2011/04/25 by David H. Cohen, Marc Gagné, Maurice A. Leutenegger +9 · 1 citation
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Emission spectrum #Line (geometry) #Physics #RADIUS #Spectral line #Stars #Stellar, planetary, and galactic studies #Supergiant #astro-ph.SR
paper · pdf · doi:10.1111/j.1365-2966.2011.18952.x
Accepted for publication in Monthly Notices of the Royal Astronomical Society. 12 pages, 10 figures (incl. 5 color)
arxiv created 2011/04/25 · openalex publication_date 2011/06/13 · arxiv updated 2015/05/28 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We present an analysis of both the resolved X-ray emission-line profiles and the broad-band X-ray spectrum of the O2 If* star HD 93129A, measured with the Chandra High Energy Transmission Grating Spectrometer (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 per cent 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 of R*. 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 broad-band X-ray spectrum is fitted with a dominant emission temperature of just kT= 0.6 keV along with significant wind absorption. The broad-band wind absorption and the line profiles provide two independent measurements of the wind mass-loss rate: and 6.8+2.8− 2.2× 10−6 M⊙ yr−1, respectively. This is the first consistent modelling of the X-ray line-profile shapes and broad-band X-ray spectral energy distribution in a massive star, and represents a reduction of a factor of 3–4 compared to the standard Hα mass-loss rate that assumes a smooth wind.