1995A&A...298..489K

Moderate spectral resolution, very high signal-to-noise optical spectra have been obtained for eight blue stragglers towards the young association Per OB1. These have been used to estimate projected rotational and radial velocities. The line profiles of hydrogen and neutral and ionized helium have been analysed using non-LTE model atmosphere calculations to deduce effective temperatures and logarithmic surface gravities. Helium abundances have also been derived, although for some targets this quantity was not well constrained. In addition, stellar radii, luminosities, and masses have been estimated both by spectroscopic methods and by comparison with evolutionary tracks. The spectroscopic estimates 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 magnitudes. Both sets of spectroscopic masses were systematically smaller than the evolutionary masses, but luminosities deduced from spectral types gave a smaller and less scattered set of mass discrepancies. None of these stars is definitely generically related to Per OB1 and they may therefore represent a more heterogeneous group than has previously been thought, containing possibly one helium and nitrogen enriched spectroscopic binary, two stars belonging to other associations/clusters, two runaway stars (nitrogen enhanced and possibly helium rich), and a group of O-type stars beyond Per OB1 containing two very fast rotators which may be helium enriched.