Author name code: tritschler ADS astronomy entries on 2022-09-14 author:"Tritschler, Aexandra" ------------------------------------------------------------------------ Title: The National Science Foundation's Daniel K. Inouye Solar Telescope — Status Update Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn, A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.; Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.; Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.; Mathioudakis, M.; Dkist Team Bibcode: 2021AAS...23810601R Altcode: The National Science Foundation's 4m Daniel K. Inouye Solar Telescope (DKIST) on Haleakala, Maui is now the largest solar telescope in the world. DKIST's superb resolution and polarimetric sensitivity will enable astronomers to unravel many of the mysteries the Sun presents, including the origin of solar magnetism, the mechanisms of coronal heating and drivers of flares and coronal mass ejections. Five instruments, four of which provide highly sensitive measurements of solar magnetic fields, including the illusive magnetic field of the faint solar corona. The DKIST instruments will produce large and complex data sets, which will be distributed through the NSO/DKIST Data Center. DKIST has achieved first engineering solar light in December of 2019. Due to COVID the start of the operations commissioning phase is delayed and is now expected for fall of 2021. We present a status update for the construction effort and progress with the operations commissioning phase. Title: Solar physics in the 2020s: DKIST, parker solar probe, and solar orbiter as a multi-messenger constellation Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.; Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi, G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.; Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.; Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R. Bibcode: 2020arXiv200408632M Altcode: The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope (DKIST) is about to start operations at the summit of Haleakala (Hawaii). DKIST will join the early science phases of the NASA and ESA Parker Solar Probe and Solar Orbiter encounter missions. By combining in-situ measurements of the near-sun plasma environment and detail remote observations of multiple layers of the Sun, the three observatories form an unprecedented multi-messenger constellation to study the magnetic connectivity inside the solar system. This white paper outlines the synergistic science that this multi-messenger suite enables. Title: An Overview of DKIST Operations Commissioning and Tools Authors: Alexov, A.; Tritschler, A.; Rimmele, T.; Marshall, H.; Parraguez, A. Bibcode: 2020ASPC..527..435A Altcode: 2020adass..29..435A The Daniel K. Inouye Solar Telescope (DKIST) is a 4-meter clear aperture solar telescope nearing the end of its construction on the summit of Haleakalā on the island of Maui, Hawai'i. It will be the largest solar telescope in the world when completed in summer 2020. We present a condensed overview of the DKIST Operations Commissioning Phase (OCP) which will start after the completion of construction. This Operations Commissioning phase will allow for a manageable transition from the end of construction into steady-state operations over the course of approximately one year. During this phase, science operations will specifically integrate, test and streamline its procedures by exercising through all steps of the DKIST's Science Operations Lifecycle. We will also briefly introduce software tools that are or will be used by Science Operations, Technical Operations and the DKIST Data Center. Title: High-resolution imaging and near-infrared spectroscopy of penumbral decay Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; Rezaei, R.; Sobotka, M.; Deng, N.; Wang, H.; Tritschler, A.; Collados, M.; Diercke, A.; González Manrique, S. J. Bibcode: 2018A&A...614A...2V Altcode: 2018arXiv180103686V
Aims: Combining high-resolution spectropolarimetric and imaging data is key to understanding the decay process of sunspots as it allows us to scrutinize the velocity and magnetic fields of sunspots and their surroundings.
Methods: Active region NOAA 12597 was observed on 2016 September 24 with the 1.5-meter GREGOR solar telescope using high-spatial-resolution imaging as well as imaging spectroscopy and near-infrared (NIR) spectropolarimetry. Horizontal proper motions were estimated with local correlation tracking, whereas line-of-sight (LOS) velocities were computed with spectral line fitting methods. The magnetic field properties were inferred with the "Stokes Inversions based on Response functions" (SIR) code for the Si I and Ca I NIR lines.
Results: At the time of the GREGOR observations, the leading sunspot had two light bridges indicating the onset of its decay. One of the light bridges disappeared, and an elongated, dark umbral core at its edge appeared in a decaying penumbral sector facing the newly emerging flux. The flow and magnetic field properties of this penumbral sector exhibited weak Evershed flow, moat flow, and horizontal magnetic field. The penumbral gap adjacent to the elongated umbral core and the penumbra in that penumbral sector displayed LOS velocities similar to granulation. The separating polarities of a new flux system interacted with the leading and central part of the already established active region. As a consequence, the leading spot rotated 55° clockwise over 12 h.
Conclusions: In the high-resolution observations of a decaying sunspot, the penumbral filaments facing the flux emergence site contained a darkened area resembling an umbral core filled with umbral dots. This umbral core had velocity and magnetic field properties similar to the sunspot umbra. This implies that the horizontal magnetic fields in the decaying penumbra became vertical as observed in flare-induced rapid penumbral decay, but on a very different time-scale. Title: High-resolution Observations of Hα Spectra with a Subtractive Double Pass Authors: Beck, C.; Rezaei, R.; Choudhary, D. P.; Gosain, S.; Tritschler, A.; Louis, R. E. Bibcode: 2018SoPh..293...36B Altcode: 2017arXiv171207077B High-resolution imaging spectroscopy in solar physics has relied on Fabry-Pérot interferometers (FPIs) in recent years. FPI systems, however, become technically challenging and expensive for telescopes larger than the 1 m class. A conventional slit spectrograph with a diffraction-limited performance over a large field of view (FOV) can be built at much lower cost and effort. It can be converted into an imaging spectro(polari)meter using the concept of a subtractive double pass (SDP). We demonstrate that an SDP system can reach a similar performance as FPI-based systems with a high spatial and moderate spectral resolution across a FOV of 100″×100″ with a spectral coverage of 1 nm. We use Hα spectra taken with an SDP system at the Dunn Solar Telescope and complementary full-disc data to infer the properties of small-scale superpenumbral filaments. We find that the majority of all filaments end in patches of opposite-polarity fields. The internal fine-structure in the line-core intensity of Hα at spatial scales of about 0.″5 exceeds that in other parameters such as the line width, indicating small-scale opacity effects in a larger-scale structure with common properties. We conclude that SDP systems in combination with (multi-conjugate) adaptive optics are a valid alternative to FPI systems when high spatial resolution and a large FOV are required. They can also reach a cadence that is comparable to that of FPI systems, while providing a much larger spectral range and a simultaneous multi-line capability. Title: Plasma flows and magnetic field interplay during the formation of a pore Authors: Ermolli, I.; Cristaldi, A.; Giorgi, F.; Giannattasio, F.; Stangalini, M.; Romano, P.; Tritschler, A.; Zuccarello, F. Bibcode: 2017A&A...600A.102E Altcode: 2017arXiv170106440E
Aims: Recent simulations of solar magneto-convection have offered new levels of understanding of the interplay between plasma motions and magnetic fields in evolving active regions. We aim at verifying some aspects of the formation of magnetic regions derived from recent numerical studies in observational data.
Methods: We studied the formation of a pore in the active region (AR) NOAA 11462. We analysed data obtained with the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope on April 17, 2012, consisting of full Stokes measurements of the Fe I 617.3 nm lines. Furthermore, we analysed SDO/HMI observations in the continuum and vector magnetograms derived from the Fe I 617.3 nm line data taken from April 15 to 19, 2012. We estimated the magnetic field strength and vector components and the line-of-sight (LOS) and horizontal motions in the photospheric region hosting the pore formation. We discuss our results in light of other observational studies and recent advances of numerical simulations.
Results: The pore formation occurs in less than 1 h in the leading region of the AR. We observe that the evolution of the flux patch in the leading part of the AR is faster (<12 h) than the evolution (20-30 h) of the more diffuse and smaller scale flux patches in the trailing region. During the pore formation, the ratio between magnetic and dark area decreases from 5 to 2. We observe strong downflows at the forming pore boundary and diverging proper motions of plasma in the vicinity of the evolving feature that are directed towards the forming pore. The average values and trends of the various quantities estimated in the AR are in agreement with results of former observational studies of steady pores and with their modelled counterparts, as seen in recent numerical simulations of a rising-tube process. The agreement with the outcomes of the numerical studies holds for both the signatures of the flux emergence process (e.g. appearance of small-scale mixed polarity patterns and elongated granules) and the evolution of the region. The processes driving the formation of the pore are identified with the emergence of a magnetic flux concentration and the subsequent reorganization of the emerged flux, by the combined effect of velocity and magnetic field, in and around the evolving structure.

Movies associated to Figs. 1 and 4 are available at http://www.aanda.org Title: Daniel K. Inouye Solar Telescope: High-resolution observing of the dynamic Sun Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.; Kuhn, J. R.; Lin, H.; Rast, M. P.; McMullin, J. P.; Schmidt, W.; Wöger, F.; DKIST Team Bibcode: 2016AN....337.1064T Altcode: The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly known as the Advanced Technology Solar Telescope (ATST) is currently under construction on Haleakalā (Maui, Hawai'i) projected to start operations in 2019. At the time of completion, DKIST will be the largest ground-based solar telescope providing unprecedented resolution and photon collecting power. The DKIST will be equipped with a set of first-light facility-class instruments offering unique imaging, spectroscopic and spectropolarimetric observing opportunities covering the visible to infrared wavelength range. This first-light instrumentation suite will include: a Visible Broadband Imager (VBI) for high-spatial and -temporal resolution imaging of the solar atmosphere; a Visible Spectro-Polarimeter (ViSP) for sensitive and accurate multi-line spectropolarimetry; a Fabry-Pérot based Visible Tunable Filter (VTF) for high-spatial resolution spectropolarimetry; a fiber-fed Diffraction-Limited Near Infra-Red Spectro-Polarimeter (DL-NIRSP) for two-dimensional high-spatial resolution spectropolarimetry (simultaneous spatial and spectral information); and a Cryogenic Near Infra-Red Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field measurements and on-disk observations of, e.g., the CO lines at 4.7 μm. We will provide an overview of the DKIST's unique capabilities with strong focus on the first-light instrumentation suite, highlight some of the additional properties supporting observations of transient and dynamic solar phenomena, and touch on some operational strategies and the DKIST critical science plan. Title: He I Vector Magnetic Field Maps of a Sunspot and Its Superpenumbral Fine-Structure Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Tritschler, A. Bibcode: 2015SoPh..290.1607S Altcode: 2015arXiv150505567S; 2015SoPh..tmp...60S Advanced inversions of high-resolution spectropolarimetric observations of the He I triplet at 1083 nm are used to generate unique maps of the chromospheric magnetic field vector across a sunspot and its superpenumbral canopy. The observations were acquired by the Facility Infrared Spectropolarimeter (FIRS) at the Dunn Solar Telescope (DST) on 29 January 2012. Multiple atmospheric models are employed in the inversions because superpenumbral Stokes profiles are dominated by atomic-level polarization, while sunspot profiles are Zeeman-dominated, but also exhibit signatures that might be induced by symmetry-breaking effects of the radiation field incident on the chromospheric material. We derive the equilibrium magnetic structure of a sunspot in the chromosphere and furthermore show that the superpenumbral magnetic field does not appear to be finely structured, unlike the observed intensity structure. This suggests that fibrils are not concentrations of magnetic flux, but are instead distinguished by individualized thermalization. We also directly compare our inverted values with a current-free extrapolation of the chromospheric field. With improved measurements in the future, the average shear angle between the inferred magnetic field and the potential field may offer a means to quantify the non-potentiality of the chromospheric magnetic field to study the onset of explosive solar phenomena. Title: Understanding the Fe I Line Measurements Returned by the Helioseismic and Magnetic Imager (HMI) Authors: Cohen, D. P.; Criscuoli, S.; Farris, L.; Tritschler, A. Bibcode: 2015SoPh..290..689C Altcode: 2015SoPh..tmp...17C; 2015arXiv150202559C The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) observes the Sun at the Fe I 6173 Å line and returns full-disk maps of line-of-sight (LOS) observables including the magnetic flux density, velocities, Fe I line width, line depth, and continuum intensity. These data are estimated through an algorithm (the MDI-like algorithm, hereafter) that combines observables obtained at six wavelength positions within the Fe I 6173 Å line. To properly interpret such data, it is important to understand any effects of the instrument and of the pipeline that generates these data products. We tested the accuracy of the line width, line depth, and continuum intensity returned by the MDI-like algorithm using various one-dimensional (1D) atmosphere models. It was found that HMI estimates of these quantities are highly dependent on the shape of the line, therefore on the LOS angle and the magnetic flux density associated with the model, and less to line shifts with respect to the central positions of the instrument transmission profiles. In general, the relative difference between synthesized values and HMI estimates increases toward the limb and with the increase of the field; the MDI-like algorithm seems to fail in regions with fields larger than approximately 2000 G. Instrumental effects were investigated by analyzing HMI data obtained at daily intervals for a span of three years at disk center in the quiet Sun and hourly intervals for a span of 200 hours. The analysis revealed periodicities induced by the variation of the orbital velocity of the observatory with respect to the Sun, and long-term trends attributed to instrument adjustments, re-calibrations, and instrumental degradation. Title: DKIST: Observing the Sun at High Resolution Authors: Tritschler, A.; Rimmele, T. R.; Berukoff, S.; Casini, R.; Craig, S. C.; Elmore, D. F.; Hubbard, R. P.; Kuhn, J. R.; Lin, H.; McMullin, J. P.; Reardon, K. P.; Schmidt, W.; Warner, M.; Woger, F. Bibcode: 2015csss...18..933T Altcode: The 4-m aperture Daniel K. Inouye Solar Telescope (DKIST) formerly known as the Advanced Technology Solar Telescope (ATST) and currently under construction on Haleakalā (Maui, Hawai'i) will be the largest solar ground-based telescope and leading resource for studying the dynamic Sun and its phenomena at high spatial, spectral and temporal resolution. Accurate and sensitive polarimetric observations at high-spatial resolution throughout the solar atmosphere including the corona is a high priority and a major science driver. As such the DKIST will offer a combination of state-of-the-art instruments with imaging and/or spectropolarimetric capabilities covering a broad wavelength range. This first-light instrumentation suite will include: a Visible Broadband Imager (VBI) for high-spatial and -temporal resolution imaging of the solar atmosphere; a Visible Spectro-Polarimeter (ViSP) for sensitive and accurate multi-line spectropolarimetry; a