Precision Astrometry of a Sample of Speckle Binaries and Multiples with the Adaptive Optics Facilities at the Hale and Keck II Telescopes

TL;DR

This study demonstrates high-precision near-infrared adaptive optics astrometry of binary and multiple stars, achieving sub-milliarcsecond accuracy, which could enable detection of planetary-mass objects around these systems.

Contribution

We present a method for high-precision relative astrometry using adaptive optics, correcting for chromatic refraction and distortions, with potential for exoplanet detection.

Findings

Achieved astrometric precision below 1 milliarcsecond

Corrected for differential chromatic refraction and chip distortions

Set limits on planetary mass objects around observed stars

Abstract

Using the adaptive optics facilities at the 200-in Hale and 10-m Keck II, we observed in the near infrared a sample of 12 binary and multiple stars and one open cluster. We used the near diffraction limited images of these systems to measure the relative separations and position angles between their components. In this paper, we investigate and correct for the influence of the differential chromatic refraction and chip distortions on our relative astrometric measurements. Over one night, we achieve an astrometric precision typically well below 1 miliarcsecond and occasionally as small as 40 microarcseconds. Such a precision is in principle sufficient to astrometrically detect planetary mass objects around the components of nearby binary and multiple stars. Since we have not had sufficiently large data sets for the observed sample of stars to detect planets, we provide the limits to planetary mass objects based on the obtained astrometric precision.