Donati, J.-F and Gregory, S. G. and Alencar, S. H. P. and Bouvier, J. and Hussain, G. and Skelly, M. and Dougados, C. and Jardine, M. M. and Ménard, F. and Romanova, M. M. and Unruh, Y. C. (2011) The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya. Monthly Notices of the Royal Astronomical Society, 417 (1). pp. 472-487. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20111121-104833727
Full text not available from this repository.
Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20111121-104833727
We report here results of spectropolarimetric observations of the ≃8 Myr classical T Tauri star (cTTS) TW Hya carried out with ESPaDOnS at the Canada–France–Hawaii Telescope in the framework of the ‘Magnetic Protostars and Planets’ programme, and obtained at two different epochs (2008 March and 2010 March). Obvious Zeeman signatures are detected at all times, both in photospheric lines and in accretion-powered emission lines. Significant intrinsic variability and moderate rotational modulation are observed in both photospheric and accretion proxies. Using tomographic imaging, we reconstruct maps of the large-scale field of the photospheric brightness and the accretion-powered emission at the surface of TW Hya at both epochs. We find that the magnetic topology is mostly poloidal and axisymmetric with respect to the rotation axis of the star and that the octupolar component of the large-scale field (2.5–2.8 kG at the pole) largely dominates the dipolar component. This large-scale field topology is characteristic of partly convective stars, supporting the conclusion (from evolutionary models) that TW Hya already hosts a radiative core. We also show that TW Hya features a high-latitude photospheric cool spot overlapping with the main magnetic pole (and producing the observed radial velocity fluctuations); this is also where accretion concentrates most of the time, although accretion at lower latitudes is found to occur episodically. We propose that the relatively rapid rotation of TW Hya (with respect to AA Tau-like cTTSs) directly reflects the weakness of the large-scale dipole, no longer capable of magnetically disrupting the accretion disc up to the corotation radius (at which the Keplerian period equals the stellar rotation period). We therefore conclude that TW Hya is in a phase of rapid spin-up as its large-scale dipole field progressively vanishes.
|Additional Information:||© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 June 20. Received 2011 June 20; in original form 2011 May 25. Article first published online: 17 Aug. 2011. We thank the referee for a detailed reading of the manuscript. This paper is based on observations obtained at the Canada–France–Hawaii Telescope (CFHT), operated by the National Research Council of Canada, the Institut National des Sciences de l’Univers of the Centre National de la Recherche Scientifique of France and the University of Hawaii. The ‘Magnetic Protostars and Planets’ (MaPP) project is supported by the funding agencies of CFHT (through the allocation of telescope time) and by CNRS/INSU in particular, as well as by the French ‘Agence Nationale pour la Recherche’ (ANR).|
|Subject Keywords:||techniques: polarimetric; stars: formation; stars: imaging; stars: individual: TW Hya; stars: magnetic field; stars: rotation|
|Official Citation:||The large-scale magnetic field and poleward mass accretion of the classical T Tauri star TW Hya (pages 472–487) J.-F. Donati, S. G. Gregory, S. H. P. Alencar, J. Bouvier, G. Hussain, M. Skelly, C. Dougados, M. M. Jardine, F. Ménard, M. M. Romanova and Y. C. Unruh, the MaPP collaboration Article first published online: 17 AUG 2011 | DOI: 10.1111/j.1365-2966.2011.19288.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||21 Nov 2011 19:20|
|Last Modified:||21 Nov 2011 19:20|
Repository Staff Only: item control page