Author name code: puschmann ADS astronomy entries on 2022-09-14 author:"Puschmann, Klaus G." ------------------------------------------------------------------------ Title: Horizontal motions in sunspot penumbrae Authors: Sobotka, Michal; Puschmann, Klaus G. Bibcode: 2022A&A...662A..13S Altcode: 2022arXiv220503171S Context. A model of penumbral filaments represented by magnetoconvective cells was derived recently from spectropolarimetric observations. This model resolves many of the inconsistencies found in the relations between intensity, magnetic, and velocity patterns in sunspot penumbrae.
Aims: High-resolution observations of horizontal motions in the penumbra are needed to complement the concept of penumbrae obtained from spectropolarimetry. Time series of intensity images of a large sunspot in AR 10634 acquired with the Swedish Solar Telescope in the G band and red continuum are analysed. The two simultaneous time series last six hours and five minutes.
Methods: Horizontal motions of penumbral grains (PGs), structures in dark bodies of filaments, the outer penumbral border, and G-band bright points are measured in time slices that cover the whole width of the penumbra and the neighbouring granulation. The spatial and temporal resolutions are 90 km and 20.1 s, respectively.
Results: In the inner penumbra, PGs move towards the umbra (inwards) with a mean speed of −0.7 km s−1. The direction of motion changes from inwards to outwards at approximately 60% of the penumbral width, and the mean speed increases gradually in the outer penumbra, approaching 0.5 km s−1. This speed is also typical of an expansion of the penumbra-granulation border during periods that typically last one hour and are followed by a fast contraction. The majority of the G-band bright points moves away from the sunspot, with a typical speed of 0.6 km s−1. High outward speeds, 3.6 km s−1 on average, are observed in dark bodies of penumbral filaments.
Conclusions: According to the model of penumbral filaments, it is suggested that the speeds detected in the dark bodies of filaments are associated with the Evershed flow and that the opposite directions of PG motions in the inner and outer penumbrae may be explained by the interaction of rising plasma in filament heads with a surrounding, differently inclined magnetic field.

Movies associated to Fig. 1 are available at https://www.aanda.org Title: Magnetic Flux Density in 3D MHD Simulations and Observations Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G. Bibcode: 2019ASPC..526..191B Altcode: We compare the polarization signals induced in three-dimensional (3D) magneto-hydrodynamical (MHD) simulations by the Zeeman effect in the presence of photospheric magnetic fields to those in observations at disc centre. We consider quantities determined from Stokes vector profiles of observations of photospheric spectral lines in the visible and near-infrared, and in corresponding synthetic spectra obtained from numerical 3D MHD simulations with an average magnetic flux density of 20-200 G. We match the spatial resolution of observations by degrading the spectra of the simulations. We find that the total unsigned vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet Sun internetwork. A value of ∼30 G best agrees with all observations we employed. Title: Remote sensing optical instrumentation for enhanced space weather monitoring from the L1 and L5 Lagrange points Authors: Kraft, S.; Puschmann, K. G.; Luntama, J. P. Bibcode: 2017SPIE10562E..0FK Altcode: As part of the Space Situational Awareness Programme (SSA), ESA has initiated the assessment of two missions currently foreseen to be implemented to enable enhanced space weather monitoring. These missions utilize the positioning of satellites at the Lagrangian L1 and L5 points. These Phase 0 or Pre-Phase A mission studies are about to be completed and will thereby have soon passed the Mission Definition Review. Phase A studies are planned to start in 2017. The space weather monitoring system currently considers four remote sensing optical instruments and several in-situ instruments to analyse the Sun and the solar wind conditions, in order to provide early warnings of increased solar activity and to identify and mitigate potential threats to society and ground, airborne and space based infrastructure. The suggested optical instruments take heritage from ESA and NASA science missions like SOHO, STEREO and Solar Orbiter, but the instruments are foreseen to be optimized for operational space weather monitoring purposes with high reliability and robustness demands. The instruments are required to provide high quality measurements particularly during severe space weather events. The program intends to utilize the results of the on-going ESA instrument prototyping and technology development activities, and to initiate pre-developments of the operational space weather instruments to ensure the required maturity before the mission implementation. Title: The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center Authors: Beck, C.; Fabbian, D.; Rezaei, R.; Puschmann, K. G. Bibcode: 2017ApJ...842...37B Altcode: 2017arXiv170506812B Before using three-dimensional (3D) magnetohydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. The amount of magnetic flux in the solar photosphere also constrains any possible heating in the outer solar atmosphere through magnetic reconnection. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112, and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SpectroPolarimeter (SP), the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow Spectrograph (POLIS), and the GREGOR Fabry-Pèrot Interferometer (GFPI), respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet-Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS, and GFPI observations. Title: Spectroscopy at the Solar Limb: II. Are Spicules Heated to Coronal Temperatures? Authors: Beck, C.; Rezaei, R.; Puschmann, K. G.; Fabbian, D. Bibcode: 2016SoPh..291.2281B Altcode: 2016arXiv160606132B; 2016SoPh..tmp..132B Spicules of the so-called type II were suggested to be relevant for coronal heating because of their ubiquity on the solar surface and their eventual extension into the corona. We investigate whether solar spicules are heated to transition-region or coronal temperatures and reach coronal heights (≫6 Mm) using multiwavelength observations of limb spicules in different chromospheric spectral lines (Ca II H, Hε , Hα , Ca II IR at 854.2 nm, He I at 1083 nm) taken with slit spectrographs and imaging spectrometers. We determine the line width of spectrally resolved line profiles in individual spicules and throughout the field of view, and estimate the maximal height that different types of off-limb features reach. We derive estimates of the kinetic temperature and the non-thermal velocity from the line width of spectral lines from different chemical elements. We find that most regular, i.e. thin and elongated, spicules reach a height of at most about 6 Mm above the solar limb. The majority of features found at larger heights are irregularly shaped with a significantly larger lateral extension, of up to a few Mm, than spicules. Both individual and average line profiles in all spectral lines show a decrease in their line width with height above the limb with very few exceptions. The kinetic temperature and the non-thermal velocity decrease with height above the limb. We find no indications that the spicules in our data reach coronal heights or transition-region or coronal temperatures. Title: Spicules and their on-disk counterparts, the main driver for solar chromospheric heating? Authors: Puschmann, Klaus Gerhard Bibcode: 2016arXiv160205185P Altcode: The question how the outer solar atmosphere is heated from solar photospheric temperatures of about 5800K up to solar chromospheric and coronal temperatures of about 20.000K and millions of degrees respectively, remained without any satisfying answer for centuries. On 4 May 2005, I recorded several time series of Halpha line scans with the GREGOR Fabry-Perot Interferometer, still deployed at the German Vacuum Tower Telescope (VTT), for different solar limb and on-disk positions as well as for quiet sun at solar disk center. The spatially and temporally highly resolved time series of Halpha line parameters reveal the entire and detailed complexity as well as the overwhelming dynamics of spicules covering the entire solar disk, thus apparently confirming spicules as the potential driver of chromospheric heating for both the Sun and sun-like stars, with an expected mass flux larger than 100 times that of the solar wind. Spicules seem to be the result of the interaction of the highly dynamic photospheric quiet-sun or active-region small-scale magnetic field, which is dominated by convective processes and is predominantly located in intergranular lanes and at meso- or supergranular scales. Title: The GREGOR Fabry Perot Interferometer (GFPI), Technical Innovations and Results achieved in 2013 Authors: Puschmann, Klaus Gerhard Bibcode: 2016arXiv160205783P Altcode: This paper shall provide a summary of not yet published technical innovations to the GREGOR Fabry-Perot Interferometer (GFPI) at the 1.5m GREGOR Solar Telescope (Europe's largest solar telescope) that I implemented in 2013 as the Instrument Scientist of the GFPI. It also represents an overview of important and not yet published observational results that I achieved with the GFPI in 2013. The results and achievements can be considered a milestone in the further development, scientific verification and final acceptance of this instrument. The instrument is now in operation and employed by the international scientific community. Title: The association between sunspot magnetic fields and superpenumbral fibrils Authors: Louis, R. E.; Balthasar, H.; Kuckein, C.; Gömöry, P.; Puschmann, K. G.; Denker, C. Bibcode: 2014AN....335..161L Altcode: 2013arXiv1312.1879L Spectropolarimetric observations of a sunspot were carried out with the Tenerife Infrared Polarimeter at Observatorio del Teide, Tenerife, Spain. Maps of the physical parameters were obtained from an inversion of the Stokes profiles observed in the infrared Fe I line at 15 648 Å. The regular sunspot consisted of a light bridge which separated the two umbral cores of the same polarity. One of the arms of the light bridge formed an extension of a penumbral filament which comprised weak and highly inclined magnetic fields. In addition, the Stokes V profiles in this filament had an opposite sign as the sunspot and some resembled Stokes Q or U. This penumbral filament terminated abruptly into another at the edge of the sunspot, where the latter was relatively vertical by about 30o. Chromospheric H\alpha and He II 304 Åfiltergrams revealed three superpenumbral fibrils on the limb-side of the sunspot, in which one fibril extended into the sunspot and was oriented along the highly inclined penumbral counterpart of the light bridge. An intense, elongated brightening was observed along this fibril that was co-spatial with the intersecting penumbral filaments in the photosphere. Our results suggest that the disruption in the sunspot magnetic field at the location of the light bridge could be the source of reconnection that led to the intense chromospheric brightening and facilitated the supply of cool material in maintaining the overlying superpenumbral fibrils. Title: Sunspot splitting triggering an eruptive flare Authors: Louis, Rohan E.; Puschmann, Klaus G.; Kliem, Bernhard; Balthasar, Horst; Denker, Carsten Bibcode: 2014A&A...562A.110L Altcode: 2013arXiv1311.5054L
Aims: We investigate how the splitting of the leading sunspot and associated flux emergence and cancellation in active region NOAA 11515 caused an eruptive M5.6 flare on 2012 July 2.
