Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph

By J. Donati, M. Jardine, S. G. Gregory, P. Petit, J. Bouvier, C. Dougados, F. Ménard, Andrew C Cameron, T. Harries, S. Jeffers and 1 more. 2007

165 citations recorded by the source corpus.

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 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 produces X-ray coronal fluxes typical of those observed in cTTSs.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/5082a954406891bc5a373d8801f75f0f70fa0771

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In Astronomy and Astrophysics

1. K. Luhman
2. G. Herczeg
3. J. Donati
4. Michael C. Liu
5. L. Hartmann
6. E. Bergin
7. A. Reiners
8. N. Calvet

Citations in the corpus

• Magnetic Fields of Nondegenerate Stars (2009, background): “7) and includes in particular a strong octupole component (Donati et al. 2007, 2 08a).”
• IDENTIFYING THE YOUNG LOW-MASS STARS WITHIN 25 PC. I. SPECTROSCOPIC OBSERVATIONS (2009, methodology): “The data were reduced using Libre-ESpRIT, a fully automated reduction package provided for the instrument and described in detail by Donati et al. (1997, 2007).”
• MHD simulations of accretion onto a dipolar magnetosphere - II. Magnetospheric ejections and stellar spin-down (2012, methodology): “While this has been observed, for example, in the case of AA Tau (Donati et al. 2010b), such a strong dipolar component does not seem to be a common feature among T Tauri stars (Donati et al. 2007, 2010a, 2011a,b,c; Hussain et al. 2009).”
• The Sun in Time: Activity and Environment (2007, background): “More recently, Donati et al. (2007) have reconstructed a rather complex, large-scale magnetic topology on the CTTS V2129 Oph; they found a relatively weak dipole but stronger octupolar fields that are tilted against the rotation axis, with strong near-polar spots.”
• Large-scale magnetic topologies of late M dwarfs★: Magnetic topologies of late M dwarfs (2010, background): “…results on young stars show that the fully convective T Tauri star BP Tau (0.7 M⊙) exhibit a strong large-scale magnetic field (Donati et al. 2008a), whereas the more massive partly convective star V2129 Oph (1.4 M⊙) possesses a weaker and more complex field (Donati et al. 2007).”
• Magnetospheric accretion on the T Tauri star BP Tauri (2008, methodology): “This technique was recently applied to V2129 Oph, a bright, mildly accreting cTTS in the Ophiucus stellar formation region (Donati et al. 2007, hereafter D07).”
• Accretion onto Pre-Main-Sequence Stars (2016, methodology): “As an example, Figure 3 shows the reconstructed magnetic field of V2129 Oph, indicating separately the complex 1.2-kG octupolar surface field and the 0.35-kG dipolar large-scale field, the latter tilted relative to the stellar rotation axis by 20◦ (Donati et al. 2007, Gregory et al. 2008).”
• EXCLUSION OF COSMIC RAYS IN PROTOPLANETARY DISKS: STELLAR AND MAGNETIC EFFECTS (2013, background): “Number of spots is less meaningful as T-Tauri stars are suggested to have single spots covering large areas (Donati et al. 2007, 2011a,b, 2012).”