Author name code: bello-gonzalez ADS astronomy entries on 2022-09-14 author:"Bello Gonzalez, Nazaret" ------------------------------------------------------------------------ Title: Evolution of the flow field in decaying active regions. II. Converging flows at the periphery of naked spots Authors: Strecker, H.; Bello González, N. Bibcode: 2022A&A...664A.195S Altcode: 2022arXiv220814272S Context. In a previous work, we investigated the evolution of the flow field around sunspots during sunspot decay and compared it with the flow field of supergranular cells. The decay of a sunspot proceeds as it interacts with its surroundings. This is manifested by the changes observed in the flow field surrounding the decaying spot.
Aims: We now investigate in detail the evolution of the flow field in the direct periphery of the sunspots of the same sample and aim to provide a complete picture of the role of large-scale flows present in sunspot cells.
Methods: We analyse the horizontal velocity profiles of sunspots obtained from observations by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). We follow their evolution across the solar disc from their stable phase to their decay and their final disappearance.
Results: We find two different scenarios for the evolution of the flow region surrounding a spot in the final stage of its decay: (i) either the flow cell implodes and disappears under the action of the surrounding supergranules or (ii) it outlives the spot. In the later case, an inwards flow towards the remaining naked spot develops in the vicinity closest to the spot followed by an outflow further out. These findings provide observational evidence to theoretical predictions by realistic magnetohydrodynamic (MHD) sunspot and moat region simulations.
Conclusions: The Evershed flow and the moat flow, both connected to the presence of fully fledged sunspots in a spot cell, vanish when penumbrae decay. Moat flows decline into supergranular flows. The final fate of a spot cell depends on its interaction with the surrounding supergranular cells. In the case of non-imploding spot cells, the remaining naked spot develops a converging inflow driven by radiative cooling and a geometrical alignment of granules in its periphery which is similar to that observed in pores.

Movies are available at https://www.aanda.org

This paper is mainly based on Part II of the Ph.D. thesis "On the decay of sunspots", https://freidok.uni-freiburg.de/data/165760. Title: Characterization of magneto-convection in sunspots. The Gough-Tayler stability criterion in MURaM sunspot simulations Authors: Schmassmann, M.; Rempel, M.; Bello González, N.; Schlichenmaier, R.; Jurčák, J. Bibcode: 2021A&A...656A..92S Altcode: Context. Observations have shown that in stable sunspots, the umbral boundary is outlined by a critical value of the vertical magnetic field component. However, the nature of the distinct magnetoconvection regimes in the umbra and penumbra is still unclear.
Aims: We analyse a sunspot simulation in an effort to understand the origin of the convective instabilities giving rise to the penumbral and umbral distinct regimes.
Methods: We applied the criterion from Gough & Tayler (1966, MNRAS, 133, 85), accounting for the stabilising effect of the vertical magnetic field, to investigate the convective instabilities in a MURaM sunspot simulation.
Results: We find: (1) a highly unstable shallow layer right beneath the surface extending all over the simulation box in which convection is triggered by radiative cooling in the photosphere; (2) a deep umbral core (beneath −5 Mm) stabilised against overturning convection that underlies a region with stable background values permeated by slender instabilities coupled to umbral dots; (3) filamentary instabilities below the penumbra nearly parallel to the surface and undulating instabilities coupled to the penumbra which originate in the deep layers. These deep-rooted instabilities result in the vigorous magneto-convection regime characteristic of the penumbra; (4) convective downdrafts in the granulation, penumbra, and umbra develop at about 2 km s−1, 1 km s−1, and 0.1 km s−1, respectively, indicating that the granular regime of convection is more vigorous than the penumbra convection regime, which, in turn, is more vigorous than the close-to-steady umbra; (5) the GT criterion outlines both the sunspot magnetopause and peripatopause, highlighting the tripartite nature of the sub-photospheric layers of magnetohydrodynamic (MHD) sunspot models; and, finally, (6) the Jurčák criterion is the photospheric counterpart of the GT criterion in deep layers.
Conclusions: The GT criterion as a diagnostic tool reveals the tripartite nature of sunspot structure with distinct regimes of magneto-convection in the umbra, penumbra, and granulation operating in realistic MHD simulations.

Movies associated with Figs. 2 and 3 are available at https://www.aanda.org Title: Magnetic properties on the boundary of an evolving pore Authors: García-Rivas, M.; Jurčák, J.; Bello González, N. Bibcode: 2021A&A...649A.129G Altcode: 2021arXiv210208459G Context. Analyses of the magnetic properties on umbrae boundaries have led to the Jurčák criterion, which states that umbra-penumbra boundaries in stable sunspots are equally defined by a constant value of the vertical magnetic field, Bvercrit, and by a 50% continuum intensity of the quiet Sun, IQS. Umbrae with vertical magnetic fields stronger than Bvercrit are stable, whereas umbrae with vertical magnetic fields weaker than Bvercrit are unstable and prone to vanishing.
Aims: We aim to investigate the existence of a critical value of the vertical magnetic field on a pore boundary and its role in the evolution of the magnetic structure.
Methods: We analysed SDO/HMI vector field maps corrected for scattered light and with a temporal cadence of 12 min during a 26.5-hour period. A continuum intensity threshold (Ic = 0.55 IQS) is used to define the pore boundary and we study the temporal evolution of the magnetic properties there.
Results: We observe well-defined stages in the pore evolution: (1) during the initial formation phase, total magnetic field strength (B) and vertical magnetic field (Bver) increase to their maximum values of ∼1920 G and ∼1730 G, respectively; (2) then the pore reaches a stable phase; (3) in a second formation phase, the pore undergoes a rapid growth in terms of size, along with a decrease in B and Bver on its boundary. In the newly formed area of the pore, Bver remains mostly below 1731 G and B remains everywhere below 1921 G; (4) ultimately, pore decay starts. We find overall that pore areas with Bver < 1731 G, or equivalently B < 1921 G, disintegrate faster than regions that fulfil this criteria.
Conclusions: We find that the most stable regions of the pore, similarly to the case of umbral boundaries, are defined by a critical value of the vertical component of the magnetic field that is comparable to that found in stable sunspots. In addition, in this case study, the same pore areas can be similarly well-defined by a critical value of the total magnetic field strength. Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: Solar pores - A magnetic evolution laboratory Authors: García-Rivas, M.; Jurčák, J.; Bello González, N. Bibcode: 2020sea..confE.198G Altcode: Analyses of the vector magnetic field on solar magnetic structures led to the Jurčák criterion, an empirical law that connects a critical value of the vertical component of the magnetic field to the umbral magnetoconvective mode in stable sunspots. We study the evolution of the vertical component of the magnetic field (Bver) on evolving pores and the existence of an equivalent critical vertical magnetic value to provide steadiness. Indeed, we find that areas with weak Bver are unstable and granulation takes over them. However, areas with strong Bver show longer lifetimes. Title: Characterization of the umbra-penumbra boundary by the vertical component of the magnetic field. Analysis of ground-based data from the GREGOR Infrared Spectrograph Authors: Lindner, P.; Schlichenmaier, R.; Bello González, N. Bibcode: 2020A&A...638A..25L Altcode: 2020arXiv200409956L Context. The vertical component of the magnetic field was found to reach a constant value at the boundary between penumbra and umbra of stable sunspots in a recent statistical study of Hinode/SP data. This finding has profound implications as it can serve as a criterion to distinguish between fundamentally different magneto-convective modes operating in the sun.
Aims: The objective of this work is to verify the existence of a constant value for the vertical component of the magnetic field (B⊥) at the boundary between umbra and penumbra from ground-based data in the near-infrared wavelengths and to determine its value for the GREGOR Infrared Spectrograph (GRIS@GREGOR) data. This is the first statistical study on the Jurčák criterion with ground-based data, and we compare it with the results from space-based data (Hinode/SP and SDO/HMI).
Methods: Eleven spectropolarimetric data sets from the GRIS@GREGOR slit-spectograph containing fully-fledged stable sunspots were selected from the GRIS archive. SIR inversions including a polarimetric straylight correction are used to produce maps of the magnetic field vector using the Fe I 15648 Å and 15662 Å lines. Averages of B⊥ along the contours between penumbra and umbra are analyzed for the 11 data sets. In addition, contours at the resulting B⊥const are drawn onto maps and compared to intensity contours. The geometric difference between these contours, ΔP, is calculated for each data set.
Results: Averaged over the 11 sunspots, we find a value of B⊥const = (1787 ± 100) gauss. The difference from the values previously derived from Hinode/SP and SDO/HMI data is explained by instrumental differences and by the formation characteristics of the respective lines that were used. Contours at B⊥ = B⊥const and contours calculated in intensity maps match from a visual inspection and the geometric distance ΔP was found to be on the order of 2 pixels. Furthermore, the standard deviation between different data sets of averages along umbra-penumbra contours is smaller for B⊥ than for B∥ by a factor of 2.4.
Conclusions: Our results provide further support to the Jurčák criterion with the existence of an invariable value B⊥const at the umbra-penumbra boundary. This fundamental property of sunspots can act as a constraining parameter in the calibration of analysis techniques that calculate magnetic fields. It also serves as a requirement for numerical simulations to be realistic. Furthermore, it is found that the geometric difference, ΔP, between intensity contours and contours at B⊥ = B⊥const acts as an index of stability for sunspots.

The data from the GRIS instrument is publicly available in the archive at http://sdc.leibniz-kis.de. Title: A distinct magnetic property of the inner penumbral boundary. III. Analysis of simulated sunspots Authors: Jurčák, Jan; Schmassmann, Markus; Rempel, Matthias; Bello González, Nazaret; Schlichenmaier, Rolf Bibcode: 2020A&A...638A..28J Altcode: 2020arXiv200403940J Context. Analyses of sunspot observations revealed a fundamental magnetic property of the umbral boundary: the invariance of the vertical component of the magnetic field.
