Events at Physics
Events on Tuesday, April 20th, 2010
- Chaos & Complex Systems Seminar
- "The Dynamics of Performance Management: Governance Reform Amidst Complexity"
- Time: 12:05 pm
- Place: 4274 Chamberlin Hall
- Speaker: Donald Moynihan, UW-Madison La Folette School of Public Affairs
- Abstract: Professor Moynihan examines efforts to make the public sector more focused on outcomes through performance measurement techniques. Bureaucrats use the data for different purposes, and with different consequences, some unintended. This talk will summarize these reforms, their consequences, and the particular factors that affect how public actors use performance data.<br>
- Astronomy Colloquium
- "Modeling surface velocity fields from tidal interactions: the one-layer approximation"
- Time: 3:30 pm - 5:00 pm
- Place: 3425 Sterling Hall
- Speaker: Gloria Konigsberger, UNAM
- Abstract: Binary stars in eccentric orbits are the clearest example of stars whose equatorial rotation velocity is not synchronized with orbital motion. Under these conditions, the surface velocity field is perturbed from its purely rotational nature, thus modifying the shape of the observationally-detectable photospheric absorption lines on a variety of timescales. Absorption lines are used to derive basic stellar parameters
and to gain a better physical understanding of stars. Although their variability is often interpreted in terms of non-radial pulsation theory, it is important to understand the nature of the surface velocity fields that are induced by the tidal interactions alone, especially under conditions of rapid rotation and large orbital eccentricity where the perturbations can become highly non-linear. We use a time-marching numerical calculation from first principles to compute the surface velocity field due to the tidal interaction (Moreno &amp;amp; Koenigsberger 1999; Toledano et al. 2007). This velocity field is then projected along the line-of-sight to the observer to predict the orbital phase-dependent line-profile variability (Moreno et al. 2005). In this talk, the general characteristics of our model will be described and we'll discuss its predictions for synchronization timescales in very eccentric binaries. In addition, we will show that the general characteristics of the theoretical photospheric line-profiles compare favorably with observational data of the short-period B-type binary system Spica (Harrington et al. 2009). It is interesting to note that because tidal flows are associated with viscous shear energy dissipation, the atmospheric structure of an asynchronously rotating binary star could differ significantly from that of a single star.
- Host: Prof John Gallagher