J/AJ/151/79ivo://CDS.VizieR/J/AJ/151/79doi:10.26093/cds/vizier.51510079CDSLe Bail K.Gipson J.M.Gordon D.MacMillan D.S.Behrend D.,Thomas C.C.Bolotin S.Himwich W.E.Baver K.D.Corey B.E.Titus M.,Bourda G.Charlot P.Collioud A.2017-10-11T05:12:59Z2016-07-20T08:22:42ZCDS support team

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

cds-question@unistra.frquasarsradio-sourcesinterferometryThe second realization of the International Celestial Reference Frame (ICRF2), which is the current fundamental celestial reference frame adopted by the International Astronomical Union, is based on Very Long Baseline Interferometry (VLBI) data at radio frequencies in X band and S band. The European Space Agency's Gaia mission, launched on 2013 December 19, started routine scientific operations in 2014 July. By scanning the whole sky, it is expected to observe ~500000 Quasi Stellar Objects in the optical domain an average of 70 times each during the five years of the mission. This means that, in the future, two extragalactic celestial reference frames, at two different frequency domains, will coexist. It will thus be important to align them very accurately. In 2012, the Laboratoire d'Astrophysique de Bordeaux (LAB) selected 195 sources from ICRF2 that will be observed by Gaia and should be suitable for aligning the radio and optical frames: they are called ICRF2-Gaia transfer sources. The LAB submitted a proposal to the International VLBI Service (IVS) to regularly observe these ICRF2-Gaia transfer sources at the same rate as Gaia observes them in the optical realm, e.g., roughly once a month. We describe our successful effort to implement such a program and report on the results. Most observations of the ICRF2-Gaia transfer sources now occur automatically as part of the IVS source monitoring program, while a subset of 37 sources requires special attention. Beginning in 2013, we scheduled 25 VLBI sessions devoted in whole or in part to measuring these 37 sources. Of the 195 sources, all but one have been successfully observed in the 12 months prior to 2015 September 01. Of the sources, 87 met their observing target of 12 successful sessions per year. The position uncertainties of all of the ICRF2-Gaia transfer sources have improved since the start of this observing program. For a subset of 24 sources whose positions were very poorly known, the uncertainty has decreased, on average, by a factor of four. This observing program is successful because the two main goals were reached for most of the 195 ICRF2-Gaia transfer sources: observing at the requested target of 12 successful sessions per year and improving the position uncertainties to better than 200{mu}as for both R.A. and decl. However, scheduling some of the transfer sources remains a challenge because of network geometry and the weakness of the sources, and this will be one focus of future sessions used in this ongoing program.2016AJ....151...79Lhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/151/79CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/324 : The Initial Gaia Source List (IGSL) (Smart, 2013)I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)J/AJ/150/58 : VLBI ICRF2 (Fey+, 2015)J/A+A/526/A102 : VLBI imaging of 105 extragalactic radio sourcesJ/A+A/520/A113 : VLBI detection of 398 extragalactic radio sourcesJ/AJ/127/3587 : VLBI ICRF. II (Fey+, 2004)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/151/79https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/151/79http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/151/79https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/151/79https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/151/79http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/151/79GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/151/79/table1 (*Candidate ICRF2-Gaia transfer sources to align the radio catalog and the Gaia catalog)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/151/79/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/151/79/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/151/79/table1?GETtext/xml+votable180.050000true4.9407765273.4583382128890.0055555555555555566/103 110 438 532 572 700 911 991 1509 1671 1702 2143 2721 2836 3024 3096 3309 3820 4054 4436 4695 4820 4964 4992 5139 5404 5423 5848 6153 6448 6496 6507 6641 6853 7570 7642 7857 7896 8057 8299 8487 8615 8915 9676 9714 9998 10163 10352 10798 11027 11116 11880 12218 12301 12547 12580 12599 12604 13545 13792 14842 14854 15023 15143 15286 16027 16049 16247 16298 16444 16676 17188 17215 17516 17579 17734 17791 17839 17857 17909 18378 18624 18661 18871 19088 19197 19271 19308 19370 19567 19622 19831 19867 21012 21121 21924 21935 21955 21960 21968 22396 22433 22501 22658 22950 22993 23121 23127 23383 23476 23786 24568 24571 24608 24623 24845 24931 25196 25503 25624 25630 25864 26115 26303 26363 26374 27060 27909 28042 28208 28383 28454 28463 28479 28517 28673 29016 29570 29675 30075 30857 31176 31334 31430 31451 31664 31894 31986 32311 32691 32764 33827 33829 34013 34123 34428 34443 34461 34517 34931 35440 36100 36863 38311 38579 38763 40344 40479 40762 43366 43399 43822 43828 44147 44899 44908 45393 45409 46055 46310 46439 46459 46529 46964 47014 47540 48023 48541 48589 48610 48798 48846 48985https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/151/79?format=asciiRadiodefaultJ/AJ/151/79/table1*Candidate ICRF2-Gaia transfer sources to align the radio catalog and the Gaia catalogSimbadNameSimbad column added by the CDSmeta.idcharCat[1/4] Initial Gaia category (4)meta.codeintrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintIVSInternational Very Long Baseline Interferometry (VLBI) Service (IVS) identifier (HHMM+DDd, B1950)meta.id;meta.maincharIAUIAU identifier (JHHMM+DDMM format)meta.idcharRAJ2000Hour of Right Ascension (J2000) (1)pos.eq.ra;meta.maine_RAJ2000[2/1015] Formal error in RAs (2)uarcsecstat.error;pos.eq.raintDEJ2000Degree of Declination (J2000) (1)pos.eq.dec;meta.maine_DEJ2000[2/1473] Formal error in DEs (2)uarcsecstat.error;pos.eq.decintNexp[10/4592] Number of VLBI sessionsmeta.numberintNobs[126/401647] Number of VLBI observationsmeta.numberintX-GSFC[0.03/10] Goddard Space Flight Center (GSFC) IVS Analysis Center X-band flux density (3)Jyphot.flux.density;em.radiofloatS-GSFC[0.03/10] Goddard Space Flight Center (GSFC) IVS Analysis Center S-band flux density (3)Jyphot.flux.density;em.radiofloatX-BVID[0.07/13.4]? Bordeaux VLBI Image Database (BVID) X-band flux density (3)Jyphot.flux.density;em.radiofloatnullableS-BVID[0.04/10.73]? Bordeaux VLBI Image Database (BVID) S-band flux density (3)Jyphot.flux.density;em.radiofloatnullable