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

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

Symposium - International Astronomical Union ◽

10.1017/s0074180900077329 ◽

1986 ◽

Vol 109 ◽

pp. 779-788 ◽

Cited By ~ 2

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.

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Analysis of the Residuals between Theoretical Nutations and VLBI Observations

Highlights of Astronomy ◽

10.1017/s1539299600013022 ◽

2002 ◽

Vol 12 ◽

pp. 124-125 ◽

Cited By ~ 1

Author(s):

V. Dehant ◽

M. Feissel ◽

O. de Viron ◽

M. Yseboodt ◽

Ch. Bizouard

Keyword(s):

Very Long Baseline Interferometry ◽

Short Description ◽

Time Intervals ◽

Long Baseline ◽

Vlbi Observations ◽

Vlbi Data ◽

Theoretical Developments

The recent theoretical developments have provided accurate series of nutations, which are close to the Very Long Baseline Interferometry (VLBI) data. At the milliarcsecond (mas) level, three series are available: MHB2000 (Mathews et al. 2000), FG2000 (Getino and Ferrándiz 2000), and SF2000 (Shirai and Fukushima 2000a,b) (see Dehant 2000, and in this volume, for more information and for a short description of these models).In the first part of our work we have compared these models with the (VLBI) observations (Ma et al. 2000) by computing rms of the residuals for several time intervals of measurements. We have concluded that these series have comparable precision.

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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.

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Receiving And Data Acquisition Systems Of Rt-32 For Vlbi Observations / Rt-32 Uztveršanas Un Datu Reģistrācijas Sistēmas Vlbi Novērojumiem

Latvian Journal of Physics and Technical Sciences ◽

10.2478/v10047-012-0040-2 ◽

2012 ◽

Vol 49 (6-II) ◽

pp. 30-42

Author(s):

Vl. Bezrukovs ◽

I. Shmeld ◽

M. Nechaeva ◽

J. Trokss ◽

D. Bezrukovs ◽

...

Keyword(s):

Data Acquisition ◽

Radio Astronomy ◽

Very Long Baseline Interferometry ◽

Low Frequency ◽

Current Status ◽

Data Acquisition Systems ◽

Long Baseline ◽

Vlbi Observations ◽

Parabolic Antenna ◽

Vlbi Data

Abstract Radiotelescope RT-32 is a fully steerable 32-m parabolic antenna located at Irbene and belonging to Ventspils International Radio Astronomy Centre (VIRAC). Currently, the work on upgrading and repair of its receiving hardware and data acquisition systems is of high priority for the VIRAC. One of the main scientific objectives for the VIRAC Radioastronomical observatory is VLBI (very long baseline interferometry) observations in centimetre wavelengths in collaboration with world VLBI networks, such as European VLBI network (EVN), Low Frequency VLBI network (LFVN), and others. During the last years the room in the secondary focus of telescope was reconstructed, and several new receivers were installed. Currently, RT-32 observations are carried out in four different bands: 92 cm, 18 cm, 6 cm, and 2.5 cm. First three of them are already successfully employed in diversified VLBI experiments. The receiver on 2.5 cm band has only one linear polarized chain and is used mainly for the methanol maser single dish observations. The apparatus system of RT-32 is equipped with two independent VLBI data acquisition systems: TN-16, and DBBC in combination with MK5b. Both systems are employed in interferometric observations depending on the purpose of experiment and the enabled radiotelescopes. The current status of RT-32, the availability of its receiving and data acquisition units for VLBI observations and the previous VLBI sessions are discussed.

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Models for Source Structure Corrections

International Astronomical Union Colloquium ◽

10.1017/s0252921100000075 ◽

2000 ◽

Vol 180 ◽

pp. 29-39

Author(s):

P. Charlot

Keyword(s):

Reference Frame ◽

Very Long Baseline Interferometry ◽

Radio Sources ◽

Time Varying ◽

Long Baseline ◽

Vlbi Observations ◽

Spatially Extended ◽

Astrometric Data ◽

Celestial Reference Frame ◽

Source Structure

AbstractAt the milliarcsecond scale, most of the extragalactic radio sources exhibit spatially-extended intrinsic structures which are variable in both time and frequency. Such radio structures set limits on the accuracy of source positions determined with the Very Long Baseline Interferometry (VLBI) technique unless their effects in the astrometric data can be accounted for. We review the modeling scheme for calculating source structure corrections and discuss the magnitude and impact of these effects for the sources that are part of the International Celestial Reference Frame (ICRF). Results obtained by applying source structure corrections to actual VLBI observations on the time-varying source 4C39.25 (0923 + 392) are also presented.

