J/MNRAS/455/2627ivo://CDS.VizieR/J/MNRAS/455/2627doi:10.26093/cds/vizier.74552627CDSArellano-Cordova K.Z.Rodriguez M.Mayya Y.D.Rosa-Gonzalez D.2024-08-15T20:16:49Z2016-07-11T07:21:30ZCDS support team

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

cds-question@unistra.frgalaxiesh-ii-regionschemical-abundancesWe study the sensitivity of the methods available for abundance determinations in HII regions to potential observational problems. We compare the dispersions they introduce around the oxygen and nitrogen abundance gradients when applied to five different sets of spectra of HII regions in the galaxy M81. Our sample contains 116 HII regions with galactocentric distances of 3 to 33kpc, including 48 regions observed by us with the OSIRIS long-slit spectrograph at the 10.4-m Gran Telescopio Canarias telescope. The direct method can be applied to 31 regions, where we can get estimates of the electron temperature. The different methods imply oxygen abundance gradients with slopes of -0.010 to -0.002dex/kpc, and dispersions in the range 0.06-0.25dex. The direct method produces the shallowest slope and the largest dispersion, illustrating the difficulty of obtaining good estimates of the electron temperature. Three of the strong-line methods, C, ONS, and N2, are remarkably robust, with dispersions of ~0.06dex, and slopes in the range -0.008 to -0.006dex/kpc. The robustness of each method can be directly related to its sensitivity to the line intensity ratios that are more difficult to measure properly. Since the results of the N2 method depend strongly on the N/O abundance ratio and on the ionization parameter, we recommend the use of the C and ONS methods when no temperature estimates are available or when they have poor quality, although the behaviour of these methods when confronted with regions that have different properties and different values of N/O should be explored.2016MNRAS.455.2627Ahttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/455/2627CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/455/2627https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/455/2627http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/455/2627https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/455/2627https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/455/2627http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/455/2627GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/455/2627/table4 (*Coordinates, sizes, galactocentric distances, physical conditions and oxygen abundances for the 48 HII regions in our sample)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/455/2627/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/455/2627/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/455/2627/table4?GETtext/xml+votable180.050000true148.6791769.060830.0055555555555555566/7606https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/455/2627?format=asciidefaultJ/MNRAS/455/2627/table4*Coordinates, sizes, galactocentric distances, physical conditions and oxygen abundances for the 48 HII regions in our sampleRegionRegion sequential numbermeta.idintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintBoxBoxmeta.id.parentcharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainSizeAngular sizes of the extracted regionarcsecphys.angSize;obs.fieldfloatRGalactocentric distancekpcpos.distance;pos.galactocentricfloatne? Electron densitycm**-3phys.density;phys.electronintnullablee_ne? rms uncertainty on necm**-3stat.errorintnullableu_neUncertainty flag on nemeta.code.errorcharTe([NII])? Effective temperature from [NII]Kphys.temperature.effectiveintnullableE_Te([NII])? Error on Te([NII]) (upper value)Kstat.error;stat.maxintnullablee_Te([NII])? Error on Te([NII]) (lower value)Kstat.errorintnullable12+log(O/H)? Oxygen abundance derived with the direct method (Te)phys.abundfloatnullableE_12+log(O/H)? Error on 12+log(O/H) (upper value)stat.error;stat.maxfloatnullablee_12+log(O/H)? Error on 12+log(O/H) (lower value)stat.errorfloatnullable12+log(O/H)POxygen abundance derived with P methodphys.abundfloat12+log(O/H)ONSOxygen abundance derived with ONS methodphys.abundfloat12+log(O/H)COxygen abundance derived with C methodphys.abundfloat12+log(O/H)O3N2Oxygen abundance derived with O3N2 methodphys.abundfloat12+log(O/H)N2Oxygen abundance derived with N2 methodphys.abundfloatJ/MNRAS/455/2627/table2The extinction coefficients c(Hbeta) and the reddening-corrected intensities for HbetarecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRegionRegion sequential numbermeta.idintc(Hbeta)Hbeta extinction coefficientphys.absorption.coeff;spect.linefloate_c(Hbeta)Error in the Hbeta extinction coefficientstat.errorfloatI0(Hbeta)Hbeta extinction-corrected intensitymW.m**-2spect.line.intensity;em.line.HbetadoubleJ/MNRAS/455/2627/table3Observed and reddening-corrected line ratios normalized to I(Hbeta)=100recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRegionRegion sequential numbermeta.idintLambdaWavelength0.1nmem.wlintIonIonphys.atmol.ionStagecharI? Observed Intensity relative to I(Hbeta)=100spect.line.intensityfloatnullableI0? Extinction-corrected intensity relative to I(Hbeta)=100phot.mag;em.opt.Ifloatnullablee_I0? Percentage error in the extinction-corrected intensity%stat.errorintnullable