Methods: Continuum intensity, line-of-sight magnetogram, and dopplergram data of the Helioseismic and Magnetic Imager were employed to analyse the photospheric evolution. Filtergrams in Hα and He I 10830 Å of the Chromospheric Telescope at the Observatorio del Teide, Tenerife, track the evolution of the flare. The corresponding coronal conditions were derived from 171 Å and 304 Å images of the Atmospheric Imaging Assembly. Local correlation tracking was utilized to determine shear flows.
Results: Emerging flux formed a neutral line ahead of the leading sunspot and new satellite spots. The sunspot splitting caused a long-lasting flow towards this neutral line, where a filament formed. Further flux emergence, partly of mixed polarity, as well as episodes of flux cancellation occurred repeatedly at the neutral line. Following a nearby C-class precursor flare with signs of interaction with the filament, the filament erupted nearly simultaneously with the onset of the M5.6 flare and evolved into a coronal mass ejection. The sunspot stretched without forming a light bridge, splitting unusually fast (within about a day, complete ≈6 h after the eruption) in two nearly equal parts. The front part separated strongly from the active region to approach the neighbouring active region where all its coronal magnetic connections were rooted. It also rotated rapidly (by 4.9° h-1) and caused significant shear flows at its edge.
Conclusions: The eruption resulted from a complex sequence of processes in the (sub-)photosphere and corona. The persistent flows towards the neutral line likely caused the formation of a flux rope that held the filament. These flows, their associated flux cancellation, the emerging flux, and the precursor flare all contributed to the destabilization of the flux rope. We interpret the sunspot splitting as the separation of two flux bundles differently rooted in the convection zone and only temporarily joined in the spot. This explains the rotation as the continued rise of the separating flux, and it implies that at least this part of the sunspot was still connected to its roots deep in the convection zone.

Movie available in electronic form at http://www.aanda.org Title: Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations (Corrigendum) Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.; Rezaei, R. Bibcode: 2013A&A...559C...1B Altcode: No abstract at ADS Title: Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations Authors: Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.; Rezaei, R. Bibcode: 2013A&A...557A.109B Altcode: 2013arXiv1306.6093B Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to check that no excessive thermodynamic fluctuations arise as a consequence of the partially incomplete treatment of radiative transfer causing radiative damping that is too modest.
Aims: We investigate the realism of the thermodynamics in recent state-of-the-art 3D convection simulations of the solar atmosphere carried out with the Stagger code.
Methods: We compared the characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565 nm) and one Si i line at 1082.7 nm in solar disc-centre observations of different spatial resolution with spectra synthesized from 3D convection simulations. The observations were taken with ground-based (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI), POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all at the Vacuum Tower Telescope on Tenerife) and space-based instruments (Hinode/Spectropolarimeter). We degraded the synthetic spectra to the spatial resolution of the observations, based on the distribution of the continuum intensity Ic. We estimated the spectral degradation to be applied to the simulation results by comparing atlas spectra with averaged observed spectra. In addition to deriving a set of line parameters directly from the intensity profiles, we used the SIR (Stokes Inversion based on Response functions) code to invert the spectra.
Results: The spatial degradation kernels yield a similar generic spatial stray-light contamination of about 30% for all instruments. The spectral stray light inside the different spectrometers is found to be between 2% and 20%. Most of the line parameters from the observational data are matched by the degraded HD simulation spectra. The inversions predict a macroturbulent velocity vmac below 10 m s-1 for the HD simulation spectra at full spatial resolution, whereas they yield vmac ≲ 1000 m s-1 at a spatial resolution of 0.″3. The temperature fluctuations in the inversion of the degraded HD simulation spectra do not exceed those from the observational data (of the order of 100-200 K rms for -2 ⪉ log τ500 nm ⪉ -0.5). The comparison of line parameters in spatially averaged profiles with the averaged values of line parameters in spatially resolved profiles indicates a significant change in (average) line properties on a spatial scale between 0.″13 and 0.″3.
Conclusions: Up to a spatial resolution of 0.″3 (GFPI spectra), we find no indications of excessive thermodynamic fluctuations in the 3D HD simulation. To definitely confirm that simulations without spatial degradation contain fully realistic thermodynamic fluctuations requires observations at even higher spatial resolution (i.e. <0.″13).

Appendices A and B are available in electronic form at http://www.aanda.org Title: GREGOR Fabry-Pérot interferometer and its companion the blue imaging solar spectrometer Authors: Puschmann, Klaus G.; Denker, Carsten; Balthasar, Horst; Louis, Rohan E.; Popow, Emil; Woche, Manfred; Beck, Christian; Seelemann, Thomas; Volkmer, Reiner Bibcode: 2013OptEn..52h1606P Altcode: 2013arXiv1302.7157P The GREGOR Fabry-Pérot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-m GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI allows fast narrow-band imaging and postfactum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic sun and its magnetic field at spatial scales down to ∼50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectrometric and spectropolarimetric observations between 530-860 nm and 580-660 nm, respectively, and possesses a theoretical spectral resolution of R≈250,000. Large-format, high-cadence charged coupled device detectors with sophisticated computer hard- and software enable the scanning of spectral lines in time-spans equivalent to the evolution time of solar features. The field-of-view (FOV) of 50″×38″ covers a significant fraction of the typical area of active regions in the spectroscopic mode. In case of Stokes-vector spectropolarimetry, the FOV reduces to 25″×38″. The main characteristics of the GFPI including advanced and automated calibration and observing procedures are presented. Improvements in the optical design of the instrument are discussed and first observational results are shown. Finally, the first concrete ideas for the integration of a second FPI, the blue imaging solar spectrometer, are laid out, which will explore the blue spectral region below 530 nm. Title: Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop Authors: Gömöry, P.; Balthasar, H.; Puschmann, K. G. Bibcode: 2013A&A...556A...7G Altcode: 2013arXiv1306.3393G
Aims: We investigate the temporal evolution of magnetic flux emergence in the quiet-Sun atmosphere close to disk center.
Methods: We combined high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 Å channel to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere.
Results: We find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appeared first in the MDI magnetograms in form of an asymmetric bipolar element, i.e., the patch with negative polarity is roughly twice as weak as the corresponding patch with opposite polarity. The average values of magnetic flux and magnetic flux densities reached 1.6 × 1018 Mx, - 8.5 × 1017 Mx, and 55 Mx cm-2, -30 Mx cm-2, respectively. The spatial distance between the opposite polarity patches of the emerged feature increased from about 2.″5 to 5.″0 during the lifetime of the loop, which was 36 min. A more precise lifetime-estimate of the feature was not possible because of a gap in the temporal sequence of the MDI magnetograms. The chromospheric response to the emerged magnetic dipole occurred ~9 min later than in the photospheric magnetograms. It consisted of a quasi-periodic sequence of time-localized brightenings visible in the 1216 Å TRACE channel for ~14 min that were co-spatial with the axis connecting the two patches of opposite magnetic polarity.
Conclusions: We identify the observed event as a small-scale magnetic loop emerging at photospheric layers that subsequently rose to the chromosphere. We discuss the possibility that the fluctuations detected in the chromospheric emission probably reflect magnetic-field oscillations which propagate to the chromosphere in the form of waves. Title: Can spicules be detected at disc centre in broad-band Ca ii H filter imaging data? Authors: Beck, C.; Rezaei, R.; Puschmann, K. G. Bibcode: 2013A&A...556A.127B Altcode: 2013arXiv1306.5199B Context. Recently, a possible identification of type II spicules in broad-band (full-width at half-maximum (FWHM) of ~0.3 nm) filter imaging data in Ca ii H on the solar disc was reported.
Aims: We estimate the formation height range contributing to broad-band and narrow-band filter imaging data in Ca ii H to investigate whether spicules can be detected in such observations at the centre of the solar disc.
Methods: We applied spectral filters of FWHMs from 0.03 nm to 1 nm to observed Ca ii H line profiles to simulate Ca imaging data. We used observations across the limb to estimate the relative intensity contributions of off-limb and on-disc structures. We compared the synthetic Ca filter imaging data with intensity maps of Ca spectra at different wavelengths and temperature maps at different optical depths obtained by an inversion of these spectra. In addition, we determined the intensity response function for the wavelengths covered by the filters of different FWHM.
Results: In broad-band (FWHM = 0.3 nm) Ca imaging data, the intensity emitted off the solar limb is about 5% of the intensity at disc centre. For a 0.3-nm-wide filter centred at the Ca ii H line core, up to about one third of the off-limb intensity comes from emission in Hɛ. On the disc, only about 10 to 15% of the intensity transmitted through a broad-band filter comes from the line-core region between the H1 minima (396.824 to 396.874 nm). No traces of elongated fibrillar structures are visible in the synthetic Ca broad-band imaging data at disc centre, in contrast to the line-core images of the Ca spectra. The intensity-weighted response function for a 0.3-nm-wide filter centred at the Ca ii H line core peaks at about log τ ~ -2 (z ~ 200 km). Relative contributions from atmospheric layers above 800 km are about 10%. The inversion results suggest that the slightly enhanced emission around the photospheric magnetic network in broad-band Ca imaging data is caused by a thermal canopy at a height of about 600 km.
Conclusions: Broad-band (~0.3 nm) Ca ii H imaging data do not trace upper chromospheric structures such as spicules in observations at the solar disc because of the too small relative contribution of the line core to the total wavelength-integrated filter intensity. The faint haze around network elements in broad-band Ca imaging observations at disc centre presumably traces thermal canopies in the vicinity of magnetic flux concentrations instead.

