Evidence for Infalling Gas of Low Angular Momentum towards the L1551 NE Keplerian Circumbinary Disk

Abstract

We report follow-up observations of the Class I binary protostellar system L1551 NE in the C18O (3--2) line with the SMA in its compact and subcompact configurations. Our previous observations at a higher angular resolution in the extended configuration revealed a circumbinary disk exhibiting Keplerian motion. The combined data having more extensive spatial coverage (~140 - 2000 AU) verify the presence of a Keplerian circumbinary disk, and reveals for the first time a distinct low-velocity (~< +-0.5 km s-1 from the systemic velocity) component that displays a velocity gradient along the minor axis of the circumbinary disk. Our simple model that reproduces the main features seen in the Position-Velocity diagrams comprises a circumbinary disk exhibiting Keplerian motion out to a radius of ~300 AU, beyond which the gas exhibits pure infall at a constant velocity of ~0.6 km s-1. The latter is significantly smaller than the expected free-fall velocity of ~2.2 km s-1 onto the L1551 NE protostellar mass of ~0.8 Msun at ~300 AU, suggesting that the infalling gas is decelerated as it moves into regions of high gas pressure in the circumbinary disk. The discontinuity in angular momenta between the outer infalling gas and inner Keplerian circumbinary disk implies an abrupt transition in the effectiveness at which magnetic braking is able to transfer angular momentum outwards, a result perhaps of the different plasma beta and ionization fractions between the outer and inner regions of the circumbinary disk.

23 pages, 5 figures

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Cited by in corpus (20)

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• No Keplerian Disk >10 AU around the Protostar B335: Magnetic Braking or Young Age?
• The impact of the Hall effect during cloud core collapse:implications for circumstellar disk evolution
• Spiral Arms, Infall, and Misalignment of the Circumbinary Disk from the Circumstellar Disks in the Protostellar Binary System L1551 NE
• Transition from the Infalling Envelope to the Keplerian Disk around L1551 IRS 5
• Active-Region Tilt Angles: Magnetic Versus White-Light Determinations of Joy's Law
• A Spitzer Five-Band Analysis of the Jupiter-Sized Planet TrES-1
• Angular Momentum Exchange by Gravitational Torques and Infall in the Circumbinary Disk of the Protostellar System L1551 NE
• The Mass Accretion Rate and Stellar Properties in Class I Protostars
• Disk structure around the Class I protostar L1489 IRS revealed by ALMA: a warped disk system
• Structure of a protobinary system: an asymmetric circumbinary disk and spiral arms
• Rotationally-Driven Fragmentation for the Formation of the Binary Protostellar System L1551 IRS 5
• Possible Counter Rotation between the Disk and Protostellar Envelope around the Class I Protostar IRAS 04169+2702
• Physical and Chemical Structure of the Disk and Envelope of the Class 0/I Protostar L1527
• Formation of the Unequal-Mass Binary Protostars in L1551 NE by Rotationally-Driven Fragmentation
• Dispersing Envelope around the Keplerian Circumbinary Disk in L1551 NE and its Implications for the Binary Growth
• Synthetic Observations of the Infalling Rotating Envelope: Links between the Physical Structure and Observational Features
• Infrared Variability from Circumbinary Disc Temperature Modulations
• A Streamer Driving Misalignment in the Circumtriple Disk of GW Ori