We present analysis of both the resolved X-ray emission line profiles and the broadband X-ray spectrum of the O2 If ^ { \ast } star HD 93129A , measured with the Chandra HETGS .
This star is among the earliest and most massive stars in the Galaxy , and provides a test of the embedded wind shock scenario in a very dense and powerful wind .
A major new result is that continuum absorption by the dense wind is the primary cause of the hardness of the observed X-ray spectrum , while intrinsically hard emission from colliding wind shocks contributes less than 10 % of the X-ray flux .
We find results consistent with the predictions of numerical simulations of the line-driving instability , including line broadening indicating an onset radius of X-ray emission of several tenths { R _ { \ast } } .
Helium-like forbidden-to-intercombination line ratios are consistent with this onset radius , and inconsistent with being formed in a wind-collision interface with the star ’ s closest visual companion at a distance of ~ { } 100 AU .
The broadband X-ray spectrum is fit with a dominant emission temperature of just k T = 0.6 keV along with significant wind absorption .
The broadband wind absorption and the line profiles provide two independent measurements of the wind mass-loss rate : \dot { M } = 5.2 _ { -1.5 } ^ { +1.8 } \times 10 ^ { -6 } { \mathrm { M _ { \sun } ~ { } { \mathrm { y } r ^ { -1 } } } } and \dot { M } = 6.8 _ { -2.2 } ^ { +2.8 } \times 10 ^ { -6 } { \mathrm { M _ { \sun } ~ { } { \mathrm { y } r ^ { -1 } } } } , respectively .
This is the first consistent modeling of the X-ray line profile shapes and broadband X-ray spectral energy distribution in a massive star , and represents a reduction of a factor of 3 to 4 compared to the standard { H } { \alpha } mass-loss rate that assumes a smooth wind .