Aims: We analyse the magnetic properties of the umbra-penumbra boundary in simulated sunspots and thus assess their similarity to observed sunspots. We also aim to investigate the role of the plasma β and the ratio of kinetic to magnetic energy in simulated sunspots in the convective motions because these quantities cannot be reliably determined from observations.
Methods: We used a set of non-gray simulation runs of sunspots with the MURaM code. The setups differed in terms of subsurface magnetic field structure and magnetic field boundary imposed at the top of the simulation domain. These data were used to synthesize the Stokes profiles, which were then degraded to the Hinode spectropolarimeter-like observations. Then, the data were treated like real Hinode observations of a sunspot, and magnetic properties at the umbral boundaries were determined.
Results: Simulations with potential field extrapolation produce a realistic magnetic field configuration on the umbral boundaries of the sunspots. Two simulations with a potential field upper boundary, but different subsurface magnetic field structures, differ significantly in the extent of their penumbrae. Increasing the penumbra width by forcing more horizontal magnetic fields at the upper boundary results in magnetic properties that are not consistent with observations. This implies that the size of the penumbra is given by the subsurface structure of the magnetic field, that is, by the depth and inclination of the magnetopause, which is shaped by the expansion of the sunspot flux rope with height. None of the sunspot simulations is consistent with the observed properties of the magnetic field and the direction of the Evershed flow at the same time. Strong outward-directed Evershed flows are only found in setups with an artificially enhanced horizontal component of the magnetic field at the top boundary that are not consistent with the observed magnetic field properties at the umbra-penumbra boundary. We stress that the photospheric boundary of simulated sunspots is defined by a magnetic field strength of equipartition field value. Title: Analysis Methods of the Flow Field around Decaying Sunspots Authors: Strecker, H.; Bello González, N. Bibcode: 2019ASPC..526..311S Altcode: 2018arXiv181101621S The moat flow, a radial outflow surrounding fully-fledged sunspots, is a well characterised phenomenon. Nevertheless, its origin and especially its relation to the penumbra is still a controversial topic. We investigate the evolution of the horizontal velocity of the flow around sunspots over several days during sunspot decay. SDO/HMI Doppler maps which allow for the continuous observation of an active region are used. We describe the analysis method used to retrieve the horizontal velocity of the flow field for different positions on the solar disc. For that purpose, several large and small scale flow patterns, like, e.g., differential rotation, the centre-to-limb variation in the convective blueshift, and a residual pattern caused by instrumental effects, have to be taken into account in order to properly measure the horizontal velocity of the flow field surrounding the sunspots. We find that the flow field around sunspots with fully developed penumbra has a decreasing velocity profile with increasing distances to the sunspot, as already found by other authors. Most important, the velocity amplitude decreases and the profile changes as the penumbra dissolves and the sunspots decay. Our findings confirm the related disappearance of the moat flow with penumbra. Yet, we observe a remnant outflow after the penumbra disappears, which hints towards the possible overtaking of the moat flow by a supergranular flow in decaying sunspots. 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: New Insights on Penumbra Magneto-Convection Authors: Bello González, N.; Jurčák, J.; Schlichenmaier, R.; Rezaei, R. Bibcode: 2019ASPC..526..261B Altcode: Fully-fledged penumbrae are a well characterised phenomenon from an observational point of view. Also, MHD simulations reproduce the observed characteristics and provide us with insights on the physical mechanisms possibly running behind the observed processes. Yet, how this penumbral magneto-convection sets in is still an open question. Due to the fact that penumbra formation is a relatively fast process (of the order of hours), it has eluded its observation with sufficient spatial resolution by both space- and ground-based solar observatories. Only recently, some researchers have witnessed the onset of both orphan and sunspot penumbrae in detail. We are one of those. In July 2009, we observed the early stages of the NOAA 11024 AR leading sunspot while developing its penumbra. The spectro-polarimetric dataset lead us to new observational findings. In this contribution, we put into context our and other authors' results to draw the overall picture of sunspot formation. Most important, the comparison on the properties of different types of penumbrae lead us to the conclusion that the formation of penumbrae is not just one mechanism. While the sole cause necessary for penumbral magneto-convection is a stably inclined magnetic field, observations show that inclined fields can be caused by flux emergence, to form orphan penumbrae, or by field lines transported down from upper photospheric layers, to form sunspot penumbra. This conclusion, together with the recent findings by Jur\čák and collaborators on a canonical value of the vertical component of the magnetic field blocking the action of penumbral magneto-convection in umbral areas, is a crucial step forward towards the understanding of the coupling of solar plasmas and magnetic fields in penumbral atmospheres. Title: Observations of solar small-scale magnetic flux-sheet emergence Authors: Fischer, C. E.; Borrero, J. M.; Bello González, N.; Kaithakkal, A. J. Bibcode: 2019A&A...622L..12F Altcode: 2019arXiv190105870F
Aims: Two types of flux emergence were recently discovered in numerical simulations: magnetic loops and magnetic sheet emergence. While magnetic loop emergence has been documented well in recent years using high-resolution full Stokes data from ground-based telescopes as well as satellites, magnetic sheet emergence is still an understudied process. We report here on the first clear observational evidence of a magnetic sheet emergence and characterise its development.
Methods: Full Stokes spectra from the Hinode spectropolarimeter were inverted with the Stokes Inversion based on Response functions (SIR) code to obtain solar atmospheric parameters such as temperature, line-of-sight velocities, and full magnetic field vector information.
Results: We analyse a magnetic flux emergence event observed in the quiet-Sun internetwork. After a large-scale appearance of linear polarisation, a magnetic sheet with horizontal magnetic flux density of up to 194 Mx cm-2 hovers in the low photosphere spanning a region of 2-3 arcsec. The magnetic field azimuth obtained through Stokes inversions clearly shows an organised structure of transversal magnetic flux density emerging. The granule below the magnetic flux sheet tears the structure apart leaving the emerged flux to form several magnetic loops at the edges of the granule.
Conclusions: A large amount of flux with strong horizontal magnetic fields surfaces through the interplay of buried magnetic flux and convective motions. The magnetic flux emerges within 10 minutes and we find a longitudinal magnetic flux at the foot points of the order of ∼1018 Mx. This is one to two orders of magnitude larger than what has been reported for small-scale magnetic loops. The convective flows feed the newly emerged flux into the pre-existing magnetic population on a granular scale.

Movie attached to Fig. 5 is available at https://www.aanda.org Title: Evolution of the flow field in decaying active regions. Transition from a moat flow to a supergranular flow Authors: Strecker, H.; Bello González, N. Bibcode: 2018A&A...620A.122S Altcode: 2018arXiv181101607S Context. Fully fledged sunspots are known to be surrounded by a radial outflow called the moat flow.
Aims: We investigate the evolution of the horizontal flow field around sunspots during their decay, that is, from fully fledged to naked spots, after they loose the penumbra, to the remnant region after the spot has fully dissolved.
Methods: We analysed the extension and horizontal velocity of the flow field around eight sunspots using SDO/HMI Doppler maps. By assuming a radially symmetrical flow field, the applied analysis method determines the radial dependence of the azimuthally averaged flow field. For comparison, we studied the flow in supergranules using the same technique.
Results: All investigated, fully fledged sunspots are surrounded by a flow field whose horizontal velocity profile decreases continuously from 881 m s-1 at 1.1 Mm off the spot boundary, down to 199 m s-1 at a mean distance of 11.9 Mm to that boundary, in agreement with other studies. Once the penumbra is fully dissolved, however, the velocity profile of the flow changes: The horizontal velocity increases with increasing distance to the spot boundary until a maximum value of about 398 m s-1 is reached. Then, the horizontal velocity decreases for farther distances to the spot boundary. In supergranules, the horizontal velocity increases with increasing distance to their centre up to a mean maximum velocity of 355 m s-1. For larger distances, the horizontal velocity decreases. We thus find that the velocity profile of naked sunspots resembles that of supergranular flows. The evolution of the flow field around individual sunspots is influenced by the way the sunspot decays and by the interplay with the surrounding flow areas.
Conclusions: Observations of the flow around eight decaying sunspots suggest that as long as penumbrae are present, sunspots with their moat cell are embedded in network cells. The disappearance of the penumbra (and consequently the moat flow) and the competing surrounding supergranular cells, both have a significant role in the evolution of the flow field: The moat cell transforms into a supergranule, which hosts the remaining naked spot.

The movies associated to Figs A.1-A.8 are available at https://www.aanda.org Title: Magnetic properties of a long-lived sunspot. Vertical magnetic field at the umbral boundary Authors: Schmassmann, M.; Schlichenmaier, R.; Bello González, N. Bibcode: 2018A&A...620A.104S Altcode: 2018arXiv181009358S Context. In a recent statistical study of sunspots in 79 active regions, the vertical magnetic field component Bver averaged along the umbral boundary is found to be independent of sunspot size. The authors of that study conclude that the absolute value of Bver at the umbral boundary is the same for all spots.
Aims: We investigate the temporal evolution of Bver averaged along the umbral boundary of one long-lived sunspot during its stable phase.
Methods: We analysed data from the HMI instrument on-board SDO. Contours of continuum intensity at Ic = 0.5Iqs, whereby Iqs refers to the average over the quiet sun areas, are used to extract the magnetic field along the umbral boundary. Projection effects due to different formation heights of the Fe I 617.3 nm line and continuum are taken into account. To avoid limb artefacts, the spot is only analysed for heliocentric angles smaller than 60°.
