Long live the disk: lifetimes of protoplanetary disks in hierarchical triple star systems and a possible explanation for HD 98800 B

RONCO, M P; GUILERA, O M; CUADRA, J; MILLER BERTOLAMI, M.

ASTROPHYSICAL JOURNAL

IOP PUBLISHING LTD

Lugar: Londres; Año: 2021

0004-637X

The gas dissipation from a protoplanetary disk is one of the key processesaffecting planet formation, and it is widely accepted that it happens ontimescales of a few million years for disks around single stars. Over the lastyears, several protoplanetary disks have been discovered in multiple starsystems, and despite the complex environment in which they find themselves,some of them seem to be quite old, a situation that may favor planet formation.A clear example of this is the disk around HD 98800 B, a binary in ahierarchical quadruple stellar system, which at a ∼10 Myr age seems tostill be holding significant amounts of gas. Here we present a 1D+1D model tocompute the vertical structure and gas evolution of circumbinary disks inhierarchical triple star systems considering different stellar and diskparameters.We show that tidal torques due to the inner binary together with thetruncation of the disk due to the external companion strongly reduce theviscous accretion and expansion of the disk. Even allowing viscous accretion bytidal streams, disks in these kind of environments can survive for more than 10Myr, depending on their properties, with photoevaporation being the main gasdissipation mechanism. We particularly apply our model to the circumbinary diskaround HD 98800 B and confirm that its longevity, along with the currentnon-existence of a disk around the companion binary HD 98800 A, can beexplained with our model and by this mechanism.