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 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 The Absolute Proper Motion of the Pleiades Cluster

1970 ◽  
Vol 7 ◽  
pp. 103-104
Author(s):  
W. F. van Altena ◽  
B. F. Jones
Keyword(s):  
Northern Hemisphere ◽  
Proper Motion ◽  
Reference System ◽  
The Absolute

The establishment of a truly inertial reference system is a problem that has defied solution for many years. However, with the completion of the Lick proper motion survey (Wright 1950) and the USSR program (Deutsch 1954) the situation for the northern hemisphere should be satisfactory.

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).

scholarly journals Errors in high precision source position determination

1991 ◽  
Vol 131 ◽  
pp. 307-311
Author(s):  
Pedro Elosegui ◽  
Juan-Maria Marcaide ◽  
Irwin I. Shapiro
Keyword(s):  
Detailed Analysis ◽  
High Precision ◽  
Proper Motion ◽  
Systematic Errors ◽  
Source Position ◽  
Position Determination ◽  
The Core ◽  
Vlbi Observations

AbstractWe have made a detailed analysis of the systematic errors in the determination, from two sets of VLBI observations, of the position of the quasar 1038+528 A relative to the quasar 1038+528 B. This analysis confirms an apparent proper motion at λ=3.6cm of 26±8 μas/yr of the core of the quasar 1038+528 A relative to the quasar 1038+528 B.

scholarly journals Status and Needs of Astrometry

1979 ◽  
Vol 50 ◽  
pp. 19-1-19-9
Author(s):  
James A. Hughes
Keyword(s):  
Stellar Evolution ◽  
Proper Motion ◽  
Reference System ◽  
Binary Star ◽  
Stellar Dynamics ◽  
Inertial Reference Frame ◽  
Star Studies ◽  
The Status ◽  
Near Future ◽  
Fundamental Reference

AbstractA review will be presented of the status of the fundamental reference system. Mention will be made of the problems limiting the accuracy of transit circles and photographic astrometry and attempts at possible improvments in the near future. The progress in the preparation of the FK5 will be briefly mentioned, as will be the various methods used to approximate an inertial reference frame. Needs for higher accuracy in Astronomy fall in the area of better modeling of the Earth's motion (rotation, nutation, precession, the ecliptic, etc.) as well as a parallax and proper motion determination for galactic structure studies, stellar dynamics and stellar evolution. It will be assumed that interferometric binary star studies will be discussed elsewhere.

Holding or Breaking with Ptolemy's Generalization: Considerations about the Motion of the Planetary Apsidal Lines in Medieval Islamic Astronomy

2017 ◽  
Vol 30 (1) ◽  
pp. 1-32 ◽  
Author(s):  
S. Mohammad Mozaffari
Keyword(s):  
Proper Motion ◽  
Reference System ◽  
Ninth Century ◽  
The Other ◽  
Islamic Period ◽  
General Proposition

ArgumentIn the Almagest, Ptolemy finds that the apogee of Mercury moves progressively at a speed equal to his value for the rate of precession, namely one degree per century, in the tropical reference system of the ecliptic coordinates. He generalizes this to the other planets, so that the motions of the apogees of all five planets are assumed to be equal, while the solar apsidal line is taken to be fixed. In medieval Islamic astronomy, one change in this general proposition took place because of the discovery of the motion of the solar apogee in the ninth century, which gave rise to lengthy discussions on the speed of its motion. Initially Bīrūnī and later Ibn al-Zarqālluh assigned a proper motion to it, although at different rates. Nevertheless, appealing to the Ptolemaic generalization and interpreting it as a methodological axiom, the dominant idea became to extend it in order to include the motion of the solar apogee as well. Another change occurred after correctly making a distinction between the motion of the apogees and the rate of precession. Some Western Islamic astronomers generalized Ibn al-Zarqālluh's proper motion of the solar apogee to the apogees of the planets. Analogously, Ibn al-Shāṭir maintained that the motion of the apogees is faster than precession. Nevertheless, the Ptolemaic generalization in the case of the equality of the motions of the apogees remained untouchable, despite the notable development of planetary astronomy, in both theoretical and observational aspects, in the late Islamic period.

