The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry

Fey, A. L.; Gordon, D.; Jacobs, Christopher S.; Ma, C.; Gaume, R. A.; Arias, E. F.; Bianco, G. Lo; Boboltz, D. A.; Böckmann, S.; Bolotin, S.; Charlot, P.; Collioud, A.; Engelhardt, G.; Gipson, John; Gontier, A. M.; Heinkelmann, Robert; Kurdubov, S.; Lambert, S. B.; Lytvyn, S. O.; MacMillan, D. S.; Malkin, Zinovy; Nothnagel, A.; Ojha, R.; Skurikhina, E.; Sokolova, Julia; Souchay, J.; Sovers, O. J.; Tesmer, V; Titov, Oleg; Wang, Gang; Zharov, V. E.

doi:10.1088/0004-6256/150/2/58

Cited by 293 publications

(252 citation statements)

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“…The current physical realisation of the ICRS at radio wavelengths is ICRF2 (Ma et al 2009;Fey et al 2015), which contains precise VLBI positions of 3414 compact radio sources, of which 295 are defining sources. Among the sources in the auxiliary quasar solution (Sect.…”

Section: Alignment To the Icrfmentioning

confidence: 99%

GaiaData Release 1

Lindegren

Lammers

Bastian

et al. 2016

A&A

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579

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Context. Gaia Data Release 1 (DR1) contains astrometric results for more than 1 billion stars brighter than magnitude 20.7 based on observations collected by the Gaia satellite during the first 14 months of its operational phase. Aims. We give a brief overview of the astrometric content of the data release and of the model assumptions, data processing, and validation of the results. Results. For about two million of the brighter stars (down to magnitude ∼11.5) we obtain positions, parallaxes, and proper motions to Hipparcostype precision or better. For these stars, systematic errors depending for example on position and colour are at a level of ±0.3 milliarcsecond (mas). For the remaining stars we obtain positions at epoch J2015.0 accurate to ∼10 mas. Positions and proper motions are given in a reference frame that is aligned with the International Celestial Reference Frame (ICRF) to better than 0.1 mas at epoch J2015.0, and non-rotating with respect to ICRF to within 0.03 mas yr −1 . The Hipparcos reference frame is found to rotate with respect to the Gaia DR1 frame at a rate of 0.24 mas yr −1 . Conclusions. Based on less than a quarter of the nominal mission length and on very provisional and incomplete calibrations, the quality and completeness of the astrometric data in Gaia DR1 are far from what is expected for the final mission products. The present results nevertheless represent a huge improvement in the available fundamental stellar data and practical definition of the optical reference frame.

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Section: Alignment To the Icrfmentioning

confidence: 99%

GaiaData Release 1

Lindegren

Lammers

Bastian

et al. 2016

A&A

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579

392

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“…The second realisation of the ICRF contains radio loud quasars observed with very long baseline interferometry (VLBI) over a period of up to 30 years (Ma et al 2009;Fey et al 2015). ICRF2 contains the precise position of 3414 compact radio sources and comes with an accuracy floor of 40 microarcsec (µas) in each coordinate for the whole set.…”

Section: Radio Positions Of Icrf Sourcesmentioning

confidence: 99%

“…In this section we compare the optical positions of the ICRF sources, as obtained in the Gaia auxiliary quasar solution, with their reference values in the radio domain taken from ICRF2 (Fey et al 2015). Coordinate differences in right ascension and declination are computed as…”

