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Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
- Source :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, 2013, 559, pp.A127. ⟨10.1051/0004-6361/201322076⟩, Astronomy and Astrophysics-A&A, EDP Sciences, 2013, 559, pp.A127. ⟨10.1051/0004-6361/201322076⟩
- Publication Year :
- 2013
- Publisher :
- HAL CCSD, 2013.
-
Abstract
- (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.<br />11 pages, 11 Figures; accepted for publication on A&A. Version with full resolution images can be found at http://www.astropa.unipa.it/~orlando/PREPRINTS/sorlando_accretion_shocks.pdf
- Subjects :
- Astrophysics::High Energy Astrophysical Phenomena
FOS: Physical sciences
Field strength
X-rays: stars
Astrophysics
stars: pre-main sequence
01 natural sciences
magnetohydrodynamics (MHD)
pre-main sequence, X-rays: stars [accretion, accretion disks, instabilities, magnetohydrodynamics (MHD), shock waves, stars]
010305 fluids & plasmas
Settore FIS/05 - Astronomia E Astrofisica
accretion
0103 physical sciences
Radiative transfer
Astrophysics::Solar and Stellar Astrophysics
010303 astronomy & astrophysics
Chromosphere
Solar and Stellar Astrophysics (astro-ph.SR)
Astrophysics::Galaxy Astrophysics
Physics
accretion disks
Astronomy and Astrophysics
Plasma
shock waves
Accretion (astrophysics)
Magnetic field
T Tauri star
Astrophysics - Solar and Stellar Astrophysics
Space and Planetary Science
instabilities
Physics::Space Physics
Oblique shock
Astrophysics::Earth and Planetary Astrophysics
accretion, accretion disks, instabilities, magnetohydrodynamics (MHD), shock waves, stars: pre-main sequence, X-rays: stars
[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]
Subjects
Details
- Language :
- English
- ISSN :
- 00046361
- Database :
- OpenAIRE
- Journal :
- Astronomy and Astrophysics-A&A, Astronomy and Astrophysics-A&A, 2013, 559, pp.A127. ⟨10.1051/0004-6361/201322076⟩, Astronomy and Astrophysics-A&A, EDP Sciences, 2013, 559, pp.A127. ⟨10.1051/0004-6361/201322076⟩
- Accession number :
- edsair.doi.dedup.....38329ca4bab8b17c29520771e49fa50c