Wittmann, Axel D.

[["dc.bibliographiccitation.firstpage","378"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","380"],["dc.bibliographiccitation.volume","324"],["dc.contributor.author","Wittmann, Axel D."],["dc.date.accessioned","2018-11-07T10:41:59Z"],["dc.date.available","2018-11-07T10:41:59Z"],["dc.date.issued","2003"],["dc.description.abstract","Measurements of the solar diameter using both visual and photoelectric drift scan techniques have been made since 1972 using two almost identical 45-cm Gregory-Coude telescopes at Locarno/Switzerland and Iza (n) over tildea/Tenerife. The method, in which a time measurement substitutes an angular measurement, is especially suited to obtain about 30 measurements of the absolute solar semidiameter per day. During the years 1972-2002 a total of 10996 visual timing measurements have been made on 320 observing days, an additional 1373 photoelectric recordings have been obtained on 117 observing days. The data were used to study the long-term behaviour of the solar semidiameter R at unit distance and its possible variations. No fluctuations dR in excess of about +/-0.05\" have been found, neither long-term nor short-term. The photoelectric semidiameter, which refers to the continuum at lambda approximate to 585 nm, is Rphot = (959.89 +/- 0.12)\". The visual semidiameter, which refers to the footpoint of the limb intensity profile at lambda approximate to 550 nm, is Rvis = (960.62 +/- 0.02)\"."],["dc.identifier.doi","10.1002/asna.200310135"],["dc.identifier.isi","000183506400042"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46677"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.publisher.place","Weinheim"],["dc.relation.conference","Workshop on From the Gregory-Coude Telescope to GREGOR - A Development from Past to Future"],["dc.relation.eventlocation","GOTTINGEN UNIV, III PHYS INST, GOTTINGEN, GERMANY"],["dc.relation.issn","0004-6337"],["dc.title","Visual and photoelectric measurements of the solar diameter (1972-2002): Methods and results"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","361"],["dc.bibliographiccitation.issue","5-6"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","362"],["dc.bibliographiccitation.volume","322"],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","von der Luhe, O."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Wiehr, E."],["dc.contributor.author","Wittmann, Axel D."],["dc.date.accessioned","2018-11-07T09:29:24Z"],["dc.date.available","2018-11-07T09:29:24Z"],["dc.date.issued","2001"],["dc.description.abstract","GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an Adaptive Optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar photosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the Gregory Coude Telescope at the Observatorio del Teide on Tenerife. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and the underlying physical processes. GREGOR will also serve as a test bed for next generation solar telescopes. We discuss briefly the postfocus instrumentation of GREGOR."],["dc.identifier.doi","10.1002/1521-3994(200112)322:5/6<361::AID-ASNA361>3.0.CO;2-2"],["dc.identifier.isi","000173097200015"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31021"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.publisher.place","Weinheim"],["dc.relation.conference","JENAM 2001 Meeting held in Conjuction with the 10th Meeting of the European-Astronomical-Society/75th Annual Assembly of the Astronomische-Gesellschaft"],["dc.relation.eventlocation","LUDWIG MAXIMILIAN UNIV, MUNICH, GERMANY"],["dc.relation.issn","0004-6337"],["dc.title","Post-focus instrumentation for GREGOR"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","880"],["dc.bibliographiccitation.issue","9"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","893"],["dc.bibliographiccitation.volume","333"],["dc.contributor.author","Puschmann, K. G."],["dc.contributor.author","Denker, C."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Al Erdogan, N."],["dc.contributor.author","Balthasar, H."],["dc.contributor.author","Bauer, S. M."],["dc.contributor.author","Beck, C."],["dc.contributor.author","Gonzalez, N. Bello"],["dc.contributor.author","Collados, M."],["dc.contributor.author","Hahn, T."],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","Louis, R. E."