Entrainment Mechanisms for Outflows in the L1551 Star‐forming Region

We present high sensitivity 12/13CO(1-0) molecular line maps covering thefull extent of the parsec scale L1551 molecular outflow, including theredshifted east-west (EW) flow. We also present 12CO(3-2) data that extendsover a good fraction of the area mapped in the 1-0 transition. We compare themolecular data to widefield, narrow-band optical emission in H$\alpha$. Whilethere are multiple outflows in the L1551 cloud, the main outflow is oriented at50\arcdeg position angle and appears to be driven by embedded source(s) in thecentral IRS 5 region. The 3-2 data indicate that there may be molecularemission associated with the L1551 NE jet, within the redshifted lobe of mainoutflow. We have also better defined the previously known EW flow and believewe have identified its blueshifted counterpart. We further speculate that theorigin of the EW outflow lies near HH 102. We use velocity dependent opacitycorrection to estimate the mass and the energy of the outflow. The resultingmass spectral indices from our analysis, are systematically lower (less steep)than the power law indices obtained towards other outflows in several recentstudies that use a similar opacity correction method. We show that systematicerrors and biases in the analysis procedures for deriving mass spectra couldresult in errors in the determination of the power-law indices. The massspectral indices, the morphological appearance of the position-velocity plotsand integrated intensity emission maps of the molecular data, compared with theoptical, suggest that jet-driven bow-shock entrainment is the best explanationfor the driving mechanism of outflows in L1551. The kinetic energy of theoutflows is found to be comparable to the binding energy of the cloud andsufficient to maintain the turbulence in the L1551 cloud.