Results: During the first disc passage, NOAA AR 11591, Bver remains constant at 1693 G with a root-mean-square deviation of 15 G, whereas the magnetic field strength varies substantially (mean 2171 G, rms of 48 G) and shows a long term variation. Compensating for formation height has little influence on the mean value along each contour, but reduces the variations along the contour when away from disc centre, yielding a better match between the contours of Bver = 1693 G and Ic = 0.5Iqs.
Conclusions: During the disc passage of a stable sunspot, its umbral boundary can equivalently be defined by using the continuum intensity Ic or the vertical magnetic field component Bver. Contours of fixed magnetic field strength fail to outline the umbral boundary.

Movies associated with Figs. 3 and 5 are available at https://www.aanda.org 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: Chromospheric impact of an exploding solar granule Authors: Fischer, C. E.; Bello González, N.; Rezaei, R. Bibcode: 2017A&A...602L..12F Altcode: 2017arXiv170600770F Context. Observations of multi-wavelength and therefore height-dependent information following events throughout the solar atmosphere and unambiguously assigning a relation between these rapidly evolving layers are rare and difficult to obtain. Yet, they are crucial for our understanding of the physical processes that couple the different regimes in the solar atmosphere.
Aims: We characterize the exploding granule event with simultaneous observations of Hinode spectroplarimetric data in the solar photosphere and Hinode broadband Ca II H images combined with Interface Region Imaging Spectrograph (IRIS) slit spectra. We follow the evolution of an exploding granule and its connectivity throughout the atmosphere and analyze the dynamics of a magnetic element that has been affected by the abnormal granule.
Methods: In addition to magnetic flux maps we use a local correlation tracking method to infer the horizontal velocity flows in the photosphere and apply a wavelet analysis on several IRIS chromospheric emission features such as Mg II k2v and Mg II k3 to detect oscillatory phenomena indicating wave propagation.
Results: During the vigorous expansion of the abnormal granule we detect radially outward horizontal flows, causing, together with the horizontal flows from the surrounding granules, the magnetic elements in the bordering intergranular lanes to be squeezed and elongated. In reaction to the squeezing, we detect a chromospheric intensity and velocity oscillation pulse which we identify as an upward traveling hot shock front propagating clearly through the IRIS spectral line diagnostics of Mg II h&k.
Conclusions: Exploding granules can trigger upward-propagating shock fronts that dissipate in the chromosphere.

Movies associated to Figs. A.1 and A.2 are available in electronic form at http://www.aanda.org Title: High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region Authors: González Manrique, S. J.; Bello González, N.; Denker, C. Bibcode: 2017A&A...600A..38G Altcode: 2017arXiv170310140G Context. Emerging flux regions mark the first stage in the accumulation of magnetic flux eventually leading to pores, sunspots, and (complex) active regions. These flux regions are highly dynamic, show a variety of fine structure, and in many cases live only for a short time (less than a day) before dissolving quickly into the ubiquitous quiet-Sun magnetic field.
Aims: The purpose of this investigation is to characterize the temporal evolution of a minute emerging flux region, the associated photospheric and chromospheric flow fields, and the properties of the accompanying arch filament system. We aim to explore flux emergence and decay processes and investigate if they scale with structure size and magnetic flux contents.
Methods: This study is based on imaging spectroscopy with the Göttingen Fabry-Pérot Interferometer at the Vacuum Tower Telescope, Observatorio del Teide, Tenerife, Spain on 2008 August 7. Photospheric horizontal proper motions were measured with Local correlation tracking using broadband images restored with multi-object multi-frame blind deconvolution. Cloud model (CM) inversions of line scans in the strong chromospheric absorption Hαλ656.28 nm line yielded CM parameters (Doppler velocity, Doppler width, optical thickness, and source function), which describe the cool plasma contained in the arch filament system.
Results: The high-resolution observations cover the decay and convergence of two micro-pores with diameters of less than one arcsecond and provide decay rates for intensity and area. The photospheric horizontal flow speed is suppressed near the two micro-pores indicating that the magnetic field is already sufficiently strong to affect the convective energy transport. The micro-pores are accompanied by a small arch filament system as seen in Hα, where small-scale loops connect two regions with Hα line-core brightenings containing an emerging flux region with opposite polarities. The Doppler width, optical thickness, and source function reach the largest values near the Hα line-core brightenings. The chromospheric velocity of the cloud material is predominantly directed downwards near the footpoints of the loops with velocities of up to 12 km s-1, whereas loop tops show upward motions of about 3 km s-1. Some of the loops exhibit signs of twisting motions along the loop axis.
Conclusions: Micro-pores are the smallest magnetic field concentrations leaving a photometric signature in the photosphere. In the observed case, they are accompanied by a miniature arch filament system indicative of newly emerging flux in the form of Ω-loops. Flux emergence and decay take place on a time-scale of about two days, whereas the photometric decay of the micro-pores is much more rapid (a few hours), which is consistent with the incipient submergence of Ω-loops. Considering lifetime and evolution timescales, impact on the surrounding photospheric proper motions, and flow speed of the chromospheric plasma at the loop tops and footpoints, the results are representative for the smallest emerging flux regions still recognizable as such. Title: A distinct magnetic property of the inner penumbral boundary. II. Formation of a penumbra at the expense of a pore Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.; Rezaei, R. Bibcode: 2017A&A...597A..60J Altcode: 2016arXiv161201745J; 2016A&A...597A..60J Context. We recently presented evidence that stable umbra-penumbra boundaries are characterised by a distinct canonical value of the vertical component of the magnetic field, Bstablever. In order to trigger the formation of a penumbra, large inclinations in the magnetic field are necessary. In sunspots, the penumbra develops and establishes by colonising both umbral areas and granulation, that is, penumbral magneto-convection takes over in umbral regions with Bver<Bstablever, as well as in granular convective areas. Eventually, a stable umbra-penumbra boundary settles at Bstablever.
Aims: Here, we aim to study the development of a penumbra initiated at the boundary of a pore, where the penumbra colonises the entire pore ultimately.
Methods: We have used Hinode/SOT G-band images to study the evolution of the penumbra. Hinode/SOT spectropolarimetric data were used to infer the magnetic field properties in the studied region.
Results: The penumbra forms at the boundary of a pore located close to the polarity inversion line of NOAA 10960. As the penumbral bright grains protrude into the pore, the magnetic flux in the forming penumbra increases at the expense of the pore magnetic flux. Consequently, the pore disappears completely giving rise to an orphan penumbra. At all times, the vertical component of the magnetic field in the pore is smaller than Bstablever ≈ 1.8 kG.
Conclusions: Our findings are in an agreement with the need of Bstablever for establishing a stable umbra-penumbra boundary: while Bver in the pore is smaller than Bstablever, the protrusion of penumbral grains into the pore area is not blocked, a stable pore-penumbra boundary does not establish, and the pore is fully overtaken by the penumbral magneto-convective mode. This scenario could also be one of the mechanisms giving rise to orphan penumbrae.

The movie associated to Fig. 1 is available at http://www.aanda.org Title: Canonical Bver value on umbra/penumbra boundaries Authors: Jurcak, Jan; Bello González, Nazaret; Schlichenmaier, Rolf; Rezaei, Reza Bibcode: 2017psio.confE.112J Altcode: No abstract at ADS Title: Magnetic field reconstruction based on sunspot oscillations Authors: Löhner-Böttcher, J.; Bello González, N.; Schmidt, W. Bibcode: 2016AN....337.1040L Altcode: 2016arXiv160105925L The magnetic field of a sunspot guides magnetohydrodynamic waves toward higher atmospheric layers. In the upper photosphere and lower chromosphere, wave modes with periods longer than the acoustic cut-off period become evanescent. The cut-off period essentially changes due to the atmospheric properties, e.g., increases for larger zenith inclinations of the magnetic field. In this work, we aim at introducing a novel technique of reconstructing the magnetic field inclination on the basis of the dominating wave periods in the sunspot chromosphere and upper photosphere. On 2013 August 21, we observed an isolated, circular sunspot (NOAA11823) for 58 min in a purely spectroscopic multi-wavelength mode with the Interferometric Bidimensional Spectro-polarimeter (IBIS) at the Dunn Solar Telescope. By means of a wavelet power analysis, we retrieved the dominating wave periods and reconstructed the zenith inclinations in the chromosphere and upper photosphere. The results are in good agreement with the lower photospheric HMI magnetograms. The sunspot's magnetic field in the chromosphere inclines from almost vertical (0°) in the umbra to around 60° in the outer penumbra. With increasing altitude in the sunspot atmosphere, the magnetic field of the penumbra becomes less inclined. We conclude that the reconstruction of the magnetic field topology on the basis of sunspot oscillations yields consistent and conclusive results. The technique opens up a new possibility to infer the magnetic field inclination in the solar chromosphere. 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: 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: 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: Quiet Sun Magnetic Field Evolution Observed with Hinode SOT and IRIS Authors: Fischer, C. E.; Bello González, N.; Rezaei, R. Bibcode: 2016ASPC..504...19F Altcode: We study two physical processes that can be commonly observed in the quiet sun and involve temporal evolution of the magnetic field: convective collapse and flux cancellation. The aim is to investigate the response of the chromosphere to the magnetic events in the photosphere below. We have calibrated and aligned a co-spatial and co-temporal 3 hour quiet sun time series observed with the Hinode SOT (Solar Optical Telescope) and the IRIS (Interface Region Imaging Spectrograph) satellites. Convective collapse events are identified in the photosphere by inverting spectropolarimetric data and searching for magnetic field intensification, preceded by a downflow and accompanied by the development of a bright point in Ca II H images. We find a corresponding downflow in the low chromosphere as deduced from IRIS Mg II k and h spectra and an ensuing oscillatory velocity pattern. We use magnetograms in the high photosphere to study pairs of magnetic elements involved in flux cancellation and find an increase in the entire quasi-continuum of the IRIS Mg II k and h spectrum following the flux cancellation process and indicating a substantial energy deposit into the lower atmosphere. 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: Signatures of running penumbral waves in sunspot photospheres Authors: Löhner-Böttcher, J.; Bello González, N. Bibcode: 2015A&A...580A..53L Altcode: 2015arXiv150309106L Context. The highly dynamic atmosphere above sunspots exhibits a wealth of magnetohydrodynamic waves. Recent studies suggest a coupled nature of the most prominent phenomena: umbral flashes and running penumbral waves (RPWs).
