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A cluster intermediate in age between the Pleiades (150 Myr) and the Hyades(600 Myr) is needed to probe the rotational evolution, especially thetransition between fast and slow rotation that occurs between the two ages. Westudy the rich 300 Myr-old open cluster NGC 3532 to provide constraints onangular momentum loss. Measuring the rotation periods builds on our prior workof providing spectroscopic membership information for the cluster, and itsupports the chromospheric activity measurements of cluster stars that weprovide in a companion paper. Using 42 d-long photometric time seriesobservations, we measured rotation periods for members of NGC 3532 and comparedthem with the predictions of angular momentum evolution models. We directlymeasured 176 photometric rotation periods for the cluster members. Anadditional 113 photometric rotation periods were identified using activityinformation resulting in a total sample containing 279 rotation periods forFGKM stars in NGC 3532. The colour-period diagram constructed from this richdata set shows a well-populated and structured slow rotator sequence, and afast rotator sequence evolved beyond zero-age main sequence age whose stars arein transition from fast to slow rotation. We also identify an extended slowrotator sequence, apparently the analogue of the one we previously identifiedin NGC 2516. We compare our period distribution to rotational isochrones incolour-period space and find that all considered models have certainshortcomings. Using more detailed spin-down models, we evolve the rotationperiods of the younger NGC 2516 forward in time and find that the spindown ofthe models is too aggressive with respect to the slow rotators. In contrast,stars on the evolved fast rotator sequence are not spun down strongly enough bythese models. Our observations suggest a shorter crossing time for therotational gap. (Abridged)

Rotation periods for cool stars in the open cluster NGC 3532. The transition from fast to slow rotation