6533b7d4fe1ef96bd1261e5d
RESEARCH PRODUCT
Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
Titos MatsakosTitos MatsakosChantal StehléMarco MiceliSalvatore OrlandoCostanza ArgiroffiCostanza ArgiroffiJ.-p. ChièzeThierry LanzL. IbguiFabio RealeFabio RealeRosaria BonitoRosaria BonitoL. De SáL. De SáGiovanni PeresGiovanni Peressubject
Astrophysics::High Energy Astrophysical PhenomenaFOS: Physical sciencesField strengthX-rays: starsAstrophysicsstars: pre-main sequence01 natural sciencesmagnetohydrodynamics (MHD)pre-main sequence X-rays: stars [accretion accretion disks instabilities magnetohydrodynamics (MHD) shock waves stars]010305 fluids & plasmasSettore FIS/05 - Astronomia E Astrofisicaaccretion0103 physical sciencesRadiative transferAstrophysics::Solar and Stellar Astrophysics010303 astronomy & astrophysicsChromosphereSolar and Stellar Astrophysics (astro-ph.SR)Astrophysics::Galaxy AstrophysicsPhysicsaccretion disksAstronomy and AstrophysicsPlasmashock wavesAccretion (astrophysics)Magnetic fieldT Tauri starAstrophysics - Solar and Stellar AstrophysicsSpace and Planetary ScienceinstabilitiesPhysics::Space PhysicsOblique shockAstrophysics::Earth and Planetary Astrophysicsaccretion accretion disks instabilities magnetohydrodynamics (MHD) shock waves stars: pre-main sequence X-rays: stars[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]description
(abridged) AIMS. We investigate the dynamics and stability of post-shock plasma streaming along nonuniform stellar magnetic fields at the impact region of accretion columns. We study how the magnetic field configuration and strength determine the structure, geometry, and location of the shock-heated plasma. METHODS. We model the impact of an accretion stream onto the chromosphere of a CTTS by 2D axisymmetric magnetohydrodynamic simulations. Our model takes into account the gravity, the radiative cooling, and the magnetic-field-oriented thermal conduction. RESULTS. The structure, stability, and location of the shocked plasma strongly depend on the configuration and strength of the magnetic field. For weak magnetic fields, a large component of B may develop perpendicular to the stream at the base of the accretion column, limiting the sinking of the shocked plasma into the chromosphere. An envelope of dense and cold chromospheric material may also develop around the shocked column. For strong magnetic fields, the field configuration determines the position of the shock and its stand-off height. If the field is strongly tapered close to the chromosphere, an oblique shock may form well above the stellar surface. In general, a nonuniform magnetic field makes the distribution of emission measure vs. temperature of the shocked plasma lower than in the case of uniform magnetic field. CONCLUSIONS. The initial strength and configuration of the magnetic field in the impact region of the stream are expected to influence the chromospheric absorption and, therefore, the observability of the shock-heated plasma in the X-ray band. The field strength and configuration influence also the energy balance of the shocked plasma, its emission measure at T > 1 MK being lower than expected for a uniform field. The above effects contribute in underestimating the mass accretion rates derived in the X-ray band.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 2013-11-01 |