Accretion dynamics in the classical T Tauri star V2129 Ophiuchi

Abstract

Context. Classical T Tauri stars are variable objects on several timescales, but just a few of them have been studied in detail, with different observational techniques and over many rotational cycles to enable the analysis of the stellar and circumstellar variations on rotational timescales. Aims. We test the dynamical predictions of the magnetospheric accretion model with synoptic data of the classical T Tauri star V2129 Oph obtained over several rotational cycles. Methods. We analyze high resolution observations obtained with the HARPS, ESPaDOnS, and SMARTS spectrographs and simultaneous photometric measurements, clearly sampling four rotational cycles, and fit them with cold/hot spot models and radiative transfer models of emission lines. Results. The photometric variability and the radial velocity variations in the photospheric lines can be explained by the rotational modulation due to cold spots, while the radial velocity variations of the He i (5876 Å) line and the veiling variability are due to hot spot rotational modulation. The hot and cold spots are located at high latitudes and about the same phase, but the hot spot is expected to sit at the chromospheric level, while the cold spot is at the photospheric level. The mass-accretion rate of the system is stable overall around (1.5 ± 0.6) × 10 −9 M yr −1 , but can increase by three times this value in a rotational cycle, during an accretion burst. The Hα and Hβ emission-line profiles vary substantially and are well-reproduced by radiative transfer models calculated from the funnel flow structure of three-dimensional magnetohydrodynamic simulations, using the dipole+octupole magnetic-field configuration previously proposed for the system. Our diskwind models do not provide a significant contribution to the emission or absorption Hα line profile of V2129 Oph. Conclusions. The global scenario proposed by magnetospheric accretion for classical T Tauri stars is able to reproduce the spectroscopic and photometric variability observed in V2129 Oph.

Particle rings and astrophysical accretion discs

“…The spectrum in several Hydrogen lines was calculated and compared with observed spectra. A good match was obtained between the modeled and observed spectra [81].…”

“…They have shown that conical winds may explain different features in the hydrogen spectral lines, in the He I line and also a relatively narrow, low-velocity blueshifted absorption components in the He I λ10830 which is often seen in observations [79]. Further, the 3D MHD+3D radiative transfer codes have been used to model the young star V2129 Oph, where the parameters of the star including the surface magnetic field distribution are known [81]. The spectrum in several Hydrogen lines was calculated and compared with observed spectra.…”

Observational clues to the physics at the magnetosphere in young stellar objects

“…The HeI (5876 Å) line also comes from the shock region and its radial velocity variability is due to the rotation of the hot spot with respect to our line of sight. The prediction of hot spot filling factor and location from the ZDI results was confirmed through the modeling of both veiling variability and HeI (5876 Å) line radial velocity variations [2].…”

“…A multiwavelength observing campaign of this system was organized in 2009, which included simultaneous optical and near-IR photometry, high resolution spectroscopy and spectropolarimetry, and Chandra X-ray observations [2,3,18].…”

MHD Simulations of Magnetospheric Accretion, Ejection and Plasma-field Interaction

“…More recently, a time-variable spectrum in hydrogen lines has been calculated from the 3D MHD model of V2129 and has been compared with the time-variable spectrum obtained from the observations of this star [44]. Comparisons show a good match between the observed and modeled spectra.…”