The Rotating Gas Toroid Surrounding the K3‐50A Ionized Bipolar Outflow

Abstract

We present high spatial resolution, aperture synthesis images of K3-50A as part of an ongoing study of high-mass star formation regions. Maps in the HCO`(J \ 1 ] 0), H13CO`(J \ 1 ] 0), and SiO (v \ 0, J \ 2 ] 1) emission lines at resolution reveal both a Ñattened cloud of dense molecular gas D2A .5 D1.1 pc in extent and a newly discovered inner torus D0.5 pc in extent. The axis of the inner torus is tilted D20¡ with respect to the outer cloud. The inner torus surrounds a bright continuum source, associated with the origin of a bipolar ionized gas outÑow, and has HCO`(J \ 1 ] 0) optical depth greater than 14. Chemical abundances in the inner torus are azimuthally asymmetric, possibly due to di †erential impact of the ionized outÑow on the inner region of the torus. Comparison with a kinematic radiative transfer model conÐrms that the torus is rotating and the rotation axis of the inner torus is aligned with the ionized outÑow. While the cloud is not in solid body rotation, the rotational velocity of material in the cloud increases with radius.We estimate molecular abundance ratios by comparison with high-resolution dust extinction maps previously obtained at the same spatial resolution.

Magnetic field structures in star-forming regions: mid-infrared imaging polarimetry of K3-50

“…However, Palmer et al (2003) pointed out that this should be rescaled to 7.4 kpc with a value of R0 = 8.5 kpc for the Sun's Galactocentric distance, and proportionate rescalings would apply for other values (e.g., d = 7.3 kpc with a more modern R0 = 8.4 kpc; Reid et al 2009). While acknowledging this, we nonetheless adopt d = 8.7 kpc to be consistent with Howard et al (1997) in particular, so that we can compare our results with their model for the molecular torus ( §4.2.1). A 16% smaller distance will obviously reduce all masses and luminosities discussed herein by 29%.…”

“…This first subset is shown in Figure 7a, and reveals two features: (i) pixels at the extreme NW and SE corners of the CanariCam frame where the field seems roughly aligned with the outflow axis from De Pree et al (1994); and (ii) mid-frame pixels that seem roughly aligned with the orientation of the molecular torus from Howard et al (1997).…”

“…Similarly, the axial polarised-emission-related magnetic field is associated with a strong outflow of material from the central source(s) of this region, suggesting that its geometry too is determined by the outflow. However, the opposite may also be true, i.e., that the magnetic field is actually dominant in both domains, and controlling the motions seen by De Pree et al (1994) and Howard et al (1997). Clearly, we need a way of discriminating between these scenarios: whether the magnetic fields in K3-50 are the driving agent for the structures and motions we see, or whether the fields are merely "passengers" as other processes control events.…”

“…Building on the previous work of De Pree et al (1994), Howard et al (1997), Hofmann et al (2004), in Figure 8 we schematically show, as a set of overlays on the Hofmann et al (2004) NIR image, the alignment of our polarisation maps with several of the salient features of K3-50. Based on these comparisons, we have constructed a toy model for the arrangement of features in this source, and especially showing the relationship of the derived magnetic field configurations to the observed phenomena; this is shown in Figure 9.…”

“…De Pree et al (1994) and Howard et al (1997) provide excellent starting points for estimates of cloud mass, gravity, rotation, and other bulk parameters.…”