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Astron. Astrophys. 318, 495-505 (1997)

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COYOTES IV: the rotational periods of low-mass Post-T Tauri stars in Taurus *

J. Bouvier 1, 2, R. Wichmann 3, K. Grankin 4, S. Allain 1, E. Covino 5, M. Fernández 6, 7, E.L. Martín 8, L. Terranegra 5, S. Catalano 9 and E. Marilli 9

1 Laboratoire d'Astrophysique, Observatoire de Grenoble, Université Joseph Fourier, B.P. 53X, F-38041 Grenoble Cedex, France (bouvier@gag.observ-gr.fr)
2 Canada-France-Hawaii Telescope Corporation, P.O. Box 1597, Kamuela, HI 96743, USA
3 Landessternwarte Königstuhl, D-69117 Heidelberg, Germany
4 Astronomical Institute, Tashkent, 700052 Uzbekistan, CIS
5 Osservatorio Astronomico di Capodimonte, Via Moiariello 16, I-80131 Napoli, Italy
6 Max-Planck-Institut für Astronomie, Königstuhl, D-69117 Heidelberg, Germany
7 Instituto de Astronomía, UNAM, Apdo. 70-264, 04510 México, D.F., México
8 Instituto de Astrofísica de Canarias, E-38200 La Laguna, Tenerife, Spain
9 Osservatorio Astrofisico di Catania, Citta' Universitaria, I-95125 Catania, Italy

Received 29 April 1996 / Accepted 1 July 1996

Abstract

We monitored the light variations of 58 weak-line T Tauri stars in Taurus, recently discovered in the X-ray wavelength range during the ROSAT All-Sky Survey. We derive photometric periods for 18 stars, all but one being ascribed to rotational modulation by stellar spots. The exception is a 37.6d period assigned to the orbital motion of a new pre-main sequence spectroscopic binary. Two thirds of the stars in our sample have an age larger than 10 Myr and up to 40 Myr, thus filling the observational gap that previously existed between T Tauri stars on convective tracks and ZAMS dwarfs for the determination of the rotational evolution of young low-mass stars. The rotational periods are found to range from 0.5 to 7.5 days, most periods being shorter than 5 days. This result provides direct evidence for the spin up of solar type stars as they contract on pre-main sequence radiative tracks, as predicted by recent models of angular momentum evolution. The paucity of long periods (P [FORMULA] 5d, i.e., [FORMULA] 10 km s-1) in the sample of post-T Tauri stars leaves, however, the origin of the numerous slow rotators observed in young clusters an open issue.

Key words: stars: pre-main sequence – stars: rotation

* Based on observations made at the Mount Maidanak Observatory, Uzbekistan; at the Observatoire de Haute-Provence (CNRS), France; at the Observatorio Astronómico Nacional at San Pedro Mártir, Baja California, México; at the IAC80 telescope of Teide Observatory, Spain; at the Serra La Nave Observatory, Catania, Italy.

Send offprint requests to: J. Bouvier

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© European Southern Observatory (ESO) 1997

Online publication: July 8, 1998
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