Discovery of a 500 au Protobinary in the Massive Prestellar Core G11.92–0.61 MM2

• Published in: Astrophysical journal. Letters Vol. 931; no. 2; p. L31
• Main Authors: Cyganowski, C. J., Ilee, J. D., Brogan, C. L., Hunter, T. R., Zhang, S., Harries, T. J., Haworth, T. J.
• Format: Journal Article
• Language: English
• Published: Austin The American Astronomical Society 01-06-2022; IOP Publishing
• Subjects: Accretion disks; Binary stars; Brightness temperature; Deposition; Dust; Dust emission; Emission; Emissions; High resolution; Magnetic fields; Outflow; Protostars; Radio telescopes; Star formation; Star forming regions; Stellar accretion; Stellar accretion disks
• ISSN: 2041-8205; 2041-8213
• DOI: 10.3847/2041-8213/ac69ca

Abstract
We present high-resolution (≲160 au) Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm observations of the high-mass prestellar core candidate G11.92−0.61 MM2, which reveal that this source is in fact a protobinary system with a projected separation of 505 au. The binary components, MM2E and MM2W, are compact (radii <140 au) sources within the partially optically thick dust emission with
α
0.9 cm−1.3 mm
= 2.47–2.94. The 1.3 mm brightness temperatures,
T
b
= 68.4/64.6 K for MM2E/MM2W, imply internal heating and minimum luminosities
L
*
> 24.7
L
⊙
for MM2E and
L
*
> 12.6
L
⊙
for MM2W. The compact sources are connected by a “bridge” of lower-surface-brightness dust emission and lie within more extended emission that may correspond to a circumbinary disk. The circumprotostellar gas mass, estimated from ∼0.″2 resolution VLA 0.9 cm observations assuming optically thin emission, is 6.8 ± 0.9
M
⊙
. No line emission is detected toward MM2E and MM2W in our high-resolution 1.3 mm ALMA observations. The only line detected is
13
CO
J
= 2–1, in absorption against the 1.3 mm continuum, which likely traces a layer of cooler molecular material surrounding the protostars. We also report the discovery of a highly asymmetric bipolar molecular outflow that appears to be driven by MM2E and/or MM2W in new deep, ∼0.″5 resolution (1685 au) ALMA 0.82 mm observations. This outflow, traced by low-excitation CH
3
OH emission, indicates ongoing accretion onto the protobinary system. Overall, the super-Alfvénic models of Mignon-Risse et al. agree well with the observed properties of the MM2E/MM2W protobinary, suggesting that this system may be forming in an environment with a weak magnetic field.