TY  - JOUR
A1  - Hünemörder, David P.
A1  - Oskinova, Lida
A1  - Ignace, Richard
A1  - Waldron, Wayne L.
A1  - Todt, Helge Tobias
A1  - Hamaguchi, Kenji
A1  - Kitamoto, Shunji
T1  - On the weak-wind problem in massive stars X-ray spectra reveal a massive hot wind in mu columbaea
JF  - The astrophysical journal : an international review of spectroscopy and astronomical physics ; Part 2, Letters
N2  - 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 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.
KW  - stars: early-type
KW  - stars: individual (mu Col)
KW  - stars: mass-loss
KW  - X-rays: stars
Y1  - 2012
U6  - https://doi.org/10.1088/2041-8205/756/2/L34
SN  - 2041-8205
VL  - 756
IS  - 2
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  -