Kneer, Franz

[["dc.bibliographiccitation.firstpage","1078"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","1086"],["dc.bibliographiccitation.volume","378"],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Kneer, F."],["dc.date.accessioned","2018-11-07T11:25:56Z"],["dc.date.available","2018-11-07T11:25:56Z"],["dc.date.issued","2001"],["dc.description.abstract","The radial variation of the Evershed ow in two small sunspots (NOAA 8737 and NOAA 9145) is studied by means of two-dimensional spectrograms of high spatial resolution. We find a systematic decrease of the flow velocity with photospheric height and a shift of the velocity maximum towards larger penumbral radii in higher layers but no clear correlation between ow velocity and continuum intensity. At the outer penumbral boundaries the Evershed flow ceases abruptly and even downward directed flow velocities in the deepest probed photospheric layers were found. Furthermore, granules adjacent to the penumbral boundary show a systematic redshift of their spot-side parts which is attributed to fast, eventually supersonic, downflows between them and the penumbral boundary."],["dc.identifier.doi","10.1051/0004-6361:20011156"],["dc.identifier.isi","000171897200034"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9719"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/56742"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","2D-spectroscopy of the Evershed flow in sunspots"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["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","1131"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","1139"],["dc.bibliographiccitation.volume","418"],["dc.contributor.author","Al, N."],["dc.contributor.author","Bendlin, C."],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Bueno, J. T."],["dc.date.accessioned","2018-11-07T10:49:08Z"],["dc.date.available","2018-11-07T10:49:08Z"],["dc.date.issued","2004"],["dc.description.abstract","This investigation is based on Halpha observations of high spatial resolution. They stem from an enhanced network region near disk centre of the sun and consist of broad-band and narrow-band images taken with the two-dimensional \"Gottingen\" Fabry-Perot spectrometer mounted in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. The \"lambdameter method\" was applied to derive intensity and velocity maps over the two-dimensional field of view reflecting the behaviour of these parameters in the solar chromosphere. The determination of the source function, the line-of-sight (LOS) velocity, the Doppler width and the optical depth was based on Beckers' cloud model (Beckers 1964). From the LOS velocity distribution along the Halpha structures we conclude that ballistic motions are unlikely to prevail. Especially the bright Ha features cannot be explained by the cloud model. It is shown how, instead, two-dimensional non-LTE radiative transfer calculations of embedded chromospheric structures lead to reasonable agreement with the observed line profiles from these bright features. It is found that many of the bright fibril-like structures near dark fibrils can be explained by radiation which is blocked by absorbing material at large heights and escapes through less opaque regions. We estimate the number densities and the temperature. With these and with the measured velocities, the kinetic energy flux and the enthalpy flux related to the motions of the fine structures can be calculated. Both fall short by at least an order of magnitude of covering energy losses by radiation of active chromospheric regions."],["dc.identifier.doi","10.1051/0004-6361:20034501"],["dc.identifier.fs","21419"],["dc.identifier.isi","000221646300031"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9823"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/48357"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Dynamics of an enhanced network region observed in H alpha"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","1011"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","1021"],["dc.bibliographiccitation.volume","367"],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Koschinsky, M."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Ritter, C."],["dc.date.accessioned","2019-07-09T11:54:48Z"],["dc.date.available","2019-07-09T11:54:48Z"],["dc.date.issued","2001"],["dc.description.abstract","Spectroscopic data with high spatial resolution are used to study the granular dynamics of the Sun. The observations were obtained with the \"Göttingen\"two-dimensional (2D) Fabry-Perot interferometer in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. Time sequences of spectral scans across the non-magnetic FeI 5576 Åline were taken from disc center. The 2D spectroscopic images were reconstructed with speckle methods, from which a spatial resolution of 0 fraction of arcsecond4-0 fraction of arcsecond5 was achieved. A power and coherence analysis of intensity and velocity maps from different photospheric heights has been carried out. The coherence between intensity and velocity fluctuations stays