. Inspection of the data indicates that the blueshift occurs because of the sudden appearance of a new, strongly displaced Stokes V profile of the same polarity. The amplification of the magnetic signal takes place in a time interval of about 13 minutes, while blueshifts and the concomitant decreasing Stokes V amplitudes last for only 2 minutes. An inversion code based on the thin flux-tube scenario has been applied to the data in order to derive the thermal, magnetic, and dynamic structures of the atmosphere. According to our results, the field strength undergoes a moderate increase from 400 to 600 G at z=0 km during the phase in which redshifts are present. The observed redshifts are produced by internal downflows of up to 6 km s-1 at z=0 km. After ~13 minutes, the material falling down inside the tube appears to bounce off in the deeper layers, originating an upward-propagating front whose manifestation on the Stokes V profiles is a large blueshift. The front moves with a speed of 2.3 km s-1 and has a downflow-to-upflow velocity difference of about 7 km s-1 initially and some 4 km s-1 after 2 minutes. It strongly weakens the magnetic field strength and may be responsible for the complete destruction of the magnetic feature. The observed behavior is in general agreement with theoretical predictions of flux expulsion, convective collapse, and development of shocks within magnetic flux tubes. Title: A proposal for the visible-light imager magnetograph Authors: von der Lühe, O.; Martinez Pillet, V.; Schmidt, W.; Collados, M. Bibcode: 2001ESASP.493..421V Altcode: 2001sefs.work..421V No abstract at ADS Title: Cold, Supersonic Evershed Downflows in a Sunspot Authors: del Toro Iniesta, Jose Carlos; Bellot Rubio, Luis R.; Collados, Manuel Bibcode: 2001ApJ...549L.139D Altcode: We report here on the discovery of supersonic Evershed downflows in the penumbra of a sunspot. These flows are shown to occur along spatially unresolved, very cold magnetic flux tubes whose downflowing footpoints are found from the middle penumbra outward. Evershed flows along magnetic field lines returning to the solar surface were discovered by Westendorp Plaza and coworkers, but only in the outer parts of the penumbra and beyond its visible boundary; on the other hand, no supersonic flows of any type have ever been reported in the photosphere of sunspots, except for the very different case of the delta spot analyzed by Martínez Pillet and coworkers. We present unequivocal evidence of such supersonic motions, already predicted theoretically by the siphon-flow model, from the interpretation of infrared spectropolarimetric observations of a sunspot with unprecedented spatial resolution. Title: Penumbral Finestructure: Need for Larger Telescopes Authors: Balthasar, H.; Sütterlin, P.; Collados, M. Bibcode: 2001AGM....18S1003B Altcode: We obtained at the same time G-band images at the Dutch Open Telescope (DOT) on La Palma and spectropolarimetric data in the near infrared at the German Vacuum Tower Telescope (VTT) on Tenerife. The spectropolarimetric data show interesting correlations. Bright filaments have a smaller magnetic field strength, and higher Evershed velocities occur in dark structures. This result is in agreement with some previous observations, but also in contradiction to others. However, we suffer from the fact that the resolution limit of the VTT at a wavelength of 1.565 μm corresponding to 400 km. Spatial power spectra derived from the DOT data indicate a typical width of 250 km for the penumbral filaments. Obviously a solar telescope with an aperture of at least 1.5 m is needed to obtain sophisticated results for penumbral structures. Title: Full Stokes LPSP Observations of the Na D1 and D2 Lines in Magnetized Regions close to the Solar Limb Authors: Martínez Pillet, V.; Trujillo Bueno, J.; Collados, M. Bibcode: 2001ASPC..236..133M Altcode: 2001aspt.conf..133M No abstract at ADS Title: Spectropolarimetric Signatures of Convective Collapse Authors: Rodrígues Hidalgo, I.; Bellot Rubio, L. R.; Collados, M.; Ruiz Cobo, B. Bibcode: 2001ASPC..236..415R Altcode: 2001aspt.conf..415R No abstract at ADS Title: Infrared Polarimetry Authors: Collados, M. Bibcode: 2001ASPC..236..255C Altcode: 2001aspt.conf..255C No abstract at ADS Title: THÉMIS Observations of the Second Solar Spectrum Authors: Trujillo Bueno, J.; Collados, M.; Paletou, F.; Molodij, G. Bibcode: 2001ASPC..236..141T Altcode: 2001aspt.conf..141T No abstract at ADS Title: Magnetic field oscillations in sunspots and active regions Authors: Balthasar, Horst; Collados, Manuel; Muglach, Karin Bibcode: 2001ESASP.464..163B Altcode: 2001soho...10..163B In order to investigate the oscillatory behaviour of the magnetic field in sunspots and pores, full Stokes measurements of 1.56 μm iron lines have been performed using the Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope on Tenerife. As expected, velocity oscillations have power peaks at five minutes. First results for temporal variations of the magnetic field show that they occur in locally restricted areas in sunspots. Periods in the five minute range are preferred. In addition, we investigate magnetograms taken with the Michelson Doppler Imager (MDI) on SOHO. Intensity images in white light and around 160 nm were obtained with TRACE as well. Intensity power is strongly with TRACE as well. Intensity power is strongly suppressed in the sunspot area, although we find powerpeaks in the five and three minute ranges. Title: Penumbral Stokes-V Asymmetries of Fe I 1564.8 nm Authors: Schlichenmaier, R.; Soltau, D.; Lühe, O. V. D.; Collados, M. Bibcode: 2001ASPC..236..579S Altcode: 2001aspt.conf..579S No abstract at ADS Title: Lagrangian and Eulerian Stratifications of Acoustic Oscillations through the Solar Photosphere Authors: Rodríguez Hidalgo, Inés; Ruiz Cobo, Basilio; Collados, Manuel; Bellot Rubio, Luis R. Bibcode: 2001ApJ...547..491R Altcode: We evaluate the stratification of acoustic oscillations in the solar photosphere in both the Lagrangian (comoving) frame of reference and the Eulerian (inertial) frame of reference, from a temporal sequence of model atmospheres in an optical depth scale obtained after a quasi-non-LTE inversion of the radiative transfer equation applied to spectral observations of the K I 7699 Å line. Our results suggest that, to first order, the photosphere moves up and down as a whole with amplitudes ranging from ~8 km in deep layers (around 0 km) to ~19 km in the upper layers (around 640 km). In Lagrangian coordinates, we observe numerous short-lived, local temperature and velocity amplitude enhancements in medium-high layers, together with asymmetric waveforms in the oscillation of these two physical quantities. The Lagrangian temperature oscillation clearly shows two nodes associated with sharp phase jumps of about 180°, whereas the velocity amplitude shows the well-known increase with geometrical height, at nearly constant phase. In Eulerian coordinates, the perturbations are dominated by the coherent oscillation of the entire photosphere. Title: Photospheric acoustic oscillations in a Langrangian reference system Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados Vera, M.; Bellot Rubio, L. R. Bibcode: 2001ESASP.464..239R Altcode: 2001soho...10..239R The stratification of acoustic oscillations through the solar photosphere in Lagrangian (comoving) coordinates has been evaluated from a quasi-NLTE inversion of the radiative transfer equation (RTE) applied to a temporal sequence of K I 7699 Å line spectra. The stratifications of amplitude and phase of the temperature and line-of-sight (LOS) velocity Lagrangian oscillations have been evaluated. Our results suggest that, to first order, the photosphere moves up and down as a whole with amplitudes ranging from ~8 km in deep layers (around 0 km) to ~19 km in the upper layers (around 640 km). Numerous short-lived, local temperature and velocity amplitude enhancements in medium-high layers are observed, together with an asymmetric waveform in the oscillation of these two physical quantities. Two nodes are clearly seen in the Lagrangian temperature oscillation run, which are associated with sharp phase jumps of about 180°. The velocity amplitude shows the well known increase with geometrical height, keeping practically in phase. Title: Structure of Plage Flux Tubes from the Inversion of Stokes Spectra. I. Spatially Averaged Stokes I and V Profiles Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 2000ApJ...535..489B Altcode: We present results of the inversion of spatially averaged Stokes I and V profiles emerging from plage regions near disk center. The observations analyzed in this work were recorded with the Advanced Stokes