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Astron. Astrophys. 319, 811-838 (1997)
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High S/N Echelle spectroscopy in young stellar groups *
II. Rotational velocities of early-type stars in Sco OB2
A.G.A. Brown 1 and
W. Verschueren 1, 2
1 Sterrewacht Leiden, P.O. Box 9513, 2300 RA Leiden,
The Netherlands
2 University of Antwerp (RUCA), Astrophysics Research
Group, Groenenborgerlaan 171, B-2020 Antwerpen, Belgium
Received 4 January 1996 / Accepted 27 August 1996
Abstract
We investigate the rotational velocities of early-type stars in the
Sco OB2 association. We measure v sin i for 156
established and probable members of the association. The measurements
are performed with three different techniques, which are in increasing
order of expected v sin i: 1) converting the widths of
spectral lines directly to v sin i, 2) comparing
artificially broadened spectra of low v sin i stars to
the target spectrum, 3) comparing the He I
![[FORMULA]](img2.gif)
026 line profile to theoretical models. The
sample is extended with literature data for 47 established members of
Sco OB2. Analysis of the v sin i distributions shows
that there are no significant differences between the subgroups of Sco
OB2. We find that members of the binary population of Sco OB2 on the
whole rotate more slowly than the single stars. In addition, we find
that the B7-B9 single star members rotate significantly faster than
their B0-B6 counterparts. We test various hypotheses for the
distribution of v sin i in the association. The results
show that we cannot clearly exclude any form of random distribution of
the direction and/or magnitude of the intrinsic rotational velocity
vector. We also investigate the effects of rotation on colours in the
Walraven photometric system. We show that positions of B7-B9 single
dwarfs above the main sequence are a consequence of rotation. This
establishes the influence of rotation on the Walraven colours, due
primarily to surface gravity effects.
Key words: stars: early-type; formation;
rotation 
open clusters and associations: individual: Sco OB2
* Based on observations obtained at the European Southern Observatory (ESO), La Silla, Chile in the framework of Key Programme 5-005-45K
Send offprint requests to: A.G.A. Brown, brown@strw.leidenuniv.nl
© European Southern Observatory (ESO) 1997
Online publication: July 3, 1998
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