scholarly journals The Gaia reference frame for bright sources examined using VLBI observations of radio stars (Corrigendum)

2020 ◽  
Vol 637 ◽  
pp. C5 ◽  
Author(s):  
Lennart Lindegren
Keyword(s):  
Reference Frame ◽  
Vlbi Observations ◽  
Radio Stars

scholarly journals Results of VLBI Observations of Radio Stars and Their Potential for Linking the HIPPARCOS and Extragalactic Reference Frames

1986 ◽  
Vol 109 ◽  
pp. 779-788 ◽  
Author(s):  
Jean-Francois Lestrade ◽  
Robert A. Preston ◽  
Arthur E. Niell ◽  
Robert L. Mutel ◽  
Robert B. Phillips
Keyword(s):  
Reference Frame ◽  
Binary Systems ◽  
Reference Frames ◽  
Proper Motions ◽  
Vlbi Observations ◽  
Angular Extent ◽  
The Future ◽  
Radio Stars

VLBI observations of bright radio stars have been initiated in an attempt to measure the positions and proper motions of their radio components in order to tie the future HIPPARCOS stellar frame to a VLBI extragalactic reference frame. Through VLBI observations of a sample of 20 known radio stars we have identified 11 stars that should be appropriate for both astrometric VLBI and HIPPARCOS observations. Our measurements indicate that the angular extent of their radio emitting regions is small, i.e. < 3 milliarcseconds for 7 of them. Most of these radio stars belong to the RS Canum Venaticorum class of binary systems.

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

2019 ◽  
Vol 633 ◽  
pp. A1 ◽  
Author(s):  
Lennart Lindegren
Keyword(s):  
Reference Frame ◽  
Positional Information ◽  
Simultaneous Estimation ◽  
Proper Motions ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Independent Observations ◽  
Vlbi Data ◽  
Single Epoch ◽  
Radio Stars

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 through Gaia’s direct observations of quasars. At brighter magnitudes, it is difficult to validate the quality of the reference frame because comparison data are scarce. Aims. The aim of this paper is to examine the use of very long baseline interferometry (VLBI) observations of radio stars to determine the spin and orientation of the bright reference frame of 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 rotates relative to the faint quasars at a rate of about 0.1 mas yr−1, which is significant at the 2σ level. This supports a similar conclusion based on a comparison with stellar positions in the HIPPARCOS frame. The accuracy is currently limited because only a few radio sources are 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.

Linking the Radio and Optical Frames with Merlin

1998 ◽  
Vol 179 ◽  
pp. 389-391 ◽  
Author(s):  
S.T. Garrington ◽  
R.J. Davis ◽  
L.V. Morrison ◽  
R.W. Argyle
Keyword(s):  
Reference Frame ◽  
The Future ◽  
Celestial Reference Frame ◽  
Radio Stars

MERLIN positions of 12 radio stars are used to link the provisional Hipparcos reference frame to the International Celestial Reference Frame. The accuracy of the link using these radio stars is 2.3 milliarcseconds. Further observations are planned to check the accuracy of the link in the future.

scholarly journals The Possibility to Link Radio and Optical Reference Frames With Artificial Satellites

1990 ◽  
Vol 141 ◽  
pp. 194-194
Author(s):  
Tong Fu
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Artificial Satellites ◽  
Radio Sources ◽  
Bl Lac Objects ◽  
Extragalactic Radio Sources ◽  
Bl Lac ◽  
Optical Reference ◽  
Radio Stars ◽  
Fundamental Reference

Based on extragalactic radio sources, a new high precision extragalactic radio reference frame can be established from radio interferometric measurements. To link the optical fundamental reference frame presently represented by the FK4/5 to the extragalactic radio frame, the optical counterparts of extragalactic radio sources (quasars, BL Lac objects etc.) and radio stars are the most important classes of objects. Besides these two classes of objects, are there any other objects which can be used to link the optical and radio frames? A posible answer is that artificial satellites could be a candidate class of objects contributing to this subject.

scholarly journals Link of the Hipparcos Stellar Reference Frame to the Distant Quasars

1998 ◽  
Vol 164 ◽  
pp. 381-382 ◽  
Author(s):  
J.-F. Lestrade ◽  
R.A. Preston ◽  
D.L. Jones ◽  
R.B. Phillips ◽  
A.E.E. Rogers ◽  
...  
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Global Orientation ◽  
Vlbi Observations

AbstractThe link of the Hipparcos and VLBI extragalactic reference frames has been achieved with a precision of 0.0005″ in global orientation at the epoch of the catalogue (1991.25) and of 0.0003″/yr in rate of rotation by VLBI observations of 12 radio-emitting stars.

scholarly journals Accuracy Assessment of Hipparcos Optical and VLA Radio Positions of Stars