double Fabry-Pérot based Visible Tunable Filter (VTF) for high-spatial resolution spectropolarimetry; a fiber-fed 2D Diffraction-Limited Near Infra-Red Spectro-Polarimeter (DL-NIRSP); and a Cryogenic Near Infra-Red Spectro-Polarimeter (Cryo-NIRSP) for coronal magnetic field measurements and on-disk observations of e.g. the CO lines at 4.7 microns. We will provide a brief overview of the DKIST's unique capabilities to perform spectroscopic and spectropolarimetric measurements of the solar atmosphere using its first-light instrumentation suite, the status of the construction project, and how facility and data access is provided to the US and international community. Title: The DKIST Operations Lifecycle: From Proposal Preparation to Completion Authors: Tritschler, A.; Berukoff, S. J.; Rimmele, T. R. Bibcode: 2014AGUFMSH41C4161T Altcode: The 4-m aperture Daniel Ken Inouye Solar Telescope (DKIST), formerly known as the Advanced Technology Solar Telescope (ATST), will be the largest ground-based solar telescope when construction is completed in 2019. Community access to the facility and its high-resolution optical and infrared instrumentation suite will be provided through a proposal merit and approval process, optimizing DKIST for high-impact scientific use and emphasizing a high operational efficiency of the facility. In this presentation we provide a high-level overview of, and guide through, the planned phases of the operations lifecycle relevant to anyone wishing to make use of this facility. The lifecycle is initiated by the preparation and submission of scientific proposals by Principal Investigators, and concluded by the successful execution of all observations relevant to an approved proposal, as well as storage and management of acquired data and metadata. Title: The Daniel K. Inouye Solar Telescope: A Project Update. Authors: Rimmele, T.; Berger, T.; McMullin, J.; Warner, M.; Casinsi, R.; Kuhn, J.; Lin, H.; Woeger, F.; Schmidt, W.; Tritschler, A.; Inouye, Daniel K.; Solar Telescope Team Bibcode: 2014amos.confE..43R Altcode: The Advanced Technology Solar Telescope will be the largest solar facility ever built. Designed and developed to meet the needs of critical high resolution and high sensitivity spectral and polarimetric observations of the sun, this facility will support key experiments for the study of solar magnetism and its influence on the solar wind, flares, coronal mass ejections and solar irradiance variability. The 4-meter diameter facility will operate over a broad wavelength range (0.35 to 28 microns), using state-of-the-art adaptive optics systems to provide diffraction limited imaging and the ability to resolve features approximately 20 km on the Sun. Five first light instruments will be available at the start of operations. Key subsystems have been designed and fabrication is well underway, including the site construction, which began in December 2012. We provide an update on the development of the facilities both on site at the Haleakala Observatories in Maui and the development of components around the world. We present the overall construction and integration schedule leading to the start of operations in mid-2019 and touch on operations aspects. Title: Spectral Signatures of Penumbral Transients Authors: Reardon, K.; Tritschler, A.; Katsukawa, Y. Bibcode: 2013ApJ...779..143R Altcode: In this work we investigate the properties of penumbral transients observed in the upper photospheric and chromospheric region above a sunspot penumbra using two-dimensional spectroscopic observations of the Ca II 854.21 nm line with a 5 s cadence. In our 30 minutes of observations, we identify several penumbral-micro jets (PMJs) with cotemporal observations from Dunn Solar Telescope/IBIS and Hinode/SOT. We find that the line profiles of these PMJ events show emission in the two wings of the line (±0.05 nm), but little modification of the line core. These are reminiscent of the line profiles of Ellerman bombs observed in plage and network regions. Furthermore, we find evidence that some PMJ events have a precursor phase starting 1 minute prior to the main brightening that might indicate initial heating of the plasma prior to an acoustic or bow shock event. With the IBIS data, we also find several other types of transient brightenings with timescales of less than 1 minute that are not clearly seen in the Hinode/SOT data. The spectral profiles and other characteristics of these events are significantly different from those of PMJs. The different appearances of all these transients are an indicator of the general complexity of the chromospheric magnetic field and underscore the highly dynamic behavior above sunspots. It also highlights the care that is needed in interpreting broadband filter images of chromospheric lines, which may conceal very different spectral profiles, and the underlying physical mechanisms at work. Title: Statistical study of magnetic cancellations and on-disk type-II spicules Authors: Chen, Xin; Deng, N.; Lamb, D.; Jing, J.; Tritschler, A.; Reardon, K. P.; Wang, H. Bibcode: 2013SPD....44...04C Altcode: We present a study using coordinated observations of the Interferometric BIdimensional Spectrometer (IBIS) at the Dunn Solar Telescope and Hinode / Solar Optical Telescope of a quiet sun (QS) region near disk center. Our goal is to analyze the relationship between the cancellation of opposite magnetic polarities in the photosphere and "Rapid Blueshifted Excursions" (RBEs) by comparing quasi-simultaneous magnetograms and chromospheric Hα line profiles. On the one hand, the RBEs are considered the on-disk counterpart of the type-II spicules observed at the limb that are most likely caused by magnetic reconnection on small scales. On the other hand, the magnetic cancellation is a signature after small-scale reconnection in the QS. We developed an automatic tracking algorithm for detecting magnetic cancellation events in the photosphere, based on the existing SWAMIS code which is good at tracking magnetic flux emergence. Our code can find characteristics of each cancellation event and the detected cancellation sites appear to outline the supergranular network. Furthermore, another automatic tracking code for RBEs has been developed for the spectroscopic observations obtained with IBIS. We are able to show a statistical distribution of the properties of RBEs, such as lifetime, shape, and line-of-sight velocity. Finally, using the spatial and temporal tracking of both magnetic cancellation events and RBEs, we find that there is no simple one-to-one correspondence. The majority of RBEs are related to magnetic cancellation events, however a subset of them are not. Title: Velocity and Magnetic Field Distribution in a Forming Penumbra Authors: Romano, P.; Frasca, D.; Guglielmino, S. L.; Ermolli, I.; Tritschler, A.; Reardon, K. P.; Zuccarello, F. Bibcode: 2013ApJ...771L...3R Altcode: We present results from the analysis of high-resolution spectropolarimetric and spectroscopic observations of the solar photosphere and chromosphere, obtained shortly before the formation of a penumbra in one of the leading polarity sunspots of NOAA active region 11490. The observations were performed at the Dunn Solar Telescope of the National Solar Observatory on 2012 May 28, using the Interferometric Bidimensional Spectrometer. The data set is comprised of a 1 hr time sequence of measurements in the Fe I 617.3 nm and Fe I 630.25 nm lines (full Stokes polarimetry) and in the Ca II 854.2 nm line (Stokes I only). We perform an inversion of the Fe I 630.25 nm Stokes profiles to derive magnetic field parameters and the line-of-sight (LOS) velocity at the photospheric level. We characterize chromospheric LOS velocities by the Doppler shift of the centroid of the Ca II 854.2 nm line. We find that, before the formation of the penumbra, an annular zone of 3''-5'' width is visible around the sunspot. In the photosphere, we find that this zone is characterized by an uncombed structure of the magnetic field although no visible penumbra has formed yet. We also find that the chromospheric LOS velocity field shows several elongated structures characterized by downflow and upflow motions in the inner and outer parts of the annular zone, respectively. Title: High-Cadence and High-Resolution Halpha Imaging Spectroscopy of a Circular Flare's Remote Ribbon with IBIS Authors: Deng, Na; Tritschler, A.; Jing, J.; Chen, X.; Liu, C.; Reardon, K. P.; Denker, C.; Xu, Y.; Wang, H. Bibcode: 2013SPD....4440404D Altcode: We present an unprecedented high-resolution halpha imaging spectroscopic observation of a C4.1 flare taken with IBIS on 2011 October 22. The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS. Such a circular-ribbon flare with a remote brightening is predicted in 3D fan-spine reconnection but so far has been rarely reported. During the flare impulsive phase, we define "core" and "halo" structures in the observed ribbon. Examining the halpha emission spectra averaged in the flare core and halo areas, we find that only those from the flare cores show typical nonthermal electron beam heating characteristics. These characteristics include: broad and centrally reversed emission spectra, excess emission in the red wing with regard to the blue wing (i.e., red asymmetry), and redshifted bisectors of the emission spectra. We also observe rather quick timescales for the heating (30 s) and cooling (14--33 s) in the flare core locations. Therefore, we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution. The flare cores show two-stage motion (a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon) during the two impulsive phases of the flare. Some cores jump quickly (30 km/s) between discrete magnetic elements implying reconnection involving different flux tubes. We observe a very high temporal correlation (>0.9) between the integrated halpha and HXR emission during the flare impulsive phase. A short time delay (4.6 s) is also found in the halpha emission spikes relative to HXR bursts. The ionization timescale of the cool chromosphere and the extra time taken for the electrons to travel to the remote ribbon site may contribute to this delay. Title: He I Spectropolarimetry with FIRS: Towards Vector Magnetometry of Chromospheric Fibrils Plus New Diagnostics of Coronal Rain Authors: Schad, T. A.; Penn, M. J.; Lin, H.; Tritschler, A. Bibcode: 2012ASPC..463...25S Altcode: At the Dunn Solar Telescope, the Interferometric Bidimensional Spectrometer (IBIS) can measure the full Stokes vector of the Ca II 854.2 nm spectral line while the Facility Infrared Spectropolarimeter (FIRS) measures the Stokes vector of the He I triplet at 1083 nm. We analyze the He I triplet observed in two widely different features above NOAA AR 11295 on 19 September 2011 - thin (< 1″) chromospheric fibrils and a large-scale loop hosting a high-velocity coronal rain event. These two features are shown to first demonstrate the diagnostic potential of the He I triplet for magnetic fields in the chromosphere/transition region and second to stress the need to pair large-aperture facilities with flexible instrumentation. Inversions of the He I triplet near the penumbral boundary return azimuthal directions of the magnetic field aligned with fine-scale fibrils observed in the line core of Ca II. The coronal rain event shows Doppler velocities up to 195 km s-1, among the largest reported. We observe measurable polarization within the raining material, which may be a good magnetic diagnostic of chromospheric-like material higher in the corona within condensating loops. Title: The Sunspot Penumbra in the Photosphere: Results from Forward Synthesized Spectroscopy Authors: Tritschler, A.; Uitenbroek, H.; Rempel, M. Bibcode: 2012ASPC..463...89T Altcode: We present first results from a spectral synthesis of the Zeeman-insensitive Fe 1 557.6 nm line for two different viewing angles (0° and 30°) using numerical simulations of a sunspot as an input model. We performed a bisector analysis to calculate two-dimensional maps of line-of-sight Doppler velocities and the line width. We analyze azimuthal cuts of the LOS velocity at different penumbral radii and calculate the radial behavior of azimuthal averages of line width and intensity. Both are compared with observational results. The properties of dark cores in penumbral filaments are discussed briefly. Within the limitations of this study, we find that the results from the forward synthesized spectroscopy are in good agreement with the observations, corroborating that the photospheric structure and dynamics of the penumbra is a signature of overturning anisotropic magneto-convection. Title: Solar Limb Adaptive Optics: A Test of Wavefront Sensors and Algorithms Authors: Taylor, G. E.; Rimmele, T. R.; Marino, J.; Tritschler, A.; McAteer, R. T. J. Bibcode: 2012ASPC..463..321T Altcode: In order to advance our understanding of solar prominences, we need to be able to observe them at high spatial, spectral and temporal resolution. In order to determine physical properties of these cool and faint coronal structures, however, one is forced to use long exposure times, particularly in spectroscopic and spectropolarimetric applications. It is thus crucial that image stabilization is provided, preferrably in form of an adaptive optics (AO) system that is capable to lock onto the off-limb prominence structure, potentially providing diffraction limited imaging. We investigate the preliminary design of such a solar-limb AO system based on a correlating Shack-Hartmann sensor. As an alternative we also studied a solar-limb AO wavefront sensor using a phase-diverse approach. Title: The Influence of Molecular Lines on the Measurement of Photospheric Velocities Authors: Uitenbroek, H.; Dumont, N.; Tritschler, A. Bibcode: 2012ASPC..463...99U Altcode: We use different solar atmospheric models to investigate the influence of molecular lines on the accuracy with which line-of-sight velocities of mass flows can be measured from Doppler shifts. Particularly in relatively cool atmospheres molecules become more abundant and give rise to a thick forest of perturbing lines. Using bisectors we estimate the apparent shift introduced in the positions of the C I 538.0 nm and Fe I 557.6 nm lines by molecular lines in one-dimensional models with different effective temperatures, ranging from 3750 K to 6250 K, and in a three-dimensional section from a solar magneto-convection simulation. We find that the core of the iron line is mostly unaffected, and that by contrast the carbon line is severely compromised by molecular lines, even in environments with effective temperatures similar to those in the quiet Sun. Title: Halpha Imaging Spectroscopy of a C-class flare with IBIS Authors: Deng, N.; Tritschler, A.; Jing, J.; Chen, X.; Reardon, K.; Liu, C.; Xu, Y.; Wang, H. Bibcode: 2012IAUSS...6E.307D Altcode: We present a rare high cadence and high spatial resolution spectroscopic observation of a C4.1 Flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in NOAA AR 11324. The IBIS with a round FOV of 90" x 90" and 0.1"/pixel detector image scale scanned the Halpha line from 6561.1 to 6563.8 Angstrom with 0.1 Angstrom stepsize for 28 steps. Each scan takes about 4.8 s. The flare occurred in a mixed polarity region with two parasite configurations. The flare shows multiple bright ribbons in the chromosphere spreading over a region of 120" x 60". IBIS observed a remote ribbon of the flare and fully covered its temporal evolution. The Halpha emission integrated over this ribbon area exhibits several bursts over four minutes during the flare impulsive phase that are temporally correlated with the subpeaks of RHESSI hard X-ray (HXR) light curves. During the strong bursts of the Halpha emission, we observe a central reversal patten in the Halpha line core, which is believed to be a signature of nonthermal process caused by direct electron precipitation. The line core shows blueward shift that increases with the Halpha emission, which might be related to chromospheric evaporation. The Halpha emission is stronger in the red wing than in the blue wing during the strong bursts. Substructures within the ribbon are also identified. A bright core feature that is 30% brighter than the entire ribbon moves at an apparent velocity of about 30 km/s within the ribbon during the strongest burst of Halpha emission co-temporal with a strong subpeak of HXR. The bright core disappeared in the decay phase of the flare. We suggest that this running bright core feature tracks the site of electron precipitation. Title: Science with Large Solar Telescopes Authors: Cauzzi, G.; Tritschler, A.; Deng, Y. Bibcode: 2012IAUSS...6E....C Altcode: With several large aperture optical/IR telescopes coming on-line, and scheduled for the near future, solar physics is on the verge of a quantum leap in observational capabilities. An efficient use of such facilities will require new and innovative approaches to both observatory operations and data handling.

