The Small‐Scale Structure of the CO Outflow in Barnard 1

We present aperture synthesis CO (J = 1-0) observations of the compact molecular outflow in the dark cloud B1 (Barnard 1). We have detected strong blueshifted emission having a peak brightness temperature of 14.3 K, while no significant emission was detected in the redshifted velocity range. The most prominent feature in our map is a distinct ringlike structure having a size of 25'' (8700 AU) × 14'' (5000 AU) at velocities blueshifted by 1.9-2.7 km s-1 from the systemic velocity. The central hole of the CO ring coincides well with the IRAS position, suggesting that this outflow is driven by the IRAS source, 03301+3057. The CO ring structure is interpreted as a conical outflow lobe with a brightened limb observed from its polar direction. The high-velocity gas that is blueshifted more than 4 km s-1 shows a V-shaped structure open to the southwest. This structure well delineates the northeast edge of the CO blue lobe observed with the single dish, where the CO lobe faces to the dense gas traced by the C18O emission. The strong peak of SiO emission observed by Yamamoto et al. is located at the interface between the CO outflow and the dense gas traced by the C18O and H13CO+ emission. This suggests that the outflow which emanates from the young star strongly interacts with the dense material and causes a shock that propagates into the surrounding cloud. The presence of strong SiO emission and the cold IRAS spectrum (log [Fν(60 μm)/Fν(100 μm)] < -0.76) suggest that the central source of B1 is a candidate for a protostar in the earliest evolutionary stage having an outflow in a nearly pole-on configuration.