J/A+A/432/1063ivo://CDS.VizieR/J/A+A/432/1063doi:10.26093/cds/vizier.34321063CDSLanzafame A.C.Brooks D.H.Lang J.2005-04-08T21:38:07Z2005-04-08T21:37:44ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frthe-sunspectroscopyultraviolet-astronomyatomic-physicsWe present a study of the differential emission measure (DEM) of a `quiet Sun' area observed in the extreme ultraviolet at normal incidence by the Coronal Diagnostic Spectrometer (CDS) on the SOHO spacecraft. The data used for this work were taken using the NISAT_S_ observing sequence. This takes the full wavelength ranges from both the NIS channels (308-381{AA} and 513-633{AA}) with the 2 arcsec by 240 arcsec slit, which is the narrowest slit available, yielding the best spectral resolution. In this work we contrast the DEM from subregions of 2*80arcsec^2^ with that obtained from the mean spectrum of the whole raster (20*240arcsec^2^). We find that the DEM maintains essentially the same shape in the subregions, differing by a constant factor between 0.5 and 2 from the mean DEM, except in areas were the electron density is below 2*10^7^cm^-3^ and downflow velocities of 50km/s are found in the transition region. Such areas are likely to contain plasma departing from ionisation equilibrium, violating the basic assumptions underlying the DEM method. The comparison between lines of Li-like and Be-like ions may provide further evidence of departure from ionisation equilibrium. We find also that line intensities tend to be lower where velocities of the order of 30km/s or higher are measured in transition region lines. The DEM analysis is also exploited to improve the line identification performed by Brooks et al. (1999A&A...347..277B) and to investigate possible elemental abundance variations from region to region. We find that the plasma has composition close to photospheric in all the subregions examined.2005A&A...432.1063Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/432/1063CatalogResearchIsServedByTAP VizieR generic servicerelated-toJ/A+AS/113/237 : Ultraviolet Spectrum of the Sun (Samain, 1995)J/A+AS/131/431 : Accurate wavelengths in Sun spectrum (Allende Prieto+ 1998)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/432/1063https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/432/1063http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/432/1063https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/432/1063https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/432/1063http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/432/1063GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapUVdefaultJ/A+A/432/1063/table5Comparison of the observed intensities with those derived from the DEM for the mean spectrum.Chi2? ChisquaredoublenullableNoteNote (4)charrecnoRecord number assigned by the VizieR team. Should Not be used for identification.intBlendBlend data (1)charn_Blend[S] S when the record contains information about the blendcharELElement symbol (2)charZ1? Ion charge + 1 (2)intnullablelambda? Adopted laboratory wavelength (2)0.1nmfloatnullabler_lambdaReference for lambda (3)charConf1Lower level electronic configuration (2)charTerm1Lower level term (2)charConf2Upper level electronic configuration (2)charTerm2Upper level term (2)charlogT? Temperature (log) of peak of line formation (2)log(K)floatnullablen_lambdaObs[2x ] For Si 11 303.326 onlycharlambdaObs? Observed wavelength0.1nmfloatnullableIntThTheoretical intensitymW.m**-2.sr**-1floatIntObs? Observed intensitymW.m**-2.sr**-1floatnullablee_IntObs? Observational uncertaintymW.m**-2.sr**-1floatnullable