The Role of Bow Shocks in Bipolar Molecular Outflows

Abstract

Observations of highly collimated bipolar molecular outflows from young stellar objects, such as NGC 2264G and NGC 2024, reveal clues that bow shocks may play an important role in the dynamics of bipolar molecular outflows. However, a general bow shock model may not provide good bipolarity of the outflows in observations. In this paper, a jet-driven collimated bow shock model is presented, and its role in explaining the general physics of molecular outflows is explored. Calculations show that the model, which assumes the shock front to be thin, may reproduce much forward motion of the resulting outflow materials, and also most of the general properties of bipolar outflows including effective forward entrainment for high bipolarity, inverse relation between swept-up mass and velocity, the velocity laws of v proportional to r, and moderate collimation. Reasonable energetics are also obtained.