Polarimeter. All atmospheric quantities determining the radiative transfer in the thin flux-tube approximation are inferred self-consistently with the help of the inversion code described by Bellot Rubio et al. With regard to thermodynamics, the retrieved model atmospheres are found to behave as expected on theoretical grounds. For the first time, velocities inside and outside the tubes have been derived empirically. The magnetic atmospheres resulting from the inversion are characterized by the absence of significant motions in high layers but show strong velocity gradients in deeper layers. These gradients turn out to be essential for reproducing the whole shape of the observed profiles and, in particular, the asymmetries and the extended red tail of Stokes V. Our scenario predicts that the Stokes V zero-crossing wavelengths of Fe I and Fe II lines are redshifted by small but nonnegligible amounts, which is indeed confirmed by observations made with the Fourier Transform Spectrometer. According to recent numerical simulations, the internal downflows derived from the inversion could be produced by the strong shear that takes place in the intermediate layer between the magnetized interior and the ambient medium. Another possible origin is magnetic flux undergoing convective collapse within the resolution element. Title: Oscillations in the Photosphere of a Sunspot Umbra from the Inversion of Infrared Stokes Profiles Authors: Bellot Rubio, L. R.; Collados, M.; Ruiz Cobo, B.; Rodríguez Hidalgo, I. Bibcode: 2000ApJ...534..989B Altcode: We report on the detection of magnetic field strength and velocity oscillations in the photosphere of a sunspot umbra. Our analysis is based on the inversion of the full Stokes vector of three Fe I lines at 15650 Å, from which the stratification with optical depth of the different atmospheric parameters has been derived. This allows us to estimate the amplitude of the oscillations and the phase lag between the fluctuations in the line-of-sight velocity and field strength. Our results suggest that the inferred magnetic field oscillations are caused by opacity fluctuations that move upward and downward the region where the spectral lines are sensitive to magnetic fields. Title: Inversion of Stokes Profiles from Solar Magnetic Elements Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 2000ApJ...535..475B Altcode: We describe a new LTE inversion code for the analysis of Stokes profiles emerging from unresolved magnetic elements. It has been specifically designed to obtain the thermal, dynamic, and magnetic properties of these structures in a self-consistent manner by fitting the whole shape of the observed spectra. The inversion code is based on a previous scheme by Ruiz Cobo & del Toro Iniesta and implements the thin flux-tube model as a reasonable description of reality. All physical parameters considered relevant for the problem (including velocity fields) are retrieved by means of a Marquardt nonlinear least-squares algorithm. We present the results of extensive tests aimed at characterizing the behavior of the code so as to understand its limitations for the analysis of real observations. The code is found to produce accurate results even with only two spectral lines and noisy Stokes I and V profiles. A detailed error treatment, in which the covariances between parameters are explicitly included, is also carried out in order to investigate the uniqueness and reliability of the inferred model atmospheres. Title: Optimum Modulation and Demodulation Matrices for Solar Polarimetry Authors: del Toro Iniesta, Jose Carlos; Collados, Manuel Bibcode: 2000ApOpt..39.1637D Altcode: No abstract at ADS Title: Oscillations in a solar pore Authors: Balthasar, H.; Collados, M.; Muglach, K. Bibcode: 2000AN....321..121B Altcode: Temporal variations of a solar pore were observed at the ground based Vacuum Tower Telescope (VTT) on Tenerife and with the satellite TRACE. At the VTT Stokes I and V of the iron line at 1.56 mu m, originating in the deep photosphere, was measured. TRACE delivered UV images at 170 nm which show chromospheric continuum. In a part of the pore we find oscillations of the magnetic field in the 5 minute range. Velocities derived from shifts of the Stokes V profiles show 5 minutes everywhere in the pore, but the coherence of magnetic field and velocities is low. The intensity at 170 nm varies with 3 minutes, and for a part of the whole time series additionally with 4 minutes. Title: Formation and Destruction of a Weak Magnetic Feature in the Solar Photosphere Authors: Khomenko, E.; Collados, M.; Bellot Rubio, L. R.; Rodríguez Hidalgo, I.; Ruiz Cobo, B. Bibcode: 1999ESASP.448..307K Altcode: 1999mfsp.conf..307K; 1999ESPM....9..307K No abstract at ADS Title: High Resolution Spectropolarimetry and Magnetography Authors: Collados, M. Bibcode: 1999ASPC..184....3C Altcode: From an observational point of view, magnetic field leaves its imprint, via Zeeman effect, on spectral line splitting and the induced wavelength dependence of the polarization state of the observed photons. The characteristics of the most recent polarimetric analyzers are described, together with their limitations. Next, inversion techniques are presented as the most accurate diagnostic tools available at present to determine the properties of magnetic field, derived from its polarization signature. Finally, the importance of feeding inversion codes with the adequate physics are stressed. Title: Velocity and Temperature 5 Minute Oscillations as Functions of Geometrical Height in the Photosphere Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999ASPC..184..176R Altcode: The stratification with geometrical height of the velocity and temperature 5 minute oscillation through the solar photosphere is obtained after the inversion of a time series of KI 7699 Å line spectra taken at disk center. Title: TIP: The Tenerife Infrared Polarimeter Authors: Martínez Pillet, V.; Collados, M.; Bellot Rubio, L. R.; Rodríiguez Hidalgo, I.; Ruiz Cobo, B.; Soltau, D. Bibcode: 1999AGAb...15...89M Altcode: 1999AGM....15..P05M The aim of the IAC Tenerife Infrared Polarimeter is to obtain quantitative measurements of the polarization state of the solar radiation collected in near-infrared wavelengths by the Gregory Coudé Telescope and the Vacuum Tower Telescope of the Observatorio del Teide (Spain). In this contribution we describe the analyzer, instrumental calibration, and detector subsystems of TIP, and give details concerning the specifications of the instrument. Title: Quiet and Active Granulation Properties Authors: Manso Sainz, R.; Rodríguez Hidalgo, I.; Collados, M. Bibcode: 1999ASSL..239..197M Altcode: 1999msa..proc..197M The preliminary results of a classical spectroscopic analysis of a facular region at mu=0.78 of ~100 arcsec x 50 arcsec are presented. The variation with magnetic activity of several spectroscopic parameters has been studied, showing clear evidence that granulation properties are modified. Title: Granular and Intergranular Model Atmospheres from Inversion of Solar Two-Dimensional Spectroscopic Data Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1999ASPC..173..313R Altcode: 1999sstt.conf..313R No abstract at ADS Title: Structure of a Facular Region From the Inversion of High Spatial and Temporal Resolution Stokes Spectra Authors: Bellot Rubio, L.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999ASPC..183...61B Altcode: 1999hrsp.conf...61B No abstract at ADS Title: An LTE code for the inversion of Stokes spectra from solar magnetic elements Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999ASSL..243..271B Altcode: 1999sopo.conf..271B No abstract at ADS Title: TIP (Tenerife Infrared Polarimeter): a near IR full Stokes Polarimeter for the German Solar Telescopes at Observatorio del Teide Authors: Collados, M.; Rodríguez Hidalgo, I.; Bellot Rubio, L.; Ruiz Cobo, B.; Soltau, D. Bibcode: 1999AGAb...15Q..11C Altcode: 1999AGM....15..A13C In this contribution, the main characteristics of the=20 Tenerife Infrared Polarimeter (TIP), recently built at the Instituto de Astrofísica de Canarias, to be operated at the German Solar Telescopes (GCT and VTT) of the Observatorio del Teide (Tenerife) are presented. Especial emphasis is put on the modulation scheme, polarisation efficiencies, signal-to-noise ratio, spatial and spectral resolution, and instrumental polarisation cross-talk. Some examples of data recently obtained are presented, which give an idea of the performance and capabilities of this instrument. Title: The Hermitian solution of the radiative transfer equation for non-LTE problems Authors: Ruiz Cobo, B.; Bellot Rubio, L. R.; Collados, M. Bibcode: 1999ASSL..243..231R Altcode: 