Hofmann, Anna Maria

[["dc.bibliographiccitation.artnumber","A8"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","596"],["dc.contributor.author","Joshi, J."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Solanki, S. K."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Orozco Suárez, D."],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Franz, M."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Hofmann, A."],["dc.contributor.author","Kiess, C."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Pastor Yabar, A."],["dc.contributor.author","Rezaei, R."],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sobotka, M."],["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","2019-07-09T11:43:08Z"],["dc.date.available","2019-07-09T11:43:08Z"],["dc.date.issued","2016"],["dc.description.abstract","Aims. The fine-structure of the magnetic field in a sunspot penumbra in the upper chromosphere is to be explored and compared to that in the photosphere. Methods. Spectropolarimetric observations with high spatial resolution were recorded with the 1.5-m GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The observed spectral domain includes the upper chromospheric Hei triplet at 10 830 Å  and the photospheric Sii 10 827.1 Å  and Cai 10 833.4 Å  spectral lines. The upper chromospheric magnetic field is obtained by inverting the Hei triplet assuming a Milne-Eddington-type model atmosphere. A height-dependent inversion was applied to the Sii 10 827.1 Å  and Cai 10 833.4 Å  lines to obtain the photospheric magnetic field. Results. We find that the inclination of the magnetic field varies in the azimuthal direction in the photosphere and in the upper chromosphere. The chromospheric variations coincide remarkably well with the variations in the inclination of the photospheric field and resemble the well-known spine and interspine structure in the photospheric layers of penumbrae. The typical peak-to-peak variations in the inclination of the magnetic field in the upper chromosphere are found to be 10°–15°, which is roughly half the variation in the photosphere. In contrast, the magnetic field strength of the observed penumbra does not vary on small spatial scales in the upper chromosphere. Conclusions. Thanks to the high spatial resolution of the observations that is possible with the GREGOR telescope at 1.08 microns, we find that the prominent small-scale fluctuations in the magnetic field inclination, which are a salient part of the property of sunspot penumbral photospheres, also persist in the chromosphere, although at somewhat reduced amplitudes. Such a complex magnetic configuration may facilitate penumbral chromospheric dynamic phenomena, such as penumbral micro-jets or transient bright dots."],["dc.identifier.doi","10.1051/0004-6361/201629214"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14289"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/58836"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312495/EU/High-Resolution Solar Physics Network/SOLARNET"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Upper chromospheric magnetic field of a sunspot penumbra: observations of fine structure"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A59"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","596"],["dc.contributor.author","Felipe, T."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Khomenko, E."],["dc.contributor.author","Kuckein, C."],["dc.contributor.author","Asensio Ramos, A."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Franz, M."],["dc.contributor.author","Hofmann, A."],["dc.contributor.author","Joshi, J."],["dc.contributor.author","Kiess, C."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Orozco Suárez, 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, 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","2019-07-09T11:43:09Z"],["dc.date.available","2019-07-09T11:43:09Z"],["dc.date.issued","2016"],["dc.description.abstract","Context. Active regions are the most prominent manifestations of solar magnetic fields; their generation and dissipation are fundamental problems in solar physics. Light bridges are commonly present during sunspot decay, but a comprehensive picture of their role in the removal of the photospheric magnetic field is still lacking. Aims. We study the three-dimensional configuration of a sunspot, and in particular, its light bridge, during one of the last stages of its decay. Methods. We present the magnetic and thermodynamical stratification inferred from full Stokes inversions of the photospheric Si i 10 827 Å and Ca i 10 839 Å lines obtained with the GREGOR Infrared Spectrograph of the GREGOR telescope at the Observatorio del Teide, Tenerife, Spain. The analysis is complemented by a study of continuum images covering the disk passage of the active region, which are provided by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. Results. The sunspot shows a light bridge with penumbral continuum intensity that separates the central umbra from a smaller umbra. We find that in this region the magnetic field lines form a canopy with lower magnetic field strength in the inner part. The photospheric light bridge is dominated by gas pressure (high-β), as opposed to the surrounding umbra, where the magnetic pressure is higher. A convective flow is observed in the light bridge. This flow is able to bend the magnetic field lines and to produce field reversals. The field lines merge above the light bridge and become as vertical and strong as in the surrounding umbra. We conclude that this occurs because two highly magnetized regions approach each other during the sunspot evolution."],["dc.identifier.doi","10.1051/0004-6361/201629586"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14290"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/58837"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312495/EU/High-Resolution Solar Physics Network/SOLARNET"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Three-dimensional structure of a sunspot light bridge"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A1"],["dc.bibliographiccitation.journal","Astronomy & Astrophysics"],["dc.bibliographiccitation.volume","596"],["dc.contributor.author","Sobotka, M."],["dc.contributor.author","Dudík, J."