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Projected rotational velocities (vsini) are presented for a sample of 350early B-type main sequence stars in the nearby Galactic disk. The stars arelocated within ~1.5 kpc from the Sun, and the great majority within 700 pc. Theanalysis is based on high-resolution spectra obtained with the MIKEspectrograph on the Magellan Clay 6.5-m telescope at the Las CampanasObservatory in Chile.Spectral types were estimated based on relativeintensities of some key line absorption ratios and comparisons to syntheticspectra. Effective temperatures were estimated from the reddening-free Q index,and projected rotational velocities were then determined via interpolation on apublished grid that correlates the synthetic full width at half maximum of theHe I lines at 4026, 4388 and 4471 A with vsini. As the sample has been selectedsolely on the basis of spectral types it contains an selection of B stars inthe field, in clusters, and in OB associations. The vsini distribution obtainedfor the entire sample is found to be essentially flat for vsini values between0-150 km/s, with only a modest peak at low projected rotational velocities.Considering subsamples of stars, there appears to be a gradation in the vsinidistribution with the field stars presenting a larger fraction of the slowrotators and the cluster stars distribution showing an excess of stars withvsini between 70 and 130 km/s. Furthermore, for a subsample of potentialrunaway stars we find that the vsini distribution resembles the distributionseen in denser environments, which could suggest that these runaway stars havebeen subject to dynamical ejection mechanisms.

Projected Rotational Velocities and Stellar Characterization of 350 B Stars in the Nearby Galactic Disk