This two-days long Special Session will discuss the science expected with large solar telescopes, and start addressing the strategies necessary to optimize their scientific return. Cutting edge solar science as derived from state of the art observations and numerical simulations will be presented, and discussions will be held on the role of large facilities in satisfying the demanding requirements of spatial and temporal resolution, stray-light, and spectro-polarimetric accuracy. Building on the experience of recently commissioned telescopes, we will then discuss critical issues for the development of future facilities including operational issues peculiar to large telecopes, and strategies for their best use. Title: The Visible Broadband Imager: The Sun at High Spatial and Temporal Resolution Authors: Wöger, F.; McBride, W.; Ferayorni, A.; Gregory, S.; Hegwer, S.; Tritschler, A.; Uitenbroek, H. Bibcode: 2012ASPC..463..431W Altcode: The Visible Broadband Imager (VBI) will be the primary first-light instrument for the Advanced Technology Solar Telescope (ATST). It is designed to observe the solar atmosphere at heights ranging from the photosphere to chromosphere. High frame-rate detectors that sample the FOV of up to 2.8 arcmin in diameter critically at the diffraction limit of ATST's 4 meter aperture will provide near real-time speckle reconstruction imaging. With its focus on high-spatial resolution, the VBI will be addressing scientific questions related to the smallest structures visible in the solar atmosphere with high photometric precision. The capability to observe the solar atmosphere with a cadence of about 3 seconds per reconstructed image will enable the VBI to temporally resolve fast evolving structures. In this contribution we present the major aspects of the current design of the VBI and highlight some scientific questions related to fast evolving, small-scale features within the solar atmosphere that the VBI will address. Title: Construction of the Advanced Technology Solar Telescope Authors: Rimmele, T. R.; Keil, S.; McMullin, J.; Knölker, M.; Kuhn, J. R.; Goode, P. R.; Rosner, R.; Casini, R.; Lin, H.; Tritschler, A.; Wöger, F.; ATST Team Bibcode: 2012ASPC..463..377R Altcode: The 4m Advance Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading ground-based resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. The project has entered its construction phase. Major subsystems have been contracted. As its highest priority science driver ATST shall provide high resolution and high sensitivity observations of the dynamic solar magnetic fields throughout the solar atmosphere, including the corona at infrared wavelengths. With its 4m aperture, ATST will resolve features at 0.″03 at visible wavelengths and obtain 0.″1 resolution at the magnetically highly sensitive near infrared wavelengths. A high order adaptive optics system delivers a corrected beam to the initial set of state-of-the-art, facility class instrumentation located in the Coudé laboratory facility. The initial set of first generation instruments consists of five facility class instruments, including imagers and spectro-polarimeters. The high polarimetric sensitivity and accuracy required for measurements of the illusive solar magnetic fields place strong constraints on the polarization analysis and calibration. Development and construction of a four-meter solar telescope presents many technical challenges, including thermal control of the enclosure, telescope structure and optics and wavefront control. A brief overview of the science goals and observational requirements of the ATST will be given, followed by a summary of the design status of the telescope and its instrumentation, including design status of major subsystems, such as the telescope mount assembly, enclosure, mirror assemblies, and wavefront correction Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from the Photosphere to the Corona Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera, M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.; Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M. Bibcode: 2012ASPC..463.....R Altcode: No abstract at ADS Title: Observing strategies for future solar facilities: the ATST test case Authors: Uitenbroek, H.; Tritschler, A. Bibcode: 2012IAUSS...6E.401U Altcode: Traditionally solar observations have been scheduled and performed very differently from night time efforts, in particular because we have been observing the Sun for a long time, requiring new combinations of observables to make progress, and because solar physics observations are often event driven on time scales of hours to days. With the proposal pressure that is expected for new large-aperture facilities, we can no longer afford the time spent on custom setups, and will have to rethink our scheduling and operations. We will discuss our efforts at Sac Peak in preparing for this new era, and outline the planned scheduling and operations planning for the ATST in particular. Title: Multi-wavelength Spectropolarimetry Of A Sunspot Superpenumbra With Firs And Ibis Authors: Schad, Thomas A.; Tritschler, A.; Penn, M. J. Bibcode: 2012AAS...22020302S Altcode: Extending nearly radially from magnetic field concentrations like sunspot umbrae or pores, threadlike fibrils observed in the chromosphere and transition region host a variety of dynamic behavior and have long been considered local tracers for the magnetic field. Morphologically, fibrils are similar to spicules seen on the limb. The connectivity of fibrils outside of the magnetic field concentrations with the photosphere and/or corona is not well understood, and probing the magnetic field in these features remains challenging. In this contribution we describe multi-wavelength spectropolarimetric observations from the Dunn Solar Telescope in New Mexico using the Facility Infrared Spectropolarimeter (FIRS) and the Interferometric BiDimensional Spectropolarimeter (IBIS). FIRS performs high resolution slit spectropolarimetry in the He I triplet at 1083 nm, which is a promising diagnostic of chromospheric vector fields. Significant progress has been made to boost the accuracy and sensitivity of these measurements. Here we present measurements of an active region sunspot at a spatial resolution of 0.3 arcsec and an RMS noise in Stokes Q,U,V spectra down to 0.0003 in units of the local continuum (SNR > 3300). We perform full inversions of these spectra taking into account both Zeeman and Hanle effects. Initial results lend support for field-aligned fibrils near the penumbral boundary of a sunspot. Jointly with the FIRS observations, we use IBIS to observe the Stokes vectors of Ca II 854.2 nm and Fe I 617.3 nm and the intensity spectrum of H-alpha 656.3 nm. As a spectral imaging instrument, IBIS rapidly scans through the three spectral lines over a 45'' by 95'' FOV at an overall cadence of 50 seconds, allowing a much better description the dynamics of fibrils observed by both FIRS and IBIS. Title: Multi-height Spectropolarimetry Of Sunspots With Firs And Ibis Authors: Jaeggli, Sarah A.; Lin, H.; Tritschler, A. Bibcode: 2012AAS...22020606J Altcode: The effects of radiative transfer prevent the characterization of the magnetic field at a single geometric height in the photosphere of a sunspot. Therefore, a full 3D characterization of the magnetic field is necessary to understand many properties of sunspots, such as the true state of hydrostatic equilibrium. Many current and proposed solar spectropolarimeters are capable of taking near-simultaneous observations at multiple wavelengths. Combining these rich datasets provides a welcome problem to the community. We present the first joint observations of the magnetically sensitive photospheric Fe I lines at 630 and 1565 nm taken with the Facility Infrared Spectropolarimeter (FIRS); and the chromospheric Ca II line at 854 nm taken with the Interferometric Bi-Dimensional Spectrometer (IBIS); both instruments operated at the Dunn Solar Telescope. These wavelengths allow us to probe the magnetic field over a broad range of heights, from the bottom of the photosphere to the chromosphere. We investigate the magnetic field topologies of several sunspots of different size and magnetic complexity. Title: High Cadence and High Resolution Halpha Imaging Spectroscopy of a C4.1 Flare with IBIS Authors: Deng, Na; Tritschler, A.; Jing, J.; Chen, X.; Reardon, K.; Liu, C.; Xu, Y.; Wang, H. Bibcode: 2012AAS...22020449D Altcode: We present a rare high cadence and high spatial resolution spectroscopic observation of a C4.1 Flare taken with the Interferometric Bidimensional Spectrometer (IBIS) in conjunction with the adaptive optics system at the 76cm Dunn Solar Telescope on 2011 October 22 in NOAA AR11324. The IBIS with a round FOV of 90"X90" and 0.1"/pix detector image scale scanned the Halpha line from 6561.1 to 6563.8 A with 0.1 A stepsize for 28 steps. Each scan takes about 4.8s. The flare occurred in a mixed polarity region with two parasite configurations. The flare shows multiple bright ribbons in the chromosphere spreading over a region of 120"X60". IBIS observed a remote ribbon of the flare and fully covered its temporal evolution. The Halpha emission integrated over this ribbon area exhibits several bursts over four minutes during the flare impulsive phase that are temporally correlated with the subpeaks of RHESSI hard X-ray (HXR) light curves. During the strongest burst of the Halpha emission, we observe a central reversal patten in the Halpha line core, which is believed to be a signature of nonthermal process caused by direct electron precipitation. The line core shows blueward shift that increases with the Halpha emission, which might be related to chromospheric evaporation. The line width also increases with the emission. The Halpha emission is stronger in the red wing than in the blue wing during the strong bursts. Substructures within the ribbon are also identified. A bright core feature that is 30% brighter than the entire ribbon moves at an apparent velocity of about 30 km/s within the ribbon during the strongest burst of Halpha emission co-temporal with a strong subpeak of HXR. The bright core disappeared in the decay phase of the flare. We suggest that this running bright core feature tracks the site of electron precipitation. Title: Coordinated Observations Of On-disk Type II Spicules With IBIS And Hinode Authors: Chen, Xin; Na, D.; Jing, J.; Tritschler, A.; Reardon, K.; Wang, H. Bibcode: 2012AAS...22020310C Altcode: Ubiquitous small-scale spicules/jets in the chromosphere are believed to be an important ingredient contributing to coronal heating and solar wind by supplying energy and mass upwards. In particular, type II spicules discovered at the solar limb (De Pontieu et al. 2007) and their highly probable chromospheric on disk counterpart "Rapid Blueshifted Excursions" (RBEs; Langangen et al. 2008) have drawn much attention in recent years. Their rapid heating, high speed upflow and association with magnetic field indicate that the most possible underlying driving mechanism is magnetic reconnection on small scales. In order to understand the physical properties of these features, we carried out a coordinated high resolution and high cadence observation of chromospheric RBEs using the Interferometric BIdimensional Spectrometer (IBIS) at the Dunn Solar Telescope and photospheric magnetic fields using Hinode SOT/SP and SOT/NFI in October 2011. Different targets near disk center were observed, such as quite sun and active regions. For each target region, both Halpha and Ca II 854.2 nm lines were scanned by IBIS with high-spatial ( 0.1 arcsec/pixel, with adaptive optics), high-temporal ( 6s) and moderate-spectral ( 0.1 angstrom) resolution. At the same time Hinode/SP and NFI pointing at the same area providing the geometry and time evolution of photospheric magnetic fields, such as flux emergence, convergence and cancellation on small spatial scales. We identify RBEs based on the IBIS observations, study their properties (velocity, density, temperature and statistical distribution) and search for signatures of small-scale magnetic reconnection in the Hinode magnetograms. The poster will show the details of the temporal and spatial relation between chromospheric RBEs and photospheric magnetic field activities.

References:

De Pontieu, B. et al. 2007, PASJ, 59, 655-662

Langangen, O. et al. 2008, ApJ, 679, L167 Title: The Observed Red Asymmetry in the Bisectors of the Chromospheric CaII 854.2 nm Line Authors: Burleigh, Kaylan; Tritschler, A.; Uitenbroek, H. Bibcode: 2011SPD....42.0304B Altcode: 2011BAAS..43S.0304B The bisector analysis of chromospheric spatially and temporally unresolved Ca II atlas profiles reveals a red asymmetry of the Doppler core in form of an "inverse C” (Uitenbroek, 2005). The origin of this red asymmetry is yet unknown. We use spatially and temporally resolved 2D spectroscopic chromospheric (CaII 854.2 nm) observations of the quiet and more active sun obtained with the Dunn Solar Telescope's Interferometric BIdimensional Spectrometer (IBIS) to determine where the inverse C-shape appears with respect to granules, inter-granular lanes, and magnetic features. To this end we generate masks of the spatial location of the red asymmetry. We also examine the temporal behavior of profiles showing this red asymmetry. In the chromosphere, we find the red asymmetry most concentrated in dark region outside of magnetic networks; it avoids nearly all bright regions. It disappears almost entirely within magnetic networks which suggests magnetic activity "damps out” the red asymmetry. Relative to the underlying photosphere, the red asymmetry preferentially occurs over or just slightly offset from inter-granular lanes; very rarely does it occur over granules. The temporal behavior of at least one red asymmetry profile shows a periodicity near 3 min. We speculate that the red asymmetry forms from upward traveling acoustic shock waves.

This work was supported by the National Solar Observatory's Research Experiences for Undergraduate (REU) program which is co-funded by the Department of Defense in partnership with the National Science foundation REU Program. Title: The Visible Broadband Imager: The Sun at High Spatial and Temporal Resolution Authors: Friedrich, Woeger; Tritschler, A.; Uitenbroek, H.; Rimmele, T. Bibcode: 2011SPD....42.2001F Altcode: 2011BAAS..43S.2001F The Visible Broadband Imager (VBI) will be the first of the five first-light instruments for the Advanced Technology Solar Telescope (ATST). It is designed to observe the solar atmosphere at heights ranging from photosphere to chromosphere. High frame-rate detectors that sample the FOV of up to 2.8 arcmin in diameter critically near or at the diffraction limit of ATST's 4 meter aperture will facilitate near real-time speckle reconstruction imaging. With its focus on high-spatial resolution, the VBI will be addressing scientific questions related to the smallest structures visible in the solar atmosphere today with high photometric precision. The capability to observe the solar atmosphere with a cadence of about 3 seconds per reconstructed image will enable the VBI to temporally resolve fast evolving structures.

In this contribution we present the current design of the VBI and highlight some scientific questions related to fast evolving, small-scale features within the solar atmosphere that the VBI will address. Title: IBIS 2D Spectropolarimetry: Analysis of G-band Bright Points Authors: Viticchiè, B.; Del Moro, D.; Berrilli, F.; Rubio, L. B.; Tritschler, A. Bibcode: 2011ASPC..437...75V Altcode: We present the results derived from the analysis of the first spectropolarimetric (SP) data obtained through the Interferometric BIdimensional Spectrometer (IBIS) at the Dunn Solar Telescope (NSO). The analysis is focused on 103 G small scale (∼100 km) magnetic field concentrations observed, in a quiet Sun region, as bright points in G-band filtergrams. The combination of high spatial and temporal resolution of both SP and G-band datasets allowed us to analyze in detail the magnetic properties of bright points over different spatial scales (from ∼eq. 0.4" up to 2"- 3") and temporal scales (from 10 min up to > 60 min) and, beside this, to focus on the dependence of significant physical quantities (i.e., magnetic field strength and filling factor derived from Stokes profile inversion) in relation with such evolutions.

