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Alison Sills Associate Professor Department of Physics and Astronomy  McMaster University  Hamilton, ON  L8S 4M1  Office:  ABB 353 Phone:  (905) 525-9140 x24189 FAX:    (905) 546-1252  E-mail:  asills@mcmaster.ca Research Area:  Astrophysics

Research Interests

In my research, I use knowledge of stars and stellar evolution to understand unusual stars in dense places, their interactions and their effect on their environment.

A selection of questions that my group is interested in:

• Stellar Collisions:
  • Are collisions between giant branch stars and something else responsible for extreme horizontal branch stars in globular clusters? Are they responsible for the colour gradients in post-core collapse clusters? What about low mass helium white dwarfs?
  • What are the surface abundances of the product of main sequence -- main sequence star collisions?
  • What happens to the angular momentum in a stellar collision and during the subsequent evolution of the product?
• Globular Cluster Formation and Dynamics:
  • What do the blue straggler populations in globular clusters tell us about the dynamical history of the cluster?
  • Did the stars in globular clusters form all at once, or was there more than one burst? Can we discover that dynamically?
  • What effect, if any, does dark matter have on the formation of globular clusters and dwarf galaxies?
• Contact Binary Stars
  • How do binary stars merge? What is the structure of the resulting star? What are its rotation properties? What do the resulting blue stragglers look like?
  • What happens to the structure of low mass stars when they lose mass through transfer onto a binary companion?
• Stars with Planets
  • Detailed characterization of stars with planets.

I answer these questions using a variety of theoretical techniques and computer codes. Depending on the situation, I use stellar evolution codes, smoothed particle hydrodynamic codes or stellar dynamics codes, running on computers which range from the PC sitting on my desk to supercomputers. I also own one of the world's fastest computers, a GRAPE, for stellar dynamics work. This computer is hard-wired to calculate the gravitational force between many many stars very quickly, and allows us to look at the dynamics in globular clusters on a reasonable time.

I am an active member of collaborations with researchers from Canada, the US and Europe, especially the MODEST (MOdelling DEnse STellar Systems) collaboration.

Publications from ADS Abstract Service