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Jurčák, J."],["dc.contributor.author","Liu, W."],["dc.contributor.author","Berkefeld, T."],["dc.contributor.author","Collados Vera, M."],["dc.contributor.author","Feller, A."],["dc.contributor.author","Hofmann, A."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Kuckein, C."],["dc.contributor.author","Lagg, A."],["dc.contributor.author","Louis, R. E."],["dc.contributor.author","von der Lühe, O."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Schlichenmaier, R."],["dc.contributor.author","Schmidt, D."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Sigwarth, 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","Waldmann, T."],["dc.date.accessioned","2019-07-09T11:43:07Z"],["dc.date.available","2019-07-09T11:43:07Z"],["dc.date.issued","2016"],["dc.description.abstract","A small flare ribbon above a sunspot umbra in active region 12205 was observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the 1.5 m GREGOR telescope, using a 1 Å Ca ii H interference filter. Context observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode, and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is part of a larger one that extends through the neighboring positive polarities and also participates in several other flares within the active region. We reconstructed a time series of 140 s of Ca ii H images by means of the multiframe blind deconvolution method, which resulted in spatial and temporal resolutions of 0.1″ and 1 s. Light curves and horizontal velocities of small-scale bright knots in the observed flare ribbon were measured. Some knots are stationary, but three move along the ribbon with speeds of 7–11 km s-1. Two of them move in the opposite direction and exhibit highly correlated intensity changes, which provides evidence of a slipping reconnection at small spatial scales."],["dc.identifier.doi","10.1051/0004-6361/201527966"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/14247"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/58832"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/312495/EU/High-Resolution Solar Physics Network/SOLARNET"],["dc.relation","info:eu-repo/grantAgreement/EC/FP7/606862/EU/Flare Chromospheres: Observations, Models and Archives/F-CHROMA"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Slipping reconnection in a solar flare observed in high resolution with the GREGOR solar telescope"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","665"],["dc.bibliographiccitation.issue","S259"],["dc.bibliographiccitation.journal","Proceedings of the International Astronomical Union"],["dc.bibliographiccitation.lastpage","666"],["dc.bibliographiccitation.volume","4"],["dc.contributor.author","Balthasar, Horst"],["dc.contributor.author","Bello González, N."],["dc.contributor.author","Collados, M."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Hofmann, A."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Puschmann, K. G."],["dc.date.accessioned","2013-05-31T07:30:46Z"],["dc.date.accessioned","2021-10-11T11:34:50Z"],["dc.date.available","2013-05-31T07:30:46Z"],["dc.date.available","2021-10-11T11:34:50Z"],["dc.date.issued","2008"],["dc.description.abstract","One of the first post-focus instruments of the new solar telescope GREGOR will be a Fabry-Perot spectrometer, which is an upgrade of the G¨ottingen Fabry-Perot interferometer at the Vacuum Tower Telescope (VTT) on Tenerife. This spectrometer is equipped with a full-Stokes polarimeter. The modulation is performed with two ferroelectric liquid crystals, one acting nominally as quarter-wave plate, and the other as half-wave plate. A modified Savart plate serves as polarimetric beam splitter. With the present liquid crystals, the optimum wavelength range of this polarimeter is between 580 and 660 nm. The spectro-polarimeter will benefit from the capabilities of the new telescope GREGOR which will provide a spatial resolution of about 0 . 1 (75 km on the solar surface). Thus we will be able to investigate small magnetic features, and we will study their development with high cadence."],["dc.identifier.citation","Balthasar, Horst; Bello González, N.; Collados, M.; Denker, C.; Hofmann, A.; Kneer, F.; Puschmann, K. G. (2008): A full-Stokes polarimeter for the GREGOR Fabry-Perot interferometer"],["dc.identifier.doi","10.1017/S1743921309031500"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9071"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/90705"],["dc.language.iso","en"],["dc.notes.intern","Migrated from goescholar"],["dc.relation.issn","1743-9221"],["dc.relation.issn","1743-9213"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights","Goescholar"],["dc.rights.access","openAccess"],["dc.rights.uri","https://goedoc.uni-goettingen.de/licenses"],["dc.subject","Instrumentation: polarimeters; instrumentation: spectrographs; Sun: magnetic fields"],["dc.title","A full-Stokes polarimeter for the GREGOR Fabry-Perot interferometer"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]