TY - JOUR A1 - Balthasar, H. A1 - Gömöry, P. A1 - González Manrique, Sergio Javier A1 - Kuckein, Christoph A1 - Kavka, J. A1 - Kucera, A. A1 - Schwartz, P. A1 - Vaskova, R. A1 - Berkefeld, T. A1 - Collados Vera, M. A1 - Denker, Carsten A1 - Feller, A. A1 - Hofmann, A. A1 - Lagg, A. A1 - Nicklas, H. A1 - Suarez, D. A1 - Pastor Yabar, A. A1 - Rezaei, R. A1 - Schlichenmaier, R. A1 - Schmidt, D. A1 - Schmidt, W. A1 - Sigwarth, M. A1 - Sobotka, M. A1 - Solanki, S. K. A1 - Soltau, D. A1 - Staude, J. A1 - Strassmeier, Klaus G. A1 - Volkmer, R. A1 - von der Lühe, O. A1 - Waldmann, T. T1 - Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope JF - Astronomische Nachrichten = Astronomical notes N2 - Arch filament systems occur in active sunspot groups, where a fibril structure connects areas of opposite magnetic polarity, in contrast to active region filaments that follow the polarity inversion line. We used the GREGOR Infrared Spectrograph (GRIS) to obtain the full Stokes vector in the spectral lines SiI lambda 1082.7 nm, He I lambda 1083.0 nm, and Ca I lambda 1083.9 nm. We focus on the near-infrared calcium line to investigate the photospheric magnetic field and velocities, and use the line core intensities and velocities of the helium line to study the chromospheric plasma. The individual fibrils of the arch filament system connect the sunspot with patches of magnetic polarity opposite to that of the spot. These patches do not necessarily coincide with pores, where the magnetic field is strongest. Instead, areas are preferred not far from the polarity inversion line. These areas exhibit photospheric downflows of moderate velocity, but significantly higher downflows of up to 30 km s(-1) in the chromospheric helium line. Our findings can be explained with new emerging flux where the matter flows downward along the field lines of rising flux tubes, in agreement with earlier results. (C) 2016 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim KW - Sun: filaments KW - Sun: photosphere KW - techniques: polarimetric KW - techniques: spectroscopic Y1 - 2016 U6 - https://doi.org/10.1002/asna.201612432 SN - 0004-6337 SN - 1521-3994 VL - 337 SP - 1050 EP - 1056 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Verma, Meetu A1 - Denker, Carsten A1 - Balthasar, H. A1 - Kuckein, Christoph A1 - González Manrique, Sergio Javier A1 - Sobotka, M. A1 - Gonzalez, N. Bello A1 - Hoch, S. A1 - Diercke, Andrea A1 - Kummerow, Philipp A1 - Berkefeld, T. A1 - Collados Vera, M. A1 - Feller, A. A1 - Hofmann, A. A1 - Kneer, F. A1 - Lagg, A. A1 - Löhner-Böttcher, J. A1 - Nicklas, H. A1 - Pastor Yabar, A. A1 - Schlichenmaier, R. A1 - Schmidt, D. A1 - Schmidt, W. A1 - Schubert, M. A1 - Sigwarth, M. A1 - Solanki, S. K. A1 - Soltau, D. A1 - Staude, J. A1 - Strassmeier, Klaus G. A1 - Volkmer, R. A1 - von der Lühe, O. A1 - Waldmann, T. T1 - Horizontal flow fields in and around a small active region The transition period between flux emergence and decay JF - Polymers N2 - Context. The solar magnetic field is responsible for all aspects of solar activity. Thus, emergence of magnetic flux at the surface is the first manifestation of the ensuing solar activity. Aims. Combining high-resolution and synoptic observations aims to provide a comprehensive description of flux emergence at photospheric level and of the growth process that eventually leads to a mature active region. Methods. The small active region NOAA 12118 emerged on 2014 July 17 and was observed one day later with the 1.5-m GREGOR solar telescope on 2014 July 18. High-resolution time-series of blue continuum and G-band images acquired in the blue imaging channel (BIC) of the GREGOR Fabry-Perot Interferometer (GFPI) were complemented by synoptic line-of-sight magnetograms and continuum images obtained with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). Horizontal proper motions and horizontal plasma velocities were computed with local correlation tracking (LCT) and the differential affine velocity estimator (DAVE), respectively. Morphological image processing was employed to measure the photometric and magnetic area, magnetic flux, and the separation profile of the emerging flux region during its evolution. Results. The computed growth rates for photometric area, magnetic area, and magnetic flux are about twice as high as the respective decay rates. The space-time diagram using HMI magnetograms of five days provides a comprehensive view of growth and decay. It traces a leaf-like structure, which is determined by the initial separation of the two polarities, a rapid expansion phase, a time when the spread stalls, and a period when the region slowly shrinks again. The separation rate of 0.26 km s(-1) is highest in the initial stage, and it decreases when the separation comes to a halt. Horizontal plasma velocities computed at four evolutionary stages indicate a changing pattern of inflows. In LCT maps we find persistent flow patterns such as outward motions in the outer part of the two major pores, a diverging feature near the trailing pore marking the site of upwelling plasma and flux emergence, and low velocities in the interior of dark pores. We detected many elongated rapidly expanding granules between the two major polarities, with dimensions twice as large as the normal granules. KW - Sun: photosphere KW - Sun: magnetic fields KW - techniques: image processing KW - methods: data analysis Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201628380 SN - 1432-0746 VL - 596 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Verma, Meetu A1 - Denker, Carsten A1 - Balthasar, H. A1 - Kuckein, Christoph A1 - Rezaei, R. A1 - Sobotka, Michal A1 - Deng, N. A1 - Wang, Haimin A1 - Tritschler, A. A1 - Collados, M. A1 - Diercke, Andrea A1 - González Manrique, Sergio Javier T1 - High-resolution imaging and near-infrared spectroscopy of penumbral decay