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Session 10 - Spiral Galaxies.
Display session, Monday, June 10
Great Hall,
Massive stars are thought to evolve horizontally on the H-R diagram, so measurements of the ratio of blue to red supergiants, B/R, can provide constraints on models of massive star evolution. This ratio has been found to vary around the Local Group, presumably because of metallicity variations. We reexamine B/R in M33 using infrared (I and K bands) photometry to minimize errors due to reddening in the associations in which supergiants are commonly found. Since M33 is the nearest relatively face-on spiral, the spatial distribution of supergiants in M33 also has implications for spiral structure theories. Studies of more distant spirals in K, designed to minimize the effects of dust lanes and young blue stars, indicate that spiral arms are still very strong features (contrast of order unity). Our K band supergiant census allows a direct estimate of the amount of young star contamination to be expected in this type of study.