Aims: From an observational point of view, we perform a height-dependent study of RPWs, compare their wave characteristics, and aim to track down these so far only chromospherically observed phenomena to photospheric layers to prove the upward propagating field-guided nature of RPWs.
Methods: We analyze a time series (58 min) of multiwavelength observations of an isolated circular sunspot (NOAA11823) taken at high spatial and temporal resolution in spectroscopic mode with the Interferometric BIdimensional Spectro-polarimeter (IBIS/DST). By means of a multilayer intensity sampling, velocity comparisons, wavelet power analysis, and sectorial studies of time slices, we retrieve the power distribution, characteristic periodicities, and propagation characteristics of sunspot waves at photospheric and chromospheric levels.
Results: Signatures of RPWs are found at photospheric layers. Those continuous oscillations occur preferably at periods between 4-6 min starting at the inner penumbral boundary. The photospheric oscillations all have a slightly delayed, more defined chromospheric counterpart with larger relative velocities, which are linked to preceding umbral flash events. In all of the layers, the power of RPWs follows a filamentary fine-structure and shows a typical ring-shaped power distribution increasing in radius for larger wave periods. The analysis of time slices reveals apparent horizontal velocities for RPWs at photospheric layers of ≈51 km s-1, which decrease to ≈37 km s-1 at chromospheric heights.
Conclusions: The observations strongly support the scenario of RPWs being upward propagating slow-mode waves guided by the magnetic field lines. Clear evidence for RPWs at photospheric layers is given. The inverse proportionality of the peak period and cut-off period on the field inclination is supported by the observations. The larger apparent horizontal velocities at photospheric heights hint at the more horizontal penumbral field inclination. Title: A distinct magnetic property of the inner penumbral boundary. Formation of a stable umbra-penumbra boundary in a sunspot Authors: Jurčák, J.; Bello González, N.; Schlichenmaier, R.; Rezaei, R. Bibcode: 2015A&A...580L...1J Altcode: Context. A sunspot emanates from a growing pore or protospot. In order to trigger the formation of a penumbra, large inclinations at the outskirts of the protospot are necessary. The penumbra develops and establishes by colonising both umbral areas and granulation. Evidence for a unique stable boundary value for the vertical component of the magnetic field strength, Bstablever, was found along the umbra-penumbra boundary of developed sunspots.
Aims: We study the changing value of Bver as the penumbra forms and as it reaches a stable state. We compare this with the corresponding value in fully developed penumbrae.
Methods: We use broadband G-band images and spectropolarimetric GFPI/VTT data to study the evolution of and the vertical component of the magnetic field on a forming umbra-penumbra boundary. For comparison with stable sunspots, we also analyse the two maps observed by Hinode/SP on the same spot after the penumbra formed.
Results: The vertical component of the magnetic field, Bver, at the umbra-penumbra boundary increases during penumbra formation owing to the incursion of the penumbra into umbral areas. After 2.5 h, the penumbra reaches a stable state as shown by the GFPI data. At this stable stage, the simultaneous Hinode/SP observations show a Bver value comparable to that of umbra-penumbra boundaries of fully fledged sunspots.
Conclusions: We confirm that the umbra-penumbra boundary, traditionally defined by an intensity threshold, is also characterised by a distinct canonical magnetic property, namely by Bverstable. During the penumbra formation process, the inner penumbra extends into regions where the umbra previously prevailed. Hence, in areas where Bver<Bstablever, the magneto-convection mode operating in the umbra turns into a penumbral mode. Eventually, the inner penumbra boundary settles at Bverstable, which hints toward the role of Bverstable as inhibitor of the penumbral mode of magneto-convection. Title: A distinct magnetic property of the inner penumbral boundary Authors: Jurčák, Jan; Bello Gonzalez, Nazaret; Schlichenmaier, Rolf; Rezaei, Reza Bibcode: 2015arXiv150608574J Altcode: A sunspot emanates from a growing pore or protospot. In order to trigger the formation of a penumbra, large inclinations at the outskirts of the protospot are necessary. The penumbra develops and establishes by colonising both umbral areas and granulation. Evidence for a unique stable boundary value for the vertical component of the magnetic field strength, $B^{\rm stable}_{\rm ver}$, was found along the umbra-penumbra boundary of developed sunspots. We use broadband G-band images and spectropolarimetric GFPI/VTT data to study the evolution of and the vertical component of the magnetic field on a forming umbra-penumbra boundary. For comparison with stable sunspots, we also analyse the two maps observed by Hinode/SP on the same spot after the penumbra formed. The vertical component of the magnetic field, $B_{\rm ver}$, at the umbra-penumbra boundary increases during penumbra formation owing to the incursion of the penumbra into umbral areas. After 2.5 hours, the penumbra reaches a stable state as shown by the GFPI data. At this stable stage, the simultaneous Hinode/SP observations show a $B_{\rm ver}$ value comparable to that of umbra-penumbra boundaries of fully fledged sunspots. We confirm that the umbra-penumbra boundary, traditionally defined by an intensity threshold, is also characterised by a distinct canonical magnetic property, namely by $B^{\rm stable}_{\rm ver}$. During the penumbra formation process, the inner penumbra extends into regions where the umbra previously prevailed. Hence, in areas where $B_{\rm ver} < B^{\rm stable}_{\rm ver}$, the magneto-convection mode operating in the umbra turns into a penumbral mode. Eventually, the inner penumbra boundary settles at $B^{\rm stable}_{\rm ver}$, which hints toward the role of $B_{\rm ver}^{\rm stable}$ as inhibitor of the penumbral mode of magneto-convection. Title: Evolution of magnetic field inclination in a forming penumbra Authors: Jurčák, Jan; Bello González, Nazaret; Schlichenmaier, Rolf; Rezaei, Reza Bibcode: 2014PASJ...66S...3J Altcode: 2014PASJ..tmp...93J As a sunspot penumbra forms, the magnetic field vector at the outer boundary of the protospot undergoes a transformation. We study the changes of the magnetic field vector at this boundary as a penumbral segment forms. We analyze a set of spectropolarimetric maps covering 2 hr during the formation of a sunspot in NOAA 11024. The data were recorded with the GFPI instrument attached to the German VTT. We observe a stationary umbra/quiet Sun boundary, where the magnetic field becomes more horizontal with time. The magnetic field inclination increases by 5°, reaching a maximum value of about 59°. The maximum inclination coincides with the onset of filament formation. In time, the penumbra filaments become longer and the penumbral bright grains protrude into the umbra, where the magnetic field is stronger and more vertical. Consequently, we observe a decrease in the magnetic field inclination at the boundary as the penumbra grows. In summary, in order to initiate the formation of the penumbra, the magnetic field at the umbral (protospot) boundary becomes more inclined. As the penumbra grows, the umbra/penumbra boundary migrates inwards, and at this boundary the magnetic field turns more vertical again, while it remains inclined in the outer penumbra. Title: First successful deployment of the ZIMPOL-3 system at the GREGOR telescope Authors: Ramelli, Renzo; Gisler, Daniel; Bianda, Michele; Bello González, Nazaret; Berdyugina, Svetlana; Soltau, Dirk Bibcode: 2014SPIE.9147E..3GR Altcode: Since several years the Zurich Imaging polarimeter (ZIMPOL) system is successfully used as a high sensitivity polarimeter. The polarimeter system, which is mainly based on a fast modulator and a special demodulating camera with a masked CCD, has been continuously improved. The third version of the system (ZIMPOL-3) is routinely used at IRSOL, Locarno. The fast modulation allows to "freeze" intensity variations due to seeing, and to achieve a polarimetric sensitivity below 10-5 if the photon statistics is large enough. In October 2013 the ZIMPOL system has been brought and installed for the first time at the GREGOR telescope in Tenerife for a spectropolarimetric observing campaign. There, the system configuration took advantage from the calibration unit installed at the primary focus of the GREGOR telescope, while the analyzer was inserted in the optical path just before the spectrograph slit after several folding mirrors. This setup has been tested successfully by the authors for the first time in this occasion. Title: On the structure and dynamics of Ellerman bombs. Detailed study of three events and modelling of Hα Authors: Bello González, N.; Danilovic, S.; Kneer, F. Bibcode: 2013A&A...557A.102B Altcode:
Aims: We study the structure and dynamics of three Ellerman bombs (EBs) observed in an evolving active region.
