scholarly journals On the estimation of a celestial reference frame in the presence of source structure

2015 ◽  
Vol 455 (1) ◽  
pp. 343-356 ◽  
Author(s):  
L. Plank ◽  
S. S. Shabala ◽  
J. N. McCallum ◽  
H. Krásná ◽  
B. Petrachenko ◽  
...  
Keyword(s):  
Reference Frame ◽  
Celestial Reference Frame ◽  
Source Structure

scholarly journals Source structure: an essential piece of information for generating the next ICRF

2007 ◽  
Vol 3 (S248) ◽  
pp. 344-347 ◽  
Author(s):  
P. Charlot ◽  
A. L. Fey ◽  
A. Collioud ◽  
R. Ojha ◽  
D. A. Boboltz ◽  
...  
Keyword(s):  
Reference Frame ◽  
Structural Evolution ◽  
Limiting Factors ◽  
Radio Structure ◽  
Long Baseline ◽  
Ongoing Work ◽  
The World ◽  
Very Long Baseline Array ◽  
Celestial Reference Frame ◽  
Source Structure

AbstractThe intrinsic radio structure of the extragalactic sources is one of the limiting factors in defining the International Celestial Reference Frame (ICRF). This paper reports about the ongoing work to monitor the structural evolution of the ICRF sources by using the Very Long Baseline Array and other VLBI telescopes around the world. Based on more than 5000 VLBI images produced from such observations, we have assessed the astrometric suitability of 80% of the ICRF sources. The number of VLBI images for a given source varies from 1 for the least-observed sources to more than 20 for the intensively-observed sources. Overall, we identify a subset of 194 sources that are highly compact at any of the available epochs and which are prime candidates for the realization of the next ICRF with the highest accuracy.

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 Variability of extragalactic sources: its contribution to the link between ICRF and the future Gaia Celestial Reference Frame

2018 ◽  
Vol 611 ◽  
pp. A52 ◽  
Author(s):  
F. Taris ◽  
G. Damljanovic ◽  
A. Andrei ◽  
J. Souchay ◽  
A. Klotz ◽  
...  
Keyword(s):  
Reference Frame ◽  
Reference Systems ◽  
New Information ◽  
Single Target ◽  
The Future ◽  
Optical Flux ◽  
Celestial Reference Frame ◽  
Source Structure ◽  
Optical Telescopes ◽  
Observation Period

Context. The first release of the Gaia catalog is available since 14 September 2016. It is a first step in the realization of the future Gaia reference frame. This reference frame will be materialized by the optical positions of the sources and will be compared with and linked to the International Celestial Reference Frame, materialized by the radio position of extragalactic sources. Aim. As in the radio domain, it can be reasonably postulated that quasar optical flux variations can alert us to potential changes in the source structure. These changes could have important implications for the position of the target photocenters (together with the evolution in time of these centers) and in parallel have consequences for the link of the reference systems.Methods. A set of nine optical telescopes was used to monitor the magnitude variations, often at the same time as Gaia, thanks to the Gaia Observation Forecast Tool. The Allan variances, which are statistical tools widely used in the atomic time and frequency community, are introduced.Results. This work describes the magnitude variations of 47 targets that are suitable for the link between reference systems. We also report on some implications for the Gaia catalog. For 95% of the observed targets, new information about their variability is reported. In the case of some targets that are well observed by the TAROT telescopes, the Allan time variance shows that the longest averaging period of the magnitudes is in the range 20−70 d. The observation period by Gaia for a single target largely exceeds these values, which might be a problem when the magnitude variations exhibit flicker or random walk noises. Preliminary computations show that if the coordinates of the targets studied in this paper were affected by a white-phase noise with a formal uncertainty of about 1 mas (due to astrophysical processes that are put in evidence by the magnitude variations of the sources), it would affect the precision of the link at the level of 50 μas.

scholarly journals The Accuracy of the ICRF: an Intercomparison of VLBI Analysis Software

1998 ◽  
Vol 11 (1) ◽  
pp. 320-321
Author(s):  
C.S. Jacobs ◽  
O.J. Sovers ◽  
D. Gordon ◽  
C. Ma ◽  
A.-M. Gontier
Keyword(s):  
Reference Frame ◽  
Internal Consistency ◽  
Significant Loss ◽  
Physical Parameters ◽  
Software Packages ◽  
Differential Group ◽  
Radio Signals ◽  
Least Squares Adjustment ◽  
Great Leap Forward ◽  
Celestial Reference Frame

