ALMA Observations of the Protostar L1527 IRS: Probing Details of the Disk and the Envelope Structures

Abstract

We have newly observed the Class 0/I protostar L1527 IRS using the Atacama Large Millimeter/submillimeter Array (ALMA) during its Cycle 1 in 220 GHz dust continuum and C18O (J=2-1) line emissions with a ~2 times higher angular resolution (~0.5") and ~4 times better sensitivity than our ALMA Cycle 0 observations. Continuum emission shows elongation perpendicular to the associated outflow, with a deconvolved size of 0.53"x0.15". C18O emission shows similar elongation, indicating that both emissions trace the disk and the flattened envelope surrounding the protostar. The velocity gradient of the C18O emission along the elongation due to rotation of the disk/envelope system is re-analyzed, identifying Keplerian rotation proportional to r^-0.5 more clearly than the Cycle 0 observations. The Keplerian-disk radius and the dynamical stellar mass are kinematically estimated to be ~74 AU and ~0.45 Mo, respectively. The continuum visibility is fitted by models without any annulus averaging, revealing that the disk is in hydrostatic equilibrium. The best-fit model also suggests a density jump by a factor of ~5 between the disk and the envelope, suggesting that disks around protostars can be geometrically distinguishable from the envelope from a viewpoint of density contrast. Importantly, the disk radius geometrically identified with the density jump is consistent with the radius kinematically estimated. Possible origin of the density jump due to the mass accretion from the envelope to the disk is discussed. C18O observations can be reproduced by the same geometrical structures derived from the dust observations, with possible C18O freeze-out and localized C18O desorption.

18 pages, 10 figures, accepted for publication in The Astrophysical Journal

References in corpus (15)

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• Signs of Early-Stage Disk Growth Revealed with ALMA
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• The Magnetic Field in the Class 0 Protostellar Disk of L1527
• 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
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• Submillimeter Structure of the Disk of the Butterfly Star

Cited by in corpus (5)

• On the diversity and statistical properties of protostellar discs
• The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars. A Statistical Characterization of Class 0 and I Protostellar Disks
• Searching for kinematic evidence of Keplerian disks around Class 0 protostars with CALYPSO
• ALMA Observations of SMM11 Reveal an Extremely Young Protostar in Serpens Main Cluster
• Time variability in the bipolar scattered light nebula of L1527 IRS: A possible warped inner disk