Appendix A is available in electronic form at http://www.aanda.org Title: The energy of waves in the photosphere and lower chromosphere. IV. Inversion results of Ca II H spectra Authors: Beck, C.; Rezaei, R.; Puschmann, K. G. Bibcode: 2013A&A...553A..73B Altcode: 2013arXiv1302.6936B Context. Most semi-empirical static one-dimensional (1D) models of the solar atmosphere in the magnetically quiet Sun (QS) predict an increase in temperature at chromospheric layers. Numerical simulations of the solar chromosphere with a variable degree of sophistication, i.e. from 1D to three-dimensional (3D) simulations; assuming local thermal equilibrium (LTE) or non-LTE (NLTE), on the other hand, only yielded an increase in the brightness temperature without any stationary increase in the gas temperature.
Aims: We investigate the thermal structure in the solar chromosphere as derived from an LTE inversion of observed Ca ii H spectra in QS and active regions (ARs).
Methods: We applied an inversion strategy based on the SIR (Stokes inversion by response functions) code to Ca ii H spectra to obtain 1D temperature stratifications. We investigated the temperature stratifications on differences between magnetic and field-free regions in the QS, and on differences between QS and ARs. We determined the energy content of individual calcium bright grains (BGs) as specific candidates of chromospheric heating events. We compared observed with synthetic NLTE spectra to estimate the significance of the LTE inversion results.
Results: The fluctuations of observed intensities yield a variable temperature structure with spatio-temporal rms fluctuations below 100 K in the photosphere and between 200 and 300 K in the QS chromosphere. The average temperature stratification in the QS does not exhibit a clear chromospheric temperature rise, unlike the AR case. We find a characteristic energy content of about 7 × 1018 J for BGs that repeat with a cadence of about 160 s. The precursors of BGs have a vertical extent of about 200 km and a horizontal extent of about 1 Mm. The comparison of observed with synthetic NLTE profiles partly confirms the results of the LTE inversion that the solar chromosphere in the QS oscillates between an atmosphere in radiative equilibrium and one with a moderate chromospheric temperature rise. Two-dimensional x - z temperature maps exhibit nearly horizontal canopy-like structures with an extent of a few Mm around photospheric magnetic field concentrations at a height of about 600 km.
Conclusions: The large difference between QS regions and ARs and the better match of AR and NLTE reference spectra suggest that magnetic heating processes are more important than commonly assumed. The temperature fluctuations in QS derived by the LTE inversion do not suffice on average to maintain a stationary chromospheric temperature rise. The spatially and vertically resolved information on the temperature structure allows one to investigate in detail the topology and evolution of the thermal structure in the lower solar atmosphere.

Appendix A is available in electronic form at http://www.aanda.org Title: Formation of a penumbra in a decaying sunspot Authors: Louis, R. E.; Mathew, S. K.; Puschmann, K. G.; Beck, C.; Balthasar, H. Bibcode: 2013A&A...552L...7L Altcode: 2013arXiv1303.3599L Context. Penumbrae are an important characteristic of sunspots, whose formation is intricately related to the nature of sub-photospheric magnetic fields.
Aims: We study the formation of a penumbra in a decaying sunspot and compare its properties with those seen during the development of a proto-spot.
Methods: High-resolution spectropolarimetric observations of active region NOAA 11283 were obtained from the spectro-polarimeter on board Hinode. These were complemented with full-disk filtergrams of continuum intensity, line-of-sight magnetograms, and dopplergrams from the Helioseismic and Magnetic Imager at high cadence.
Results: The formation of a penumbra in the decaying sunspot occurs after the coalescence of the sunspot with a magnetic fragment/pore, which initially formed in the quiet Sun close to an emerging flux region. At first, a smaller set of penumbral filaments develop near the location of the merger with very bright penumbral grains with intensities of 1.2 IQS, upflows of 4 km s-1, and a lifetime of 10 h. During the decay of these filaments, a larger segment of a penumbra forms at the location of the coalescence. These new filaments are characterized by nearly supersonic downflows of 6.5 km s-1 that change to a regular Evershed flow nearly 3 h later.
Conclusions: The coalescence of the pore with the decaying sunspot provided sufficient magnetic flux for the penumbra to form in the sunspot. The emerging flux region could have played a decisive role in this process because the formation occurred at the location of the merger and not on the opposite side of the sunspot.

An animation of the HMI data is available in electronic form at http://www.aanda.org Title: Properties of a Decaying Sunspot Authors: Balthasar, H.; Beck, C.; Gömöry, P.; Muglach, K.; Puschmann, K. G.; Shimizu, T.; Verma, M. Bibcode: 2013CEAB...37..435B Altcode: 2013arXiv1301.1562B A small decaying sunspot was observed with the Vacuum Tower Telescope (VTT) on Tenerife and the Japanese Hinode satellite. We obtained full Stokes scans in several wavelengths covering different heights in the solar atmosphere. Imaging time series from Hinode and the Solar Dynamics Observatory (SDO) complete our data sets. The spot is surrounded by a moat flow, which persists also on that side of the spot where the penumbra already had disappeared. Close to the spot, we find a chromospheric location with downflows of more than 10 km s^{-1} without photospheric counterpart. The height dependence of the vertical component of the magnetic field strength is determined in two different ways that yielded different results in previous investigations. Such a difference still exists in our present data, but it is not as pronounced as in the past. Title: The energy of waves in the photosphere and lower chromosphere. III. Inversion setup for Ca II H spectra in local thermal equilibrium Authors: Beck, C.; Rezaei, R.; Puschmann, K. G. Bibcode: 2013A&A...549A..24B Altcode: 2012arXiv1209.6194B Context. The Ca II H line is one of the strongest lines in the solar spectrum, and it provides continuous information on the solar atmosphere from the photosphere to the lower chromosphere.
Aims: We describe an inversion approach that reproduces observed Ca II H spectra by assuming local thermal equilibrium (LTE).
Methods: We developed an inversion strategy based on the SIR code that reproduces Ca II H spectra in the LTE approximation. The approach uses a two-step procedure with an archive of pre-calculated spectra to fit the line core and a subsequent iterative modification to improve the fit mainly in the line wing. Simultaneous spectra in the 630 nm range can optionally be used to fix the continuum temperature. The method retrieves one-dimensional (1D) temperature stratifications while neglecting lateral radiative transport. Line-of-sight velocities are included post facto with an empirical approach.
Results: An archive of about 300 000 pre-calculated spectra is more than sufficient to reproduce the line core of observed Ca II H spectra both in the quiet Sun and in active regions. The subsequent iterative adjustment of the thermodynamical stratification matches observed and best-fit spectra to a level of about 0.5% of Ic in the line wing and about 1% of Ic in the line core.
Conclusions: The successful application of the LTE inversion strategy suggests that inversion schemes based on pre-calculated spectra allow a reliable and relatively fast retrieval of solar properties from observed chromospheric spectra. The approach can be easily extended to a 1D non-LTE (NLTE) case by a simple exchange of the pre-calculated archive spectra. Using synthetic NLTE spectra from numerical three-dimensional (3D) simulations instead will finally allow one to extend the approach from the static 1D-case to dynamical atmosphere models, including the complete 3D radiative transport.

The animation is available in electronic form at http://www.aanda.org 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: The GREGOR Fabry-Pérot Interferometer: A New Instrument for High-Resolution Spectropolarimetric Solar Observations Authors: Puschmann, K. G.; Balthasar, H.; Bauer, S. -M.; Hahn, T.; Popow, E.; Seelemann, T.; Volkmer, R.; Woche, M.; Denker, C. Bibcode: 2012ASPC..463..423P Altcode: 2011arXiv1111.5509P Fabry-Pérot interferometers have advantages over slit spectrographs because they allow fast narrow-band imaging and post-factum image reconstruction of the retrieved data. Temperature, plasma velocity, and magnetic field maps can be derived from inversions of spectral lines, thus, advancing our understanding of the dynamic Sun and its magnetic fields at the smallest spatial scales. The GREGOR Fabry-Pérot Interferometer (GFPI) is one of two first-light instruments of the 1.5-meter GREGOR solar telescope, which is currently being commissioned at the Observatorio del Teide, Tenerife, Spain. 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 of 52″×40″ is sufficiently large to cover significant area fraction of active regions. The GFPI is a tuneable dual-etalon system in a collimated mounting. Equipped with a full-Stokes polarimeter, it records spectropolarimetric data with a spectral resolution of R ≍ 250,000 over the wavelength range from 530-860 nm. Large-format, high-cadence CCD detectors with powerful computer hard- and software facilitate scanning of spectral lines in time spans corresponding to the evolution time-scale of solar features. We present the main characteristics of the GFPI including the latest developments in software, mechanical mounts, and optics. 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: The GREGOR Fabry-Perot interferometer: status report and prospects Authors: Puschmann, Klaus G.; Balthasar, Horst; Beck, Christian; Louis, Rohan E.; Popow, Emil; Seelemann, Thomas; Volkmer, Reiner; Woche, Manfred; Denker, Carsten Bibcode: 2012SPIE.8446E..79P Altcode: 2012arXiv1207.2084P The GREGOR Fabry-Ṕerot 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 allows fast narrow-band imaging and post-factum image restoration. The retrieved physical parameters will be a fundamental building block for understanding the dynamic Sun and its magnetic field at spatial scales down to 50 km on the solar surface. The GFPI is a tunable dual-etalon system in a collimated mounting. It is designed for spectropolarimetric observations over the wavelength range from 530-860 nm with a theoretical spectral resolution of R ≍ 250,000. The GFPI is equipped with a full-Stokes polarimeter. Large-format, high-cadence CCD detectors with powerful computer hard- and software enable the scanning of spectral lines in time spans equivalent to the evolution time of solar features. The field-of-view of 50''×38'' covers a significant fraction of the typical area of active regions. We present the main characteristics of the GFPI including advanced and automated calibration and observing procedures. We discuss improvements in the optical design of the instrument and show first observational results. Finally, we lay out first concrete ideas for the integration of a second FPI, the Blue Imaging Solar Spectrometer, which will explore the blue spectral region below 530 nm. Title: The energy of waves in the photosphere and lower chromosphere. II. Intensity statistics Authors: Beck, C.; Rezaei, R.; Puschmann, K. G. Bibcode: 2012A&A...544A..46B Altcode: 2012arXiv1206.1759B Context. The energy source powering the solar chromosphere is still undetermined, but leaves its traces in observed intensities.
