Extending the very long baseline interferometry celestial reference frame to the Southern Hemisphere

1993 ◽  
Vol 105 ◽  
pp. 353 ◽  
Author(s):  
D. S. Robertson ◽  
W. E. Carter ◽  
J. R. Ray ◽  
W. H. Dillinger ◽  
G. D. Nicolson ◽  
...  
Keyword(s):  
Reference Frame ◽  
Southern Hemisphere ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
Celestial Reference Frame

scholarly journals The Celestial Frame and the Weighting of the Celestial Pole Offsets in the Computation of VLBI-Based Corrections for the Main Lunisolar Nutation Terms

Sensors ◽  
2021 ◽  
Vol 21 (24) ◽  
pp. 8276
Author(s):  
Víctor Puente ◽  
Marta Folgueira
Keyword(s):  
Stochastic Model ◽  
Least Squares ◽  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
Celestial Pole ◽  
Two Factors ◽  
Least Squares Adjustment ◽  
Empirical Corrections ◽  
Celestial Reference Frame

Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.

The International Celestial Reference Frame as Realized by Very Long Baseline Interferometry

1998 ◽  
Vol 116 (1) ◽  
pp. 516-546 ◽  
Author(s):  
C. Ma ◽  
E. F. Arias ◽  
T. M. Eubanks ◽  
A. L. Fey ◽  
A.-M. Gontier ◽  
...  
Keyword(s):  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
Celestial Reference Frame

scholarly journals The third realization of the International Celestial Reference Frame by very long baseline interferometry

2020 ◽  
Vol 644 ◽  
pp. A159 ◽  
Author(s):  
P. Charlot ◽  
C. S. Jacobs ◽  
D. Gordon ◽  
S. Lambert ◽  
A. de Witt ◽  
...  
Keyword(s):  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Galactic Center ◽  
Motion Field ◽  
Dual Frequency ◽  
Extended Source ◽  
Long Baseline ◽  
Radio Frequencies ◽  
Celestial Reference Frame ◽  
24 Ghz

A new realization of the International Celestial Reference Frame (ICRF) is presented based on the work achieved by a working group of the International Astronomical Union (IAU) mandated for this purpose. This new realization follows the initial realization of the ICRF completed in 1997 and its successor, ICRF2, adopted as a replacement in 2009. The new frame, referred to as ICRF3, is based on nearly 40 years of data acquired by very long baseline interferometry at the standard geodetic and astrometric radio frequencies (8.4 and 2.3 GHz), supplemented with data collected at higher radio frequencies (24 GHz and dual-frequency 32 and 8.4 GHz) over the past 15 years. State-of-the-art astronomical and geophysical modeling has been used to analyze these data and derive source positions. The modeling integrates, for the first time, the effect of the galactocentric acceleration of the solar system (directly estimated from the data) which, if not considered, induces significant deformation of the frame due to the data span. The new frame includes positions at 8.4 GHz for 4536 extragalactic sources. Of these, 303 sources, uniformly distributed on the sky, are identified as “defining sources” and as such serve to define the axes of the frame. Positions at 8.4 GHz are supplemented with positions at 24 GHz for 824 sources and at 32 GHz for 678 sources. In all, ICRF3 comprises 4588 sources, with three-frequency positions available for 600 of these. Source positions have been determined independently at each of the frequencies in order to preserve the underlying astrophysical content behind such positions. They are reported for epoch 2015.0 and must be propagated for observations at other epochs for the most accurate needs, accounting for the acceleration toward the Galactic center, which results in a dipolar proper motion field of amplitude 0.0058 milliarcsecond yr−1 (mas yr−1). The frame is aligned onto the International Celestial Reference System to within the accuracy of ICRF2 and shows a median positional uncertainty of about 0.1 mas in right ascension and 0.2 mas in declination, with a noise floor of 0.03 mas in the individual source coordinates. A subset of 500 sources is found to have extremely accurate positions, in the range of 0.03–0.06 mas, at the traditional 8.4 GHz frequency. Comparing ICRF3 with the recently released Gaia Celestial Reference Frame 2 in the optical domain, there is no evidence for deformations larger than 0.03 mas between the two frames, in agreement with the ICRF3 noise level. Significant positional offsets between the three ICRF3 frequencies are detected for about 5% of the sources. Moreover, a notable fraction (22%) of the sources shows optical and radio positions that are significantly offset. There are indications that these positional offsets may be the manifestation of extended source structures. This third realization of the ICRF was adopted by the IAU at its 30th General Assembly in August 2018 and replaced the previous realization, ICRF2, on January 1, 2019.

scholarly journals Models for Source Structure Corrections

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.

scholarly journals The Progress of The Reference Frame

1998 ◽  
Vol 11 (1) ◽  
pp. 280-280
Author(s):  
L.V. Morrison
Keyword(s):  
International Cooperation ◽  
Reference Frame ◽  
Radio Astronomy ◽  
International Collaboration ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
Celestial Reference Frame ◽  
Northern And Southern Hemispheres ◽  
Global Reference Frame ◽  
Better Than

F.W. Argelander proposed to a meeting of the Astronomischen Gessellschaft in 1867 that an accurate catalogue of all stars down to 9th magnitude should be compiled. The sky was divided into zones of declination and observations were undertaken with transit circles at a number of observatories in an international collaboration. The importance of fitting these zonal observations to one global reference frame was realized, and for this purpose A. Auwers produced a Fundamental Catalog (FC) for the Northern and Southern hemispheres in 1879 and 1883, respectively. The accuracy of the positions was about half of an arcsecond. This was the first international celestial reference frame. This reference frame was improved over the next hundred years by continued international cooperation which was later coordinated through the IAU. These efforts culminated in the FK5 which was issued in 1988. The progress in accuracy from the FC to the FK5 is shown in Figure 1. Meanwhile, radio astronomy through the technique of Very Long Baseline Interferometry (VLBI) began to produce positions of extragalactic sources with an accuracy of a milliarcsecond (mas), which is almost two orders of magnitude better than that of the optical positions of the stars in the FK5.