1999sopo.conf..231R No abstract at ADS Title: Probing downflows in solar magnetic elements: the Fe II test Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1999A&A...341L..31B Altcode: In an attempt to assess the physical realism of the plage flux tube model derived by Bellot Rubio, Ruiz Cobo & Collados (\cite{brc}, \cite{bellot}) we extend its predictions to the Stokes V zero-crossing shifts of a number of Fe ii lines. For this analysis, accurate Fe ii central wavelengths are required. We have devised a procedure for bringing the available Fe ii laboratory wavelengths to the system of accurate Fe i wavelengths of Nave et al. (\cite{nav}). It is shown that, relative to this system, the Fe ii system of Kurucz (\cite{kur}) is shifted by 6.4 m Angstroms/ towards longer wavelengths. Some lines, however, are displaced by more than 10 m Angstroms/. Corrected central wavelengths have been used to extract the observed Stokes V zero-crossing shifts of 16 Fe ii lines. Comparison with the values resulting from the model of Bellot Rubio et al. (\cite{brc}, \cite{bellot}) suggests that the velocity gradients derived by these authors are esentially correct. Title: Thermodynamical properties of granulation in active regions. Authors: Rodríguez Hidalgo, I.; Collados, M.; Manso Sainz, R.; Barkler, J. Bibcode: 1999joso.proc..195R Altcode: A two-dimensional spectroscopic study of two solar active regions is presented. A magnetic filling factor has been defined, and a new technique to separate large and small spatial scale motions has been used. Different types of features in the fields of view have been classified according to their magnetic and convective properties, and have been analysed with varying magnetic activity. Title: LPSP & TIP: Full Stokes Polarimeters for the Canary Islands Observatories Authors: Mártinez Pillet, V.; Collados, M.; Sánchez Almeida, J.; González, V.; Cruz-Lopez, A.; Manescau, A.; Joven, E.; Paez, E.; Diaz, J.; Feeney, O.; Sánchez, V.; Scharmer, G.; Soltau, D. Bibcode: 1999ASPC..183..264M Altcode: 1999hrsp.conf..264M No abstract at ADS Title: Oscillations in a sunspot umbra from the inversion of infrared Stokes profiles Authors: Bellot Rubio, Luis R.; Collados, Manuel; Ruiz Cobo, Basilio; Rodríguez Hidalgo, Inés; Bogdan, Thomas J. Bibcode: 1999AGM....15..A07B Altcode: We report on the detection of magnetic field strength and velocity oscillations in the photosphere of a sunspot umbra. Our analysis is based on the inversion of the full Stokes profiles of three Fe I lines at 15650 Å, from which the stratification with optical depth of the different atmospheric parameters has been derived. This allows us to estimate the amplitude of the oscillations and the phase lag between the fluctuations in the line-of-sight velocity and field strength. Our results suggest that the inferred magnetic field oscillations are caused by opacity fluctuations that move upward and donward the region where the spectral lines are sensitive to magnetic fields. Title: An Hermitian Method for the Solution of Polarized Radiative Transfer Problems Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1998ApJ...506..805B Altcode: Spectral synthesis calculations in stellar (magnetized) atmospheres are based on the solution of the radiative transfer equation (RTE) for polarized light. The thermodynamic and magnetic properties of the atmospheres, along with the radiation field, completely specify the basic ingredients of the RTE, after which numerical methods have to be employed to calculate the emergent Stokes spectra. The advent of powerful analysis techniques for the inversion of Stokes spectra has evidenced the need for accurate and fast solutions of the RTE. In this paper we describe a novel Hermitian strategy to integrate the polarized RTE that is based on the Taylor expansion of the Stokes parameter vector to fourth order in depth. Our technique makes use of the first derivatives of the absorption matrix and source vector with respect to the coordinate measured along the ray path. Both analytical and numerical results indicate that the new strategy is superior to other methods in terms of speed and accuracy. It also gives an approximation to the evolution operator at no extra cost, which is of interest for inversion algorithms based on response functions. The Hermitian technique can be straightforwardly particularized to the scalar case, providing a very efficient solution of the RTE in the absence of magnetic fields. We investigate in detail the consequences of the oscillations that appear in the evolution operator for large values of line strength η0. The problems they pose are shared by all integration schemes, but can be minimized by adopting nonequally spaced grids. Title: Near-infrared camera for solar research: a photometric application Authors: Reyes, Marcos; Joven-Alvarez, Enrique; Collados, Manuel; Bonet, Jose A.; Vazquez, Manuel; Diaz, Jose J.; Fuentes, F. Javier; Escalera, Victor G.; Rodriguez, Luis F.; Garcia-Herrero, Jose L. Bibcode: 1998SPIE.3410..233R Altcode: We report here the main characteristics of a near IR camera devoted to astrophysical solar research, which has been developed by the Instituto de Astrofisica de Canarias (IAC). The system is now being used for photometric and spectroscopic applications, and it will also be used for spectropolarimetry in the near future. The first application is described below in detail. The IACs IR camera is based on a Rockwell 256 X 256 HgCdTe NICMOS3 array, sensitive from 1 to 2.5 microns. The necessary cooling system is a LN2- cryostat, designed and built by IR labs under out requirements. The main electronics are the standard VME- based, FPGA programmable MCE-3 system, also developed by IR labs. We have implemented different readout schemes to improve sped, reduce noise and avoid seeing effects, taking into account each specific application. Data are transferred via fiber optics to a control unit, which re-send them to the main data acquisition system. Several acquisition modes to select the best images have been implemented, and a real- time data processing is available, the entire camera has been characterized and calibrated, and the main radiometric parameters given. Preliminary test in spectroscopic observations have been made in the German Towers at the Observatorio del Teide in Tenerife, Spain, and a series of photometric measurements performed in the Swedish Solar Telescope, at the Observatorio del Roque de los Muchachos in La Palma, Spain. As examples, some scientific results are also presented. Title: Stratification with Optical Depth of the 5 Minute Oscillation through the Solar Photosphere Authors: Ruiz Cobo, Basilio; Rodríguez Hidalgo, Inés; Collados, Manuel Bibcode: 1997ApJ...488..462R Altcode: An analysis of the 5 minute oscillation in the solar photosphere has been carried out using an inversion of the radiative transfer equation applied to a time-series of K I λ7699 line spectra with a 5" × 5" window at disk center. A thorough discussion of the inversion conditions, with special emphasis on the LTE approach and a careful error treatment, is offered. The inversion has been performed introducing fixed non-LTE departure coefficients taken from the literature. A sequence of instantaneous model atmospheres has been obtained, reliable from log τ ~= 0 to log τ ~= -3.5. From the temporal power spectra of line-of-sight velocity and temperature fluctuations, the amplitude and phase stratifications of the oscillations of these magnitudes have been obtained as functions of the optical depth. The amplitude accuracies are better than 4 m s-1 and 2 K in most of the photosphere. The increase of the velocity oscillation amplitude toward higher photospheric layers has been confirmed and quantified. Its phase angle remains constant through the photosphere, and significant power is obtained in temperature. Title: Stratification of the 5-min oscillation through the solar photosphere Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M. Bibcode: 1997SoPh..172...77R Altcode: 1997ESPM....8...77R The inversion of the radiative transfer equation has been applied to a time series of low spatial resolution Ki 7699 Å line spectra, allowing us to obtain a sequence of instantaneous models which are compared to the mean one to derive the 5-min oscillation stratification. The resulting models are reliable from log τ ≃ 0 to log τ ≃ -3.5. The increase of the velocity oscillation amplitude towards higher photospheric layers has been confirmed and quantified. Significant oscillation is observed in temperature. Title: Flux-Tube Model Atmospheres and Stokes V Zero-crossing Wavelengths Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1997ApJ...478L..45B Altcode: 1997astro.ph..1059B; 1997astro.ph..1059R First results of the inversion of Stokes I and V profiles from plage regions near disk center are presented. Both low and high spatial resolution spectra of Fe I 6301.5 and Fe I 6302.5 Å obtained with the Advanced Stokes Polarimeter (ASP) have been considered for analysis. The thin flux-tube approximation, implemented in an LTE inversion code based on response functions, is used to describe unresolved magnetic elements. The code allows the simultaneous and consistent inference of all atmospheric quantities determining the radiative transfer with the sole assumption of hydrostatic equilibrium. By considering velocity gradients within the tubes, we are able to match the full ASP Stokes profiles. The magnetic atmospheres derived from the inversion are characterized by the absence of significant motions in high layers and strong velocity gradients in deeper layers. These are essential to reproduce the asymmetries of the observed profiles. Our scenario predicts a shift of the Stokes V zero-crossing wavelengths, which is indeed present in observations made with the Fourier Transform Spectrometer. Title: (Erratum) Response functions for the inversion of data from unresolved solar magnetic elements. Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1997A&A...319.1036B Altcode: Erratum to Astron. Astrophys. 306, 960 (1996). Title: The IAC Solar Polarimeters: Goals and Review of Two Ongoing Projects Authors: Sanchez Almeida, J.; Collados, M.; Martinez Pillet, V.; Gonzalez Escalera, V.; Scharmer, G. B.; Shand, M.; Moll, L.; Joven, E.; Cruz, A.; Diaz, J. J.; Rodriguez, L. F.; Fuentes, J.; Jochum, L.; Paez, E.; Ronquillo, B.; Carranza, J. M.; Escudero-Sanz, I. Bibcode: 1997ASPC..118..366S Altcode: 1997fasp.conf..366S The IAC is currently developing two similar polarimeters, one for optical wavelengths and one for near infra-red wavelengths (1.5 mu m). Both instruments will provide spectra of the four Stokes parameters over 2D solar regions. The visible spectro-polarimeter will be operated at the Swedish Tower (La Palma), and it is being developed in collaboration with the Royal Swedish Academy of Sciences. We intend to take advantage of the excellent seeing conditions at this telescope, while maintaining high polarimetric precision. The IR polarimeter is being designed for the German VTT (Tenerife) which has better angular resolution in the near infra-red. This report describes the goals and technical solutions. It also briefs on the current status of the projects. Title: The IAC's Near Infrared Camera Authors: Collados, M.; Joven, E.; Fuentes, F. J.; Diaz, J. J.; Gonzalez Escalera, V.; Bonet, J. A.; Vazquez, M. Bibcode: 1997ASPC..118..361C Altcode: 1997fasp.conf..361C Here we report the main characteristics of the recently acquired near infrared camera. It is based on a 256x256 HgCdTe Nicmos-3 array, sensitive from 1 mu m to 2.5mu m. The pixel size is 40mu mx40mu m, adequate for the spatial and spectral scales at the different telescopes operating at the observatories of La Palma and Tenerife. The cooling system operates with LN2 with a hold time larger than 20 hours. The camera will be used for photometric, spectroscopic and spectropolarimetric observations. Title: Two-dimensional, high spatial resolution, solar spectroscopy using a correlation tracker. I. Correlation tracker description. Authors: Ballesteros, E.; Collados, M.; Bonet, J. A.; Lorenzo, F.; Viera, T.; Reyes, M.; Rodriguez Hidalgo, I. Bibcode: 1996A&AS..115..353B Altcode: In this paper the description of the Solar Correlation Tracker prototype built by the Instituto de Astrof isica de Canarias is presented. The system is mainly conceived as a solar image tranquilizer, although a scanning utility has also been included in order to displace the image on the final focal plane with sub-arcsecond steps, thus allowing to perform two-dimensional high spatial resolution spectroscopy. The behaviour of the different elements of the tracker is shown, as well as their influence in the performance of the system. The restrictions of the Absolute Differences algorithm, used to detect image motion when granulation fields are considered, are extensively discussed. Laboratory and telescope tests have demonstrated the capabilities of the system. The electronic components have been adapted to new optics and mechanics developed at the Kiepenheuer Institut to build an Advanced Solar Correlation Tracker. The final version of the system has been installed at the German VTT of the Spanish Observatorio del Teide. The tests carried out have demonstrated that a bandwidth of about 60Hz (for an attenuation factor of two) is achieved, which is approximately four times larger than that of previous Correlation Trackers, at the same level of attenuation. Title: Two-dimensional, high spatial resolution, solar spectroscopy using a Correlation Tracker. II. Maps of spectral quantities. Authors: Collados, M.; Rodriguez Hidalgo, I.; Ballesteros, E.; Ruiz Cobo, B.; Sanchez Almeida, J.; del Toro Iniesta, J. C. Bibcode: 1996A&AS..115..367C Altcode: In this paper we illustrate some of the capabilities of the Correlation Tracker prototype developed at the Instituto de Astrofisica de Canarias used for two-dimensional, high spatial resolution, solar spectroscopy. Slit spectra have been taken, using the Correlation Tracker as a stabilizer (minimizing image motion during exposures) and as an accurate positioning device (allowing to precisely locate the entrance slit of the spectrograph at adjacent positions on the solar disc). Spectral information is obtained from several solar regions of different sizes. Granules (including some exploding ones) and intergranules are clearly resolved. Several sub-arcsecond structures are undoubtedly distinguished as well. The two-dimensional variation of several spectral quantities in the solar atmosphere is shown, demonstrating the power of this technique and its future possibilities. Title: Response functions for the inversion of data from unresolved solar magnetic elements. Authors: Bellot Rubio, L. R.; Ruiz Cobo, B.; Collados, M. Bibcode: 1996A&A...306..960B Altcode: By adopting the thin flux tube model as representative of spatially unresolved magnetic elements in the photosphere of the Sun, we identify an adequate set of parameters for the model and derive the corresponding response functions (RFs) which inform about the variation of the emergent Stokes spectrum when such parameters are perturbed. We numerically compute these RFs for reasonable values of the parameters and explore their main properties. It turns out that the RFs at a given height often depend on the state of layers above as a result of the constraints imposed by flux tube geometry. As a whole, RFs can be classified into two well defined groups: one containing RFs dominated by local effects and another which contains RFs governed by non-local effects (i.e., contributions coming from layers other than that where the perturbation takes place). In particular, the RFs to the temperature, line of sight velocity and microturbulence of both the internal and the external atmospheres belong to the first group, while the RFs to the magnetic field strength, external gas pressure and radius of the tube at the base of the atmosphere must be ascribed to the second group. The RFs presented in this paper constitute a first step for the inversion of Stokes spectra from faculae and the network. Title: Book-Review : Observational and Physical Cosmology Authors: Sanchez, R.; Collados, M.; Rebolo, R.; Andrews, A. D. Bibcode: 1996IrAJ...23R.127S Altcode: No abstract at ADS Title: Amplitude and phase stratification of the solar 5-minute temperature and velocity oscillations through the photosphere Authors: Rodriguez Hidalgo, I.; Ruiz Cobo, B.; Collados, M. Bibcode: 1996ASPC..109..151R Altcode: 1996csss....9..151R No abstract at ADS Title: Empirical granular/intergranular average model atmospheres. Authors: Rodríguez Hidalgo, I.