Feller, Alex

[["dc.bibliographiccitation.firstpage","1050"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","1056"],["dc.bibliographiccitation.volume","337"],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Gomory, P."],["dc.contributor.author","Manrique, S. J. Gonzalez"],["dc.contributor.author","Kuckein, C."],["dc.contributor.author","Kavka, J."],["dc.contributor.author","Kucera, A."],["dc.contributor.author","Schwartz, P."],["dc.contributor.author","Vaskova, R."],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Collados Vera, M."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Suarez, D."],["dc.contributor.author","Pastor Yabar, A."],["dc.contributor.author","Rezaei, R."],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sigwarth, M."],["dc.contributor.author","Sobotka, M."],["dc.contributor.author","Solanki, Parth K."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Strassmeier, K. G."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","von der Luhe, O."],["dc.contributor.author","Waldmann, T."],["dc.date.accessioned","2018-11-07T10:06:05Z"],["dc.date.available","2018-11-07T10:06:05Z"],["dc.date.issued","2016"],["dc.description.abstract","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"],["dc.identifier.doi","10.1002/asna.201612432"],["dc.identifier.isi","000391297900010"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39025"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.publisher.place","Weinheim"],["dc.relation.conference","12th Potsdam Thinkshop Conference on Dynamic Sun - Exploring the Many Facets of Solar Eruptive Events"],["dc.relation.eventlocation","Potsdam, GERMANY"],["dc.relation.issn","1521-3994"],["dc.relation.issn","0004-6337"],["dc.title","Spectropolarimetric observations of an arch filament system with the GREGOR solar telescope"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A4"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","596"],["dc.contributor.author","Franz, M."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Bethge, C."],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Borrero, J. M."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Kiess, C."],["dc.contributor.author","Rezaei, R."],["dc.contributor.author","Schmidt, Christian D."],["dc.contributor.author","Sigwarth, M."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","Luhe, O. von der"],["dc.contributor.author","Waldmann, T."],["dc.contributor.author","Orozco, D."],["dc.contributor.author","Pastor Yabar, A."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Hofmann, A."],["dc.contributor.author","Strassmeier, K."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Sobotka, M."],["dc.date.accessioned","2020-07-01T07:16:29Z"],["dc.date.available","2020-07-01T07:16:29Z"],["dc.date.issued","2016"],["dc.description.abstract","Context. A significant part of the penumbral magnetic field returns below the surface in the very deep photosphere. For lines in the visible, a large portion of this return field can only be detected indirectly by studying its imprints on strongly asymmetric and three-lobed Stokes V profiles. Infrared lines probe a narrow layer in the very deep photosphere, providing the possibility of directly measuring the orientation of magnetic fields close to the solar surface. Aims. We study the topology of the penumbral magnetic field in the lower photosphere, focusing on regions where it returns below the surface. Methods. We analyzed 71 spectropolarimetric datasets from Hinode and from the GREGOR infrared spectrograph. We inferred the quality and polarimetric accuracy of the infrared data after applying several reduction steps. Techniques of spectral inversion and forward synthesis were used to test the detection algorithm. We compared the morphology and the fractional penumbral area covered by reversed-polarity and three-lobed Stokes V profiles for sunspots at disk center. We determined the amount of reversed-polarity and three-lobed Stokes V profiles in visible and infrared data of sunspots at various heliocentric angles. From the results, we computed center-to-limb variation curves, which were interpreted in the context of existing penumbral models. Results. Observations in visible and near-infrared spectral lines yield a significant difference in the penumbral area covered by magnetic fields of opposite polarity. In the infrared, the number of reversed-polarity Stokes V profiles is smaller by a factor of two than in the visible. For three-lobed Stokes V profiles the numbers differ by up to an order of magnitude."],["dc.identifier.arxiv","1608.00513v2"],["dc.identifier.doi","10.1051/0004-6361/201628407"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/66810"],["dc.language.iso","en"],["dc.relation.eissn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.title","Magnetic fields of opposite polarity in sunspot penumbrae"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","28"],["dc.bibliographiccitation.issue","S327"],["dc.bibliographiccitation.journal","Proceedings of the International Astronomical Union"],["dc.bibliographiccitation.lastpage","33"],["dc.bibliographiccitation.volume","12"],["dc.contributor.author","Manrique, S. J. González"],["dc.contributor.author","Denker, C."],["dc.contributor.author","Kuckein, C."],["dc.contributor.author","Yabar, A. Pastor"],["dc.contributor.author","Collados, M."],["dc.contributor.author","Verma, M."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Diercke, A."],["dc.contributor.author","Fischer, C. E."],["dc.contributor.author","Gömöry, P."],["dc.contributor.author","González, N. Bello"],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Armas, M. Cubas"],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Hoch, S."],["dc.contributor.author","Hofmann, A."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Suárez, D. Orozco"],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sigwarth, M."],["dc.contributor.author","Sobotka, M."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Strassmeier, K. G."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","von der Lühe, O."],["dc.contributor.author","Waldmann, T."],["dc.date.accessioned","2020-12-10T15:22:25Z"],["dc.date.available","2020-12-10T15:22:25Z"],["dc.date.issued","2017"],["dc.identifier.doi","10.1017/S1743921317000278"],["dc.identifier.eissn","1743-9221"],["dc.identifier.issn","1743-9213"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/73394"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-354"],["dc.title","Flows along arch filaments observed in the GRIS ‘very fast spectroscopic mode’"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1057"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","1063"],["dc.bibliographiccitation.volume","337"],["dc.contributor.author","Manrique, S. J. Gonzalez"],["dc.contributor.author","Kuckein, C."],["dc.contributor.author","Pastor Yabar, A."