Coordinated Optical/X-ray observations of the CTTS V2129 Oph The Chandra View

Young low-mass accreting stars (classical T Tauri stars; CTTSs) possess strong magnetic fields that are responsible for the regulation of the accretion and outflow processes, and the confinement and heating of coronal plasma. Understanding the physics of CTTS magnetospheres and of their interaction with circumstellar disks can elucidate the history and evolution of our own Sun and Solar System, at the stage when planets were being formed. In June 2009 we have conducted an extensive multi-wavelength observing campaign of V2129 Oph, a K5 CTTS in the ρ Ophiuchi molecular cloud, with the goal of obtaining a synoptic view of its photosphere, magnetic field, coronal plasma, and of its accretion spot(s) and funnel flow(s). We here report on the X-ray emission, as observed by the Chandra High Energy Transmission Grating (HETG). High-density plasma, presumably from the accretion shock, is responsible for the soft X-ray emission, at least during the first half of the observation. The X-ray emission from both the coronal plasma (T̃20MK) and the cooler and denser material from the accretion spot (T̃3MK) is observed to vary between the first and second half of the observation. From the high-resolution X-ray spectra we constrain the emission measure of the two components and the density of the cool plasma. Finally we interpret the time variability of the cool plasma component in terms of stellar rotation and the time-changing viewing angle of the accretion stream, as constrained by simultaneous optical observations.