Aims: We investigate the statistics of the intensity distributions as a function of the wavelength for Ca ii H and the Ca ii IR line at 854.2 nm to estimate the energy content in the observed intensity fluctuations.
Methods: We derived the intensity variations at different heights of the solar atmosphere, as traced by the line wings and line cores of the two spectral lines. We converted the observed intensities to absolute energy units employing reference profiles calculated in non-local thermal equilibrium (NLTE). We also converted the intensity fluctuations to corresponding brightness temperatures assuming LTE.
Results: The root-mean-square (rms) fluctuations of the emitted intensity are about 0.6 (1.2) W m-2 ster-1 pm-1 near the core of the Ca ii IR line at 854.2 nm (Ca ii H), corresponding to relative intensity fluctuations of about 20% (30%). For the line wing, we find rms values of about 0.3 W m-2 ster-1 pm-1 for both lines, corresponding to relative fluctuations below 5%. The relative rms values show a local minimum for wavelengths forming at a height of about 130 km, but otherwise increase smoothly from the wing to the core, i.e., from photosphere to chromosphere. The corresponding rms brightness temperature fluctuations are below 100 K for the photosphere and up to 500 K in the chromosphere. The skewness of the intensity distributions is close to zero in the outer line wing and positive throughout the rest of the line spectrum, owing to the frequent occurrence of high-intensity events. The skewness shows a pronounced local maximum at locations with photospheric magnetic fields for wavelengths in-between those of the line wing and the line core (z ≈ 150-300 km), and a global maximum at the very core (z ≈ 1000 km) for both magnetic and field-free locations.
Conclusions: The energy content of the intensity fluctuations is insufficient to create a chromospheric temperature rise that would be similar to the one in most reference models of the solar atmosphere. The increase in the rms fluctuations with height indicates the presence of upwardly propagating acoustic waves of increasing oscillation amplitude. The intensity and temperature variations indicate that there is a clear increase in dynamical activity from photosphere towards the chromosphere, but the variations fall short of the magnitude predicted by fully dynamical chromospheric models by a factor of about five. The enhanced skewness between the photosphere and lower solar chromosphere at magnetic locations is indicative of a mechanism that acts solely on magnetized plasma.

Appendices are available in electronic form at http://www.aanda.org Title: Twist, Writhe, and Helicity in the Inner Penumbra of a Sunspot Authors: Ruiz Cobo, B.; Puschmann, K. G. Bibcode: 2012ApJ...745..141R Altcode: 2011arXiv1111.3881R The aim of this work is the determination of the twist, writhe, and self-magnetic helicity of penumbral filaments located in an inner sunspot penumbra. For this purpose, we inverted data taken with the spectropolarimeter on board Hinode with the SIR (Stokes Inversion based on Response function) code. For the construction of a three-dimensional geometrical model we applied a genetic algorithm minimizing the divergence of \vec{B} and the net magnetohydrodynamic force, consequently a force-free solution would be reached if possible. We estimated two proxies to the magnetic helicity frequently used in literature: the force-free parameter α z and the current helicity term h_{c_{z}}. We show that both proxies are only qualitative indicators of the local twist as the magnetic field in the area under study significantly departs from a force-free configuration. The local twist shows significant values only at the borders of bright penumbral filaments with opposite signs on each side. These locations are precisely correlated to large electric currents. The average twist (and writhe) of penumbral structures is very small. The spines (dark filaments in the background) show a nearly zero writhe. The writhe per unit length of the intraspines diminishes with increasing length of the tube axes. Thus, the axes of tubes related to intraspines are less wrung when the tubes are more horizontal. As the writhe of the spines is very small, we can conclude that the writhe reaches only significant values when the tube includes the border of an intraspine. Title: Application of speckle and (multi-object) multi-frame blind deconvolution techniques on imaging and imaging spectropolarimetric data Authors: Puschmann, K. G.; Beck, C. Bibcode: 2011A&A...533A..21P Altcode: 2011arXiv1107.0703P Context. Ground-based imaging and imaging spectropolarimetric data are often subjected to post-facto reconstruction techniques to improve the spatial resolution.
Aims: We test the effects of reconstruction techniques on two-dimensional data to determine the best approach to improve our data.
Methods: We obtained an 1-h time-series of spectropolarimetric data in the Fe i line at 630.25 nm with the Göttingen Fabry-Pérot Interferometer (FPI) that are accompanied by imaging data in the blue continuum at 431.3 nm and Ca ii H at 396.85 nm. We apply both speckle and (multi-object) multi-frame blind deconvolution ((MO)MFBD) techniques. We use the "Göttingen" speckle and speckle deconvolution codes and the MOMFBD code in the implementation of Van Noort et al. (2005). We compare the resulting spatial resolution and investigate the impact of the image reconstruction on spectral characteristics of the Göttingen FPI data.
Results: The speckle reconstruction and MFBD perform similar for our imaging data with nearly identical intensity contrasts. MFBD provides a better and more homogeneous spatial resolution at the shortest wavelength when applied to a series of image bursts. The MOMFBD and speckle deconvolution of the intensity spectra lead to similar results, but our choice of settings for the MOMFBD yields an intensity contrast smaller by about 2% at a comparable spatial resolution. None of the reconstruction techniques introduces significant artifacts in the intensity spectra. The speckle deconvolution (MOMFBD) has a rms noise in Stokes V/I of 0.32% (0.20%). The deconvolved spectra thus require a high significance threshold of about 1.0% to separate noise peaks from true signal. A comparison to spectra with a significantly higher signal-to-noise (S/N) ratio and to spectra from a magneto-hydrodynamical simulation reveals that the Göttingen FPI can only detect about 30% of the polarization signal present in quiet Sun areas. The distribution of NCP values for the speckle-deconvolved data matches that of observations with higher S/N better than MOMFBD, but shows seemingly artificially sharp boundaries and unexpected changes of the sign.
Conclusions: For our imaging data, both MFBD and speckle reconstruction are equivalent, with a slightly better and more stable performance of MFBD. For the spectropolarimetric data, the higher intensity contrast of the speckle deconvolution is balanced by the smaller amplification of the noise level in the MOMFBD at a comparable spatial resolution. The noise level prevents the detection of weak and diffuse magnetic fields. Future efforts should be directed to improve the S/N of the Göttingen FPI spectra for spectropolarimetric observations to lower the final significance thresholds. Title: Polarimetry with GREGOR Authors: Balthasar, H.; Bello González, N.; Collados, M.; Denker, C.; Feller, A.; Hofmann, A.; Lagg, A.; Nagaruju, L.; Puschmann, K. G.; Soltau, D.; Volkmer, R. Bibcode: 2011ASPC..437..351B Altcode: A brief description of the new 1.5-meter solar telescope GREGOR located at the Observatorio del Teide in Tenerife will be given. GREGOR will provide a spatial resolution of about 75 km on the Sun, and with its light collecting capability we will be able to study the development of small magnetic features with high cadence. From the beginning, it will be equipped with the GREGOR Fabry-Pérot Interferometer (GFPI) for the visible spectral range and with a GRating Infrared Spectrograph (GRIS). Both postfocus instruments can be combined with a polarimeter, and in both cases the light is modulated by two ferro-electric liquid crystals. A calibration unit can be inserted to determine the instrumental polarization. Because of the altazimuthal mount, time-dependent rotation of the polarimetric reference plane is introduced, and we have to develop a polarization model of the telescope. Measurements to verify this model are in preparation. Title: The Electrical Current Density Vector in the Inner Penumbra of a Sunspot Authors: Puschmann, K. G.; Ruiz Cobo, B.; Martínez Pillet, V. Bibcode: 2010ApJ...721L..58P Altcode: 2010arXiv1008.2131P We determine the entire electrical current density vector in a geometrical three-dimensional volume of the inner penumbra of a sunspot from an inversion of spectropolarimetric data obtained with Hinode/SP. Significant currents are seen to wrap around the hotter, more elevated regions with lower and more horizontal magnetic fields that harbor strong upflows and radial outflows (the intraspines). The horizontal component of the current density vector is 3-4 times larger than the vertical; nearly all previous studies only obtain the vertical component Jz , thus strongly underestimating the current density. The current density \vec{J} and the magnetic field \vec{B} form an angle of about 20°. The plasma β at the 0 km level is larger than 1 in the intraspines and is one order of magnitude lower in the background component of the penumbra (spines). At the 200 km level, the plasma β is below 0.3, nearly everywhere. The plasma β surface as well as the surface optical depth unity is very corrugated. At the borders of intraspines and inside, \vec{B} is not force-free at deeper layers and nearly force-free at the top layers. The magnetic field of the spines is close to being potential everywhere. The dissipated ohmic energy is five orders of magnitudes smaller than the solar energy flux and thus negligible for the energy balance of the penumbra. Title: A Geometrical Height Scale for Sunspot Penumbrae Authors: Puschmann, K. G.; Ruiz Cobo, B.; Martínez Pillet, V. Bibcode: 2010ApJ...720.1417P Altcode: 2010arXiv1007.2779P Inversions of spectropolarimetric observations of penumbral filaments deliver the stratification of different physical quantities in an optical depth scale. However, without establishing a geometrical height scale, their three-dimensional geometrical structure cannot be derived. This is crucial in understanding the correct spatial variation of physical properties in the penumbral atmosphere and to provide insights into the mechanism capable of explaining the observed penumbral brightness. The aim of this work is to determine a global geometrical height scale in the penumbra by minimizing the divergence of the magnetic field vector and the deviations from static equilibrium as imposed by a force balance equation that includes pressure gradients, gravity, and the Lorentz force. Optical depth models are derived from the inversion of spectropolarimetric data of an active region observed with the Solar Optical Telescope on board the Hinode satellite. We use a genetic algorithm to determine the boundary condition for the inference of geometrical heights. The retrieved geometrical height scale permits the evaluation of the Wilson depression at each pixel and the correlation of physical quantities at each height. Our results fit into the uncombed penumbral scenario, i.e., a penumbra composed of flux tubes with channeled mass flow and with a weaker and more horizontal magnetic field as compared with the background field. The ascending material is hotter and denser than their surroundings. We do not find evidence of overturning convection or field-free regions in the inner penumbral area analyzed. The penumbral brightness can be explained by the energy transfer of the ascending mass carried by the Evershed flow, if the physical quantities below z = -75 km are extrapolated from the results of the inversion. Title: Three Dimensional Structure of Penumbral Filaments from Hinode Observations Authors: Puschmann, K. G.; Cobo, B. Ruiz; Pillet, V. Martínez Bibcode: 2010ASSP...14..457P Altcode: 2010hsa5.conf..457P; 2008arXiv0810.2432P We analyze spectropolarimetric observations of the penumbra of the NOAA AR 10953 at high spatial resolution (0.3 ″ ). The full Stokes profiles of the Fe I lines at 630.1 nm and 630.2 nm have been obtained with the Solar Optical Telescope (SOT) on board the Hinode satellite. The data have been inverted by means of the SIR code, deriving the stratifications of temperature, line-of-sight velocity, and the components of the magnetic field vector in optical depth. In order to evaluate the gas pressure and to obtain an adequate geometrical height scale, the motion equation has been integrated for each pixel taking into account the terms of the Lorentz force. To establish the boundary condition, a genetic algorithm has been applied. The final resulting magnetic field has a divergence compatible with 0 inside its uncertainties. First analyzes of the correlation of the Wilson depression with velocity, temperature, magnetic field strength, and field inclination strongly support the uncombed penumbral model proposed by Solanki & Montavon (1993, A&A, 275, 283). Title: Morphology and evolution of umbral dots and their substructures Authors: Sobotka, M.; Puschmann, K. G. Bibcode: 2009A&A...504..575S Altcode: 2009arXiv0907.4236S Context: Substructures - dark lanes and tails - of umbral dots (UDs) were predicted by numerical simulations of magnetoconvection and have been detected later in some observations.
