I/325ivo://CDS.VizieR/I/325CDSZacharias M.I.Zacharias N.2017-09-29T09:02:43Z2013-12-10T12:02:09ZCDS support team

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

cds-question@unistra.froptical-observationcatalogsastrometryvery-long-baseline-interferometryBetween 1997 and 2004 several observing runs were conducted mainly with the CTIO 0.9m to image ICRF counterparts (mostly QSOs) in order to determine accurate optical positions. Contemporary to these deep CCD images the same fields were observed with the USNO astrograph in the same bandpass. These provide accurate positions on the Hipparcos/Tycho-2 system for stars in the 10 to 16 magnitude range used as reference stars for the deep CCD imaging data. Here we present final optical position results of 413 sources based on astrograph data reductions using UCAC2 and UCAC4 type reference stars. These optical positions are compared to radio VLBI positions. The current optical system is not perfectly aligned to the ICRF radio system with rigid body rotation angles of 3 to 5 mas (3{sigma}) found between them for all 3 axes. Furthermore, statistically, the optical-radio position differences are found to exceed the total, combined, known errors in the observations. Systematic errors in the optical reference stars as well as physical offsets between the centers of optical and radio emissions are both identified as likely causes. A detrimental, astrophysical, random noise (DARN) component is postulated to be on about the 10mas level. If confirmed by future observations, this could severely limit the Gaia to ICRF reference frame alignment accuracy to an error of about 0.5mas per coordinate axis with the current number of sources envisioned to provide the link. A list of 36 ICRF sources without the detection of an optical counterpart to a limiting magnitude of about R=22 is provided as well.2014AJ....147...95Zhttps://cdsarc.cds.unistra.fr/viz-bin/cat/I/325CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/289 : UCAC2 Catalogue (Zacharias+ 2004)I/324 : UCAC4 Catalogue (Zacharias+ 2012)VII/258 : Quasars and Active Galactic Nuclei (13th Ed.) (Veron+ 2010)I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)J/A+A/520/A113 : VLBI detection of 398 extragalactic radio sources (Bourda+, 2J/A+A/526/A102 : VLBI imaging of 105 extragalactic radio sources (Bourda+, 201J/A+A/553/A122 : Time stability of the ICRF2 axes (Lambert, 2013)J/A+A/537/A99 : Large Quasar Astrometric Catalogue 2 (LQAC-2) (Souchay+ 2012)http://www.obs.u-bordeaux1.fr/BVID/content.html : the Bordeaux VLBI Imagehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=I/325https://vizier.iucaa.in/viz-bin/VizieR-2?-source=I/325http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=I/325https://vizier.cds.unistra.fr/viz-bin/votable?-source=I/325https://vizier.iucaa.in/viz-bin/votable?-source=I/325http://vizieridia.saao.ac.za/viz-bin/votable?-source=I/325GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table I/325/icrf-u2 (Results from UCAC2-type reductions of ICRF optical counterparts (sample in table 4 of paper))https://vizier.cds.unistra.fr/viz-bin/conesearch/I/325/icrf-u2?https://vizier.iucaa.in/viz-bin/conesearch/I/325/icrf-u2?http://vizieridia.saao.ac.za/viz-bin/conesearch/I/325/icrf-u2?GETtext/xml+votable180.050000true1.148551667-47.6054452780.005555555555555556Cone search capability for table I/325/icrf-u4 (Results from UCAC4-type reductions of ICRF optical counterparts (sample in table 5 of paper))https://vizier.cds.unistra.fr/viz-bin/conesearch/I/325/icrf-u4?https://vizier.iucaa.in/viz-bin/conesearch/I/325/icrf-u4?http://vizieridia.saao.ac.za/viz-bin/conesearch/I/325/icrf-u4?GETtext/xml+votable180.050000true1.148553333-47.6054444440.0055555555555555566/18 