Velocity Shifts in L1228: The Disruption of a Core by an Outflow

Abstract

We present 12CO(1-0),13CO(1-0), CS(2-1), and C3H2(212-101) observations of the L1228 outflow and dense core with resolutions between 50'' and 25''. The bipolar molecular outflow originates from IRAS 20582+7724 and extends over almost 15' (≈ 1.2 pc). It has a well-collimated blue lobe and a less collimated red lobe, which is split into two branches that diverge from the IRAS position. The two CO outflow lobes are well aligned with previously observed high-excitation emission from H2 and Hα, although these emissions present bendings from a straight line, suggesting that the outflow driving wind changes direction by interacting with the ambient cloud. The dense gas in the core also shows evidence for acceleration in the outflow direction, although its velocity is significantly lower than that of the CO emission. The dense gas acceleration appears in the CS and C3H2 spectra as velocity shifts in the line centroid on the order of one C3H2 full line width (≈ 0.4 km s-1). These shifted line profiles are not accompanied by any significant emission at ambient core velocities. Furthermore, there is very little or no quiescent C3H2 emission toward the outflow lobes, as if the outflow acceleration had been so efficient that all the dense gas has been set into motion. This acceleration, in addition, has occurred without appreciable line width enhancement, suggesting that it has not increased substantially the turbulence of the gas. From the large size of the velocity shifts (comparable to the gas escape velocity) and from our energetics estimates, we infer that the L1228 outflow could significantly disperse the dense gas in the core by the time the outflow phase ends.