A study of the Orion cometary cloud L1616

Abstract

With its cometary appearance and a reflection nebula near its edge facing some bright Orion stars, Lynds' cloud L1616 shows ample evidence of being affected by one or more of these massive stars. To estimate its mass and star formation efficiency, as well as to determine if it is gravitationally bound, we mapped this cloud in J=1--〉0 transitions of ^12CO and ^13CO. It is found that the distribution of the emission in the line wings shows clear evidence for substantial mass motions. Also, the `virial' mass of the cloud is found to be five times the actual cloud mass determined from the ^13CO column density map. It is argued that this cloud has abnormally high star formation efficiency and is possibly disintegrating. The morphology and the location of the cloud indicate that it is being affected by the star epsilon Orionis, which is also (possibly) responsible for the cloud's unusual star formation efficiency. Over a range of values of the relevant parameters, the star is found to satisfy quantitatively the requirements of being the cause of the observed characteristics of the cloud.