Results from The COPAINS Pilot Survey: four new brown dwarfs and a high companion detection rate for accelerating stars

TL;DR

The COPAINS survey used Gaia astrometry to efficiently identify sub-stellar companions, discovering four new brown dwarfs and demonstrating a high detection rate for accelerating stars, thus enhancing understanding of companion formation.

Contribution

This study introduces the COPAINS survey and FORECAST tool, demonstrating an effective method for detecting sub-stellar companions using astrometric signatures from Gaia data.

Findings

Discovered four new brown dwarfs among 25 stars observed.

Achieved a high companion detection rate for stars with significant proper motion differences.

Validated the effectiveness of Gaia-based astrometric signatures in revealing sub-stellar companions.

Abstract

The last decade of direct imaging (DI) searches for sub-stellar companions has uncovered a widely diverse sample that challenges the current formation models, while highlighting the intrinsically low occurrence rate of wide companions, especially at the lower end of the mass distribution. These results clearly show how blind surveys, crucial to constrain the underlying planet and sub-stellar companion population, are not an efficient way to increase the sample of DI companions. It is therefore becoming clear that efficient target selection methods are essential to ensure a larger number of detections. We present the results of the COPAINS Survey conducted with SPHERE/VLT, searching for sub-stellar companions to stars showing significant proper motion differences (Delta mu) between different astrometric catalogues. We observed twenty-five stars and detected ten companions, including four new brown dwarfs: HIP 21152 B, HIP 29724 B, HD 60584 B and HIP 63734 B. Our results clearly demonstrates how astrometric signatures, in the past only giving access to stellar companions, can now thanks to Gaia reveal companions well in the sub-stellar regime. We also introduce FORECAST (Finley Optimised REtrieval of Companions of Accelerating STars), a tool which allows to check the agreement between position and mass of the detected companions with the measured Delta mu. Given the agreement between the values of the masses of the new sub-stellar companions from the photometry with the model-independent ones obtained with FORECAST, the results of COPAINS represent a significant increase of the number of potential benchmarks for brown dwarf and planet formation and evolution theories.