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About 775 papers for “celestial reference frame”

The Celestial Reference Frame

Chopo Ma · NASA Technical Reports Server (NASA) · 1999

The conceptual basis of reference frames defined by extragalactic objects is straightforwaxd: that the universe as a whole does not rotate so very distant objects cannot have an overall rotational motion. Experimentally, the global rotation of the universe is less than 10(exp -12) arcsecond/yr as inferred from the 3K microwave background radiation. At the distance of 10(exp 8) parsecs, even if an object were moving transversely at the speed of light, its angular velocity would be less than 0.6 x 10(exp -3) arcsecond/yr, while an object moving at a physically more reasonable speed comparable to the Sun would show a motion of 10(exp -6) arcsecond/yr, entirely undetectable by current technology. Since neither systematic universal motion nor random motion at such great distance is measurable, it is reasonable to construct a static celestial reference frame on the basis that such objects axe fixed in the sky.

Cited by 2

Hipparcos and Celestial Reference Frame

J. Kovalevsky · Highlights of Astronomy · 1986

Abstract A discussion of four methods that can be used to link HIPPARCOS to an absolute reference system shows that the best method is to refer it to extragalactic objects. This would free the resulting frame from any parameter describing Earth’s motion.

Cited by 0Open access

The Next Generation Celestial Reference Frame

Megan Johnson, F. K. Schinzel, Jeremy Darling et al. · arXiv (Cornell University) · 2019

Astrometry, the measurement of positions and motions of the stars, is one of the oldest disciplines in Astronomy, extending back at least as far as Hipparchus' discovery of the precession of Earth's axes in 190 BCE by comparing his catalog with those of his predecessors. Astrometry is fundamental to Astronomy, and critical to many aspects of Astrophysics and Geodesy. In order to understand our planet's and solar system's context within their surroundings, we must be able to to define, quantify, study, refine, and maintain an inertial frame of reference relative to which all positions and motions can be unambiguously and self-consistently described. It is only by using this inertial reference frame that we are able to disentangle our observations of the motions of celestial objects from our own complex path around our star, and its path through the galaxy, and the local group. Every aspect of each area outlined in the call for scientific frontiers in astronomy in the era of the 2020-2030 timeframe will depend on the quality of the inertial reference frame. In this white paper, we propose support for development of radio Very Long Baseline Interferometry (VLBI) capabilities, including the Next Generation Very Large Array (ngVLA), a radio astronomy observatory that will not only support development of a next generation reference frame of unprecedented accuracy, but that will also serve as a highly capable astronomical instrument in its own right. Much like its predecessors, the Very Long Baseline Array (VLBA) and other VLBI telescopes, the proposed ngVLA will provide the foundation for the next three decades for the fundamental reference frame, benefitting astronomy, astrophysics, and geodesy alike.

Cited by 0Open access

Extension of the Celestial Reference Frame

S. Bolotin · 2005

A set of VLBI observations carried out since 1992 till August 2004 were analyzed to construct a Celestial Reference Frame. Data processing was conducted according to IERS Conventions 2003 with the software SteelBreeze. Coordinates of stations and Earth Rotation Parameters were fixed and their values were taken as a priori from the VTRF2003 and EOP(IERS) C 04 solutions. In total, the obtained extension of Celestial Reference Frame consists of positions of 2028 radio sources. 1. CONSTRUCTION OF EXTENDED CELESTIAL REFERENCE FRAME In common practice of Very Long Baseline Interferometry (VLBI) observations a set of determined radio sources are used. These 667 radio sources from ICRF-Ext.1 catalogue are defining the realization of the International Celestial Reference System (IERS, 1999). However, there are VLBI experiments which are aimed on observing and determining positions of new radio sources (Beasley at al., 2002). Available geodetic VLBI observations contain about 2300 radio sources. Most of them were observed during one or two sessions, and, usually, these sessions are not suitable for determining TRF, CRF and EOP in common solution due to geometry of network. In order to extend the Celestial Reference Frame on these rarely observed radio sources we fixed Terrestrial Reference Frame (TRF) by the values from VTRF2003 catalogue, the motion of the Celestial Intermediate Pole (CIP) in TRF by the EOP(IERS) C 04 solution and the motion of the CIP in Celestial Reference Frame by the model of IAU-2000A Nutation-Precession Theory. 2. OBSERVATIONS AND ANALYSIS Almost all available VLBI observations, which were conducted since begin of 1992 till the end of August 2004 were processed. In total, 3,830,124 dual frequency delays acquired on 1,911 VLBI sessions were analyzed. Observations of 2256 radio sources were carried out by 72 stations. Data analysis was performed by the software SteelBreeze. Coordinates of radio sources were estimated as global parameters. Station clock function, wet zenith delay and its gradients were estimated as the stochastic ones. VLBI data processing was performed according to models which are described in IERS Conventions (2003): the IAU-2000A Nutation-Precession Theory with non-rotating origin procedure was applied for transformation between CRF and TRF; hydrostatic zenith delays were modeled

