Constraining the weak-wind problem: An XMM-HST campaign for the magnetic O9.7 V star HD54879

T. Shenar, L. M. Oskinova, S. P. Järvinen, P. Luckas, R. Hainich, H. Todt, S. Hubrig, A. A.C. Sander, I. Ilyin, W. R. Hamann

Research output: Contribution to journalArticlepeer-review


Mass-loss rates of massive, late type main sequence stars are much weaker than currently predicted, but their true values are very difficult to measure. We suggest that confined stellar winds of magnetic stars can be exploited to constrain the true mass-loss rates M˙ of massive main sequence stars. We acquired UV, X-ray, and optical amateur data of HD54879 (O9.7 V), one of a few O-type stars with a detected atmospheric magnetic field (Bd > ≳ 2 kG). We analyze these data with the Potsdam Wolf-Rayet (PoWR) and xspec codes. We can roughly estimate the mass-loss rate the star would have in the absence of a magnetic field as log M˙B=0 ≈ -9.0M yr-1. Since the wind is partially trapped within the Alfvén radius rA ≳ 12R*, the true mass-loss rate of HD54879 is log M˙ ≲ -10.2M⊙ yr-1. Moreover, we find that the microturbulent, macroturbulent, and projected rotational velocities are lower than previously suggested (< 4 kms-1). An initial mass of 16M⊙ and an age of 5Myr are inferred. We derive a mean X-ray emitting temperature of log TX = 6.7K and an X-ray luminosity of log LX = 32 erg s-1. The latter implies a significant X-ray excess (log LX/LBol≈ - 6.0), most likely stemming from collisions at the magnetic equator. A tentative period of P ≈ 5 yr is derived from variability of the Hα line. 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.

Original languageEnglish
Pages (from-to)139-143
Number of pages5
JournalAstronomical Observatory on Skalnate Pleso. Contributions
Issue number1
Publication statusPublished - 1 Jan 2018


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