  Low-mass members of young stellar associations exhibit a wide spread of
rotation periods. Such a spread originates from distributions of masses and
initial rotation periods. However, multiplicity can also play a significant
role. We investigate the role played by physical companions in shortening the
primordial disc lifetime. We have compiled the most extensive list of low-mass
members of the young 25-Myr beta Pictoris association. We have measured the
rotation periods of about all members and used updated UVWXYZ components to
assess their membership. We built the rotation period distribution
distinguishing between bona fide members and candidate members and according to
their multiplicity status. We found that single stars and components of
multiple systems in wide orbits (>80 AU) have rotation periods that exhibit a
well defined sequence arising from mass distribution. All components of
multiple systems in close orbits (<80 AU) have rotation periods significantly
shorter than their equal-mass single counterparts. A comparison with the
younger 13 Myr h Per cluster and with the older 40-Myr open clusters/stellar
associations NGC2547, IC2391, Argus, and IC2602 and the 130-Myr Pleiades shows
that whereas the evolution of F-G stars is well reproduced by angular momentum
evolution models, this is not the case for the slow K and early-M stars.
Finally, we found that the amplitude of their light curves is correlated
neither with rotation nor with mass. Once single stars and wide components of
multiple systems are separated from close components of multiple systems, the
rotation period distributions exhibit a well defined dependence on mass that
allows to make a meaningful comparison with similar distributions of either
younger or older associations/clusters. Such cleaned distributions allow to use
the stellar rotation period as age indicator, meaningfully for F and G type
stars.
