W49N MCN-a: a disk accreting massive protostar embedded in an early-phase hot molecular core

Abstract

We present ALMA archival data for 219-235 GHz continuum and line observations toward the hot molecular core (HMC) W49N MCN-a (UCHII region J1) at a resolution of ~0."3. The dust continuum emission, showing an elongated structure of 1."40x0."95 (PA=43.5deg) perpendicular to the outflow seen in SiO and SO, represents a rotating flattened envelope, or torus, with a radius of 7,800au inclined at 47.5deg or larger. The emissions from CH3CN and 11 molecular lines exhibit a consistent velocity gradient as a result of rotation. The magnitude of each velocity gradient is different, reflecting that each line samples a specific radial region. This allows us to derive a rotation curve as Vrot prop R^0.44+-0.11 for 2,400au < R < 14,000au, giving the dynamical mass as Mdyn = 57.0+24.5-17.1 (R [au]/3, 000)^1.88 Msun. The envelope mass independently estimated from the dustemission is 910Msun (for Tdust =180K) for R<7,800au and 32Msun (for Tdust=300K) for R<1,700 au. The dynamical mass formula agrees well with these mass estimates within an uncertainty of a factor of three in the latter. The envelope is self-gravitating and is unstable to form spiral arms and fragments, allowing rapid accretion to the inner radii with a rate of order 10^-2 Msun yr^-1, although inward motion was not detected. The envelope may become a non self-gravitating Keplerian disk at R<(300-1,000) au. The formula is also consistent with the total mass ~10^4 Msun of the entire HMC 0.15 pc (31,000 au) in radius. Multiple transitions of CH3CN, HNCO and CH3OH provide the rotation temperatures, suggesting that the central source of MCN-a has an intrinsic bolometric luminosity of ~10^6 Lsun. These results have revealed the structure and kinematics of MCN-a at its intermediate radii. With no broad-line H30alpha emission detected, MCN-a may be in the earliest phase of massive star formation.

arXiv comment29 pages, 29 figures, 3 Tables

References in corpus (36)

• Evolution of Massive Protostars with High Accretion Rates
• Accretion disks in luminous young stellar objects
• The formation of massive stars: accretion, disks and the development of hypercompact HII regions
• Parallaxes for W49N and G048.60+0.02: Distant Star Forming Regions in the Perseus Spiral Arm
• Disk-Driven Rotating Bipolar Outflow in Orion Source I
• A detailed study of the rotating toroids in G31.41+0.31 and G24.78+0.08
• A Keplerian-like disk around the forming O-type star AFGL 4176
• Masses and Luminosities of O and B - type stars and red super giants
• Rotating disks in high-mass young stellar objects
• Fragmentation of massive dense cores down to ~1000 AU: Relation between fragmentation and density structure
• A Keplerian disk around Orion Source I, a ~15 Msun YSO
• Spherical Infall in G10.6-0.4: Accretion Through an Ultracompact HII Region
• Outflow-Confined H II Regions. I. First Signposts of Massive Star Formation
• On the Relationship of UC H II Regions and Class II Methanol Masers: I. Source Catalogs
• Substructures in the Keplerian disc around the O-type (proto)star G17.64+0.16
• Modeling disk fragmentation and multiplicity in massive star formation
• Testing the massive disk scenario for IRAS 18089-1732
• 3-D Models of Embedded High-Mass Stars: Effects of a Clumpy Circumstellar Medium
• SMA outflow/disk studies in the massive star-forming region IRAS18089-1732
• Online Database of Class I Methanol Masers
• Chemical segregation toward massive hot cores: The AFGL2591 star forming region
• The Molecular Accretion Flow in G10.6-0.4
• Structure of the hot molecular core G10.47+0.03
• An Ordered Envelope-disk Transition in the Massive Protostellar Source G339.88-1.26
• Salt, Hot Water, and Silicon Compounds Tracing Massive Twin Disks
• OH maser emission in the THOR survey of the northern Milky Way
• Dynamical Expansion of H II Regions from Ultracompact to Compact Sizes in Turbulent, Self-Gravitating Molecular Clouds
• An Infalling Torus of Molecular Gas Around the Ultra-Compact HII Region G28.20-0.05
• The Lifetimes of Phases in High-Mass Star-Forming Regions
• Infall, outflow, and rotation in the G19.61-0.23 hot molecular core
• ALMA observations of the Extended Green Object G19.01$-$0.03: I. A Keplerian disc in a massive protostellar system
• The Morphology of M17-UC1 - A Disk Candidate Surrounding a Hypercompact HII Region
• The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1
• Chemical modeling of internal photon-dominated regions surrounding deeply embedded HC/UCHII regions
• Star burst in W49N presumably induced by cloud-cloud collision
• Hot Molecular Core Candidates in the Galactic Center 50 km/s Molecular Cloud