scholarly journals The Effect of Companions on the SIM Reference Frame

2000 ◽  
Vol 180 ◽  
pp. 386-391
Author(s):  
Christopher S. Jacobs ◽  
Slava G. Turyshev
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Field Of View ◽  
Optical Interferometer ◽  
Galactic Astronomy ◽  
Celestial Reference Frame ◽  
Right Ascension ◽  
Precision Astrometry ◽  
Accuracy And Stability ◽  
Space Interferometry

AbstractThe Space Interferometry Mission (SIM) is a 10-m Michelson space-based optical interferometer designed for precision astrometry (4μas, 3μas/yr) with better accuracy hoped for over a narrow field of view. It is intended to search for planets and investigate a number of problems in Galactic and extra-galactic astronomy.The accuracy and stability of SIM’s celestial reference frame is subject to degradation over the 5-year mission from the reflex motion induced by massive companions of the objects used to construct the celestial reference frame. We present the results of simulations which show the sensitivity of reference frame accuracy to companions as a function of mass and period. We assume that pre-launch ground surveys will eliminate all objects with RMS radial velocity > 10 m/s. We further assume that the standard astrometric parameters of position, parallax, and proper motion plus acceleration terms in right ascension and declination will be allowed to absorb reflex motion.

scholarly journals Quasar Astrophysics with the Space Interferometry Mission

2002 ◽  
Vol 19 (1) ◽  
pp. 5-9 ◽  
Author(s):  
S. C. Unwin ◽  
A. E. Wehrle ◽  
D. L. Jones ◽  
D. L. Meier ◽  
B. G. Piner
Keyword(s):  
Accretion Disk ◽  
Optical Emission ◽  
Galaxy Mergers ◽  
Proper Motions ◽  
Optical Interferometer ◽  
Photometric Variability ◽  
Relativistic Jet ◽  
Precision Astrometry ◽  
Insight Into ◽  
Space Interferometry

AbstractPrecision optical astrometry of quasars and active galaxies can provide important insight into the spatial distribution and variability of emission in compact nuclei. SIM — the Space Interferometry Mission — will be the first optical interferometer capable of precision astrometry on quasars. Although it is not expected to resolve the emission, it will be very sensitive to astrometric shifts, for objects as faint as R magnitude 20. In its wide-angle mode, SIM will yield 4 microarcsecond absolute positions, and proper motions to about 2 microarcsecond/yr. A variety of AGN phenomena are expected to be visible to SIM on these scales, including time and spectral dependence in position offsets between accretion disk and jet emission. SIM should be able to answer the following questions. Does the most compact optical emission from an AGN come from an accretion disk or from a relativistic jet? Do the relative positions of the radio core and optical photocentre of quasars used for the reference frame tie change on the timescales of their photometric variability? Do the cores of galaxies harbour binary supermassive black holes remaining from galaxy mergers? In this paper we briefly describe the operation of SIM and the quasar measurements it will make. We estimate the size of the astrometric signatures which may be expected, and we discuss prospects for using astrometry as a fundamental tool for understanding quasar nuclei.

scholarly journals Stability of the Extragalactic Reference Frame Realized by VLBI

1991 ◽  
Vol 127 ◽  
pp. 135-144 ◽  
Author(s):  
C. Ma ◽  
D.B. Shaffer
Keyword(s):  
Reference Frame ◽  
Radio Sources ◽  
Dual Frequency ◽  
Real Motion ◽  
Rates Of Change ◽  
Upper Limits ◽  
Crustal Dynamics ◽  
Vlbi Data ◽  
Celestial Reference Frame ◽  
Right Ascension

AbstractThe 318 compact extragalactic radio sources with positions derived from dual frequency Mark III VLBI data acquired by the geodetic and astrometric programs of NASA, NOAA, NRL and USNO form a celestial reference frame with stability in orientation and relative position at the 1 mas level. This paper examines the reference frame realized using 461,000 observations from 1021 observing sessions between 1979 August and 1990 August in the NASA Crustal Dynamics Project VLBI data base. Catalogs of positions estimated from subsets of data (annual, seasonal, network) show differences in orientation typically less than 1 mas provided precession and nutation are adjusted using a reference day. For 17 sources with >5 year time span and >200 one-day position estimates, the rates of change of right ascension and declination are generally less than 5 mas/century, giving upper limits on real motion.

