Absolute parameters of young stars - I. U Ophiuci

Abstract

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: M 1 = 5.13, M 2 = 4.56 (±2 per cent); R 1 = 3.41, R 2 = 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 Paczynski'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.