Methods: The active region NOAA 11271 was observed with the Vacuum Tower Telescope at Observatorio del Teide/Tenerife on August 18, 2011. We used the two-dimensional Triple Etalon SOlar Spectrometer (TESOS) to obtain time sequences of the active region and of EBs in Hα at a cadence of 15 s. Simultaneously, we obtained full Stokes profiles with the Tenerife Infrared Polarimeter (TIP II) in the two magnetically sensitive Fe i infrared lines (IR) at 1.56 μ, scanning spatial sections of the area with cadences of 28-46 s. The Hα data were reconstructed with speckle methods to study the evolution of the atmospheric stratification. Two methods were used to extract magnetic field information from the IR Stokes profiles: 1) fitting of the (Q,U,V) profiles by Gaussians; and 2) applying the Milne-Eddington approximation, assuming two separate magnetic structures in the resolution element and fitting by trial and error some profiles from the EB areas. Data from SDO-HMI and -AIA were also used. We performed two-dimensional (2D) non-LTE radiative transfer calculations of Hα in parameterised models of EBs.
Results: The three EBs studied in detail occurred in a complex active region near sunspots. They were very bright with a factor of 1.5-2.8 brighter than the nearby area. They lived for 1/2 h and longer. They were related to broadband faculae, but the latter were not the brightest features in the field of view. The EBs occurred in magnetic field configurations with opposite polarity close together. One EB was located at the outskirts of a penumbra of a complex sunspot and showed repeated "flaring" in SDO-AIA data. Another was close to a strong field patch and moved into this during the end of its lifetime. The third EB showed clear changes of field structure during the time it was observed. We obtained from the 2D modelling that heating and increase in Hα opacity are likely to occur at heights of 300-800 km. Line shifts and asymmetries can well be reproduced by velocities at these heights and also at much larger heights.
Conclusions: The three EBs occurred at sites with magnetic fields of opposite polarity, which were likely the cause of the Hα brightening upon reconnection. Title: The project of installing a ZIMPOL_3 polarimeter at GREGOR in Tenerife Authors: Bianda, M.; Ramelli, R.; Stenflo, J.; Berdyugina, S.; Gisler, D.; Defilippis, I.; Bello González, N. Bibcode: 2013MmSAI..84..413B Altcode: A project of collaboration between Kiepenheuer Institut für Sonnenphysik, KIS, and Istituto Ricerche Solari Locarno, IRSOL, includes the installation of a ZIMPOL_3 high resolution polarimeter at the 1.5 meter aperture solar telescope GREGOR in Tenerife. Important scientific topics are expected to be investigated, in particular in the case of events showing faint amplitude polarization signatures like scattering polarization effects, and the Hanle effect. This project has also a technical importance, this combination can be used as test bench for future polarimeters to be installed on the new generation solar telescopes. 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: 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: Comparing Simultaneous Measurements of two High-Resolution Imaging Spectropolarimeters: The `Göttingen' FPI@VTT and CRISP@SST Authors: Bello González, N.; Bellot Rubio, L. R.; Ortiz, A.; Rezaei, R.; Rouppe van der Voort, L.; Schlichenmaier, R. Bibcode: 2012ASPC..463..251B Altcode: 2012arXiv1204.1023B In July 2009, the leading spot of the active region NOAA11024 was observed simultaneously and independently with the ‘Göttingen’ FPI at VTT and CRISP at SST, i.e., at two different sites, telescopes, instruments and using different spectral lines. The data processing and data analysis have been carried out independently with different techniques. Maps of physical parameters retrieved from 2D spectro-polarimetric data observed with ‘Göttingen’ FPI and CRISP show an impressive agreement. In addition, the ‘Göttingen’ FPI maps also exhibit a notable resemblance with simultaneous TIP (spectrographic) observations. The consistency in the results demonstrates the excellent capabilities of these observing facilities. Besides, it confirms the solar origin of the detected signals and the reliability of FPI-based spectro-polarimeters. 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: Shear and vortex motions in a forming sunspot . Twist relaxation in magnetic flux ropes Authors: Bello González, N.; Kneer, F.; Schlichenmaier, R. Bibcode: 2012A&A...538A..62B Altcode:
Aims: We measure proper motions of fine structures in a forming sunspot to infer information about the dynamics of flux emergence at the sub-photospheric level.
Methods: The active region NOAA 11024 was observed with the Vacuum Tower Telescope at Observatorio del Teide/Tenerife over several days in July 2009. Here, we concentrate on a two-hour sequence taken on July 4, when the leading spot was at an early stage of its evolution. Speckle reconstructions from Ca ii K images and polarimetric data in Fe i λ6173 allow us to study proper motions of umbral fine structures.
Results: We detect three prominent features: (1) A light bridge, divided by a dark lane along its axis, shows proper motions in opposing directions on its sides, with velocities of ~100-500 m s-1. The flows are seen in both the Ca ii K and the broadband time sequences. (2) Umbral dots in one umbral region outline a vortex with speeds of up to 550 m s-1. The direction of the motion of the umbral dots is different from that in the light bridge. (3) At one rim of the umbra, the fine structure of the magnetic field moves horizontally with typical velocities of 250-300 m s-1, prior to the formation of the penumbra.
Conclusions: We report on shear and vortex motions in a forming sunspot and interpret them as tracers of twist relaxation in magnetic flux ropes. We suggest that the forming sunspot contains detached magnetic flux ropes that emerge at the surface with different amounts of twist. As they merge to form a sunspot, they untwist giving rise to the observed shear and vortex motions. Title: The formation of sunspot penumbra. Magnetic field properties Authors: Rezaei, R.; Bello González, N.; Schlichenmaier, R. Bibcode: 2012A&A...537A..19R Altcode: 2011arXiv1111.3189R
Aims: We study the magnetic flux emergence and formation of a sunspot penumbra in the active region NOAA 11024.
Methods: We simultaneously observed the Stokes parameters of the photospheric iron lines at 1089.6 nm with the TIP and 617.3 nm with the GFPI spectropolarimeters along with broad-band images using G-band and Ca ii K filters at the German VTT. The photospheric magnetic field vector was reconstructed from an inversion of the measured Stokes profiles. Using the AZAM code, we converted the inclination from line-of-sight (LOS) to the local reference frame (LRF).
Results: Individual filaments are resolved in maps of magnetic parameters. The formation of the penumbra is intimately related to the inclined magnetic field. No penumbra forms in areas with strong magnetic field strength and small inclination. Within 4.5 h observing time, the LRF magnetic flux of the penumbra increases from 9.7 × 1020 to 18.2 × 1020 Mx, while the magnetic flux of the umbra remains constant at ~3.8 × 1020 Mx. Magnetic flux in the immediate surroundings is incorporated into the spot, and new flux is supplied via small flux patches (SFPs), which on average have a flux of 2-3 × 1018 Mx. The spot's flux increase rate of 4.2 × 1016 Mx s-1 corresponds to the merging of one SFP per minute. We also find that, during the formation of the spot penumbra, a) the maximum magnetic field strength of the umbra does not change; b) the magnetic neutral line keeps the same position relative to the umbra; c) the new flux arrives on the emergence side of the spot while the penumbra forms on the opposite side; d) the average LRF inclination of the light bridges decreases from 50° to 37°; and e) as the penumbra develops, the mean magnetic field strength at the spot border decreases from 1.0 to 0.8 kG.
Conclusions: The SFPs associated with elongated granules are the building blocks of structure formation in active regions. During the sunspot formation, their contribution is comparable to the coalescence of pores. Besides a set of critical parameters for the magnetic field, a quiet environment in the surroundings is important for penumbral formation. As remnants of trapped granulation between merging pores, the light bridges are found to play a crucial role in the formation process. They seem to channel the magnetic flux through the spot during its formation. Light bridges are also the locations where the first penumbral filaments form. Title: On acoustic and gravity waves in the solar photosphere and their energy transport Authors: Kneer, F.; Bello González, N. Bibcode: 2011A&A...532A.111K Altcode:
Aims: We study acoustic and atmospheric gravity waves in the quiet Sun to estimate their energy transport to the chromosphere.
Methods: A two-dimensional time sequence from quiet Sun disc centre was analysed with simultaneous spectroscopic observations in Fe i 5576 Å and Fe i 5434 Å (both with Landé factor g = 0). We calculated response functions of the velocities for the line minimum shifts and atmospheric transmissions of waves for the two lines. For this, NLTE line formation in granular and intergranular model atmospheres from numerical simulations were performed. For the interpretation of the observed waves and for the estimates of energy fluxes, we assumed adiabatic propagation of plane waves in an isothermal model atmosphere. Fourier analyses of intensity and velocity fluctuations were carried out. They yield power, phase, and coherence as functions of frequency ν (from temporal Fourier transforms) and in the kh - ν plane (from three-dimensional transforms). The power spectra, together with the mass densities at velocity formation heights, give then the energy fluxes.
