The structure and spectrum of the accretion shock in the atmospheres of young stars

Abstract

The structure and spectrum of the accretion shock have been self-consistently simulated for a wide range of parameters typical for Classical T Tauri Stars (CTTS). Radiative cooling of the shocked gas was calculated, taking into account the self-absorption and non-equilibrium (time-dependent) effects in the level populations. These effects modify the standard cooling curve for an optically thin plasma in coronal equilibrium, however the shape of high-temperature ($T>3\times 10^5$ K) part of the curve remains unchanged. The applied methods allow us to smoothly describe the transition from the cooling flow to the hydrostatic stellar atmosphere. Thanks to this approach, it has been found that the narrow component of HeII lines is formed predominantly in the irradiated stationary atmosphere (hotspot), i.e. at velocities of the settling gas $<2$ km s${}^{-1}$. The structure of the pre-shock region is calculated simultaneously with the heated atmosphere. The simulation shows that the pre-shock gas produces a noticeable emission component in HeII lines and practically does not manifest itself in HeI lines ($\lambda \lambda$ 5876, 10830 Å). The UV spectrum of the hotspot is distorted by the pre-shock gas, namely numerous red-shifted emission and absorption lines overlap each other forming a pseudo-continuum. The spectrum of the accretion region at high pre-shock densities $\sim 10^{14}$ cm${}^{-3}$ is fully formed in the in-falling gas and can be qualitatively described as a spectrum of a star with an effective temperature derived from the Stefan-Boltzmann law via the full energy flux.

arXiv comment12 pages, 9 figures. Accepted for publication in MNRAS

References in corpus (24)

• Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: I. Magnetospheric Flow at Different Theta
• Accretion Rates for T Tauri Stars Using Nearly Simultaneous Ultraviolet and Optical Spectra
• Magnetospheric accretion on the T Tauri star BP Tauri
• Magnetic fields and accretion flows on the classical T Tauri star V2129 Oph
• Non-stationary dynamo & magnetospheric accretion processes of the classical T Tauri star V2129 Oph
• Multidimensional models of hydrogen and helium emission line profiles for classical T Tauri Stars: method, tests and examples
• Spectral variability of classical T Tauri stars accreting in an unstable regime
• Non-axisymmetric accretion on the classical TTS RW Aur A
• Hot Gas Lines in T Tauri Stars
• Boundary between Stable and Unstable Regimes of Accretion. Ordered and Chaotic Unstable Regimes
• Accretion dynamics in the classical T Tauri star V2129 Oph
• X-ray emission from dense plasma in CTTSs: Hydrodynamic modeling of the accretion shock
• Magnetospheric accretion on the fully-convective classical T Tauri star DN Tau
• Oscillations of MHD shock waves on the surfaces of T Tauri stars
• X-ray emitting MHD accretion shocks in classical T Tauri stars. Case for moderate to high plasma-beta values
• YSO accretion shocks: magnetic, chromospheric or stochastic flow effects can suppress fluctuations of X-ray emission
• Radiative accretion shocks along nonuniform stellar magnetic fields in classical T Tauri stars
• Interpretation of the Veiling of the Photospheric Spectrum for T Tauri Stars in Terms of an Accretion Model
• The absence of sub-minute periodicity in classical T Tauri stars
• On the source of dense outflows from T Tauri Stars. and III. Winds driven from the star-disc shear layer
• Impacts of fragmented accretion streams onto Classical T Tauri Stars: UV and X-ray emission lines
• Hydrodynamic Modeling of Accretion Impacts in Classical T Tauri Stars: Radiative Heating of the Pre-shock Plasma
• Non-LTE Modelling of the Structure and Spectra of the Hot Accretion Spots on the Surface of Young Stars
• Results of magnetic field measurements in young stars DO Tau, DR Tau, DS Tau

Cited by in corpus (12)

• Analysis of colour and polarimetric variability of RW Aur A in 2010-2018
• Photometric variability of TW~Hya from seconds to years as seen from space and the ground in 2013-2017
• Insights into the inner regions of the FU Orionis disc
• Hydrogen Emission from Accretion and Outflow in T Tauri Stars
• Laboratory modeling of jets from young stars using plasma focus facilities
• S Coronae Australis -- a T Tauri Twin
• Inhomogeneous dust eclipses in young stars. The case of CQ Tauri
• RW Aur B: a modest UX Ori type companion of the famous primary
• Orbital parameters and activity of ZZ Tau -- a low mass young binary with circumbinary disc
• Magnetospheric accretion at the late phases of the Pre-Main-Sequence evolution. The case of RZ Psc
• Continuum And Line Emission From Accretion Shocks at T Tauri Stars I. Correlations With Shock Parameters
• Ultraviolet accretion continua reveal a transition in T Tauri magnetic topology