Context :

Aims : We aim at measuring the stellar parameters of the two Chemically Peculiar components of the B9.5Vp HgMn + A2 Vm double-lined spectroscopic binary HD141556 ( \chi Lup ) , whose period is 15.25 days .

Methods : We combined historical radial velocity measurements with new spatially resolved astrometric observations from PIONIER/VLTI to reconstruct the three-dimensional orbit of the binary , and thus obtained the individual masses .
We fit the available photometric points together with the flux ratios provided by interferometry to constrain the individual sizes , which we compared to predictions from evolutionary models .

Results : The individual masses of the components are M _ { \mathrm { a } } = 2.84 \pm 0.12 \mathrm { M _ { \sun } } and M _ { \mathrm { b } } = 1.94 \pm 0.09 \mathrm { M _ { \sun } } .
The dynamical distance is compatible with the Hipparcos parallax .
We find linear stellar radii of R _ { \mathrm { a } } = 2.85 \pm 0.15 \mathrm { R _ { \sun } } and R _ { \mathrm { b } } = 1.75 \pm 0.18 \mathrm { R _ { \sun } } .
This result validates a posteriori the flux ratio used in previous detailed abundance studies .
Assuming coevality , we determine a slightly sub-solar initial metallicity Z = 0.012 \pm 0.003 and an age of ( 2.8 \pm 0.3 ) \times 10 ^ { 8 } years .
Finally , our results imply that the primary rotates more slowly than its synchronous velocity , while the secondary is probably synchronous .
We show that strong tidal coupling during the pre-main sequence evolution followed by a full decoupling at zero-age main sequence provides a plausible explanation for these very low rotation rates .

Conclusions :