Formation and Atmosphere of Complex Organic Molecules of the HH 212 Protostellar Disk

• Published in: The Astrophysical journal Vol. 843; no. 1; pp. 27 - 40
• Main Authors: Lee, Chin-Fei, Li, Zhi-Yun, Ho, Paul T. P., Hirano, Naomi, Zhang, Qizhou, Shang, Hsien
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.07.2017; IOP Publishing
• Subjects: ABUNDANCE; ACCRETION DISKS; accretion, accretion disks; Astronomical models; Astrophysics; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; Atmosphere; ATMOSPHERES; Atmospheric models; Constraint modelling; Deuteration; DIFFUSION BARRIERS; FORMALDEHYDE; FORMAMIDE; INTERSTELLAR SPACE; ISM: individual objects (HH 212); ISM: jets and outflows; Kinematics; LIMITING VALUES; Low mass stars; MASS; METHANOL; MOLECULAR IONS; MOLECULES; Organic chemistry; PRECURSOR; PROTOSTARS; Radio telescopes; RESOLUTION; Rotating disks; Rotation; Space telescopes; SPATIAL DISTRIBUTION; Star & galaxy formation; Star formation; STARS; stars: formation; THIOLS
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/aa7757

HH 212 is a nearby (400 pc) Class 0 protostellar system recently found to host a "hamburger"-shaped dusty disk with a radius of ∼60 au, deeply embedded in an infalling-rotating flattened envelope. We have spatially resolved this envelope-disk system with the Atacama Large Millimeter/submillimeter Array at up to ∼16 au (0 04) resolution. The envelope is detected in HCO+ J = 4-3 down to the dusty disk. Complex organic molecules (COMs) and doubly deuterated formaldehyde (D2CO) are detected above and below the dusty disk within ∼40 au of the central protostar. The COMs are methanol (CH3OH), deuterated methanol (CH2DOH), methyl mercaptan (CH3SH), and formamide (NH2CHO, a prebiotic precursor). We have modeled the gas kinematics in HCO+ and COMs and found a centrifugal barrier (CB) at a radius of ∼44 au, within which a Keplerian rotating disk is formed. This indicates that HCO+ traces the infalling-rotating envelope down to the CB and COMs trace the atmosphere of a Keplerian rotating disk within the CB. The COMs are spatially resolved for the first time, both radially and vertically, in the atmosphere of a disk in the earliest, Class 0 phase of star formation. Our spatially resolved observations of COMs favor their formation in the disk rather than a rapidly infalling (warm) inner envelope. The abundances and spatial distributions of the COMs provide strong constraints on models of their formation and transport in low-mass star formation.