Long-lived protoplanetary disks in multiple systems: the VLA view of HD 98800

TL;DR

This study uses VLA observations to analyze the protoplanetary disk in the quadruple system HD 98800, revealing a small, massive, and possibly gas-rich disk that challenges typical disk evolution models and suggests extended planet formation timescales in multiple systems.

Contribution

First detailed VLA imaging of HD 98800's disk, showing its small size, structure, and potential gas content, and proposing a new scenario for disk evolution influenced by tidal torques and photoevaporation.

Findings

HD 98800 B hosts a small, massive, optically thick disk.

The disk shows signs of ongoing gas retention and photoevaporative winds.

The system's dynamics may prolong planet formation in multiple star systems.

Abstract

The conditions and evolution of protoplanetary disks in multiple systems can be considerably different from those around single stars, which may have important consequences for planet formation. We present Very Large Array (VLA) 8.8 mm (34 GHz) and 5 cm (6 GHz) observations of the quadruple system HD 98800, which consists of two spectroscopic binary systems (Aa-Ab, Ba-Bb). The Ba-Bb pair is surrounded by a circumbinary disk, usually assumed to be a debris disk given its $\sim$10 Myr age and lack of near infrared excess. The VLA 8.8 mm observations resolve the disk size (5-5.5 au) and its inner cavity ($\approx$3 au) for the first time, making it one of the smallest disks known. Its small size, large fractional luminosity, and millimeter spectral index consistent with blackbody emission support the idea that HD 98800 B is a massive, optically thick ring which may still retain significant amounts of gas. The disk detection at 5 cm is compatible with free-free emission from photoionized material. The diskless HD 98800 A component is also detected, showing partial polarization at 5 cm compatible with non-thermal chromospheric activity. We propose that tidal torques from Ba-Bb and A-B have stopped the viscous evolution of the inner and outer disk radii, and the disk is evolving via mass loss through photoevaporative winds. This scenario can explain the properties and longevity of HD 98800 B as well as the lack of a disk around HD 98800 A, suggesting that planet formation could have more time to proceed in multiple systems than around single stars in certain system configurations.