Results: The rms velocities found here in the acoustic and gravity wave domains are lower by a factor ~1.5 as in earlier work. We therefore admit a factor of 2 for an upward correction of the estimated fluxes. For acoustic waves we find: 1) upward propagating waves are present on the Sun with frequencies up to 14-15 mHz (periods U ≈ 70 s); 2) the approximation of plane adiabatic waves in an isothermal atmosphere appears adequate for estimating the energy fluxes; 3) the acoustic energy fluxes are in the same range as found in our earlier work from ground-based, two-dimensional spectroscopy, 1500-3100 W m-2 at an atmospheric height of ~380 km and 1300-2700 W m-2 at 570 km. The energy flux carried by gravity waves is difficult to determine. We find: 1) phase and coherence spectra between continuum and velocity fluctuations show that convective overshoot and gravity waves are superimposed. We account for the convective flows using these coherence spectra. 2) At low frequencies, the vertical wavelength Λz can be short (≪300 km), yielding large corrections for atmospheric transmissions (factors > 100). We thus exclude from the flux estimates waves with |kz| > 20 Mm-1 and with vertical group velocities υgr,z < 0.3 km s-1. They are likely to be strongly reduced in amplitude by radiative damping. 3) With these caveats, the energy fluxes carried by gravity waves are found in the range of 4000 - 8200 W m-2 at 380 km and 700-1400 W m-2 at 570 km. Gravity waves thus also contribute to the energy transport into the chromosphere. 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: SUNRISE: Instrument, Mission, Data, and First Results Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.; Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.; Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.; Franz, M.; Schmidt, W.; Title, A. M. Bibcode: 2010ApJ...723L.127S Altcode: 2010arXiv1008.3460S The SUNRISE balloon-borne solar observatory consists of a 1 m aperture Gregory telescope, a UV filter imager, an imaging vector polarimeter, an image stabilization system, and further infrastructure. The first science flight of SUNRISE yielded high-quality data that revealed the structure, dynamics, and evolution of solar convection, oscillations, and magnetic fields at a resolution of around 100 km in the quiet Sun. After a brief description of instruments and data, the first qualitative results are presented. In contrast to earlier observations, we clearly see granulation at 214 nm. Images in Ca II H display narrow, short-lived dark intergranular lanes between the bright edges of granules. The very small-scale, mixed-polarity internetwork fields are found to be highly dynamic. A significant increase in detectable magnetic flux is found after phase-diversity-related reconstruction of polarization maps, indicating that the polarities are mixed right down to the spatial resolution limit and probably beyond. Title: Detection of Vortex Tubes in Solar Granulation from Observations with SUNRISE Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.; Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt, W.; Barthol, P.; Gandorfer, A. Bibcode: 2010ApJ...723L.180S Altcode: 2010arXiv1009.4723S We have investigated a time series of continuum intensity maps and corresponding Dopplergrams of granulation in a very quiet solar region at the disk center, recorded with the Imaging Magnetograph eXperiment (IMaX) on board the balloon-borne solar observatory SUNRISE. We find that granules frequently show substructure in the form of lanes composed of a leading bright rim and a trailing dark edge, which move together from the boundary of a granule into the granule itself. We find strikingly similar events in synthesized intensity maps from an ab initio numerical simulation of solar surface convection. From cross sections through the computational domain of the simulation, we conclude that these granular lanes are the visible signature of (horizontally oriented) vortex tubes. The characteristic optical appearance of vortex tubes at the solar surface is explained. We propose that the observed vortex tubes may represent only the large-scale end of a hierarchy of vortex tubes existing near the solar surface. Title: Bright Points in the Quiet Sun as Observed in the Visible and Near-UV by the Balloon-borne Observatory SUNRISE Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.; Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz, M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta, J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W. Bibcode: 2010ApJ...723L.169R Altcode: 2010arXiv1009.1693R Bright points (BPs) are manifestations of small magnetic elements in the solar photosphere. Their brightness contrast not only gives insight into the thermal state of the photosphere (and chromosphere) in magnetic elements, but also plays an important role in modulating the solar total and spectral irradiance. Here, we report on simultaneous high-resolution imaging and spectropolarimetric observations of BPs using SUNRISE balloon-borne observatory data of the quiet Sun at the disk center. BP contrasts have been measured between 214 nm and 525 nm, including the first measurements at wavelengths below 388 nm. The histograms of the BP peak brightness show a clear trend toward broader contrast distributions and higher mean contrasts at shorter wavelengths. At 214 nm, we observe a peak brightness of up to five times the mean quiet-Sun value, the highest BP contrast so far observed. All BPs are associated with a magnetic signal, although in a number of cases it is surprisingly weak. Most of the BPs show only weak downflows, the mean value being 240 m s-1, but some display strong down- or upflows reaching a few km s-1. Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet, J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer, A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M. Bibcode: 2010ApJ...723L.134B Altcode: 2010arXiv1009.4795B We study the energy flux carried by acoustic waves excited by convective motions at sub-photospheric levels. The analysis of high-resolution spectropolarimetric data taken with IMaX/SUNRISE provides a total energy flux of ~6400-7700 W m-2 at a height of ~250 km in the 5.2-10 mHz range, i.e., at least twice the largest energy flux found in previous works. Our estimate lies within a factor of two of the energy flux needed to balance radiative losses from the chromosphere according to the estimates of Anderson & Athay and revives interest in acoustic waves for transporting energy to the chromosphere. The acoustic flux is mainly found in the intergranular lanes but also in small rapidly evolving granules and at the bright borders, forming dark dots and lanes of splitting granules. Title: Acoustic waves in the solar atmosphere at high spatial resolution. II. Measurement in the Fe I 5434 Å line Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O.; Shchukina, N. Bibcode: 2010A&A...522A..31B Altcode:
Aims: We investigate the energy supply of the solar chromosphere by acoustic waves.
Methods: A time sequence with high spatial and temporal resolution from the quiet Sun disc centre in Fe i 5434 Å (Landé factor g = 0) is analysed. We used models from a numerical simulation of granular convection and apply NLTE spectral line transfer to determine the height of formation. For estimates of acoustic energy flux, we adopted wave propagation with inclinations of the wave vector with respect to the vertical of 0°, 30°, and 45°. For a granular and an intergranular model, the transmissions of the atmosphere to high-frequency waves were determined for the three inclination angles. Wavelet and Fourier analyses were performed and the resulting power spectra were corrected for atmospheric transmission.
Results: We find waves with periods down to ~40 s. They occur intermittently in space and time. The velocity signal is formed at a height of 500 km in the granular model and at 620 km in the intergranule. At periods shorter than the acoustic cutoff (~190 s), ~40% of the waves occur above granules and ~60% above intergranules. By adopting vertical propagation, we estimate total fluxes above granules of 2750-3360 W m-2, and of 910-1 000 W m-2 above intergranules. The weighted average is 1730-2 060 W m-2. The estimates of the total fluxes increase by 15% when inclined wave propagation of 45° is assumed. Title: Surface Waves in Solar Granulation Observed with SUNRISE Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet, V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.; Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.; Knölker, M. Bibcode: 2010ApJ...723L.175R Altcode: 2010arXiv1009.4790R Solar oscillations are expected to be excited by turbulent flows in the intergranular lanes near the solar surface. Time series recorded by the IMaX instrument on board the SUNRISE observatory reveal solar oscillations at high spatial resolution, which allow the study of the properties of oscillations with short wavelengths. We analyze two time series with synchronous recordings of Doppler velocity and continuum intensity images with durations of 32 minutes and 23 minutes, respectively, recorded close to the disk center of the Sun to study the propagation and excitation of solar acoustic oscillations. In the Doppler velocity data, both the standing acoustic waves and the short-lived, high-degree running waves are visible. The standing waves are visible as temporary enhancements of the amplitudes of the large-scale velocity field due to the stochastic superposition of the acoustic waves. We focus on the high-degree small-scale waves by suitable filtering in the Fourier domain. Investigating the propagation and excitation of f- and p 1-modes with wavenumbers k>1.4 Mm-1, we also find that exploding granules contribute to the excitation of solar p-modes in addition to the contribution of intergranular lanes. Title: The GREGOR Fabry-Perot interferometer: a new instrument for high-resolution solar observations Authors: Denker, Carsten; Balthasar, Horst; Hofmann, Axel; Bello González, Nazaret; Volkmer, Reiner Bibcode: 2010SPIE.7735E..6MD Altcode: 2010SPIE.7735E.217D The GREGOR Fabry-Ṕerot Interferometer (GFPI) is one of the first-light instruments of the 1.5-meter GREGOR solar telescope currently being commissioned at Observatorio del Teide (OT), Tenerife, Spain. A spectral resolution of R ~ 250, 000 over the wavelength range from 530-860 nm can be achieved using a tunable dual etalon system. A high spectral resolving power is needed to extract physical parameters (e.g., temperature, plasma velocity and the magnetic field vector) from inversions of photospheric and chromospheric spectral lines. The GFPI is outfitted with a polarimeter, which accurately measures the full Stokes vector. Precision polarimetry is facilitated by a calibration unit in the immediate vicinity of GREGOR's secondary focus. The GFPI operates close to the diffraction limit of GREGOR, thus providing access to fine structures as small as 60 km on the solar surface. The field-of-view (FOV) of 52" × 40" is sufficiently large to cover significant portions of active regions. Large-format, high-cadence CCD detectors are an integral part of the instrument to ensure that scans of spectral lines can be obtained in time spans corresponding to the evolution time scale of solar phenomena such as granulation, evolving magnetic fields or dynamic chromospheric features. Besides describing the technical features of the GFPI and providing a status report on commissioning the instrument, we will use two-dimensional spectropolarimetric data obtained with the Vacuum Tower Telescope (VTT) at OT to illustrate GFPI's science capabilities. Title: The role of emerging bipoles in the formation of a sunspot penumbra Authors: Schlichenmaier, R.; Bello González, N.; Rezaei, R.; Waldmann, T. A. Bibcode: 2010AN....331..563S Altcode: 2010arXiv1003.1313S The generation of magnetic flux in the solar interior and its transport from the convection zone into the photosphere, the chromosphere, and the corona will be in the focus of solar physics research for the next decades. With 4 m class telescopes, one plans to measure essential processes of radiative magneto-hydrodynamics that are needed to understand the nature of solar magnetic fields. One key-ingredient to understand the behavior of solar magnetic field is the process of flux emergence into the solar photosphere, and how the magnetic flux reorganizes to form the magnetic phenomena of active regions like sunspots and pores. Here, we present a spectropolarimetric and imaging data set from a region of emerging magnetic flux, in which a proto-spot without penumbra forms a penumbra. During the formation of the penumbra the area and the magnetic flux of the spot increases. First results of our data analysis demonstrate that the additional magnetic flux, which contributes to the increasing area of the penumbra, is supplied by the region of emerging magnetic flux. We observe emerging bipoles that are aligned such that the spot polarity is closer to the spot. As an emerging bipole separates, the pole of the spot polarity migrates towards the spot, and finally merges with it. We speculate that this is a fundamental process, which makes the sunspot accumulate magnetic flux. As more and more flux is accumulated a penumbra forms and transforms the proto-spot into a full-fledged sunspot. Title: The formation of a sunspot penumbra Authors: Schlichenmaier, R.; Rezaei, R.; Bello González, N.; Waldmann, T. A. Bibcode: 2010A&A...512L...1S Altcode: Context. The formation of a penumbra is crucial for our understanding of solar magnetism, but it has not been observed in detail.
