6533b86ffe1ef96bd12ce841
RESEARCH PRODUCT
YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppress fluctuations of X-ray emission
L. De SáL. De SáRosaria BonitoRosaria BonitoThierry LanzM. GonzálezSalvatore OrlandoGiovanni PeresGiovanni PeresL. IbguiChantal StehléJ.-p. ChièzeFabio RealeFabio RealeCostanza ArgiroffiCostanza ArgiroffiTitos MatsakosTitos Matsakossubject
Astrophysics::High Energy Astrophysical Phenomenaaccretion accretion disks magnetohydrodynamics (MHD) radiative transfer shock waves instabilitiesFOS: Physical sciencesPerturbation (astronomy)Astrophysics01 natural sciencesmagnetohydrodynamics (MHD)Settore FIS/05 - Astronomia E Astrofisicaaccretion0103 physical sciencesRadiative transferAstrophysics::Solar and Stellar Astrophysics010306 general physics010303 astronomy & astrophysicsChromosphereSolar and Stellar Astrophysics (astro-ph.SR)Astrophysics::Galaxy AstrophysicsPhysicsaccretion disksAstronomy and AstrophysicsObservablePlasmashock wavesThermal conductionMagnetic fieldAmplitudeAstrophysics - Solar and Stellar Astrophysics13. Climate actionSpace and Planetary Scienceradiative transferinstabilities[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]description
Context. Theoretical arguments and numerical simulations of radiative shocks produced by the impact of the accreting gas onto young stars predict quasi-periodic oscillations in the emitted radiation. However, observational data do not show evidence of such periodicity. Aims. We investigate whether physically plausible perturbations in the accretion column or in the chromosphere could disrupt the shock structure influencing the observability of the oscillatory behavior. Methods. We performed local 2D magneto-hydrodynamical simulations of an accretion shock impacting a chromosphere, taking optically thin radiation losses and thermal conduction into account. We investigated the effects of several perturbation types, such as clumps in the accretion stream or chromospheric fluctuations, and also explored a wide range of plasma-\beta values. Results. In the case of a weak magnetic field, the post-shock region shows chaotic motion and mixing, smoothing out the perturbations and retaining a global periodic signature. On the other hand, a strong magnetic field confines the plasma in flux tubes, which leads to the formation of fibrils that oscillate independently. Realistic values for the amplitude, length, and time scales of the perturbation are capable of bringing the fibril oscillations out of phase, suppressing the periodicity of the emission. Conclusions. The strength of a locally uniform magnetic field in YSO accretion shocks determines the structure of the post-shock region, namely, whether it will be somewhat homogeneous or if it will split up to form a collection of fibrils. In the second case, the size and shape of the fibrils is found to depend strongly on the plasma-\beta value but not on the perturbation type. Therefore, the actual value of the protostellar magnetic field is expected to play a critical role in the time dependence of the observable emission.
| year | journal | country | edition | language |
|---|---|---|---|---|
| 2013-07-20 |