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Astron. Astrophys. 339, 113-122 (1998)

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Using polarimetry to check rotation alignment in PMS binary stars

Principles of the method and first results *

J.-L. Monin 1, 2, F. Ménard 1 and G. Duchêne 1

1 Laboratoire d'Astrophysique, CNRS UMR 5571, Observatoire de Grenoble, Université Joseph Fourier, BP 53, F-38041 Grenoble Cedex 9, France
2 Institut Universitaire de France

Received 16 March 1998 / Accepted 27 August 1998


We present a new method to use polarimetric measurements to estimate the relative orientations of the star+disk system in each component of Pre Main Sequence (PMS) T Tauri binary stars. The principles of the method are presented, together with a review of polarimetric data available in the literature on wide systems ([FORMULA]) in Taurus. We show that this method can be subject to a bias introduced by the interstellar polarization, but we find that in four sources that are not affected by this bias, the rotation axes of both components are preferentially parallel. We also find one system where the axes are clearly not parallel. Because it concerns wide binaries, this alignment is thought to result from initial binary formation itself rather than via a posteriori tidal interactions. The method is promising but requires the use of more accurate polarimeters. In order to test the possibility to study tighter systems, we have also obtained imaging polarimetric measurements and spectra for each components of closer binaries ([FORMULA]). Our first polarimetric measurements lack S/N, but the spectra of individual components of these close binaries provide information on their respective spectral types and their accretion rate through [FORMULA] equivalent widths and fluxes. We use these spectra to confirm the nature and the pairing tendency of the TTS under study. Implications on the binary formation mechanism are discussed.

Key words: techniques: polarimetric – techniques: spectroscopic – stars: pre-main sequence – stars: binaries: close – circumstellar matter

* Based on observations made with the Bernard-Lyot Telescope at the Pic-du-Midi observatory and with the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii.

Send offprint requests to: J.-L. Monin, (Jean-Louis.Monin@obs.ujf-grenoble.fr)

© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998