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PHYSICS/STAR CLUSTER MSc THESIS SEMINAR: A new channel for the formation and evolution of subdwarf stars
January 17 @ 1:00 pm - 1:30 pm
Subdwarfs are fascinating and important objects in astronomy. There are two primary types of hot subdwarfs. They are very hot with surface temperatures between 20,000 and 100,000K which makes them very blue because of their strong ultraviolet emission. It is thought that they can explain the unexpected UV excess seen in old elliptical galaxies that do not have young, massive, and thus hot stars.
Based on an analysis of a computational grid of about 4000 evolutionary tracks (starting from the primordial binary), we conclude that our Roche lobe overflow model can form binaries containing subdwarfs with orbital periods in the range of 20 to 300 days. We also find two very distinct types of evolutionary behaviors that can lead to the formation of subdwarfs and show that subdwarf masses can vary over a substantially wider range than previously thought (0.4 < M/M8 < 0.8). Finally, we show how the effects of decreased metallicity can be taken into account and discuss the observational implications.