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

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.

Download Full-text

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936161 ◽

2019 ◽

Vol 633 ◽

pp. A1 ◽

Cited By ~ 10

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.

Download Full-text

Phase referencing VLBI astrometry observation system: VERA

Proceedings of the International Astronomical Union ◽

10.1017/s1743921308018930 ◽

2007 ◽

Vol 3 (S248) ◽

pp. 148-155

Author(s):

H. Kobayashi ◽

N. Kawaguchi ◽

S. Manabe ◽

K. M. Shibata ◽

M. Honma ◽

...

Keyword(s):

Observation System ◽

Baseline Length ◽

Radio Telescopes ◽

Proper Motions ◽

3 Dimensional ◽

Japanese Archipelago ◽

Vlbi Observations ◽

The Future ◽

The Galaxy

AbstractVERA aims at astrometric observations using phase referencing VLBI techniques, whose goal is a 10 micro arc-second accuracy for annual parallax measurements. VERA has four 20-m diameter VLBI radio telescopes in Japanese archipelago with the maximum baseline length of 2,300 km. They have the two-beam observing system, which makes simultaneous observations of two objects possible. This leads to very accurate phase referencing VLBI observations. An important science goal is to make a 3-dimensional map of the Galaxy and reveal its dynamics. In order to achieve this, VERA has the 22GHz and 43GHz bands for H2O and SiO maser objects, respectively. Maser objects are compact and suitable for astrometry observations. VERA's construction was started in 2000 and the array became operational in 2004. We have already measured annual parallaxes and proper motions of some galactic objects. In the future, VERA will collaborate with Korean and Chinese VLBI stations.

Download Full-text

The Role of Observation With Horizontal Meridian Circle in China for Establishing an Inertial Frame

Symposium - International Astronomical Union ◽

10.1017/s0074180900086526 ◽

1990 ◽

Vol 141 ◽

pp. 142-142

Author(s):

Li Zhi-gang ◽

Qi Guan-Rong

Keyword(s):

Inertial Frame ◽

Minor Planets ◽

Meridian Circle ◽

Horizontal Meridian ◽

Proper Motions ◽

The Earth ◽

The Future ◽

History Of ◽

Radio Stars

While HIPPARCOS is expected to measure positions and proper motions with more accuracy than those obtained by ground-based instruments, what can we do in the future for ground-based instruments? The observations with them still are important for establishing an inertial frame because of the long history of observations with them and improvements in the instruments. Moreover, it is necessary to have data of observations from them for research on problems related to the Earth. The horizontal meridian circle in China (DCMT) is expected to have advantage over the classical meridian circles. The DCMT will be assembled and tested this year. It should work in the following fields: (1) observing radio stars, (2) observation of minor planets, (3) absolute determinations of IRS.

Download Full-text

Linking the Radio and Optical Frames with Merlin

Symposium - International Astronomical Union ◽

10.1017/s0074180900129122 ◽

1998 ◽

Vol 179 ◽

pp. 389-391 ◽

Cited By ~ 1

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.

Download Full-text

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900086794 ◽

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.

Download Full-text

Uses and Required Characteristics of Reference Frames for Galactic Astronomy

Highlights of Astronomy ◽

10.1017/s1539299600006158 ◽

1986 ◽

Vol 7 ◽

pp. 51-54

Author(s):

Roland Wielen

Keyword(s):

Reference Frame ◽

Reference Frames ◽

Inertial System ◽

Proper Motions ◽

Upper Limits ◽

Galactic Astronomy

AbstractGalactic astronomy requires mainly accurate proper motions of stars, referred to a system which represents an inertial system as closely as possible. We discuss the required accuracy, give an outlook on forthcoming reference frames of use for galactic astronomy, and discuss observationally determined upper limits on the rotation of the extra-galactic reference frame.

Download Full-text

Link of the Hipparcos Stellar Reference Frame to the Distant Quasars

International Astronomical Union Colloquium ◽

10.1017/s0252921100046030 ◽

1998 ◽

Vol 164 ◽

pp. 381-382 ◽

Cited By ~ 3

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.

Download Full-text

Accuracy Assessment of Hipparcos Optical and VLA Radio Positions of Stars

Symposium - International Astronomical Union ◽

10.1017/s007418090017353x ◽

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.

Download Full-text

Astrometry and Geodesy from VLBI

Symposium - International Astronomical Union ◽

10.1017/s0074180900173140 ◽

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.

Download Full-text