Errors in high precision source position determination

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.

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Supernova 1993J in M81

Symposium - International Astronomical Union ◽

10.1017/s0074180900221529 ◽

2001 ◽

Vol 205 ◽

pp. 380-383

Author(s):

M. F. Bietenholz ◽

N. Bartel ◽

M. P. Rupen ◽

A. J. Beasley ◽

D. A. Graham ◽

...

Keyword(s):

High Precision ◽

Proper Motion ◽

Supernova Remnants ◽

Dynamic Evolution ◽

Expansion Velocity ◽

The Core ◽

Early Stages ◽

Geometric Center ◽

The Galaxy ◽

Precision Astrometry

Twenty-two consecutive VLBI images of supernova 1993J in the galaxy M81 taken over 7 years show, in unprecedented detail, the dynamic evolution of the expanding radio shell of an exploded star. High precision astrometry using phase-referencing shows that the supernova expands isotropically, and that its geometric center has a formal proper motion of 190±110 km s−1 w.r.t. the core of M81. Systematic changes in the images most likely reflect a pattern of inhomogeneities in the medium left over from the progenitor star, or possibly instabilities in the expanding shell. As the shockfront sweeps up the medium, it is progressively decelerated, and after 7 years it has slowed to less than 1/2 its original expansion velocity. SN1993J is likely now entering the early stages of the adiabatic phase common in much older supernova remnants.

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The Binary Population of the Hyades

International Astronomical Union Colloquium ◽

10.1017/s0252921100099097 ◽

1984 ◽

Vol 88 ◽

pp. 385-388

Author(s):

Robert D. Mathieu ◽

Robert P. Stefanik ◽

David W. Latham

Keyword(s):

Star Formation ◽

Radial Velocity ◽

Detailed Analysis ◽

High Precision ◽

Formation Process ◽

Proper Motion ◽

Motion Data ◽

Chromospheric Activity ◽

Age Relations ◽

Insight Into

The nature of the binary population in clusters is of interest for numerous reasons. Through their study we gain insight into the star-formation process, dynamical interactions in the clusters, mass-luminosity-age relations, chromospheric activity and more. We have made a detailed analysis of the binary population of the Hyades, using radial-velocity, visual and proper-motion data in the literature and new multiple high-precision (σ = 0.85 km/sec) radial-velocity observations of over 100 Hyads with 6 < V < 14 (see Latham and Stefanik 1985 and this colloquium). Complete details are given in Mathieu 1983 and Mathieu, Stefanik and Latham 1985. In this report we focus our analysis on the 95 Hyads found by van Bueren (1952) with 6 < V < 9 (0.9 to 1.7 M⊙), thus providing a stellar sample analogous to that of the classic study of the field binary population by Abt and Levy (1976).

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Amateur Astronomers’ Contribution to the HIPPARCHOS Programme

International Astronomical Union Colloquium ◽

10.1017/s0252921100092289 ◽

1988 ◽

Vol 98 ◽

pp. 90-92

Author(s):

P. Bacchus

Keyword(s):

High Precision ◽

Proper Motion ◽

Thermal Deformation ◽

Thermal Control ◽

Systematic Errors ◽

Seasonal Effects ◽

List Type ◽

Type Number

The HIPPARCHOS satellite (High Precision Parallax Collecting Satellite) is designed to determine position, proper motion and parallax for a large number of stars. The precision expected (0.002 arcsec), and the absence of systematic errors with position in the sky arise from the following characteristics of the system: –Measurements of angular distances between stars a long way apart (58°), are by comparison with a very stable angular reference. This reference is formed by an optical block consisting of two plane mirrors, rigidly mounted, forming an angle of 29° between them, and sending two separate stellar fields into the same telescope;–the absence of flexure (thanks to weightlessness) and of thermal deformation (non-expansion material and thermal control) ensure that the angular reference is very stable;–operation outside the atmosphere allows the theoretical resolution to be reached; refraction, dispersion and atmospheric scintillation are avoided; diurnal and seasonal effects that interfere with ground-based measurements are non-existent.

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Proper Motion of Components of the Quasar 3C 345

Symposium - International Astronomical Union ◽

10.1017/s0074180900077809 ◽

1984 ◽

Vol 110 ◽

pp. 113-116

Author(s):

N. Bartel ◽

M. I. Ratner ◽

I.I. Shapiro ◽

T. A. Herring ◽

B. E. Corey

Keyword(s):

Proper Motion ◽

Single Component ◽

The Core ◽

Vlbi Observations

From five sets of VLBI observations spaced between 1972 and 1981, we estimated the positions of components of the superluminal quasar 3C 345 relative to the position of the single component of the quasar NRAO 512. The relative proper motion of the easternmost component of 3C 345, believed to be the “core”, was found to be 0.02±0.02 mas/yr. This result is consistent with the “core” being stationary and the “jet” components moving with respect to NRAO 512.

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VLBI Observations of the Radio Jet in 3C 273

Symposium - International Astronomical Union ◽

10.1017/s0074180900133844 ◽

1988 ◽

Vol 129 ◽

pp. 27-28

Author(s):

S. C. Unwin ◽

R. J. Davis

Keyword(s):

Dynamic Range ◽

Large Range ◽

High Dynamic Range ◽

No Emission ◽

The Core ◽

Vlbi Observations ◽

High Dynamic ◽

Quasar 3C 273

We present a new high dynamic range map of the quasar 3C 273, made from observations with a VLBI network of 12 telescopes. This new map at 18 cm wavelength has one of the highest dynamic ranges yet achieved with VLBI, and it shows the ‘jet’ extending to at least 180 milliarcsec, or 330 pc from the nucleus of the quasar. Strong limits can be placed on the brightness of any ‘counter-jet’ on kiloparsec-scales, as no emission is visible on the opposite side of the ‘core’. Combining with other VLBI, VLA and MERLIN maps shows that the jet is visible and continuous over a very large range of scales, from 1 pc to 40 kpc.

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Hipparcos Astrometric Results

Highlights of Astronomy ◽

10.1017/s1539299600021973 ◽

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.

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VLBI Pulsar Astrometry

Symposium - International Astronomical Union ◽

10.1017/s007418090022161x ◽

2001 ◽

Vol 205 ◽

pp. 404-407

Author(s):

R.M. Campbell

Keyword(s):

Proper Motion ◽

Vlbi Observations ◽

Recent Developments

I briefly review the means by which VLBI observations can determine the position, proper motion, and parallax of a pulsar, consider a subset of the applications of such results, and highlight recent developments in pulsar gating at JIVE.

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Progress Report on the Southern Proper Motion Program

Symposium - International Astronomical Union ◽

10.1017/s0074180900228404 ◽

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.

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