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.; Collados, M.; Sánchez Almeida, J. Bibcode: 1996joso.proc..162R Altcode: No abstract at ADS Title: Empirical model of an average solar granule Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Rodriguez Hidalgo, I.; Collados, M.; Sanchez Almeida, J. Bibcode: 1996ASPC..109..155R Altcode: 1996csss....9..155R No abstract at ADS Title: LTE polarized radiative transfer through interlaced atmospheres. Authors: del Toro Iniesta, J. C.; Ruiz Cobo, B.; Bellot Rubio, L. R.; Collados, M. Bibcode: 1995A&A...294..855D Altcode: We show that the solution of the radiative transfer equation (RTE) through a line of sight that pierces several times two alternate atmospheres can be obtained in terms of the solutions of the RTE through both single atmospheres separately considered. This also applies to the response functions of the observed Stokes spectrum to perturbations of the physical quantities. The analytic solution of the RTE in case that the single atmospheres are Milne-Eddington is presented. The simplification of the solution in the case of a longitudinal or transversal (with constant azimuth) magnetic field is presented as well. Finally, as a numerical example, we synthesize the Stokes I- and V-spectrum emerging from a thin magnetic flux tube, achieving a considerable decrease in computation time with respect to conventional integrations and without loss of accuracy. Title: A morphological description of the Sun observed in Honduras during the total solar eclipse of 11 July 1991 Authors: Pineda de Carías, María Cristina; Zamorano, Jaime; Collados, Manuel Bibcode: 1995AIPC..320..144P Altcode: 1995bss..conf..144P; 1995ESAC....4..144P A morphological description of the solar photosphere, chromosphere, and the corona is presented from a complete sequence of visual and spectroscopic observations made in Honduras (Amapala), during the total solar eclipse of 11 July 1991 and from the analysis of some emission and absorption lines at all the eclipse phases. Title: Lest Detector and Data Acquisition System - Part One - Specifications Authors: Collados, M.; Keller, C. U.; Steiner, P. Bibcode: 1995lest.rept....1C Altcode: No abstract at ADS Title: LEST detector and data acquisition systems. Authors: Collados, M.; Keller, C. U.; Steiner, P. Bibcode: 1995LFTR...61.....C Altcode: Contents: 1. Specifications (M. Collados, C. U. Keller, P. Steiner). 2. Design considerations for the data acquisition system (P. Steiner). Title: Observed differences between large and small sunspots. Authors: Collados, M.; Martinez Pillet, V.; Ruiz Cobo, B.; del Toro Iniesta, J. C.; Vazquez, M. Bibcode: 1994A&A...291..622C Altcode: We confirm recent results about the differences in temperature and magnetic field strength between the umbra of large and small sunspots. Five Stokes I- and V-spectra from the darkest cores of three different umbrae have been analysed with the inversion code of the radiative transfer equation by Ruiz Cobo & del Toro Iniesta (1992). The run with depth of temperature, magnetic field (strength and inclination) and velocity along the line of sight are obtained. The larger sunspots turn out to be cooler and possesing a larger magnetic field strength, practically throughout the whole atmosphere. Neither significant gradients of the line-of-sight velocity, nor of the magnetic field inclination, are detected in any of the spots analysed. Two model atmospheres are given corresponding to hot (small) and cool (large) sunspots. The models are, to a large extent, free from effects of penumbral/photospheric stray-light because it is nearly absent in the large spots and because in the small one, where it is important for the Stokes I-profile, only Stokes V is considered to obtain the model atmosphere. These are the first umbral models in the literature for which a simultaneous determination of the magnetic field and thermodynamic stratifications is presented. The implications of these stratifications for the energy transport in sunspot umbrae are discussed. Title: Variations of properties of the quiet photosphere along the equator and the central meridian: Spectroscopic results Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M. Bibcode: 1994A&A...283..263R Altcode: Spectra of four lines (CI5380.3 A, MnI 5394.7 A, FeI 5930.2 A and SiI 5948.5 A) have been obtained in the quiet photosphere, at regular intervals along the polar axis and the equator. The spatially averaged spectra have been analyzed, studying the center-to-limb variation (CLV) and possible changes with the heliographic latitude of the residual intensity (RI), equivalent width (EW), full width at half line minimum (FWHM), and bisector of the line profiles. The aim of this spectroscopic study is to complete the photometric work carried out and recently published by the authors (Rodriguez Hildago et al. 1992, hereafter Paper I). It allows us to test some conclusions of Paper I and to extend our analysis to higher photospheric layers. Firstly the general behavior of the CLV is shown and discussed. From the comparison betwen the CLV along the North-South and East-West diameters, it is observed that the Cl line, formed very deep in the photosphere, broadens and shows raised minima with latitude, not showing variations in its EW, except at very high latitudes. The other three lines, which inform about the physical conditions in the middle photosphere, become deeper and stronger, and the FeI one seems broader, with latitude. The observational results are discussed in terms of physical scenarios based on changes in the velocity fields present in the photosphere (mainly of the granulation), possible spatial anisotropies in the distribution of network bright points (which would be related to differences in the mean temperature gradient) and the latitudinal variation of the granulation contrast found in Paper I. Title: A multiline method to determine stellar magnetic fields Authors: Ripodas, P.; Collados, M.; Sanchez Almeida, J.; Garcia Lopez, R. J. Bibcode: 1993ASPC...40..196R Altcode: 1993IAUCo.137..196R; 1993ist..proc..196R No abstract at ADS Title: Variation of properties of the quiet photosphere with heliographic latitude. Authors: Hidalgo, I. R.; Collados, M.; Vázquez, M. Bibcode: 1993sova.conf...96H Altcode: Spectra of four selected lines (CI 5380.3 Å, MnI 5394.7 Å, FeI 5930.2 Å and SiI 5948.5 Å) have been obtained in the quiet photosphere, at regular intervals along the polar axis and the equator. The spatially averaged spectra have been analysed, studying the centre-to-limb variation and possible changes with heliographic latitude of the residual intensity equivalent width, full width at half line minimum and bisector of the lines. Title: Centre-to-limb variation of solar granulation along the equator and the central meridian Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M. Bibcode: 1992A&A...264..661R Altcode: The paper analyzes white-light images of solar granulation taken outside active regions, at regular intervals along the polar axis and the equator, in order to study its center-to-limb variation and possible changes with the solar latitude. The 2D spatial power spectra of the brightness distribution are calculated and corrected for the distortions produced by the atmosphere and the telescope. One-dimensional integrated spectra are obtained for each position, with the geometrical foreshortening effect taken into account. A lower contrast, a smaller mean wavenumber, and a steeper center-to-limb variation of the contrast are found in the central meridian as compared to the equator. Sources of error are discussed, and different scenarios are presented in order to interpret these observational facts. Intensity fluctuations were detected until the extreme limb, with a spatial scale of about 10 arcsec. Title: Book-Review - Solar Observations - Techniques and Interpretation - First Canary Islands Winter School of Astrophysics Authors: Sanchez, F.; Collados, M.; Vazquez, M.; Staude, J. Bibcode: 1992AN....313Q.302S Altcode: No abstract at ADS Title: Book-Review - Observational and Physical Cosmology - 2ND Canary Islands Winter School of Astrophysics Authors: Sanchez, F.; Collados, M.; Rebolo, R.; Gottlober, S. Bibcode: 1992AN....313R.302S Altcode: No abstract at ADS Title: Book-Review - Observational and Physical Cosmology Authors: Sanchez, F.; Collados, M.; Rebolo, R. Bibcode: 1992Sci...257R.278S Altcode: No abstract at ADS Title: Book-Review - Observational and Physical Cosmology Authors: Sanchez, F.; Collados, M.; Rebolo, R. Bibcode: 1992Sci...257Q.278S Altcode: No abstract at ADS Title: Book-Review - Observational and Physical Cosmology Authors: Sanches, F.; Collados, M.; Rebolo, R. Bibcode: 1992JBAA..102R.175S Altcode: No abstract at ADS Title: Book-Review - Solar Observations - Techniques and Interpretations Authors: Sanchez, F.; Collados, M.; Vazquez, M. Bibcode: 1992Sci...255.1757S Altcode: No abstract at ADS Title: Estimating the Degradation of Brightness Power Spectra of Solar Granulation from Images Outside the Disk Centre Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M. Bibcode: 1992A&A...254..371R Altcode: A method is presented to estimate the influence of the atmospheric turbulence and the telescope on the mean power spectra of the granulation brightness distribution at positions outside the disk centre, derived using the determination of Fried's parameter.

