Astrophys. J., 695, 1648-1656 (2009/April-3)
Disk braking in young stars: probing rotation in Chamaeleon I and Taurus-Auriga.
NGUYEN D.C., JAYAWARDHANA R., VAN KERKWIJK M.H., BRANDEKER A., SCHOLZ A. and DAMJANOV I.
Abstract (from CDS):
We present a comprehensive study of rotation, disk, and accretion signatures for 144 T Tauri stars in the young (∼2 Myr old) Chamaeleon I and Taurus-Auriga star-forming regions based on multi-epoch high-resolution optical spectra from the Magellan Clay 6.5 m telescope supplemented by mid-infrared photometry from the Spitzer Space Telescope. In contrast to previous studies in the Orion Nebula Cluster and NGC 2264, we do not see a clear signature of disk braking in Tau-Aur and Cha I. We find that both accretors and non-accretors have similar distributions of vsin i. This result could be due to different initial conditions, insufficient time for disk braking, or a significant age spread within the regions. The rotational velocities in both regions show a clear mass dependence, with F-K stars rotating on average about twice as fast as M stars, consistent with results reported for other clusters of similar age. Similarly, we find the upper envelope of the observed values of specific angular momentum j varies as M 0.5 for our sample which spans a mass range of ∼0.16-3 M☉. This power law complements previous studies in Orion which estimated j ∝ M 0.25 for ≲2 Myr stars in the same mass regime, and a sharp decline in j with decreasing mass for older stars (∼10 Myr) with M < 2 M☉. Furthermore, the overall specific angular momentum of this ∼10 Myr population is five times lower than that of non-accretors in our sample, and implies a stellar braking mechanism other than disk braking could be at work. For a subsample of 67 objects with mid-infrared photometry, we examine the connection between accretion signatures and dusty disks: in the vast majority of cases (63/67), the two properties correlate well, which suggests that the timescale of gas accretion is similar to the lifetime of inner disks.
accretion, accretion disks - circumstellar matter - stars: evolution - stars: formation - stars: pre-main sequence - stars: rotation - stars: statistics
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