Aims: To provide constraints for realistic theoretical models of sunspot umbrae, we describe the observed properties and evolutionary characteristics of UDs (including their substructure) and of other umbral structures.
Methods: We analyse a 6 h 23 min time series of broadband images of a large umbra in the active region NOAA 10634, acquired with the 1-m Swedish Solar Telescope, in the wavelength band around 602 nm. A 43 min part of this series was reconstructed with the MFBD method, reaching a spatial resolution of 0.14 arcsec. With the help of image segmentation, feature tracking, and local correlation tracking, we measured brightness, size, lifetime, and horizontal velocities of various umbral structures.
Results: Large structures in the umbra - strong and faint light bridges (LBs) and an extended penumbral filament - evolve on time scales of hours. Most (90%) of UDs and bright point-like features in faint LBs split and merge, and their median lifetimes are 3.5 or 5.7 min, depending on whether the split or merge event is considered as the end of their life. Both UDs and features in faint LBs that do not split or merge are clearly smaller (0.15 arcsec) than the average size (0.17 arcsec) of all features. Horizontal motions of umbral bright small-scale features are directed either into the umbra or along faint LBs with mean horizontal velocities of 0.34 km s-1. Features faster than 0.4 km s-1 appear mostly at the periphery of the umbra. The motion of peripheral UDs (PUDs) seems to be the continuation of the motion of penumbral grains (PGs). The intensity of dark lanes, measured in four bright central UDs (CUDs), is by a factor 0.8 lower than the peak intensity of CUDs. The width of dark lanes is probably less than the resolution limit 0.14 arcsec. The characteristic time of substructure changes of UDs is ~4 min. We observe narrow (0.14 arcsec) bright and dark filaments connected with PUDs. The bright filaments are 0.06 I_ph brighter than the dark ones. Usually one dark and two bright filaments form a 0.4 arcsec wide tail attached to one PUD, resembling a short dark-cored penumbral filament.
Conclusions: Our results indicate the similarity between PUDs and PGs located at the tips of bright penumbral filaments. The features seen in numerical MHD simulations are consistent with our observations of dark lanes in CUDs and tails attached to PUDs. Title: Supersonic Continuation of the Evershed Flow Outside a Sunspot as Observed with Hinode Authors: Martínez Pillet, V.; Katsukawa, Y.; Puschmann, K. G.; Ruiz Cobo, B. Bibcode: 2009ApJ...701L..79M Altcode: 2009arXiv0907.3835M We report on the discovery of mostly horizontal field channels just outside sunspot penumbrae (in the so-called "moat" region) that are seen to sustain supersonic flows (line-of-sight component of 6 km s-1). The spectral signature of these supersonic flows corresponds to circular polarization profiles with an additional, satellite, third lobe of the same sign as the parent sunspot' Stokes V blue lobe, for both downflows and upflows. This is consistent with an outward directed flow that we interpret as the continuation of the magnetized Evershed flow outside sunspots at supersonic speeds. In Stokes Q and U, a clear signature of a transverse field connecting the two flow streams is observed. Such an easily detectable spectral signature should allow for a clear identification of these horizontal field channels in other spectropolarimetric sunspot data. For the spot analyzed in this paper, a total of five channels with this spectral signature have been unambiguously found. 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: Local Helioseismology with GFPI at the Vacuum Tower Telescope, Tenerife Authors: Staiger, J.; Roth, M.; Wöhl, H.; Schleicher, H.; Puschmann, K. Bibcode: 2008ESPM...12..2.3S Altcode: Local Helioseimology has recently become an important tool to investigate the Solar Interior in the vicinity of localized phenomena like sunspots. It possibly holds the promise to give informations about subsurface magnetic fields and material flows. We are currently modifying the GFPI Instrument at the VTT which will also be a First Light Instrument at GREGOR Telescope to the needs of ground-based helioseismologic observations (GFPI: Göttingen Fabry Perot Interferomer).

The upgrade consists of a CCD-camera with a larger Field-of-View (100"-by-100"), a modified Interfacing Hardware and dedicated Control- and Recording-Software. Direct Interfacing to the VTT's telescope control system allows for mosaic type patching of the observations field. Cadence times of below 1 Minute for a 300"-by-300" field at the telescope's resolution limit of 0.2" are possible. Data are stored to USB-based external harddisks. An of-the-shelf beamer allows for optical adjustments with an artificial light source.

Available Preprocessing Tools allow to immediately visualize the quality of the observational data. This includes a prelimary Ringdiagram Analysis. Future Online Preprocessing Capabilities are to further reduce the achievable cycle times.

We will present some details of the instrumental setup and some prelimiary observational results. 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: Kinematics of Umbral Fine Structure Authors: Sobotka, M.; Puschmann, K. G.; Hamedivafa, H. Bibcode: 2008CEAB...32..125S Altcode: A 2-hour long series of white-light images of a large sunspot acquired in June 2004 with the 1-m Swedish Solar Telescope at La Palma is utilized to study the evolution and motions of small-scale umbral structures - umbral dots and features in faint light bridges. For this purpose, a newly improved feature-tracking code is applied. The small-scale structures move with average speeds of 0.34 km s^{-1} either into the umbra or along the faint light bridges. Structures that do not split or merge are smaller (0.15 arcsec) than the average size (0.17 arcsec). Brightness and size variations of individual non-split/merge structures are positively correlated during their evolution. Title: On the properties of faculae at the poles of the Sun Authors: Blanco Rodríguez, J.; Okunev, O. V.; Puschmann, K. G.; Kneer, F.; Sánchez-Andrade Nuño, B. Bibcode: 2007A&A...474..251B Altcode: Context: Faculae at the poles of the Sun, or polar faculae (PFe), take part in the solar magnetic cycle. Their occurrence maximum is shifted by 5-6 years with respect to the sunspot cycle. PFe are stable phenomena, with lifetimes of several hours to days, and harbour magnetic fields of kilo-Gauss strength. Yet their role for the global magnetic field at the solar poles is unknown.
Aims: To contribute to the knowledge of the physical properties of PFe and to the understanding of their role in the global magnetism of the Sun.
Methods: PFe were observed on 21-24 August 2005 with the Vacuum Tower Telescope at the Observatorio del Teide. The “Göttingen” Fabry-Perot spectrometer was used with a Stokes V polarimeter to scan the Fe i 6173 Å line (Landé factor g = 2.5) and the Hα line in two-dimensional fields of view (FOVs). A large observational coverage of the polar caps was obtained. The data were analysed with speckle methods. Magnetic field strengths were determined with the weak field approximation, with the approximation of the strong field regime, and with the centre of gravity (COG) method. Velocities were measured with the COG method and from the zero-crossing of the Stokes V profiles.
Results: PFe show a decrease of the continuum and broadband intensity contrast towards the disc centre and no decrease of contrast towards the limb, similar to as faculae in active regions near the equator. Extrapolating from the observed FOVs to the total areas of PF occurrence around the solar poles, we find 4 120 PFe in the northern polar cap and, asymmetrically to this number, 1 250 PFe near the south pole. The total area coverages by PFe are ~7.6×108 km2 and ~3.4×108 km2 near the solar north and south poles, respectively. Some of the PFe exhibit magnetic polarities opposite to the global polarity at the time of observation. The resulting total magnetic fluxes in PFe fall short by an order of magnitude from those found in the literature for the fluxes at the polar caps. This also holds if we include magnetic structures which are not related to brightenings. We conclude that with the present spatial resolution of 0.4 arcsec-0.5 arcsec (FWHM), PFe represent the “large-scale” end of a distribution of unipolar strands near the solar poles. The velocities in PFe show amplitudes of 2 km s-1, with systematic up-flows in the Stokes I profile, but no average velocity measured in the V zero-crossings. Title: Spicule emission profiles observed in He i 10 830 Å Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.; Trujillo Bueno, J.; Blanco Rodríguez, J.; Kneer, F. Bibcode: 2007A&A...472L..51S Altcode: 2007arXiv0707.4421S Aims:Off-the-limb observations with high spatial and spectral resolution will help us understand the physical properties of spicules in the solar chromosphere.