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Okunev, O."],["dc.contributor.author","Martinez Pillet, V."],["dc.contributor.author","Popow, E."],["dc.contributor.author","Seelemann, T."],["dc.contributor.author","Volkmer, R."],["dc.contributor.author","Wittmann, A. D."],["dc.contributor.author","Woche, M."],["dc.date.accessioned","2018-11-07T09:04:01Z"],["dc.date.available","2018-11-07T09:04:01Z"],["dc.date.issued","2012"],["dc.description.abstract","The GREGOR Fabry-Perot Interferometer (GFPI) is one of three first-light instruments of the German 1.5-meter GREGOR solar telescope at the Observatorio del Teide, Tenerife, Spain. The GFPI uses two tunable etalons in collimated mounting. Thanks to its large-format, high-cadence CCD detectors with sophisticated computer hard- and software it is capable of scanning spectral lines with a cadence that is sufficient to capture the dynamic evolution of the solar atmosphere. The field-of-view (FOV) of 50 ' x38 ' is well suited for quiet Sun and sunspot observations. However, in the vector spectropolarimetric mode the FOV reduces to 25 ' x38 '. The spectral coverage in the spectroscopic mode extends from 530-860 nm with a theoretical spectral resolution of R approximate to 250 000, whereas in the vector spectropolarimetric mode the wavelength range is at present limited to 580-660 nm. The combination of fast narrow-band imaging and post-factum image restoration has the potential for discovery science concerning the dynamic Sun and its magnetic field at spatial scales down to similar to 50 km on the solar surface. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim"],["dc.identifier.doi","10.1002/asna.201211734"],["dc.identifier.isi","000310799500015"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/25018"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","0004-6337"],["dc.title","The GREGOR Fabry-Perot Interferometer"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.subtype","letter_note"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","689"],["dc.bibliographiccitation.issue","5-6"],["dc.bibliographiccitation.journal","NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA C-GEOPHYSICS AND SPACE PHYSICS"],["dc.bibliographiccitation.lastpage","693"],["dc.bibliographiccitation.volume","25"],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Hofmann, Albrecht W."],["dc.contributor.author","von der Luhe, O."],["dc.contributor.author","Schmidt, W."],["dc.contributor.author","Soltau, D."],["dc.contributor.author","Staude, J."],["dc.contributor.author","Wiehr, E."],["dc.contributor.author","Wittmann, Axel D."],["dc.date.accessioned","2018-11-07T10:08:07Z"],["dc.date.available","2018-11-07T10:08:07Z"],["dc.date.issued","2002"],["dc.description.abstract","GREGOR is a high-resolution solar telescope with an aperture of 1.5 m. It will be equipped with an adaptive optics system and is designed for high-precision measurements of magnetic fields and plasma motions in the solar atmosphere and chromosphere with a resolution of 70 km on the Sun. GREGOR will replace the 30 years old Gregory Coude Telescope at the Observatorio del Teide on Tenerife. We describe the optical design and the focal plane instrumentation. In concert with the other solar telescopes at Teide Observatory it will be useful for studying the dynamics of the solar atmosphere and of the underlying processes. GREGOR will also serve as a test bed for next-generation solar telescopes."],["dc.identifier.isi","000181412800025"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39409"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Editrice Compositori Bologna"],["dc.publisher.place","Siena"],["dc.relation.conference","International Meeting on THEMIS and the New Frontiers of Solar Atmosphere Dynamics"],["dc.relation.eventlocation","ROME, ITALY"],["dc.relation.issn","1124-1896"],["dc.title","GREGOR, a 1.5 m Gregory-type telescope for solar observation"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","283"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","284"],["dc.bibliographiccitation.volume","324"],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Wiehr, E."],["dc.contributor.author","Wittmann, Axel D."],["dc.date.accessioned","2018-11-07T10:41:56Z"],["dc.date.available","2018-11-07T10:41:56Z"],["dc.date.issued","2003"],["dc.identifier.doi","10.1002/asna.200310094"],["dc.identifier.isi","000183506400001"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46660"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Wiley-v C H Verlag Gmbh"],["dc.relation.issn","0004-6337"],["dc.title","From the Gregory-Coude Telescope to GREGOR: a development from past to future"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.subtype","letter_note"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","940"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","The Astrophysical Journal"],["dc.bibliographiccitation.lastpage","959"],["dc.bibliographiccitation.volume","538"],["dc.contributor.author","Cuberes, M. S."],["dc.contributor.author","Bonet, J. A."],["dc.contributor.author","Vazquez, M."],["dc.contributor.author","Wittmann, Axel D."],["dc.date.accessioned","2018-11-07T10:34:53Z"],["dc.date.available","2018-11-07T10:34:53Z"],["dc.date.issued","2000"],["dc.description.abstract","We have measured the center-to-limb variation (CLV) of parameters describing geometric and photometric statistical properties of the solar granulation at 6708 A. This work is based