Shadows and Photoevaporated Flows from Neutral Clumps Exposed to Two   Ionizing Sources
  Neutral clumps immersed in HII regions are frequently found in star formation regions. We investigate here the formation of tail of neutral gas, which are not reached by the direct ionizing flux coming from two massive stars, using both an analytical approximation, that allows us to estimate the shadow geometry behind the clumps for different initial geometric configurations, and three-dimensional numerical simulations. We found a good agreement between both approaches to this theoretically interesting problem. A particularly important application could be the proplyds that are found in the Trapezium cluster in Orion, which are being photoevaporated primordially by the O stars theta-1 Ori C and theta-2 Ori A. 
A.H. Cerqueira (1), J. Canto (2), A.C. Raga (3) and M.J. Vasconcelos   (1) ((1) Lato-Uesc, (2) Ia-Unam, (3) Icn-Unam)