scholarly journals Improvement of the Optical Reference System by Photographic Astrometry: First Results of Simulations with Global Block Adjustment Methods

1991 ◽  
Vol 127 ◽  
pp. 399-403
Author(s):  
N. Zacharias
Keyword(s):  
Reference System ◽  
Systematic Errors ◽  
Reference Star ◽  
Star Catalog ◽  
Optical Reference ◽  
First Results

AbstractBlock adjustment (BA) simulations of an entire hemisphere show major improvements in individual as well as systematic accuracy of star positions obtained by photographic astrometry, independent of systematic errors of the reference star catalog used. Results for the accuracy estimates obtained from a patch-like plate pattern in the sky are not valid for closed plate pattern. The importance of BA methods for the realisation of a reference system is stressed.

scholarly journals CPC2 Reduction with Hipparcos and Proper Motions in The Southern Hemisphere

1998 ◽  
Vol 11 (1) ◽  
pp. 551-551
Author(s):  
N. Zacharias ◽  
M.I. Zacharias ◽  
C. de Vegt ◽  
C.A. Murray
Keyword(s):  
Southern Hemisphere ◽  
Systematic Errors ◽  
Reference Star ◽  
Proper Motions ◽  
Positional Accuracy ◽  
Star Catalog ◽  
Naval Observatory ◽  
Celestial Reference System ◽  
First Time ◽  
Better Than

The Second Cape Photographic Catalog (CPC2) contains 276,131 stars covering the entire Southern Hemisphere in a 4-fold overlap pattern. Its mean epoch is 1968, which makes it a key catalog for proper motions. A new reduction of the 5687 plates using on average 40 Hipparcos stars per plate has resulted in a vastly improved catalog with a positional accuracy of about 40 mas (median value) per coordinate, which comes very close to the measuring precision. In particular, for the first time systematic errors depending on magnitude and color can be solved unambiguously and have been removed from the catalog. In combination with the Tycho Catalogue (mean epoch 1991.25) and the upcoming U.S. Naval Observatory CCD Astrograph Catalog (UCAC) project proper motions better than 2 mas/yr can be obtained. This will lead to a vastly improved reference star catalog in the Southern Hemisphere for the final Astrographic Catalogue (AC) reductions, which will then provide propermotions for millions of stars when combined with new epoch data. These data then will allow an uncompromised reduction of the southern Schmidt surveys on the International Celestial Reference System (ICRS).

scholarly journals Astrometry for New Reductions: The ANR method

2017 ◽  
Vol 12 (S330) ◽  
pp. 96-97
Author(s):  
Vincent Robert ◽  
Christophe Le Poncin-Lafitte
Keyword(s):  
Reference System ◽  
Reference Data ◽  
Reference Star ◽  
Error Budget ◽  
Star Catalog ◽  
Gaia Dr1 ◽  
Planets And Satellites

AbstractAccurate positional measurements of planets and satellites are used to improve our knowledge of their orbits and dynamics, and to infer the accuracy of the planet and satellite ephemerides. With the arrival of the Gaia-DR1 reference star catalog and its complete release afterward, the methods for ground-based astrometry become outdated in terms of their formal accuracy compared to the catalog's which is used. Systematic and zonal errors of the reference stars are eliminated, and the astrometric process now dominates in the error budget.We present a set of algorithms for computing the apparent directions of planets, satellites and stars on any date to micro-arcsecond precision. The expressions are consistent with the ICRS reference system, and define the transformation between theoretical reference data, and ground-based astrometric observables.

scholarly journals Hipparcos Astrometric Results

1998 ◽  
Vol 11 (1) ◽  
pp. 536-538
Author(s):  
J. Kovalevsky
Keyword(s):  
Proper Motion ◽  
Reference System ◽  
Systematic Errors ◽  
One Dimensional

Abstract The astrometric results of Hipparcos include the positions at epoch (1991.25), the proper motion in the new IAU extragalactic reference system (ICRS), and parallaxes for about 118 000 stars. One dimensional positions are also given for 48 asteroids and 3 satellites. Due to the non-isotropy of the scanning law, the uncertainties are position dependent. Some indications of the remaining correlations are given. Various tests and comparisons show that systematic errors in parallax, if any, are not larger than 0.1 millisecond of arc.

scholarly journals Progress Report on the Southern Proper Motion Program

1995 ◽  
Vol 166 ◽  
pp. 357-357
Author(s):  
I. Platais ◽  
T. M. Girard ◽  
V. Kozhurina-Platais ◽  
R. A. Mendez ◽  
W. F. Van Altena ◽  
...  
Keyword(s):  
Reference Frame ◽  
Proper Motion ◽  
Systematic Errors ◽  
Progress Report ◽  
Model Choice ◽  
Plate Model ◽  
Field Independent ◽  
The Status ◽  
First Results ◽  
Galaxy Model

We present the status of the Yale/San Juan Southern Proper Motion program (SPM) which is the southern hemisphere extension of the Lick Observatory Northern Proper Motion program with respect to faint galaxies (Platais et al., 1993). To date, measurements and reductions in the South Galactic Pole region comprising ≈ 1000 square-degrees on the sky have been finished. At this stage of the SPM program particular attention has been paid to the plate model choice along with an assessment of and accounting for systematic errors. For our establishing of a secondary reference frame we have noticed the presence of a potentially dangerous effect, so–called field–independent coma which is caused by lens decentering. We acknowledge the superb Hipparcos preliminary positions without which such analysis would be virtually impossible. The SPM data at the SGP region have also been used to constrain a multi–component Galaxy model. First results of this analysis are presented.

