J/A+A/520/A113ivo://CDS.VizieR/J/A+A/520/A113doi:10.26093/cds/vizier.35200113CDSBourda G.Charlot P.Porcas R.W.Garrington S.T.2011-01-06T07:11:48Z2010-12-11T10:55:53ZCDS support team

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

cds-question@unistra.frvery-long-baseline-interferometryinterferometryradio-sourcesquasarsactive-galactic-nucleibl-lacertae-objectsThe European space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames with the highest possible accuracy. It has been found that only 70 (10%) of the sources from the International Celestial Reference Frame (ICRF) are suitable for establishing this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. The sample consists of 447 optically- bright (magnitude <=18) extragalactic radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating an optical quasar catalog with the NRAO VLA Sky Survey (NVSS, Cat. VIII/65). This paper presents the observing strategy to detect, image, and measure accurate radio positions for these sources. It also provides results on the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, a high detection rate of 89% is found, which is promising for the continuation of this project. This high VLBI detection rate for sources from the NVSS catalog is probably due to the selection process, suggesting that optically-bright quasars have compact radio structures.2010A&A...520A.113Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/520/A113CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toVIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)VIII/71 : The FIRST Survey Catalog, Version 03Apr11 (Becker+ 2003)VIII/72 : CLASS survey of radio sources (Myers+, 2003)VII/248 : Quasars and Active Galactic Nuclei (12th Ed.) (Veron+ 2006)J/ApJS/171/61 : All-Sky Survey of Flat-Spectrum Radio Sources (Healey+, 2007)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/520/A113https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/520/A113http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/520/A113https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/520/A113https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/520/A113http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/520/A113GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/520/A113/table4 (List of the 49 extragalactic radio sources not detected in one or both bands during EC025A and EC025B (7 sources out of 218 observed during EC025A and 42 sources out of 229 observed during EC025B))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/520/A113/table4?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/520/A113/table4?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/520/A113/table4?GETtext/xml+votable180.050000true4.63054166716.3450.005555555555555556Cone search capability for table J/A+A/520/A113/table3 (List of the 398 extragalactic radio sources detected during EC025A and EC025B experiments (211 out of 218 detected during EC025A, and 187 out of 229 detected during EC025B))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/520/A113/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/520/A113/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/520/A113/table3?GETtext/xml+votable180.050000true0.3487388896.5419350.0055555555555555566/29 49 171 447 615 696 988 1535 1702 2074 2149 2164 2217 2225 2257 2276 2295 2456 2549 2619 2628 2630 2650 2762 3930 3932 4103 4123 4143 4232 4253 4255 4322 4333 4347 4369 4472 4475 4568 4693 4705 4733 4882 4888 4892 4923 4947 5035 5065 5072 5091 5169 5202 5244 5268 5303 5312 5336 5352 5361 5364 5371 5379 5439 5462 5483 5510 5513 5528 5588 5636-5637 5648 5831 5846 5918 5940 5957-5958 5985 6015 6021 6067 6143 6173 6204 6206 6209 6234 6237 6244 6362 6436 6499 6515 6519 6534 6607 6618 6628 6648 6723 6764 6889 7176 7186 7220 7223 7254 7285 7316 7341 7354 7381 7404 7426 7448 7469 7488 7495 7518 7576 7604 7640 7656 7699 7779 7896 7902 8067 8071 8080 8117 8300 8315 8372 8374 8415 8525 8556 8578 8595 8652 8673-8674 8716 8753 8758 8912 8918 8938 8951 8972 9049 9181 9185 9196 9311 9372 9383 9385 9402 9444 9463 9490 9501 9613-9614 9637 9664 9684 9716 9796 9877 