Cited by 0

Status of the Celestial Reference Frame

Mignard, Francois · Zenodo (CERN European Organization for Nuclear Research) · 2022

Since the advent of the ICRF1 in 1998 as the formal realisation of the ICRS, the successive solutions (ICRF2, ICRF3) have been produced from VLBI astrometric observations of distant compact sources in the radio domain. Originally in the S/X-band, this was recently extended with independent solutions in the K- and X/Ka-bands, allowing already to see systematic differences, probably not all linked to the change of the emission centre with the wavelength. This choice of a solution in the radio domain, was not imposed by ICRS prescriptions, but just a contingent temporary situation when only the VLBI technique was in position to reach a sub-mas astrometric accuracy for this realisation, widely outperforming the available optical astrometry. As expected this has dramatically changed in the recent years with the optical realisations achieved with the Gaia spacecraft released in 2018 and 2021. An IAU resolution in September 2021 has now recognised the availability multiple solutions and redefined the fundamental reference frame accordingly.<br> I will present in parallel the main properties of these solutions, together with the key issues that have emerged from their comparisons. We see now plain differences that clearly won't be resolved by more accurate solutions and give evidence of positional difference in a large fraction of the common sources, to such an extent that one must select strict procedures to ensure that these frames have compatible fundamental planes and origins.

Cited by 0Open access

Vienna Celestial Reference Frame S/X 2022

Krasna, Hana · TU Wien Research Data · 2023

Global Celestial Reference Frame estimated from Very Long Baseline Interferometry (VLBI) observations at the Vienna International VLBI Service for Geodesy and Astrometry (IVS) Analysis Center (VIE) at the standard geodetic and astrometric radio frequencies 2.3 and 8.4 GHz (S/X band). Data span: 1979.5 - 2023.0 VIE2022-sx global solution computed with VieVS (Vienna VLBI and Satellite Software)

Cited by 0Open access

Blazars define a stable celestial reference frame

N.J. Secrest, S. Lambert · Springer Link (Chiba Institute of Technology) · 2026

Context. Recent work has shown that optical-radio position offsets and radio position variability are inversely correlated with the optical photometric variability of active galactic nuclei (AGN). A key prediction of these findings is that a reference frame constructed using highly photometrically variable AGN should be more stable than a frame that does not account for variability and that photometric variability can be used to optimally weight all sources in order to maximize frame stability. Aims. To test this prediction by determining the stability of reference frames constructed using sources selected on photometric variability. Methods. Using ICRF3 matched to Gaia DR3, we employed a bootstrap method to estimate the multi-epoch stability of frames constructed using AGN selected at varying levels of photometric variability. We fit vector spherical harmonics to the coordinate differences between the three ICRF3 frames (S/X, K, and X/Ka) and Gaia DR3 and quantified the statistical dispersion as a function of blazar-like (high variability), quasar-like (low variability), and intermediate-variability class. Results. An S/X reference frame constructed using blazars exceeds the stability of a frame constructed with quasars by a factor of 6 and is twice as stable as the ICRF3 defining sources. At K and X/Ka, a blazar-based frame matches or exceeds the stability of the defining sources by a factor of 1.4 in the case of X/Ka and exceeds the stability of a frame based on quasars by over a factor of 2 in both cases. The smaller improvement at K and X/Ka is likely arises because sources selected at higher frequency are more likely to be blazars. We derived a variability-based astrometric covariance scaling method that results in factor of 2 reduction in frame distortions and instabilities between ICRF3 S/X and Gaia DR3, with a mild improvement for ICRF3 K but no difference for ICRF3 X/Ka, which is dominated by known distortions. Conclusions. A celestial reference frame defined using blazars is likely to be stable over time. This confirms the prediction that an optimal weighting of the link between the optical and radio celestial reference frames is enabled by accounting for photometric variability.

