Context: High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at temperature T~2-3×10^6 K and density n_e~10^11-10^13 cm^-3, which are unobserved in non-accreting stars. Stationary models suggest that this emission is due to shock-heated accreting material, but do not allow us to analyze the stability of the material and its position in the stellar atmosphere. Aims: We investigate the dynamics and stability of shock-heated accreting material in classical T Tauri stars and the role of the stellar chromosphere in determining the position and thickness of the shocked region. Methods: We perform one-dimensional hydrodynamic simulations of the impact of an accretion flow on the chromosphere of a CTTS, including the effects of gravity, radiative losses from optically thin plasma, thermal conduction and a well tested detailed model of the stellar chromosphere. We present the results of a simulation based on the parameters of the CTTS MP Mus. Results: We find that the accretion shock generates an hot slab of material above the chromosphere with a maximum thickness of 1.8 × 10^9 cm, density n_e~10^11-10^12 cm^-3, temperature T~3×10^6 K, and uniform pressure equal to the ram pressure of the accretion flow (~450 dyn cm^-2). The base of the shocked region penetrates the chromosphere and remains at a position at which the ram pressure is equal to the thermal pressure. The system evolves with quasi-periodic instabilities of the material in the slab leading to cyclic disappearance and re-formation of the slab. For an accretion rate of ~10^-10 Msun yr^-1, the shocked region emits a time-averaged X-ray luminosity of L_X=7×10^29 erg s^-1, which is comparable with the X-ray luminosity observed in CTTSs of identical mass. Furthermore, the X-ray spectrum synthesized from the simulation reproduces in detail all the main features of the O VIII and O VII lines of the star MP Mus.

SACCO, G.G., ARGIROFFI, C., ORLANDO, S., MAGGIO, A., PERES, G., & REALE, F. (2008). X-ray emission from dense plasma in classical T Tauri stars: hydrodynamic modeling of the accretion shock. ASTRONOMY & ASTROPHYSICS, 491, L17-L20 [10.1051/0004-6361:200810753].

X-ray emission from dense plasma in classical T Tauri stars: hydrodynamic modeling of the accretion shock

ARGIROFFI, Costanza;PERES, Giovanni;REALE, Fabio
2008

Abstract

Context: High spectral resolution X-ray observations of classical T Tauri stars (CTTSs) demonstrate the presence of plasma at temperature T~2-3×10^6 K and density n_e~10^11-10^13 cm^-3, which are unobserved in non-accreting stars. Stationary models suggest that this emission is due to shock-heated accreting material, but do not allow us to analyze the stability of the material and its position in the stellar atmosphere. Aims: We investigate the dynamics and stability of shock-heated accreting material in classical T Tauri stars and the role of the stellar chromosphere in determining the position and thickness of the shocked region. Methods: We perform one-dimensional hydrodynamic simulations of the impact of an accretion flow on the chromosphere of a CTTS, including the effects of gravity, radiative losses from optically thin plasma, thermal conduction and a well tested detailed model of the stellar chromosphere. We present the results of a simulation based on the parameters of the CTTS MP Mus. Results: We find that the accretion shock generates an hot slab of material above the chromosphere with a maximum thickness of 1.8 × 10^9 cm, density n_e~10^11-10^12 cm^-3, temperature T~3×10^6 K, and uniform pressure equal to the ram pressure of the accretion flow (~450 dyn cm^-2). The base of the shocked region penetrates the chromosphere and remains at a position at which the ram pressure is equal to the thermal pressure. The system evolves with quasi-periodic instabilities of the material in the slab leading to cyclic disappearance and re-formation of the slab. For an accretion rate of ~10^-10 Msun yr^-1, the shocked region emits a time-averaged X-ray luminosity of L_X=7×10^29 erg s^-1, which is comparable with the X-ray luminosity observed in CTTSs of identical mass. Furthermore, the X-ray spectrum synthesized from the simulation reproduces in detail all the main features of the O VIII and O VII lines of the star MP Mus.
Settore FIS/05 - Astronomia E Astrofisica
SACCO, G.G., ARGIROFFI, C., ORLANDO, S., MAGGIO, A., PERES, G., & REALE, F. (2008). X-ray emission from dense plasma in classical T Tauri stars: hydrodynamic modeling of the accretion shock. ASTRONOMY & ASTROPHYSICS, 491, L17-L20 [10.1051/0004-6361:200810753].
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/10447/36638
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