Variations of Absolute Source Positions Determined from Quad-band VLBI Observations
Active 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 a...
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IOP Publishing
2025-01-01
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| Series: | The Astronomical Journal |
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| Online Access: | https://doi.org/10.3847/1538-3881/adb133 |
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| author | Ming Hui Xu Patrick Charlot |
| author_facet | Ming Hui Xu Patrick Charlot |
| author_sort | Ming Hui Xu |
| collection | DOAJ |
| description | Active 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 10.5 GHz. 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° decl., while the sensitivity of the observations to the decl. coordinate predominates for sources below 20° 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 2.2/8.6 GHz are found for 15% of the sources. For 6% of the sources, the offsets are larger than 0.8 mas. 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. |
| format | Article |
| id | doaj-art-b453f64bcfb44939b00fff40bbe748c4 |
| institution | DOAJ |
| issn | 1538-3881 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astronomical Journal |
| spelling | doaj-art-b453f64bcfb44939b00fff40bbe748c42025-08-20T03:04:49ZengIOP PublishingThe Astronomical Journal1538-38812025-01-01169317310.3847/1538-3881/adb133Variations of Absolute Source Positions Determined from Quad-band VLBI ObservationsMing Hui Xu0https://orcid.org/0000-0001-9602-9489Patrick Charlot1https://orcid.org/0000-0002-9142-716XGFZ Helmholtz Centre for Geosciences , Telegrafenberg, 14476, Potsdam, Germany ; minghui.xu@gfz-potsdam.deLaboratoire d’astrophysique de Bordeaux, Univ. Bordeaux , CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, FranceActive 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 10.5 GHz. 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° decl., while the sensitivity of the observations to the decl. coordinate predominates for sources below 20° 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 2.2/8.6 GHz are found for 15% of the sources. For 6% of the sources, the offsets are larger than 0.8 mas. 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.https://doi.org/10.3847/1538-3881/adb133Active galactic nucleiEquatorial coordinate system |
| spellingShingle | Ming Hui Xu Patrick Charlot Variations of Absolute Source Positions Determined from Quad-band VLBI Observations The Astronomical Journal Active galactic nuclei Equatorial coordinate system |
| title | Variations of Absolute Source Positions Determined from Quad-band VLBI Observations |
| title_full | Variations of Absolute Source Positions Determined from Quad-band VLBI Observations |
| title_fullStr | Variations of Absolute Source Positions Determined from Quad-band VLBI Observations |
| title_full_unstemmed | Variations of Absolute Source Positions Determined from Quad-band VLBI Observations |
| title_short | Variations of Absolute Source Positions Determined from Quad-band VLBI Observations |
| title_sort | variations of absolute source positions determined from quad band vlbi observations |
| topic | Active galactic nuclei Equatorial coordinate system |
| url | https://doi.org/10.3847/1538-3881/adb133 |
| work_keys_str_mv | AT minghuixu variationsofabsolutesourcepositionsdeterminedfromquadbandvlbiobservations AT patrickcharlot variationsofabsolutesourcepositionsdeterminedfromquadbandvlbiobservations |