scholarly journals Interrelation of Present Optical and Radio Reference Frames

1984 ◽  
Vol 110 ◽  
pp. 357-360
Author(s):  
Chr. de Vegt
Keyword(s):  
Reference Frame ◽  
Northern Hemisphere ◽  
Reference Frames ◽  
Systematic Errors ◽  
Future Developments ◽  
Optical Reference

Comparison of optical and radio positions in the northern hemisphere yields local systematic differences up to 0″.2, mainly due to combined systematic errors of current optical reference frame and contributing main catalogues. Interrelations of radio/optical frame and future developments are discussed.

scholarly journals Precision vs. Accuracy in Star Catalogs

1995 ◽  
Vol 166 ◽  
pp. 372-372
Author(s):  
L. G. Taff ◽  
J. E. Morrison ◽  
R. L. Smart
Keyword(s):  
Random Error ◽  
A Priori ◽  
Systematic Errors ◽  
A Posteriori ◽  
New Techniques ◽  
Star Catalog ◽  
True Value ◽  
Reduction Methods ◽  
Star Catalogs ◽  
Comparable Amplitude

As better precision is achieved and more sophisticated reduction methods are created previously invisible biases surface. This has been especially true in astrometric Schmidt plate work. The problem of their amelioration is not fully solved and precision per se is meaningless in the presence of poor accuracy of comparable amplitude. Continuing to benignly neglect this issue puts us in the position of standing on only one statistical leg. New techniques have been designed to further minimize systematic errors. Of especial interest to star catalog analysis is the method of infinitely overlapping circles (Taff, Bucciarelli & Lattanzi, ApJ 361, 667, 1990; Taff, Bucciarelli & Lattanzi, ApJ 392, 746 1992; Bucciarelli, Taff & Lattanzi, J. Stat. Comp. and Sim. 48, 29 1993). With it almost complete success has occurred with regard to the removal of systematic errors which creep into compilation catalogs as a result of inadequate treatment of catalog-to-catalog systematic errors; they can essentially be eliminated a priori or a posteriori (Bucciarelli, Lattanzi & Taff, in press in ApJ 1994; Taff & Bucciarelli, in press in ApJ 1994). What infinitely overlapping circles does can be briefly described as follows: Let X (x) be the measured (true) value of a standard coordinate, S(x,y) (ε) be the systematic (random) error in x at this point, let w∞ be the infinitely overlapping circle weight, a be the standard deviation of the random error in x, N be the total number of stars in this circle which has radius R, and x0,y0 be the coordinates of the center of this circle.

scholarly journals Modernization of Chinese Photoelectric Astrolabes and Improvement of Optical Reference System

1990 ◽  
Vol 141 ◽  
pp. 519-520
Author(s):  
Li Dong-Ming ◽  
Wang Hong-Qi ◽  
Zhao Gang ◽  
Wang Ze-Zhi ◽  
Wang Rui
Keyword(s):  
High Precision ◽  
Reference System ◽  
Optical Reference ◽  
Set Up

The features of the astrolabe are that:(1) a span of 6 hour of R.A. of star positions can be tied in a group of observation of 2 hours, all-night observation can cover more than half of the sky, and(2) the declination system can be set up with high precision without the need of a precise circle (Li 1987).

scholarly journals Intermediate Star Reference Systems in the Vicinity of Radio Sources

1991 ◽  
Vol 127 ◽  
pp. 363-367
Author(s):  
V.V. Tel’nyuk-Adamchuk ◽  
I.I. Kumkova ◽  
S. Sadzakov ◽  
E. Toma ◽  
M.Yu. Volianska
Keyword(s):  
Reference System ◽  
Mutual Orientation ◽  
Radio Sources ◽  
Reference Star ◽  
Reference Systems ◽  
Fundamental Reference

AbstractIn the framework of CONFOR program the formation of star lists of two intermediate reference star systems is being carried out. The first list, RRS2, contains meridian stars in the fields centered at extragalactic radio/optical sources. The second one is formed on the base of 12-14 magnitude stars. The observations are in progress now. The main purpose of this program is to form a base for investigation of mutual orientation of fundamental reference system and new ones.

scholarly journals Desiderata for Fk5

1968 ◽  
Vol 1 ◽  
pp. 301-305 ◽  
Author(s):  
W. Fricke ◽  
W. Gliese
Keyword(s):  
Celestial Mechanics ◽  
Reference System ◽  
Inertial Frame ◽  
Large Range ◽  
Fundamental System ◽  
Systematic Errors ◽  
Frame Of Reference ◽  
Proper Motions ◽  
Astronomical Research ◽  
Positional Astronomy

A fundamental catalogue compiled from independent and differential observations of stellar positions at various epochs provides the fundamental system of positions and proper motions of the stars. The system ought to be compiled in such a way that it represents the inertial frame of reference as accurately as practicable. Its direct purpose is to serve as the reference system of positional astronomy. It should fulfil the requirements of astronomical research, in particular in celestial mechanics and galactic research, as well as the demands of the astronomical determinations of time and of latitudes. It has also to fulfil the requirements of geodesy and navigation. For all these purposes the system must be uniform over the whole sky (free from regional systematic errors), and it has to be uniform over a large range of stellar magnitudes (free from errors depending on the magnitude of the stars).

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