J/AJ/169/173ivo://CDS.VizieR/J/AJ/169/173doi:10.26093/cds/vizier/be-59-5dCDSXu M.H.Charlot P.2026-07-02T11:45:27Z2026-01-07T10:28:35ZCDS support team

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

cds-question@unistra.fractive-galactic-nucleivery-long-baseline-interferometryastrometryradio-galaxiesinterferometryastronomical-reference-materialsquasarsActive galactic nuclei (AGNs) observed with the very long baseline interferometry (VLBI) technique are used as fiducial references on the sky to precisely measure the shape and orientation of the Earth. Their positions form a celestial reference frame that plays an important role in both astronomy and geodesy. This study investigates the accuracy and stability of the positions of the AGNs that are measured by simultaneous VLBI observations at 3.3, 5.5, 6.6, and 10.5GHz. Based on position time series from dedicated geodetic solutions, we characterize the observed source position variations and identify the possible factors causing such variations. We find that the primary contributor is source structure for sources above 20{deg} decl., while the sensitivity of the observations to the decl. coordinate predominates for sources below 20{deg} decl. The position time series are further explored to derive more realistic uncertainties for the quad-band positions. Significant position offsets with respect to the positions at 2.2/8.6GHz are found for 15% of the sources. For 6% of the sources, the offsets are larger than 0.8mas. The source structure may be divided into two parts: the invisible structure (within the beam size) and the visible structure (on larger scales). The latter causes closure delays enlarging postfit delay residuals in geodetic solutions, whereas the former causes source position changes. Such position changes will contribute significantly to the offsets between radio and optical positions. Overall, this work highlights the necessity to have a specific quad-band catalog for processing operational quad-band observations.2025AJ....169..173Xhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/169/173CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toI/151 : Precise Radio Source Positions from Mark III VLBI (Ma+ 1990)I/251 : VLBI International Celestial Reference Frame (ICRF) (Ma+, 1997)I/323 : International Celestial Reference Frame 2, ICRF2 (Ma+, 2009)I/325 : Radio-optical reference frame link (Zacharias+ 2013)J/AJ/127/3587 : VLBI ICRF. II (Fey+, 2004)J/AZh/81/1032 : VLBI Position Measurements (Titov, 2004)J/AJ/127/3609 : VLBI observations of southern ICRF sources (Ojha+, 2004)J/AJ/130/2529 : 8.4GHz VLBI observations of Southern ICRF sources (Ojha+, 2005)J/A+A/493/317 : Radio source selection for the ICRF (Lambert+, 2009)J/AJ/139/1695 : Celestial Reference Frame at 24 and 43 GHz (Lanyi+, 2010)J/AJ/139/1713 : Celestial Reference Frame at 24 and 43GHz. II (Charlot+, 2010)J/AJ/142/35 : The VLBA Galactic Plane Survey (VGaPS) (Petrov+, 2011)J/AJ/142/89 : Precise astrometry with VLBA (VIPS) (Petrov+, 2011)J/MNRAS/430/2633 : The epoch ICRF (Xu+, 2013)J/A+A/553/A122 : Time stability of the ICRF2 axes (Lambert, 2013)J/MNRAS/445/845 : Implications of the Galac. aberration for CRF (Malkin, 2014)J/AJ/150/58 : VLBI ICRF2 (Fey+, 2015)J/A+A/578/A67 : AGN in IFRS. VLBA observations (Herzog+, 2015)J/AJ/151/154 : Second epoch VLBA Calibrator Survey (VCS-II) (Gordon+, 2016)J/MNRAS/467/L71 : Significance of VLBI/Gaia position offsets (Petrov+, 2017)J/ApJS/234/12 : MOJAVE XV.VLBA 15GHz obs. of AGN jets 1996-2016 (Lister+, 2018)J/A+A/618/A80 : Astrometric classification of 647 VLBI sources (Gattano+, 2018)J/ApJS/242/5 : 40yr of geodetic/astrometric VLBI obs. of ICRF srcs (Xu+, 2019)J/MNRAS/493/L54 : Optical polarization properties of AGNs (Kovalev+, 2020)J/A+A/644/A159 : The third realization of the ICRF, ICRF3 (Charlot+, 2020)J/A+A/651/A64 : Position difference vectors and of the jets (Lambert+, 2021)J/AJ/165/139 : The celestial ref. frame at K-band; imaging.I (de Witt+, 2023)J/ApJS/274/28 : Metrics of astrometric variability in the ICRF.I (Cigan+, 2024)J/A+A/684/A93 : Position and photometric variability (Lambert+, 2024)J/A+A/691/A35 : Optical polarimetry of 152 AGN (Blinov+, 2024)J/ApJS/276/38 : The Radio Fundamental Catalog - RFC (Petrov+, 2025)http://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn36 : IERS Conventionhttp://cddis.nasa.gov/archive/vlbi/ivsdata/vgosdb : IVS archive (2012)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/169/173https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/169/173http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/169/173https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/169/173https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/169/173http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/169/173GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/169/173/table3 (Source position catalog from quad-band VLBI observations)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/169/173/table3?