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Fischer, C. E."],["dc.contributor.author","Gomory, P."],["dc.contributor.author","Diercke, A."],["dc.contributor.author","Gonzalez, N. Bello"],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Hoch, S."],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Orozco Suarez, D."],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sigwarth, M."],["dc.contributor.author","Sobotka, M."],["dc.contributor.author","Solanki, Parth K."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Strassmeier, K. G."],["dc.contributor.author","Verma, M."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","von der Luhe, O."],["dc.contributor.author","Waldmann, T."],["dc.date.accessioned","2018-11-07T10:06:06Z"],["dc.date.available","2018-11-07T10:06:06Z"],["dc.date.issued","2016"],["dc.description.abstract","The new generation of solar instruments provides better spectral, spatial, and temporal resolution for a better understanding of the physical processes that take place on the Sun. Multiple-component profiles are more commonly observed with these instruments. Particularly, the He i 10830 triplet presents such peculiar spectral profiles, which give information on the velocity and magnetic fine structure of the upper chromosphere. The purpose of this investigation is to describe a technique to efficiently fit the two blended components of the He i 10830 triplet, which are commonly observed when two atmospheric components are located within the same resolution element. The observations used in this study were taken on 2015 April 17 with the very fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar telescope, located at the Observatorio del Teide, Tenerife, Spain. We apply a double-Lorentzian fitting technique using Levenberg-Marquardt least-squares minimization. This technique is very simple and much faster than inversion codes. Line-of-sight Doppler velocities can be inferred for a whole map of pixels within just a few minutes. Our results show sub-and supersonic downflow velocities of up to 32 km s(-1) for the fast component in the vicinity of footpoints of filamentary structures. The slow component presents velocities close to rest. (C) 2016 WILEY-VCH Verlag GmbH& Co. KGaA, Weinheim"],["dc.identifier.doi","10.1002/asna.201512433"],["dc.identifier.isi","000391297900011"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39026"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.publisher.place","Weinheim"],["dc.relation.conference","12th Potsdam Thinkshop Conference on Dynamic Sun - Exploring the Many Facets of Solar Eruptive Events"],["dc.relation.eventlocation","Potsdam, GERMANY"],["dc.relation.issn","1521-3994"],["dc.relation.issn","0004-6337"],["dc.title","Fitting peculiar spectral profiles in He I 10830 angstrom absorption features"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1090"],["dc.bibliographiccitation.issue","10"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","1098"],["dc.bibliographiccitation.volume","337"],["dc.contributor.author","Verma, M."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Boehm, F."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Fischer, C. E."],["dc.contributor.author","Kuckein, C."],["dc.contributor.author","Gonzalez, N. Bello"],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Diercke, A."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Manrique, S. J. Gonzalez"],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Orozco Suarez, D."],["dc.contributor.author","Pator Yabar, A."],["dc.contributor.author","Rezaei, R."],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sigwarth, M."],["dc.contributor.author","Sobotka, M."],["dc.contributor.author","Solanki, Parth K."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Strassmeier, K. G."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","von der Luhe, O."],["dc.contributor.author","Waldmann, T."],["dc.date.accessioned","2018-11-07T10:06:06Z"],["dc.date.available","2018-11-07T10:06:06Z"],["dc.date.issued","2016"],["dc.description.abstract","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"],["dc.identifier.doi","10.1002/asna.201612447"],["dc.identifier.isi","000391297900016"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39027"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.publisher.place","Weinheim"],["dc.relation.conference","12th Potsdam Thinkshop Conference on Dynamic Sun - Exploring the Many Facets of Solar Eruptive Events"],["dc.relation.eventlocation","Potsdam, GERMANY"],["dc.relation.issn","1521-3994"],["dc.relation.issn","0004-6337"],["dc.title","Flow and magnetic field properties in the trailing sunspots of active region NOAA 12396"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","810"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","815"],["dc.bibliographiccitation.volume","333"],["dc.contributor.author","Denker, C."],["dc.contributor.author","Luehe, O. von der"],["dc.contributor.author","Feller, A."],["dc.contributor.author","Arlt, K."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Bauer, S.-M."],["dc.contributor.author","Gonzalez, N. Bello"],["dc.contributor.author","Berkefeld, Th."],["dc.contributor.author","Caligari, P."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Fischer, A."],["dc.contributor.author","Granzer, T."],["dc.contributor.author","Hahn, T."],["dc.contributor.author","Halbgewachs, C."],["dc.contributor.author","Heidecke, F."],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","Kentischer, T."],["dc.contributor.author","Klvana, M."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Popow, E."],["dc.contributor.author","Puschmann, K. G."],["dc.contributor.author","Rendtel, J."],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sobotka, M."],["dc.contributor.author","Solanki, Parth K."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Strassmeier, K. G."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","Waldmann, T."],["dc.contributor.author","Wiehr, E."],["dc.contributor.author","Wittmann, Axel D."],["dc.contributor.author","Woche, M."],["dc.date.accessioned","2018-11-07T09:04:00Z"],["dc.date.available","2018-11-07T09:04:00Z"],["dc.date.issued","2012"],["dc.description.abstract","In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the historical context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim"],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft (DFG) [DE 787/3-1]"],["dc.identifier.doi","10.1002/asna.201211728"],["dc.identifier.isi","000310799500006"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/25016"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.relation.issn","0004-6337"],["dc.title","A retrospective of the GREGOR solar telescope in scientific literature"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dspace.entity.type","Publication"]]