on an excellent series of white-light images obtained with the Swedish Vacuum Solar Telescope at Rogue de los Muchachos Observatory, La Palma, during the partial solar eclipse of 1994 May 10. The lunar limb profile, which is visible in each frame, was used as a calibration tool for estimating the point-spread function of the combined optical system formed by the atmosphere and the telescope. Before restoration, noise was removed from the images by a novel application of the so-called optimum filter for two-dimensional objects. The latter was optimized in terms of rms error and was constructed from very precise smoothed models of the specific power spectrum of the granulation at each position on the solar disk. The determination of the positions on the solar disk was achieved with high accuracy by matching the position of the Moon's limb in our images to a numerical simulation of the eclipse geometry. The CLV curve of the Delta I(rms) granular contrast shows one of the steepest gradients among those reported in the literature and quite a high value (9.6%) at the disk center considering that our working wavelength is in the far-red range of the solar spectrum. The elliptical shape of the restored power spectra with ellipticities equal to those expected just from foreshortening proves that radiative transfer effects do not alter the isotropy of the horizontal intensity pattern of the solar granulation, at least up to mu = 0.4. The mean wavenumber, (k) over bar, derived from the two-dimensional power spectra azimuthally integrated along the ellipses amounts to a value of 6.15 Mm(-1) at the center of the solar disk and then shows a decrease toward the limb. Apart from the power spectra analysis, a direct statistical study of the granulation size and brightness, based on the image segmentation for defining granular contours, has also been performed. A general increase in both granular and intergranular areas is found as we move toward the solar limb. The mean granular cell area varies from 1.36 Mm(2) at mu = 1 up to 2.06 Mm(2) at mu = 0.6, and in parallel, the granular filling factor (the percentage of area of the image covered by granules) decreases from 44.2% to 42.8%. In the small area range, the granular brightness increases linearly with the granular cell size and is preserved constant, on average, for granular cells larger than similar to 2.\" 0. No slope variation is found for the intergranular intensities versus granular cell areas. Observations close to the solar limb detect granular structures as small as 0.\" 53 or even smaller up to a distance of at least approximate to 0.\" 5 from the limb, showing that the AT associated with the granulation persist at least until z approximate to 200 km. However, this penetration could be different for small and large granules because we find several hints indicating the progressive disappearance of small structures toward the limb."],["dc.identifier.isi","000088824800049"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/44971"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Iop Publishing Ltd"],["dc.relation.issn","0004-637X"],["dc.title","Center-to-limb variation of solar granulation from partial eclipse observations"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","e269"],["dc.bibliographiccitation.journal","Brain: A Journal of Neurology"],["dc.bibliographiccitation.volume","137"],["dc.contributor.author","Schweizer, Renate"],["dc.contributor.author","Wittmann, Axel D."],["dc.contributor.author","Frahm, Jens"],["dc.date.accessioned","2018-11-07T09:42:00Z"],["dc.date.available","2018-11-07T09:42:00Z"],["dc.date.issued","2014"],["dc.identifier.doi","10.1093/brain/awt296"],["dc.identifier.isi","000333260900005"],["dc.identifier.pmid","24163274"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/33859"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.relation.issn","1460-2156"],["dc.relation.issn","0006-8950"],["dc.title","A rare anatomical variation newly identifies the brains of CF Gauss and CH Fuchs in a collection at the University of Gottingen"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","199"],["dc.bibliographiccitation.issue","2"],["dc.bibliographiccitation.journal","History of Geo- and Space Sciences"],["dc.bibliographiccitation.lastpage","205"],["dc.bibliographiccitation.volume","11"],["dc.contributor.author","Wittmann, Axel D."],["dc.date.accessioned","2021-04-14T08:32:26Z"],["dc.date.available","2021-04-14T08:32:26Z"],["dc.date.issued","2020"],["dc.identifier.doi","10.5194/hgss-11-199-2020"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/83918"],["dc.language.iso","en"],["dc.notes.intern","DOI Import GROB-399"],["dc.relation.eissn","2190-5029"],["dc.title","Carl Friedrich Gauss and the Gauss Society: a brief overview"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["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"]]