Cited by 0Open access

The Celestial Reference Frame Defined by VLBI

Chao Ma, D. B. Shaffer · Symposium - International Astronomical Union · 1988

VLBI currently produces the most accurate positions of celestial objects. From 1979 to 1987, 114 extragalactic radio sources have been observed with dual-frequency Mark III VLBI as part of the NASA Crustal Dynamics Project and the NGS POLARIS/IRIS program. The formal statistical errors of conventional celestial coordinates are as small as 0.3 milliarcseconds. The fundamental quantity measured by VLBI is the arc length between radio sources. Thus, we suggest that VLBI be used to establish a coordinate reference frame based solely on radio positions, and that this system not necessarily be coupled to right ascension and declination.

Cited by 2Open access

Blazars define a stable celestial reference frame

Nathan J. Secrest, Sebastien Lambert · arXiv (Cornell University) · 2026

Recent work has shown that optical-radio position offsets and radio position variability are inversely correlated with the photometric variability of active galactic nuclei (AGN). A key prediction of these findings is that a reference frame constructed using highly photometrically variable AGN should be more stable than a frame that does not account for variability and that variability can be used to optimally weight all sources in order to maximize frame stability. Using ICRF3 matched to Gaia DR3, we employed a bootstrap method to estimate the multi-epoch stability of frames constructed using AGN selected at varying levels of photometric variability. We fit vector spherical harmonics to the coordinate differences between the three ICRF3 frames (S/X, K, and X/Ka) and Gaia and quantified the statistical dispersion as a function of blazar-like (high variability), quasar-like (low variability), and intermediate-variability class. An S/X reference frame constructed using blazars exceeds the stability of a frame constructed with quasars by a factor of 6 and is twice as stable as the ICRF3 defining sources. At K and X/Ka, a blazar-based frame matches or exceeds the stability of the defining sources by a factor of 1.4 in the case of X/Ka and exceeds the stability of a frame based on quasars by over a factor of 2 in both cases. The smaller improvement at K and X/Ka is likely because sources selected at higher frequency are more likely to be blazars. We derived a variability-based astrometric covariance scaling method that results in factor of 2 reduction in frame distortions and instabilities between S/X and Gaia, with a mild improvement for K but no difference for X/Ka, which is dominated by known distortions. Our results confirm the prediction that an optimal weighting of the link between the optical and radio celestial reference frames is enabled by accounting for photometric variability.

Cited by 0Open access

Blazars define a stable celestial reference frame

Nathan J. Secrest, Sebastien Lambert · ArXiv.org · 2026

Recent work has shown that optical-radio position offsets and radio position variability are inversely correlated with the photometric variability of active galactic nuclei (AGN). A key prediction of these findings is that a reference frame constructed using highly photometrically variable AGN should be more stable than a frame that does not account for variability and that variability can be used to optimally weight all sources in order to maximize frame stability. Using ICRF3 matched to Gaia DR3, we employed a bootstrap method to estimate the multi-epoch stability of frames constructed using AGN selected at varying levels of photometric variability. We fit vector spherical harmonics to the coordinate differences between the three ICRF3 frames (S/X, K, and X/Ka) and Gaia and quantified the statistical dispersion as a function of blazar-like (high variability), quasar-like (low variability), and intermediate-variability class. An S/X reference frame constructed using blazars exceeds the stability of a frame constructed with quasars by a factor of 6 and is twice as stable as the ICRF3 defining sources. At K and X/Ka, a blazar-based frame matches or exceeds the stability of the defining sources by a factor of 1.4 in the case of X/Ka and exceeds the stability of a frame based on quasars by over a factor of 2 in both cases. The smaller improvement at K and X/Ka is likely because sources selected at higher frequency are more likely to be blazars. We derived a variability-based astrometric covariance scaling method that results in factor of 2 reduction in frame distortions and instabilities between S/X and Gaia, with a mild improvement for K but no difference for X/Ka, which is dominated by known distortions. Our results confirm the prediction that an optimal weighting of the link between the optical and radio celestial reference frames is enabled by accounting for photometric variability.

Cited by 0Open access