ALMA Observations and Modeling of the Rotating Outflow in Orion Source I

Abstract

We present 29 SiO( J = 8–7) ν  = 0, SiS ( J = 19–18) ν  = 0, and 28 SiO ( J = 8–7) ν  = 1 molecular line archive observations made with the Atacama Large Millimeter/Submillimeter Array (ALMA) of the molecular outflow associated with Orion Source I. The observations show velocity asymmetries about the flow axis that are interpreted as outflow rotation. We find that the rotation velocity (∼4–8 km s −1 ) decreases with the vertical distance to the disk. In contrast, the cylindrical radius (∼100–300 au), the expansion velocity (∼2–15 km s −1 ), and the axial velocity v z (∼−1–10 km s −1 ) increase with the vertical distance. The mass estimated of the molecular outflow M outflow  ∼ 0.66–1.3 M ⊙ . Given a kinematic time ∼130 yr, this implies a mass-loss rate M ⊙ yr −1 . This massive outflow sets important constraints on disk wind models. We compare the observations with a model of a shell produced by the interaction between an anisotropic stellar wind and an Ulrich accretion flow that corresponds to a rotating molecular envelope in collapse. We find that the model cylindrical radii are consistent with the 29 SiO( J = 8–7) ν  = 0 data. The expansion velocities and the axial velocities of the model are similar to the observed values, except for the expansion velocity close to the disk ( z  ∼ ±150 au). Nevertheless, the rotation velocities of the model are a factor ∼3–10 lower than the observed values. We conclude that the Ulrich flow alone cannot explain the rotation observed and other possibilities should be explored, like the inclusion of the angular momentum of a disk wind.