Reconsidering the Galactic coordinate system

Liu, Jiacheng; Zhu, Zi; Zhang, Hong

doi:10.1051/0004-6361/201014961

Cited by 11 publications

(14 citation statements)

References 33 publications

(37 reference statements)

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“…′′ 7043 are the positional angle and north Galactic pole equatorial coordinates defining the Galactic frame orientation while R x and R z denote the rotation with respect to OX and OZ axes respectively. See Liu et al (2011) for a recent discussion on the Galactic frame orientation.…”

Section: Units Definitions Reference Framesmentioning

confidence: 99%

On the accuracy of close stellar approaches determination

Dybczyński

Berski

2015

Monthly Notices of the Royal Astronomical Society

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The aim of this paper is to demonstrate the accuracy of our knowledge of close stellar passage distances in the pre-GAIA era. We used the most precise astrometric and kinematic data available at the moment and prepared a list of 40 stars nominally passing (in the past or future) closer than 2 pc from the Sun. We used a full gravitational potential of the Galaxy to calculate the motion of the Sun and a star from their current positions to the proximity epoch. For this calculations we used a numerical integration in rectangular, Galactocentric coordinates. We showed that in many cases the numerical integration of the star motion gives significantly different results than popular rectilinear approximation. We found several new stellar candidates for close visitors in past or in future.We used a covariance matrices of the astrometric data for each star to estimate the accuracy of the obtained proximity distance and epoch. To this aim we used a Monte Carlo method, replaced each star with 10 000 of its clones and studied the distribution of their individual close passages near the Sun. We showed that for contemporary close neighbours the precision is quite good but for more distant stars it strongly depends on the quality of astrometric and kinematic data. Several examples are discussed in detail, among them the case of HIP 14473. For this star we obtained the nominal proximity distance as small as 0.22 pc 3.78 Myr ago. However there exist strong need for more precise astrometry of this star since the proximity point uncertainty is unacceptably large.

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Section: Units Definitions Reference Framesmentioning

confidence: 99%

On the accuracy of close stellar approaches determination

Dybczyński

Berski

2015

Monthly Notices of the Royal Astronomical Society

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“…Analysis of systematic differences in the galactic coordinates allows us to find the discrepancies between the galactic coordinate frames, which are implemented by various catalogues. In this connection, we estimated that the orientation angles of the XPM and UCAC4 galactic frames did not exceed 10 mas, while the new versions of the galactic coordinate system are believed to deviate from the standard version introduced by IAU in 1958 at few minutes of arc (Liu, Zhu, & Hu, ; Liu, Zhu, & Zhang, ). For this reason, it can be said that the differences of the XPM and UCAC4 galactic coordinate frames are negligible compared to the precision of the current galactic coordinate system.…”

Section: Discussionmentioning

confidence: 96%

“…There is reason to believe (Liu, Zhu, & Hu, ; Liu, Zhu, & Zhang, ) that the accuracy of fixing the axes of the standard galactic coordinate system MAS 1958 (Blaauw et al, ) was done within a few minutes of arc. Therefore, we can say that the orientations of the XPM and UCAC4 galactic axes are virtually identical, since the differences found (although they have a high statistical reliability) are significantly less than the precision of the standard galactic reference frame.…”

Section: Analysis Of the Xpm−ucac4 Coordinate Systematic Differencesmentioning

confidence: 99%

“…The currently used galactic coordinate system was introduced by the International Astronomical Union in 1958 (Blaauw, Gum, Pawsey, & Westerhout, ) based on a study of the distribution of neutral hydrogen in the galaxy. In recent papers (Liu, Zhu, & Hu, ; Liu, Zhu, & Zhang, ), the problem is posed of improving the galactic coordinate system by identifying the galactic plane with new observational data on the coordinates of the various objects in the infrared range of the catalogue 2MASS (Skrutskie, Cutri, & Stiening, ) and radio frequency (Vollmer et al, ). All of these motivate the study of different implementations of the galactic coordinate system.…”

Section: Introductionmentioning

confidence: 99%

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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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“…Starting from the J2000.0 system, Liu et al (2011) derived the GalCS in the ICRS by using the bias matrix B, and the authors also tentatively proposed a new definition of the GalCS using the position of the compact radio source Sagittarius A* (Sgr A*). They only used a single observation of the GC (ICRS position of Sgr A*) to construct a new coordinate system, failing to using other data to ensure that this revised definition is the optimal choice.…”

Section: Introductionmentioning

confidence: 99%

Constructing a Galactic coordinate system based on near-infrared and radio catalogs

Liu

Zhu

2011

A&A

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Context. The definition of the Galactic coordinate system was announced by the IAU Sub-Commission 33b on behalf of the IAU in 1958. An unrigorous transformation was adopted by the Hipparcos group to transform the Galactic coordinate system from the FK4-based B1950.0 system to the FK5-based J2000.0 system or to the International Celestial Reference System (ICRS). For more than 50 years, the definition of the Galactic coordinate system has remained unchanged from this IAU1958 version. On the basis of deep and all-sky catalogs, the position of the Galactic plane can be revised and updated definitions of the Galactic coordinate systems can be proposed. Aims. We re-determine the position of the Galactic plane based on modern large catalogs, such as the Two-Micron All-Sky Survey (2MASS) and the SPECFIND v2.0. This paper also aims to propose a possible definition of the optimal Galactic coordinate system by adopting the ICRS position of the Sgr A* at the Galactic center. Methods. The near-infrared 2MASS point source catalog and the SPECFIND v2.0 catalog of radio continuum spectra are used to determine the mean position of the Galactic plane on the celestial sphere. By fitting the data to an ideal Galactic equator, the parameters defining the Galactic coordinate system are obtained. Results. We find that the obliquity of the Galactic equator on the ICRS principal plane is about 0.4 • (2MASS) and 0.6 • (SPECFIND v2.0) larger than the J2000.0 value, which is widely used in coordinate transformations between the equatorial (α, δ) and the Galactic ( , b). Depending on the adopted parameters, data, and methods, the largest difference between the resulting Galactic coordinate systems is several arcminutes. We derive revised transformation matrices and parameters describing the orientation of the Galactic coordinate systems in the ICRS at the 1 milliarcsecond level to match the precision of modern observations. Conclusions. For practical applications, we propose that a revised definition of the Galactic coordinate system should be required in the near future.

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Reconsidering the Galactic coordinate system

Cited by 11 publications

References 33 publications

On the accuracy of close stellar approaches determination

On the accuracy of close stellar approaches determination

Comparison of XPM and UCAC4 catalogues in the galactic coordinate system

Constructing a Galactic coordinate system based on near-infrared and radio catalogs

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