We present two main results of our analysis: i) evolution of bright points over small spatial scales and short time intervals (by considering the coalescence of small and faint bright points into a single high brightness one); ii) magnetic properties of bright points over large spatial scales (by examining a small network patch). Our study indicates an interesting correlation between G-band brightness and magnetic filling factor fluctuations. On the contrary, we have not observed any correlation between G-band brightness and magnetic field strength. Such a result can help us to conclude on the possible fine structuring of kG concentrations in the solar photosphere which produce brightness enhancement in G-band filtergrams. Title: Line Shape Effects on Intensity Measurements of Solar Features: Brightness Correction to SOHO MDI Continuum Images Authors: Criscuoli, S.; Ermolli, I.; Del Moro, D.; Giorgi, F.; Tritschler, A.; Uitenbroek, H.; Vitas, N. Bibcode: 2011ApJ...728...92C Altcode: 2010arXiv1012.2561C Continuum intensity observations obtained with the Michelson Doppler Imager (MDI) on board the SOHO mission provide long time series of filtergrams that are ideal for studying the evolution of large-scale phenomena in the solar atmosphere and their dependence on solar activity. These filtergrams, however, are not taken in a pure continuum spectral band, but are constructed from a proxy, namely a combination of filtergrams sampling the Ni I 6768 Å line. We studied the sensitivity of this continuum proxy to the shape of the nickel line and to the degradation in the instrumental transmission profiles. We compared continuum intensity measurements near the nickel line with MDI proxy values in three sets of high-resolution spectro-polarimetric data obtained with the Interferometric Bidimensional Spectrometer, and in synthetic data, obtained from multi-dimensional simulations of magneto-convection and one-dimensional atmosphere models. We found that MDI continuum measurements require brightness corrections which depend on magnetic field strength, temperature and, to a smaller extent, plasma velocity. The correction ranges from 2% to 25% in sunspots, and is, on average, less than 2% for other features. The brightness correction also varies with position on the disk, with larger variations obtained for sunspots, and smaller variations obtained for quiet Sun, faculae, and micropores. Correction factors derived from observations agree with those deduced from the numerical simulations when observational effects are taken into account. Finally, we found that the investigated potential uncertainties in the transmission characteristics of MDI filters only slightly affect the brightness correction to proxy measurements. Title: Magnetic Field Measurements at the Photosphere and Coronal Base Authors: Judge, P. G.; Centeno, R.; Tritschler, A.; Uitenbroek, H.; Jaeggli, S.; Lin, H. Bibcode: 2010AGUFMSH31A1783J Altcode: We have obtained vector polarimetric measurements in lines of Fe I (630nm), Ca II (854nm) and He I (1083nm) of several active regions during 3-14 June 2010. The measurements were made at the Dunn Solar Telescope at Sacramento Peak Observatory, using the FIRS and IBIS instruments simultaneously. We discuss these and SDO data for NOAA 11076. The seeing was very good or excellent and the adaptive optics system functioned well. In this preliminary analysis we compare extrapolations of photospheric fields with the constraints available from Stokes polarimetry, including the morphology and kinematic properties of fibrils. Connections to the corona will also be discussed. The implications for field extrapolations from photospheric measurements will be discussed. We will make the reduced data freely available on the web for interested researchers. Title: Two-dimensional solar spectropolarimetry with the KIS/IAA Visible Imaging Polarimeter Authors: Beck, C.; Bellot Rubio, L. R.; Kentischer, T. J.; Tritschler, A.; Del Toro Iniesta, J. C. Bibcode: 2010A&A...520A.115B Altcode: 2010arXiv1007.1153B Context. Spectropolarimetry at high spatial and spectral resolution is a basic tool to characterize the magnetic properties of the solar atmosphere.
Aims: We introduce the KIS/IAA Visible Imaging Polarimeter (VIP), a new post-focus instrument that upgrades the TESOS spectrometer at the German Vacuum Tower Telescope (VTT) into a full vector polarimeter. VIP is a collaboration between the Kiepenheuer Institut für Sonnenphysik (KIS) and the Instituto de Astrofísica de Andalucía (IAA-CSIC).
Methods: We describe the optical setup of VIP, the data acquisition procedure, and the calibration of the spectropolarimetric measurements. We show examples of data taken between 2005 and 2008 to illustrate the potential of the instrument.
Results: VIP is capable of measuring the four Stokes profiles of spectral lines in the range from 420 to 700 nm with a spatial resolution better than 0farcs5. Lines can be sampled at 40 wavelength positions in 60 s, achieving a noise level of about 2 × 10-3 with exposure times of 300 ms and pixel sizes of 0farcs17 × 0farcs17 (2 × 2 binning). The polarization modulation is stable over periods of a few days, ensuring high polarimetric accuracy. The excellent spectral resolution of TESOS allows the use of sophisticated data analysis techniques such as Stokes inversions. One of the first scientific results of VIP presented here is that the ribbon-like magnetic structures of the network are associated with a distinct pattern of net circular polarization away from disk center.
Conclusions: VIP performs spectropolarimetric measurements of solar magnetic fields at a spatial resolution that is only slightly worse than that of the Hinode spectropolarimeter, while providing a 2D field field of view and the possibility to observe up to four spectral regions sequentially with high cadence. VIP can be used as a stand-alone instrument or in combination with other spectropolarimeters and imaging systems of the VTT for extended wavelength coverage. Title: Magnetic field measurements at the photosphere and coronal base Authors: Judge, Philip; Centeno, R.; Tritschler, A.; Uitenbroek, H.; Jaeggli, S.; Lin, H. Bibcode: 2010shin.confE..56J Altcode: We have obtained vector polarimetric measurements in lines of Fe I (630nm), Ca II (854nm) and He I (1083) of several active regions during 3-14 June 2010. The measurements were made at the Dunn Solar Telescope at Sacramento Peak Observatory, using the FIRS and IBIS instruments simultaneously. We discuss data for NOAA 11076 observed on 4 June 2010. The seeing was very good or excellent and the adaptive optics system functioned well. In this preliminary analysis we compare linear extrapolations of photospheric fields with the constraints available from Stokes polarimetry, including the morphology and kinematic properties of fibrils. The implications for field extrapolations from photospheric measurements will be discussed. We will make the reduced data freely available on the web for interested researchers. Title: The Big Bear Solar Observatory Ca II K-line index for solar cycle 23 Authors: Naqvi, M. F.; Marquette, W. H.; Tritschler, A.; Denker, C. Bibcode: 2010AN....331..696N Altcode: No abstract at ADS Title: A chromospheric dark-cored fibril in Ca II IR spectra Authors: Beck, C.; Tritschler, A.; Wöger, F. Bibcode: 2010AN....331..574B Altcode: We investigate the thermodynamical and magnetic properties of a ``dark-cored" fibril seen in the chromospheric Ca II IR line at 854.2 nm to determine the physical process behind its appearance. We analyse a time series of spectropolarimetric observations obtained in the Ca II IR line at 854.2 nm and the photospheric Fe I line at 630.25 nm. We simultaneously invert the spectra in both wavelength ranges with the SIR code to obtain the temperature and velocity stratification with height in the solar atmosphere and the magnetic field properties in the photosphere. The structure can be clearly traced in the line-of-sight (LOS) velocity and the temperature maps. It connects from a small pore with kG fields to a region with lower field strength. The flow velocity and the temperature indicate that the height of the structure increases with increasing distance from the inner footpoint. The Stokes V signal of 854.2 nm shows a Doppler-shifted polarization signal with the same displacement as in the intensity profile, indicating that the supersonic flow seen in the LOS velocity is located within magnetized plasma. We conclude that the chromospheric dark-cored fibril traces a siphon flow along magnetic field lines, driven by the gas pressure difference caused by the higher magnetic field strength at the inner footpoint. We suggest that fast flows guided by the magnetic field lead to the appearance of ``dark-cored" fibrils in intensity images. Although the observations included the determination of the polarization signal in the chromospheric Ca II IR line, the signal could not be analysed quantitatively due to the low S/N. Chromospheric polarimetry will thus require telescopes of larger aperture able to collect a sufficient number of photons for a reliable determination of polarization in deep and only weakly polarized spectral lines. Title: Delving into the Chromosphere: New Observational Tools Authors: Reardon, Kevin P.; Cauzzi, G.; Tritschler, A.; Uitenbroek, H. Bibcode: 2010AAS...21630503R Altcode: The chromosphere lies at the boundary between the near-equilibrium photosphere and the hot, expanding corona. This region combines both large interconnecting magnetic structures, and fine-scaled dynamics into an intriguingly complex whole. Studying this behavior is a significant observational challenge, requiring sizable fields of view (60-90") sampled at high spatial (< 0.3") and temporal resolution (< 30 seconds), with full spectral information in multiple lines. We will describe how instruments based on Fabry-Perot interferometers have recently begun to routinely deliver such observations. We will review some of the most exciting results obtained and the deeper insights they have provided into the characteristics of the solar chromosphere. Title: Chromospheric Structure and Dynamics. From Old Wisdom to New Insights Authors: Tritschler, A.; Reardon, K.; Uitenbroek, H. Bibcode: 2010MmSAI..81..533T Altcode: 2010MmSAI..81..533R No abstract at ADS Title: The Growth of a Primitive Penumbra Authors: Sreejith, P.; Tritschler, A.; Sankarasubramanian, K. Bibcode: 2010ASSP...19..413S Altcode: 2010mcia.conf..413S We report on the penumbral formation in active region NOAA 10837. The penumbra observed on continuum intensity images grew from a quiet-Sun area to a primitive penumbra and then to a fully developed penumbra over about 5 h. The growth indicates nonlinear development with time. Title: Dual-Line Spectral Imaging of the Chromosphere Authors: Cauzzi, G.; Reardon, K.; Rutten, R. J.; Tritschler, A.; Uitenbroek, H. Bibcode: 2010ASSP...19..513C Altcode: 2010mcia.conf..513C Hα filtergrams are notoriously difficult to interpret, "beautiful to view but not fit for analysis." We try to remedy this by using the IBIS bi-dimensional spectrometer at the Dunn Solar Telescope at NSO/Sacramento Peak to compare the quiet-sun chromosphere observed in Hα to what is observed simultaneously in Ca II 854.2 nm, sampling both lines with high angular and spectral resolution and extended coverage of space, time, and wavelength. Per (x, y, t) pixel we measured the intensity and Dopplershift of the minimum of each line's profile at that pixel, as well as the width of their inner chromospheric cores. A paper submitted to A&A (December 2008) compares these measurements in detail. Title: Service-Mode Observations for Ground-Based Solar Physics Authors: Reardon, K. P.; Rimmele, T.; Tritschler, A.; Cauzzi, G.; Wöger, F.; Uitenbroek, H.; Tsuneta, S.; Berger, T. Bibcode: 2009ASPC..415..332R Altcode: 2009arXiv0909.1522R There are significant advantages in combining Hinode observations with ground-based instruments that can observe additional spectral diagnostics at higher data rates and with greater flexibility. However, ground-based observations, because of the random effects of weather and seeing as well as the complexities data analysis due to changing instrumental configurations, have traditionally been less efficient than satellite observations in producing useful datasets. Future large ground-based telescopes will need to find new ways to optimize both their operational efficiency and scientific output.

We have begun experimenting with service-mode or queue-mode observations at the Dunn Solar Telescope using the Interferometric Bidimensional Spectrometer (IBIS) as part of joint Hinode campaigns. We describe our experiences and the advantag es of such an observing mode for solar physics. Title: Structure and Dynamics of Sunspots (Keynote) Authors: Tritschler, A. Bibcode: 2009ASPC..415..339T Altcode: 2009arXiv0903.1300T The physics of Sunspots is a fascinating and demanding field of research in solar astronomy. Interaction of magnetic fields and plasma flows takes place in a tangled magnetic geometry and occurs on spatial scales that pose a continuous challenge for existing instrumentation and for the unambiguous interpretation of spectropolarimetric observations. Thus, the main properties of sunspots are well established but its fine structure is not yet fully understood.