60 110 124 180 198 304 532 4436 4448 4696 4770 4820 5154 5163 6164 8199 8299 8345 8487 8521 8615 8717 8805 8858 8905 9232 9347 10321 10501 12301 12352 12475 12580 12599 13156 13213 13230 14338 14520 16592 16962 17019 17110 17184 17188 17215 17351 17516 17529 17541 17579 17734 17791 17857 17909 18002 18022 18035 18037 18084 18214 18239 18242 18271 18378 18438 18457 18506 18545 18624 18661 18669 18718 18755 18769 18871 18907 19088 19101 19166 19190 19271 19370 19398 19523 19567 19609 19629 20503 20610 20657 20935 21012 21049 21117 21121 21163 21266 21358 21437 21564 21758 21768 21924 21935 21960 21968 21972 21990 22363 22396 22501 22658 22659 22917 22943 22950 22965 23014 23022 23099 23121 23127 23335 23383 23478 23761 23805 24003 24084 24116 24123 24608 24809 24845 25196 25255 25256 25302 25428 25493 25503 25630 25647 25677 25742 25864 25990 26000 26083 26100 26115 26131 26244 26292 26297 26301 26303 26363 26491 26550 26769 26816 26900 26966 26983 27060 27220 27310 27322 27423 27446 27464 27466 27514 27583 27773 27909 27926 28167 28184 28208 28339 28453 28454 28799 29016 29218 29384 29570 29675 29714 29795 30527 30657 31176 31190 31211 31334 31355 31391 31430 31451 31529 31535 31559 31664 31857 31894 32311 32325 32594 32660 32841 32916 32948 32961 33010 33043 33048 33549 33560 33626 33684 33816 33825 33827 33829 33833 33973 34013 34038 34099 34123 34209 34210 34264 34330 34428 34461 34517 34571 34572 34675 34699 34870 34871 34931 35079 35249 35294 35370 35440 35482 35651 35786 35801 36155 36188 36417 36551 36554 36785 36877 36941 36988 37064 37138 37190 37205 37217 37229 37269 37385 37450 37474 37480 37819 37919 37994 38189 38277 38383 38416 38470 38474 38579 38734 38763 38802 38918 39181 39489 39557 39577 39695 39848 40060 40344 40479 40527 40692 40730 40990 41003 41033 41043 41051 41059 41072 41088 41110 41262 41275 41310 41335 41374 41426 41511 41578 41701 41942 42046 42060 42366 42609 42853 42883 42901 42980 43085 43257 43366 43399 43417 43469 43549 43566 43694 43822 43936 44034 44043 44147 44247 44502 44614 44658 44661 44724 44776 44805 44832 44899 44908 45011 45110 45158 45162 45178 45196 45393 45446 45483 45487 45614 45621 45763 45774 45795 45843 46055 46251 46265 46310 46337 46373 46394 46442 46459 46568 46588 46709 46762 46764 46851 46868 46921 46964 47014 47016 47080 47106 47107 47255 47375 47534 47540 47747 47941 48023 48123 48142 48228 48362 48589 48595 48610 48798 48846 48965https://cdsarc.cds.unistra.fr/viz-bin/moc/I/325?format=asciiOpticalRadiodefaultI/325/icrf-u2Results from UCAC2-type reductions of ICRF optical counterparts (sample in table 4 of paper)SimbadNameSimbad column added by the CDSmeta.idcharz[0/5]? Redshift from LQAC-2 (J/A+A/537/A99)src.redshiftfloatnullablerecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension ICRSpos.eq.ra;meta.mainDEJ2000Declination ICRSpos.eq.dec;meta.mainDist[0/1821] Distance between the optical and radio positionsmaspos.angDistancefloatdRA*Distance(optical-radio) in RA*cos(Dec)maspos.eq.ra;arith.difffloatdDecDistance(optical-radio) in Decmaspos.eq.decfloateRA[4/250] total, formal error of optical position (RA*cos(Dec))masstat.error;spect.dopplerVeloc.opt;em.optfloateDE[4/250] total, formal error of optical position (Dec)masstat.error;spect.dopplerVeloc.opt;em.optfloatsRAratio dRA*/eRA (position difference in RA in {sigma}s)stat.fit.goodnessfloatsDEratio dDE/eDE (position difference in Dec in {sigma}s)stat.fit.goodnessfloateRad? error of radio position (per coordinate)masstat.error;spect.dopplerVeloc.radio;em.radiofloatnullableNccdnumber of deep CCD