high for structural scales >0 fraction of arcsecond5, which underlines the high spatial resolution of the data. Furthermore, the vertical flow field and its time evolution within exploding granules have been analyzed. We find fast downflows in the dark centers of exploding granules with velocities up to 1.2 km s-1. Additionally, we estimated the flow velocities of so-called \"dark dots\". We discuss indications that these structures represent a new type of downflow within the centers of bright granules."],["dc.identifier.doi","10.1051/0004-6361:20000448"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9702"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60729"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1432-0756"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","High resolution 2D-spectroscopy of granular dynamics"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","364"],["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","365"],["dc.bibliographiccitation.volume","324"],["dc.contributor.author","Al, N."],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Kneer, F."],["dc.date.accessioned","2018-11-07T10:41:59Z"],["dc.date.available","2018-11-07T10:41:59Z"],["dc.date.issued","2003"],["dc.description.abstract","In May 2002, the solar chromosphere was observed with a two-dimensional spectrometer which is mounted in the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide/Tenerife. The aim of this observation was to investigate the fine structure of the solar chromosphere seen in Halpha..We took narrow-band filtergrams (Deltalambda approximate to 72 mAngstrom) by scanning through this line. broad-band images taken strictly simultaneously with the narrow-band filtergrams were restored by speckle methods. The instantaneous optical transfer function from this restoration procedure was used for the reconstruction of the narrow-band images. Some results of this high spatial resolution observation are presented below."],["dc.identifier.doi","10.1002/asna.200310129"],["dc.identifier.isi","000183506400036"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46676"],["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","Two-dimensional speckle spectroscopy of H alpha features"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","375"],["dc.bibliographiccitation.issue","5-6"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.lastpage","378"],["dc.bibliographiccitation.volume","322"],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Hirzberger, J."],["dc.date.accessioned","2018-11-07T09:29:27Z"],["dc.date.available","2018-11-07T09:29:27Z"],["dc.date.issued","2001"],["dc.description.abstract","Fabry-Perot interferometers (FPIs) are powerful instruments for spectro-polarimetry of the Sun with high spatial resolution. They allow easy image reconstruction of two-dimensional fields of view. Some examples of high quality results obtained with the \"Gottingen\" FPI spectrometer, mounted in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife, are presented in a poster to this workshop. We thus concentrate on the design of a new instrument for the 1.5 m GREGOR solar telescope. We discuss the pros and cons of telecentric and collimated mounting and describe the expected performance, especially the spectral resolution, of our design."],["dc.identifier.isi","000173097200019"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31032"],["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","A Fabry-Perot spectrometer for high-resolution observation of the Sun"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","588"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","597"],["dc.bibliographiccitation.volume","365"],["dc.contributor.author","Koschinsky, M."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Hirzberger, J."],["dc.date.accessioned","2019-07-09T11:54:48Z"],["dc.date.available","2019-07-09T11:54:48Z"],["dc.date.issued","2001"],["dc.description.abstract","We present speckle observations of small-scale magnetic structures on the Sun. They were obtained with the \"Göttingen\"Fabry-Perot interferometer (FPI) in the Vacuum Tower Telescope at the Observatorio del Teide, Tenerife, from quiet and active regions close to disc center. A Stokes V polarimeter was added to the FPI to measure V profiles in the Fe I 6302.5 Åline. The setup allows image reconstruction with speckle methods. The achieved spatial resolution in the magnetograms is $0\\hbox{$.\\!\\!^{\\prime\\prime}$ }4$- $0\\hbox{$.\\!\\!