Análise geométrica e dinâmica da parte interna de discos de acreção em estrelas T Tauri clássicas

Abstract

We present here CoRoT light curves of classical T Tauri stars that show similar photometric behavior to that which was observed in the star AA Tau. The goal of this work is to reproduce these light curves using the occultation model that was proposed for AA Tau, where an inner disk warp periodically obscures the stellar photosphere. This warp is a resultof the interaction between the inner disk region, near the co-rotation radius, and an inclined magnetosphere, as is predicted by magnetohydrodinamic simulations. An AA Tau-like light curve is characterized by a roughly constant maximum brightness level, interrupted by periodic minima that vary in width and depth from cycle to cycle. To learn more about the inner disk structure we believe to be the cause of this modulation, a geometrical model for the occultation can be used to reproduce the observed light curves. In order to do this, it is necessary to know the star-disk system's inclination, as well as themass and radius of the star, to compute the co-rotation radius, where we assume the warp is located. An analysis of the co-rotation, truncation, and sublimation radii of these disks shows that this assumption is valid.We used spectra from the literature to nd these stars' effective temperatures. We then inserted these values, along with the values of bolometric luminosity calculated using the J magnitude of each star, into an HR diagram to nd their masses and radii. Using periods determined with a periodogram, and values of v sin i determined when analyzing thespectra, we estimated the systems' inclinations. Kepler's third law was used to calculate the co-rotation radius of each disk. Knowing the co-rotation radii and systems' inclinations, we were able to model eachminimum of each light curve individually, so as to nd the values of warp height and azimuthal extension that best reproduce it. The average value found for the ratio between the warp's height and the radius at which it is located was h=Rd 0:18, but the individual minima show heights of 0.04 Rd up to 0.30 Rd, varying up to 70% between rotation cycles,in time-scales of a few days. This demonstrates how dynamic the interaction between the inner disk and the stellar magnetosphere is.We used a spot model to attempt to reproduce the light curves of two stars that had simultaneous BV(RI)c and CoRoT photometry. The possibility that a conguration of hot or cold spots on the surface of these stars is the main reason for their photometric behavior was discarded in both cases. We conclude that the obscuration of the stellar photosphere by an inner disk warp must be the main cause of the photometric modulation of these stars. The variability observed in the width and depth of the light curves' minima is due to the constant change in shape andheight of the structure responsible for them, which in turn is due to the dynamic interaction between this region of the accretion disk and the stellar magnetosphere.