TY - JOUR A1 - Diercke, Andrea A1 - Kuckein, Christoph A1 - Denker, Carsten T1 - Dynamics and connectivity of an extended arch filament system JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. In this study, we analyzed a filament system, which expanded between moving magnetic features (MMFs) of a decaying sunspot and opposite flux outside of the active region from the nearby quiet-Sun network. This configuration deviated from a classical arch filament system (AFS), which typically connects two pores in an emerging flux region. Thus, we called this system an extended AFS. We contrasted classical and extended AFSs with an emphasis on the complex magnetic structure of the latter. Furthermore, we examined the physical properties of the extended AFS and described its dynamics and connectivity. Methods. The extended AFS was observed with two instruments at the Dunn Solar Telescope (DST). The Rapid Oscillations in the Solar Atmosphere (ROSA) imager provided images in three different wavelength regions, which covered the dynamics of the extended AFS at different atmospheric heights. The Interferometric Bidimensional Spectropolarimeter (IBIS) provided spectroscopic Ha data and spectropolarimetric data that was obtained in the near-infrared (NIR) Call lambda 8542 angstrom line. We derived the corresponding line-of-sight (LOS) velocities and used He II lambda 304 angstrom extreme ultraviolet (EUV) images of the Atmospheric Imaging Assembly (AIA) and LOS magnetograms of the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) as context data. Results. The NIR Call Stokes-V maps are not suitable to definitively define a clear polarity inversion line and to classify this chromospheric structure. Nevertheless, this unusual AFS connects the MMFs of a decaying sunspot with the network field. At the southern footpoint, we measured that the flux decreases over time. We find strong downflow velocities at the footpoints of the extended AFS, which increase in a time period of 30 min. The velocities are asymmetric at both footpoints with higher velocities at the southern footpoint. An EUV brigthening appears in one of the arch filaments, which migrates from the northern footpoint toward the southern one. This activation likely influences the increasing redshift at the southern footpoint. Conclusions. The extended AFS exhibits a similar morphology as classical AFSs, for example, threaded filaments of comparable length and width. Major differences concern the connection from MMFs around the sunspot with the flux of the neighboring quietSun network, converging footpoint motions, and longer lifetimes of individual arch filaments of about one hour, while the extended AFS is still very dynamic. KW - methods: observational KW - Sun: filaments, prominences KW - Sun: activity KW - techniques: image processing KW - Sun: chromosphere Y1 - 2019 U6 - https://doi.org/10.1051/0004-6361/201935583 SN - 1432-0746 VL - 629 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Diercke, Andrea A1 - Kuckein, Christoph A1 - Verma, Meetu A1 - Denker, Carsten T1 - Counter-streaming flows in a giant quiet-Sun filament observed in the extreme ultraviolet JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. The giant solar filament was visible on the solar surface from 2011 November 8-23. Multiwavelength data from the Solar Dynamics Observatory (SDO) were used to examine counter-streaming flows within the spine of the filament. Methods. We use data from two SDO instruments, the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI), covering the whole filament, which stretched over more than half a solar diameter. H alpha images from the Kanzelhohe Solar Observatory (KSO) provide context information of where the spine of the filament is defined and the barbs are located. We apply local correlation tracking (LCT) to a two-hour time series on 2011 November 16 of the AIA images to derive horizontal flow velocities of the filament. To enhance the contrast of the AIA images, noise adaptive fuzzy equalization (NAFE) is employed, which allows us to identify and quantify counter-streaming flows in the filament. We observe the same cool filament plasma in absorption in both H alpha and EUV images. Hence, the counter-streaming flows are directly related to this filament material in the spine. In addition, we use directional flow maps to highlight the counter-streaming flows. Results. We detect counter-streaming flows in the filament, which are visible in the time-lapse movies in all four examined AIA wavelength bands (lambda 171 angstrom, lambda 193 angstrom, lambda 304 angstrom, and lambda 211 angstrom). In the time-lapse movies we see that these persistent flows lasted for at least two hours, although they became less prominent towards the end of the time series. Furthermore, by applying LCT to the images we clearly determine counter-streaming flows in time series of lambda 171 angstrom and lambda 193 angstrom images. In the lambda 304 angstrom wavelength band, we only see minor indications for counter-streaming flows with LCT, while