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","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","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"]]