Star Formation in the Orion-monoceros Complex

Pre-main sequence stars in the Orion-Monoceros Complex are either distributed in groups closed associated with dense cores, or dispersed along molecular filaments. Some molecular clouds are apparently affected by the OrionEridanus Superbubble created by the Wolf-Rayet winds and supernovae from the OriOB1 association, whose shock fronts compressed and triggered starbirth in adjacent molecular clouds. We present evidence of a formation sequence from the older star association OriOB1a, which no longer is associated with molecular gas, to OriOB1b and 1c, which are associated respectively with OrionA and B molecular clouds, and eventually to OriOB1d currently active in star formation. The Orion-Eridanus Superbubble continues to spread out to NGC2149, vdB64, and the Crossbones, and likely also to MonR2. The triggering by ionization or the superbubble—both consequences of massive stars—would produce stars and disperse molecular clouds much more efficiently than isolation star formation via spontaneous cloud collapse. As the superbubble expands, it may incite star formation along the way and perhaps inject nuclides synthesized by the Wolf-Rayet stars or supernovae into the protostellar nebulae. Some of the now extinct shortlived nuclides have been found in the meteorites of our solar system , implying that the Sun was likely formed in an environment similar to that of the OriOB1 association. Subject headings: stars: formation — stars: pre-main-sequence — ISM: clouds — ISM: molecules Institute of Astronomy, National Central University, Taiwan 320, R.O.C. Department of Physics, National Central University, Taiwan, 320, R.O.C.