In this contribution we summarize the current knowledge of the magnetic and dynamic properties of sunspots at the photospheric level based on selected observations featuring the highest possible spatial and spectral resolution. We concentrate on light bridges, umbral dots, penumbral filaments and the notorious dark cores in penumbral filaments. We report on the morphology of the fine structure elements but mostly focus on observations of their line-of-sight velocities and magnetic field parameters. We briefly comment on results from recent radiative MHD simulations and more schematic model ideas that attempt to rationalize observations of the penumbra. Title: The solar chromosphere at high resolution with IBIS. IV. Dual-line evidence of heating in chromospheric network Authors: Cauzzi, G.; Reardon, K.; Rutten, R. J.; Tritschler, A.; Uitenbroek, H. Bibcode: 2009A&A...503..577C Altcode: 2009arXiv0906.2083C The structure and energy balance of the solar chromosphere remain poorly known. We used the imaging spectrometer IBIS at the Dunn Solar Telescope to obtain fast-cadence, multi-wavelength profile sampling of Hα and Ca ii 854.2 nm over a sizable two-dimensional field of view encompassing quiet-Sun network. We provide a first inventory of how the quiet chromosphere appears in these two lines by comparing basic profile measurements in the form of image displays, temporal-average displays, time slices, and pixel-by-pixel correlations. We find that the two lines can be markedly dissimilar in their rendering of the chromosphere, but that, nevertheless, both show evidence of chromospheric heating, particularly in and around network: Hα in its core width and Ca ii 854.2 nm in its brightness. We discuss venues for improved modeling. Title: Imaging Spectropolarimetry with IBIS: Evolution of Bright Points in the Quiet Sun Authors: Viticchié, B.; Del Moro, D.; Berrilli, F.; Bellot Rubio, L.; Tritschler, A. Bibcode: 2009ApJ...700L.145V Altcode: 2009arXiv0906.2663V We present the results from first spectropolarimetric observations of the solar photosphere acquired at the Dunn Solar Telescope with the Interferometric Bidimensional Spectrometer. Full Stokes profiles were measured in the Fe I 630.15 nm and Fe I 630.25 nm lines with high spatial and spectral resolutions for 53 minutes, with a Stokes V noise of 3 × 10-3 the continuum intensity level. The data set allows us to study the evolution of several magnetic features associated with G-band bright points (BPs) in the quiet Sun. Here we focus on the analysis of three distinct processes, namely the coalescence, fragmentation, and cancellation of G-band BPs. Our analysis is based on an SIR inversion of the Stokes I and V profiles of both Fe I lines. The high spatial resolution of the G-band images combined with the inversion results helps to interpret the undergoing physical processes. The appearance (dissolution) of high-contrast G-band BPs is found to be related to the local increase (decrease) of the magnetic filling factor, without appreciable changes in the field strength. The cancellation of opposite-polarity BPs can be the signature of either magnetic reconnection or the emergence/submergence of magnetic loops. Title: Spectropolarimetry of Ca II 8542: Probing the Chromospheric Magnetic Field Authors: Kleint, L.; Reardon, K.; Stenflo, J. O.; Uitenbroek, H.; Tritschler, A. Bibcode: 2009ASPC..405..247K Altcode: We present spectropolarimetric observations of the chromospheric Ca II 8542 and photospheric Fe I 6302 lines obtained with the Interferometric Bidimensional Spectrometer (IBIS) at the Dunn Solar Telescope. The high spatial resolution over a large field of view (FOV) allows us to connect the observed profiles to the overall topology of the target region. After suitable calibrations we can extract Stokes profiles for each point in the FOV. The Stokes V profiles observed in the Ca II line show a large variety of shapes, indicating widely varying vertical behavior of the field strength, velocity, and temperature. We examine the center-of-gravity method for determining a representative field strength from the observed profiles and use it to directly compare photospheric and chromospheric magnetic fields. Title: High-resolution observations of extremely bright penumbral grains Authors: Denker, C.; Tritschler, A.; Deng, N.; Verdoni, A. P. Bibcode: 2008AN....329..773D Altcode: We observed a cluster of extremely bright penumbral grains located at the inner limb-side penumbra of the leading sunspot in active region NOAA 10892. The penumbral grains in the cluster showed a typical peak intensity of 1.58 times the intensity I_0 of the granulation surrounding the sunspot. The brightest specimen even reached values of 1.8--2.0 I_0, thus, exceeding the temperatures of the brightest granules in the immediate surroundings of the sunspot. We find that the observed sample of extremely bright penumbral grains is an intermittent phenomenon, that disappears on time scales of hours. Horizontal flow maps indicating proper motions reveal that the cluster leaves a distinct imprint on the penumbral flow field. We find that the divergence line co-located with the cluster is displaced from the middle penumbra closer towards the umbra and that the radial outflow velocities are significantly increased to speeds in excess of 2 km s^{-1}. The extremely bright penumbral grains, which are located at the inner limb-side penumbra, are also discernible in off-band Hα images down to Hα ± 0.045 nm. We interpret the observations in the context of the moving flux tube model arguing that hotter than normal material is rapidly ascending along the inner footpoint of the embedded flux tube, i.e., the ascending hot material is the cause of the extremely bright penumbral grains. This study is based on speckle-reconstructed broad-band images taken at 600 nm and chromospheric Hα observations obtained with two-dimensional spectroscopy. All data were taken with adaptive optics under very good seeing conditions at the Dunn Solar Telescope, National Solar Observatory/Sacramento Peak, New Mexico on 2006 June 10. Title: Evidence for a Current Sheet above a Sunspot Umbra Authors: Tritschler, A.; Uitenbroek, H.; Reardon, K. Bibcode: 2008ApJ...686L..45T Altcode: We present observational evidence for the existence of a current sheet in the chromosphere above a sunspot umbra based on high angular resolution two-dimensional spectroscopic observations in the Ca II 854.21 nm line. In the core of this line we observe a very stable bright ribbon-like structure separating magnetic field configurations that connect to different parts of the active region. We make plausible that the structure is a string of sheets carrying vertical currents that result from dissipation when the different parts of the active region are moved around in the photosphere. To our knowledge this is the first direct observation of the heating caused by the dissipation in such a current sheet in the chromosphere. Title: Imaging Spectropolarimetry of the Photosphere and Chromosphere with IBIS Authors: Reardon, K.; Tritschler, A.; Uitenbroek, H.; et al. Bibcode: 2008ESPM...12.2.31R Altcode: We present recent results based on high-resolution spectropolarimetry using IBIS, a dual Fabry-Perot imaging spectrometer. We describe the characteristics of the instrument and its capability to measure the full Stokes vector in a range of photospheric and chromospheric spectral lines.

Since late 2006 IBIS has been regularly used in spectropolarimetric mode and observations have included solar pores, quiet sun network and internetwork areas, and the disk passage of active regions NOAA 10941 and 10940. Measurements are primarily performed in the Fe I 630.2 and the Ca II 854.2 nm lines to provide information on both photospheric to chromospheric heights. We present results on the highly dynamical nature of both the vertical and horizontal components of quiet Sun magnetic fields. We also show the fine structure and height variation of the magnetic field in a large sunspot. Title: Solar Chromospheric Dynamics: Onwards and Upwards Authors: Cauzzi, G.; Reardon, K.; Rimmele, T.; Rutten, R.; Tritschler, A.; Uitenbroek, H.; Woeger, F. Bibcode: 2008AGUSMSP41B..03C Altcode: We present a study of chromospheric dynamics and its relation with the driving photospheric magneto-convection in a variety of solar targets, from quiet Sun to more active regions. To this end high resolution observations were obtained in CaII 854.2 nm, Hα, and photospheric FeI lines with the Interferometric BIdimensional Spectrometer (IBIS) installed at the Dunn Solar Telescope of the NSO. The availability of full spectroscopic information on extended fields of view allows us to derive a comprehensive view of the intrinsically 3-D chromospheric scene. A coherent picture is emerging that involves the propagation and dissipation of photospheric acoustic waves into the chromospheric layers, but selected and guided by the local and highly variable magnetic topology. In particular, ubiquitous fibrilar structures, apparently originating from even the smallest magnetic elements, appear an integral part of the dynamic chromosphere. Title: WHI Targeted Campaigns on Coronal Holes and Quiet Sun: High Resolution Observations of the Lower Atmosphere With IBIS Authors: Cauzzi, G.; Reardon, K. P.; Rimmele, T.; Tritschler, A.; Uitebroek, H.; Woeger, F.; Deforest, C.; McIntosh, S. Bibcode: 2008AGUSMSH51A..02C Altcode: The Interferometric BIdimensional Spectrometer (IBIS) is a dual Fabry-Perot instrument installed at the Dunn Solar Telescope that allows two-dimensional spectroscopic observations in a variety of spectral lines. The IBIS/DST will participate in the WHI targeted campaigns on coronal holes (April 3-9) and quiet Sun dynamics (April 10-16) performing simultaneous high-resolution observations of the dynamics of the photosphere and chromosphere in the coordinated targets. The aim is to obtain insights on the role of the lower atmosphere's dynamics and energetics into the structuring of the coronal plasma and, possibly, into the origin of the solar wind. In this paper we will present the observations obtained as well as first results, and attempt to relate them with recent work performed on quiet Sun chromospheric dynamics. Title: Simulations of Atmospheric Turbulence and Instrumentation on Solar Observations Authors: Weber, M.; Tritschler, A.; Woeger, F. Bibcode: 2008AGUSMSP51B..08W Altcode: We investigate the influence of atmospheric turbulence and instrumentation on solar observations. The focus of this study is the determination of the amount of bias introduced in velocity measurements by these effects. The magnetically insensitive Fe I 557.6 nm line is synthesized using three-dimensional simulations of solar magneto-convection as an input model for a radiation transfer code. The synthesized spectra are then subjected to different atmospheric conditions characterized by the Fried parameters r0 = 7, 10, and 15 cm. To simulate realistic observations at NSO's Dunn solar telescope (DST), we mimic the influence of a 0.76 m aperture telescope, a high-order adaptive optics (AO) system and a tunable filtergraph on the atmospherically distorted spectra. Title: Spectropolarimetry of a Decaying Sunspot Penumbra Authors: Bellot Rubio, L. R.; Tritschler, A.; Martínez Pillet, V. Bibcode: 2008ApJ...676..698B Altcode: 2007arXiv0712.2937B We report on high angular resolution, high-precision spectropolarimetric measurements of a decaying sunspot. The spot gradually lost its penumbra during the course of 3 days. In the late stages of evolution, where the only remnant of the spot is a naked umbra, we find small-scale inhomogeneities in the magnetic canopy surrounding it. The inhomogeneities are observed as finger-like structures of weak and nearly horizontal magnetic fields extending 1''-2'' from the border of the umbra. These fields are not associated with filamentary structures in continuum intensity or with conspicuous Evershed flows. The Stokes profiles emerging from the fingers exhibit blueshifts, which we interpret as upward motions. This previously unknown fine structure may be related to penumbral field lines that no longer carry strong Evershed flows and rise to the chromosphere, producing the disappearance of the penumbra at photospheric levels. Title: Fine Structure of the Net Circular Polarization in a Sunspot Penumbra Authors: Tritschler, A.; Müller, D. A. N.; Schlichenmaier, R.; Hagenaar, H. J. Bibcode: 2007ApJ...671L..85T Altcode: 2007arXiv0710.4545T We present novel evidence for fine structure observed in the net circular polarization (NCP) of a sunspot penumbra based on spectropolarimetric measurements utilizing the Zeeman-sensitive Fe I 630.2 nm line. For the first time we detect filamentary organized fine structure of the NCP on spatial scales that are similar to the inhomogeneities found in the penumbral flow field. We also observe an additional property of the visible NCP, a zero-crossing of the NCP in the outer parts of the center-side penumbra, which has not been recognized before. In order to interpret the observations we solve the radiative transfer equations for polarized light in a model penumbra with embedded magnetic flux tubes. We demonstrate that the observed zero-crossing of the NCP can be explained by an increased magnetic field strength inside magnetic flux tubes in the outer penumbra combined with a decreased magnetic field strength in the background field. Our results strongly support the concept of the uncombed penumbra. Title: Two-Dimensional Spectroscopy of Photospheric Shear Flows in a Small δ Spot Authors: Denker, C.; Deng, N.; Tritschler, A.; Yurchyshyn, V. Bibcode: 2007SoPh..245..219D Altcode: 2007arXiv0708.3490D In recent high-resolution observations of complex active regions, long-lasting and well-defined regions of strong flows were identified in major flares and associated with bright kernels of visible, near-infrared, and X-ray radiation. These flows, which occurred in the proximity of the magnetic neutral line, significantly contributed to the generation of magnetic shear. Signatures of these shear flows are strongly curved penumbral filaments, which are almost tangential to sunspot umbrae rather than exhibiting the typical radial filamentary structure. Solar active region NOAA 10756 was a moderately complex βδ sunspot group, which provided an opportunity to extend previous studies of such shear flows to quieter settings. We conclude that shear flows are a common phenomenon in complex active regions and δ spots. However, they are not necessarily a prerequisite condition for flaring. Indeed, in the present observations, the photospheric shear flows along the magnetic neutral line are not related to any change of the local magnetic shear. We present high-resolution observations of NOAA 10756 obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO). Time series of speckle-reconstructed white-light images and two-dimensional spectroscopic data were combined to study the temporal evolution of the three-dimensional vector flow field in the βδ sunspot group. An hour-long data set of consistent high quality was obtained, which had a cadence of better than 30 seconds and subarcsecond spatial resolution. Title: The Discrepancy in G-Band Contrast: Where is the Quiet Sun? Authors: Uitenbroek, H.; Tritschler, A.; Rimmele, T. Bibcode: 2007ApJ...668..586U Altcode: 2007arXiv0704.3637U We compare the rms contrast in observed speckle reconstructed G-band images with synthetic filtergrams computed from two magnetohydrodynamic simulation snapshots. The observations consist of 103 bursts of 80 frames each, taken at the Dunn Solar Telescope (DST), sampled at twice the diffraction limit of the telescope. The speckle reconstructions account for the actions of the adaptive optics (AO) system at the DST in order to supply reliable photometry. We find a considerable discrepancy between the observed rms contrast of 14.1% for the best reconstructed images and the synthetic rms contrast of 21.5% in a simulation snapshot thought to be representative of the quiet Sun. The areas of features in the synthetic filtergrams that have positive or negative contrast beyond the minimum and maximum values in the reconstructed images have spatial scales that should be resolved. This leads us to conclude that there are fundamental differences in the rms G-band contrast between observed and computed filtergrams. On the basis of the substantially reduced granular contrast of 16.3% in the synthetic plage filtergram, we speculate that the quiet Sun may contain more weak magnetic field than previously thought. Title: Synoptic Observing at Big Bear Solar Observatory Authors: Denker, C.; Naqvi, M.; Deng, N.; Tritschler, A.; Marquette, W. H. Bibcode: 2007ASPC..368..515D Altcode: Synoptic solar observations in the chromospheric absorption lines Ca II K and Hα have a long tradition at Big Bear Solar Observatory (BBSO). The advent of the New Solar Telescope (NST) will shift the focus of BBSO's synoptic observing program toward high-resolution observations. We present an overview of the telescopes and instrumentation and show some of the most recent results. This includes Ca II K data to track solar irradiance variations, Hα full-disk data to monitor eruptive events, Dopplergrams from two-dimensional spectroscopy, as well as image restorations of diffraction-limited quality. Title: Two-dimensional Spectroscopy Of Chromospheric And Photospheric Sunspot Fine-structure Authors: Denker, Carsten; Verdoni, A. P.; Naqvi, M.; Deng, N.; Tritschler, A. Bibcode: 2007AAS...21010002D Altcode: 2007BAAS...39..227D In preparation for the future 1.6-meter New Solar Telescope (NST) at Big Bear Solar Observatory, a suite of instruments has been developed for observations with high-spatial and high-temporal resolution. Two of these instruments, a fast CCD camera system for image restoration and the Visible-light Imaging Magnetograph (VIM), were moved to the National Solar Observatory/Sacramento Peak, while NST is under construction. In this study, we report results of observations obtained with the high-order adaptive optics system at the Dunn Solar Telescope on 2006 June 10. We observed active region NOAA 10892 in broad-band continuum (600 nm) and in the chromsopheric lines (Hα and Na D2). We obtained photospheric and chromospheric flow fields based on local correlation tracking and Doppler measurements and discuss them in the context of sunspot fine-structure.

This work was supported by NSF under grants ATM 00-86999, ATM 02-36945, IIS ITR 03-24816, and AST MRI 00-79482 and by NASA under grant NAG 5-12782. Title: Three-Dimensional Structure of Evershed Flows Authors: Deng, Na; Choudhary, D. P.; Denker, C.; Verdoni, A.; Tritschler, A. Bibcode: 2007AAS...210.9506D Altcode: 2007BAAS...39..224D The Evershed flow is known as the unceasing radially outward mass flow in sunspot penumbrae observed in the photosphere, which is most clearly seen near the solar limb. The Evershed flow reverses its direction in the chromosphere, where an inward mass flow is observed. In order to quantitatively explore the three-dimensional structure of the Evershed flow from photosphere to chromosphere, we observed a sunspot group (NOAA 10892) at the limb using the Horizontal Spectrograph (HSG) at the National Solar Observatory/Sacramento Peak (NSO/SP) on 2006 June 04. Spectral data sets were obtained simultaneously at four solar absorbtion lines: Fe 630.15 nm and 630.25 nm (photosphere), NaD 588.99 nm (lower chromosphere), and Hα 656.28 nm (chromosphere). Spectral analysis and different methods of determining Doppler velocities will be presented and compared.

