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Project Progress

The discovery that the short-lived radionucleide, 60-Fe, was present in the oldest meteorites suggests that the formation of the Earth closely followed the death of a massive star. I have been studying different mechanisms for the delivery of 60-Fe and other short-lived radionucleides to the solar system. This work resulted in one paper published in the Astrophysical Journal (Williams & Gaidos 2007) and I was invited to lecture on the subject at a winter school on planet formation in France in early 2008. The lecture is available on the web at http://www-laog.obs.ujf-grenoble.fr/heberges/Houches08/index.htm and has been written up for publication in the workshop proceedings. I conclude that there are few ways to reconcile the astrophysical and cosmochemical pictures but the most likely is that the Sun formed in a large cluster of stars in a massive molecular clump (about 10,000 solar masses and several parsecs in size) on or near the boundary of an HII region. An example of such a situation is in the Rosette molecular cloud where I find more than half the protostars lie close enough to the most massive stars that they could incorporate supernova ejecta were it to explode at the current time (see figure). The delivery of 60-Fe is also likely accompanied by the delivery of 26-Al, a more abundant short-lived radionucleide that has a significant effect on the thermal history of planetesimals and potentially the snowline in a proto-planetary disk. Eric Gaidos is leading the effort on this related subject.

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