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

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.

scholarly journals Realization of a multifrequency celestial reference frame through a combination of normal equation systems

2019 ◽  
Vol 630 ◽  
pp. A101 ◽  
Author(s):  
M. Karbon ◽  
A. Nothnagel
Keyword(s):  
Radio Source ◽  
Reference Frame ◽  
Reference Frames ◽  
Very Long Baseline Interferometry ◽  
Normal Equation ◽  
Long Baseline ◽  
Combination Approach ◽  
Celestial Reference Frame ◽  
Right Ascension ◽  
24 Ghz

Context. We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of very long baseline interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources. Aims. We produce a multifrequency catalog of radio source positions with full variance–covariance information across all radio source positions of all input catalogs. Methods. We combined three catalogs, one observed at 8 GHz (X band), one at 24 GHz (K band) and one at 32 GHz (Ka band). Rather than only using the radio source positions, we developed a new, rigorous combination approach by carrying over the full covariance information through the process of adding normal equation systems. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined catalog. Results. The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8 GHz, 824 sources also observed at 24 GHz, and 674 at 32 GHz. The frame is aligned with ICRF3 within ±3 μas and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.

scholarly journals Possible systematics in the VLBI catalogs as seen from Gaia

2017 ◽  
Vol 609 ◽  
pp. A19 ◽  
Author(s):  
N. Liu ◽  
Z. Zhu ◽  
J.-C. Liu
Keyword(s):  
Southern Hemisphere ◽  
Spherical Harmonics ◽  
Very Long Baseline Interferometry ◽  
Systematic Errors ◽  
Vector Spherical Harmonics ◽  
Long Baseline ◽  
Quadrupole Component ◽  
Data Release ◽  
Celestial Reference Frame ◽  
Rotation Component

Aims. In order to investigate the systematic errors in the very long baseline interferometry (VLBI) positions of extragalactic sources (quasars) and the global differences between Gaia and VLBI catalogs, we use the first data release of Gaia (Gaia DR1) quasar positions as the reference and study the positional offsets of the second realization of the International Celestial Reference Frame (ICRF2) and the Goddard VLBI solution 2016a (gsf2016a) catalogs. Methods. We select a sample of 1032 common sources among three catalogs and adopt two methods to represent the systematics: considering the differential orientation (offset) and declination bias; analyzing with the vector spherical harmonics (VSH) functions. Results. Between two VLBI catalogs and Gaia DR1, we find that: i) the estimated orientation is consistent with the alignment accuracy of Gaia DR1 to ICRF, of ~0.1 mas, but the southern and northern hemispheres show opposite orientations; ii) the declination bias in the southern hemisphere between Gaia DR1 and ICRF2 is estimated to be +152 μas, much larger than that between Gaia DR1 and gsf2016a which is +34 μas. Between two VLBI catalogs, we find that: i) the rotation component shows that ICRF2 and gsf2016a are generally consistent within 30 μas; ii) the glide component and quadrupole component report two declination-dependent offsets: dipolar deformation of ~+50 μas along the Z-axis, and quadrupolar deformation of ~−50 μas that would induce a pattern of sin2δ. Conclusions. The significant declination bias between Gaia DR1 and ICRF2 catalogs reported in previous studies is possibly attributed to the systematic errors of ICRF2 in the southern hemisphere. The global differences between ICRF2 and gsf2016a catalogs imply that possible, mainly declination-dependent systematics exit in the VLBI positions and need further investigations in the future Gaia data release and the next generation of ICRF.

scholarly journals Improving the Accuracy of Radio Astrometry

2000 ◽  
Vol 180 ◽  
pp. 40-46
Author(s):  
Alan L. Fey
Keyword(s):  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Tropospheric Propagation ◽  
Intrinsic Structure ◽  
Long Baseline ◽  
Propagation Effects ◽  
Celestial Reference Frame

AbstractThe International Celestial Reference Frame (ICRF) is currently realized by the radio positions of compact extragalactic objects obtained by the technique of Very Long Baseline Interferometry (VLBI). The positions of the defining sources with the highest quality are estimated to be accurate at the 0.25 milliarcsecond (mas) level. The limiting accuracy is thought to be due mostly to tropospheric propagation effects and by the apparent motions of the sources due to variable intrinsic structure. Increasing the accuracy of VLBI astrometry beyond current levels will require an improved understanding of the variable emission structures associated with compact extragalactic sources as well as improvements in the modeling of the Earth’s troposphere.

scholarly journals THE SECOND REALIZATION OF THE INTERNATIONAL CELESTIAL REFERENCE FRAME BY VERY LONG BASELINE INTERFEROMETRY

2015 ◽  
Vol 150 (2) ◽  
pp. 58 ◽  
Author(s):  
A. L. Fey ◽  
D. Gordon ◽  
C. S. Jacobs ◽  
C. Ma ◽  
R. A. Gaume ◽  
...  
Keyword(s):  
Reference Frame ◽  
Very Long Baseline Interferometry ◽  
Long Baseline ◽  
Celestial Reference Frame
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