Precision Millimeter Astrometry of the $\alpha$ Centauri AB System
Rachel Akeson, Charles Beichman, Pierre Kervella, Edward Fomalont, and, G. Fritz Benedict

TL;DR
This paper reports initial high-precision millimeter-wavelength astrometric measurements of the alpha Centauri AB system, improving knowledge of its properties and demonstrating potential for detecting Earth-sized exoplanets in its habitable zone.
Contribution
It presents new absolute astrometric data and assesses ALMA's capability to detect terrestrial exoplanets around alpha Centauri A and B.
Findings
Improved measurements of proper motion, orbital motion, and parallax.
Estimated sensitivity to planets of a few tens of Earth masses.
Potential to detect planets in the 1-3 AU habitable zone.
Abstract
Centauri A is the closest solar-type star to the Sun and offers the best opportunity to find and ultimately to characterize an Earth-sized planet located in its Habitable Zone (HZ). Here we describe initial results from an ALMA program to search for planets in the Cen AB system using differential astrometry at millimeter wavelengths. Our initial results include new absolute astrometric measurements of the proper motion, orbital motion, and parallax of the Cen system. These lead to an improved knowledge of the physical properties of both Cen A and B. Our estimates of ALMA's relative astrometric precision suggest that we will ultimately be sensitive to planets of a few 10s of Earth mass in orbits from 1-3 AU, where stable orbits are thought to exist.
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