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

Abstract

Context: HD 54879 (O9.7 V) is one of a dozen O-stars for which an organized atmospheric magnetic field has been detected. To gain insights into the interplay between atmospheres, winds, and magnetic fields of massive stars, we acquired UV and X-ray data of HD 54879 using the Hubble Space Telescope and the XMM-Newton satellite. In addition, 35 optical amateur spectra were secured to study the variability of HD 54879. A multiwavelength (X-ray to optical) spectral analysis is performed using the Potsdam Wolf-Rayet (PoWR) model atmosphere code and the xspec software. Results: The photospheric parameters are typical for an O9.7 V star. The microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (<4 km/s). An initial mass of 16$M_{\odot }$ and an age of 5 Myr are inferred from evolutionary tracks. We derive a mean X-ray emitting temperature of $\log T_{\mathrm{X}}=6.7$[K] and an X-ray luminosity of $\log L_{\text{X}}=32$[erg/s]. Short- and long-scale variability is seen in the H-alpha line, but only a very long period of $P\approx 5$yr could be estimated. Assessing the circumstellar density of HD 54879 using UV spectra, we can roughly estimate the mass-loss rate HD 54879 would have in the absence of a magnetic field as $\log {\dot{M}}_{B=0}\approx -9.0[M_{\odot }/\mathrm{yr}]$. The magnetic field traps the stellar wind up to the Alfvén radius > $12R_{\odot }$, implying that its true mass-loss rate is $\log \dot{M}<-10.2[M_{\odot }/\mathrm{yr}]$. Hence, density enhancements around magnetic stars can be exploited to estimate mass-loss rates of non-magnetic stars of similar spectral types, essential for resolving the weak wind problem. Conclusions: Our study confirms that strongly magnetized stars lose little or no mass, and supplies important constraints on the weak-wind problem of massive main sequence stars.

Accepted for publication in A&A on Aug. 9, 2017, 12 + 1 pages, 15 figures. Paper replaced due to typos and missing acknowledgments

References in corpus (15)

• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• Pre-Supernova Evolution of Massive Single and Binary Stars
• Dynamical Simulations of Magnetically Channeled Line-Driven Stellar Winds: II. The Effects of Field-Aligned Rotation
• The MiMeS survey of magnetism in massive stars: Magnetic analysis of the O-type stars
• BONNSAI: a Bayesian tool for comparing stars with stellar evolution models
• Nitrogen enrichment, boron depletion and magnetic fields in slowly-rotating B-type dwarfs
• Magnetic massive stars as progenitors of "heavy" stellar-mass black holes
• X-rays from Magnetically Confined Wind Shocks: Effect of Cooling-Regulated Shock Retreat
• B fields in OB stars (BOB): Concluding the FORS2 observing campaign
• An `Analytic Dynamical Magnetosphere' formalism for X-ray and optical emission from slowly rotating magnetic massive stars
• The detection of variable radio emission from the fast rotating magnetic hot B-star HR7355 and evidence for its X-ray aurorae
• Discovery of new magnetic early-B stars within the MiMeS HARPSpol survey
• B fields in OB stars (BOB): FORS2 spectropolarimetric follow-up of the two rare rigidly rotating magnetosphere stars HD23478 and HD345439
• The Tarantula Massive Binary Monitoring project: II. A first SB2 orbital and spectroscopic analysis for the Wolf-Rayet binary R145
• New multiwavelength observations of the Of?p star CPD -28 2561

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