^{\\prime\\prime}$ }5$. We describe the observational technique and the data reduction. The results from small-scale magnetic flux elements in a very quiet region, in an active region with pores and abnormal granulation, and in a sunspot with its surroundings are discussed. In the quiet Sun, granular dynamics dominate the time evolution of the magnetic elements. Flux occurs in both bright intergranular points and in dark intergranular spaces. Likewise, with the present spatial resolution, no preference of magnetic flux in abnormal granulation in an active region can be found. Flux occurs in both bright (abnormal) small-scale granules and in the darker spaces in between them. The small sunspot studied has very little magnetic flux in its ambient quiet regions, especially no strong, conspicuous concentrations of returned flux, i.e. of flux with polarity opposite to that in the sunspot."],["dc.identifier.doi","10.1051/0004-6361:20000478"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9700"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/60727"],["dc.language.iso","en"],["dc.notes.intern","Merged from goescholar"],["dc.relation.issn","1432-0756"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Speckle spectro-polarimetry of solar magnetic structures"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","551"],["dc.bibliographiccitation.issue","5-6"],["dc.bibliographiccitation.journal","NUOVO CIMENTO DELLA SOCIETA ITALIANA DI FISICA C-GEOPHYSICS AND SPACE PHYSICS"],["dc.bibliographiccitation.lastpage","555"],["dc.bibliographiccitation.volume","25"],["dc.contributor.author","Wunnenberg, M."],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Kneer, F."],["dc.date.accessioned","2018-11-07T10:08:02Z"],["dc.date.available","2018-11-07T10:08:02Z"],["dc.date.issued","2002"],["dc.description.abstract","The data for this contribution were taken in August 2000 with the \"Gottingen\" two-dimensional spectrometer in the VTT on Tenerife. Our spectrometer is based on two scanning Fabry-Perot Interferometers (FPIs). The non-magnetic Fe I 5434 Angstrom line was observed in the quiet Sun at disk center. Time sequences of 41 min duration and with 25 s cadence were taken. Strictly simultaneously with the narrow-band FPI images (32 mAngstrom FWHM), broad-band images were recorded. The latter were reconstructed with speckle methods. With the known \"true\" broad-band object we are able to restore the narrow-band images as well. Our aim is to find propagating acoustic waves at short periods and small scales. The results obtained so far are presented and the prospects are discussed."],["dc.identifier.isi","000181412800006"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/39399"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Editrice Compositori Bologna"],["dc.publisher.place","Siena"],["dc.relation.eventlocation","ROME, ITALY"],["dc.relation.issn","1124-1896"],["dc.title","Search for short-period acoustic waves with high-resolution 2D spectra"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.issue","4"],["dc.bibliographiccitation.journal","Astronomische Nachrichten"],["dc.bibliographiccitation.volume","324"],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Al, N."],["dc.contributor.author","Hirzberger, J."],["dc.contributor.author","Nicklas, H."],["dc.contributor.author","Puschmann, K. G."],["dc.date.accessioned","2018-11-07T10:41:57Z"],["dc.date.available","2018-11-07T10:41:57Z"],["dc.date.issued","2003"],["dc.format.extent","302"],["dc.identifier.doi","10.1002/asna.200310102"],["dc.identifier.isi","000183506400009"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/46663"],["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","A Fabry-Perot spectrometer for high-resolution observation of the Sun"],["dc.type","conference_paper"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","L51"],["dc.bibliographiccitation.issue","3"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.lastpage","L54"],["dc.bibliographiccitation.volume","395"],["dc.contributor.author","Wunnenberg, M."],["dc.contributor.author","Kneer, F."],["dc.contributor.author","Hirzberger, J."],["dc.date.accessioned","2018-11-07T09:43:26Z"],["dc.date.available","2018-11-07T09:43:26Z"],["dc.date.issued","2002"],["dc.description.abstract","Short-period acoustic waves are thought to supply the energy for the radiative losses of the non-magnetic chromosphere of the Sun and, in general, of late-type stars. Here, we present evidence for the existence of waves in the solar atmosphere with periods in the range of 50s < P < 100 s. Two-dimensional time sequences with a cadence of 25 s were obtained from quiet Sun disk center in Fe I 5434 Angstrom. The observations were performed with the \"Gottingen\" Fabry-Perot spectrometer in the Vacuum Tower Telescope at the Observatorio del Teide/Tenerife. They are subjected to speckle reconstruction and to a wavelet analysis. The atmospheric ranges forming the velocity signals are narrowed by linear combinations of Doppler maps from wavelengths near line center. The power in the short-period range is concentrated above intergranular spaces. We estimate an acoustic flux into the chromosphere of approximately 3 x 10(6) erg cm(-2) s(-1), as needed for the chromospheric radiative losses."],["dc.identifier.doi","10.1051/0004-6361:20021531"],["dc.identifier.isi","000179291200002"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/34184"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","E D P Sciences"],["dc.relation.issn","0004-6361"],["dc.title","Evidence for short-period acoustic waves in the solar atmosphere"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dspace.entity.type","Publication"]]