On the Weak-Wind Problem in Massive Stars: X-ray Spectra Reveal a Massive Hot Wind in μ Columbae

Abstract

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-S 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 5 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.

Accepted for publication in ApJ Letters

References in corpus (5)

• An Extensive Collection of Stellar Wind X-ray Source Region Emission Line Parameters,Temperatures, Velocities, and Their Radial Distributions as Obtained from Chandra Observations of 17 OB Stars
• High-resolution X-ray spectroscopy of the evolving shock in the 2006 outburst of RS Ophiuchi
• High-Resolution Chandra X-ray Imaging and Spectroscopy of the Sigma Orionis Cluster
• Constraints on porosity and mass loss in O-star winds from modeling of X-ray emission line profile shapes
• The XMM-Newton EPIC X-ray Light Curve Analysis of WR 6

Cited by in corpus (42)

• Mass Loss: Its Effect on the Evolution and Fate of High-Mass Stars
• The Red MSX Source Survey: the Massive Young Stellar Population of our Galaxy
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• Towards a unified view of inhomogeneous stellar winds in isolated supergiant stars and supergiant high mass X-ray binaries
• Mass loss in main-sequence B stars
• Measuring mass-loss rates and constraining shock physics using X-ray line profiles of O stars from the Chandra archive
• New predictions for radiation-driven, steady-state mass-loss and wind-momentum from hot, massive stars. I. Method and first results
• The VLT-FLAMES Tarantula Survey XXVI: Properties of the O-dwarf population in 30 Doradus
• No breakdown of the radiatively-driven wind theory in low-metallicity environments
• Modeling the early evolution of massive OB stars with an experimental wind routine
• Blowing in the wind: The dust wave surrounding $\sigma$ Ori AB
• The stellar and wind parameters of six prototypical HMXBs and their evolutionary status
• Global hot-star wind models for stars from Magellanic Clouds
• Radiation-pressure-driven dust waves inside bursting interstellar bubbles
• The X-ray catalog of spectroscopically identified Galactic O stars: Investigating the dependence of X-ray luminosity on stellar and wind parameters
• Low-metallicity massive single stars with rotation. II. Predicting spectra and spectral classes of chemically-homogeneously evolving stars
• Observational properties of massive black hole binary progenitors
• X-ray Observations of Bow Shocks around Runaway O Stars. The case of $\zeta$ Oph and BD+43${}^{\circ }$3654
• Bow shocks, bow waves, and dust waves. I. Strong coupling limit
• Collective non-thermal emission from an extragalactic jet interacting with stars
• Wind properties of Milky Way and SMC massive stars: empirical Z dependence from CMFGEN models
• Discovery of X-ray emission from young suns in the Small Magellanic Cloud
• Demonstration of a novel method for measuring mass-loss rates for massive stars
• Shock-heated radiation-driven outflows as a solution to the weak-wind problem of late O-type stars
• UV diagnostic of porosity-free mass-loss estimates in B stars
• X-ray diagnostics of massive star winds
• A combined HST and XMM-Newton campaign for the magnetic O9.7 V star HD 54879: towards constraining the weak-wind problem of massive stars
• A Report on the X-ray Properties of the tau Sco Like Stars
• Atmospheric NLTE-Models for the Spectroscopic Analysis of Blue Stars with Winds. III. X-ray emission from wind-embedded shocks
• Empirical mass-loss rates and clumping properties of O-type stars in the LMC
• Chandra grating spectroscopy of embedded wind shock X-ray emission from O stars shows low plasma temperatures and significant wind absorption
• Whispering in the dark: Faint X-ray emission from black holes with OB star companions
• Period change and stellar evolution of $\beta$ Cephei stars
• Zeta Oph and the weak-wind problem
• Modeling X-ray Emission Line Profiles from Massive Star Winds - A Review
• B stars seen at high resolution by XMM-Newton
• Moving inhomogeneous envelopes of stars
• An X-ray Study of Two B+B Binaries: AH Cep and CW Cep
• The lack of X-ray pulsations in the extreme helium star BD+37${}^{\circ }$442 and its possible stellar wind X-ray emission
• The wind properties of O-type stars at sub-SMC metallicity
• Probing Thin Winds in Massive OB Stars of the SMC with JWST/NIRSPEC Br-alpha Spectroscopy
• X-ray diagnostics of massive star winds