Issue |
A&A
Volume 491, Number 2, November IV 2008
|
|
---|---|---|
Page(s) | L17 - L20 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:200810753 | |
Published online | 27 October 2008 |
Letter to the Editor
X-ray emission from dense plasma in classical T Tauri stars: hydrodynamic modeling of the accretion shock
1
Consorzio COMETA, via S. Sofia 64, 95123 Catania, Italy e-mail: sacco@astropa.inaf.it
2
INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3
DSFA - Università degli Studi di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
Received:
5
August
2008
Accepted:
1
October
2008
Context. High spectral resolution X-ray observations of classical T Tauri
stars (CTTSs) demonstrate the presence of plasma at temperature K and density
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 cm, density
cm-3,
temperature
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 ~
yr-1, the shocked region
emits a time-averaged X-ray luminosity of
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
and
lines of the star MP Mus.
Key words: X-rays: stars / stars: formation / accretion, accretion disks / hydrodynamics / shock waves / methods: numerical
© ESO, 2008
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