Measuring the shock-heating rate in the winds of O stars using X-ray line spectra

David H. Cohen (1), Zequn Li (1), Kenneth G. Gayley (2), Stanley P. Owocki (3), Jon O. Sundqvist (3,4), Veronique Petit (3,5), Maurice A. Leutenegger (6,7)

(1) Swarthmore College
(2) Univ. Iowa
(3) Univ. Delaware
(4) Univ. Munich
(5) Florida Tech

We present a new method for measuring the shock-heating rate in O star winds directly from wind-absorption-corrected X-ray emission line luminosities. This analysis method, applied to an ensemble of lines each with different temperature sensitivity, naturally generates a cumulative probability distribution of the wind shock-heating rate. We apply this new technique to the analysis of the Chandra grating spectra of five O stars and find similar results for all the sample stars: (1) roughly a tenth of the wind mass passes through a shock of 2 million K or more; (2) the distribution of shock temperatures is a strongly declining function, consistent with a power-law of index n = -3; and (3) there are indications of a cut-off or faster fall-off in the heating rate for shock temperatures above about 10 million K. These results provide direct constraints for hydrodynamic simulations of X-ray production in O star winds.

Reference: MNRAS in press
Status: Manuscript has been accepted