ASTRONOMY COLLOQUIUM - FEBRUARY 21, 2006

Eric Feigelson, Penn State

What are X-rays Telling Us About Star and Planet Formation?

X-ray studies have established that low-mass stars exhibit their highest levels of magnetic activity during their pre-main sequence phases when planet formation occurs. Our understanding of this activity, and particularly violent magnetic reconnection flares, has been greatly advanced by recent studies such as the Chandra Orion Ultradeep Project (COUP). COUP provides several lines of evidence that X-rays efficiently illuminate the protoplanetary disks. This may have dramatically affect disk gases: induction of MHD turbulence via the MRI instability with subsequent suppression of protoplanetary migration, heating of disk outer layers, catalysis of nonequilibrium chemistry, and so forth. Flare effects on disk solids address long-standing meteoritic issues such as the production of short-lived radionuclides and the flash melting of chondrules. We conclude that solar systems form in cool dark disks which are likely irradiated by 108 violent magnetic reconnection flare events.