Astronomy Seminar
| Date/Time: | Friday, 01 Apr 2016 at 4:10 pm |
|---|---|
| Location: | 38 Physics |
| Contact: | Steve Kawaler, Physics and Astronomy |
| Phone: | 515-294-5440 |
| Channel: | College of Liberal Arts and Sciences |
| Categories: | Lectures |
| Actions: | Download iCal/vCal | Email Reminder |
Precessing, power ellipses (p-ellipses) are simple, yet accurate approximations for orbits in potentials like those of galaxy disks. Very few terms (or parameters) are needed for the approximation of even nearly radial orbits. The orbit approximations indicate the existence of a range of eccentric resonances associated with the usual, near-circular Lindblad resonances. Orbits in these Lindblad Zones can be excited at a common pattern speed, aiding the formation of bars and spirals from the eccentric orbits. Such waves do not wind up or disperse, since differences in their precession frequencies offset different circular velocities at the radii of their parent orbits. The p-ellipse approximation further reveals how a non-axisymmetric component of the gravitational potential (e.g., due to bar gravity) modifies precession frequencies, and thus, the Lindblad Zones.