The procedure is based on the differential degradation suffered by the directions perpendicular and parallel to the solar limb; the former one is more affected because it contains more power at high frequencies, due to the geometrical foreshortening effect. A certain spectral ratio is defined, which can be evaluated after the observed power spectra and can be described directly by a Korff's function for a given value of the Fried parameter r0. The best fit of the measured attenuation to the theoretical one is calculated, allowing to obtain the adequate Modulation Transfer Function to reconstruct the original power spectra. A test has been performed by evaluating the mentioned ratio after restored spectra showing that these present the required elongation up to a resolution of about 0".4. Title: Book-Review - Solar Observations - Techniques and Interpretation Authors: Sanches, F.; Collados, M.; Vazques, M. Bibcode: 1992JBAA..102T..62S Altcode: No abstract at ADS Title: Observational and Physical Cosmology Authors: Sanchez, F.; Collados, M.; Reboldo, R. Bibcode: 1992opc..book.....S Altcode: 1. Lectures on the very early universe V. N. Lukash and I. D. Novikov; 2. Primordial nucleosynthesis Hubert Reeves; 3. Big Bang nucleosynthesis and abundances of light elements Bernard E. J. Pagel; 4. The microwave sky Jose Luis Sanz; 5. The large scale structure of the universe Bernard J. T. Jones; 6. Large-scale structure of the universe Jaan Einasto. Title: Solar observations : techniques and interpretation Authors: Sanchez, F.; Collados, M.; Vazquez, M. Bibcode: 1992soti.book.....S Altcode: This book includes four chapters devoted to techniques and interpretation of solar observations. The chapter on high spatial resolution techniques considers basic concepts, single frame analysis, interferometry techniques, and other methods. The magnetic field measurements chapter discusses a prototype polarimeter, physical components of polarimeters, radiative transfer for polarized radiation, transfer equations for the Stokes parameters in a magnetized atmosphere, and magnetic field measurements in unresolved structures and in prominences. The chapter on solar postfocus instrumentation gives particular attention on the locations of postfocus instrumentation, postfocus imaging, spectrometers, detectors for spectrometers, and special instruments at spectrometer foci. The chapter on the dynamics of the solar atmosphere focuses on the features of the solar structure, diagnostic methods for velocity measurements, rotation and convection, motions in magnetic flux tubes and spots, and velocity fields in prominences and filaments. Title: Observational and physical cosmology. Lectures. Authors: Sánchez, F.; Collados, M.; Rebolo, R. Bibcode: 1992opcl.book.....S Altcode: The lectures presented deal with theories on the very early universe, capable of providing the initial conditions of the Friedmann model and of generating inhomogeneities in the inflationary period; modelling of the epoch of primordial nucleosynthesis. The properties of the cosmic microwave background are examined both its spectrum and the anisotropy at different angular scales. The book includes a state-of-the-art review of the large scale structure of statistical measurements of the distribution of galaxies, large-scale flows, the origin and distribution of voids and superclusters. Title: Solar Observations Authors: Sánchez, F.; Collados, M.; Vazquez, M. Bibcode: 1991soob.book.....S Altcode: This book is a collection of papers by four internationally known speakers who explore some key areas in solar physics. O. von der Lühe discusses new techniques that are being developed for observing the sun at high spatial resolution and which have played a key role in most of the recent discoveries about the Sun. Egidio Landi Degl'Innocenti describes the magnetic field that dominates much of the structure we see and many of the active phenomena on the Sun. An understanding of how to measure the field is important. New solar telescopes in Europe and the United States have led the way in the present revolution in the understanding of the sun and important new breakthroughs are expected from LEST. In particular, the post-focus instrumentation has been crucial, and this is detailed by Hubertus Wohl; finally Pierre Mein writes about the solar atmosphere, which is now known to be a dynamic atmosphere with many puzzling features. Title: Magnetic Flux Determination in Late-Type Dwarfs Authors: Rípodas, P.; Sánchez Almeida, J.; García López, R. J.; Collados, M. Bibcode: 1991LNP...380..417R Altcode: 1991IAUCo.130..417R; 1991sacs.coll..417R We present a very preliminary and simplified analysis designed to measure photospheric magnetic fields in late-type stars, using the FeI 5247.06 Å and 5250.22 Å lines. We show how the use of the equivalent widths of the lines and differences in their depth can give a rapid estimation of the magnetic flux. Title: Numerical Test of a New V-Profile Inversion Technique Authors: Ruiz Cobo, B.; del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J. Bibcode: 1990Ap&SS.170..113R Altcode: The diagnostic method proposed by Landi Degl'Innocenti and Landolfi (1982), based on the observation of circular polarization, has been generalized to derive the thermodynamic properties of unresolved magnetic elements in the solar atmosphere. The final aim is to derive the height dependence of several parameters of the flux tube atmosphere (such as temperature, magnetic field and velocity distributions, macroturbulence and filling factor). We have used a perturbation method based on the concept of response functions for the Stokes profiles introduced by Landi Degl'Innocenti and Landi Degl'Innocenti (1977). We present here the preliminary results of invertingV-profiles by an iterative standard least-squares technique, which allows to find the magnetic 1-D atmosphere consistent with simulated data. Title: Fried's Parameter Derived from Observations of Granulation Outside the Disk Centre Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M. Bibcode: 1990Ap&SS.170..155R Altcode: A new method has recently been developed to obtain the Fried's parameter from observations of granulation outsude the disk centre, based on the different degradation suffered by the images on the directions parallel and perpendicular to the solar limb, due to the geometrical foreshortening. This procedure has been applied to CCD images obtained at the Swedish Solar Tower of the Observatorio del Roque de los Muchachos, with satisfactory results which are presented and discussed. Title: Facular points and small-scale magnetic elements Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.; Martinez Pillet, V.; Ruiz Cobo, B. Bibcode: 1990Ap&SS.170....9D Altcode: We present spectroscopic observations, with high spatial resolution, of Ca ii K bright points very near the disc centre. Magnetic concentrations have been detected in these network (facular) points by only using intensity profiles of the well-known pair of lines Fe i5250.22 Å and 5247.06 Å. No brightening of these structures with respect to the quiet photosphere can be ascertained within an accuracy threshold of 1.2%. Title: Velocity Fields Associated with the Magnetic Component of Solar Faculae Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1990Ap&SS.170...31S Altcode: The StokesV asymmetries observed in solar faculae can be interpreted by invoking the presence of magnetic and velocity fields variations along the line-of-sight. By means of a perturbative approach, we develop the theoretical dependence on magnetic and velocity fields of the StokesV profile around its zero-crossing point. We find that the empirical curves of growth for theV zero-crossing point and the slope, as well as the curve of growth for the integral (previously derived by Sánchez Almeidaet al., 1989, through the same approach), are reproduced quite well with a single atmosphere which assumes such simultaneous variations. The depth dependence of the fields that give the best fit in our model presents several striking properties which cannot be released without totally compromising the goodness of the fit. Namely, the magnetic field strength increases towards the observer while the downflowing velocity field decreases. Both variations must occur co-spatially, in the same atmospheric layers. This fact seems to contradict theoretical models for the fanning out parts of magnetic concentrations which foresee a sharp separation between a static magnetic layer and a deep zone with velocity fields. We discuss a possible solution of such contradiction in terms of a finite optical thickness of the boundary layer between zones with and without magnetic field in faculae. Title: Photometry and Spectroscopy of the Solar Granulation Along the Polar Axis and Equator Authors: Rodriguez Hidalgo, I.; Collados, M.; Vazquez, M. Bibcode: 1990Ap&SS.170...23R Altcode: From high-resolution CCD images of granulation obtained at the Swedish Solar Tower of the Observatorio del Roque de los Muchachos at different positions on the solar disk, mean bi-dimensional spatial power spectra have been obtained at each position and restored following the method proposed by Rodríguez Hidalgoet al. (1990). The variation with latitude of the power spectrum, of the granular brightness contrast and of the mean wave number of the power spectrum are presented. The analysis is completed with spectroscopic observations obtained at the Gregory Coudé Telescope of the Observatorio del Teide. The centre-to-limb and latitudinal variation of the bisectors, residual intensities and equivalent widths are shown for several photometric lines. Title: Are small-scale magnetic concentrations spatially coincident with bright facular points? Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.; Martinez Pillet, V.; Ruiz Cobo, B. Bibcode: 1990A&A...233..570D Altcode: The usually assumed identification of small-scale magnetic concentrations with bright facular or network points on the photosphere is observationally checked by using high spatial resolution spectra of Ca II K bright points very near the disk center. The detection of spatially unresolved magnetic structures is made via a new differential analysis of the well-known pair of Fe I lines 5247.06 A and 5250.22 A; these concentrations are present in the central part of a line weakening zone, which is of some 2 arcsec wide. No continuum intensity enhancement with respect to the quiet photosphere can be ascertained of these structures, within an accuracy threshold of 1.2 percent. In spite of this, magnetic concentrations brighter than the quiet photosphere are compatible with the observations, but if so, they must be narrower than 0.2 arcsec. Title: CCD Photometry of Stars in the Old Open Cluster NGC 188 Authors: Caputo, F.; Chieffi, A.; Castellani, V.; Collados, M.; Martinez Roger, C.; Paez, E. Bibcode: 1990AJ.....99..261C Altcode: CCD photometry for stars in three fields centered on the old open cluster NGC 188 is presented, with the aim of investigating the HR diagram distribution of cluster main-sequence stars. A sequence of subgiant, turnoff, and main-sequence stars has been detected, extending the observed lower main sequence down to about m(v) = 20 mag. It is found that the observed color-magnitude diagram appears well fitted by a theoretical isochrone for an age of about 6-billion yr, provided that Yale transformations from the theoretical into the observational plane are assumed. From the distribution of the stellar luminosities, it is found that the turnoff stars should have masses of about 1.3 solar mass. The cluster evolutionary scenario is discussed in connection with the reported luminosity of the clump of He-burning giants. Title: Spectropolarimetry of solar faculae - High spatial resolution results Authors: del Toro Iniesta, J. C.; Collados, M.; Sanchez Almeida, J.; Semel, M. Bibcode: 1990A&A...227..591D Altcode: A new method to measure the magnetic field strength of small-scale solar magnetic concentrations is presented. It is based on the center of gravity method (Semel, 1967), is independent of radiative transfer calculations and only observable parameters are needed. This method also provides parameters like filling factor (area fraction occupied by the tubes), continuum intensity contrast between flux tubes and their surroundings, in a two-component model scheme. The method is applied to spectropolarimetric high spatial resolution data. Local variations of the above parameters inside single faculae are found. This result suggests some indications about flux tube evolution. A comparison with low spatial resolution results is also made. Title: An example of the cancellation of magnetic fields during the decay of an active region Authors: De La Rosa, J. I. García; Aballe, M. A.; Collados, M. Bibcode: 1989SoPh..124..219D Altcode: A case of cancellation of magnetic fields is observed during the decay of a small active region. Three different sources of information were simultaneously used: high resolution magnetograms, chromospheric CaII filtergrams and transverse velocity fields. Title: On the generation of the net circular polarization observed in solar faculae Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1989A&A...222..311S Altcode: The net circular polarization observed in solar faculae (Stenflo et al., 1984) follows a law expected from the combination of velocity and magnetic field gradients in the photosphere. To show this, the theoretical curve of growth (net circular polarization produced by a single line versus its absorption coefficient) predicted by this mechanism is developed. An empirical curve of growth with more than 80 Fe I lines is also constructed. The agreement between theory and observation seems to point toward this mechanism as responsible for circular polarization in faculae at the disk center. Title: An example of the cancellation of magnetic fields during the decay of an active region Authors: Garcia de La Rosa, J. I.; Aballe, M. A.; Collados, M. Bibcode: 1989SoPh..124..219G Altcode: 1989SoPh..124..219D A case of cancellation of magnetic fields is observed during the decay of a small active region. Three different sources of information were simultaneously used: high resolution magnetograms, chromospheric Ca ii filtergrams and transverse velocity fields. A magnetic structure is apparently dragged to the network by the supergranular velocity field while it splits into two. There, they meet another structure with opposite magnetic polarity. After a period of coexistence, the magnetic pairs vanish, leaving no trace of either magnetic or chromospheric structures. Title: Numerical determination of the modulation transfer function from observations of granulation outside the disk centre Authors: Rodriguez Hidalgo, I.; Collados, M. Bibcode: 1989hsrs.conf..203R Altcode: No abstract at ADS Title: Numerical determination of the modulation transfer function from observations of granulation outside the disk centre. Authors: Hidalgo, I. R.; Collados, M. Bibcode: 1989hsrs.conf..203H Altcode: A spectral ratio, similar to that of von der Lühe (1984), is proposed to derive information on the degradation of the mean granular power spectrum at a position outside the disk centre. It has the advantage that the modulation transfer function is obtained directly from the data, without making any assumption on turbulence theory to describe the atmospheric behaviour. Title: Les facules solaires ou comment observer l'invisible. Authors: Sanchez Almeida, J.; Collados, M.; Del Toro Iniesta, J. C. Bibcode: 1989Rech...20..810S Altcode: 1989Rech...20..810A No abstract at ADS Title: An explanation for the Stokes V asymmetry in solar faculae Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C. Bibcode: 1988A&A...201L..37S Altcode: The asymmetry in the Stokes V profile observed in solar faculae can be explained by assuming that the magnetic field increases with height while downflow speed decreases. The MHD compatibility of such solution is briefly discussed together with an observational test for that possibility. Title: Magnetic field strength in solar flux tubes - A model atmosphere independent determination Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.; Solanki, S. K. Bibcode: 1988A&A...196..266S Altcode: The "line ratio method" (Stenflo, 1973) has been extensively used in the past to carry out measurements of the magnetic field strength in spatially unresolved magnetic flux concentrations. The authors present here a new variant of this technique, which is particularly simple as it does not depend on any radiative transfer calculations and thus the assumption of a model atmosphere is not required. General properties of the transfer equation lead to a relationship between the circular polarization generated by two lines which are identical except for their Landé factors. This can be used to directly determine the field strength from the measured line profiles. In order to test the method the authors have applied it to experimental data. A comparison with the traditional line ratio method is shown. Title: Photometry of sunspot penumbrae Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M. Bibcode: 1988A&A...195..315C Altcode: The authors present the results of a statistical analysis of the penumbra of sunspots. The intensity distribution, and several parameters derived from it, is analysed at different heliocentric angles and positions on the spot. It has revealed, on the one hand, that