BLUE STRAGGLERS IN THE YOUNG GALACTIC ASSOCIATION PERSEUS OB1

Moderate spectral resolution, very high signal-to-noise optical spectr a have been obtained for eight blue stragglers towards the young assoc iation Per OB1. These have been used to estimate projected rotational and radial velocities. The line profiles of hydrogen and neutral and i onized helium have been analysed using non-LTE model atmosphere calcul ations to deduce effective temperatures and logarithmic surface gravit ies. Helium abundances have also been derived, although for some targe ts this quantity was not well constrained. In addition, stellar radii, luminosities, and masses have been estimated both by spectroscopic me thods and by comparison with evolutionary tracks. The spectroscopic es timates were based on absolute magnitudes deduced from either assuming a unique distance modulus, or from a spectral type-absolute magnitude calibration; the latter leads to a range of distance moduli of 1.4 ma gnitudes. Both sets of spectroscopic masses were systematically smalle r than the evolutionary masses, but luminosities deduced from spectral types gave a smaller and less scattered set of mass discrepancies. No ne of these stars is definitely generically related to Per OB1 and the y may therefore represent a more heterogeneous group than has previous ly been thought, containing possibly one helium and nitrogen enriched spectroscopic binary, two stars belonging to other associations/cluste rs, two runaway stars (nitrogen enhanced and possibly helium rich), an d a group of O-type stars beyond Per OB1 containing two very fast rota tors which may be helium enriched.