Section: Comparison Of the Optical And Radio Positionsmentioning

confidence: 99%

GaiaData Release 1

Mignard

Klioner

Lindegren

et al. 2016

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Context. As part of the data processing for Gaia Data Release 1 (Gaia DR1) a special astrometric solution was computed, the so-called auxiliary quasar solution. This gives positions for selected extragalactic objects, including radio sources in the second realisation of the International Celestial Reference Frame (ICRF2) that have optical counterparts bright enough to be observed with Gaia. A subset of these positions was used to align the positional reference frame of Gaia DR1 with the ICRF2. Although the auxiliary quasar solution was important for internal validation and calibration purposes, the resulting positions are in general not published in Gaia DR1. Aims. We describe the properties of the Gaia auxiliary quasar solution for a subset of sources matched to ICRF2, and compare their optical and radio positions at the sub-mas level. Methods. Descriptive statistics are used to characterise the optical data for the ICRF sources and the optical-radio differences. The most discrepant cases are examined using online resources to find possible alternative explanations than a physical optical-radio offset of the quasars. Results. In the auxiliary quasar solution 2191 sources have good optical positions matched to ICRF2 sources with high probability. Their formal standard errors are better than 0.76 milliarcsec (mas) for 50% of the sources and better than 3.35 mas for 90%. Optical magnitudes are obtained in Gaia's unfiltered photometric G band. The Gaia results for these sources are given as a separate table in Gaia DR1. The comparison with the radio positions of the defining sources shows no systematic differences larger than a few tenths of a mas. The fraction of questionable solutions, not readily accounted for by the statistics, is less than 6%. Normalised differences have extended tails requiring case-by-case investigations for around 100 sources, but we have not seen any difference indisputably linked to an optical-radio offset in the sources. Conclusions. With less than a quarter of the data expected from the nominal mission it has been possible to obtain positions at the sub-mas level for most of the ICRF sources having an optical counterpart brighter than 20.5 mag.

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“…(5) in Lindegren et al (2016), as performed in the alignment between ICRF1 and ICRF2 (Fey et al 2015). As such, the equation for alignment can be written as (e.g.…”

Section: Overall Property Of the Auxiliary Quasar Solutionmentioning

confidence: 99%

Overall properties of theGaiaDR1 reference frame

Liu

Zhu

Liu

et al. 2017

A&A

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Aims. The first Gaia data release (Gaia DR1) provides 2 191 ICRF2 sources with their positions in the auxiliary quasar solution and five astrometric parameters -positions, parallaxes, and proper motions -for stars in common between the Tycho-2 catalogue and Gaia in the joint Tycho-Gaia astrometric solution (TGAS). We aim to analyze the overall properties of Gaia DR1 reference frame. Methods. We compare quasar positions of the auxiliary quasar solution with ICRF2 sources using different samples and evaluate the influence on the Gaia DR1 reference frame owing to the Galactic aberration effect over the J2000.0-J20015.0 period. Then we estimate the global rotation between TGAS with Tycho-2 proper motion systems to investigate the property of the Gaia DR1 reference frame. Finally, the Galactic kinematics analysis using the K-M giant proper motions is performed to understand the property of Gaia DR1 reference frame.Results. The positional comparison between the auxiliary quasar solution and ICRF2 shows negligible orientation and validates the declination bias of ∼−0.1 mas in Gaia quasar positions with respect to ICRF2. Galactic aberration effect is thought to cause an offset ∼0.01 mas of the Z axis direction of Gaia DR1 reference frame. The global rotation between TGAS and Tycho-2 proper motion systems, obtained by different samples, shows a much smaller value than the claimed value 0.24 mas yr −1 . For the Galactic kinematics analysis of the TGAS K-M giants, we find possible non-zero Galactic rotation components beyond the classical Oort constants: the rigid part ω Y G = −0.38±0.15 mas yr −1 and the differential part ω ′ Y G = −0.29±0.19 mas yr −1 around the Y G axis of Galactic coordinates, which indicates possible residual rotation in Gaia DR1 reference frame or problems in the current Galactic kinematical model. Conclusions. The Gaia DR1 reference frame is well aligned to ICRF2, and the possible influence of the Galactic aberration effect should be taken into consideration for the future Gaia-ICRF link. The cause of the rather small global rotation between TGAS and Tycho-2 proper motion systems is unclear and needs further investigation. The possible residual rotation in Gaia DR1 reference frame inferred from the Galactic kinematic analysis should be noted to and examined in future data release.

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The Second Realization of the International Celestial Reference Frame by Very Long Baseline Interferometry

Cited by 293 publications

References 28 publications

GaiaData Release 1

GaiaData Release 1

GaiaData Release 1

Overall properties of theGaiaDR1 reference frame

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