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Title: EVIDENCE FOR INFALLING GAS OF LOW ANGULAR MOMENTUM TOWARD THE L1551 NE KEPLERIAN CIRCUMBINARY DISK

We report follow-up C{sup 18}O(3-2) line observations of the Class I binary protostellar system L1551 NE with the Submillimeter Array 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, with more extensive spatial coverage (∼140-2000 AU), verify the presence of a Keplerian circumbinary disk and reveal for the first time a distinct low-velocity (∼< ± 0.5 km s{sup –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{sup –1}. This velocity is significantly smaller than the expected free-fall velocity of ∼2.2 km s{sup –1} onto the L1551 NE protostellar mass of ∼0.8 M{sub ☉} 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 the innermore » Keplerian circumbinary disk implies an abrupt transition in the effectiveness at which magnetic braking is able to transfer angular momentum outward, a result perhaps of the different plasma β values and the ionization fractions between the outer and inner regions of the circumbinary disk.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4]
  1. Academia Sinica Institute of Astronomy and Astrophysics, P.O. Box 23-141, Taipei 10617, Taiwan (China)
  2. Joint ALMA Observatory, Ave. Alonso de Cordova 3107, Vitacura, Santiago (Chile)
  3. Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong)
  4. ALMA Project Office, National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo 181-8588 (Japan)
Publication Date:
OSTI Identifier:
22270735
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 776; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ANGULAR MOMENTUM; ANGULAR MOMENTUM TRANSFER; ASTRONOMY; ASTROPHYSICS; CARBON 18; DIAGRAMS; MASS; MOLECULES; PLASMA; PROTOSTARS; RESOLUTION; STARS; VELOCITY