Based on observations obtained at the Canada–France–Hawaii Telescope (CFHT) which is 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.
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Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph†
Article first published online: 6 SEP 2007
DOI: 10.1111/j.1365-2966.2007.12194.x
Issue
Monthly Notices of the Royal Astronomical Society
Volume 380, Issue 4, pages 1297–1312, October 2007
Additional Information
How to Cite
Donati, J.-F., Jardine, M. M., Gregory, S. G., Petit, P., Bouvier, J., Dougados, C., Ménard, F., Cameron, A. C., Harries, T. J., Jeffers, S. and Paletou, F. (2007), Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph. Monthly Notices of the Royal Astronomical Society, 380: 1297–1312. doi: 10.1111/j.1365-2966.2007.12194.x
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Publication History
- Issue published online: 6 SEP 2007
- Article first published online: 6 SEP 2007
- Accepted 2007 June 28. Received 2007 June 22; in original form 2007 April 13
- Abstract
- Article
- References
- Cited By
Keywords:
- accretion, accretion discs;
- techniques: spectroscopic;
- stars: formation;
- stars: individual: V2129 Oph;
- stars: magnetic fields;
- stars: rotation
ABSTRACT
From observations collected with the ESPaDOnS spectropolarimeter, we report the discovery of magnetic fields at the surface of the mildly accreting classical T Tauri star (cTTS) V2129 Oph. Zeeman signatures are detected, both in photospheric lines and in the emission lines formed at the base of the accretion funnels linking the disc to the protostar, and monitored over the whole rotation cycle of V2129 Oph. We observe that rotational modulation dominates the temporal variations of both unpolarized and circularly polarized line profiles.
We reconstruct the large-scale magnetic topology at the surface of V2129 Oph from both sets of Zeeman signatures simultaneously. We find it to be rather complex, with a dominant octupolar component and a weak dipole of strengths 1.2 and 0.35 kG, respectively, both slightly tilted with respect to the rotation axis. The large-scale field is anchored in a pair of 2-kG unipolar radial field spots located at high latitudes and coinciding with cool dark polar spots at photospheric level. This large-scale field geometry is unusually complex compared to those of non-accreting cool active subgiants with moderate rotation rates.
As an illustration, we provide a first attempt at modelling the magnetospheric topology and accretion funnels of V2129 Oph using field extrapolation. We find that the magnetosphere of V2129 Oph must extend to about 7R★ to ensure that the footpoints of accretion funnels coincide with the high-latitude accretion spots on the stellar surface. It suggests that the stellar magnetic field succeeds in coupling to the accretion disc as far out as the corotation radius, and could possibly explain the slow rotation of V2129 Oph. The magnetospheric geometry we derive qualitatively reproduces the modulation of Balmer lines and produces X-ray coronal fluxes typical of those observed in cTTSs.