This work is supported by NSF under grant ATM 02-36945, ATM 03-42560, ATM 05-48260 and MRI AST 00-79482 and by NASA under grant NAG 5-13661. Title: Observations of Quiet Sun Chromosphere Dynamics Authors: Verdoni, Angelo; Denker, C.; Deng, N.; Tritschler, A. Bibcode: 2007AAS...21010003V Altcode: 2007BAAS...39..228V The quiet Sun shows a multitude of fine structure in both the photosphere and chromosphere. Observations with high spatial and temporal resolution are required to study their dynamics. In June 2006, simultaneous broad-band continuum (600 nm) and narrow-band spectroscopic (Hα and Na 589.0 nm) data were obtained of a quiet Sun region near disk center using the Dunn Solar Telescope and high-order adaptive optics at the National Solar Observatory/Sacramento Peak. The time-series of continuum data was restored using the speckle masking technique to achieve almost diffraction-limited resolution across the entire field-of-view (80" by 80"). The spectroscopic data were taken with a two-dimensional spectrometer, which is currently being upgraded for spectro-polarimetry. The Visible-light Imaging Magnetograph (VIM) is a telecentric two-dimensional Fabry-Perot based spectro-polarimeter, which will become one of the first-light instruments of the future 1.6-meter New Solar Telescope (NST) at Big Bear Solar Observatory (BBSO).

This work was supported by NSF under grants ATM 00-86999, ATM 02-36945, IIS ITR 03-24816, and AST MRI 00-79482 and by NASA under grant NAG 5-12782. Title: Field-Dependent Adaptive Optics Correction Derived with the Spectral Ratio Technique Authors: Denker, C.; Deng, N.; Rimmele, T. R.; Tritschler, A.; Verdoni, A. Bibcode: 2007SoPh..241..411D Altcode: In this empirical study, we compare high-resolution observations obtained with the 65-cm vacuum reflector at Big Bear Solar Observatory (BBSO) in 2005 and with the Dunn Solar Telescope (DST) at the National Solar Observatory/Sacramento Peak (NSO/SP) in 2006. We measure the correction of the high-order adaptive optics (AO) systems across the field of view (FOV) using the spectral ratio technique, which is commonly employed in speckle masking imaging, and differential image motion measurements. The AO correction is typically much larger (10'' to 25'') than the isoplanatic angle and can be described by a radially symmetric function with a central core and extended wings. The full-width at half-maximum (FWHM) of the core represents a measure of the AO correction. The average FWHM values for BBSO and NSO/SP are 23.5'' and 18.2'', respectively. The extended wings of the function show that the AO systems still contribute to an improved speckle reconstruction at the periphery of the 80''×80'' FOV. The major differences in the level of AO correction between BBSO and NSO/SP can be explained by different contributions of ground-layer- and free-atmosphere-dominated seeing, as well as different FOVs of the wavefront sensors. In addition, we find an anisotropic spectral ratio in sunspot penumbrae caused by the quasi-one-dimensional nature of penumbral filaments, which introduces a significant error in the estimation of the Fourier amplitudes during the image restoration process. Title: Narrow-band imaging in the CN band at 388.33 nm Authors: Uitenbroek, H.; Tritschler, A. Bibcode: 2007A&A...462.1157U Altcode: 2006astro.ph.11407U Aims:We promote the use of narrow-band (0.05-0.20 nm FWHM) imaging in the molecular CN band head at 388.33 nm as an effective method for monitoring small-scale magnetic field elements because it renders them with exceptionally high contrast.
Methods: We create synthetic narrow-band CN filtergrams from spectra computed from a three-dimensional snapshot of a magnetohydrodynamic simulation of the solar convection to illustrate the expected high contrast and explain its nature. In addition, we performed observations with the horizontal slit spectrograph at the Dunn Solar Tower at 388.3 nm to experimentally confirm the high bright-point contrast, and to characterize and optimize the transmission profile of a narrow-band (0.04 FWHM) Lyot filter, which was built by Lyot and tailored to the CN band at Sacramento Peak in the early 70's.
Results: The presented theoretical computations predict that bright-point contrast in narrow-band (0.04 FWHM) CN filtergrams is more than 3 times higher than in CN filtergrams taken with 1 nm FWHM wide filters, and in typical G-band filtergrams. Images taken through the Lyot filter after optimizing its passband confirm that the filter is capable of rendering small-scale magnetic elements with contrasts that are much higher than in traditional G-band imaging. The filter will be available as an user instrument at the Dunn Solar Tower. Title: On the fine structure of the quiet solar Ca II K atmosphere Authors: Tritschler, A.; Schmidt, W.; Uitenbroek, H.; Wedemeyer-Böhm, S. Bibcode: 2007A&A...462..303T Altcode: 2006astro.ph.11402T Aims:We investigate the morphological, dynamical, and evolutionary properties of the internetwork and network fine structure of the quiet sun at disk centre.
Methods: The analysis is based on a ~6 h time sequence of narrow-band filtergrams centred on the inner-wing Ca II K2v reversal at 393.3 nm. To examine the temporal evolution of network and internetwork areas separately we employ a double-Gaussian decomposition of the mean intensity distribution. An autocorrelation analysis is performed to determine the respective characteristic time scales. In order to analyse statistical properties of the fine structure we apply image segmentation techniques.
Results: The results for the internetwork are related to predictions derived from numerical simulations of the quiet sun. The average evolutionary time scale of the internetwork in our observations is 52 s. Internetwork grains show a tendency to appear on a mesh-like pattern with a mean cell size of ~4-5 arcsec. Based on this size and the spatial organisation of the mesh we speculate that this pattern is related to the existence of photospheric downdrafts as predicted by convection simulations. The image segmentation shows that typical sizes of both network and internetwork grains are in the order of 1.6 arcsec. Title: The Contrast of Magnetic Flux Concentrations at Near-Infrared and Visible Wavelengths Authors: Tritschler, A.; Uitenbroek, H. Bibcode: 2006ApJ...648..741T Altcode: To reconcile discrepancies in the observed contrast of magnetic flux concentrations, we compute synthetic filtergrams from solar magnetoconvection models in four different passbands: two continuum bands, at 1626 and 575 nm, the G band, and the line wing of the Ca II K line. Magnetic flux concentrations are selected by their G-band brightness. In the near-infrared the selected flux concentrations appear inconspicuous with intensities that are on average below that of the synthetic average quiet Sun, while their contrast in the visible passband is mostly positive. When we account for limited telescope resolution and imperfect seeing, the contrasts of bright points in the visible become increasingly negative as a result of mixing with the dark intergranular lanes in which they are embedded. The correlation in bright-point intensity between different passbands becomes increasingly poor from the G band to the visible and the near-infrared. This is caused in part by the varying amount of spectral lines in each of the bands. Further, we find that the largest magnetic field concentrations, representative of micropores or magnetic knots, are dark in all four passbands. The brightenings in the Ca II K line wing do not coincide with magnetic flux concentrations on the spatial scale of the simulation. Finally, we find that the rms intensity contrast in all four passbands depends on the amount of magnetic field present in the simulation, with higher contrast for lower average magnetic field strength. Title: VIP - 2D Vector Spectropolarimetry of the Solar Atmosphere near the Diffraction Limit Authors: Bellot Rubio, L. R.; Tritschler, A.; Kentischer, T.; Beck, C.; Del Toro Iniesta, J. C. Bibcode: 2006IAUJD...3E..58B Altcode: The KIS/IAA Vector Imaging Polarimeter (VIP) is a new instrument for two-dimensional spectropolarimetry of the solar atmosphere. It is used with TESOS, the triple etalon Fabry-Perot interferometer installed at the German Vacuum Tower Telescope of Observatorio del Teide (Tenerife, Spain). The polarimeter is based on a pair of nematic liquid crystal retarders and a Wollaston prism. VIP and TESOS are able to observe any spectral line in the range from 450 nm to 750 nm with a spectral resolving power of about 250000 and spatial resolutions better than 0.5" (thanks to the Kiepenheuer Adaptive Optics System). Typically, the four Stokes parameters of a line can be measured at 40 wavelength points in less than 60 s, with a noise level of 1-2 x 10^-3 and a pixel size of 0.18" x 0.18" (2x2 binning). The modulation matrix of VIP is derived using the polarimetric calibration unit installed at the telescope. Here we present first-light observations of VIP carried out in November 2005. We recorded the full Stokes profiles of the 630.1 and 630.2 nm Fe I lines emerging from a solar pore and its surroundings at a spatial resolution of ~0.4". Based on these data, we discuss the performance and capabilities of VIP as a powerful instrument for high spatial and temporal resolution measurements of vector magnetic fields in the solar atmosphere. Title: Evidence for a Siphon Flow Ending near the Edge of a Pore Authors: Uitenbroek, H.; Balasubramaniam, K. S.; Tritschler, A. Bibcode: 2006ApJ...645..776U Altcode: Observations of NOAA AR 9431, taken with the Vacuum Tower at Kitt Peak on 2001 April 18 in the Ca II 854.21 nm line in both circular polarizations, show evidence for a strong supersonic downflow ending near the edge of a magnetic pore. The observed supersonic motion is interpreted as a siphon flow along a magnetic loop connecting a patch of weaker field to the pore of opposite polarity in the same active region. The 854.21 nm line data reveal the upflow at one footpoint of the loop, as well as the acceleration of the flow toward the footpoint at the pore, where the flow reaches line-of-sight velocities of well over 20 km s-1, substantially larger than the critical speed. Numerical radiative transfer modeling of the 854.21 nm line indicates the presence of a strong discontinuity in the flow velocity, which we interpret as evidence for a tube shock in the downwind leg of the siphon. Title: The influence of image reconstruction on two-dimensional spectrograms of the solar photosphere Authors: Mikurda, K.; Tritschler, A.; Schmidt, W. Bibcode: 2006A&A...454..359M Altcode: Aims.We present a spectral analysis of small-scale structures in the solar photosphere and investigate the influence of the speckle deconvolution technique on the line profiles.
Methods: . A short sequence of two-dimensional spectra is used, taken with the Telecentric Etalon Solar Spectrometer (TESOS) at the German Vacuum Tower Telescope on Tenerife. We observed two small pores surrounded by disturbed and by regular granulation in the non-magnetic neutral Iron line at 557.6 nm. In a first step, a speckle reconstruction is computed by applying an extended Knox-Thompson algorithm to the broad-band data. In a second step, the individual narrow-band filtergrams are deconvolved utilizing the information gained in the first step. We then perform a spectral analysis of the 2D spectra and compare the results obtained with the raw and the restored data.
Results: .Important spectral quantities, e.g. line position, line depression and line asymmetry are largely unchanged by the image reconstruction process. We derive the line asymmetry and the line-of-sight flow for granules and intergranular lanes and also for an isolated G-band bright point and find important differences between quiet and magnetically disturbed granulation: the granule centers in the quiet region show a strong asymmetry with significant blue shift (300 m/s) toward deeper layers, while the velocity in the disturbed area show virtually no height dependence. For the intergranular lanes the situation is reversed: no height dependence in the quiet area, significant red-shift toward deeper layers in the disturbed part. An isolated G-band bright point does not show any line-of-sight motion relative to its immediate surroundings. The map of LOS velocities derived from line-wing shifts shows a significant downflow around one of the pores measured in deep layers of the photosphere.
