EXor outbursts from disk amplification of stellar magnetic cycles

Abstract

EXor outbursts - moderate-amplitude disk accretion events observed in Class I and Class II protostellar sources - have time scales and amplitudes that are consistent with the viscous accumulation and release of gas in the inner disk near the dead zone boundary. We suggest that outbursts are indirectly triggered by stellar dynamo cycles, via poloidal magnetic flux that diffuses radially outward through the disk. Interior to the dead zone the strength of the net field modulates the efficiency of angular momentum transport by the magnetorotational instability. In the dead zone changes in the polarity of the net field may lead to stronger outbursts because of the dominant role of the Hall effect in this region of the disk. At the level of simple estimates we show that changes to kG-strength stellar fields could stimulate disk outbursts on 0.1 AU scales, though this optimistic conclusion depends upon the uncertain efficiency of net flux transport through the inner disk. The model predicts a close association between observational tracers of stellar magnetic activity and EXor events.

ApJL, in press

References in corpus (4)

• Accretion Outbursts in Self-gravitating Protoplanetary Disks
• Advection/Diffusion of Large-Scale B-Field in Accretion Disks
• Global evolution of the magnetic field in a thin disc and its consequences for protoplanetary systems
• The Differential Rotation of FU Ori

Cited by in corpus (11)

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• Accretion bursts in magnetized gas-dust protoplanetary disks
• Radiative Transfer modeling of EC 53: An Episodically Accreting Class I Young Stellar Object
• The circumstellar environment around the embedded protostar EC 53
• Inferring possible magnetic field strength of accreting inflows in EXor-type objects from scaled laboratory experiments
• Large amplitude periodic outbursts and long period variables in the VVV VIRAC2-$\beta$ database
• Accretion Burst Echoes as Probes of Protostellar Environments and Episodic Mass Assembly
• EXORCISM: a spectroscopic survey of young eruptive variables (EXor and candidates)
• JWST captures a sudden stellar outburst and inner disk wall destruction
• Halting Migration in Magnetospherically Sculpted Protoplanetary Disks