TY  - JOUR
A1  - Verma, Meetu
A1  - Denker, Carsten
A1  - Böhm, F.
A1  - Balthasar, H.
A1  - Fischer, C. E.
A1  - Kuckein, Christoph
A1  - Gonzalez, N. Bello
A1  - Berkefeld, T.
A1  - Collados Vera, M.
A1  - Diercke, Andrea
A1  - Feller, A.
A1  - Gonzalez Manrique, Sergio Javier
A1  - Hofmann, A.
A1  - Lagg, A.
A1  - Nicklas, H.
A1  - Orozco Suarez, D.
A1  - Pator 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  - Flow and magnetic field properties in the trailing sunspots of active region NOAA 12396
JF  - Astronomische Nachrichten = Astronomical notes
N2  - Improved measurements of the photospheric and chromospheric three-dimensional magnetic and flow fields are crucial for a precise determination of the origin and evolution of active regions. We present an illustrative sample of multi-instrument data acquired during a two-week coordinated observing campaign in August 2015 involving, among others, the GREGOR solar telescope (imaging and near-infrared spectroscopy) and the space missions Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS). The observations focused on the trailing part of active region NOAA 12396 with complex polarity inversion lines and strong intrusions of opposite polarity flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV spectral profiles in the photospheric Si i.1082.7 nm line, the chromospheric He I lambda 1083.0 nm triplet, and the photospheric Ca I lambda 1083.9 nm line. Carefully calibrated GRIS scans of the active region provided maps of Doppler velocity and magnetic field at different atmospheric heights. We compare quick-look maps with those obtained with the " Stokes Inversions based on Response functions" (SIR) code, which furnishes deeper insight into the magnetic properties of the region. We find supporting evidence that newly emerging flux and intruding opposite polarity flux are hampering the formation of penumbrae, i.e., a penumbra fully surrounding a sunspot is only expected after cessation of flux emergence in proximity to the sunspots. (C) 2016 WILEY-VCH Verlag GmbH& Co.KGaA, Weinheim
KW  - Sun: magnetic fields
KW  - sunspots
KW  - methods: data analysis
KW  - techniques: polarimetric
KW  - techniques: spectroscopic
Y1  - 2016
U6  - https://doi.org/10.1002/asna.201612447
SN  - 0004-6337
SN  - 1521-3994
VL  - 337
SP  - 1090
EP  - 1098
PB  - Wiley-VCH
CY  - Weinheim
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  -