Conclusions: .In most cases we do not find any artefacts in the reconstructed line profiles that would compromise their usage for quantitative spectroscopy. Title: Two-dimensional spectroscopy of a sunspot. III. Thermal and kinematic structure of the penumbra at 0.5 arcsec resolution Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Tritschler, A. Bibcode: 2006A&A...453.1117B Altcode: 2006astro.ph..1423B We investigate the thermal and kinematic configuration of a sunspot penumbra using high spectral and spatial resolution intensity profiles of the non-magnetic Fe I 557.6 nm line. The data set was acquired with the 2D solar spectrometer TESOS. The profiles are inverted using a one-component model atmosphere with gradients of the physical quantities. From this inversion we obtain the stratification with depth of temperature, line-of-sight velocity, and microturbulence across the penumbra. Our results suggest that the physical mechanism(s) responsible for the penumbral filaments operate preferentially in the lower photosphere. The spot, located at an heliocentric angle of 23°, exhibits larger continuum intensities in the center-side penumbra as compared with the limb side, which translates into an average temperature difference of 100-150 K at log τ500 = 0. We investigate the nature of the bright ring that appears in the inner penumbra when sunspots are observed in the wing of spectral lines. It is suggested that the bright ring does not reflect a temperature enhancement in the mid photospheric layers. The line-of-sight velocities retrieved from the inversion are used to determine the flow geometry at different heights in the photosphere. Both the flow speed and flow angle increase with optical depth and radial distance. Downflows are detected in the mid and outer penumbra, but only in deep layers (log τ500 ≥ -1.4). We demonstrate that the velocity stratifications retrieved from the inversion are consistent with the idea of penumbral flux tubes channeling the Evershed flow. Finally, we show that larger Evershed flows are associated with brighter continuum intensities in the inner center-side penumbra. Dark structures, however, are also associated with significant Evershed flows. This leads us to suggest that the bright and dark filaments seen at 0.5 arcsec resolution are not individual flow channels, but a collection of them. Our analysis highlights the importance of very high spatial resolution spectroscopic and spectropolarimetric measurements for a better understanding of sunspot penumbrae. Title: Progress on the 1.6-meter New Solar Telescope at Big Bear Solar Observatory Authors: Denker, C.; Goode, P. R.; Ren, D.; Saadeghvaziri, M. A.; Verdoni, A. P.; Wang, H.; Yang, G.; Abramenko, V.; Cao, W.; Coulter, R.; Fear, R.; Nenow, J.; Shoumko, S.; Spirock, T. J.; Varsik, J. R.; Chae, J.; Kuhn, J. R.; Moon, Y.; Park, Y. D.; Tritschler, A. Bibcode: 2006SPIE.6267E..0AD Altcode: 2006SPIE.6267E..10D The New Solar Telescope (NST) project at Big Bear Solar Observatory (BBSO) now has all major contracts for design and fabrication in place and construction of components is well underway. NST is a collaboration between BBSO, the Korean Astronomical Observatory (KAO) and Institute for Astronomy (IfA) at the University of Hawaii. The project will install a 1.6-meter, off-axis telescope at BBSO, replacing a number of older solar telescopes. The NST will be located in a recently refurbished dome on the BBSO causeway, which projects 300 meters into the Big Bear Lake. Recent site surveys have confirmed that BBSO is one of the premier solar observing sites in the world. NST will be uniquely equipped to take advantage of the long periods of excellent seeing common at the lake site. An up-to-date progress report will be presented including an overview of the project and details on the current state of the design. The report provides a detailed description of the optical design, the thermal control of the new dome, the optical support structure, the telescope control systems, active and adaptive optics systems, and the post-focus instrumentation for high-resolution spectro-polarimetry. Title: High-Resolution Studies of Complex Solar Active Regions Authors: Deng, Na; Wang, H.; Liu, C.; Yang, G.; Xu, Y.; Tritschler, A.; Cao, W.; Rimmele, T. R.; Denker, C. Bibcode: 2006SPD....37.3401D Altcode: 2006BAAS...38..258D Most Flares and CMEs occur or originate in solar active regions, typically in sunspots with complex magnetic fields such as delta-spots. Rapid and substantial changes of the sunspot structure have been discovered to be associated with flares/CMEs. Rapid penumbral decay and umbral enhancements are intensity changes, which are interpreted as signatures of magnetic reconnection during the flare. The magnetic field lines switch from an inclined to a more vertical orientation. Strong and long-lived shear flows near the flaring magnetic inversion line have been detected using Local Correlation Tracking (LCT) techniques based on multi-wavelength high resolution observations. A newly observed and important phenomenon is the increased local shear flow and magnetic shear right after the flare in spite of theoretical models requiring an overall decrease in the magnetic free energy. The emergence of a twisted or pre-sheared flux rope near the neutral line is a possible interpretation. Using high-order adaptive optics combined post-facto speckle masking image reconstruction, we can obtain time-series with highly improved image quality and spatial resolution in the order of 0.14" or about 100 km on the solar surface. We combine the observed longitudinal Dopplergrams obtained with two-dimensional imaging spectrometer and transverse LCT flow maps derived from time-series of speckle reconstructed images to create real local 3D flow maps (view from above). Using these precise 3D flow maps observed in a typical sunspot in the course of its center to limb disc passage, we observe distinct division line between radially inward and outward flow in the penumbra and its evolution during the decaying phase of the sunspot. The inclination angles of penumbral flow channels are also calculated.Acknowledgments: This work is supported by NSF under grant ATM 03-42560, ATM 03-13591, ATM 02-36945, ATM 05-48952, and MRI AST 00-79482 and by NASA under grant NAG 5-13661. Title: Two-Dimensional Spectroscopy at Big Bear Solar Observatory Authors: Denker, Carsten; Deng, N.; Tritschler, A. Bibcode: 2006SPD....37.3702D Altcode: Two-dimensional spectroscopy is an important tool to measure the physical parameters related to solar activity in both the photosphere and chromosphere. We present a description of the visible-light post-focus instrumentation at the Big Bear Solar Observatory (BBSO) including adaptive optics and image restoration. We report the first science observations obtained with two-dimensional spectroscopy during the 2005 observing season. In particular we discuss the properties of flows associated with a small delta-spot in solar active region NOAA 10756. Title: Narrow-band Imaging In Ihe Cn Band Head Authors: Uitenbroek, Han; Tritschler, A. Bibcode: 2006SPD....37.0717U Altcode: 2006BAAS...38..662U We report on results of an observing campaign intended to revive an old CN Lyot filter originally built by Bernhard Lyot himself, but modified at Sacramento Peak. The filter has two band-width settings of 0.025 nm and 0.05 nm which can be fine tuned thermally. We characterise the passband of the Lyot filter and the employed prefilter based on osbervations performed with a spectrograph. We also performed an imaging experiment in an attempt to obtain data visualizing the imaging capability of the filter. Our results show that the CN filter is in a surprisingly good condition and is most suited for observations to verify theoretical predictions about the brightness of magnetic elements in the CN bandhead at 388.3\,nm. Title: The Contrast of Magnetic Elements in Synthetic CH- and CN-Band Images of Solar Magnetoconvection Authors: Uitenbroek, H.; Tritschler, A. Bibcode: 2006ApJ...639..525U Altcode: 2005astro.ph.10333U We present a comparative study of the intensity contrast in synthetic CH-band and violet CN-band filtergrams computed from a high-resolution simulation of solar magnetoconvection. The underlying simulation has an average vertical magnetic field of 250 G with kilogauss fields concentrated in its intergranular lanes and is representative of a plage region. To simulate filtergrams typically obtained in CH- and CN-band observations we computed spatially resolved spectra in both bands and integrated these spectra over 1 nm FWHM filter functions centered at 430.5 and 388.3 nm, respectively. We find that the average contrast of magnetic bright points in the simulated filtergrams is lower in the CN band by a factor of 0.96. In comparison, earlier semiempirical modeling and recent observations both estimated that the bright point contrast in the CN band is higher by a factor of 1.4. We argue that the near equality of the bright point contrast in the two bands in the present simulation is a natural consequence of the mechanism that causes magnetic flux elements to be particularly bright in the CN and CH filtergrams, namely, the partial evacuation of these elements and the concomitant weakening of molecular spectral lines in the filter passbands. We find that the rms intensity contrast in the whole field of view of the filtergrams is 20.5% in the G band and 22.0% in the CN band and conclude that this slight difference in contrast is caused by the shorter wavelength of the latter. Both the bright point and rms intensity contrast in the CN band are sensitive to the precise choice of the central wavelength of the filter. Title: The Visible--Light Magnetograph at the Big Bear Solar Observatory: Hardware and Software Authors: Shumko, S.; Abramenko, V.; Denker, C.; Goode, P.; Tritschler, A.; Varsik, J. Bibcode: 2005ASPC..347..509S Altcode: 2005adass..14..509S In this paper we report about the current status of the control and acquisition software package developed to control the visible-light imaging magnetograph (VIM) system at the Big Bear Solar Observatory (BBSO). The instrument is designed to perform high-spatial and high-temporal observations of the solar photosphere and chromosphere utilizing the remodeled Coudé-feed of the 65 cm vacuum telescope. Title: The New Solar Telescope at Big Bear Solar Observatory - A Progress Report Authors: Denker, C.; Cao, W.; Chae, J.; Coulter, R.; Kuhn, J. R.; Marquette, W. H.; Moon, Y.; Park, Y.; Ren, D.; Tritschler, A.; Varsik, J. R.; Wang, H.; Yang, G.; Shoumko, S.; Goode, P. R. Bibcode: 2005AGUSMSP43A..07D Altcode: The New Solar Telescope (NST) is a new 1.6-meter, off-axis telescope for the Big Bear Solar Observatory (BBSO) in California. The NST is collaboration between BBSO, the Korean Astronomical Observatory (KAO) and Institute for Astronomy (IfA) at the University of Hawaii. BBSO is an ideal site for high-spatial resolution observations, since this mountain-lake site provides consistent seeing conditions with extended periods of excellent seeing from sunrise to sunset. These unique seeing characteristics make BBSO ideally suited for combined high-resolution campaigns and synoptic observations, which are essential for studies of solar activity and space weather. In this progress report, we present the latest information on the optical design, the optical support structure, the telescope control system and the requisite instrumentation for the telescope. Acknowledgements: This work has been supported by NSF under grants ATM-0236945, ATM-0342560, MRI-0320540, and Air Force DURIP F-49620-03-1-0271. Title: Flow filaments linking bright and dark filaments in a sunspot penumbra Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rubio, L. R. Bibcode: 2005AGUSMSP11A..08T Altcode: We present two-dimensional spectroscopic sunspot observations of high spatial (≍ 0.5 arcsec) and high spectral resolution (λ/Δλ = 250000). The observations were taken with the Telecentric Solar Spectrometer (TESOS) operated at the German Vacuum Tower Telescope on Tenerife. We examine a single scan taken in the popular non-magnetic neutral iron line at 557.6 nm and concentrate our analysis on the unsettled issue of the relation between the Evershed flow and the intensity structure in a sunspot penumbra. At the end of the 20th century, observers concluded that the highest flow velocities are connected to the dark filaments which harbour more horizontal magnetic fields than the bright filaments. Based on a correlation analysis we find that the correlation between flows and intensity varies from the inner to the outer penumbra, from the center-side to the limb-side penumbra, and depends on the length of the trace used to perform the correlation. The line-of-sight velocity maps reveal that the Evershed flow on the center-side penumbra appears highly organised in narrow flow filaments, while the flows in the red-shifted limb-side penumbra do not show a filamentary fine-structure. A high correlation between flow speed and intensity is only observed over small spatial scales, i.e. considering short traces cutting individual features. The correlation is positive in the inner centre and limb-side penumbra, and tends to be negative in the outer penumbra. Our results imply that the Evershed flow is present in bright and dark filaments. In individual cases we find that flow filaments connect bright and dark filaments supporting the moving tube model for the penumbral fine structure. Title: High Resolution Chromospheric Flow Fields in Solar Active Region NOAA 9393 Before and After an X20 Flare Authors: Smith, G. A.; Tritschler, A.; Denker, C. Bibcode: 2005AGUSMSP23B..02S Altcode: Hα full-disk images of the Sun obtained at the Big Bear Solar Observatory (BBSO) are used to measure the chromospheric flow field before and after the X20 flare in solar active region NOAA 9393 on April 2, 2001. Local correlation tracking is used to determine global (differential rotation) and local flow fields (flows in active regions and filaments). We present high-resolution (2k × 2k pixel) flow maps to analyze the dynamics of the chromosphere before and after the flare. If there is a typical pattern in the motions of a flaring active region, it can be used to predict flare activity and/or the onset of Coronal Mass Ejections (CMEs). The high quality of the limb-darkening corrected and contrast-enhanced Hα full-disk images make them an ideal data set for these types of studies due to their high-temporal resolution (1-minute cadence) and extended coverage (more than 500 filtergrams). Title: Spectro-polarimetry of the G band Authors: Uitenbroek, H.; Balasubramaniam, K.; Tritschler, A. Bibcode: 2005AGUSMSP41B..03U Altcode: Narrow-band filter imaging in the G band at 430 nm has been used to track the evolution of small-scale magnetic field elements for more than two decades. Because of the presence of many lines of the CH molecule, and the relatively high contrast at this short wavelength the G-band region is exceptionally suitable for this task. However, despite the frequent use of G-band brightness as magnetic field proxy it has not yet been well established what the precise mechanism is that makes the small scale magnetic elements appear bright. In particular, it is unclear why there is no one-to-one correlation between G-band brightness and magnetic field, as established from co-spatial magnetograms in atomic lines. To obtain a better understanding of the elusive G-band brightening mechanism we obtained high spatial- and spectral resolution spectra of the G-band region in Stokes I and V at the Dunn Solar Telescope on Sacramento Peak. We use the molecular Zeeman effect to determine line-of-sight magnetic field strength directly in the CH lines that provide most of the opacity in the G band, avoiding difficulties with co-aligning images and magnetograms taken seperately. We compare our observations with radiative transfer modeling of the Stokes profiles in snapshots of a magneto-hydrodynamic simulation of solar convection. Title: On the relation between penumbral intensity and flow filaments Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Tritschler, A. Bibcode: 2005AN....326..301S Altcode: Taking advantage of high spatial (≈ 0.5 arcsec) and high spectral (λ/δλ = 250 000) resolution observations obtained with the 2D spectrometer TESOS, we analyze a sunspot located at a heliocentric angle of 23o. We elaborate on the issue of a correlation between dark filaments and the Evershed flow in sunspot penumbrae. Controversies on the existence of such a correlation are resolved: It varies from the inner to the outer penumbra, from the center-side to the limb-side penumbra, and depends on the length of the trace which is used to perform the correlation. The flow map exhibits flow filaments in the center-side penumbra while the red-shifted limb-side penumbra does not show filamentary fine-structure. High correlation coefficients, |C| ≈ 0.9 are only found if small scales, i.e. short traces cutting individual features are considered. C is positive in the inner center and limb-side penumbra, and tends to be negative in the outer penumbra. Our results imply that the Evershed flow is present in bright and dark filaments. In individual cases we find that bright and dark intensities are connected by a flow filament supporting the moving tube model for the penumbral fine structure. Title: Phase diversity restoration of sunspot images. I. Relations between penumbral and photospheric features Authors: Bonet, J. A.; Márquez, I.; Muller, R.; Sobotka, M.; Tritschler, A. Bibcode: 2004A&A...423..737B Altcode: 2004astro.ph..5542B We investigate the dynamics of and the relations between small-scale penumbral and photospheric features near the outer penumbral boundary: penumbral grains (PGs), dark penumbral fibrils, granules, and photospheric G-band bright points. The analysis is based on a 2 h time sequence of a sunspot close to disc center, taken simultaneously in the G-band and in the blue continuum at 450.7 nm. Observations were performed at the Swedish Vacuum Solar Telescope (La Palma) in July 1999. A total of 2564 images (46 arcsec × 75 arcsec) were corrected for telescope aberrations and turbulence perturbations by applying