Improving Ground-Based Astrometry of the Galactic Center from Keck

Details Improving Ground-Based Astrometry of the Galactic Center from Keck Improving Ground-Based Astrometry of the Galactic Center from Keck

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21360603y&link_type=abstract

American Astronomical Society, AAS Meeting #213, #606.03

Physics

Optics

Scientific paper

With the advent of Laser Guide Star Adaptive Optics, sub-milliarcsecond astrometry has consistently been achieved on a wide variety of astronomical objects. High precision ground-based relative astrometry of the Galactic center (GC) is currently limited to 0.2 mas, while the absolute astrometry is known to 5 mas. Improving the level of astrometric precision even further could lead to ultra-precise measurements of the distance to the Galactic center, measurements of individual stellar orbits at larger galactocentric radii, and measurements of post-Newtonian effects in the orbits of short-period stars. Here we identify and correct two major limitations to our absolute astrometry - geometric optical distortions and differential atmospheric refraction. These effects introduce 1-5 mas scale distortions over the spatial scales of the SiO masers that are used to define the absolute reference frame for proper motions of stars at the GC. We improve upon existing geometric distortion solutions for the NIRC2 narrow camera at the W. M. Keck II 10 m telescope by a factor of more than 2 over previous solutions, and subsequently improve our knowledge of the Galactic center absolute reference frame. We also identify an unexpected time variable distortion effect that appears under low Strehl ratio conditions and has a high spatial frequency structure. While this work has been carried out in the context of the GC, the new distortion solution benefits the wide array of other science that is currently being carried out with NIRC2.

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