1993 ◽  
Vol 156 ◽  
pp. 377-380
Author(s):  
H. G. Walter ◽  
R. Hering ◽  
H. Lenhardt ◽  
Chr. deVegt ◽  
D.R. Florkowski ◽  
...  
Keyword(s):  
Radio Emission ◽  
Reference Frame ◽  
Accuracy Assessment ◽  
Optical Emission ◽  
Relative Orientation ◽  
Large Array ◽  
Proper Motions ◽  
Data Noise ◽  
Very Large Array ◽  
Radio Stars

Optical positions of some 30 radio stars derived from 12 months of HIPPARCOS measurements are compared with their radio positions obtained with the Very Large Array (VLA). — Once the lengths of arcs between optical and radio positions of pairs of stars are calculated the differences of the arcs are formed. They provide an estimate of the coincidence of the optical and radio emission centres. — From the comparison of optical and radio positions infinitesimal rotation angles of the HIPPARCOS frame with respect to the VLA extragalactic reference frame are determined by rigid rotations. After taking account of the relative orientation of the frames the standard deviations of the remaining residuals are approximately of the order of the VLA observation errors, thus demonstrating the reliability of the HIPPARCOS results. However, they also indicate some data noise very likely caused by the low accuracy of optical proper motions used to bridge the HIPPARCOS-radio epoch differences up to 9 years, and possible discrepancies of radio-optical emission centres of some stars.

scholarly journals Improving the Reference Frame by Radio–and Optical Astrometry of Radio Stars

1991 ◽  
Vol 127 ◽  
pp. 246-249 ◽  
Author(s):  
Chr. de Vegt ◽  
N. Zacharias ◽  
K.J. Johnston ◽  
R. Hindsley
Keyword(s):  
Reference Frame ◽  
Southern Hemisphere ◽  
Radio Stars

AbstractA longterm program of precise radio – and optical astrometry of selected radio stars has been conducted in the last decade by our observatories using the VLA and astrographs on both hemispheres. Positions of 54 stars north of −26 deg. declination including 6 MASER stars have been obtained. The program status and some results from the southern hemisphere are reported.

scholarly journals On the Feasibility of a Star Coordinate Determination in the Radio Astrometry Reference System

1986 ◽  
Vol 109 ◽  
pp. 765-771
Author(s):  
V.S. Gubanov
Keyword(s):  
Reference Frame ◽  
Mutual Orientation ◽  
Radio Sources ◽  
Extragalactic Source ◽  
Vlbi Observations ◽  
Artificial Earth ◽  
Sufficient Magnitude ◽  
The Stability ◽  
The Relationship ◽  
Star Field

At present it is evident that the stability of a celestial coordinates system with an accuracy of at least per century, with respect to an internal frame can be derived only from VLBI observations of compact extragalactic radio sources. At the same time it is expected that the need for improved stars' coordinates will be strongly felt at least up to the end of this century, because stars are important and more convenient observational objects then very weak extragalactic sources or artificial Earth satellites (AES). One therefore wonders if one can use the high precision and stability of the radio astrometric reference frame to stabilize and improve the reference frame given by star catalogues. The problem of the relationship between these systems has so far been investigated in the form of determining the parameters of their mutual orientation, and/or studying systematic errors of star catalogues (Gubanov, 1978; Gubanov and Kumkova, 1978, 1981). This problem has been attacked by direct photography of several optically identified radio sources or VLBI observations of few radio stars. The present paper shows the feasibility of determining the place of any star of sufficient magnitude with reference to the radio astrometric frame, as given by extragalactic source positions (Gubanov, 1983). This is done by introducing an AES, equipped with radio signal for VLBI observations and a corner reflector for laser ranging, which can be observed by radio methods as well as optically (Gubanov, 1976). This satellite should also be bright enough in the reflected sun's light to be observed in the star field with a precision photoelectric satellite camera.

scholarly journals Astrometry and Geodesy from VLBI

1993 ◽  
Vol 156 ◽  
pp. 159-171
Author(s):  
C. Ma ◽  
J. L. Russell
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Radio Sources ◽  
Dual Frequency ◽  
Terrestrial Reference Frames ◽  
Vlbi Observations ◽  
Using Data ◽  
Celestial Reference Frame ◽  
Right Ascension ◽  
Better Than

Dual frequency Mark III VLBI observations acquired since 1979 by several geodetic and astrometric observing programs have been used to establish precise celestial and terrestrial reference frames. The program to establish a uniformly distributed celestial reference frame of ∼400 compact radio sources with optical counterparts was begun in 1987. Some 700 sources have been considered as part of this effort and a preliminary list of ∼400 has been observed. At present, 308 sources have formal 1σ errors less than 1 mas in right ascension and 308 have similar precision in declination. The astrometric results include some data acquired for geodetic purposes. The geodetic results using data to September, 1992 include the positions of 105 sites with formal 1σ horizontal errors generally less than 1 cm at 1992.6 and the velocities of 64 sites with formal 1σ horizontal errors generally better than 2 mm/yr.

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