Methods: Spectropolarimetric observations of spicules in the He i 10 830 Å multiplet were obtained with the Tenerife Infrared Polarimeter on the German Vacuum Tower Telescope at the Observatorio del Teide (Tenerife, Spain). The analysis shows the variation of the off-limb emission profiles as a function of the distance to the visible solar limb. The ratio between the intensities of the blue and the red components of this triplet (R=I_blue/I_red) is an observational signature of the optical thickness along the light path, which is related to the intensity of the coronal irradiation.
Results: We present observations of the intensity profiles of spicules above a quiet Sun region. The observable R as a function of the distance to the visible limb is also given. We have compared our observational results to the intensity ratio obtained from detailed radiative transfer calculations in semi-empirical models of the solar atmosphere assuming spherical geometry. The agreement is purely qualitative. We argue that future models of the solar chromosphere and transition region should account for the observational constraints presented here. Title: Modern Solar Facilities - Advanced Solar Science Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D. Bibcode: 2007msfa.conf.....K Altcode: An international workshop entitled: Modern Solar Facilities - Advanced Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop, which was attended by 88 participants from 24 different countries, gave a broad overview of the current state of solar research, with emphasis on telescopes and instrumentation, high-resolution and high-precision observations, and theory and interpretation. The book collects written versions of 71 papers presented at the conference. Title: GREGOR: the New German Solar Telescope Authors: Balthasar, H.; von der Lühe, O.; Kneer, F.; Staude, J.; Volkmer, R.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Nicklas, H.; Popow, E.; Puschmann, K.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.; Wittmann, A. Bibcode: 2007ASPC..368..605B Altcode: 2007arXiv0704.2693B GREGOR is a new open solar telescope with an aperture of 1.5 m. It replaces the former 45-cm Gregory Coudé telescope on the Canary island Tenerife. The optical concept is that of a double Gregory system. The main and the elliptical mirrors are made from a silicon-carbide material with high thermal conductivity. This is important to keep the mirrors on the ambient temperature avoiding local turbulence. GREGOR will be equipped with an adaptive optics system. The new telescope will be ready for operation in 2008. Post-focus instruments in the first stage will be a spectrograph for polarimetry in the near infrared and a 2-dimensional spectrometer based on Fabry-Pérot interferometers for the visible. Title: 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: Off-limb spectroscopy of the He I 10830 Å multiplet: observations vs. modelling Authors: Sánchez-Andrade Nuño, B.; Centeno, R.; Puschmann, K. G.; Trujillo Bueno, J.; Kneer, F. Bibcode: 2007msfa.conf..177S Altcode: Spectropolarimetric observations of spicules were carried out with the new optical setup of the Tenerife Infrared Polarimeter (TIP 2) at the VTT, showing the variation of the He I 10830Å multiplet off-limb emission profiles with increasing distance to the solar visible limb. The ratio between the intensities of the blue and the red components of this triplet (R = Iblue/Ired) is an observational signature of the optical thickness along the light path, which, at the same time, is proportional to the population of the lower (metastable) level that takes part in these transitions. Our observational results show a variation of R as a function of the distance to the limb. In agreement with recent theoretical results we conclude that R could be used as a diagnostic tool for downward UV coronal irradiance, which is believed to be responsible for the population of the metastable level of the He I 10830 Å triplet. We have compared our observational results with the ratio obtained from detailed radiative transfer calculations in semi-empirical models of the solar atmosphere (assuming spherical geometry) finding a fairly poor agreement. We argue that future models of the solar chromosphere and transition region should account for the observational constraints presented here. Title: From the "Göttingen" Fabry-Perot Interferometer to the GREGOR FPI Authors: Puschmann, K. G.; Kneer, F.; Nicklas, H.; Wittmann, A. D. Bibcode: 2007msfa.conf...45P Altcode: Fabry-Perot Interferometers (FPIs) have advantages over slit spectrographs, allowing fast two-dimensional, narrowband imaging and post factum image reconstruction of the spectropolarimetric data obtained. The resulting intensity, velocity and magnetic field maps are a fundamental base for the understanding of the dynamics of the solar atmosphere and its magnetic fields at smallest spatial scales. Efforts are undertaken to provide, with the Göttingen Fabry-Perot interferometer, an up-todate post-focus instrument for the German 1.5 m GREGOR solar telescope. Therefore a renewal of the spectrometer has been achieved during the first half of 2005. First observations at the German Vacuum Tower Telescope (VTT) reveal new scientific aspects and a very promising outlook for the future at GREGOR. In this contribution a general description of the upgraded spectrometer is given. Its final optical design at GREGOR is described and an optical analysis of the GREGOR FPI is outlined. Latest results with the new instrument obtained at the VTT are presented. Title: New high resolution solar telescope GREGOR Authors: Volkmer, R.; von der Lühe, O.; Kneer, F.; Staude, J.; Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaña, M.; Sobotka, M.; Nicklas, H.; Popow, E.; Puschmann, K. G.; Schmidt, W.; Soltau, D.; Strassmeier, K.; Wittmann, A. D. Bibcode: 2007msfa.conf...39V Altcode: The 1.5m solar telescope GREGOR is being constructed at Tenerife, Spain. Its purpose is to observe with high spatial and spectral resolution small-scale dynamic magnetic features on the Sun. The telescope is completely open with retractable dome and actively cooled primary mirror made of silicon carbide to minimize thermal effects on the image quality. After completion it will be one of the most powerful solar telescopes. This paper presents a general overview of the telescope characteristics and the current status. Title: Modern solar facilities - advanced solar science Authors: Kneer, Franz; Puschmann, Klaus G.; Wittmann, Axel D. Bibcode: 2007msfa.conf....0K Altcode: An international workshop entitled: Modern Solar Facilities - Advanced Solar Science was held in Göttingen Sept. 27-29, 2006. The workshop, which was attended by 88 participants from 24 different countries, gave a broad overview of the current state of solar research, with emphasis on telescopes and instrumentation, high-resolution and high-precision observations, and theory and interpretation. The book collects written versions of 71 papers presented at the conference. Title: Observations of a flaring active region in H[alpha] Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F. Bibcode: 2007msfa.conf..273S Altcode: A 40 min time series of the active region NOAA AR10875 was obtained on April 26th, 2006 under very good seeing conditions using the new "Göttingen" - Fabry-Perot interferometer at the German Vacuum Tower Telescope, Observatorio del Teide, Tenerife. The Hα line was scanned giving two-dimensional images at 21 different wavelength positions with a cadence of ~ 20 s per scan. After speckle reconstruction the spatial resolution achieved was better than 0".35. The data provide a unique possibility to study the temporal evolution of a pre-flaring, flaring and post-flaring solar active region in Hα. From the analysis of the present spectrometric data set we expect important advances in the understanding of Alfén waves, dynamics of fibrils and filaments and the physical nature of the sigmoid structure seen in the core of Hα. Here we present first results from this data set. Title: Dynamics of the quiet photosphere and its magnetic field under high spatial resolution Authors: Puschmann, K. G.; Kneer, F.; Domínguez Cerdeña, I. Bibcode: 2007msfa.conf..151P Altcode: An excellent 1 h 10 min time series of a quiet solar region near disk centre was acquired on 4th of May 2006 at the German Vacuum Tower Telescope. Using the new "Göttingen" Fabry-Perot interferometer together with the Kiepenheuer Adaptive Optics system spectropolarimetric images were obtained, scanning the Fe I 5247Å and Fe I 5250Å lines with a temporal cadence of 17 s each. Thanks to speckle reconstruction methods the achieved spatial resolution of the obtained intensity, velocity and magnetic field maps is ~ 0."3. First results on the dynamics of the quiet photosphere and magnetic fields reveal strengthening and weakening of the polarisation signal in interaction to granular convection processes indicating advection and diffusion of magnetic flux at smallest scales. Field structures, very elongated along intergranular lanes, show high dynamics, combine and split, and leave strong fingerprints at high photospheric layers where related temperatures fluctuate. Recent numerical MHD simulations come close to our findings. Possible indications of magnetic flux annihilation, flux tube evacuation or signs of upward-propagating shock fronts are illustrated. Title: Fine structure in a dark umbra Authors: Sobotka, M.; Puschmann, K. G. Bibcode: 2007msfa.conf..205S Altcode: An excellent-quality time series of images of a large dark umbra of the leading sunspot of NOAA 10634 was acquired on 18 June 2004 with the 1-m Swedish Solar Telescope at La Palma, simultaneously in blue, red, and G-band channels. The temporal and spatial resolutions are 20 s and 0".14. A 2-hour long series of the red continuum images is analysed, showing the faintest umbral fine structures. In addition to umbral dots, often clustered to more stable "granules" or aligned to short chains, we observe large, low-intensity elongated structures with dark central channels, resembling extremely faint light bridges. At the periphery of the umbra, bright umbral dots move inwards, showing a similarity to penumbral grains. Kinematic properties of umbral fine structures are studied. Title: Study of polar faculae with north pole coverage of the Sun Authors: Blanco Rodríguez, J.; Okunev, O.; Puschmann, K. G.; Kneer, F. Bibcode: 2007msfa.conf..181B Altcode: We present here a description of the main characteristics of faculae at the poles of the Sun (polar faculae PFe) observed in a series of observations covering the north solar pole. Statistics of a group of these PFe are used to estimate the contrast behaviour from [mμ] = 0.6 towards the limb as well as their magnetic field. Hα is also observed to analyse the behaviour of PFe in the chromosphere. Title: Dynamics of Magnetic Bright Points in an Active Region Authors: Möstl, C.; Hanslmeier, A.; Sobotka, M.; Puschmann, K.; Muthsam, H. J. Bibcode: 