Three Novel Methods to Predict Traffic Time Series in Reconstructed State Spaces

2012 ◽  
pp. 16-35 ◽  
Author(s):  
Lawrence W. Lan ◽  
Feng-Yu Lin ◽  
April Y. Kuo
Keyword(s):  
Time Series ◽  
Temporal Evolution ◽  
Fuzzy Reasoning ◽  
Systematic Errors ◽  
Short Term ◽  
Traffic Counts ◽  
State Spaces ◽  
One Dimensional ◽  
Traffic Time Series ◽  
Novel Methods

This article proposes three novel methods—temporal confined (TC), spatiotemporal confined (STC) and spatial confined (SC)—to forecast the temporal evolution of traffic parameters. The fundamental rationales are to embed one-dimensional traffic time series into reconstructed state spaces and then to perform fuzzy reasoning to infer the future changes in traffic series. The TC, STC and SC methods respectively employ different fuzzy reasoning logics to select similar historical traffic trajectories. Theil inequality coefficient and its decomposed components are used to evaluate the predicting power and source of errors. Field observed one-minute traffic counts are used to test the predicting power. The results show that overall prediction accuracies for the three methods are satisfactorily high with small systematic errors and little deviation from the observed data. It suggests that the proposed three methods can be used to capture and forecast the short-term (e.g., one-minute) temporal evolution of traffic parameters.

scholarly journals Multidimensional and inhomogeneity effects on scattering polarization in solar prominences

2013 ◽  
Vol 8 (S300) ◽  
pp. 453-455
Author(s):  
Ivan Milić ◽  
Marianne Faurobert
Keyword(s):  
Magnetic Field ◽  
Systematic Errors ◽  
Single Scattering ◽  
Slab Model ◽  
One Dimensional ◽  
Solar Prominences ◽  
Scattering Approximation ◽  
Self Consistent ◽  
The Magnetic Field ◽  
Single Scattering Approximation

AbstractMeasurements of magnetic fields in solar prominences via Hanle effect usually assume either single scattering approximation or simple, one-dimensional, slab model in order to perform an inversion and find the unknown magnitude and the orientation of the magnetic field from spectropolarimetric observations. Here we perform self-consistent NLTE modeling of scattering polarization in inhomogeneous 2D slab, illuminated from its sides by the solar continuum radiation. We show that even in the absence of a magnetic field, in the non-optically thin regime, significant non-zero Stokes U is to be expected. Neglecting these effects, in principle, could cause systematic errors in spectropolarimetric inversions, in the case when the prominence is optically thick.

scholarly journals Comparison of Hipparcos Proper-Motion System to the FK5

2000 ◽  
Vol 180 ◽  
pp. 104-109
Author(s):  
Zi Zhu ◽  
Wenjing Jin
Keyword(s):  
Proper Motion ◽  
Systematic Errors ◽  
Proper Motions ◽  
Motion System ◽  
Two Systems ◽  
External Galaxies

AbstractWe present an intensive analysis of the FK5 proper-motion system via the two large astrographic catalogs, the PPM and ACRS catalogs, compared with the Hipparcos proper motions. Regional, magnitude, and color-dependent systematic errors in the PPM and ACRS proper motions are found, and exhibit similar tendencies for both catalogs. The term of the global rotation between the FK5 and Hipparcos proper-motion systems cannot be explained by the constant of the FK5 precessional correction, which is given by the VLBI and LLR observations. Comparing the Hipparcos proper motions with those of the SPM 2.0 Catalog, which provides absolute proper motions of objects measured directly relative to external galaxies, we found neither strong systematic nor large regional errors between the two systems.

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