Analysis of variability of TW Hya as observed by MOST and ASAS in 2009

Michal Siwak, Slavek M. Rucinski, Jaymie M. Matthews, Grzegorz Pojmanski, Rainer Kuschnig, David B. Guenther, Anthony F. J. Moffat, Dimitar Sasselov, Werner W. Weiss

Published 2010-09-06Version 1

As a continuation of our previous studies in 2007 and 2008, new photometric observations of the T Tauri star TW Hya obtained by the MOST satellite and the ASAS project over 40 days in 2009 with temporal resolution of 0.2 days are presented. A wavelet analysis of the combined MOST-ASAS data provides a rich picture of coherent, intermittent, variable-period oscillations, similarly as discovered in the 2008 data. The periods (1.3 - 10 days) and systematic period shortening on time scales of weeks can be interpreted within the model of magneto-rotationally controlled accretion processes in the inner accretion disk around the star. Within this model and depending on the assumed visibility of plasma parcels causing the oscillations, the observed shortest-period oscillation period may indicate the stellar rotation period of 1.3 or 2.6 d, synchronized with the disk at 4.5 or 7.1 solar radii, respectively.