TAC Seminar Spring 1999

• Jan 27: Introductions and Organization
• Feb 10: Greg Laughlin: "The Fate of Unstable Gravitational Modes"
  The evolution of self-gravitating disks is important in a variety of astrophysical contexts, ranging from spiral galaxies to protoplanetary nebulae. Laughlin will discuss his current research effort that seeks to understand how such disks evolve. In particular, he will discuss how the nonlinear interaction of global spiral instabilities are capable of efficiently transporting mass and angular momentum through disks, and will show a detailed example of this process at work.

  Feb 24: Alex Lazarian: "Microwave Emission and Polarization from Dust"

  Lazarian will discuss microwave emission and polarization from dust grains in the range of 10-100 GHz. This emission accounts for the "anomalous emissivity" discovered recently. Ways of separating this emission from the CMB signal will also be discussed.

  March 24: Andrew Melatos: "Evolution of the Magnetic Field of a Neutron Star during Accretion"

  Melatos will discuss the observational evidence for accretion-induced decay of neutron-star magnetic fields and summarise theoretical work on the topic to date. He will describe an ideal-MHD theory of polar-cap accretion which predicts the formation of an equatorial magnetic tutu and gives the final magnetic dipole moment after accretion, B_s, in terms of the initial field B_0 and accreted mass M_a and NO OTHER PARAMETERS. The theory predicts several relations which are testable against existing and future data. It also sheds light on the puzzle of why all millisecond pulsars have B_s ~ 10^8 G.

  April 7: Ed Brown: TBD

  May 5: Dean McLaughlin 'Constraints on Star and Galaxy Formation from Globular Cluster Systems' Systems of old globular clusters are ubiquitous in galaxy halos, and they therefore contain important clues to aspects of galaxy formation. At the same time, star formation today appears to proceed largely in a clustered mode; thus, the study of old globulars stands potentially to illuminate generic aspects of star formation at any epoch. Recent theoretical and empirical work concerning (1) the frequency distribution of globular cluster masses in galaxies, and (2) the total populations and spatial structures of globular cluster systems, will be presented in this light. In particular, implications will be discussed for the star-gas interactions (i.e., feedback) that must accompany star and galaxy formation.