Aims: We aim to enhance our knowledge of how a sunspot penumbra forms and how sunspots grow in size.
Methods: We present a data set of the active region NOAA 11024 acquired at the German VTT with speckle-reconstructed images in the G-band and Ca ii K. The data set includes spectropolarimetric profiles from GFPI in Fe i 617.3 nm and TIP in Fe i 1089.6 nm.
Results: On 2009 July 4, at 08:30 UT, a leading spot without penumbra and pores of opposite polarity were present in the active region. For the next 4:40 h, we observed the formation of a penumbra in the leading spot at a cadence of 5 images per second. We produced speckle reconstructed images of 0.3 arcsec spatial resolution or better, interrupted by one large gap of 35 min and a few more small gaps of about 10 min. The leading spot initially has a size of 230 arcsec2 with only a few penumbral filaments and then grows to a size of 360 arcsec2. The penumbra forms in segments, and it takes about 4 h until it encircles half of the umbra, on the side opposite the following polarity. On the side towards the following polarity, elongated granules mark a region of magnetic flux emergence.
Conclusions: This ongoing emergence appears to prevent a steady penumbra from forming on this side. While the penumbra forms, the umbral area is constant; i.e., the increase in the total spot area is caused exclusively by the growth of the penumbra. From this we conclude that the umbra has reached an upper size limit and that any new magnetic flux that joins the spot is linked to the process of penumbral formation.

Movies are only available in electronic form at http://www.aanda.org Title: On the energy flux in acoustic waves in the solar atmosphere . Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O. Bibcode: 2010MmSAI..81..757B Altcode: The energy supply for the radiative losses of the quiet solar chromosphere is studied. Time sequences from quiet Sun disc centre were obtained with the ``Göttingen'' Fabry-Pérot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the non-magnetic Fe I 5576 Å line. The data were reconstructed with speckle methods. The velocities as measured at the line minimum were subjected to Fourier and wavelet analysis. The energy fluxes were corrected for the transmission of the solar atmosphere. We find an energy flux of ∼ 3 000 W m-2 at a height of h=250 km. Approximately 2/3 of it is carried by waves in the 5-10 mHz range, and 1/3 in the 10-20 mHz band. The waves occur predominantly above inter-granular areas. We speculate that the acoustic flux in waves with periods shorter than the acoustic cutoff period (U≈190 s) can contribute to the basal heating of the solar chromosphere, in addition to atmospheric gravity waves. Title: Acoustic waves in the solar atmosphere at high spatial resolution Authors: Bello González, N.; Flores Soriano, M.; Kneer, F.; Okunev, O. Bibcode: 2009A&A...508..941B Altcode: Aims. The energy supply for the radiative losses of the quiet solar chromosphere is studied. On the basis of high spatial resolution data, we investigate the amount of energy flux carried by acoustic waves in the solar photosphere.
Methods: Time sequences from quiet Sun disc centre were obtained with the “Göttingen” Fabry-Perot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the non-magnetic Fe i 5576 Å line. The data were reconstructed with speckle methods. The velocity and intensity fluctuations at line minimum were subjected to Fourier and wavelet analyses. The energy fluxes at frequencies higher than the acoustic cutoff frequency (period U ≈ 190 s) were corrected for the transmission of the solar atmosphere, which reduces the signal from short-period waves.
Results: Both Fourier and wavelet analysis give an amount of energy flux of ~3000 W m-2 at a height h = 250 km. Approximately 2/3 of it is carried by waves in the 5-10 mHz range, and 1/3 in the 10-20 mHz band. Extrapolation of the flux spectra gives an energy flux of 230-400 W m-2 at frequencies ν > 20 mHz. We find that the waves occur predominantly above inter-granular areas.
Conclusions: We conclude that the acoustic flux in waves with periods shorter than the acoustic cutoff period can contribute to the basal heating of the solar chromosphere, in addition to the atmospheric gravity waves found recently. Title: Full-Stokes Polarimetry with Speckle Techniques Authors: Bello González, N.; Kneer, F.; Okunev, O. Bibcode: 2009ASPC..405..407B Altcode: The new full-Stokes polarimeter implemented in the 2D `Göttingen' Fabry-Perot spectrometer, based on ferroelectric liquid crystals, yields magnetograms with minimised seeing induced crosstalk. A spatial resolution of 0."30--0."35 is achieved after applying speckle methods. The detection limit for the magnetic field strength is 16 G (≡ 3σ), yielding a polarimetric sensitivity of 7--8×1015 Mx. Examples of intensity maps, Dopplergrams and magnetograms from quiet Sun are discussed. 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: Dynamics of small-scale magnetic fields on the Sun: observations and numerical simulations Authors: Bello González, N.; Yelles Chaouche, L.; Okunev, O.; Kneer, F. Bibcode: 2009A&A...494.1091B Altcode: Context: Small-scale magnetic fields play an important role in the structure and the dynamics of the solar atmosphere.
Aims: This study aims at revealing the evolution of magnetic fields, together with granular convection in the quiet Sun by means of observations with high spatial, spectral, and temporal resolution and of numerical MHD simulations.
Methods: Time sequences from quiet Sun disc centre were obtained with the upgraded “Göttingen” Fabry-Perot spectropolarimeter at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, in the Fe I 6173 Å line. The data were reconstructed with speckle methods. For comparison with the observations, numerical simulations of granular magnetoconvection were carried out with the MURaM code. The intensities and Stokes vectors emerging from the simulation box were degraded in wavelength, spatial co-ordinates, and noise to the quality of the observations.
Results: The noise in the observed magnetograms from the centre-of-gravity method is σ_B≈2 G, yielding a polarimetric sensitivity of 3 × 1015 Mx, at a cadence of 23 s with 0.33 arcsec spatial resolution in a field of view of ∼33 arcsec× 25 arcsec. Many of the observed V profiles in network and internetwork (IN) areas exhibit strong asymmetries that indicate strong magnetoconvection. The temporal evolutions of IN structures and of a bright point (BP), as seen in broadband and line-minimum images, in Dopplergrams, and in magnetograms, are presented. The magnetic field structure in the numerical MHD simulations is even more complex than seen in the observations. Correspondingly, the emergent Stokes profiles are often very abnormal. The degradation yields a reduction of the intrinsic field strength to the “observed” one by a factor 4-5. The spectral resolution of the spectrometer is adequate, yet the limitation in spatial resolution and by noise filtering swamps the details seen in the non-degraded simulations. A BP was not found in the simulations, presumably because BP's are not so common and the simulated box is quiet small: only 6 Mm wide in both horizontal directions.
Conclusions: The combination of high-resolution observations with numerical simulation is a highly valuable means for studying small-scale magnetic fields on the Sun. Two-dimensional, low-noise data with spectral resolution as good as achieved here and with spatial resolution of 0.1 arcsec and better are needed to better understand this important part of the solar magnetism.

A movie is only available in electronic form at http://www.aanda.org Title: Small-scale magnetic field dynamics on the Sun at high spatial and temporal resolution Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2008A&A...490L..23B Altcode: Aims: We present examples of the time evolution of phenomena occurring in the quiet Sun photosphere as seen from observations of high spatial and spectral resolution and with a time cadence of 23 s.
Methods: A time sequence of about 5 min has been taken with the Göttingen Fabry-Perot spectropolarimeter at the VTT in the Fe I 6173 Å line. The data were reconstructed with speckle methods.
Results: With a polarimetric sensitivity of 2 × 10-3~Ic (σ_B=2 G), the formation of a bright point as seen from broadband and line-minimum intensities, as well as in magnetograms and Dopplergrams can be traced in detail. Other events, like a stable mixed-polarity configuration in the intergranules and the appearance of magnetic signature above granules in both dark and bright areas are presented. Title: Evolution of Small-scale Magnetodynamics on the Sun with High Spatial and Temporal Resolution Authors: Bello González, N.; Kneer, F. Bibcode: 2008ESPM...12..2.6B Altcode: For the detection and study of small-scale magnetic fields on the Sun, observations with both high spatial resolution and high polarimetric sensitivity are required. The combination formed by the upgraded Göttingen FPI spectrometer (spectral resolution of 25mÅ, at 617.3nm), full Stokes polarimeter, Adaptive Optics (KAOS) and speckle reconstruction techniques, provide broadband images of 0.25 arcsec spatial resolution and magnetograms of 0.33 arcsec, with minimised seeing induced signals yielding a polarimetric sensitivity of ~0.002 Ic. A description of the optical system as well as results from the analysis of intensity maps, Dopplergrams and magnetograms from quiet and active regions on the Sun will be presented. The data were taken in the FeI 6173Å. We select few examples from the huge variety of magnetodynamic processes seen in the observations, e.g. the fast evolution of a bright point in broadband and line minimum intensity, in magnetograms, and in Dopplergrams is shown. Further examples indicate convective collapse, magnetic field advection, and magnetic field diffusion. Title: High-resolution Spectropolarimetry with the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife: History and Success of the Göttingen Programme Authors: Kneer, F.; Bello Gonzalez, N. Bibcode: 2008ESPM...12.2.30K Altcode: The efforts of the Göttingen solar physics group on high spatial resolution and 2D spectroscopy started in 1986. First results were obtained with speckle broadband imaging (de Boer 1992) and with 2D spectroscopy by means of one Fabry-Perot etalon (FPI) and a Universal Birefringent Filter (UBF). 2D Stokes V polarimetry followed soon. The UBF was replaced by a 2nd FPI which allowed short exposures also in the narrow-band channel of the spectrometer. Thus 2D spectropolari- metry could be combined with speckle reconstruction. The ``Göttingen FPI'' has been upgraded in 2005 for high efficiency and in 2007 for full Stokes polarimetry and good spectral resolution. It has become a fast and versatile instrument that has been, and will be, operated sucessfully for many scientific programmes on the atmospheric dynamics of the Sun. 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: Fast events and waves in an active region of the Sun observed in Hα with high spatial resolution Authors: Sánchez-Andrade Nuño, B.; Bello González, N.; Blanco Rodríguez, J.; Kneer, F.; Puschmann, K. G. Bibcode: 2008A&A...486..577S Altcode: Context: We study the chromosphere of an active region of the Sun in the Hα line.