2006SoPh..237...13M Altcode: 2006SoPh..tmp....2M A high-quality 80-minute time series of a part of a sunspots moat (18 ″ × 23 ″) in the G-band (4308.64 Å) has been analysed to measure the horizontal velocities of Magnetic Bright Points (MBPs). The observations were carried out in June 2004 at the new 1-meter Swedish Solar Telescope in La Palma. Spatial resolution was estimated to be 0.17 ″ or 125 km on the Sun, and images were taken in a frame selection mode in a 20-seconds interval. Individual feature tracking of MBPs with manual selection and automated tracking has been performed. The intensity of MBPs increases with size. The mean value in a MBP-velocity histogram was found to be 1.11 km s −1 and it shows good accordance with an abnormal granulation-velocity histogram. MBP velocity histograms as presented here can be taken as an input for coronal heating models in an active region. However, MBPs move slower in an active region than in the network (presumably because of the higher active region magnetic flux) and hence, a process that includes dissipation of MHD waves through fast MBP motions (>2 km s −1) may not alone explain the observed properties of the corona. Title: Speckle reconstruction of photometric data observed with adaptive optics Authors: Puschmann, K. G.; Sailer, M. Bibcode: 2006A&A...454.1011P Altcode: To achieve the highest spatial resolution for ground-based observations one has to correct for degradations by the Earth's atmosphere. This can be done by on-line and post-facto techniques. Here we combine observations with Adaptive Optics (AO) and speckle reconstruction. As possible techniques we present two modified versions (methods B and C) of the Göttingen speckle masking code and describe their application to observations of a solar active region obtained with the Swedish 1-m Solar Telescope (La Palma) by means of AO. By comparing the results with those obtained from the conventional method (method A), the influence of AO on the post-facto reconstruction is revealed. One has to account for the field dependence of the AO correction and the fitting errors of the calculated surface of the deformable mirror with respect to the according wave fronts. Both new approaches enhance the contrast in the lockpoint region less than the conventional method. Method C uses simulated AO corrected speckle transfer functions (STFs). This method shows the most uniform image quality over the whole field of view and indicates the importance of the atmospheric model assumptions and the partial character of the WF correction by AO with appropriate WF error statistics. However, the consideration of field dependent speckle transfer functions in the classical speckle reconstruction (Method B) can serve as a first approach to avoid an intensity over-amplification around the AO-lockpoint region, although the rms of the contrast in the reconstructed images tends to rise slightly towards the outer parts of the field of view. Even the apparently small differences between the speckle transfer functions, used in the different reconstruction methods, cause the modulus of the estimated intensity differences to vary by up to 22%. Title: The new Göttingen Fabry-Pérot spectrometer for two-dimensional observations of the Sun Authors: Puschmann, K. G.; Kneer, F.; Seelemann, T.; Wittmann, A. D. Bibcode: 2006A&A...451.1151P Altcode: Studies of small-scale dynamics and magnetic fields in the solar atmosphere require spectroscopy and polarimetry with high spatial resolution. For this purpose, spectrometers based on Fabry-Pérot interferometers (FPIs) have advantages over slit spectrographs. They possess a high throughput and allow fast two-dimensional, narrow-band imaging and image reconstruction of the data. In the present contribution we describe an upgrade, essentially renewal, of the Göttingen FPI spectrometer achieved during the first half of 2005. A new etalon from IC Optical Systems Ltd. (formerly Queensgate), England, with 70 mm free aperture for high spectral resolution has been mounted. New CCD detectors from LaVision GmbH (Göttingen) with powerful computer hard- and software were implemented. We consider the product of signal-to-noise ratio, frame rate, and field of view as a measure of the efficiency. At low light levels, e.g. in narrow-band speckle applications, this product has increased by a factor ~60 compared to the old system. In addition, several spectral regions can now be scanned quasi-simultaneously. We present first results obtained with the upgraded spectrometer. The efforts are undertaken to provide an up-to-date post-focus instrument for the new German 1.5 m GREGOR solar telescope presently under construction at the Observatorio del Teide on Tenerife. Title: The flux-gap between bright and dark solar magnetic structures Authors: Puschmann, K. G.; Wiehr, E. Bibcode: 2006A&A...445..337P Altcode: The upper size limit of solar small-scale magnetic flux concentrations ("G-band bright points", BP) is reconsidered from speckle-reconstructed images taken at the 1-m SST on La Palma. The size-histogram shows a sharp drop towards 250 km diameter, variation of the noise filter threshold diminishes that value due to segmentation of the elongated structures. A further artificial segmentation of still elongated (i.e. not round) BP indicates that the upper limit may well be below 200 km diameter, corresponding to a flux smaller than 2.5×1017 Mx which is more than 40 times smaller than that of smallest dark (mini-) pores. BP with diameters of 130 km would already yield to a flux gap of two orders of magnitude. The drop of BP numbers between the histogram maximum and the 90 km resolution limit achieved is found to depend on the low-pass filtering and is thus probably virtual. Higher spatial resolution data will still increase the flux gap between bright and dark solar magnetic flux concentrations which might be a signature of differently deep rooting in the solar atmosphere. Title: Chromospheric Dynamics of a Solar Active Region Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Sánchez Cuberes, M.; Blanco Rodríguez, J.; Kneer, F. Bibcode: 2005ESASP.600E..70S Altcode: 2005dysu.confE..70S; 2005ESPM...11...70S No abstract at ADS Title: Study of Polar Faculae Authors: Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F. Bibcode: 2005ESASP.600E..59B Altcode: 2005dysu.confE..59B; 2005ESPM...11...59B No abstract at ADS Title: Analysis of a Wide Chromospheric Active Region Authors: Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Sánchez Cuberes, M.; Blanco Rodríguez, J.; Kneer, F. Bibcode: 2005ESASP.596E..62S Altcode: 2005ccmf.confE..62S No abstract at ADS Title: Magnetic Structures on the Sun: Osbervations with the New "GÖTTINGEN" Two-Dimensional Spectrometer on Tenerife Authors: Kneer, F.; Puschmann, K. G.; Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Wittmann, A. D. Bibcode: 2005ESASP.596E..71K Altcode: 2005ccmf.confE..71K No abstract at ADS Title: Study of Polar Faculae Authors: Blanco Rodríguez, J.; Sánchez-Andrade Nuño, B.; Puschmann, K. G.; Kneer, F. Bibcode: 2005ESASP.596E..52B Altcode: 2005ccmf.confE..52B 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: The structure of a penumbral connection between solar pores Authors: Hirzberger, J.; Stangl, S.; Gersin, K.; Jurčák, J.; Puschmann, K. G.; Sobotka, M. Bibcode: 2005A&A...442.1079H Altcode: High resolution 2D-spectro-polarimetric observations have been used to analyse the magnetic field and flow topologies of a penumbral connection between two opposite polarity solar pores. A filamentary structured Evershed-like material flow from one pore to the other along the magnetic field lines has been detected. The flow channels are co-spatial with bright penumbral filaments close to the pore which feeds the flow and the clear brightness-velocity relation vanishes close to the pore which represents the sink of the flow. The boundary between umbra and penumbra of the two pores show significant differences: bright comet-like penumbral grains represent endings of penumbral filaments at the flow sources whereas no such grains were found at the sinks of the flow. Furthermore, a systematic variation of the asymmetries of measured Stokes V profiles across the penumbral connection have been found. The obtained results are in accordance with the widely-accepted uncombed penumbra hypothesis and the moving flux tube model. Title: The Size of Small-Scale Solar Magnetic Regions Authors: Wiehr, E.; Puschmann, K. G. Bibcode: 2005ESASP.596E..20W Altcode: 2005ccmf.confE..20W No abstract at ADS Title: Time series of high resolution photospheric spectra in a quiet region of the Sun. II. Analysis of the variation of physical quantities of granular structures Authors: Puschmann, K. G.; Ruiz Cobo, B.; Vázquez, M.; Bonet, J. A.; Hanslmeier, A. Bibcode: 2005A&A...441.1157P Altcode: 2012arXiv1205.1725P From the inversion of a time series of high resolution slit spectrograms obtained from the quiet sun, the spatial and temporal distribution of the thermodynamical quantities and the vertical flow velocity is derived as a function of optical depth (logτ) and geometrical height (z). Spatial coherence and phase shift analyses between temperature and vertical velocity depict the height variation of these physical quantities for structures of different size. An average granular cell model is presented, showing the granule-intergranular lane stratification of temperature, vertical velocity, gas pressure and density as a function of logτ and z. Studies of a specific small and a specific large granular cell complement these results. A strong decay of the temperature fluctuations with increasing height together with a less efficient penetration of smaller cells is revealed. The T-T coherence at all granular scales is broken already at logτ = -1 or z ~ 170 km. At the layers beyond, an inversion of the temperature contrast at granular scales >1.5 arcsec is revealed, both in logτ and z. At deeper layers the temperature sensitivity of the H- opacity leeds to much smaller temperature fluctuations at equal logτ than at equal z, in concordance with Stein & Nordlund (1998, ApJ, 499, 914). Vertical velocities are in phase throughout the photosphere and penetrate into the highest layers under study. Velocities at the largest granular scales (~ 4´´) are still found even at logτ ~ -2.8 or z ~ 370 km. Again a less efficient height penetration of smaller cells concerning convective velocities is revealed, although still at logτ ~ -2 or z ~ 280 km structures >1.4 arcsec are detected. A similar size distribution of velocity and temperature structures with height provides observational evidence for substantial overshoot into the photosphere. At deep photospheric layers, the behaviour of the vertical velocities reflected in simulations is for the first time qualitatively reproduced by observations: intergranular velocities are larger than the granular ones and, both reach extrema, where the granular one is shifted towards higher