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Full-Text Articles in Stars, Interstellar Medium and the Galaxy
On The Weak-Wind Problem In Massive Stars: X-Ray Spectra Reveal A Massive Hot Wind In Mu Columbae., David P. Huenemoerder, Lidia M. Oskinova, Richard Ignace, Wayne L. Waldron, Helge Todt, Kenji Hamaguchi, Shunji Kitamoto
On The Weak-Wind Problem In Massive Stars: X-Ray Spectra Reveal A Massive Hot Wind In Mu Columbae., David P. Huenemoerder, Lidia M. Oskinova, Richard Ignace, Wayne L. Waldron, Helge Todt, Kenji Hamaguchi, Shunji Kitamoto
Richard Ignace
Mu Columbae is a prototypical weak-wind O star for which we have obtained a high-resolution X-ray spectrum with the Chandra LETG/ACIS instrument and a low-resolution spectrum with Suzaku. This allows us, for the first time, to investigate the role of X-rays on the wind structure in a bona fide weak-wind system and to determine whether there actually is a massive hot wind. The X-ray emission measure indicates that the outflow is an order of magnitude greater than that derived from UV lines and is commensurate with the nominal wind-luminosity relationship for O stars. Therefore, the "weak-wind problem"--identified from cool wind …
X-Ray Emission Line Profiles From Wind Clump Bow Shocks In Massive Stars., R. Ignace, W. L. Waldron, J. P. Cassinelli, A. E. Burke
X-Ray Emission Line Profiles From Wind Clump Bow Shocks In Massive Stars., R. Ignace, W. L. Waldron, J. P. Cassinelli, A. E. Burke
Richard Ignace
The consequences of structured flows continue to be a pressing topic in relating spectral data to physical processes occurring in massive star winds. In a preceding paper, our group reported on hydrodynamic simulations of hypersonic flow past a rigid spherical clump to explore the structure of bow shocks that can form around wind clumps. Here we report on profiles of emission lines that arise from such bow shock morphologies. To compute emission line profiles, we adopt a two-component flow structure of wind and clumps using two “beta” velocity laws. While individual bow shocks tend to generate double-horned emission line profiles, …
High-Resolution X-Ray Spectroscopy Reveals The Special Nature Of The Wolf-Rayet Star Winds., L. M. Oskinova, K. G. Gayley, W.-R. Hamann, D. P. Huenemoerder, R. Ignace, A. M. T. Pollock
High-Resolution X-Ray Spectroscopy Reveals The Special Nature Of The Wolf-Rayet Star Winds., L. M. Oskinova, K. G. Gayley, W.-R. Hamann, D. P. Huenemoerder, R. Ignace, A. M. T. Pollock
Richard Ignace
We present the first high-resolution X-ray spectrum of a putatively single Wolf–Rayet (WR) star. 400 ks observations of WR 6 by the XMM-Newton telescope resulted in a superb quality high-resolution X-ray spectrum. Spectral analysis reveals that the X-rays originate far out in the stellar wind, more than 30 stellar radii from the photosphere, and thus outside the wind acceleration zone where the line-driving instability (LDI) could create shocks. The X-ray emitting plasma reaches temperatures up to 50 MK and is embedded within the unshocked, “cool” stellar wind as revealed by characteristic spectral signatures. We detect a fluorescent Fe line at …
Variability In X-Ray Line Ratios In Helium-Like Ions Of Massive Stars: The Radiation-Driven Case., K. T. Hole, R. Ignace
Variability In X-Ray Line Ratios In Helium-Like Ions Of Massive Stars: The Radiation-Driven Case., K. T. Hole, R. Ignace
Richard Ignace
Line ratios in "fir" triplets of helium-like ions have proven to be a powerful diagnostic of conditions in X-ray emitting gas surrounding massive stars. Recent observations indicate that these ratios can be variable with time. The possible causes of variation in line ratios are limited: changes in the radiation field or changes in density, and changes in mass-loss or geometry. In this paper, we investigate the ability of changes in the radiation field to induce variability in the ratio R=f/i. To isolate the radiative effect, we use a heuristic model of temperature and radius changes in variable stars in the …