J/A+A/619/A50ivo://CDS.VizieR/J/A+A/619/A50doi:10.26093/cds/vizier.36190050CDSGrosboel P.Carraro G.2018-12-03T15:10:01Z2018-11-07T08:17:40ZCDS support team

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

cds-question@unistra.frradial-velocityextinctionspectroscopygalaxy-planesmilky-way-galaxyThe location of young sources in the Galaxy suggests a four-armed spiral structure, whereas tangential points of spiral arms observed in the integrated light at infrared and radio wavelengths indicate that only two arms are massive. Variable extinction in the Galactic plane and high light-to-mass ratios of young sources make it difficult to judge the total mass associated with the arms outlined by such tracers. The current objective is to estimate the mass associated with the Sagittarius arm by means of the kinematics of the stars across it. Spectra of 1726 candidate B- and A-type stars within 3{deg} of the Galactic center (GC) were obtained with the FLAMES instrument at the VLT with a resolution of ~6000 in the spectral range of 396-457nm. Radial velocities were derived by least-squares fits of the spectra to synthetic ones. The final sample was limited to 1507 stars with either Gaia DR2 parallaxes or main-sequence B-type stars having reliable spectroscopic distances. The solar peculiar motion in the direction of the GC relative to the local standard of rest (LSR) was estimated to U_{sun}_=10.7+/-1.3km/s. The variation in the median radial velocity relative to the LSR as a function of distance from the sun shows a gradual increase from slightly negative values near the sun to almost 5km/s at a distance of around 4kpc. A sinusoidal function with an amplitude of 3.4+/-1.3km/s and a maximum at 4.0+/-0.6kpc inside the sun is the best fit to the data. A positive median radial velocity relative to the LSR around 1.8kpc, the expected distance to the Sagittarius arm, can be excluded at a 99% level of confidence. A marginal peak detected at this distance may be associated with stellar streams in the star-forming regions, but it is too narrow to be associated with a major arm feature. A comparison with test-particle simulations in a fixed galactic potential with an imposed spiral pattern shows the best agreement with a two-armed spiral potential having the Scutum-Crux arm as the next major inner arm. A relative radial forcing dFr~1.5% and a pattern speed in the range of 20-30km/s/kpc yield the best fit. The lack of a positive velocity perturbation in the region around the Sagittarius arm excludes it from being a major arm. Thus, the main spiral potential of the Galaxy is two-armed, while the Sagittarius arm is an inter-arm feature with only a small mass perturbation associated with it.2018A&A...619A..50Ghttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/619/A50CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/345 : Gaia DR2 (Gaia Collaboration, 2018)II/348 : VISTA Variable in the Via Lactea Survey DR2 (Minniti+, 2017)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/619/A50https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/619/A50http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/619/A50https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/619/A50https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/619/A50http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/619/A50GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/619/A50/catalog (Catalog of radial velocities)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/619/A50/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/619/A50/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/619/A50/catalog?GETtext/xml+votable180.050000true266.65825-29.112361110.0055555555555555566/28814-28815 28819-28820 28822-28823 28825 28828-28830 28837 288487.952274030004205e-20 3.916500758235022e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/619/A50?format=asciidefaultJ/A+A/619/A50/catalogCatalog of radial velocitiesspPlot of spectrummeta.ref.urlcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIdentObjective identifiermeta.id;meta.maincharFieldField identifiermeta.id;obs.fieldcharFiberFiber in fieldmeta.noteintRAJ2000Right ascension (J2000)degpos.eq.ra;meta.mainDEJ2000Declination (J2000)degpos.eq.dec;meta.mainObs.DateMJD of mean observationdtime.epoch;obs;stat.meandoubleSNRSignal-to-noise ratiostat.snrdoubleGaia? Gaia DR2 identifiermeta.idnullableGmag? Gaia G magnitudemagphot.mag;em.optdoublenullableVVV? VVV identifiermeta.idnullableKmag? VVV Ks MAG1APmagphot.mag;em.IR.KfloatnullableBRVBarycentric radial velocitykm/sphys.veloc;pos.barycenterdoublee_BRVRadial velocity errorkm/sstat.errordoublelogTefflog10 of effective temperaturelog(K)phys.temperature.effectivedoublee_logTefflog10 of effective temperature errorlog(K)stat.error;phys.temperature.effectivedoublelogg? log10 of surface gravitylog(cm.s**-2)phys.gravitydoublenullableAk? Extinction in Ksmagphys.absorptiondoublenullableDist? Distance from sunkpcpos.distance;pos.heliocentricdoublenullableDist-sp? Spectroscopic distance from sunkpcpos.distance;pos.heliocentricdoublenullableStart[396] Wavelength start of spectrumnmem.wlintStep[0.02] Step size of spectrumnmspect.resolutionfloat