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Complex Demodulation in Monitoring Earth Rotation by VLBI: Testing the Algorithm by Analysis of Long Periodic EOP Components

Artificial Satellites ◽

10.1515/arsa-2016-0012 ◽

2016 ◽

Vol 51 (4) ◽

pp. 135-147 ◽

Cited By ~ 1

Author(s):

A. Wielgosz ◽

A. Brzeziński ◽

S. Böhm

Keyword(s):

Earth Rotation ◽

Low Frequency ◽

Simultaneous Estimation ◽

Complex Demodulation ◽

Vlbi Observations ◽

Celestial Pole ◽

Frequency Components ◽

Vlbi Data ◽

Past Data ◽

Good Agreement

Abstract The complex demodulation (CD) algorithm is an efficient tool for extracting the diurnal and subdiurnal components of Earth rotation from the routine VLBI observations (Brzeziński, 2012). This algorithm was implemented by Böhm et al (2012b) into a dedicated version of the VLBI analysis software VieVs. The authors processed around 3700 geodetic 24-hour observing sessions in 1984.0-2010.5 and estimated simultaneously the time series of the long period components as well as diurnal, semidiurnal, terdiurnal and quarterdiurnal components of polar motion (PM) and universal time UT1. This paper describes the tests of the CD algorithm by checking consistency of the low frequency components of PM and UT1 estimated by VieVS CD and those from the IERS and IVS combined solutions. Moreover, the retrograde diurnal component of PM demodulated from VLBI observations has been compared to the celestial pole offsets series included in the IERS and IVS solutions. We found for all three components a good agreement of the results based on the CD approach and those based on the standard parameterization recommended by the IERS Conventions (IERS, 2010) and applied by the IERS and IVS. We conclude that an application of the CD parameterization in VLBI data analysis does not change those components of EOP which are included in the standard adjustment, while enabling simultaneous estimation of the high frequency components from the routine VLBI observations. Moreover, we deem that the CD algorithm can also be implemented in analysis of other space geodetic observations, like GNSS or SLR, enabling retrieval of subdiurnal signals in EOP from the past data.

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Linking the optically bright Gaia frame to the third International Celestial Reference Frame

10.5194/egusphere-egu21-8604 ◽

2021 ◽

Author(s):

Susanne Lunz ◽

James Anderson ◽

Ming H. Xu ◽

Robert Heinkelmann ◽

Oleg Titov ◽

...

Keyword(s):

Reference Frame ◽

European Space Agency ◽

Global Navigation Satellite Systems ◽

Satellite Systems ◽

The Third ◽

Long Baseline ◽

Data Release ◽

Radio Frequencies ◽

Celestial Reference Frame ◽

Radio Stars

<p>The new data release of the Gaia satellite operated by the European Space Agency recently published its 3rd data release (Early Data Release 3, EDR3). The dataset contains astrometric data of about 1.8 billion objects detected at optical frequencies and therefore it outperforms any catalog of astrometric information up to date. The reference frame defined by Gaia EDR3 is aligned to the International Celestial Reference System by referring to counterparts in its realization, the third International Celestial Reference Frame (ICRF3), which is calculated from very long baseline interferometry (VLBI) observations of extragalactic objects at radio frequencies. <br>The Gaia dataset is known to be magnitude-dependent in terms of astrometric calibration. As the objects in ICRF3, although bright at radio frequencies, are mostly faint at optical frequencies, the optically bright Gaia frame has to be linked to ICRF3 by additional counterparts besides objects in ICRF3. The non-rotation of the optically bright Gaia frame is especially important as optically bright objects can, besides astrophysical studies, be used for navigation in space, where other geodetic systems like global navigation satellite systems are out of reach. Suitable additional counterparts are radio stars which are observed by VLBI relative to extragalactic objects in ICRF3. We discuss the orientation and spin differences between the optically bright Gaia EDR3 and VLBI data of radio stars and their impact on the Gaia data usage.</p>

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Relationship between the JPL radio celestial reference frame and a preliminary FK5 frame

Symposium - International Astronomical Union ◽

10.1017/s007418090011928x ◽

1988 ◽

Vol 128 ◽

pp. 67-70

Author(s):

Jean-François Lestrade ◽

Yves Requième ◽

Michel Rapaport ◽

Robert A. Preston

Keyword(s):

Reference Frame ◽

Very Long Baseline Interferometry ◽

Long Baseline ◽

The Mean ◽

Mean Differences ◽

Celestial Reference Frame ◽

Right Ascension ◽

Radio Stars

Very Long Baseline Interferometry (VLBI) and optical positions of 8 radio stars are compared in the J2000.0 system. The mean differences in right ascension and declination found are +0.02″ ± 0.04″ and −0.02″ ± 0.07″, respectively. These differences show that the JPL radio celestial reference frame is aligned on a preliminary FK5 frame to at least this level.

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