JF - Astronomy and astrophysics : an international weekly journal N2 - 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 degrees 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. KW - Sun: photosphere KW - sunspots KW - Sun: magnetic fields KW - Sun: infrared KW - techniques: imaging spectroscopy KW - techniques: spectroscopic Y1 - 2018 U6 - https://doi.org/10.1051/0004-6361/201731801 SN - 1432-0746 VL - 614 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Gömöry, Peter A1 - Balthasar, Horst A1 - Kuckein, Christoph A1 - Koza, Julis A1 - Veronig, Astrid M. A1 - González Manrique, Sergio Javier A1 - Kucera, Ales A1 - Schwartz, Pavol A1 - Hanslmeier, Arnold T1 - Flare-induced changes of the photospheric magnetic field in a delta-spot deduced from ground-based observations JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. Changes of the magnetic field and the line-of-sight velocities in the photosphere are being reported for an M-class flare that originated at a delta-spot belonging to active region NOAA 11865. Methods. High-resolution ground-based near-infrared spectropolarimetric observations were acquired simultaneously in two photospheric spectral lines, Fe I 10783 angstrom and Si I 10786 angstrom, with the Tenerife Infrared Polarimeter at the Vacuum Tower Telescope (VTT) in Tenerife on 2013 October 15. The observations covered several stages of the M-class flare. Inversions of the full-Stokes vector of both lines were carried out and the results were put into context using (extreme)-ultraviolet filtergrams from the Solar Dynamics Observatory (SDO). Results. The active region showed high flaring activity during the whole observing period. After the M-class flare, the longitudinal magnetic field did not show significant changes along the polarity inversion line (PIL). However, an enhancement of the transverse magnetic field of approximately 550G was found that bridges the PIL and connects umbrae of opposite polarities in the delta-spot. At the same time, a newly formed system of loops appeared co-spatially in the corona as seen in 171 angstrom filtergrams of the Atmospheric Imaging Assembly (AIA) on board SDO. However, we cannot exclude that the magnetic connection between the umbrae already existed in the upper atmosphere before the M-class flare and became visible only later when it was filled with hot plasma. The photospheric Doppler velocities show a persistent upflow pattern along the PIL without significant changes due to the flare. Conclusions. The increase of the transverse component of the magnetic field after the flare together with the newly formed loop system in the corona support recent predictions of flare models and flare observations. KW - Sun: magnetic fields KW - sunspots KW - Sun: photosphere KW - Sun: flares KW - techniques: polarimetric Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201730644 SN - 1432-0746 VL - 602 SP - 14 EP - 27 PB - EDP Sciences CY - Les Ulis ER - TY - JOUR A1 - Kuckein, Christoph A1 - Diercke, Andrea A1 - González Manrique, Sergio Javier A1 - Verma, Meetu A1 - Loehner-Boettcher, Johannes A1 - Socas-Navarro, H. A1 - Balthasar, Horst A1 - Sobotka, M. A1 - Denker, Carsten T1 - Ca II 8542 angstrom brightenings induced by a solar microflare JF - Astronomy and astrophysics : an international weekly journal N2 - Aims. We study small-scale brightenings in Ca II 8542 angstrom line-core images to determine their nature and effect on localized heating and mass transfer in active regions. Methods. High-resolution two-dimensional spectroscopic observations of a solar active region in the near-infrared Ca II 8542 angstrom line were acquired with the GREGOR Fabry-Perot Interferometer attached to the 1.5-m GREGOR telescope. Inversions of the spectra were carried out using the NICOLE code to infer temperatures and line-of-sight (LOS) velocities. Response functions of the Ca II line were computed for temperature and LOS velocity variations. Filtergrams of the Atmospheric Imaging Assembly (AIA) and magnetograms of the Helioseismic and Magnetic Imager (HMI) were coaligned to match the ground-based observations and to follow the Ca II brightenings along all available layers of the atmosphere. Results. We identified three brightenings of sizes up to 2 ' x 2 ' that appeared in the Ca II 8542 angstrom line-core images. Their lifetimes were at least 1.5 min. We found evidence that the brightenings belonged to the footpoints of a microflare (MF). The properties of the observed brightenings disqualified the scenarios of Ellerman bombs or Interface Region Imaging Spectrograph (IRIS) bombs. However, this MF shared some common properties with flaring active-region fibrils or flaring arch filaments (FAFs): (1) FAFs and MFs are both apparent in chromospheric and coronal layers according to the AIA channels; and (2) both show flaring arches with lifetimes of about 3.0-3.5 min and lengths of similar to 20 ' next to the brightenings. The inversions revealed heating by 600 K at the footpoint location in the ambient chromosphere during the impulsive phase. Connecting the footpoints, a dark filamentary structure appeared in the Ca II line-core images. Before the start of the MF, the spectra of this structure already indicated average blueshifts, meaning upward motions of the plasma along the LOS. During the impulsive phase, these velocities increased up to -2.2 km s(-1). The structure did not disappear during the observations. Downflows dominated at the footpoints. However, in the upper photosphere, slight upflows occurred during the impulsive phase. Hence, bidirectional flows are present in the footpoints of the MF. KW - Sun: photosphere KW - Sun: chromosphere KW - Sun: corona KW - Sun: activity KW - techniques: imaging spectroscopy Y1 - 2017 U6 - https://doi.org/10.1051/0004-6361/201731319 SN - 1432-0746 VL - 608 PB - EDP Sciences CY - Les Ulis ER -