A nearby young M dwarf with a wide, possibly planetary-mass companion

TL;DR

This paper reports the discovery of a very wide, likely planetary-mass companion to a young M dwarf, providing insights into wide binary formation and evolution in the context of young stellar associations.

Contribution

It identifies a likely bound, extremely wide binary with a planetary-mass secondary, and refines its age, mass, and kinematic properties, linking it to young stellar groups.

Findings

The secondary has a mass of 11.6-15 M_J.

The pair is likely a bound system with a separation >4500 AU.

The system's age is estimated between 10-45 Myr.

Abstract

We present the identification of two previously known young objects in the solar neighbourhood as a likely very wide binary. TYC 9486-927-1, an active, rapidly rotating early-M dwarf, and 2MASS J21265040-8140293, a low-gravity L3 dwarf previously identified as candidate members of the $\sim$45 Myr old Tucana Horologium association (TucHor). An updated proper motion measurement of the L3 secondary, and a detailed analysis of the pair's kinematics in the context of known nearby, young stars, reveals that they share common proper motion and are likely bound. New observations and analyses reveal the primary exhibits Li 6708~\AA~absorption consistent with M dwarfs younger than TucHor but older than the $\sim$10 Myr TW Hydra association yielding an age range of 10-45 Myr. A revised kinematic analysis suggests the space motions and positions of the pair are closer to, but not entirely in agreement with, the $\sim$24 Myr old $\beta$ Pictoris moving group. This revised 10-45 Myr age range yields a mass range of 11.6--15 M$_J$ for the secondary. It is thus likely 2MASS J21265040-8140293short is the widest orbit planetary mass object known ($>$4500AU) and its estimated mass, age, spectral type, and $T_{eff}$ are similar to the well-studied planet $\beta$ Pictoris b. Because of their extreme separation and youth, this low-mass pair provide an interesting case study for very wide binary formation and evolution.