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Project Progress

In collaboration with Henry Throop (SWRI), we realized that UV radiation may trigger the rapid formation of kilometer-scale planetesimals in protoplanetary disks (Throop & Bally, 2005). Thus, contrary to previous view that massive stars in a cluster may be hazardous to planet formation, new models indicate that their UV radiation may promote it. If grains grow and sediment to the disk mid-plane when the external UV radiation turns-on, photo-ablation selectively removes dust-depleted gas (mostly H and He). Continued mass-loss increases the disk dust:gas ratio until km-scale planetesimals form by gravitational instability. This UV-radiation induced instability may solve a long-standing problem in planetesimal formation – the in-spiral of solids as they grow.

We have continued our studies of the nearest star-cluster forming clouds such as Perseus and Orion. Recent results include the discovery of many proto-planetary disks surrounding stars which are NOT proplyds on the Hubble Space Telescope images. We used the thermal-infrared camera at the Gemini South telescope to find warm dust emission from Orion’s “naked” stars (those not surrounded by photo-evaporating disks).

Graduate student Nick Moeckell has continued his numerical simulations of disk evolution in dense clusters. The close-passages with separations of only a few hundred AU are fairly common in Orion-like environments. Such interactions can generate spiral shock waves in protoplanetary disks. We have proposed that such shocks may lead to significant chemical processing, and possibly may explain the properties of chondrules found in some primitive meteorites.