Systematic effect of the Galactic aberration on the ICRS realization and the Earth orientation parameters

Zhu

et al. 2017

A&A

Self Cite

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.

Section: Overall Property Of the Auxiliary Quasar Solutionmentioning

confidence: 99%

Overall properties of theGaiaDR1 reference frame

Zhu

et al. 2017

A&A

Self Cite

“…See discussion in Sect. 3.2. v. The effect from Galactic aberration (Liu et al 2012). The Galactic aberration in proper motions is caused by the acceleration of the solar system barycenter (SSB) toward the Galactic center, which induces global rotation of the ICRS depending on the distribution of sources.…”

Section: Upgraded Contributions To the Precession Ratesmentioning

confidence: 99%

Evaluation of a possible upgrade of the IAU 2006 precession

Capitaine

2017

A&A

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Context. The International Astronomical Union (IAU) adopted a new precession model at its 2006 General Assembly. After more than ten years since the publication of the so-called IAU 2006 precession, we have noticed progress in solar system ephemerides and geophysical observations, which can be used to refine the precession model. Another progress is the increase by 30% since 2003, of the length of the very long baseline interferometry (VLBI) observations to be compared with the theoretical model. Results. For the precession of the ecliptic, the changes in the new solutions with respect to the IAU 2006 are about several tens of microarcseconds in the linear terms of P A and Q A . The upgraded precession of the equator is such that the quadratic and cubic terms in the quantity ψ A differ significantly from IAU 2006 due to the revised J 2 model. The statistics of the VLBI celestial pole offsets and least squares fits with different empirical models, show that the LC precession is slightly more consistent with the VLBI observations, but the improvement relative to the IAU 2006 model is not definitely convincing at present. Conclusions. The upgraded LC precession obtained with the latest theoretical and observational improvements has shown some advantages with respect to the IAU 2006 model. However, due to negligible changes in the precession of the ecliptic and large uncertainties in the J 2 variation, we recommend that the standard IAU 2006 model be retained for practical use and continuity reason. The next precession-nutation model should be constructed with a uniform dynamical approach in the framework of ICRF3 and Gaia reference frame and without the use of a conventional ecliptic.

Mon. Not. R. Astron. Soc.

“…The mean declination of subset is one of assessing indexes for such purposes. Liu et al (2012) provided an approximate approach to assess uniformity of source distribution. In that method, a dipolar vector field is generated based on the coordinates of sources with certain amplitude (e.g 5 µas yr −1 ), then global rotation vector g g g is obtained with an unweighted least square fit.…”

Section: Considerations Of the Sky Distributionmentioning

confidence: 99%

Test of source selection for constructing a more stable and uniform celestial reference frame

Zhu¹

2016

Self Cite

We aim to evaluate the possibility of improving the ICRS realization starting from the ICRF2 catalogue by investigating the coordinate time series of radio sources observed by VLBI between 1979 and 2016. Sources with long observational history are selected as the candidates and the least squares fits with special handling of the weights are performed to derive the linear drifts of the source coordinates. Then the sources are sorted based on the normalized linear drift (i) over the whole sky and (ii) in four homolographic areas divided by declinations. The axial stability of the reference system and sky distribution defined by the selected sources are evaluated, which are acted as the criterion for the final source lists. With our improved source selection scheme, two groups of sources are proposed and considered suitable for defining a more stable and homogeneous celestial reference system compared to the current ICRF2. The number of sources in the final lists are 323 and 294, respectively, and the global rotation of the axes derived from apparent motion of the sources are about two times better than the ICRF2.