Overall properties of theGaiaDR1 reference frame

Abstract

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.

Possible systematics in the VLBI catalogs as seen from Gaia

“…From the column dz in Table 2, one can clearly find a significant bias in both ICRF2 and gsf2016a catalogs. The bias was estimated to be of 78 ∼ 152 µas between ICRF2 and Gaia DR1 catalogs, which agrees with the declination bias of about −0.1 mas as reported in Mignard et al (2016) and later confirmed in our previous work (Liu et al 2017). For gsf2016a, dz was estimated to be smaller in comparison, strictly beneath 100 µas for all five groups, especially for the "Defining" group which yielded zero bias.…”

“…Comparing the results of different groups in the same catalog, however, some inconsistencies are presented. For the ICRF2 catalog, the relative orientation angles for groups "North" and "South" have opposite signs, as found in Liu et al (2017). Using the new gsf2016a data, we attained similar results, indicating that there are possible zonal deformations between VLBI and Gaia DR1 catalogs.…”

Kinematic Properties of Open Star Clusters with Data from the Gaia DR2 Catalogue

“…Indeed, the mean distance for the sample of stars used in obtaining the solution (6) is 2.0 kpc; then ω 1 = 0.051 ± 0.016 mas yr −1 and ω 2 = 0.034 ± 0.021 mas yr −1 . We see that here ω 2 differs from the result of Liu et al (2017) by an order of magnitude.…”

“…Liu et al (2017) performed a kinematic analysis of ∼23 000 K-M giants from the TGAS catalogue(Brown et al 2016) based on the Ogorodnikov-Milne model and found a nonzero component ω 2 = −0.38 ± 0.15 mas yr −1 (rotation around the Galactic y axis). They interpreted this as a possible residual rotation in the TGAS frame or the presence of problems in the kinematic model.…”

A Review of Surface Treatments for Sliding Bearings Used at Different Temperature

“…However, there are few research materials on self-lubricating coatings in China. In the year of 1983, the first MoS 2 self-lubricating coatings prepared by liquid dope was studied by Liu of the Institute of Coatings, however, the coatings were not applied to sliding bearings [38]. The sliding bearing surface coating technology of China started late, and it is still a new technology.…”