layers. Title: Spectropolarimetry of a sunspot at disk centre Authors: Sánchez Cuberes, M.; Puschmann, K. G.; Wiehr, E. Bibcode: 2005A&A...440..345S Altcode: The magnetic, thermal and velocity structure of a sunspot at the solar disk centre (θ=2°) is investigated by inverting the full Stokes profiles of three infrared lines. A single magnetic component atmosphere is assumed with height gradients of the physical quantities. Since the line-of-sight (LOS) is perpendicular to the solar surface, differential optical or projection effects do not interfere, as often is the case for the usual observations at oblique LOS. We find a symmetric configuration of the field and flow and the downward motion that increases with radial distance by up to 3 km s-1 near the outer penumbral border. The magnetic field is found to be highly axially symmetric without any indication of azimuthal vortices. A tight relation between field strength and inclination is obtained with a gradient of 35°/1000 G independent of height. The penumbra shows "spines" hosting a pronounced negative correlation between field strength and inclination in the sense that steeper and stronger magnetic fields are related to brightenings in the line cores but not in the continuum. We discuss the dependence of the obtained results on different assumptions of parasitic light, and present indications of its overestimation by the inversion code. Title: On super-resolution in astronomical imaging Authors: Puschmann, K. G.; Kneer, F. Bibcode: 2005A&A...436..373P Altcode: Our work is an attempt to fulfil one of the aims of astronomical imaging, that is, to obtain information at high angular resolution. Stars as point sources can be represented by Dirac δ-functions whose Fourier transforms contain information about the position and the (integrated) intensity at all angular frequencies. Thus, we can deconvolve unresolved images of star fields even at angular distances smaller than the diffraction limit of the telescope with which the observations are performed. We give an example of reconstruction of the image of two stars with an angular separation of a factor 2.5 less than α_Ra=1.22×λ/D. However, we find that super-resolution is feasible only for point sources. For extended objects the information about intensity fluctuations at angular frequencies u>u_max=D/λ=1/α_min is irretrievably lost. We discuss the impossibility of super-resolution for the Sun using a numerically simulated image of solar granulation. However, one can enhance the contrast of solar images, though without increasing angular resolution beyond the diffraction limit. 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: Quiet sun magnetic fields vs. polar faculae - local vs. global dynamo? Authors: Okunev, O. V.; Domínguez Cerdeña, I.; Puschmann, K. G.; Kneer, F.; Sánchez Almeida, J. Bibcode: 2005AN....326..205O Altcode: Quiet Sun magnetic fields in the internetwork are almost ubiquitous. Simultaneous observations in infra-red and visible lines and high spatial resolution (< 0.5'') data in visible lines show that their field strengths range from below few hundred Gauss to kilo-Gauss. Most of the flux is contained in small-scale, strong-field features located mainly in intergranular lanes. The average unsigned flux density exceeds 20 Gauss. The new detections are confirmed by recent quiet Sun observations in the G band. The generation of the strong fields in the internetwork, which may be due to a local dynamo, poses a challenging problem. - Polar faculae (PFe) are small-scale magnetic features at the polar caps of the Sun. They take part in the solar cycle and are thus likely to be rooted deeply in the solar interior. They are the result of the global dynamo at the solar poles. PFe also possess kilo-Gauss magnetic fields which have the same polarity as the global magnetic field. The rôle of quiet Sun magnetic field structures and of PFe for the dynamics of the corona and for the solar wind are addressed. Title: Polarimetry of a sunspot at disk centre Authors: Sánchez Cuberes, M.; Puschmann, K. G.; Wiehr, E. Bibcode: 2004IAUS..223..237S Altcode: 2005IAUS..223..237S No abstract at ADS Title: Time series of high resolution photospheric spectra in a quiet region of the sun. I. Analysis of global and spatial variations of line parameters Authors: Puschmann, K.; Vázquez, M.; Bonet, J. A.; Ruiz Cobo, B.; Hanslmeier, A. Bibcode: 2003A&A...408..363P Altcode: 2012arXiv1205.1723P A 50 min time series of one-dimensional slit-spectrograms, taken in quiet sun at disk centre, observed at the German Vacuum Tower Telescope (Observatorio del Teide), was used to study the global and spatial variations of different line parameters. In order to determine the vertical structure of the photosphere two lines with well separated formation heights have been considered. The data have been filtered of p-modes to isolate the pure convective phenomenon. From our studies of global correlation coefficients and coherence and phase shift analyses between the several line parameters, the following results can be reported. The convective velocity pattern preserves structures larger than 1.0 arcs to the highest layers of the photosphere ( ~ 435 km). However, at these layers, in the intensity pattern only structures larger than 2.0 arcs are still connected with those at the continuum level although showing inverted brightness contrast. This confirms an inversion of temperature that we have found at a height of ~ 140 km. A possible evidence of gravity waves superimposed to the convective motions is derived from the phase shift analysis. We interprete the behaviour of the full width at half maximum and the equivalent width as a function of the distance to the granular borders, as a consequence of enhanced turbulence and/or strong velocity gradients in the intergranular lanes. Title: Models of a Small and a Large Mean Granular Cell Obtained from Inversion of Spectrometric Data Observed with Adaptive Optics Authors: Puschmann, K.; Ruiz Cobo, B. Bibcode: 2003ANS...324...21P Altcode: 2003ANS...324..C01P No abstract at ADS Title: Models of a mean granular cell Authors: Puschmann, K.; Ruiz Cobo, B.; Vázquez, M.; Bonet, J. A.; Hanslmeier, A. Bibcode: 2003AN....324..352P Altcode: From inversion of a time series of slit spectra, observed in a quiet region of the solar photosphere, averaged models of a granular cell have been obtained showing the stratification of physical quantities versus optical depth and geometrical height. Furthermore a semi-empiric dynamic model of a mean granular cell has been derived and the results are presented. Title: A Fabry-Perot spectrometer for high-resolution observation of the Sun Authors: Kneer, F.; Al, N.; Hirzberger, J.; Nicklas, H.; Puschmann, K. G. Bibcode: 2003AN....324..302K Altcode: No abstract at ADS Title: Size-dependent properties of simulated 2-D solar granulation Authors: Gadun, A. S.; Hanslmeier, A.; Pikalov, K. N.; Ploner, S. R. O.; Puschmann, K. G.; Solanki, S. K. Bibcode: 2000A&AS..146..267G Altcode: Two time-dependent sets of two-dimensional hydrodynamic models of solar granulation have been analyzed to obtain dependence of simulated thermal convection on the horizontal size of the convection cells. The two sets of models treat thermal convection either as fully non-stationary, multiscale convection (granular convection is a surface phenomenon) or as quasi-steady-state convection cells (they treat granular convection as a collection of deep-formed cells). The following results were obtained: 1) quasi-steady convection cells can be divided into 3 groups according to their properties and evolution, namely small-scale (up to L ~ 900 km), intermediate-scale (1000-1500 km) and large-scale (larger 1500 km) convection cells. For the first group thermal damping due to radiative exchange of energy, mostly in the horizontal direction, is very important. Large-scale cells build up a pressure excess, which can lead to their total fragmentation. Similar processes also acts on the fully non-stationary convection. 2) The largest horizontal size of convection cells for which steady-state solutions can be obtained is about 1500 km. This corresponds to granules, i.e. the bright parts of the convection cells, with a diameter of about 1000 km. 3) In addition to the zone of high convective instability associated with the partial ionization of hydrogen, we identify another layer harboring important dynamic processes in steady-state models. Just below the hydrogen-ionization layer pressure fluctuations and the acoustic flux are reduced. Steady-state models with reflecting lateral boundaries even exhibit an inversion of pressure fluctuations there. 4) From observational point of view the surface convection differs from steady-state deep treatment of thermal convection in the dependence of vertical granular velocities on their sizes for small-scale inhomogeneous. However, they cannot be distinguished by the dependence of temperature or emergent intensity of brightness structures. 5) Both kinds of models demonstrate the inversion of density in subphotospheric layers. It is more pronounced in small-scale cells and inside hot upflows. 6) The brightness of simulated granules linearly increases with their size for small granules and is approximately constant or even decreases slightly for larger granules. For intergranular lanes the simulations predict a decrease of their brightness with increasing size. It falls very rapidly for narrow lanes and remains unchanged for broader lanes. 7) A quantitative comparison of the brightness properties of simulated granulation with real observations shows that the strong size-dependence of the properties of the smallest simulated granules is not accessible to current observations due to their limited spatial resolution. The observed size dependences result rather from spatial smoothing and the granule-finding algorithm. We do not exclude, however, an influence of the limitations of the 2-D treatment of thermal convection on the present results. Title: Solar Line Bisectors in the Infrared Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K. Bibcode: 1999ASSL..239..227P Altcode: 1999msa..proc..227P In the present work we made some analysis with respect to shifts and asymmetries of infrared solar spectral lines to get information about vertical velocity fields in the deep layers of the Solar Photosphere. For the analysis of shifts and asymmetries of bisectors were used. We averaged bisectors belonging to a group of similar line parameter. Therefore it was possible, to analyse correlations between asymmetries and line shifts and corresponding vertical velocities with line parameters and to discuss the results with other literature. Title: Solar line bisectors in the infrared Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K. Bibcode: 1995IAUS..176P.117P Altcode: No abstract at ADS Title: Solar line bisectors in the infrared. Authors: Puschmann, K.; Anslmeier, A.; Solanki, S. Bibcode: 1994AGAb...10..117P Altcode: No abstract at ADS