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J. J. Hester, K. R. Healy, S. J. Desch (ASU)
While studies of the formation of low-mass stars have typically focussed on regions like Taurus-Auriga where low-mass stars form in relative isolation, these regions are atypical. Most low-mass stars form instead in much richer environments that are shaped by the energy input from massive stars. (Were Orion 140 pc from the Sun and Taurus-Auriga 500 pc distant, the history of studies of star formation would be very different.) In particular, the recent confirmation of decay products of 60Fe in meteorites rules out the possibility that our own Sun formed in isolation. This neutron-rich short-lived radionuclide has no plausible source other than a supernova very near the forming Solar System. The stark contrast between HST images of YSOs in H II regions and images of YSOs in Taurus-Auriga makes the point that the evolution of a young low-mass star is quite different in these two types of environments. YSOs seen in the interiors of H II regions did not form in such warm, low density environments. Rather, they formed in molecular clouds surrounding H II regions, and were subsequently uncovered by the advance of ionization fronts. The result is a well-ordered process that begins with the likely triggering of star formation by compression in advance of ionization fronts, passes through EGG and proplyd stages as the natal environment and outer portions of the disk are photoevaporated, then ends with a YSO and truncated ~ 30 AU disk sitting in close proximity to one or more massive stars that will end their lives in supernovae. These events are responsible for injecting newly synthesized short-lived radionuclides into the existing disk. These ideas, which build on our earlier work on M16, make a host of predictions about the properties of YSOs in H II region environments that are born out by observation.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.