The ionized warped disk and disk wind of the massive protostar Monoceros R2-IRS2 seen with ALMA

Abstract

Theories of massive star formation predict that massive protostars accrete gas through circumstellar disks. Although several cases have been found already thanks to high-angular resolution interferometry, it remains unknown the internal physical structure of these disks and, in particular, whether they present warps or internal holes as observed in low-mass proto-planetary disks. Here, we report very high angular resolution observations of the H21alpha radio recombination line carried out in Band 9 with the Atacama Large Millimeter/submillimeter Array (beam of 80 mas x 60 mas, or 70 au x 50 au) toward the IRS2 massive young stellar object in the Monoceros R2 star-forming cluster. The H21alpha line shows maser amplification, which allows us to study the kinematics and physical structure of the ionised gas around the massive protostar down to spatial scales of ~1-2 au. Our ALMA images and 3D radiative transfer modelling reveal that the ionized gas around IRS2 is distributed in a Keplerian circumstellar disk and an expanding wind. The H21alpha emission centroids at velocities between -10 and 20 km s-1 deviate from the disk plane, suggesting a warping for the disk. This could be explained by the presence of a secondary object (a stellar companion or a massive planet) within the system. The ionized wind seems to be launched from the disk surface at distances ~11 au from the central star, consistent with magnetically-regulated disk wind models. This suggests a similar wind launching mechanism to that recently found for evolved massive stars such as MWC349A and MWC922.

Accepted for publication in ApJ Letters

References in corpus (8)

• Star formation through gravitational collapse and competitive accretion
• Substructures in the Keplerian disc around the O-type (proto)star G17.64+0.16
• A Photoevaporating Rotating Disk in the Cepheus A HW2 Star Cluster
• SMA Imaging of the Maser Emission from the H30$\alpha$ Radio Recombination Line in MWC349A
• Modeling the accretion disk around the high-mass protostar GGD 27-MM1
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Cited by in corpus (11)

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• Massive Protostars in a Protocluster -- A Multi-Scale ALMA View of G35.20-0.74N
• Observing protoplanetary discs with the Square Kilometre Array -- I. Characterising pebble substructure caused by forming planets
• Unveiling the traits of massive young stellar objects through a multi-scale survey
• The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1
• Tying the geometrical traits of massive young stellar objects and their discs to a potential evolutionary sequence using infrared observations
• Clustered Formation of Massive Stars within an Ionized Rotating Disk
• Imaging the jet of MWC 349A with resolved Radio Recombination Line emission from ALMA
• Surveys of clumps, cores, and condensations in Cygnus-X: Searching for Keplerian disks on the scale of 500 au
• The SOFIA Massive (SOMA) Star Formation Q-band Follow-up. II. Hydrogen Recombination Lines Toward High-Mass Protostars