Evidence from stellar rotation for early disc dispersal owing to close companions
Journal
Date Issued
2019
Author(s)
Abstract
Young low-mass stars of equal-mass exhibit a distribution of rotation
periods. At the very early phases of stellar evolution, this distribution is
set by the star-disc locking mechanism. The primordial disc lifetime and,
consequently, the duration of the disc-locking mechanism, can be significantly
shortened by the presence of a close companion, making the rotation period
distribution of close binaries different from that of either single stars or
wide binaries. We use new data to investigate and better constrain the range of
ages, the components separation and the mass ratio dependence at which the
rotation period distribution has been significantly affected by the disc
dispersal that is enhanced by close companions. We select a sample of close
binaries in the Upper Scorpius association (age $\sim$8 Myr) whose components
have measured the separation and the rotation periods and compare their period
distribution with that of coeval stars that are single stars. We find that
components of close binaries have on average rotation periods shorter than
single stars. More precisely, binaries with about equal-mass components (0.9
$\le$ M2/M1 $\le$ 1.0) have rotation periods on average by $\sim$0.4 d shorter
than single stars; binaries with smaller mass ratios (0.8 $<$ M2/M1 $<$ 0.9)
have rotation periods on average by $\sim$1.9 d the primary components, and by
$\sim$1.0 d the secondary components shorter than single stars. A comparison
with the older 25-Myr $\beta$ Pictoris association shows that, whereas in the
latter all close binaries with projected separation $\rho$ $\le$ 80 AU all
rotate faster than single stars, in the Upper Scorpius that has happened for
about 70% stars, yet. We interpret the enhanced rotation in close binaries with
respect to single stars as the consequence of an early disc dispersal induced
by the presence of close companions.
Volume
627
Start page
A97
Issn Identifier
0004-6361
Rights
open.access
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