The X-ray activity-rotation relation of T Tauri stars in Taurus-Auriga

¹ Paul Scherrer Institut, Villigen und Würenlingen, 5232, Switzerland e-mail: briggs@astro.phys.ethz.ch
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

Received: 27 November 2006
Accepted: 10 January 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, , and the surface-averaged X-ray flux, F_XS – on rotation period and compared them with predictions based solely on the observed dependence of L_X 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 L_X 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 L_X 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.