J/MNRAS/475/1680ivo://CDS.VizieR/J/MNRAS/475/1680doi:10.26093/cds/vizier.74751680CDSHarris A.Drew J.E.Farnhill H.J.Monguio M.Gebran M.Wright N.J.,Drake J.J.Sale S.E.2024-08-18T20:17:53Z2018-11-23T14:25:40ZCDS support team

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

cds-question@unistra.frgalaxy-planesmilky-way-galaxyradial-velocityspectrophotometryearly-type-starsPrevious studies of the rotation law in the outer Galactic disc have mainly used gas tracers or clump giants. Here, we explore A and F stars as alternatives: these provide a much denser sampling in the outer disc than gas tracers and have experienced significantly less velocity scattering than older clump giants. This first investigation confirms the suitability of A stars in this role. Our work is based on spectroscopy of roughly 1300 photometrically selected stars in the red calcium-triplet region, chosen to mitigate against the effects of interstellar extinction. The stars are located in two low Galactic latitude sightlines, at longitudes l=118{deg}, sampling strong Galactic rotation shear, and l=178{deg}, near the anticentre. With the use of Markov Chain Monte Carlo parameter fitting, stellar parameters and radial velocities are measured, and distances computed. The obtained trend of radial velocity with distance is inconsistent with existing flat or slowly rising rotation laws from gas tracers (Brand & Blitz, 1993A&A...275...67B, Cat J/A+A/275/67; Reid et al., 2014ApJ...783..130R, Cat. J/ApJ/783/130). Instead, our results fit in with those obtained by Huang et al. (2016MNRAS.463.2623H) from disc clump giants that favoured rising circular speeds. An alternative interpretation in terms of spiral arm perturbation is not straight forward. We assess the role that undetected binaries in the sample and distance error may have in introducing bias, and show that the former is a minor factor. The random errors in our trend of circular velocity are within +/-5km/s.2018MNRAS.475.1680Hhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/MNRAS/475/1680CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/MNRAS/475/1680https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/MNRAS/475/1680http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/MNRAS/475/1680https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/MNRAS/475/1680https://vizier.iucaa.in/viz-bin/votable?-source=J/MNRAS/475/1680http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/MNRAS/475/1680GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/MNRAS/475/1680/catalog (Stellar parameters and distances)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/MNRAS/475/1680/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/MNRAS/475/1680/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/MNRAS/475/1680/catalog?GETtext/xml+votable180.050000true1.6187564.59896861110.0055555555555555566/3067 3070 24475 24478 24497 24500https://cdsarc.cds.unistra.fr/viz-bin/moc/J/MNRAS/475/1680?format=asciidefaultJ/MNRAS/475/1680/catalogStellar parameters and distancesSimbadNameSimbad column added by the CDSmeta.idcharnullableE_vsinivsini positive errorkm/sstat.error;stat.maxintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIDTarget ID (NNN.NN.NNN)meta.id;meta.maincharRAJ2000Right ascension (J2000.0)degpos.eq.ra;meta.mainDEJ2000Declination (J2000.0)degpos.eq.dec;meta.mainGLONGalactic longitudedegpos.galactic.lonGLATGalactic latitudedegpos.galactic.latdoubleRVlsrRadial velocity corrected to LSR frame (1)km/sphys.veloc;pos.lsrfloatrmagIPHAS apparent r magnitudemagphot.mag;em.opt.Rdoublee_rmagIPHAS apparent r magnitude errormagstat.error;phot.magdoubleimagIPHAS apparent i magnitudemagphot.mag;em.opt.Idoublee_imagIPHAS apparent i magnitude errormagstat.error;phot.magdoubleiMAGAbsolute i magnitudemagphys.magAbsfloate_iMAGAbsolute i magnitude errormagstat.errorfloatr-iintr-i intrinsic colour indexmagphot.color;em.opt.R;em.opt.Ifloate_r-iintr-i intrinsic colour index errormagstat.errorfloatAii band extinctionmag/kpcphys.absorptionfloate_Aii band extinction errormag/kpcstat.errorfloatDistHeliocentric distancekpcpos.distancefloate_DistHeliocentric distance errorkpcstat.errorfloatDMDistance modulusmagphot.mag.distModfloate_DMDistance modulus errormagstat.errorfloatTeffEffective temperature, TeffKphys.temperature.effectiveinte_TeffTeff negative errorKstat.error;phys.temperature.effectiveintE_TeffTeff positive errorKstat.error;stat.maxintloggSurface gravity, logglog(cm.s**-2)phys.gravityfloate_logglogg negative errorlog(cm.s**-2)stat.errorfloatE_logglogg positive errorlog(cm.s**-2)stat.error;stat.maxfloatvsiniRotational velocity, vsinikm/sphys.veloc.rotatinte_vsinivsini negative errorkm/sstat.error;phys.veloc.rotatintRVMeasured radial velocitykm/sphys.veloc;pos.heliocentricfloate_RVMeasured radial velocity negative errorkm/sstat.errorfloatE_RVMeasured radial velocity positive errorkm/sstat.error;stat.maxfloat