9908 9955 10039 10123 10148-10149 10152 10183 10198 10202 10280 10318 10337 10348 10395 10402 10433 10448 10461 10472 10512 10561 10563 10572 10596 10605 10650 10688 10715 10755 10780 10788 10800 10843 10893 10938 10948 10978 10987 10994 10996 10999 11033 11045 11065 11126 11143 11209 11290 11345 11362 11374 11386 11429 11440 11557 11627 11682 11692 11703 11706 11734 11736 11748 11765 11786 11800 11813 11829 11854 11912 11924 11936 11991 11993 12038 12057 12164 12231 12684 12690 12722 12772 12886 12924 13071 13092 13175 13344 13464 13603 13613 13664 13705 13783 15059 15100 15269 15271 15306 16036 16039 16042 16184 16323 17346 17601 17639 17690 17730 17819 17843 17979 17990 18023 18027 18125 18209 18270 18402 18538 18540 18756 18895 18992 19036 19099 19190 19214 19287 19315 19370 19397 19413 19466 19503 19507 19655 19671 19698 19700 19757 19776 19789 19803 19842 19848 19907 20005 20019-20020 20032 20065 20083 20116 20141 20184 20286 20327 20389-20390 21763 21829 22014 22372 22389 22789 22914 23011 23085 23181 23222 23369 23427 24027 25542 25810 25902 25912 25956 25977 26010 26036 26072 26083 26090 26197-26198 26242 26259 26298 26305 26322 26373 26382 26416 26499 26595 26615 26798 26833 26939 27025 27062 27217 27253 27394 27472 27481 27524 27560 27602 27610 27650 27656 27717 27722 27726 27750 27755 27787 27807 27815 27846 27952 28043 28132 28138 28199 28245 28248 28319 28352 28369 28450 28454 28482 28517 28529 28539 28546 28549 28575 28616 28647 28666 30036 30115 31652 32159 32230 32261 32410 32427 32461 32570 32621 32647 32715 36862 45006 45038 45044 48983 48985 490151.5239959695752804e-24 5.5658981862942334e-24https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/520/A113?format=asciiRadiodefaultJ/A+A/520/A113/table4List of the 49 extragalactic radio sources not detected in one or both bands during EC025A and EC025B (7 sources out of 218 observed during EC025A and 42 sources out of 229 observed during EC025B)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIERSIERS designation (HHMM+DDd)meta.id;meta.maincharn_IERS[*] Gravitational lenses (1)meta.notecharSourceSource name (2)meta.idcharCatCatalog (2)meta.idcharVmagOptical magnitude from Veron-Cetty and Veron, 2006, Cat. VII/248magphot.mag;em.optfloatz? Redshift from Veron-Cetty and Veron, 2006, Cat. VII/248src.redshiftfloatnullableType[BL QUA] Type of the object: BL Lac or Quasar (from Veron-Cetty and Veron, Cat. VII/248)src.classcharSs? S-band (2.3GHz) mean correlated flux density (3)mJyphot.flux.density;em.radio.1500-3000MHzintnullableSx? X-band (8.4GHz) mean correlated flux density (3)mJyphot.flux.density;em.radio.6-12GHzintnullablealpha? S/X spectral index (only in table3.dat)spect.indexfloatnullableEXP[A/B] Experiment when the source was observed: 'A' = EC025A (18-20 June 2007) 'B' = EC025B (26-28 October 2007)meta.id;obscharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.mainJ/A+A/520/A113/table3List of the 398 extragalactic radio sources detected during EC025A and EC025B experiments (211 out of 218 detected during EC025A, and 187 out of 229 detected during EC025B)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIERSIERS designation (HHMM+DDd)meta.id;meta.maincharn_IERS[*] Gravitational lenses (1)meta.notecharSourceSource name (2)meta.idcharCatCatalog \linkRole{Data from any of the possible catalogs} (2)meta.notecharVmagOptical magnitude from Veron-Cetty and Veron, 2006, Cat. VII/248magphot.mag;em.optfloatz? Redshift from Veron-Cetty and Veron, 2006, Cat. VII/248src.redshiftfloatnullableType[BL QUA] Type of the object: BL Lac or Quasar (from Veron-Cetty and Veron, Cat. VII/248)src.classcharSs? S-band (2.3GHz) mean correlated flux density (3)mJyphot.flux.density;em.radio.1500-3000MHzintnullableSx? X-band (8.4GHz) mean correlated flux density (3)mJyphot.flux.density;em.radio.6-12GHzintnullablealpha? S/X spectral index (only in table3.dat)spect.indexfloatnullableEXP[A/B] Experiment when the source was observed: 'A' = EC025A (18-20 June 2007) 'B' = EC025B (26-28 October 2007)meta.id;obscharRAJ2000Right ascension (J2000)pos.eq.ra;meta.mainDEJ2000Declination (J2000)pos.eq.dec;meta.main