Limits of ultra-high-precision optical astrometry

Limits of ultra-high-precision optical astrometry: Stellar surface structures

Aims. To investigate the astrometric effects of stellar surface structures as a practical limitation to ultra-high-precision astrometry, e.g. in the context of exoplanet searches, and to quantify the expected effects in different regions of the HR-diagram. Methods. Stellar surface structures (spots, plages, granulation, non-radial oscillations) are likely to produce fluctuations in the integrat...

High Precision Differential Astrometry

While conventional imaging in VLBI provides information only about the relative position between different features of a given source, phase-referenced observations can provide precise positional information with respect to an external reference. The use of differential techniques relies on the fact that most of the instrumental and propagation effects are common for radio sources sufficiently ...

High-precision Timing of Millisecond Pulsars and Precision Astrometry

We present the technique of long-term, high-precision timing of millisecond pulsars as applied to precision astrometry. We provide a tutorial on pulsars and pulsar timing, as well as up-to-date results of long-term timing observations of two millisecond pulsars, PSRs B1855+09 and B1937+21. We consider the feasibility of tying the extragalactic and optical reference frames to that deened by sola...

Ultra-precision Float Polishing of Optical Materials

Modelling of a Space-based Ronchi Ruling High-precision Astrometry

An end-to-end rnodelling program for an astrometric telescope employing a Ronclli ruling has been developed. The program models the aberrated images formed anywhere in the field-of-view. It then determines apparent centroids by simulating the motion of a Ronchi ruling across the field. Photo-electran statistic+ are included. A 6 term plate-constant model is used to determine the apparent motion...