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.

scholarly journals Dense optical reference frames: UCAC and URAT

2007 ◽  
Vol 3 (S248) ◽  
pp. 310-315
Author(s):  
N. Zacharias
Keyword(s):  
Reference Frame ◽  
Focal Plane ◽  
Reference Frames ◽  
Field Of View ◽  
Radio Sources ◽  
Proper Motions ◽  
Naval Observatory ◽  
Optical Reference ◽  
Celestial Reference Frame ◽  
The U.S

AbstractA series of ground-based, dedicated astrometric, observational programs have been performed or are in preparation which provide a dense and accurate optical reference frame. Integral to all these programs are new observations to link the Hipparcos Celestial Reference Frame (HCRF) to the International Celestial Reference Frame (ICRF), based on compact, extragalactic radio sources.The U.S. Naval Observatory CCD Astrograph Catalog (UCAC) 3rd release is in preparation. A pixel re-reduction is in progress to improve astrometric and photometric accuracy as well as completeness of this all-sky reference catalog to 16th magnitude. Optical counterparts of ICRF radio sources have been observed with 0.9-meter telescopes contemporaneously. Scanning of over 5000 early-epoch astrograph plates on StarScan has been completed. These data will improve the proper motions of stars in the 10 to 14 mag range for the UCAC3 release.A 111 million-pixel CCD was successfully fabricated in 2006 and test observations at the USNO astrograph are underway. Four of such detectors will be used for the USNO Robotic Astrometric Telescope (URAT) focal plane assembly. Phase I of URAT will use the astrograph to reach 18th magnitude, while the new 0.85-meter telescope with a 4.5 deg diameter field of view will reach 21st magnitude. The URAT primary mirror has been fabricated.

scholarly journals How Accurate are SuperCOSMOS Positions?

2014 ◽  
Vol 31 ◽  
Author(s):  
Adam Schaefer ◽  
Richard Hunstead ◽  
Helen Johnston
Keyword(s):  
Reference Frame ◽  
Stellar Objects ◽  
The North ◽  
Sky Survey ◽  
The Uk ◽  
Celestial Reference Frame ◽  
Right Ascension

AbstractOptical positions from the SuperCOSMOS Sky Survey have been compared in detail with accurate radio positions that define the second realisation of the International Celestial Reference Frame (ICRF2). The comparison was limited to the IIIaJ plates from the UK/AAO and Oschin (Palomar) Schmidt telescopes. A total of 1 373 ICRF2 sources was used, with the sample restricted to stellar objects brighter than BJ = 20 and Galactic latitudes |b| > 10°. Position differences showed an rms scatter of $0.16\text{ arcsec}$ in right ascension and declination. While overall systematic offsets were < $0.1\text{ arcsec}$ in each hemisphere, both the systematics and scatter were greater in the north.

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 Astrometric Reduction of Cassini ISS Images of Enceladus in 2015 Based on Gaia DR1

2017 ◽  
Vol 12 (S330) ◽  
pp. 411-412
Author(s):  
Q. F. Zhang ◽  
V. Lainey ◽  
A. Vienne ◽  
N. J. Cooper ◽  
Q. Y. Peng ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Reference Frame ◽  
Gaia Dr1 ◽  
Astrometric Observation ◽  
Celestial Reference Frame ◽  
Right Ascension

AbstractThe Gaia DR1 catalogue stars are taken as reference ones to reduce the Cassini ISS images of Enceladus in 2015, and a total of 494 Cassini-centered astrometric observation are obtained in right ascension(α) and declination (δ) in the international Celestial Reference Frame(ICRF). Compared with JPL ephemerides SAT367, we derive that their mean residuals are a few tens meters in α*cos(δ) and a few kilometers in δ, and their standard deviation is not over 2 kilometers. Compared with the results from UCAC4 catalogue stars, The Gaia DR1 has the equivalent precision of reduction.

scholarly journals Proper motion and densification of the International Celestial Reference Frame in the direction of the Galactic bulge

2011 ◽  
Vol 534 ◽  
pp. A91 ◽  
Author(s):  
R. Teixeira ◽  
P. A. B. Galli ◽  
P. Benevides-Soares ◽  
J. F. Le Campion ◽  
M. Fidêncio ◽  
...  
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Galactic Bulge ◽  
Celestial Reference Frame

scholarly journals The VLBI celestial reference frame of the NASA Crustal Dynamics Project

1988 ◽  
Vol 128 ◽  
pp. 73-81 ◽  
Author(s):  
C. Ma
Keyword(s):  
Reference Frame ◽  
Weighted Average ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Statistical Errors ◽  
Crustal Dynamics ◽  
Vlbi Data ◽  
Celestial Reference Frame ◽  
Right Ascension ◽  
Average Position

A celestial reference frame can be defined by precise positions of extragalactic radio sources using Mark III VLBI data available to the NASA Crustal Dynamics Project for geodynamic research. Seven years of such data have been analyzed to generate a catalogue of 101 sources with formal statistical errors between 0.01 and 0.77 ms in right ascension and between 0.2 and 9.3 mas in declination. In order to achieve such precision it is necessary to adjust the standard IAU nutation model. The rotations and scatter of the positions from year to year are generally less than 1 mas. A comparison of this catalogue with a completely independent catalogue derived from Mark II data shows a weighted average position difference, after a rotation, of 1.9 mas.

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