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/169/173/table3?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/169/173/table3?GETtext/xml+votable180.050000true1.5578870306667-6.39314879130560.0055555555555555566/80 124 438 532 556 579 700 911 991 1154 1509 1521 1546 1584 1616 1622 1701 1740 1782 1956 2098 2143 2158 2404 2414 2564 2836 2867 3024 3096 3402 3656 3675 3820 3882 3886 4027 4054 4285 4572 4575 4695 4754 4820 5139 5154 5163 5200 5306 5353 5423 5448 5458 5546 5597 5693 5766-5767 5817 5848 6153 6164 6167 6193 6219 6252 6448 6496 6507 6548 6633 6641 6686 6716 6790 6824 6853 6923 6948 6976 6996 7091 7181 7351 7371 7389 7570 7623 7653 7709 7851 7896 8031 8057 8112 8123 8199 8299 8487 8615 8729 8773 8858 9075 9204 9232 9248 9442 9460 9545 9612 9632-9633 9676 9681 9688 9714 9723 9899 9976 9998 10163 10228 10249-10250 10321 10422 10474 10548 11216 11430 11715 11880 12091 12173 12241 12301 12352 12475 12505 12580 12599 12604 12619 12851 13156 13230 13352-13353 13410 13485 13496 13545 13572 13693 13792 13927 14150 14338 14520 14737 14820 14842 14854 15023 15036 15147 15286 15494 15819 15936 16027 16049 16059 16281 16298 16676 16720 17184 17215 17351 17541 17579 17734 17857 17909 17937 18035 18037 18214 18242 18271 18378 18506 18624 18661 18669 18718 18755 18907 19088 19166 19190 19271 19370 19398 19436 19523 19609 19622 19743 19831 19867 19890 20213 20476 20657 20725 20781 20836 20888 20935 21121 21163 21266 21437 21564 21758 21768 21924 21935 21960 21968 22363 22375 22396 22433 22501 22558 22658 22917 22950 23015 23099 23121 23306 23383 23416 23786 23882 24084 24123 24335 24357 24453 24571 24608 24809 24845 25016 25036 25196 25255-25256 25302 25501 25503 25630 25750 25818 25864 25990 26115 26303 26363 26550 26946 27322 27417 27423 27436 27583 27765 27909 28042 28167 28208 28339 28383 28454 28463 28479 28673 29016 29218 29384 29570 29620 29675 29714 30542 30836 30857 30928 31176 31190 31211 31334 31355 31430 31451 31529 31535 31559 31664 31857 31894 32068 32311 32660 32764 34038 34123 34264 34461 34572 34675 34931 35440 35769 36100 36151 36155 36188 36554 36863 38579 38663 38763 39377 39848 40060 40344 40527 40730 40762 40766 42571 42853 42901 42980 43366 43936 44043 44147 44776 44805 44899 44908 45011 46055 46373 46459 46921 46964 47080 47540 47585 48023 48610 48798 48846 48965 49071https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/169/173?format=asciiRadiodefaultJ/AJ/169/173/table3Source position catalog from quad-band VLBI observationsrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintICRFInternational Celestial Reference Frame identifier (JHHMMSS.s+DDMMSS)meta.id;meta.maincharIERSInternational Earth Rotation and Reference Systems Service identifier (HHMM+DDd, B1950 equinox)meta.idcharCatSource category (1)meta.codecharRAICRSHour of Right Ascension (ICRF) at Ep=2015.0pos.eq.ra;meta.mainDEICRSDegree of Declination (ICRF) at Ep=2015.0pos.eq.dec;meta.maine_RAICRS[5.5e-7/5e-5] Uncertainty in RAssstat.error;pos.eq.radoublee_DEICRS[4.9e-6/7.7e-4] Uncertainty in DEsarcsecstat.error;pos.eq.decdoubleCorrel[-0.9/0.4] Correlation between RA and DE coordinatesstat.correlationfloat<MJD>[58861/60403] Mean Modified Julian Date (JD-2400000.5) of sessions where the source was observeddtime.epoch;stat.meanfloat1stMJD[58090/60403] Modified Julian Date (JD-2400000.5) of first sessiondtime.epochfloatLastMJD[58910/60487] Modified Julian Date (JD-2400000.5) of last sessiondtime.epochfloatNses[1/174] Number of sessionsmeta.numberintNdel[20/96951] Number of group delay observations used to estimate its coordinatesmeta.numberintNrat[0/0] Number of delay rate observations used (2)meta.numberintSimbadSimbad column added by the CDSmeta.ref.urlchar