Rotationally modulated X-ray emission from the accretion shock in CTTS

Abstract

To study the accretion shocks of classical T Tauri stars (CTTS) we obtained high-resolution X-ray spectra of two CTTS, V2129 Oph and V4046 Sgr, to look for phase-resolved X-ray signatures of shock-heated plasma. The 200 ks Chandra/HETGS observation of V2129 Oph (a 1.35 M sun star, rotating in 6.5 d) covered 0.5 stellar rotation. The 360 ks XMM/RGS observation of V4046 Sgr (a binary system, with two 0.9 M sun components, synchronously rotating in 2.42 d) monitored 2.2 system rotations. The stellar photosphere, magnetic field, and accretion geometry of both stars were constrained by quasi-simultaneous optical monitoring (photometry, spectroscopy, and spectropolarimetry). The cool plasma component of V2129 Oph varies, with high density plasma and high EM observed during the first observing segment, and lower density and lower EM observed during the second. The emission lines, produced by the high density cool plasma of V4046 Sgr, display periodic flux variations with a period of half the system rotational period. Our results confirm that the dense cool plasma in CTTS is material heated in the accretion shock, and that the observed X-ray variability can be explained in terms different viewing angles at different rotational phases of the accretion-shock region.