The X-ray activity-rotation relation of T
Tauri stars in Taurus-Auriga
Briggs, K. R.; Guedel, M.; Telleschi,
A.; Preibisch, Th.; Stelzer, B.; Bouvier, J.; Rebull, L.; Audard, M.;
Scelsi, L.; Micela, G.; Grosso, N.; Palla, F.
A&A, Volume 468, Issue 2, pg.413-424 (2007)
Abstract
Context: The Taurus-Auriga star-forming complex hosts the only
population of T Tauri stars in which an anticorrelation of X-ray
activity and rotation period has been observed.
Aims: We aim to explain the origin of the X-ray activity-rotation
relation in Taurus-Auriga. We also aim to put the X-ray activity of
these stars into the context of the activity of late-type main-sequence
stars and T Tauri stars in the Orion Nebula Cluster.
Methods: We have used XMM-Newton's European Photon Imaging Cameras to
perform the most sensitive survey to date of X-ray emission (0.3-10
keV) from young stars in Taurus-Auriga. We investigated the dependences
of X-ray activity measures - X-ray luminosity, L_X, its ratio with the
stellar luminosity, L_X/Lstar, and the surface-averaged
X-ray flux, F_XS - on rotation period and compared them with
predictions based solely on the observed dependence of LX on a star's Lstar
and whether it is accreting or not. We tested for differences in
the distributions of L_X/Lstar of fast and slow rotators,
accretors and non-accretors, and compared the dependence of L_X/Lstar
on the ratio of the rotation period and the convective turnover
timescale, the Rossby number, with that of late-type main-sequence
stars.
Results: We found significant anticorrelations of LX and F_XS with
rotation period, but these could be explained by the typically higher
stellar luminosity and effective temperature of fast-rotators in
Taurus-Auriga and a near-linear dependence of LX on Lstar.
We found no evidence for a dependence of L_X/Lstar on
rotation period, but for accretors to have lower L_X/Lstar
than non-accretors at all rotation periods. The Rossby numbers of
accretors and non-accretors were found to be the same as those of
late-type main-sequence stars showing saturated X-ray emission.
Conclusions: Non-accreting T Tauri stars show X-ray activity entirely
consistent with the saturated activity of fast-rotating late-type
main-sequence stars. Accreting T Tauri stars show lower X-ray activity,
but this cannot be attributed to their slower rotation.
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