Star-disk interaction in classical T Tauri stars revealed using wavelet analysis

Context. The extension of the corona of classical T Tauri stars (CTTS) is is being widely discussed. The standard model of magnetic configuration of CTTS predicts that coronal magnetic flux tubes connect the stellar atmosphere to the inner region of the disk. However, differential rotation may disrupt these long loops. The results from hydrodynamic modeling of X-ray flares observed in CTTS that confirm the star-disk connection hypothesis are still controversial. Some authors suggest the presence of the accretion disk prevents the stellar corona extending beyond the co-rotation radius, while others are simply not confident with the methods used to derive loop lengths. Aims. We use independent procedures to determine the length of flaring loops in stars of the Orion Nebula Cluster, which has previously been analyzed using hydrodynamic models. Our aim is to disentangle the two scenarios that have been proposed. Methods. We present a different approach for determining the length of flaring loops that is based on the oscillatory nature of the loops after strong flares. We use wavelet tools to reveal oscillations during several flares. The subsequent analysis of these oscillations is based on the physics of coronal seismology. Results. Our results likely confirm the large extension of the corona of CTTS and the hypothesis of star-disk magnetic interaction in at least three CTTS of the Orion Nebula Cluster. Conclusions. Analyzing oscillations in flaring events is a powerful tool to determine the physical characteristics of magnetic loops in coronae in stars other than the Sun. The results presented in this work confirm the star-disk magnetic connection in CTTS.