Authors / CoAuthors
Titov, O.
Abstract
Many of the compact extragalactic radio sources that are used as fiducial points to define the celestial reference frame are known to have proper motions detectable with long-term geodetic/astrometric Very Long Baseline Interferometry (VLBI) measurements. These changes can be as high as several hundred micro-arcseconds per year for certain objects. When imaged with VLBI at milli-arcsecond (mas) angular resolution, these sources (radio-loud active galactic nuclei) typically show structures dominated by a compact, often unresolved ``core'' and a one-sided ``jet''. The positional instability of compact radio sources is believed to be connected with the changes in their brightness distribution structure. We test this assumption, not for individual objects, but in a statistical sense on a large sample. We investigate a sample of 68 radio sources for which reliable long-term time series of astrometric positions as well as detailed 8-GHz VLBI brightness distribution models are available. We compare the characteristic direction of their extended jet structure and the direction of their apparent proper motion. We present our data and analysis method, and conclude that the correlation between the two characteristic directions is weak. This can be naturally explained if the VLBI jet directions are misaligned between the 1-10 mas and sub-mas angular scales in a significant fraction of sources. It is also possible that systematic all-sky effects are present in the measured apparent proper motion data.
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nonGeographicDataset
eCat Id
69179
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- External Publication
- ( Theme )
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- geodesy
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2009-01-01T00:00:00
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