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Title:
Precision Astrometry With Adaptive Optics
Authors:
Cameron, P. B.; Britton, M. C.; Kulkarni, S. R.
Affiliation:
AA(California Institute of Technology, Division Physics, Mathematics and Astronomy, MC 105-24, Pasadena, CA 91125, USA ), AB(California Institute of Technology, Division Physics, Mathematics and Astronomy, MC 105-24, Pasadena, CA 91125, USA), AC(California Institute of Technology, Division Physics, Mathematics and Astronomy, MC 105-24, Pasadena, CA 91125, USA)
Publication:
The Astronomical Journal, Volume 137, Issue 1, pp. 83-93 (2009). (AJ Homepage)
Publication Date:
01/2009
Origin:
IOP
AJ Keywords:
astrometry, globular clusters: individual: M5, instrumentation: adaptive optics, methods: statistical
DOI:
10.1088/0004-6256/137/1/83
Bibliographic Code:
2009AJ....137...83C

Abstract

We investigate the limits of ground-based astrometry with adaptive optics using the core of the Galactic globular cluster M5. Adaptive optics systems provide near diffraction-limit imaging with the world's largest telescopes. The substantial improvement in both resolution and signal-to-noise ratio enables high-precision astrometry from the ground. We describe the dominant systematic errors that typically limit ground-based differential astrometry, and enumerate observational considerations for mitigating their effects. After implementing these measures, we find that the dominant limitation on astrometric performance in this experiment is caused by tilt anisoplanatism. We then present an optimal estimation technique for measuring the position of one star relative to a grid of reference stars in the face of this correlated random noise source. Our methodology has the advantage of reducing the astrometric errors to {\sim}1/\sqrt{t} and faster than the square root of the number of reference stars, effectively eliminating noise caused by atmospheric tilt to the point that astrometric performance is limited by centering accuracy. Using 50 reference stars, we demonstrate a single-epoch astrometric precision of ≈1 mas in 1 s, decreasing to lsim100 μas in 2 minutes of integration time at the Hale 200 inch telescope. We also show that our astrometry is accurate to lsim100 μas for observations separated by 2 months. Finally, we discuss the limits and potential of differential astrometry with current and next-generation large-aperture telescopes. At this level of accuracy, numerous astrometric applications become accessible, including planet detection, astrometric microlensing signatures, and kinematics of distant Galactic stellar populations.
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