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Lucia Plank
Type of contribution: oral

On the estimation of a celestial reference frame in the presence of source structure

Lucia Plank, University of Tasmania Stas Shabala, University of Tasmania Jamie McCallum, University of Tasmania Hana Kr{'a}sn{'a}, Technische Universit{"a}t Wien Liza Rastorgueva-Foi, University of Tasmania Bill Petrachenko, Natural Resources Canada

The presence of source structure has long been identified as a non-zero contribution to the group delay measured by VLBI. It has also been shown that the positions of sources with high structure show larger variability or even systematic apparent motion. Using simulations of the IVS rapid session schedules, we investigate the effects of simple two-component sources on globally estimated source positions. We find that sources with nominal structure indices 2, 3, and 4 can all cause systematic displacements of source positions at the level of tens to hundreds of microarcseconds, clearly above today’s level of source position uncertainties. In a thorough simulation study we compare multiple source models with only slightly changed parameters, namely the relative brightness of the two components and their separation. We then investigate the characteristics of the effects, i.e. that the source position is apparently moved along the jet axis of the source, which is the line between the two components of the source model. Finally we present an idea how to account for this dislocation in the analysis when estimating a celestial reference frame.