A 10 micron search for truncated disks among pre-main-sequence stars with photometric rotation periods

We use mid-IR (primarily 10 mum) photometry as a diagnostic for the presenc e of disks with inner cavities among 32 pre-main-sequence stars in Orion an d in Taurus-Auriga for which rotation periods are known and for which there is no evidence of inner disks at near-IR wavelengths. Disks with inner cav ities are predicted by magnetic disk-locking models that seek to explain th e regulation of angular momentum in T Tauri stars. Only three stars in our sample show evidence of excess mid-IR emission. Although these three stars may possess truncated disks consistent with magnetic disk-locking models, t he remaining 29 stars in our sample do not. Apparently, stars lacking near- IR excesses in general do not possess truncated disks to which they are mag netically coupled. We discuss the implications of this result for the hypot hesis of disk-regulated angular momentum. Evidently, young stars can exist as slow rotators without the aid of present disk locking, and there exist v ery young stars already rotating at nearly breakup velocity whose subsequen t angular momentum evolution will not be regulated by disks. Moreover, we q uestion whether disks, when present, truncate in the manner required by dis k-locking scenarios. Finally, we discuss the need for rotational evolution models to take full account of the large dispersion of rotation rates prese nt at 1 Myr; doing so may allow the models to explain the rotational evolut ion of low-mass pre-main-sequence stars in a way that does not depend on br aking by disks.