ALMA Observations of Orion Source I at 350 and 660 GHz

Abstract

Orion Source I (`SrcI') is the protostar at the center of the Kleinmann-Low Nebula. ALMA observations of SrcI with 0.2" angular resolution were made at 350 and 660 GHz to search for the H26alpha and H21alpha hydrogen recombination lines and to measure the continuum flux densities. The recombination lines were not detected, ruling out the possibility that SrcI is a hypercompact HII region. The deconvolved size of the continuum source is approximately 0.23 x 0.07" (100 x 30 AU); it is interpreted as a disk viewed almost edge-on. Optically thick thermal emission from ~500 K dust is the most plausible source of the continuum, even at frequencies as low as 43 GHz; the disk mass is most likely in the range 0.02 to 0.2 Mo. A rich spectrum of molecular lines is detected, mostly from sulfur- and silicon-rich molecules like SO, SO2, and SiS, but also including vibrationally excited CO and several unidentified transitions. Lines with upper energy levels E_U > 500 K appear in emission and are symmetric about the source's LSR velocity of 5 km/sec, while lines with E_U < 500 K appear as blueshifted absorption features against the continuum, indicating that they originate in outflowing gas. The emission lines exhibit a velocity gradient along the major axis of the disk that is consistent with rotation around a 5-7 Mo central object. The relatively low mass of SrcI and the existence of a 100 AU disk around it are difficult to reconcile with the model in which SrcI and the nearby Becklin-Neugebauer Object were ejected from a multiple system 500 years ago.

17 pages, 14 figures; revised version accepted for publication in ApJ

References in corpus (5)

• The distance to the Orion Nebula
• Monitoring the Large Proper Motions of Radio Sources in the Orion BN/KL Region
• Imaging the Ionized Disk of the High-Mass Protostar Orion-I
• ALMA Imaging of Millimeter/Submillimeter Continuum Emission in Orion KL
• A study of dynamical processes in the Orion KL region using ALMA-- Probing molecular outflow and inflow

Cited by in corpus (23)

• Disk-Driven Rotating Bipolar Outflow in Orion Source I
• Formation and Evolution of Disks around Young Stellar Objects
• Zooming in on Individual Star Formation: Low- and High-mass Stars
• Orion Source I's disk is salty
• The Orion Protostellar Explosion and Runaway Stars Revisited: Stellar Masses, Disk Retention, and an Outflow from BN
• New Evidence for the Dynamical Decay of a Multiple System in the Orion Kleinmann-Low Nebula
• The SEDIGISM survey: a search for molecular outflows
• ALMA Images of the Orion Hot Core at 349 GHz
• VLBA imaging of the 3mm SiO maser emission in the disk-wind from the massive protostellar system Orion Source I
• A Detailed View of the Circumstellar Environment and Disk of the Forming O-star AFGL 4176
• Sulfur-bearing molecules in Orion KL
• ALMA observations of the archetypal "hot core" that isn't: Orion KL
• A Face-on Accretion System in High-Mass Star-Formation: Possible Dusty Infall Streams within 100 AU
• Observations of Orion Source I Disk and Outflow Interface
• Magnetic Field Structure of Orion Source I
• ALMA band 8 continuum emission from Orion Source I
• Outflow-Confined HII regions. II. The Early Break-Out Phase
• Structure of the Source I disk in Orion-KL
• Extremely high excitation SiO lines in disk-outflow system in Orion Source I
• A molecular-line study of the interstellar bullet engine IRAS 05506+2414
• An ionized outflow in Orion-KL source I?
• Formation of Orion Fingers
• Synthetic Polarization Maps of an Outflow Zone from Magnetohydrodynamic Simulations