date: 2023-10-02T06:13:54Z
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pdf:docinfo:title: Enhancing the alignment between the celestial reference frames from very long baseline interferometry and Gaia
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subject: The ICRS is the reference system used for astrometry and geodesy in space. The latest realizations are ICRF3 S/X, ICRF3 K, and ICRF3 X/Ka at radio frequencies observed by geodetic VLBI, and Gaia-CRF3 from observations by the Gaia spacecraft at optical frequencies. The ICRFs are independently derived catalogs of mean positions (and proper motions as well as parallaxes in case of Gaia) of distant compact extragalactic sources with approximately comparable precision. Within the error bounds, the different observation setups should ideally produce identical source positions. However, previous research discovered variances related to the variable nature of the sources as a function of frequency and time. A deeper understanding of the individual source position differences as well as the alignment of the ICRF in terms of global systematic source position differences benefits the large ICRF and Gaia user community, such as geodetic VLBI for connecting VLBI products across frequencies.  This work adds several case studies to the existing research on the comparison and the alignment of the ICRFs. At optical frequencies, the set of ICRF3 counterparts in the Gaia spacecraft's Early Data Release 3 (Gaia EDR3, including Gaia-CRF3) and in Gaia DR2, the predecessor of Gaia EDR3, are investigated. The position differences of the individual counterparts at the various frequencies are re-evaluated, focusing on the correlation of the normalized distances, offset directions, and global systematic differences with the number of VLBI observations or the extent of radio source structure. The individual VLBI and Gaia position offsets tend to be in the same direction, especially in case of significant offsets. It is shown that large normalized position offsets are related to sources with large radio structure. The global systematic differences, which are an order of magnitude smaller than the individual differences, can be accurately determined, especially if the set of counterparts has be
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dc:title: Enhancing the alignment between the celestial reference frames from very long baseline interferometry and Gaia
modified: 2023-10-02T06:13:54Z
cp:subject: The ICRS is the reference system used for astrometry and geodesy in space. The latest realizations are ICRF3 S/X, ICRF3 K, and ICRF3 X/Ka at radio frequencies observed by geodetic VLBI, and Gaia-CRF3 from observations by the Gaia spacecraft at optical frequencies. The ICRFs are independently derived catalogs of mean positions (and proper motions as well as parallaxes in case of Gaia) of distant compact extragalactic sources with approximately comparable precision. Within the error bounds, the different observation setups should ideally produce identical source positions. However, previous research discovered variances related to the variable nature of the sources as a function of frequency and time. A deeper understanding of the individual source position differences as well as the alignment of the ICRF in terms of global systematic source position differences benefits the large ICRF and Gaia user community, such as geodetic VLBI for connecting VLBI products across frequencies.  This work adds several case studies to the existing research on the comparison and the alignment of the ICRFs. At optical frequencies, the set of ICRF3 counterparts in the Gaia spacecraft's Early Data Release 3 (Gaia EDR3, including Gaia-CRF3) and in Gaia DR2, the predecessor of Gaia EDR3, are investigated. The position differences of the individual counterparts at the various frequencies are re-evaluated, focusing on the correlation of the normalized distances, offset directions, and global systematic differences with the number of VLBI observations or the extent of radio source structure. The individual VLBI and Gaia position offsets tend to be in the same direction, especially in case of significant offsets. It is shown that large normalized position offsets are related to sources with large radio structure. The global systematic differences, which are an order of magnitude smaller than the individual differences, can be accurately determined, especially if the set of counterparts has be
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pdf:docinfo:subject: The ICRS is the reference system used for astrometry and geodesy in space. The latest realizations are ICRF3 S/X, ICRF3 K, and ICRF3 X/Ka at radio frequencies observed by geodetic VLBI, and Gaia-CRF3 from observations by the Gaia spacecraft at optical frequencies. The ICRFs are independently derived catalogs of mean positions (and proper motions as well as parallaxes in case of Gaia) of distant compact extragalactic sources with approximately comparable precision. Within the error bounds, the different observation setups should ideally produce identical source positions. However, previous research discovered variances related to the variable nature of the sources as a function of frequency and time. A deeper understanding of the individual source position differences as well as the alignment of the ICRF in terms of global systematic source position differences benefits the large ICRF and Gaia user community, such as geodetic VLBI for connecting VLBI products across frequencies.  This work adds several case studies to the existing research on the comparison and the alignment of the ICRFs. At optical frequencies, the set of ICRF3 counterparts in the Gaia spacecraft's Early Data Release 3 (Gaia EDR3, including Gaia-CRF3) and in Gaia DR2, the predecessor of Gaia EDR3, are investigated. The position differences of the individual counterparts at the various frequencies are re-evaluated, focusing on the correlation of the normalized distances, offset directions, and global systematic differences with the number of VLBI observations or the extent of radio source structure. The individual VLBI and Gaia position offsets tend to be in the same direction, especially in case of significant offsets. It is shown that large normalized position offsets are related to sources with large radio structure. The global systematic differences, which are an order of magnitude smaller than the individual differences, can be accurately determined, especially if the set of counterparts has be
