New insights: The accretion process and variable wind from TW Hya


  • Data were obtained with the Chandra satellite, the 6.5m Magellan/Clay telescope at Las Campanas Observatory, and Gemini-S which is operated by the Association of Universities for Research in Astronomy, Inc. under a cooperative agreement with the US-NSF on behalf of the Gemini partnership.


For the first time in a classical T Tauri star, we are able to trace an accretion event signaled by an hour-long enhancement of X-rays from the accretion shock and revealed through substantial sequential changes in optical emission line profiles. Downflowing turbulent material appears in Hα and Hβ emission. He D3 (5876 Å) broadens, coupled with an increase in flux. Two hours after the X-ray accretion event, the optical veiling increases due to continuum emission from the hot splashdown region. The response of the stellar coronal emission to the heated photosphere follows about 2.4 hours later, giving direct evidence that the stellar corona is heated in part by accretion. Then, the stellar wind becomes re-established. A model that incorporates the dynamics of this sequential series of events includes: an accretion shock, a cooling downflow in a supersonically turbulent region, followed by photospheric and later, coronal heating. This model naturally explains the presence of broad optical and ultraviolet lines, and affects the mass accretion rates currently determined from emission line profiles. These results, coupled with the large heated coronal region revealed from X-ray diagnostics, suggest that current models are not adequate to explain the accretion process in young stars. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)