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Eclipsing systems of massive stars allow one to explore the properties oftheir components in great detail. We perform a multi-wavelength, non-LTEanalysis of the three components of the massive multiple system $\delta$ Ori A,focusing on the fundamental stellar properties, stellar winds, and X-raycharacteristics of the system. The primary's distance-independent parametersturn out to be characteristic for its spectral type (O9.5 II), but usage of the${\rm \it Hipparcos}$ parallax yields surprisingly low values for the mass,radius, and luminosity. Consistent values follow only if $\delta$ Ori lies atabout twice the ${\rm \it Hipparcos}$ distance, in the vicinity of the$\sigma$-Orionis cluster. The primary and tertiary dominate the spectrum andleave the secondary only marginally detectable. We estimate the V-bandmagnitude difference between primary and secondary to be $\Delta V \approx2.\!\!^{\rm m}8$. The inferred parameters suggest the secondary is an earlyB-type dwarf ($\approx$ B1 V), while the tertiary is an early B-type subgiant($\approx$ B0 IV). We find evidence for rapid turbulent velocities ($\sim 200$km ${\rm s}^{-1}$) and wind inhomogeneities, partially optically thick, in theprimary's wind. The bulk of the X-ray emission likely emerges from theprimary's stellar wind ($\log L_{\text{X}} / L_{\text{Bol}} \approx -6.85$),initiating close to the stellar surface at $R_0 \sim 1.1\,R_*$. Accounting forclumping, the mass-loss rate of the primary is found to be $\log \dot{M}\approx -6.4\,[M_\odot\,{\rm yr}^{-1}]$, which agrees with hydrodynamicpredictions, and provides a consistent picture along the X-ray, UV, optical andradio spectral domains.

astrophysical journal/the astrophysical journal

A coordinated X-ray and Optical Campaign of the Nearest Massive  Eclipsing Binary, $\delta$ Orionis Aa: IV. A multiwavelength, non-LTE  spectroscopic analysis