Determining the Impulsive Heating Rate from Shocks in O Star Winds Directly from High-Resolution X-ray Spectra
David Cohen, Swarthmore College
Monday, 18 May 2015, 12:00
Pratt Conference Room, 60 Garden Street
O star winds are dense, powerful, radiation-driven outflows. The line-deshadowing instability intrinsic to these winds generates copious shock structure, heating and compressing the wind plasma, leading to the observed strong X-ray emission and also the clumped wind structure that affects various spectral diagnostics. In this talk, I will describe the shock physics that is thought to explain the X-ray emission from massive stars and I will present a new spectral analysis technique that enables us to directly determine the temperature-dependent shock heating rate from a Chandra grating spectrum of an O star. This analysis depends on radiative cooling being the dominant cooling mechanism, and it should be applicable to impulsively heated and radiatively cooled plasmas in other contexts. I will also briefly summarize what we have learned about O star wind mass-loss rates and clumping from the analysis of spectrally resolved X-ray emission line profiles. Correcting the X-ray line fluxes for the effects of wind attenuation is, in fact, a crucial component of the shock heating rate analysis technique that I will discuss.