Query : 2010A&A...510A..71O

2010A&A...510A..71O - Astronomy and Astrophysics, volume 510, A71-71 (2010/2-1)

X-ray emitting MHD accretion shocks in classical T Tauri stars. Case for moderate to high plasma-β values.


Abstract (from CDS):

Plasma accreting onto classical T Tauri stars (CTTS) is believed to impact the stellar surface at free-fall velocities, generating a shock. Current time-dependent models describing accretion shocks in CTTSs are one-dimensional, assuming that the plasma moves and transports energy only along magnetic field lines (β≪1). We investigate the stability and dynamics of accretion shocks in CTTSs, considering the case of β>1 in the post-shock region. In these cases the 1D approximation is not valid and a multi-dimensional MHD approach is necessary. We model an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere by performing 2D axisymmetric MHD simulations. The model takes into account the stellar magnetic field, the gravity, the radiative cooling, and the thermal conduction (including the effects of heat flux saturation). The dynamics and stability of the accretion shock strongly depend on the plasma β. In the case of shocks with β>10, violent outflows of shock-heated material (and possibly MHD waves) are generated at the base of the accretion column and intensely perturb the surrounding stellar atmosphere and the accretion column itself (therefore modifying the dynamics of the shock). In shocks with β≃1, the post-shock region is efficiently confined by the magnetic field. The shock oscillations induced by cooling instability are strongly influenced by β: for β>10, the oscillations may be rapidly dumped by the magnetic field, approaching a quasi-stationary state, or may be chaotic with no obvious periodicity due to perturbation of the stream induced by the post-shock plasma itself; for β≃1 the oscillations are quasi-periodic, although their amplitude is smaller and the frequency higher than those predicted by 1D models.

Abstract Copyright:

Journal keyword(s): accretion, accretion disks - magnetohydrodynamics (MHD) - shock waves - stars: pre-main sequence - X-rays: stars - instabilities

Simbad objects: 5

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Number of rows : 5
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 V* BP Tau Or* 04 19 15.8339827632 +29 06 26.926959492   13.13 12.12 11.89   K5/7Ve 636 0
2 V* TW Hya TT* 11 01 51.9053285064 -34 42 17.033218380   11.94 10.50 10.626 9.18 K6Ve 1774 1
3 CD-33 7795 TT* 11 31 55.2608963280 -34 36 27.203892120   12.97 11.524 11.150 9.150 M2Ve 187 0
4 CPD-68 1894 TT* 13 22 07.5421944624 -69 38 12.219391716   11.38 10.393   9.117 K1Ve 145 0
5 HD 319139 SB* 18 14 10.4818675368 -32 47 34.516836060   11.47 10.68   9.11 K5+K7 340 0

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