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pdf:docinfo:creator: Susanne Lunz
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meta:creation-date: 2023-08-01T18:15:30Z
created: Tue Aug 01 20:15:30 CEST 2023
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Creation-Date: 2023-08-01T18:15:30Z
Author: Susanne Lunz
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dc:description: The ICRS is the reference system used for astrometry and geodesy in space. The latest realizations are ICRF3 S/X, ICRF3 K, and ICRF3 X/Ka at radio frequencies observed by geodetic VLBI, and Gaia-CRF3 from observations by the Gaia spacecraft at optical frequencies. The ICRFs are independently derived catalogs of mean positions (and proper motions as well as parallaxes in case of Gaia) of distant compact extragalactic sources with approximately comparable precision. Within the error bounds, the different observation setups should ideally produce identical source positions. However, previous research discovered variances related to the variable nature of the sources as a function of frequency and time. A deeper understanding of the individual source position differences as well as the alignment of the ICRF in terms of global systematic source position differences benefits the large ICRF and Gaia user community, such as geodetic VLBI for connecting VLBI products across frequencies.  This work adds several case studies to the existing research on the comparison and the alignment of the ICRFs. At optical frequencies, the set of ICRF3 counterparts in the Gaia spacecraft's Early Data Release 3 (Gaia EDR3, including Gaia-CRF3) and in Gaia DR2, the predecessor of Gaia EDR3, are investigated. The position differences of the individual counterparts at the various frequencies are re-evaluated, focusing on the correlation of the normalized distances, offset directions, and global systematic differences with the number of VLBI observations or the extent of radio source structure. The individual VLBI and Gaia position offsets tend to be in the same direction, especially in case of significant offsets. It is shown that large normalized position offsets are related to sources with large radio structure. The global systematic differences, which are an order of magnitude smaller than the individual differences, can be accurately determined, especially if the set of counterparts has be
Keywords: VLBI; Gaia; reference frame
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dc:creator: Susanne Lunz
description: The ICRS is the reference system used for astrometry and geodesy in space. The latest realizations are ICRF3 S/X, ICRF3 K, and ICRF3 X/Ka at radio frequencies observed by geodetic VLBI, and Gaia-CRF3 from observations by the Gaia spacecraft at optical frequencies. The ICRFs are independently derived catalogs of mean positions (and proper motions as well as parallaxes in case of Gaia) of distant compact extragalactic sources with approximately comparable precision. Within the error bounds, the different observation setups should ideally produce identical source positions. However, previous research discovered variances related to the variable nature of the sources as a function of frequency and time. A deeper understanding of the individual source position differences as well as the alignment of the ICRF in terms of global systematic source position differences benefits the large ICRF and Gaia user community, such as geodetic VLBI for connecting VLBI products across frequencies.  This work adds several case studies to the existing research on the comparison and the alignment of the ICRFs. At optical frequencies, the set of ICRF3 counterparts in the Gaia spacecraft's Early Data Release 3 (Gaia EDR3, including Gaia-CRF3) and in Gaia DR2, the predecessor of Gaia EDR3, are investigated. The position differences of the individual counterparts at the various frequencies are re-evaluated, focusing on the correlation of the normalized distances, offset directions, and global systematic differences with the number of VLBI observations or the extent of radio source structure. The individual VLBI and Gaia position offsets tend to be in the same direction, especially in case of significant offsets. It is shown that large normalized position offsets are related to sources with large radio structure. The global systematic differences, which are an order of magnitude smaller than the individual differences, can be accurately determined, especially if the set of counterparts has be
dcterms:created: 2023-08-01T18:15:30Z
Last-Modified: 2023-10-02T06:13:54Z
dcterms:modified: 2023-10-02T06:13:54Z
title: Enhancing the alignment between the celestial reference frames from very long baseline interferometry and Gaia
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pdf:docinfo:keywords: VLBI; Gaia; reference frame
pdf:docinfo:modified: 2023-10-02T06:13:54Z
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dc:subject: VLBI; Gaia; reference frame
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