Frauke Alexander, Thomas Preibisch
The physical origin of the strong magnetic activity in T Tauri stars and its
relation to stellar rotation is not yet well understood. We investigate the
relation between the X-ray activity, rotation, and Rossby number for a sample
of 82 young stars in the ~3 Myr old cluster IC 348. We use the data of four
Chandra observations of IC 348 to derive the X-ray luminosities of the young
stars. The young stars in IC 348 show no correlation between X-ray activity and
rotation period. Considering the Rossby numbers, nearly all IC 348 stars are in
the saturated regime of the activity-rotation relation defined by main-sequence
stars. Searching for possible super-saturation effects, we find a marginal (but
statistically in-significant) trend that the stars with the smallest Rossby
numbers show slightly lower X-ray activity levels. We compare the dispersion of
fractional X-ray luminosities of the stars in the saturated rotation regime in
IC 348 to that seen in younger and older stellar populations. The scatter seen
in the ~3 Myr old IC 348 is considerably smaller than for the ~1 Myr old ONC,
but, at the same time, considerably larger than the dispersion seen in the ~30
Myr old cluster NGC 2547 and in main-sequence stars. The results of our X-ray
analysis of IC 348 show that neither the rotation rates nor the
presence/absence of circumstellar disks are of fundamental importance for
determining the level of X-ray activity in TTS. Our results suggest that the
scatter of X-ray activity levels shown by the fast-rotating members of young
clusters decreases with the age of the stellar population. We interpret this as
a signature of the changing interior structure of PMS stars and the consequent
changes in the dynamo mechanisms that are responsible for the magnetic field
generation.
View original:
http://arxiv.org/abs/1112.4290
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