EXor OUTBURSTS FROM DISK AMPLIFICATION OF STELLAR MAGNETIC CYCLES

Journal Article · Tue Dec 20 04:00:00 EST 2016 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8213/833/2/L15· OSTI ID:22654138

EXor outbursts—moderate-amplitude disk accretion events observed in Class I and Class II protostellar sources—have timescales 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.

• OSTI ID: 22654138
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 833; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
AMPLIFICATION
AMPLITUDES
ANGULAR MOMENTUM
EFFICIENCY
INSTABILITY
MAGNETIC FLUX
PLANETS
PROTOPLANETS
SATELLITES
STARS