List of Past CTC Theory Lunches : 01-Sep-2000 to 31-Dec-2000

Date:   Thursday 03-Aug-00
Speaker:   Keiichi Wada
Title:   Global simulations of the Interstellar Matter with Stellar Energy Feedback in Galaxies

Date:   Tuesday 31-Oct-00
Speaker:   Derek Richardson
Title:   Numerical Simulations of Planetesimal Dynamics: When Things Go Bump in the Night

Date:   Tuesday 07-Nov-00
Speaker:   Steve Desch
Title:  Generation of Lightning in the Solar Nebula

I will discuss the generation (and consequences) of lightning in the solar nebula. Lightning has been suggested as the mechanism, as yet unidentified, that melted the chondrules, mm-sized glassy beads found in profusion in meteorites. No viable model of lightning generation has yet been advanced. I present a model demonstrating how lightning could have been generated in the solar nebula which differs from previous models in two important aspects. First, it assumes triboelectric charging due to differences in contact potentials between particles of different composition. In the presence of fine metal grains, silicate chondrule precursors can acquire charges greater than +10^5 e. Second, turbulence is assumed to selectively concentrate chondrule precursors into clumps about 100 km in size. The concentration of highly charged particles into clumps, amid a background of negatively charged metal grains, leads to large electric fields and triggers the lightning discharge. It is estimated that electric discharges over about 100 km could dissipate around 10^{16} erg of energy. I will discuss the implications for chondrule formation and for disequilibrium chemistry in the solar nebula.

Date:   Tuesday 14-Nov-00
Speaker:   Satoshi Inaba
Title:   Formation of Jupiter: the Effect of Fragmentation

Date:   Tuesday 28-Nov-00
Speaker:   Gary Hinshaw
Title:   Observing the Cosmic Microwave Background - Present and Future

Date:   Tuesday 12-Dec-00
Speaker:   Daniel Proga
Title:   On the role of the UV and X-ray radiation in driving a disk wind in X-ray binaries and AGN

Date:   Tuesday 19-Dec-00
Speaker:   Sergei Nayakshin
Title:  Recent developments in photo-ionized X-ray reflection calculations: implications for accretion disk theories

An important thermal ionization instability has been missed in the previous decade of studies of Fe K-alpha line emission from accretion disks. Here we discuss implications of our results (obtained with a code that includes the instability) for (1) absence of broad lines in Galactic BH candidates; (2) proposed Fe K-alpha line reverberation campaigns of AGN; and (3) line profiles in Soft X-ray transients and Low Luminosity AGN. One of our conclusions is that current observations do not present any hard evidence for the Shakura-Sunyaev disk to be evaporating to form ADAF-like flows.

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