Donati, J.-F and Gregory, S. G. and Montmerle, T. and Maggio, A. and Argiroffi, C. and Sacco, G. and Hussain, G. and Kastner, J. and Alencar, S. H. P. and Audard, M. and Bouvier, J. and Damiani, F. and Güdel, M. and Huenemoerder, D. and Wade, G. A. (2011) The close classical T Tauri binary V4046 Sgr: complex magnetic fields and distributed mass accretion. Monthly Notices of the Royal Astronomical Society, 417 (3). pp. 1747-1759. ISSN 0035-8711 http://resolver.caltech.edu/CaltechAUTHORS:20111213-110723500
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We report here the first results of a multi-wavelength campaign focusing on magnetospheric accretion processes within the close binary system V4046 Sgr, hosting two partly convective classical T Tauri stars of masses ≃0.9 M_⊙ and age ≃12 Myr. In this paper, we present time-resolved spectropolarimetric observations collected in 2009 September with ESPaDOnS at the Canada–France–Hawaii Telescope (CFHT) and covering a full span of 7 d or ≃2.5 orbital/rotational cycles of V4046 Sgr. Small circularly polarized Zeeman signatures are detected in the photospheric absorption lines but not in the accretion-powered emission lines of V4046 Sgr, thereby demonstrating that both system components host large-scale magnetic fields weaker and more complex than those of younger, fully convective classical T Tauri stars (cTTSs) of only a few Myr and similar masses. Applying our tomographic imaging tools to the collected data set, we reconstruct maps of the large-scale magnetic field, photospheric brightness and accretion-powered emission at the surfaces of both stars of V4046 Sgr. We find that these fields include significant toroidal components, and that their poloidal components are mostly non-axisymmetric with a dipolar component of 50–100 G strongly tilted with respect to the rotation axis; given the similarity with fields of partly convective main-sequence stars of similar masses and rotation periods, we conclude that these fields are most likely generated by dynamo processes. We also find that both stars in the system show cool spots close to the pole and extended regions of low-contrast, accretion-powered emission; it suggests that mass accretion is likely distributed rather than confined in well-defined high-contrast accretion spots, in agreement with the derived magnetic field complexity.
|Additional Information:||© 2011 The Authors. Monthly Notices of the Royal Astronomical Society © 2011 RAS. Accepted 2011 July 1. Received 2011 June 17; in original form 2011 April 21. Article first published online: 29 Aug 2011. We thank an anonymous referee for comments that improved the manuscript. This paper is based on observations obtained at the 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 and TBL (through the allocation of telescope time) and by CNRS/INSU in particular, as well as by the French ‘Agence Nationale pour la Recherche’ (ANR). SHPA acknowledges financial support from Fapemig, CAPES and COFECUB.|
|Subject Keywords:||techniques: polarimetric; stars: formation; stars: imaging; stars: individual: V4046 Sgr; stars: magnetic fields; stars: rotation|
|Official Citation:||Donati, J.-F., Gregory, S. G., Montmerle, T., Maggio, A., Argiroffi, C., Sacco, G., Hussain, G., Kastner, J., Alencar, S. H. P., Audard, M., Bouvier, J., Damiani, F., Güdel, M., Huenemoerder, D. and Wade, G. A. (2011), The close classical T Tauri binary V4046 Sgr: complex magnetic fields and distributed mass accretion. Monthly Notices of the Royal Astronomical Society, 417: 1747–1759. doi: 10.1111/j.1365-2966.2011.19366.x|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||13 Dec 2011 20:48|
|Last Modified:||13 Dec 2011 20:48|
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