J/A+A/565/A21ivo://CDS.VizieR/J/A+A/565/A21doi:10.26093/cds/vizier.35650021CDSLazorenko P.F.Sahlmann J.Segransan D.Martin E.L.Queloz D.Mayor M.,Udry S.2014-10-15T21:49:21Z2014-04-28T13:01:51ZCDS support team

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

cds-question@unistra.frastrometrymultiple-starsproper-motionsvisible-astronomytrigonometric-parallaxWe describe the astrometric reduction of images obtained with the FORS2/VLT camera in the framework of an astrometric planet search around 20 M/L-transition dwarfs. We present the correction of systematic errors, the achieved astrometric performance, and a new astrometric catalogue containing the faint reference stars in 20 fields located close to the galactic plane. Remote reference stars are used both to determine the astrometric trajectories of the nearby planet search targets and to identify and correct systematic errors. We detected three types of systematic errors in the FORS2 astrometry: the relative motion of the camera's two CCD chips, errors that are correlated in space, and an error contribution of yet unexplained origin. The relative CCD motion has probably a thermal origin and usually is 0.001-0.010px (0.1-1mas), but sometimes amounts to 0.02-0.05px (3-6mas). This instability and space- correlated errors are detected and mitigated using reference stars. The third component of unknown origin has an amplitude of 0.03-0.14mas and is independent of the observing conditions. We find that a consecutive sequence of 32 images of a well-exposed star over 40min at 0.6arcsec seeing results in a median r.m.s. of the epoch residuals of 0.126mas. Overall, the epoch residuals are distributed according to a normal law with a {chi}^2^ value near unity. We compiled a catalogue of 12000 stars with I-band magnitudes of 16-22 located in 20 fields, each covering 2x2'. It contains I-band magnitudes, ICRF positions with 40-70mas precision, and relative proper motions and absolute trigonometric parallaxes with a precision of 0.1mas/yr and 0.1mas at the bright end, respectively. This work shows that an astrometric accuracy of ~100 micro-arcseconds over two years can be achieved with a large optical telescope in a survey covering several targets and varying observing conditions.2014A&A...565A..21Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/565/A21CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toJ/A+A/556/A133 : Astrometric orbit of DENIS-P J082303.1-49120 (Sahlmann+, 2013)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/565/A21https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/565/A21http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/565/A21https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/565/A21https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/565/A21http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/565/A21GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/565/A21/cat_fors (Deep astrometric catalogue)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/565/A21/cat_fors?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/565/A21/cat_fors?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/565/A21/cat_fors?GETtext/xml+votable180.050000true93.92561139-1.008245560.0055555555555555566/20738 20754 20760 20891 20894 21728 22177 29301 29305 38039 38145 38164 39185 39760 39807 40485 40669 42090 42261 42308-42309 42633 42635 430622.5861814575694973e-19 2.5861814575694973e-19https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/565/A21?format=asciiOpticaldefaultJ/A+A/565/A21/table1Target list (ultracool subdwarfs)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNr[1/20] Sequential numbermeta.recordintprimaryIDShort identifier, which refer to approximate field sky positionmeta.id;meta.maincharImagI-band magnitude (Bessel filter, center=768nm)magphot.mag;em.opt.IfloatNe[9/16] Number of observing epochsmeta.numberintN*Number of stars in this fieldmeta.numberintnullableJ/A+A/565/A21/cat_forsDeep astrometric cataloguerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintNr[1/20] Field number (1)meta.id;obs.fieldintSeq[1/1915] Sequential star number in the fieldmeta.id;obs.fieldintImag[13.8/25.1] I-band magnitude (2)magphot.mag;em.opt.Ifloate_ImagStandard uncertainty of I-band magnitudemagstat.error;phot.mag;em.opt.IfloatRAJ2000Right Ascension J2000.0, epoch J2000.0 (3)degpos.eq.ra;meta.maine_RAJ2000Standard uncertainty of RAdegarcsecstat.error;pos.eq.rafloatDEJ2000Declination J2000.0, epoch J2000.0 (3)degpos.eq.dec;meta.maine_DEJ2000Standard uncertainty of DEdegarcsecstat.error;pos.eq.decfloatpmRAProper motion in RA, pmRA*cosDE, relative to field starsmas/yrpos.pm;pos.eq.radoublee_pmRA[0/5.4] Standard uncertainty of pmRAmas/yrstat.error;pos.pm;pos.eq.rafloatpmDEProper motion in DE, relative to field starsmas/yrpos.pm;pos.eq.decdoublee_pmDE[0/5.2] Standard uncertainty of pmDEmas/yrstat.error;pos.pm;pos.eq.decfloatplx[-19/106] Parallax, absolute (4)maspos.parallax.trigfloate_plx[0.04/4.4] Standard uncertainty of PLXmasstat.error;pos.parallaxfloatEp[2011.4/2012.2] Mean epoch of observationsyrtime.epochdoubleQual[0.1/306] {chi}^2^ of the epoch residuals (5)stat.fit.chi2float