exposures usedmeta.numberintNr*average number of reference stars per deep exposure usedmeta.numberintNrxaverage number of reference stars excludedmeta.numberinterrmean "plate" solution error of individual deep CCD exposuresstat.errorfloatS/N[1/1639] Approximate signal/noise ratio of target on individual deep CCDstat.snr;instr.detintmag? Optical brightness from LQAC-2 (J/A+A/537/A99)magphot.mag;em.optfloatnullableT[0/3] Object type: 0=unknown, 1=AGN, 2=BL-Lac, 3=QSO (from Veron's 13th ed. (VII/258)src.classintS[0.8/7.2]? Radio X-band (8-12GHz) structure index from Bordeaux database: 1=very good, 2=good, 3=use with caution, 4=unacceptablemeta.code.qualfloatnullableU[2/4] UCAC-type reductions (2 or 4)meta.id;meta.datasetintRnameB1950 coordinate based name of targetmeta.id;meta.maincharRNumber of results for this source with UCAC2- and UCAC4-type reductionsmeta.numberintnullableRun[abo-zJ] Code of deep CCD observing run (1)meta.code;instr.detcharn_Run[rc] Type of target: r=regular target, c=also used as calibration fieldmeta.notecharQ[ufplgn] Quality letter of optical image (2)meta.code.qual;spect.dopplerVeloc.opt;em.optcharMSimbad column added by the CDSmeta.ref.urlintnullableNotesRemarks; if a double the separation (pixel) and flux ratio (source/companion) is givenmeta.numbercharI/325/icrf-u4Results from UCAC4-type reductions of ICRF optical counterparts (sample in table 5 of paper)SimbadNameSimbad column added by the CDSmeta.idcharrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension ICRSpos.eq.ra;meta.mainDEJ2000Declination ICRSpos.eq.dec;meta.mainDist[0/1821] Distance between the optical and radio positionsmaspos.angDistancefloatdRA*Distance(optical-radio) in RA*cos(Dec)maspos.eq.ra;arith.difffloatdDecDistance(optical-radio) in Decmaspos.eq.decfloateRA[4/250] total, formal error of optical position (RA*cos(Dec))masstat.error;spect.dopplerVeloc.opt;em.optfloateDE[4/250] total, formal error of optical position (Dec)masstat.error;spect.dopplerVeloc.opt;em.optfloatsRAratio dRA*/eRA (position difference in RA in {sigma}s)stat.fit.goodnessfloatsDEratio dDE/eDE (position difference in Dec in {sigma}s)stat.fit.goodnessfloateRad? error of radio position (per coordinate)masstat.error;spect.dopplerVeloc.radio;em.radiofloatnullableNccdnumber of deep CCD exposures usedmeta.numberintNr*average number of reference stars per deep exposure usedmeta.numberintNrxaverage number of reference stars excludedmeta.numberinterrmean "plate" solution error of individual deep CCD exposuresstat.errorfloatS/N[1/1639] Approximate signal/noise ratio of target on individual deep CCDstat.snr;instr.detintmag? Optical brightness from LQAC-2 (J/A+A/537/A99)magphot.mag;em.optfloatnullablez[0/5]? Redshift from LQAC-2 (J/A+A/537/A99)src.redshiftfloatnullableT[0/3] Object type: 0=unknown, 1=AGN, 2=BL-Lac, 3=QSO (from Veron's 13th ed. (VII/258)src.classintS[0.8/7.2]? Radio X-band (8-12GHz) structure index from Bordeaux database: 1=very good, 2=good, 3=use with caution, 4=unacceptablemeta.code.qualfloatnullableU[2/4] UCAC-type reductions (2 or 4)meta.id;meta.datasetintRnameB1950 coordinate based name of targetmeta.id;meta.maincharRNumber of results for this source with UCAC2- and UCAC4-type reductionsmeta.numberintnullableRun[abo-zJ] Code of deep CCD observing run (1)meta.code;instr.detcharn_Run[rc] Type of target: r=regular target, c=also used as calibration fieldmeta.notecharQ[ufplgn] Quality letter of optical image (2)meta.code.qual;spect.dopplerVeloc.opt;em.optcharMSimbad column added by the CDSmeta.ref.urlintnullableNotesRemarks; if a double the separation (pixel) and flux ratio (source/companion) is givenmeta.numberchar