The X-ray activity-rotation relation of T Tauri stars in Taurus-Auriga
Paul Scherrer Institut, Villigen und Würenlingen, 5232, Switzerland e-mail: email@example.com
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3 INAF, Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
4 Laboratoire d'Astrophysique de Grenoble, Université Joseph Fourier, BP 53, 38041, Grenoble Cedex 9, France
5 Spitzer Science Center, Caltech M/S 220-6, 1200 East California Boulevard, Pasadena, CA 91125, USA
6 Columbia Astrophysics Laboratory, Mail Code 5247, 550 West 120th Street, New York, NY 10027, USA
7 Integral Science Data Center, Ch. d'Ecogia 16, 1290 Versoix, Switzerland
8 Geneva Observatory, University of Geneva, Ch. des Maillettes 51, 1290 Sauverny, Switzerland
9 Dipartimento di Scienze Fisiche ed Astronomiche, Sezione di Astronomia, Università di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
10 INAF, Osservatorio Astrofisica di Arcetri, Largo E. Fermi 5, 50125 Florence, Italy
Accepted: 10 January 2007
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, LX, its ratio with the stellar luminosity, , and the surface-averaged X-ray flux, FXS – on rotation period and compared them with predictions based solely on the observed dependence of LX on a star's and whether it is accreting or not. We tested for differences in the distributions of of fast and slow rotators, accretors and non-accretors, and compared the dependence of 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 FXS 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 . We found no evidence for a dependence of on rotation period, but for accretors to have lower 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.
Key words: stars: pre-main sequence / stars: activity / stars: rotation / X-rays: stars / open clusters and associations: individual: Taurus-Auriga
© ESO, 2007