in the lambda 211 angstrom wavelength band the counter-streaming flows are not detectable with this method. The diverse morphology of the filament in H alpha and EUV images is caused by different absorption processes, i.e., spectral line absorption and absorption by hydrogen and helium continua, respectively. The horizontal flows reach mean flow speeds of about 0.5 km s(-1) for all wavelength bands. The highest horizontal flow speeds are identified in the lambda 171 angstrom band with flow speeds of up to 2.5 km s(-1). The results are averaged over a time series of 90 minutes. Because the LCT sampling window has finite width, a spatial degradation cannot be avoided leading to lower estimates of the flow velocities as compared to feature tracking or Doppler measurements. The counter-streaming flows cover about 15-20% of the whole area of the EUV filament channel and are located in the central part of the spine. Conclusions. Compared to the ground-based observations, the absence of seeing effects in AIA observations reveal counter-streaming flows in the filament even with a moderate image scale of 0 '.6 pixel(-1). Using a contrast enhancement technique, these flows can be detected and quantified with LCT in different wavelengths. We confirm the omnipresence of counter-streaming flows also in giant quiet-Sun filaments. KW - methods: observational KW - Sun: filaments, prominences KW - Sun: activity KW - Sun: chromosphere KW - Sun: corona KW - techniques: image processing Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201730536 SN - 1432-0746 VL - 611 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gonzalez Manrique, Sergio Javier A1 - Kuckein, Christoph A1 - Collados, M. A1 - Denker, Carsten A1 - Solanki, S. K. A1 - Gomory, P. A1 - Verma, Meetu A1 - Balthasar, H. A1 - Lagg, A. A1 - Diercke, Andrea T1 - Temporal evolution of arch filaments as seen in He I 10 830 angstrom JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. We study the evolution of an arch filament system (AFS) and of its individual arch filaments to learn about the processes occurring in them. Methods. We observed the AFS at the GREGOR solar telescope on Tenerife at high cadence with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) in the He I 10 830 angstrom spectral range. The He I triplet profiles were fitted with analytic functions to infer line-of-sight (LOS) velocities to follow plasma motions within the AFS. Results. We tracked the temporal evolution of an individual arch filament over its entire lifetime, as seen in the He I 10 830 angstrom triplet. The arch filament expanded in height and extended in length from 13 ' to 21 '. The lifetime of this arch filament is about 30 min. About 11 min after the arch filament is seen in He I, the loop top starts to rise with an average Doppler velocity of 6 km s(-1). Only two minutes later, plasma drains down with supersonic velocities towards the footpoints reaching a peak velocity of up to 40 km s(-1) in the chromosphere. The temporal evolution of He I 10 830 angstrom profiles near the leading pore showed almost ubiquitous dual red components of the He I triplet, indicating strong downflows, along with material nearly at rest within the same resolution element during the whole observing time. KW - Sun: chromosphere KW - Sun: activity KW - methods: observational KW - methods: data analysis KW - techniques: high angular resolution Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201832684 SN - 1432-0746 VL - 617 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Martinez Gonzalez, M. J. A1 - Pastor Yabar, A. A1 - Lagg, A. A1 - Asensio Ramos, A. A1 - Collados Vera, M. A1 - Solanki, S. K. A1 - Balthasar, H. A1 - Berkefeld, T. A1 - Denker, Carsten A1 - Doerr, H. P. A1 - Feller, A. A1 - Franz, M. A1 - González Manrique, Sergio Javier A1 - Hofmann, A. A1 - Kneer, F. A1 - Kuckein, Christoph A1 - Louis, R. A1 - von der Lühe, O. A1 - Nicklas, H. A1 - Orozco, D. A1 - Rezaei, R. A1 - Schlichenmaier, R. A1 - Schmidt, D. A1 - Schmidt, W. A1 - Sigwarth, M. A1 - Sobotka, M. A1 - Soltau, D. A1 - Staude, J. A1 - Strassmeier, Klaus G. A1 - Verma, Meetu A1 - Waldman, T. A1 - Volkmer, R. T1 - Inference of magnetic fields in the very quiet Sun JF - Journal of geophysical research : Earth surface N2 - Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution. Aims. We present high-precision spectro-polarimetric data with high spatial resolution (0.4") of the very quiet Sun at 1.56 mu m obtained with the GREGOR telescope to shed some light on this complex magnetism. Methods. We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component. Results. Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak (similar to 150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area similar to 50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised. KW - Sun: atmosphere KW - Sun: magnetic fields KW - techniques: polarimetric KW - methods: observational Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201628449 SN - 1432-0746 VL - 596 PB - EDP Sciences CY - Les Ulis ER -