ON THE WEAK-WIND PROBLEM IN MASSIVE STARS: X-RAY SPECTRA REVEAL A MASSIVE HOT WIND IN μ COLUMBAE
Author(s)Huenemoerder, David P.; Oskinova, Lidia M.; Ignace, R.; Waldron, Wayne L.; Todt, Helge; Hamaguchi, Kenji; Kitamoto, Shunji; ... Show more Show less
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μ 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 UV/optical spectra—is largely resolved by accounting for the hot wind seen in X-rays. From X-ray line profiles, Doppler shifts, and relative strengths, we find that this weak-wind star is typical of other late O dwarfs. The X-ray spectra do not suggest a magnetically confined plasma—the spectrum is soft and lines are broadened; Suzaku spectra confirm the lack of emission above 2 keV. Nor do the relative line shifts and widths suggest any wind decoupling by ions. The He-like triplets indicate that the bulk of the X-ray emission is formed rather close to the star, within five stellar radii. Our results challenge the idea that some OB stars are "weak-wind" stars that deviate from the standard wind-luminosity relationship. The wind is not weak, but it is hot and its bulk is only detectable in X-rays.
DepartmentKavli Institute for Astrophysics and Space Research
The Astrophysical Journal. Letters
Huenemoerder, David P., Lidia M. Oskinova, Richard Ignace, Wayne L. Waldron, Helge Todt, Kenji Hamaguchi, and Shunji Kitamoto. “ON THE WEAK-WIND PROBLEM IN MASSIVE STARS: X-RAY SPECTRA REVEAL A MASSIVE HOT WIND IN μ COLUMBAE.” The Astrophysical Journal 756, no. 2 (August 22, 2012): L34. © 2012 The American Astronomical Society
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