J/ApJ/741/100ivo://CDS.VizieR/J/ApJ/741/100doi:10.26093/cds/vizier.17410100CDSLepine S.Koch A.Rich R.M.Kuijken K.2013-05-08T07:30:44Z2013-04-19T10:09:27ZCDS support team

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

cds-question@unistra.frgalaxiesproper-motionshst-photometryWe use 14 year baseline images obtained with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope (HST) to derive a proper motion for one of the Milky Way's most distant dwarf spheroidal companions, Leo II, relative to an extragalactic background reference frame. Astrometric measurements are performed in the effective point-spread function formalism using our own developed code. An astrometric reference grid is defined using 3224 stars that are members of Leo II and brighter than a magnitude of 25 in the F814W band. We identify 17 compact extragalactic sources, for which we measure a systemic proper motion relative to this stellar reference grid. We derive a proper motion [{mu}_{alpha}_,{mu}_{delta}_]=[+104+/-113,-33+/-151]uas/yr for Leo II in the heliocentric reference frame. Though marginally detected, the proper motion yields constraints on the orbit of Leo II. Given a distance of d~230kpc and a heliocentric radial velocity v_r_=+79km/s, and after subtraction of the solar motion, our measurement indicates a total orbital motion v_G_=266.1+/-128.7km/s in the Galactocentric reference frame, with a radial component v_rG_=21.5+/-4.3km/s and tangential component v_tG_=265.2+/-129.4km/s. The small radial component indicates that Leo II either has a low-eccentricity orbit or is currently close to perigalacticon or apogalacticon distance. We see evidence for systematic errors in the astrometry of the extragalactic sources which, while close to being point sources, are slightly resolved in the HST images. We provide a detailed catalog of the stellar and extragalactic sources identified in the HST data which should provide a solid early-epoch reference for future astrometric measurements.2011ApJ...741..100Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/741/100CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toB/hst : HST Archived Exposures Catalog (STScI, 2007)J/ApJ/726/108 : Dispersion-supported stellar systems (Tollerud+, 2011)J/ApJS/191/352 : Abundances in stars of Milky Way satellites (Kirby+, 2010)J/AJ/134/566 : Leo II stellar kinematics (Koch+, 2007)J/AJ/133/270 : Metallicities and ages in Leo II dSph (Koch+, 2007)J/MNRAS/378/318 : Chemical abundances in Leo I and II dSph (Bosler+, 2007)J/MNRAS/360/185 : VI photometry of the Leo II galaxy (Bellazzini+, 2005)J/AJ/120/284 : Variables in Leo II dwarf spheroidal (Siegel+, 2000)J/MNRAS/261/657 : Deep CCD photometry of Leo II (Demers+ 1993)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/ApJ/741/100https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/ApJ/741/100http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/ApJ/741/100https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/ApJ/741/100https://vizier.iucaa.in/viz-bin/votable?-source=J/ApJ/741/100http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/ApJ/741/100GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/ApJ/741/100/table1 (Stellar members of Leo II defining the astrometric grid)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/741/100/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/741/100/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/741/100/table1?GETtext/xml+votable180.050000true168.355196222.14857580.005555555555555556Cone search capability for table J/ApJ/741/100/table2 (Extragalactic Reference sources in the Leo II field)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/ApJ/741/100/table2?https://vizier.iucaa.in/viz-bin/conesearch/J/ApJ/741/100/table2?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/ApJ/741/100/table2?GETtext/xml+votable180.050000true168.357727322.17516750.0055555555555555566/283612.0401237512456292e-19 4.2441532724171825e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/ApJ/741/100?format=asciiOpticaldefaultJ/ApJ/741/100/table1Stellar members of Leo II defining the astrometric gridrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000[168.355/168.395] Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.maine_RAJ2000Uncertainty in RAdegmasstat.error;pos.eq.rafloatDEJ2000[22.144/22.185] Declination in decimal degrees (J2000)degpos.eq.dec;meta.maine_DEJ2000Uncertainty in DEdegmasstat.error;pos.eq.decfloatpmRA[-4.1/3.6] Relative proper motion along RA (1)mas/yrpos.pm;pos.eq.rafloate_pmRA[0.02/3.6] Uncertainty in pmRAmas/yrstat.error;pos.pm;pos.eq.rafloatpmDE[-4.6/6.4] Relative proper motion along DE (1)mas/yrpos.pm;pos.eq.decfloate_pmDE[0.03/2.02] Uncertainty in pmDEmas/yrstat.error;pos.pm;pos.eq.decfloatVmag[19.62/27.56] HST/WFPC2 F555W band magnitudemagphot.mag;em.opt.VfloatImag[18.25/27.82] HST/WFPC2 F814W band magnitudemagphot.mag;em.opt.IfloatV-I[-1.02/3.1] The HST (F555W-F814W) color indexmagphot.color;em.opt.V;em.opt.IfloatLambda[-21/1.1] Second moment of the source profile (2)stat.fit.paramfloatWF[2/4] Wide Field camera frame in which the source was detectedmeta.id;instrintJ/ApJ/741/100/table2Extragalactic Reference sources in the Leo II fieldrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000[168.355/168.395] Right Ascension in decimal degrees (J2000)degpos.eq.ra;meta.maine_RAJ2000Uncertainty in RAdegmasstat.error;pos.eq.rafloatDEJ2000[22.144/22.185] Declination in decimal degrees (J2000)degpos.eq.dec;meta.maine_DEJ2000Uncertainty in DEdegmasstat.error;pos.eq.decfloatpmRA[-4.1/3.6] Relative proper motion along RA (1)mas/yrpos.pm;pos.eq.rafloate_pmRA[0.02/3.6] Uncertainty in pmRAmas/yrstat.error;pos.pm;pos.eq.rafloatpmDE[-4.6/6.4] Relative proper motion along DE (1)mas/yrpos.pm;pos.eq.decfloate_pmDE[0.03/2.02] Uncertainty in pmDEmas/yrstat.error;pos.pm;pos.eq.decfloatVmag[19.62/27.56] HST/WFPC2 F555W band magnitudemagphot.mag;em.opt.VfloatImag[18.25/27.82] HST/WFPC2 F814W band magnitudemagphot.mag;em.opt.IfloatV-I[-1.02/3.1] The HST (F555W-F814W) color indexmagphot.color;em.opt.V;em.opt.IfloatLambda[-21/1.1] Second moment of the source profile (2)stat.fit.paramfloatWF[2/4] Wide Field camera frame in which the source was detectedmeta.id;instrintIDExtragalactic Reference source number (EGR-NN); only for table 2meta.id;meta.mainchar