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We present evidence for rotational modulation of X-ray flares by an analysis of four outbursts on late-type stars. Three of these flares have been observed on T Tauri Stars and one on Algol. The structure of the X-ray lightcurves observed in this selection of flare events is untypical in that the maximum emission extends over several hours producing a round hump in the lightcurve instead of a sharp peak. We explain this deviation from the standard shape of a flare lightcurve as the result of a flare erupting on the back side of the star and gradually moving into the line of sight due to the stars rotation. An estimate for the decay timescale and the size of the X-ray emitting volume is derived. Spectral information supports our proposition that changes of the visible volume are responsible for the observed time development of these flares.
Context: T Tauri stars have X-ray luminosities ranging from L_X = 10^28-10^32 erg/s. These luminosities are similar to UV luminosities (L_UV 10^30-10^31 erg/s) and therefore X-rays are expected to affect the physics and chemistry of the upper layers
Young stars emit strong flares of X-ray radiation that penetrate the surface layers of their associated protoplanetary disks. It is still an open question as to whether flares create significant changes in disk chemical composition. We present models
We report on a multiplicity survey of a sample of X-ray selected young stars in the Chamaeleon association. We used speckle-interferometry and direct imaging to find companions in the separation range 0.13 to 6. After correction for chance alignment
Depending on whether a T Tauri star accretes material from its circumstellar disk or not, different X-ray emission properties can be found. The accretion shocks produce cool heating of the plasma, contributing to the soft X-ray emission from the star
The Taurus-Auriga star-forming complex hosts the only population of T Tauri stars in which an anticorrelation of X-ray activity and rotation period has been observed. We have used XMM-Newtons European Photon Imaging Cameras to perform the most sensit