Residual HCRF rotation relative to the inertial coordinate system

Бобылев, В. В.

doi:10.1134/s1063773715040039

Cited by 5 publications

(3 citation statements)

References 50 publications

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“…It is evident that a non-zero residual spin of the HCRF with respect to the ICRF introduces a systematic error in the Hipparcos proper motions. Depending on the orientation and on the magnitude of the spin vector, the associated systematic proper motions can interfere or amplify a warp signature and must therefore be investigated and taken into account (Abedi et al 2015;Bobylev 2010Bobylev , 2015. In the following section, when modelling the HIP2 sample, we consider the effects of such a possible spin, adding the resulting systematic proper motions to the simulated catalogues following Equation 18 of Lindegren & Kovalevsky (1995), and using the residual spin vector (ω x , ω y , ω z ) (−0.126, +0.185, +0.076) mas yr −1 as measured by Gaia (Lindegren et al 2016).…”

Section: Kinematicsmentioning

confidence: 99%

The kinematic signature of the Galactic warp inGaiaDR1

Poggio

Drimmel

Smart

et al. 2017

A&A

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Context. The mechanism responsible for the warp of our Galaxy, as well as its dynamical nature, continues to remain unknown. With the advent of high precision astrometry, new horizons have been opened for detecting the kinematics associated with the warp and for constraining possible warp formation scenarios for the Milky Way. Aims. The aim of this contribution is to establish whether the first Gaia data release (DR1) shows significant evidence of the kinematic signature expected from a long-lived Galactic warp in the kinematics of distant OB stars. As the first paper in a series, we present our approach for analyzing the proper motions and apply it to the subsample of Hipparcos stars. Methods. We select a sample of 989 distant spectroscopically-identified OB stars from the new reduction of Hipparcos, of which 758 are also in the first Gaia data release (DR1), covering distances from 0.5 to 3 kpc from the Sun. We develop a model of the spatial distribution and kinematics of the OB stars from which we produce the probability distribution functions of the proper motions, with and without the systematic motions expected from a long-lived warp. A likelihood analysis is used to compare the expectations of the models with the observed proper motions from both Hipparcos and Gaia DR1. Results. We find that the proper motions of the nearby OB stars are consistent with the signature of a kinematic warp, while those of the more distant stars (parallax <1 mas) are not. Conclusions. The kinematics of our sample of young OB stars suggests that systematic vertical motions in the disk cannot be explained by a simple model of a stable long-lived warp. The warp of the Milky Way may either be a transient feature, or additional phenomena are acting on the gaseous component of the Milky Way, causing systematic vertical motions that are masking the expected warp signal. A larger and deeper sample of stars with Gaia astrometry will be needed to constrain the dynamical nature of the Galactic warp.

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Section: Kinematicsmentioning

confidence: 99%

The kinematic signature of the Galactic warp inGaiaDR1

Poggio

Drimmel

Smart

et al. 2017

A&A

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“…where µ α * = (dα/dt) cos δ, µ δ = dδ/dt are the components of the proper motion in frame C and μα * = (d α/dt) cos δ, μδ = d δ/dt the components in C. In the small-angle approximation one can use either set of coordinates, (α, δ) or ( α, δ), for the trigonometric factors in ( 6)-( 9); the choice made here is arbitrary. The use of equations such as ( 6)-( 9) for estimating the difference in orientation and spin between two astrometric catalogues is since many years well established in the literature (among many others, e.g., Fricke 1977;Froeschle & Kovalevsky 1982;Arias et al 1988;Brosche et al 1991;Lestrade et al 1995;Zhu 2000;Metz & Geffert 2004;Fedorov et al 2011;Bobylev 2015). To estimate the difference in spin (ω) the typical procedure has been to set up Eqs.…”

Section: Differences In Position and Proper Motionmentioning

confidence: 99%

The Gaia reference frame for bright sources examined using VLBI observations of radio stars

Lindegren

2019

A&A

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Context. Positions and proper motions of Gaia sources are expressed in a reference frame that ideally should be non-rotating relative to distant extragalactic objects, coincident with the International Celestial Reference System (ICRS), and consistent across all magnitudes. For sources fainter than 16th magnitude this is achieved thanks to Gaia's direct observations of quasars. At brighter magnitudes it is difficult to validate the quality of the reference frame due to the scarcity of comparison data. Aims. The aim of this paper is to examine the use of VLBI observations of radio stars to determine the spin and orientation of the bright reference frame of the current and future Gaia data releases. Methods. Simultaneous estimation of the six spin and orientation parameters makes optimal use of VLBI data and makes it possible to include even single-epoch VLBI observations in the solution. The method is applied to Gaia Data Release 2 (DR2) using published VLBI data for 41 radio stars.Results. The VLBI data for the best-fitting 26 sources indicate that the bright reference frame of Gaia DR2 is rotating relative to the faint quasars at a rate of about 0.1 mas yr −1 , significant at 2σ level. This supports a similar conclusion based on a comparison with stellar positions in the Hipparcos frame. The accuracy is currently limited by the small number of radio sources included in the solution, by uncertainties in the Gaia DR2 proper motions, and by issues related to the astrophysical nature of the radio stars. Conclusions. While the origin of the indicated rotation is understood and can be avoided in future data releases, it remains important to validate the bright reference frame of Gaia by independent observations. This can be achieved using VLBI astrometry, which may require re-observing the old sample of radio stars as well as measuring new objects. The unique historical value of positional measurements is stressed and VLBI observers are urged to ensure that relevant positional information is preserved for the future.

