Extreme adaptive optics astrometry of R136. Searching for high proper motion stars

TL;DR

This study used ground-based adaptive optics to measure the proper motions of stars in R136's core, identifying candidates with extremely high velocities that could indicate dynamic interactions or ejections.

Contribution

First ground-based adaptive optics monitoring of R136's core to detect high proper motion stars, revealing potential candidates with extreme velocities.

Findings

Identified two stars with proper motions of ~1.3 mas/yr (~300 km/s).

Demonstrated the feasibility of ground-based AO for dynamic studies in dense stellar regions.

Highlighted the need for future observations to confirm the nature of these high-velocity stars.

Abstract

We compared high-contrast near-infrared images of the core of R136 taken by VLT/SPHERE, in two epochs separated by 3.06 years. For the first time we monitored the dynamics of the detected sources in the core of R136 from a ground-based telescope with adaptive optics. The aim of these observations was to search for High prOper Motion cAndidates (HOMAs) in the central region of R136 (r<6") where it has been challenging for other instruments. Two bright sources (K<15mag and V<16mag) are located near R136a1 and R136c (massive WR stars) and have been identified as potential HOMAs. These sources have significantly shifted in the images with respect to the mean shift of all reliable detected sources and their neighbours, and six times their own astrometric errors. We calculate their proper motions to be 1.36\pm0.22 mas/yr (321\pm52 km/s) and 1.15\pm0.11 mas/yr (273\pm26 km/s). We discuss different possible scenarios to explain the magnitude of such extreme proper motions, and argue for the necessity to conduct future observations to conclude on the nature of HOMAs in the core of R136.