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

Abstract

1 braganca@on.br -2 -Projected rotational velocities (v sin i) 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 λλ4026, 4388 and 4471Å with v sin i. 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 v sin i distribution obtained for the entire sample is found to be essentially flat for v sin i values between 0 -150 km s −1 , with only a modest peak at low projected rotational velocities. Considering subsamples of stars, there appears to be a gradation in the v sin i distribution with the field stars presenting a larger fraction of the slow rotators and the cluster stars distribution showing an excess of stars with v sin i between 70 and 130 km s −1 . Furthermore, for a subsample of potential runaway stars we find that the v sin i distribution resembles the distribution seen in denser environments, which could suggest that these runaway stars have been subject to dynamical ejection mechanisms.

Detection of Additional Be+sdO Systems from IUE Spectroscopy

“…Based on spectroscopic studies, Bragança et al (2012) reported that the star has V sin i = 86 km s −1 , similar to the half-width of the CCF peak. However, Bragança et al (2012) estimate that the star's temperature is T eff = 19.6 kK, and we would usually expect little correlation with the features of such a relatively cooler object. However, the CCFs show no significant peak velocity variations.…”

Influence of Rotation on Stellar Evolution

“…1,ab): υ sin i measurements in the Galaxy and in the Magellanic Clouds indicate that these are rapidly rotating stars, with a mean projected velocity of about 130 km.s −1 for B-type stars (Bragança et al 2012, Hunter et al 2008b, Mokiem et al 2006, Abt et al 2002, and about 110 km.s −1 for O-type stars (Penny 1996, Penny & Gies 2009). Some stars in the On subtype (with nitrogen enrichment) can reach projected velocities of about 420 km.s −1 (Walborn et al 2011) but the number of these very rapid rotators is actually limited.…”

Chemical abundances of fast-rotating massive stars

“…In the blue part, R ∼ 53 000. The spectral reduction was carried out using the Carnegie Observatories python pipeline 2 (Bragança et al 2012;Garmany et al 2015). …”

“…To further validate our method, we compared the v sin i for eight stars with those obtained by Bragança et al (2012) and Garmany et al (2015) with a different method based on the full width at half-minimum [FWHM] of He i lines. The results are presented in Table 1: they show a good agreement within errors, although there is some indication of slightly larger values in our case.…”