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“…Although quasars and galaxies can theoretically provide a basis for the construction of inertial reference systems, the difference in the specific observations of these objects may lead to systematic differences in the proper motions of stars (especially regarding the magnitude equation). The use of all currently available observational data suggests that the residual rotation of the HCRF system is determined with an error of 0.1 mas/year (Bobylev, ).…”

Section: Introductionmentioning

confidence: 99%

Comparison of XPM and UCAC4 catalogues in the galactic coordinate system

et al. 2017

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This paper presents the results of the comparison of the galactic reference frames realized by the catalogues XPM and UCAC4. Based on about 40 million stars common to both catalogues, the systematic differences of the galactic coordinates and proper motions have been derived for 12 magnitudes in 0.5 m width bins with the mean J-values from 10 m .25 to 15 m .75. The systematic differences were represented by vector spherical harmonics, with the magnitude equation taken into consideration. The mutual orientation of the frames was found to be at the level of 10 mas. It is concluded that these differences are negligible in comparison with the accuracy of the implementation of the standard galactic coordinate system MAS 1958. We investigated two features of the XPM catalogue. First, unlike the HCRF and UCAC4 catalogues, whose proper motions are tied to the quasars and galaxies, the XPM catalogue implements a reference system based only on galaxies. Second, the XPM catalogue has two systems of proper motions-XPM x and XPM p , referred to the two galaxy sub-catalogues of the project 2MASS-PSC and XSC. The study of the differences XPM x −XPM p showed that they are free of the magnitude equation. The speed of relative rotation of XPM x over XPM p was found to be = 0.453 ± 0.003 mas/year, which exceeds the residual rotation of the HCRF (0.25 mas/year). Analysis of systematic differences XPM x −UCAC4 and XPM p −UCAC4 showed that both frames XPM x and XPM p have an appreciable rotation speed relative to the UCAC4 (hence the ICRF), especially large (up to 2 mas/year) for the brightest stars in our range. This shows that a relatively high speed of rotation of the two frames XPM x and XPM p with respect to the UCAC4 is a consequence of the transition from a combined "quasar-galaxy" to a purely "galactic" reference system. It is shown that the systematic difference between the proper motions of stars can be interpreted within the Ogorodnikov-Milne kinematic model of the velocity field. 489 t 1,0,1,0 −26.75 ± 0.65 t 3,3,0,1 −3.44 ± 0.76 t 5,5,0,0 12.97 ± 0.65 t 1,1,0,0 −22.86 ± 0.69 t 3,3,0,2 1.71 ± 0.75 t 5,5,0,1 −4.83 ± 0.76 t 1,1,0,1 −1.30 ± 0.76 t 3,3,1,0 8.79 ± 0.66 t 6,3,0,0 5.41 ± 0.72 t 1,1,0,2 2.81 ± 0.75 t 4,3,1,0 6.86 ± 0.65 t 6,3,0,1 −1.93 ± 0.79 t 1,1,1,0 18.71 ± 0.66 t 4,3,1,1 −4.10 ± 0.76 t 6,3,0,2 2.24 ± 0.78 t 2,0,1,0 −11.05 ± 0.65 t 5,0,1,0 −9.27 ± 0.69 t 6,5,0,0 3.71 ± 0.65 t 2,1,0,0 27.92 ± 0.69 t 5,0,1,1 6.08 ± 0.76 t 6,5,0,1 −4.97 ± 0.76 t 2,1,0,1 2.18 ± 0.90 t 5,0,1,2 −1.82 ± 0.75 t 6,6,0,0 −5.66 ± 0.69 t 2,1,0,2 −4.63 ± 0.75 t 5,1,0,0 13.97 ± 0.71 t 6,6,0,1 5.46 ± 0.76 t 2,1,0,3 −2.67 ± 0.79 t 5,1,0,1 −5.58 ± 0.82 t 6,6,0,2 −2.40 ± 0.75 t 2,1,1,0 −18.42 ± 0.65 t 5,1,1,0 −6.21 ± 0.76 t 8,4,1,0 4.69 ± 0.65 t 2,1,1,1 −2.36 ± 0.76 t 5,2,0,0 −10.70 ± 0.74 t 8,6,1,0 7.46 ± 0.65 t 2,2,0,0 −35.89 ± 0.69 t 5,2,0,1 6.19 ± 0.86 t 8,6,1,1 −4.14 ± 0.76 t 2,2,0,2 2.15 ± 0.75 t 5,2,1,0 −7.66 ± 0.69 t 8,7,1,0 −6.30 ± 0.65 t 2,2,1,0 −16.97 ± 0.66 t 5,2,1,1 4.66 ± 0.76 t 8,7,1,1 2.15 ± 0.76 t 2,2,1,1 2.42 ± 0.76 t 5,2,1,2 −...

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Residual HCRF rotation relative to the inertial coordinate system

Cited by 5 publications

References 50 publications

The kinematic signature of the Galactic warp inGaiaDR1

The kinematic signature of the Galactic warp inGaiaDR1

The Gaia reference frame for bright sources examined using VLBI observations of radio stars

Comparison of XPM and UCAC4 catalogues in the galactic coordinate system

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