| Abstract
| - The bright southern star δ Vel is a multiple system comprising at least three stars, with two of these stars in an eclipsing binary system. We searched for infrared excess and determined fundamental stellar parameters for the three components from a combination of photometry, spectroscopy, adaptive optics imaging (VLT/NACO), thermal infrared imaging (VLT/VISIR) and near-infrared interfero- metry (VLTI/AMBER). The main eclipsing component is a pair of A-type stars in rapid rotation. We modeled the photometric and radial velocity measurements of the eclipsing pair Aa-Ab using a self consistent method based on physical parameters (mass, radius, luminosity, rotational velocity). From this modeling, we derive the fundamental parameters of the eclipsing stars with a typical accuracy of 1%. We find that they have similar masses, respectively 2.43 ± 0.02 and 2.27 ± 0.02 M⊙. As we spatially resolve the eclisping binary orbit, we also derive the parallax of the system, 39.8 ± 0.4 mas, in satisfactory agreement (− 1.2σ) with the Hipparcos value (40.5 ± 0.4 mas). Finally, we measured the differential astrometric displacement of the center of light of the eclipsing binary relatively to δ Vel B with an uncertainty of ≈100 microarcseconds per epoch, from adaptive optics imaging, thus demonstrating the capabilities of this technique for high-precision astrometry. This accuracy appears to be limited by astrophysical noise (activity of the Aa or Ab stars).
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