Prof. David Cohen
Swarthmore College, Dept. of Physics and Astronomy

The strong X-ray emission from the most massive stars in the Galaxy was
a surprising discovery of the first generation of X-ray telescopes in
the late 1970s. Massive stars, unlike the Sun, are not supposed to have
a magnetic dynamo, and thus were not expected to be X-ray sources at
all. Now, nearly 30 years later, the newest generation of X-ray
telescopes, with high spectral resolution, have shown that massive star
X-rays are very different from solar-type X-rays. My students and I have
worked on two different models - one stellar-wind based and one hybrid
magnetic-wind model that applies to very young massive stars - which we
have used to help us understand the new X-ray observations of massive
stars with NASA's Chandra X-ray Telescope. I will discuss the basics of
stellar X-ray emission, present the new Chandra data and our fits to it,
and briefly describe - using numerical simulations - the hybrid
magnetic-wind model.