Aims: The development of new instrumentation and new methods of data analysis allows to scrutinize the dynamics of the solar chromosphere with high spatial, spectral, and temporal resolution. The observations we present shed light on some magneto-dynamic processes occurring above an active region in the chromosphere.
Methods: We took a time series of 55 min in Hα from AR 10875 at θ≈36°. We used the “Göttingen” Fabry-Perot spectrometer at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife, to obtain two-dimensional spectrograms in Hα. Adaptive optics and image reconstruction yielded a spatial resolution better than 0.5 arcsec throughout the time sequence. From the wealth of structures, we selected areas of interest to study further, in detail, some ongoing processes.
Results: A small straight surge developed aside of a pore with upward phase speed of 100 km s-1 and line-of-sight (LOS) velocity of 15 km s-1. The surge retreated rapidly with LOS velocity of 45 km s-1 at its mouth. It underwent a rebound and fell back again. Two sympathetic mini-flares were observed that lasted only approximately 40 s, but showed strong Hα emission. We found magnetoacoustic waves in long fibrils as mainly short wave trains, short packets or pulses, i.e., solitary waves consisting of small (1´´-2´´) blobs. They start at either end of the fibrils and travel with phase speeds of 12-14 km s-1, i.e., close to the tube speed and approximately the sound velocity for sufficiently large magnetic field strengths. Some waves speed up to reach velocities of the order of 30 km s-1. This is much lower than the expected Alfvén velocity of ≥200 km s-1 for reasonable magnetic field strengths and mass densities. We suggest that slow waves are not purely longitudinal, but possess gas velocities perpendicular to the direction of propagation of few km s-1. Also, fast waves travel along sinuous lines suggesting entangled magnetic fields. They spread out along the direction of propagation in the course of their evolution and often vanish. We discuss the implications. Title: Narrow-band full Stokes polarimetry of small structures on the Sun with speckle methods Authors: Bello González, N.; Kneer, F. Bibcode: 2008A&A...480..265B Altcode: Aims:For the detection and the study of small-scale magnetic fields on the Sun, it is important to obtain observations with both high spatial resolution and high polarimetric sensitivity.
Methods: A second narrow-band etalon and a full Stokes polarimeter, based on ferroelectric liquid crystals, were implemented in the two-dimensional “Göttingen” Fabry-Perot spectrometer/polarimeter at the Vacuum Tower Telescope, Observatorio del Teide/Tenerife. First observations with the Fe I 6173 Å line and their data analysis with speckle methods are described.
Results: The new polarimeter yields magnetograms of a field of view of 31 arcsec×52 arcsec with minimised seeing induced signals and without spurious signals as from the use of beam-splitting calcites. The achieved spatial and temporal resolution are 0.30-0.35 arcsec and 36 s, respectively. With a detection limit for the field strength of 16 G (\cor3σ), a polarimetric sensitivity of 7-8×1015 Mx is obtained. Examples of intensity maps, Dopplergrams, and magnetograms from quiet and active regions on the Sun are discussed. Some of the results on solar magnetism are on 1) a pore with small-scale structure where we find a region with very low temperature gradient, 2) polar faculae with strong magnetic field signals and weaker signals in other areas surrounding them, and 3) small-scale inter-network magnetic fields with area fillings in the resolution elements of the order of 0.15. Title: Temporal evolution of intensity, velocity and magnetic field of sunspots at high spatial resolution Authors: Bello González, N.; Kneer, F.; Puschmann, K. G. Bibcode: 2007msfa.conf..217B Altcode: We present results of sunspot observations obtained in April 2006 with the new "Göttingen" Fabry-Perot spectrometer. Thanks to the large field of view (77"x58") of the new optical setup it has been possible to perform 2D-spectropolarimetric observations of a small sunspot and ist surroundings at a heliocentric angle [Theta] ~ 40Å. A long time series of about one hour has been taken scanning along the magnetic Fe I 6173 Å and the non-magnetic Fe I 5576 Å spectral lines quasi-simultaneously. Hence, with the help of image reconstruction techniques, the temporal evolution of the sunspot fine-structure in intensity as well as in velocity and magnetic field is analysed at high spatial resolution. Title: Spectropolarimetry of sunspot penumbrae Authors: Bello Gonzalez, Nazaret Bibcode: 2006PhDT.......345B Altcode: No abstract at ADS Title: Synthesis of Stokes Profiles from a Two Component Penumbral Model Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2005ESASP.600E..56B Altcode: 2005ESPM...11...56B; 2005dysu.confE..56B No abstract at ADS Title: Analysis of Polarimetric Sunspot Data from Tesos/vtt/tenerife Authors: Valdivielso Casas, L.; Bello González, N.; Puschmann, K. G.; Sánchez-Andrade Nuño, B.; Kneer, F. Bibcode: 2005ESASP.596E..67V Altcode: 2005ccmf.confE..67V No abstract at ADS Title: Study of Asymmetries of Stokes Profiles from High Spatial Resolution Spectropolarimetry Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2005ESASP.596E..50B Altcode: 2005ccmf.confE..50B No abstract at ADS Title: Polarimetry of sunspot penumbrae with high spatial resolution Authors: Bello González, N.; Okunev, O. V.; Domínguez Cerdeña, I.; Kneer, F.; Puschmann, K. G. Bibcode: 2005A&A...434..317B Altcode: We present two-dimensional high-spatial-resolution spectropolarimetric observations of sunspot penumbrae. They were obtained in April 2002 and May 2003 with the "Göttingen" Fabry-Pérot spectrometer at the Vacuum Tower Telescope at the Observatorio del Teide (Tenerife). Speckle methods were applied for image reconstruction which resulted in a spatial resolution of 0.5 arcsec in the magnetograms of the penumbrae. We analysed Stokes I and V profiles of the Fe II 6149 Å line, which exhibits no instrumental Stokes Q/U→ V crosstalk, and of the Fe I line pair at 6302 Å. The main results are the following: 1) on scales larger than 0.5 arcsec, the intensity pattern of penumbrae stays the same in the continuum and core images of the 6301.5 Å line, which stem from 0 km and 300 km (above τ_5=1), respectively. Yet at scales of 0.5 arcsec and smaller the pattern in the two spectral features is clearly different. 2) On the limb side of sunspots the Evershed flow is carried by dark filaments and on the centre side by bright features and their somewhat weakened tails. We explain this with a picture in which the velocity of hot rising gas is best seen on the centre side, while on the limb side the horizontal outward and possibly downward flows are seen when the gas has cooled down. 3) The un-combed structure of the magnetic field is confirmed. On the limb side, the more horizontal fields coincide with dark fibrils or with diffuse intensity structures. Generally, the more horizontal fields are located at the positions of strong outflows. 4) Strong line-of-sight components of the magnetic fields are not found in bright filaments but in dark structures, somewhat displaced from the darkest parts. Their positions do not coincide with those of the strongest velocity fields. In general, our results are compatible with the picture of low lying flow channels coincident with the horizontal magnetic field, or possibly emerging and diving down into sub-photospheric layers, like a "sea serpent". Some further dynamic phenomena are discussed, which demonstrate the richness of processes in penumbrae, and reveal unexpected properties. Title: Spectropolarimetry in a sunspot penumbra at high spatial resolution Authors: Bello González, N.; Okunev, O.; Kneer, F. Bibcode: 2005ASSL..320..183B Altcode: 2005smp..conf..183B We present results from polarimetric data on sunspot penumbrae obtained with the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife, using the `Göttingen' Fabry-Pérot Interferometer. Speckle image reconstruction has been performed giving us a spatial resolution of 0.6''. The observations were taken in the Fe II 6149.2 Å line which, given its particular Zeeman splitting, has no instrumental (Q,U) to V crosstalk and provides us measurements of I and V Stokes profiles to analyse velocities and magnetic fields in penumbrae. Title: Polarimetry in sunspot penumbrae at high spatial resolution. Authors: Bello Gonzalez, N.; Okunev, O.; Dominguez Cerdena, I.; Kneer, F. Bibcode: 2004ANS...325...79B Altcode: 2004ANS...325..P03B; 2004ANS...325a..79B No abstract at ADS Title: Velocity and Magnetic Fields in Sunspot Penumbrae at Hight Spatial and Spectral Resolution Authors: Bello González, Nazaret; Kneer, Franz Bibcode: 2003ANS...324...28B Altcode: 2003ANS...324..D03B No abstract at ADS