As discussed in other papers in this volume, the IAU XXIII General Assembly adopted a new fundamental celestial reference frame: the International Celestial Reference Frame (ICRF) based on VLBI observations of extragalactic radio sources (Ma et al., 1997). It is approximately 300 times more accurate than its predecessor, the FK5. At present, no other technique has produced a more accurate celestial frame than VLBI, Since no other astrometric technique provides an external standard of accuracy, the VLBI claim of a great leap forward in accuracy must be verified by internal consistency tests. This paper addresses one aspect of internal consistency: the ability of independent VLBI software packages to reproduce a celestial frame without significant loss of accuracy. This is no small task since the software packages are large - involving on the order of 100 000 lines of code. What does VLBI software do? Aside from routines designed to collect the data and extract raw observables which will not be considered here, its principal task is to model the differential group delay and phase delay rate of radio signals received at two widely separated antennas (Sovers, Fanselow & Jacobs, 1998). The software then refines this model via a least squares adjustment of relevant physical parameters which describe station locations, source positions, clock offsets, atmospheric refraction, tidal effects, etc. In the early 1990s, studies revealed that differences in software implementation and analyst’s choices of model options were one of the largest contributors to differences in independent calculations of VLBI celestial frames. These differences were of comparable size to the formal uncertainties of the celestial frame’s source positions.

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.

scholarly journals Relativistic Effects in the Rotation of Jupiter’s Inner Satellites

2020 ◽  
Vol 55 (3) ◽  
pp. 118-129
Author(s):  
Vladimir V. Pashkevich ◽  
Andrey N. Vershkov
Keyword(s):  
Solar System ◽  
Reference Frame ◽  
Central Body ◽  
Relativistic Effects ◽  
Euler Angles ◽  
Coordinate Systems ◽  
Geodetic Precession ◽  
Long Time ◽  
Celestial Reference Frame ◽  
Jupiter’S Satellites

AbstractThe most significant relativistic effects (the geodetic precession and the geodetic nutation, which consist of the effect of the geodetic rotation) in the rotation of Jupiter’s inner satellites were investigated in this research. The calculations of the most essential secular and periodic terms of the geodetic rotation were carried out by the method for studying any bodies of the solar system with long-time ephemeris. As a result, for these Jupiter’s satellites, these terms of their geodetic rotation were first determined in the rotational elements with respect to the International Celestial Reference Frame (ICRF) equator and the equinox of the J2000.0 and in the Euler angles relative to their proper coordinate systems. The study shows that in the solar system there are objects with significant geodetic rotation, due primarily to their proximity to the central body, and not to its mass.

scholarly journals Contributions of the USNO to the Optical Reference Frame

1997 ◽  
Vol 165 ◽  
pp. 453-462
Author(s):  
Thomas Corbin
Keyword(s):  
Reference Frame ◽  
Reverse Order ◽  
Good Working ◽  
Working Definition ◽  
Optical Reference ◽  
Definition Of ◽  
Celestial Sphere ◽  
Celestial Reference Frame ◽  
Frame Rigidity ◽  
Zero Points

A good, working definition of what is required in a celestial reference frame is that it must provide observable fiducial points on the Celestial Sphere with internally consistent positions that are referred to coordinate axes of known direction. In reality, this statement gives the goals in the reverse order from that in which each must be achieved, the definition of the axes, or zero points of the system give orientation to the observationally defined set of primary objects whose coordinate relation to each other must give the frame rigidity. Finally, the primary objects are generally too sparse to define the frame within areas of less than tens of square degrees, and so additional objects must be related to the frame to increase the density. This last step is required to make the frame useful for most observational applications.

scholarly journals A Proposal for Astrometric Observations From Space

1990 ◽  
Vol 141 ◽  
pp. 77-80 ◽  
Author(s):  
M.S. Chubey ◽  
V.V. Makarov ◽  
V.N. Yershov ◽  
I.I. Kanayev ◽  
V.A. Fomin ◽  
...  
Keyword(s):  
Reference Frame ◽  
Single Observation ◽  
The Earth ◽  
Space Astrometry ◽  
Celestial Reference Frame ◽  
Observational Program

Some aspects of the realisation of a celestial reference frame using a space astrometry facility are considered. An observational program is described, consisting of observing stars up to magnitude 14, radiostars and bright QSO's, planets, asteroids and of laser signals from the Earth. A scheme of an astrometric facility consisting of two telescopes on board the satellite is proposed. The overview strategy with “inita” is estimated, and the estimates of the accuracy of a single observation (0.″02-0.″05) and of the output catalogues (0.″001-0.″007) are made.

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