Testing the Disk Regulation Paradigm withSpitzerObservations. I. Rotation Periods of Pre–Main‐Sequence Stars in the IC 348 Cluster

We present 75 new stellar rotation periods in the young cluster IC348. Starsestimated to be less massive than 0.25 Mo show a unimodal distribution with apeak at P ~1-2 d) and a tail of slower rotators, while stars estimated to bemore massive than 0.2 Mo show a bimodal distribution with peaks at ~2 and ~8 d.We combine all published rotation periods in IC348 with Spitzer/IRAC photometryin order to test the disk-braking paradigm. We find no evidence that the tailof slow rotators in low-mass stars or the long period peak in high-mass starsare preferentially populated by objects with disks as might be expected basedon the current disk-braking model. Also, we find no significant correlationbetween period and the magnitude of the IR-excess, regardless of the mass rangeconsidered. Our results do not support a strong correlation in this clusterbetween rotation period and the presence of a disk as predicted by disk-brakingtheory. Rather, they are consistent with the suggestion that the correlationbetween period and the amplitude of the (I-K) excess reported in the past is asecondary manifestation of the correlation between the amplitude of near-IRexcess and mass. Finally, we find some indication that the disk fractiondecreases significantly for stars with very short periods (P < 1.5 d). This isthe only feature of our sample that could potentially be interpreted asevidence for disk braking. It has been proposed that the observationalsignatures of disk braking might be significantly masked by the intrinsicbreadth of the initial period distribution. We argue that more rigorousmodeling of angular momentum evolution and a quantitative analysis of theobservational data are required before the disk-braking model can be regardedas inconsistent with observations.Comment: 40 pages, 11 figures. Accepted for publication in Ap