Lucky Imaging Adaptive Optics of the brown dwarf binary GJ569Bab

TL;DR

This study demonstrates that combining Adaptive Optics and Lucky Imaging enables high-precision optical astrometry and photometry of a brown dwarf binary, resolving the system and deriving new orbital parameters.

Contribution

It introduces a novel application of AO+LI techniques for detailed analysis of brown dwarf binaries, achieving high-resolution imaging and accurate measurements.

Findings

Resolved GJ569Bab binary at 98.4 mas separation

Measured I-band magnitudes and colors consistent with M8.5-M9 types

Derived orbital parameters aligning with previous data

Abstract

The potential of combining Adaptive Optics (AO) and Lucky Imaging (LI) to achieve high precision astrometry and differential photometry in the optical is investigated by conducting observations of the close 0\farcs1 brown dwarf binary GJ569Bab. We took 50000 $I$-band images with our LI instrument FastCam attached to NAOMI, the 4.2-m William Herschel Telescope (WHT) AO facility. In order to extract the most of the astrometry and photometry of the GJ569Bab system we have resorted to a PSF fitting technique using the primary star GJ569A as a suitable PSF reference which exhibits an $I$-band magnitude of $7.78\pm0.03$. The AO+LI observations at WHT were able to resolve the binary system GJ569Bab located at $4\farcs 92 \pm 0\farcs05$ from GJ569A. We measure a separation of $98.4 \pm 1.1$ mas and $I$-band magnitudes of $13.86 \pm 0.03$ and $14.48 \pm 0.03$ and $I-J$ colors of 2.72$\pm$0.08 and 2.83$\pm$0.08 for the Ba and Bb components, respectively. Our study rules out the presence of any other companion to GJ569A down to magnitude I$\sim$ 17 at distances larger than 1\arcsec. The $I-J$ colors measured are consistent with M8.5-M9 spectral types for the Ba and Bb components. The available dynamical, photometric and spectroscopic data are consistent with a binary system with Ba being slightly (10-20%) more massive than Bb. We obtain new orbital parameters which are in good agreement with those in the literature.