Role of local absorption on the X-ray emission from MHD accretion shocks in classical T Tauri stars
1 Dipartimento di Fisica e Chimica, Universita’ degli Studi di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
2 INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90134 Palermo, Italy
3 CEA, IRAMIS, Service Photons, Atomes et Molecules, 91191 Gif-sur-Yvette, France
4 Laboratoire AIM, CEA/DSM - CNRS - Universite’ Paris Diderot, IRFU/Service d’Astrophysique, CEA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette France
5 LERMA, Observatoire de Paris, Universite’ Pierre et Marie Curie and CNRS, 5 Place J. Janssen 92195 Meudon, France
a e-mail: firstname.lastname@example.org
Published online: 8 January 2014
Accretion processes onto classical T Tauri stars (CTTSs) are believed to generate shocks at the stellar surface due to the impact of supersonic downflowing plasma. Although current models of accretion streams provide a plausible global picture of this process, several aspects are still unclear. For example, the observed X-ray luminosity in accretion shocks is, in general, well below the predicted value. A possible explanation discussed in the literature is in terms of significant absorption of the emission due to the thick surrounding medium. Here we consider a 2D MHD model describing an accretion stream propagating through the atmosphere of a CTTS and impacting onto its chromosphere. The model includes all the relevant physics, namely the gravity, the thermal conduction, and the radiative cooling, and a realistic description of the unperturbed stellar atmosphere (from the chromosphere to the corona). From the model results, we synthesize the X-ray emission emerging from the hot slab produced by the accretion shock, exploring different configurations and strengths of the stellar magnetic field. The synthesis includes the local absorption by the thick surrounding medium and the Doppler shift of lines due to the component of plasma velocity along the line-of-sight. We explore the effects of absorption on the emerging X-ray spectrum, considering different inclinations of the accretion stream with respect to the observer. Finally we compare our results with the observations.
© Owned by the authors, published by EDP Sciences, 2014
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