Two jets from the Orion ( M 42 ) ‘ proplyds ’ – kinematics , morphologies and origins

Two jets from the Orion (M42) 'proplyds' – kinematics, morphologies and origins. ABSTRACT A spatially unresolved velocity feature, with an approaching radial velocity of ≈ 100 km s −1 with respect to the systemic radial velocity, in a position–velocity array of [O iii] 5007Å line profiles is identified as the kinematical counterpart of a jet from the proplyd LV 5 (158–323) in the core of the Orion Nebula. The only candidate in HST imagery for this jet appears to be a displaced, ionized knot. Also an elongated jet projects from the proplyd GMR 15 (161–307). Its receding radial velocity difference appears at ≈ 80 km s −1 in the same position–velocity array. A 'standard' model for jets from young, low mass stars invokes an accelerating, continuous flow outwards with an opening angle of a few degrees. Here an alternative explanation is suggested which may apply to some, if not all, of the proplyd jets. In this, a 'bullet' of dense material is ejected which ploughs through dense circumstellar ambient gas. The decelerating tail of material ablated from the bullet's surface would be indistinguishable from a continuously emitted jet in current observations.