We have carried out an investigation of the early‐type multiple star U Oph. We have used new high‐resolution spectroscopy with the High Efficiency and Resolution Canterbury University Large Echelle Spectrograph (HERCULES) and 1‐m McLellan Telescope of the University of Canterbury at Mt John University Observatory and literature‐sourced optical and ultraviolet photometry. We applied the local reduction package [HERCULES Reduction Software Package (HRSP)] and other software to the spectroscopic data to find radial velocities. Information limit optimization techniques (ILOT) utilizing physically realistic fitting functions were applied to these data to yield new sets of absolute parameters: M1= 5.13, M2= 4.56 (±2 per cent); R1= 3.41, R2= 3.08 (±1 per cent); for the early‐type eclipsing binary that dominates the system. We have combined times‐of‐minima photometry with other data for the triple system that makes up ADS 10428A, utilizing the wide orbit of Wolf et al. as well as HIPPARCOS astrometry of U Oph. ILOT techniques applied to the astrometric orbit yield a mass of the third star as 0.83 M⊙. We estimate an age of the system of around 30–40 Myr, from the isochrones of Bertelli, results given by Vaz, Andersen & Claret, as well as our own tests with an updated version of Paczyński's stellar modelling code. This age and other details are consistent with a possible origin in Gould's Belt. Such information for this, and comparable young multiple star systems, may help to clarify general properties of star formation and the subtle interactions of stars and their environment.

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Literature photometry and new high‐resolution spectroscopy of V831 Cen are presented and analysed. Light and radial velocity curve fittings confirm the central pair of this young multiple system to be close to contact. Absolute parameters are found as follows: M1= 4.08 ± 0.07 M⊙, M2= 3.35 ± 0.06 M⊙, R1= 2.38 ± 0.03 R⊙, R2= 2.25 ± 0.03 R⊙, T1= 13 000 ± 300 K, T2= 11 800 ± 300 K; distance of 110 ± 10 pc and age of ∼20 ± 5 Myr. Detailed examination of the spectrograms indicates the third component (V831 Cen B) to be an Ap star. The orbit of the third star about the close binary is analysed using historic astrometric measurements. This allows an estimate of the third star's mass to be about 2.5 M⊙, but this is sensitive to the adopted distance and inclination values. It is, however, confirmed by the measured radial velocity of the third star. To some extent, such analysis can also be applied to the fourth star (V831 Cen C). The derived properties can be checked against the system's membership of the Scorpius–Centaurus OB2 association.

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