the inversion method of phase diversity. Our findings can by summarized as follows: (a) one third of the outward-moving PGs pass through the outer penumbral boundary and then either continue moving as small bright features or expand and develop into granules. (b) Former PGs and G-band bright points next to the spot reveal a different nature. The latter have not been identified as a continuation of PGs escaping from the penumbra. The G-band bright points are mostly born close to dark penumbral fibrils where the magnetic field is strong, whereas PGs stem from the less-magnetized penumbral component and evolve presumably to non-magnetic granules or small bright features. Title: Towards 2D-Spectropolarimetry with TESOS and Adaptive Optics Authors: Tritschler, A.; Bellot Rubio, L. R.; Kentischer, T. J. Bibcode: 2004AAS...204.6902T Altcode: 2004BAAS...36Q.794T The TElecentric SOlar Spectrometer (TESOS) is a 2D tunable filtergraph installed at the Vacuum Tower Telescope of Teide Observatory (Tenerife, Spain). The instrument features a high spectral resolution (λ /Δ λ ∼ 250000 at 633 nm) and is capable of scanning solar lines over a broad wavelength range (430 - 700 nm). Together with the Kiepenheuer-Institute Adaptive Optics System (KAOS), it is able to achieve spatial resolutions of the order of 0.5 arcsec on a regular basis. Here we present the first spectropolarimetric observations of a sunspot and its immediate surroundings using TESOS. We describe the optical setup, characterize the performance of TESOS operated in the polarimetric mode, and investigate the appearance of the sunspot as seen in circular polarized light with an angular resolution better than 0.5 arcsec. Our results demonstrate the feasibility of using TESOS as a polarimeter, and may be of interest for the design of a TESOS-like multiple-etalon magnetograph for the 4-m NSO/Advanced Technology Solar Telescope. Title: The VIsible and InfraRed Imaging Magnetograph (VIM-IRIM) at Big Bear Solar Observatory Authors: Cao, W.; Tritschler, A.; Denker, C.; Wang, H.; Shumko, S.; Ma, J.; Wang, J.; Marquette, B. Bibcode: 2004AAS...204.6907C Altcode: 2004BAAS...36..795C The Visible-light and the InfraRed Imaging Magnetograph (VIM-IRIM) are Fabry-Perot based filtergraphs working in a telecentric configuration, planned to upgrade the capability for measuring solar magnetic fields at BBSO. Both filtergraph instruments are designed to work with the combination of a narrow-band prefilter and a single Fabry-Perot etalon. VIM and IRIM will provide high temporal resolution, high spatial resolution (< 0.2 "/pixel image scale), high spectral resolution (< 0.1 Å) simultaneous observation at 600-700 nm and 1.0-1.6 μ m with a substantial field of view 170", respectively. Modifications in the setup allow also for scanning different spectral lines that cover the height range from the solar photosphere up to the solar chromopshere. Here we describe the optical setup and present first observations to demonstrate the feasibility of the instrument. After the instrument has proven to work as a 2D-spectrometer, the upgrade to a 2D spectropolarimeter is planned. Title: Two-dimensional spectroscopy of a sunspot. II. Penumbral line asymmetries Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Tritschler, A. Bibcode: 2004A&A...415..731S Altcode: We present, analyse, and interpret line asymmetries from Fe I 557.6 nm of a sunspot penumbra at a heliocentric angle of 23o with high spatial (0.5 arcsec) and spectral (λ/\triangleλ=250 000) resolution. The data set is described and presented in the first paper of this series \citep{tritschler+etal2003}. Line bisectors are used to quantify the line asymmetries. Our findings are: (1) For averaged limb and center side bisectors the shift increases linearly with the bisector intensity level, but the limb side bisector is more inclined than the center side bisector. (2) Individual bisectors exhibit kinks, such that the bisector at high intensity levels is shifted towards the red for both, limb and center side bisectors. Some of the kinks produce bisector reversals in the outer center side penumbra. The bisector properties and their intriguing differences between center and limb side can be explained if one assumes downflows in deep atmospheric layers (\log τ > -1). This is demonstrated by synthetic bisectors. The differences between the two penumbral sides are due to projection effects of non-horizontal flow channels. Our findings also imply that bisectors reversals are not due to elevated channels, but due to the presence of downflows. Along a specific center side flow filament the bisector shift is found to be largest in the line wing, except for the outer end of the filament, where a kink at high bisector intensities toward the red is found. This is consistent with an upflow at the inner footpoint, a deep lying horizontal flow, and, after a spatial distance of 4 arcsec, with a downflow at the end of the flow filament. Title: Two-dimensional spectroscopy of a sunspot. I. Properties of the penumbral fine structure Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rubio, L. R.; KAOS Team; Berkefeld, T.; Schelenz, T. Bibcode: 2004A&A...415..717T Altcode: We investigate the properties of the fine structure of a sunspot penumbra based on spectroscopic measurements with high spectral (λ/δλ=250 000) and high spatial (≈0.5 arcsec) resolution. The magnetically insensitive Fe I 557.6 nm line is used to probe the penumbral atmosphere. The data was taken at the German Vacuum Tower Telescope with the 2D-spectrometer TESOS, taking advantage of the recently installed Kiepenheuer Adaptive Optics System (KAOS). The field of view covers a sunspot located at 23o off the disk center and its immediate surroundings. The penumbral structure is studied by means of maps computed for the line-of-sight velocity, the line width, the equivalent width and the line depression. Line-of-sight velocities are derived from the Doppler shifts at different bisector levels. From these maps we infer the flow field geometry and study the azimuthal and radial dependences of the line parameters. Our findings can be summarized as follows: (a) the flow pattern has a conspicuous filamentary structure in the deep photospheric layers and is rather diffuse in the high layers. (b) The flow field slightly spreads and fans out with height. (c) The flow geometry confirms the presence of an upflow component in the inner penumbra and a downflow component in the middle and outer penumbra. (d) We find an enhanced brightness of the mid-penumbra (``bright ring'') in the line wings, but not in the continuum or line core. (e) The azimuthal average of the equivalent width, the line width and the absolute flow velocity increase with radial distance within the penumbra. (f) Small-scale variations of the equivalent width and the line width on the center-side penumbra are co-spatial and correlated with (blue-shifted) fluctuations in the line-of-sight velocity. (g) Inner limb-side penumbral grains are associated with blue-shifts of v≤-400 m s-1, indicating upflows. (h) One umbral dot in our sample is associated with a blue-shift of v=-200 m s-1. Title: Thermal Kinematic Structure of a Sunspot at 0.5 arcsec Resolution Authors: Bellot Rubio, L. R.; Schlichenmaier, R.; Tritschler, A. Bibcode: 2003ANS...324..104B Altcode: 2003ANS...324..P10B No abstract at ADS Title: Penumbral Line Asymmetries of Fe I 557.6 nm: Implications on the Flow Geometry of a Sunspot Penumbra Authors: Schlichenmaier, P.; Bellot Rubio, L.; Tritschler, A. Bibcode: 2003ANS...324..105S Altcode: 2003ANS...324..P11S No abstract at ADS Title: Two-dimensional Spectroscopy of G-band Bright Structures in the Solar Photosphere Authors: Langhans, K.; Schmidt, W.; Tritschler, A. Bibcode: 2003ANS...324...54L Altcode: 2003ANS...324..P06L; 2003ANS...324b..54L No abstract at ADS Title: 2D Spectroscopy with a Triple Gabry-Perot Spectrometer and Adaptive Optics Authors: Tritschler, A.; Schlichenmaier, R.; Bellot Rutbio, L. Bibcode: 2003ANS...324...21T Altcode: 2003ANS...324..C02T No abstract at ADS Title: Observations of G-band bright structures with TESOS Authors: Langhans, K.; Schmidt, W.; Tritschler, A. Bibcode: 2003AN....324..354L Altcode: No abstract at ADS Title: High-resolution solar spectroscopy with TESOS - Upgrade from a double to a triple system Authors: Tritschler, A.; Schmidt, W.; Langhans, K.; Kentischer, T. Bibcode: 2002SoPh..211...17T Altcode: We present the characteristics and demonstrate the performance of the Triple Etalon SOlar Spectrometer (TESOS) operated at the German Vacuum Tower Telescope (VTT) on Tenerife. The Fabry-Pérot interferometer TESOS is ideally suited for precise measurements of photospheric and chromospheric motion. Installed in 1997 and equipped with two etalons, TESOS has recently been completed with a third etalon and upgraded with two high-speed, backside-illuminated CCD cameras. The image scale of 0.089 arc sec pixel−1 is adapted to the resolution of the telescope. The improved system enables frame rates up to 5 frames per second. The spectral resolution of 300 000 allows for spectral diagnostics of weak photospheric lines, including individual CH-lines within the G-band at 430.6 nm. Title: Network and internetwork bright points in the solar chromosphere Authors: Tritschler, A.; Schmidt, W. Bibcode: 2002ESASP.506..785T Altcode: 2002ESPM...10..785T; 2002svco.conf..785T We investigate the properties of chromospheric bright points from time sequences of narrow-band filtergrams centered on the Ca II K2v emission peak at 393.3 nm. We compute power maps and extract the contributions with periods at 3 min and 5 min and find that the internetwork is dominated by the power at 3 min, whereas the network shows strong signal at 5 min, cospatial with concentrated magnetic field seen in the photosphere. We use image segmentation techniques to derive the size by means of the cell size and an effective diameter as well as the peak brightness and the local background intensity of the bright points. Title: Downflows around a solar pore Authors: Tritschler, A.; Schmidt, W.; Rimmele, T. Bibcode: 2002ESASP.506..477T Altcode: 2002svco.conf..477T; 2002ESPM...10..477T We used the Fabry-Perot interferometer TESOS to observe a solar pore near disk center in two photospheric spectral lines (Fe I 557.6 nm and Fe I 569.1 nm) which correspond to different heights in the atmosphere. The measurements were made during the joint campaign with the NSO/Sacramento-Peak adaptive optics system installed at the German Vacuum Tower Telescope (VTT). The Doppler-velocity measurements show an annular downflow around the outer edge of the pore. This downflow is persistent during the whole observation period, which is demonstrated in the time-averaged Dopplergrams and the corresponding azimuthally integrated and time-averaged radial velocity profiles. Title: 2D-spectroscopic observations of G-band bright structures Authors: Langhans, K.; Schmidt, W.; Tritschler, A. Bibcode: 2002ESASP.506..455L Altcode: 2002ESPM...10..455L; 2002svco.conf..455L We took two-dimensional spectra with the filter spectrometer TESOS at the German Vacuum Tower Telescope, Tenerife, of an absorption line of the CH-molecule and a Fe II-line in the G-band at 430.3 nm. We observed a region of granulation near a pore, close to disk center that showed many structures with enhanced G-band intensity. We introduce a Bright Point Index (BPI) defined by the ratio of the normalized line depressions of the Fe II and the CH-line. The BPI allows to characterize the bright structures by a quantity based on their spectroscopic signature. Bright structures, caused by significant weakening (up to 40% less absorption) of the absorption lines of the CH-molecule, have high BPI values and are accompanied by downflows. The remaining G-band bright structures, only caused by an enhanced continuum intensity, have low BPI and are related to granules. Title: 2D-spectroscopic observations of vec G-band bright structures in the solar photosphere Authors: Langhans, K.; Schmidt, W.; Tritschler, A. Bibcode: 2002A&A...394.1069L Altcode: We took two-dimensional spectra with the filter spectrometer TESOS at the German Vacuum Tower Telescope, Tenerife, of an absorption line of the CH molecule and a Fe II-line in the G-band at 430.3 nm. We observed a region, close to disk center of the Sun, that showed a lot of structures with enhanced G-band intensity (up to 1.3 times the mean intensity of normal granulation). Our spectroscopic investigation of these structures suggests two classes which differ in their spectroscopic signature: (a) Bright structures caused by significant (up to 40\%) weakening of absorption lines of the CH molecule; (b) bright structures only caused by an enhanced continuum intensity. In order to distinguish between those two classes we introduce a Bright Point Index (BPI) defined by the ratio of the normalized line depressions of the Fe~II and the CH-line. The bright structures caused by weakening of the CH-lines have high BPI values and are accompanied by downflows. The remaining G-band bright structures have low BPI and are related to granules. Title: Sunspot photometry with phase diversity. II. Fine-structure characteristics Authors: Tritschler, A.; Schmidt, W. Bibcode: 2002A&A...388.1048T Altcode: We investigate the thermal and morphological fine structure of a small sunspot, which includes the determination of brightness temperatures and characteristic spatial scales as well as their distribution inside the sunspot. The identification and isolation of sunspot fine structure is accomplished by means of a feature-finding algorithm applied to a high-resolution time sequence taken simultaneously in three continuum bands of the solar spectrum. In order to compensate for seeing and instrumental effects, we apply the phase-diversity technique combined with a deconvolution method. The findings can be summarized as follows: (1) umbral dots are found to be on average 760 K cooler than the immediate surrounding photosphere outside the spot. (2) Some exceptional hot penumbral grains exceed the average temperature of the brightest granules of the spots surroundings by typically 150 K. (3) The size distribution of umbral dots and penumbral grains support the idea that the smallest structures are still spatially unresolved. (4) The distribution function of umbral dot peak intensities points to the existence of two umbral dot ``populations'' indicating different efficiency of energy transport. (5) The classification of penumbral filaments into ``dark'' and ``bright'' depends on the immediate surroundings. Title: Sunspot photometry with phase diversity. I. Methods and global sunspot parameters Authors: Tritschler, A.; Schmidt, W. Bibcode: 2002A&A...382.1093T Altcode: The global brightness structure of a small sunspot is investigated. Seeing and instrumental effects are compensated by application of the phase-diversity technique and a conventional deconvolution method. We calculate brightness temperatures for the reconstructed data in three simultaneously observed continuum bands of the solar spectrum (402.1 nm, 569.5 nm, 709.1 nm). The darkest umbral regions are on average 0.17Isun, 0.27Isun and 0.32Isun bright. The corresponding temperatures lie in the range around 4790 K, 4600 K and 4460 K. The spatially averaged penumbral brightness amounts to 0.72Isun, 0.81Isun and 0.85Isun, which corresponds to 5910 K, 5750 K and 5640 K, respectively. Although the spectral distribution of the umbral and penumbral intensities is consistent with former measurements, the derived values support the idea that there exist a real difference in the thermal properties between the umbrae of small and large sunspots. Title: Thermal Structure of a Sunspot: An Application of Phase Diversity Authors: Tritschler, A.; Schmidt, W.; Knölker, M. Bibcode: 1999ASPC..183..108T Altcode: 1999hrsp.conf..108T No abstract at ADS Title: Some properties of sunspot umbral dots. Authors: Tritschler, A.; Schmidt, W. Bibcode: 1997A&A...321..643T Altcode: High resolution Stokes-I spectra of the Zeeman-sensitive lines at λ846.85nm and λ 630.25nm were used to determine the magnetic field strength and the brightness temperature of a simple, relatively symmetric sunspot umbra and its umbral dots (UDs). We find a decrease in brightness temperature for central (~30%) and peripheral UDs (20-25%) compared to the surrounding quiet sun. This corresponds to a difference in temperature of about 1600K and 1200-1400K respectively. The magnetic field strength within the umbra is derived from the Zeeman splitting of the Stokes-I profile. Field strengths within the umbra vary between 1500 and 3000G. Further analysis of the λ846.85nm spectra indicates that the magnetic field strength within the umbral features is not significantly reduced neither for centrally (<=3%) nor for peripherically located UDs (1-2%). The λ630.25nm line yields an enhanced weakening of field strength of 7% for an isolated located UD. The measured properties of UDs do not vary significantly during a 40min observation sequence. Title: Phase Diversity Applied to Sunspot Observations Authors: Tritschler, A.; Schmidt, W.; Knolker, M. Bibcode: 1997ASPC..118..170T Altcode: 1997fasp.conf..170T We present preliminary results of a multi-colour phase diversity experiment carried out with the Multichannel Filter System of the Vacuum Tower Telescope at the Observatorio del Teide on Tenerife. We apply phase-diversity imaging to a time sequence of sunspot filtergrams taken in three continuum bands and correct the seeing influence for each image. A newly developed phase diversity device allowing for the projection of both the focused and the defocused image onto a single CCD chip was used in one of the wavelength channels. With the information about the wavefront obtained by the image reconstruction algorithm the restoration of the other two bands can be performed as well. The processed and restored data set will then be used to derive the temperature and proper motion of the umbral dots. Data analysis is still under way, and final results will be given in a forthcoming article. Title: Phase diversity image reconstruction of sunspot umbral dots. Authors: Tritschler, A.; Schmidt, W. Bibcode: 1996AGAb...12...93T Altcode: No abstract at ADS