The visual binary AG Tri in $\beta$ Pictoris Association: can a debris disc cause very different rotation periods of its components?

TL;DR

This study measures rotation periods of binary star components in a young association, exploring how debris discs might influence their differing rotation rates through primordial disc dispersal or angular momentum transfer.

Contribution

It provides the first detailed rotation period measurements for both components of AG Tri, linking debris disc presence to rotation period differences in young binaries.

Findings

AG Tri A has a rotation period of 12.4 days.

AG Tri B has a rotation period of 4.66 days.

Detection of a flare event on AG Tri B.

Abstract

We measure the photometric rotation periods of the components of multiple systems in young stellar associations to investigate the causes of the observed rotation period dispersion. We present the case of the wide binary AG Tri in the 23-Myr young beta Pictoris Association consisting of K4 + M1 dwarfs. Our multi-band, multi-season photometric monitoring allowed us to measure the rotation periods of both components P_A = 12.4d and P_B = 4.66d, to detect a prominent magnetic activity in the photosphere, likely responsible for the measured radial velocity variations, and for the first time, a flare event on the M1 component AG Tri B. We investigate either the possibility that the faster rotating component may have suffered an enhanced primordial disc dispersal, starting its PMS spin-up earlier than the slower rotating component, or the possibility that the formation of a debris disc may have prevented AG Tri A from gaining part of the angular momentum from the accreting disc.