a two-component model is compatible with the observations and that both components lie at the same height, and on the other, that the penumbral asymmetry found by Collados et al. (1987) is confirmed under a photometrical point of view, the western penumbra being slightly shorter than the eastern one. Title: On the Age Dependence of the Asymmetry of Penumbrae of Sunspots Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M.; Woehl, H. Bibcode: 1988SoPh..117..199C Altcode: The age dependence of the recently described asymmetry of penumbrae of large stable sunspots was analyzed. Young sunspots showed shorter eastern penumbrae, which differed by a maximum of ± 10 % from their mean width. For older sunspots the western penumbrae became smaller than the mean penumbra reaching differences of 20 % for spots of two months age. Title: A Statistical Study of the Geometrical Wilson Effect Authors: Collados, M.; del Toro Iniesta, J. C.; Vazquez, M. Bibcode: 1987SoPh..112..281C Altcode: An analysis has been carried out of the centre-to-limb variation of the apparent sizes of the umbra, penumbra and whole spot. It has revealed that the umbral size decreases with height. We have interpreted this result in terms of the penumbral geometrical height scale. A value of 230 km, which is larger than that of the photosphere or the umbra, explains the observed decrease. An intrinsic asymmetry in the penumbra of old sunspots has also been found, the western penumbra being slightly shorter that the rest of the penumbra. This explains why the inverse Wilson effect is present, preferentially, in the western hemisphere, as found in previous investigations. A comparison with other works is also made. Title: A new determination of the solar granulation contrast Authors: Collados, M.; Vazquez, M. Bibcode: 1987A&A...180..223C Altcode: The contrast of the photospheric granulation in the centre of the disk at a wavelength of 500 nm has been determined by means of photographs taken during the solar eclipse of May 30th 1984. After restoration, values of 17.3% and 20.4%, using the sum of two lorentzians to define the instrumental profile, and of 11.7% and 14.3%, using the sum of two gaussians, have been obtained. This suggests that the results are quite sensitive to the particular choice which is made of the analytical approximation to the point spread function. The corrected power spectrum does not show significant differences to those of previous works. A comparison between the method for correcting the image degradation which the authors propose with those used by other investigators is also made. Title: Detailed processes accompanying the decay of an active region. Authors: Garcia de La Rosa, J. I.; Collados, M. Bibcode: 1987PAICz..66...55G Altcode: 1987eram....1...55G High resolution (better than 1arcsec) magnetograms obtained at the Sacramento Peak Vacuum Tower Telescope were used to study the decay of a small active region. The reduction process allows one to match intensity and magnetic pictures exactly. Title: Observations of the Magnetic Fine Structure of a Facula Authors: del Toro Iniesta, J. C.; Semel, M.; Collados, M. Bibcode: 1987rfsm.conf..122D Altcode: No abstract at ADS Title: Continuum intensity and magnetic flux of solar fluxtubes. Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M.; Sánchez Almeida, J. Bibcode: 1987PAICz..66..265D Altcode: 1987eram....1..265D The continuum contrast between fluxtubes and their quiet background, and the magnetic flux carried by these magnetic elements, have been determined at different points of a solar facula, in the frame of a two-component model from spectropolarimetric observations of 1arcsec spatial resolution. Local spatial variations of these two parameters have been obtained. Title: The Wilson Effect in Sunspots Authors: Collados, M.; del Toro Iniesta, J. C.; Vázquez, M. Bibcode: 1987rfsm.conf..183C Altcode: An analysis of the center to limb variation of the geometrical properties of spots has been carried out. It has revealed that spots do not have a symmetrical behaviour with respect to the centre of solar disk. Thus, the Wilson effect is not zero at δ = 0°, but at δ ≡ 45°W. Moreover, the inverse Wilson effect is the general rule in that interval, while the normal phenomenon is maximum at a heliocentric angle of 40° - 50°E. Title: Intensity profiles in fluxtubes. Authors: Sanches Almeida, J.; Collados, M.; del Toro Iniesta, J. C.; Solanki, S. K. Bibcode: 1987PAICz..66..261S Altcode: 1987eram....1..261S Spectroscopic analysis of the light coming from an atmosphere is a powerful tool for revealing its properties. The problem when using conventional spectroscopy for solar fluxtubes is their unresolved character: magnetic and non-magnetic regions of a plage have to be observed as a whole. With the aim of obtaining the true intensity spectrum of an unresolved tube, the authors have developed a simple method which can reconstruct the intensity generated in the magnetic component. Only observed parameters are used: intensity and circular polarization in the plage and intensity in the quiet photosphere. Title: The Intensity Distribution in Sunspot Penumbras Authors: Collados, M.; del Toro Iniesta, J. C.; Vázquez, M. Bibcode: 1987rfsm.conf..214C Altcode: The intensity distribution of the penumbra at different stages of evolution has been analyzed. The results have been different for both evolved and primitive penumbras. While the former present almost symmetrical, single-peaked histograms, the same does not occur for the latter, their distributions being, preferentially, asymmetrical or double-peaked. These results are interpreted in terms of bright and dark elements. Thus, an evolutionary process has been proposed to explain the diverse characteristics found at the different stages. Title: Observations of the magnetic fine structure of a facula. Authors: Del Toro Iniesta, J. C.; Semel, M.; Collados, M. Bibcode: 1987rfsm.conf..127D Altcode: Simultaneous spectropolarimetric observations of a facula have been carried out in 10 spectral lines with a spatial resolution of 1arcsec. Local variations of the magnetic field strength and the filling factor of fluxtubes were obtained. The analysis of the velocities inside fluxtubes shows that positive and negative Doppler shifts are present, at the same time, at different points of the facula. Title: Variation of the granulation with the solar latitude. Authors: Collados, M.; Rodriguez Hidalgo, I.; Vazquez, M. Bibcode: 1987PAICz..66...41C Altcode: 1987eram....1...41C Preliminary results of a search for the variation of the solar granulation properties with the heliographic latitude are presented. Within errors, no changes are found in the power spectra and sizes between N-S and E-W scans. Title: Granulation Deformation Near and in Sunspot Regions Authors: Collados, M.; Marco, E.; del Toro, J. C.; Vazquez, M. Bibcode: 1986SoPh..105...17C Altcode: High-resolution white-light pictures are analyzed to study the differences between the granular size near sunspot penumbrae and in light-bridges presenting granular structure and that of the quiet photosphere. No difference is found between the mean granular diameter in light-bridges and the quiet photosphere. The dispersion found in the results corresponding to different zones around the sunspots indicates that the size of the granulation may vary from place to place near the sunspots, its mean value not differing significantly from that of the quiet photosphere. A possible systematic bias in the selection of the granules by Macris (1979) is found. Title: Estudio fotométrico de estructuras fotosféricas solares Title: Estudio fotométrico de estructuras fotosféricas solares Title: Photometric study of solar photosphere structures; Authors: Collados Vera, Manuel Arturo Bibcode: 1986PhDT.......146C Altcode: No abstract at ADS Title: Observations of the Birth and Fine Structure of Sunspot Penumbrae Authors: Collados, M.; Garcia de La Rosa, J. I.; Moreno-Insertis, F.; Vazquez, M. Bibcode: 1985LNP...233..133C Altcode: 1985hrsp.proc..133C High resolution white-light pictures of sunspot penumbrae are presented. These include pictures showing details of their filamentary structure and some instances of the birth of a penumbra. The observations are discussed in the framework of current penumbra theories. Title: Photometry of Light-Bridges in Sunspots Authors: Collados, M.; Marco, E.; Vazquez, M. Bibcode: 1985LNP...233..299C Altcode: 1985hrsp.proc..299C The decay of a sunspot region was studied using high resolution white-light pictures. The photometric and geometric parameters of a light-bridge showing granular structure were determined. No difference is found comparing it with the quiet photosphere.