  Projected rotational velocities (vsini) are presented for a sample of 350
early B-type main sequence stars in the nearby Galactic disk. The stars are
located within ~1.5 kpc from the Sun, and the great majority within 700 pc. The
analysis is based on high-resolution spectra obtained with the MIKE
spectrograph on the Magellan Clay 6.5-m telescope at the Las Campanas
Observatory in Chile.Spectral types were estimated based on relative
intensities of some key line absorption ratios and comparisons to synthetic
spectra. Effective temperatures were estimated from the reddening-free Q index,
and projected rotational velocities were then determined via interpolation on a
published grid that correlates the synthetic full width at half maximum of the
He I lines at 4026, 4388 and 4471 A with vsini. As the sample has been selected
solely on the basis of spectral types it contains an selection of B stars in
the field, in clusters, and in OB associations. The vsini distribution obtained
for the entire sample is found to be essentially flat for vsini values between
0-150 km/s, with only a modest peak at low projected rotational velocities.
Considering subsamples of stars, there appears to be a gradation in the vsini
distribution with the field stars presenting a larger fraction of the slow
rotators and the cluster stars distribution showing an excess of stars with
vsini between 70 and 130 km/s. Furthermore, for a subsample of potential
runaway stars we find that the vsini distribution resembles the distribution
seen in denser environments, which could suggest that these runaway stars have
been subject to dynamical ejection mechanisms.
