Micro-arcsecond relative astrometry by ground-based and single-aperture observations

Testing general relativity by micro-arcsecond global astrometry

The global astrometric observations of a GAIA-like satellite were modeled within the PPN formulation of Post-Newtonian gravitation. An extensive experimental campaign based on realistic end-to-end simulations was conducted to establish the sensitivity of global astrometry to the PPN parameter γ, which measures the amount of space curvature produced by unit rest mass. The results show that, with...

Improvements of astrometry from ground based observatories

The analysis of planetary satellites or asteroids ground based observations is quite similar. Our first goal was to improve the astrometric reduction for digitized photographic plates in case of too few reference stars and to propose solutions. We here present astrometric techniques used for old observations of the Galilean satellites made with the 26-inch refractor of USNO in Washington DC fro...

Getting ready for the micro-arcsecond era

As the title of this symposium implies, one of the aims is to examine the future of astrometry as we move from an era in which thanks to the Hipparcos Catalogue everyone has become familiar with milliarcsecond astrometry to an era in which microarcsecond astrometry will become the norm. I will take this look into the future by first providing an overview of present astrometric programmes and ho...

Spectro - Astrometry : Studying Structure on Milli - Arcsecond Scales with the Aat

Differential Astrometry of Sub-arcsecond Scale Binaries at the Palomar Testbed Interferometer

We have used the Palomar Testbed Interferometer to perform very high precision differential astrometry on the 0.25 arcsecond separation binary star HD 171779. In 70 minutes of observation we achieve a measurement uncertainty of ≈ 9 micro-arcseconds in one axis, consistent with theoretical expectations. Nightto-night repeatability over four nights is at the level of 16 micro-arcseconds. This met...